WO2013054481A1

WO2013054481A1 - Lithium ion secondary cell, negative electrode for lithium ion secondary cell, and negative electrode material for lithium ion secondary cell

Info

Publication number: WO2013054481A1
Application number: PCT/JP2012/006177
Authority: WO
Inventors: 林　圭一; 貴之弘瀬; 佳世水野; 三好　学; 石川　英明; 正彰鈴木; めぐみ田島; 栄克河端; 英明篠田; 雄一平川
Original assignee: 株式会社豊田自動織機
Priority date: 2011-10-12
Filing date: 2012-09-27
Publication date: 2013-04-18

Abstract

Provided is a lithium ion secondary cell having high capacity and high energy density. The lithium ion secondary cell comprises a negative electrode having a negative electrode active substance containing SiO_x (0.5 ≤ x ≤ 1.5) and graphite and, when the percentage of SiO_x and graphite added is 100 mass%, the ratio of SiO_x added is between 27 and 51 mass%. Moreover, by bringing the ratio (D₁/D₂₎ of the D₅₀ (D₁) of carbon-based particles and D₅₀ (D₂) of the Li-storing particles to greater than 1 but 2 or less and the ratio (D₁/t) of the D₅₀ (D₁) of the carbon-based particles and the thickness (t) of the negative electrode active substance layer to between 1/4 and 5/6, the cycle properties of the lithium ion secondary cell that uses the negative electrode active substance formed from the carbon-based particles and the Li-storing particles is improved.

Description

Lithium ion secondary battery, negative electrode for lithium ion secondary battery, and negative electrode material for lithium ion secondary battery

The present invention relates to a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a negative electrode material for a lithium ion secondary battery.

2. Description of the Related Art In recent years, with the development of portable electronic devices such as mobile phones and laptop computers, and the commercialization of electric vehicles, a small, lightweight, high-capacity secondary battery is required. At present, lithium ion secondary batteries using lithium cobaltate (LiCoO ₂ ) as a positive electrode active material and a carbon-based material as a negative electrode active material have been commercialized as high-capacity secondary batteries meeting this requirement. Such a lithium ion secondary battery can be miniaturized and reduced in weight because of its high energy density, and hence its use as a power source is attracting attention in a wide range of fields.

However, since LiCoO _2, which is a positive electrode active material, is manufactured using Co, which is a rare metal, as a raw material, it is expected that resource shortage will worsen in the future. Furthermore, since Co is expensive and price fluctuations are large, development of a cheap and stable supply of positive electrode active material is desired. Therefore, in order to reduce the use of Co, use is made of lithium manganese nickel-based oxides containing manganese (Mn) and nickel (Ni) in the basic composition at low prices and stable supply of constituent elements, instead of Co. Is considered promising.

In addition, as for the negative electrode active material, development of a next-generation negative electrode active material having a charge and discharge capacity which greatly exceeds the theoretical capacity of the carbon material has been promoted. For example, silicon-based materials, such as silicon and silicon oxide, having higher capacities than carbon materials have been studied as negative electrode active materials. However, when a silicon-based material is used as a negative electrode active material, it is known that the negative electrode active material expands and shrinks in association with absorption and release of lithium (Li) in a charge and discharge cycle. Such expansion and contraction degrade the cycle characteristics of the battery more than what it should have. Various studies have been conducted to suppress the deterioration of the cycle characteristics and the like. For example, in patent document 1, the fall of cycling characteristics is suppressed using the composite which compounded the silicon oxide and the carbon material to the negative electrode active material.

In addition, use of silicon oxide (SiO _x : x is about 0.5 ≦ x ≦ 1.5) has been studied as a negative electrode active material. It is known that SiO _x decomposes into Si and SiO ₂ when heat-treated. This is called disproportionation reaction, and in the case of homogeneous solid silicon monoxide SiO, in which the ratio of Si to O is approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by the internal reaction of the solid. . The Si phase obtained by separation is very fine. In addition, the SiO ₂ phase covering the Si phase has the function of suppressing the decomposition of the electrolytic solution. Therefore, a secondary battery using a negative electrode active material composed of SiO _x decomposed into Si and SiO ₂ is excellent in cycle characteristics.

However, since SiO _x has low conductivity, graphite and amorphous carbon materials are mixed as a conductive material, and the conductive material powder and SiO _x powder are brought into contact with each other at a point or a surface to provide conductivity to the negative electrode. For example, Patent Document 2 describes that a lithium ion secondary battery using a negative electrode material made of a mixture of lithium silicate powder and natural graphite powder has improved cycle characteristics. However, in a lithium ion secondary battery using a negative electrode material composed of a mixture of SiO _x and graphite powder, cracks repeatedly develop due to the difference in volume expansion due to repeated expansion and contraction of SiO _x accompanying charge and discharge. There is a problem that peeling occurs between the current collector and the negative electrode active material layer.

Therefore, in Patent Document 3, in the negative electrode material containing Li occluding particles and graphite particles, the (002) interplanar spacing d (002) by X-ray diffraction method is 0.3354 nm or more and 0.338 nm or less, and G by Raman spectroscopic analysis. It has been proposed to use a graphite particle having an area ratio of peak to D peak of G / D ≧ 9. The use of Si or SiO as Li storage particles is described, and the use of Si or SiO together with such graphite particles is described to improve the cycle characteristics of the secondary battery.

Further, in Patent Document 4, composite particles are formed by a spray dry method or the like from a material containing an element that can be alloyed with Li such as Si and a conductive material such as graphite, and the composite particles are internally voided. A negative electrode material has been proposed in which the void volume occupancy of the composite particles is in a predetermined range. As described above, by using the composite particles in which the void volume occupancy is in the optimum range as the negative electrode material, the composite particles have a gap that absorbs the expansion component, and the deterioration of the electrode characteristics can be prevented. In addition, since the gap does not increase too much, the conductive network can be sufficiently constructed to prevent the decrease in charge / discharge capacity of the non-aqueous secondary battery.

In addition, a buffer material that suppresses the volume change of the negative electrode due to expansion and contraction of the negative electrode active material is added to the negative electrode mixture layer to suppress the volume change of the entire negative electrode, thereby suppressing deterioration of the cycle characteristics of the battery. It is being considered. Patent Document 5 proposes a negative electrode material which is made of a mixture of a silicon compound and a carbon material as a buffer material, and the average particle diameter of the silicon compound is smaller than the average particle diameter of the carbon material. Furthermore, in Patent Document 5, the weight composition of the carbon material is made larger than the weight composition of the silicon compound. Patent Document 5 describes that the voids formed by the carbon material absorb the expansion of the silicon compound to suppress the volume change of the entire negative electrode. The example of Patent Document 5 describes a negative electrode in which 60 parts by weight of the carbon material and 30 parts by weight of the silicon compound are mixed in a case where the average particle size of the silicon compound is 1/10 of the average particle size of the carbon material. In Patent Document 5, at least a non-graphitizable carbon material is used as a buffer material, and Mg ₂ Si powder is used as a negative electrode active material.

Patent Document 6 has a negative electrode whose active material is an alloyed material that can be alloyed with lithium and a carbon material that also functions as a buffer material, and the ratio of the alloyed material is the total amount of the alloyed material and the carbon material A non-aqueous secondary battery has been proposed in which the average particle size of the alloying material is 1 to 30% by weight, and the average particle size of the alloying material is 2/5 or less of that of the carbon material. In Patent Document 6, soft carbon is used as a buffer material, and Si powder or SiO powder is used as a negative electrode active material.

SiO _x is relatively poor in conductivity. In order to improve the conductivity of the negative electrode, it is considered to be preferable to blend a material having excellent conductivity, that is, a conductive additive into the negative electrode. Also, usually, the particle size of the conductive additive is smaller than the particle size of the negative electrode active material. For this reason, the surface of the negative electrode active material is covered with the conductive aid by blending a large amount of the conductive aid. The conductive aid also has a function of holding the electrolytic solution, so the electrolytic solution is sufficiently spread near the surface of the negative electrode active material. For this reason, it is considered that the discharge capacity of the lithium ion secondary battery is improved. However, if the conductive aid is compounded in excess, the surface area of the conductive aid becomes excessive, so the adhesion between the negative electrode active material and the conductive aid may be reduced, and the discharge capacity may be reduced. In addition, when the conductive aid is excessively blended, the amount of the negative electrode active material to the conductive aid decreases. This may also reduce the discharge capacity of the lithium ion secondary battery.

For example, Patent Document 7 discloses a composite particle for an electrode in which an electrode active material (core particle) containing a silicate is coated with an electron conductive layer containing carbon and a particulate active material for electrode. The particle size of the particles contained in the electron conductive layer is 300 nm or less. According to Patent Document 7, it is considered that, by configuring the electrode composite particles in this manner, it is possible to suppress the decrease in discharge capacity of the lithium ion secondary battery while improving the conductivity of the electrode.

However, the composite particle for electrode introduced in Patent Document 7 is one in which core particles are coated with an electron conductive layer containing carbon and a particulate active material. In order to manufacture such a negative electrode active material, since many man-hours are required, there is a problem that it is difficult to manufacture the electrode composite particles introduced in Patent Document 7 at low cost. In addition, the technology introduced in Patent Document 7 is diverted, and even when SiO _x is used instead of a substance such as Li ₂ FeSiO ₄ or Li ₂ MnSiO ₄ introduced as silicate in Patent Document 7 It is not always possible to simultaneously achieve the improvement in the conductivity of the negative electrode and the reduction in the discharge capacity of the lithium ion secondary battery.
JP, 2010-212228, A JP-A-11-312518 JP 2004-362789 A JP 2003-303588 A JP 2000-357515 A JP, 2009-238663, A JP, 2009-87682, A

As described above, various studies have been conducted on the positive electrode active material, the negative electrode active material, and the like. As a first problem, lithium ion secondary batteries are required to have higher capacity and higher energy density. Therefore, in the combination of a positive electrode active material and a negative electrode active material, a combination that makes a lithium ion secondary battery have high capacity and high energy density is required.

Here, the energy density refers to energy that can be taken out per unit mass or unit volume, and is expressed in units of Wh / Kg and Wh / L. Energy can be calculated by voltage × current capacity value. However, in the case of a battery, the voltage changes with remaining capacity, so the voltage uses the rated voltage. The rated voltage indicates the voltage at a discharge amount which is exactly 1/2 of the total energy when discharged at a current of 0.2C. It can be said that this is an average voltage. Therefore, energy can be calculated by multiplying the average voltage at the time of 0.2 C discharge and the current capacity value. The voltage corresponds to the potential difference between the discharge potential of the positive electrode and the discharge potential of the negative electrode.

The discharge potential of the positive electrode is determined by the material of the positive electrode active material used for the positive electrode. For example, a lithium ion secondary battery using a lithium manganese nickel oxide as a positive electrode active material discharges the positive electrode at a charge of up to 4.3 V as compared to a lithium ion secondary battery using lithium cobaltate as a positive electrode active material The potential is low. Therefore, if the negative electrode is the same, a lithium ion secondary battery using a lithium manganese nickel oxide as a positive electrode active material has an average voltage compared to a lithium ion secondary battery using lithium cobaltate as a positive electrode active material It becomes smaller.

Similarly, the discharge potential of the negative electrode is determined by the material of the negative electrode active material used for the negative electrode. A lithium ion secondary battery using a silicon material having a theoretical capacity larger than that of a carbon material as a negative electrode active material has a negative electrode of a lithium ion secondary battery as compared to a lithium ion secondary battery using a carbon material as a negative electrode active material Discharge potential is high. Therefore, if the positive electrode is the same, the average voltage of the lithium ion secondary battery using the silicon-based material as the negative electrode active material is smaller than that of the lithium ion secondary battery using the carbon material as the negative electrode active material.

As described above, since the energy density is calculated by the average voltage x current capacity value at the time of 0.2 C discharge, even if the current capacity value is large, the energy density decreases as the average voltage decreases. There is also.

The present invention has been made in view of such circumstances, and has a first object to provide a lithium ion secondary battery capable of achieving both high capacity and high energy density.

The second object of the present invention is to prevent peeling of the interface between the current collector and the negative electrode active material layer by reducing the volume change during charge and discharge in a negative electrode material containing Li storage particles and carbon-based particles. Another object is to improve the cycle characteristics of a lithium ion secondary battery using the negative electrode.

A third object of the present invention is to use a negative electrode for a lithium ion secondary battery and its negative electrode which can further suppress the volume change of the whole negative electrode when using a negative electrode active material having a large volume change due to lithium absorption and release. Providing a lithium ion secondary battery. As described in Patent Document 5 and Patent Document 6, various studies have been made on adding a buffer material, suppressing a volume change of the entire negative electrode, and suppressing deterioration of cycle characteristics. Specifically, in

Patent Documents

5 and 6, the mass of the negative electrode active material is reduced in the examples, and the mass of the buffer material is increased by about 2 times the mass of the negative electrode active material, and the average particle diameter of the negative electrode active material is The volume change of the whole negative electrode is suppressed by setting it as 2/5 or less of the average particle diameter of these. However, for higher capacity batteries, it is desirable that the amount of the negative electrode active material be higher.

In addition, development of various positive electrode active materials has led to development of lithium ion secondary batteries in which a higher voltage is applied to the negative electrode than before. By applying a higher voltage to the negative electrode than in the past, the degree of expansion and contraction of the negative electrode active material is further increased. Therefore, there is a demand for a negative electrode for a lithium ion secondary battery capable of further suppressing the volume change of the entire negative electrode.

The present invention has been made in view of such circumstances, and it is possible to further suppress the volume change of the entire negative electrode when the negative electrode active material having a large volume change associated with lithium absorption and release is used. A third object is to provide a lithium ion secondary battery using a negative electrode for a secondary battery and the negative electrode thereof.

Furthermore, the fourth object of the present invention is to use lithium ion secondary battery as a negative electrode material for lithium ion secondary battery, which uses SiO _x as a negative electrode active material, is excellent in conductivity and can suppress a decrease in discharge capacity of lithium ion secondary battery. An object of the present invention is to provide a negative electrode for a secondary battery and a lithium ion secondary battery.

The fifth object of the present invention is to improve the dispersibility of Li occluding particles and carbon-based particles in the negative electrode active material layer even if the ratio (D ₁ / t) is small, and secondary lithium ion using the negative electrode It is about improving the output of the battery.

In the lithium ion secondary battery, it is required to make the positive electrode and the negative electrode as thin as possible. However, in the negative electrode active material layer containing Li occluding particles and carbon-based particles, when the thickness of the negative electrode active material layer is reduced, the dispersibility of the Li occluding particles and the carbon-based particles is poor and the conductivity is lowered. there were. In particular, natural graphite which is generally used as the carbon-based particles has a large D _50, since a large difference occurs in comparison with the D ₅₀ of Li occlusion particles, that tends to occur unevenness in the distribution of both in the anode active material layer There's a problem.

Therefore, the inventors of the present application decided to use the ratio (D ₁ / t) of D ₅₀ (D ₁ ) of the carbon-based particles to the thickness (t) of the negative electrode active material layer as an indicator of dispersibility. That is, as the ratio (D ₁ / t) is smaller, the dispersibility of the carbon-based particles in the negative electrode active material layer is improved. However, when the ratio (D ₁ / t) is reduced, there is a problem that the dispersibility of the Li storage particles and the carbon-based particles is reduced, and both are in a relation of conflicting events. The fifth object of the present invention is to improve the dispersibility of Li occluding particles and carbon-based particles in the negative electrode active material layer even if the ratio (D ₁ / t) is small, and secondary lithium ion using the negative electrode It is about improving the output of the battery.

(First means)
The inventors of the present inventors, have conducted extensive studies, the positive electrode and, when a negative electrode having a negative electrode active material containing SiO _x and graphite, a lithium ion secondary battery having a content of SiO _x and graphite in the negative electrode active material It has been found that by defining the range of (1), it is possible to have a high capacity and yet have a high energy density.

That is, the lithium ion secondary battery of the present invention comprises a positive _electrode, a negative electrode having a negative electrode active material containing SiO x (0.5 ≦ x ≦ 1.5 ) and graphite, have, a SiO _x and graphite 100 It is characterized in that the blending ratio of SiO _x when it is mass% is 27 mass% to 51 mass%.

By setting it as the lithium ion secondary battery using the negative electrode active material whose compounding ratio of SiO _x is the said range, compared with the lithium ion secondary battery using a carbon material for the negative electrode active material, the electric capacity of a negative electrode increases. Thus, the increase in discharge potential of the negative electrode can be suppressed, and a lithium ion secondary battery having high capacity and high energy density can be obtained.

Furthermore, the positive electrode has the general formula:
It is preferable to have a positive electrode active material containing a composite metal oxide represented by LiCo _p Ni _q Mn _r O ₂ (p + q + r = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1). When the composite metal oxide is used as a positive electrode active material, the discharge potential of the positive electrode is lower compared to the case where other positive electrode active materials are used, and therefore the electric capacity of the negative electrode is obtained by combining the positive electrode and the negative electrode. Since the increase of the discharge potential of the negative electrode can be suppressed, the lithium ion secondary battery can have high capacity and high energy density even if the discharge potential of the positive electrode decreases.

The composite metal oxide is preferably LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ .

It is more preferable that the blending ratio of SiO _x when SiO _x and graphite are 100 wt% is 27 wt% to 45 wt%.

The lithium ion secondary battery of the present invention comprises a positive electrode, an element capable of alloying with lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, And a negative electrode having a negative electrode active material containing a compound of Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi and / or an element, and graphite and an element and / or an element The compounding ratio of the element and / or the compound of the element when the compound is 100% by mass is characterized in that it is 27% by mass to 51% by mass. When the compounding ratio of the element and / or the compound of the element is in the above range, a lithium ion secondary battery having a high capacity and a high energy density can be obtained.

(Second means)
The feature of the negative electrode for a lithium ion secondary battery of the present invention to solve the second problem is a negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector. there are a carbon-based particles in the anode active material layer includes a storage capable Li occluding particles lithium ions, _D 50 of _{_D} 50 _(D ₁₎ and Li occlusion particles of the carbon-based particles _{(D 2)} Ratio (D ₁ / D ₂ ) is more than 1 and 2 or less, and the ratio (D ₁ / t) of D ₅₀ (D ₁ ) of the carbon-based particles to the thickness (t) of the negative electrode active material layer is One or more and five or less. Incidentally, it refers to a particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50% and D _50. That is, D ₅₀ refers to the median diameter measured on a volume basis.

The feature of the lithium ion secondary battery of the present invention for solving the second problem lies in the use of the negative electrode of the present invention.

(Third means)
As a result of intensive investigations of the third problem by the present inventors, it was found that graphite powder capable of functioning as a buffer material is incorporated in a predetermined manner in an active material layer containing SiO _x powder (0.5 ≦ x ≦ 1.5) as an active material. It has been found that the volume change of the entire negative electrode can be largely suppressed by mixing the amounts and specifying the ratio of the sizes of both powders.

That is, in the negative electrode for a lithium ion secondary battery of the present invention, in the negative electrode for a lithium ion secondary battery having a current collector and an active material layer formed on the surface of the current collector, the active material layer is an active material, includes a binder and a buffer material, the active material consists of SiO _x powder (0.5 ≦ x ≦ 1.5), the buffer material is made of graphite powder, _{D 50} of the SiO _x powder, 1 _{D 50} of the graphite powder The blending amount of the graphite powder is 36% by mass to 61% by mass when the total of the mass of the graphite powder and the mass of the SiO _x powder is 100% by mass, and The content is characterized in that it is 5% by mass to 25% by mass when the mass of the entire active material layer is 100% by mass.

When the D _{50 of the} SiO _x powder and the graphite powder is in the above relationship, the blending amount of the graphite powder is in the above range, and the binder content is in the above range, SiO _x is formed in the voids formed by the graphite powder. powder is placed, and also expands SiO _x powder, SiO _x powder and graphite powder to avoid thick negative electrode thickness is rearranged. Repositioning refers to the fact that the SiO _x powder is disposed in the void formed again by the graphite powder so that the SiO _x powder and the graphite powder do not expand in the thickness direction of the negative electrode active material layer. As such, by repositioning the SiO _x powder and the graphite powder so as not to expand in the thickness direction of the negative electrode active material layer, the volume change of the negative electrode can be significantly suppressed.

_{D 50} of the SiO _x powder, by a 1 / 4-1 / 2 of the _{D 50} of the graphite powder, SiO _x powder enters well into the gap graphite powder forms more and the graphite powder and SiO _x powder Arranged with high density. 1/4 smaller than _{D 50} _{D 50} of the graphite powder of SiO _x powder, SiO _x powder would make a aggregate to coarse particles containing a binder, coarse particles are well within voids graphite powder to form I can not get in. SiO _x powder is not impenetrable well within _{void D 50} of SiO _x powder form is larger than 1/2 and graphite powder _{D 50} of the graphite powder.

If the blending amount of the graphite powder is 36% by mass or more when the sum of the mass of the graphite powder and the mass of the SiO _x powder is 100 mass%, the SiO _x powder enters the void formed by the graphite powder well The volume change of the negative electrode can be suppressed, and if it is 61% by mass or less, the electrode capacity of the negative electrode can not be reduced much.

Moreover, the above-mentioned effect is remarkable when content of a binder is the said range. When the mass of the entire active material layer is 100% by mass and the binder content is less than 5% by mass, the SiO _x powder and the graphite powder are preferably rearranged because the graphite powder and the SiO _x powder are peeled off from the current collector. However, if the amount of the binder is more than 25% by mass, the amount of the insulating binder increases, which is not preferable because the conductivity of the entire electrode decreases and the internal resistance increases.

When the negative electrode active material layer expands in the thickness direction, the conductive path formed between the active material, the conductive additive, and the like is broken, and the conductivity of the negative electrode is lowered. When the conductivity of the negative electrode decreases, lithium ions are less likely to be released during discharge. By suppressing the volume change of the negative electrode, it is possible to suppress the lithium ion from becoming difficult to be released during discharge, and to suppress the decrease in the initial efficiency of the battery (the ratio of the initial discharge capacity to the initial charge capacity). it can.

In addition, when the negative electrode active material layer expands in the thickness direction, the adhesion between the negative electrode active material and the current collector is reduced, or the negative electrode active material is distorted due to the repetition of expansion and contraction of the negative electrode active material, and thus finer Desorption from the electrode leads to deterioration of the battery capacity and cycle characteristics. By suppressing the volume change of the negative electrode, it is possible to suppress the deterioration of the electric capacity and the cycle characteristics of the battery.

The blending amount of the above-mentioned graphite powder is more preferably 36% by mass to 49% by mass. By making the compounding quantity of graphite powder into the said range, the volume change of a negative electrode can be suppressed further and it can be set as the battery which suppressed deterioration of cycle characteristics more. If the amount of the graphite powder is more than 49 wt%, the charging and discharging of the repetition, since a large graphite powder D ₅₀ than SiO _x powder is easily detached from the binder, the cycle characteristics are deteriorated.

Further, the negative electrode for lithium ion secondary battery is formed through a compression molding step, and in the case of compressing the negative electrode for lithium ion secondary battery with a press pressure higher than the press pressure in the compression molding step, the negative electrode in the compression direction. It is preferable that the thickness of the active material layer be reduced.

The fact that the thickness of the negative electrode active material layer can be reduced by using such a higher pressing pressure means that the SiO _x powder can further enter into the void formed by the graphite powder by applying a high pressing pressure. That indicates that the negative electrode active material layer, be SiO _x powder expands, there is room for SiO _x powder and graphite powder is rearranged with the expansion of SiO _x powder.

By using the above negative electrode for a lithium ion secondary battery, it is possible to obtain a lithium ion secondary battery capable of suppressing the volume change of the negative electrode.

In the lithium ion secondary battery, xLi ₂ M ¹ O _3. (1-x) LiM ² O ₂ (0 <x ≦ 1, M ¹ is one or more metal elements having a tetravalent Mn essential, M ² preferably has a positive electrode containing a positive electrode active material a basic composition of lithium manganese oxide represented by a tetravalent Mn two or more metal elements as essential). When the above lithium manganese oxide is used as the positive electrode active material, a voltage of 4.5 V is applied to the battery in the activation step of the active material. This is because the above lithium manganese oxide can not be activated without applying 4.5 V. When applying a voltage of 4.3 V or more to the battery, the electrolytic solution is likely to be decomposed. Therefore, the voltage applied to the battery is usually 4.3 V as the upper limit. When a voltage of 4.5 V is applied to the battery, the expansion of the SiO _x powder, which is a negative electrode active material, is twice as large as that of 4.3 V applied. When the negative electrode of the present invention is used, the volume change of the entire negative electrode can be suppressed even in the case of such a high voltage.

(4th means)
The negative electrode containing SiO _x as a negative electrode active material has a relatively large volume change during charge and discharge. The inventors of the present invention have estimated that the conductive path formed in the negative electrode is cut off during the contraction of SiO _x to deteriorate the conductivity of the negative electrode. At least a portion of the conductive path is considered to be formed by the conductive aid disposed on the surface of SiO _x . And, _if the amount of the conductive auxiliary agent per unit surface area of SiO _x is sufficiently large, it is considered that the conductive path is hardly cut even when the SiO _x contracts.

The SEM photograph which image | photographed the mode that the surface of the negative electrode material with few amounts of conductive support agents was observed with the scanning electron microscope (SEM; Scanning Electron Microscope) is shown in FIG. The SEM photograph which imaged the mode which observed the surface of the negative electrode material with many amounts of conductive support agents by SEM is shown in FIG. As shown in FIG. 14, when the amount of the conductive auxiliary agent is small, the surface of the relatively large particles SiO _x is not sufficiently covered with the conductive auxiliary agent which is a fine particle, and the conductive path is sufficiently It is considered not to be formed. On the other hand, as shown in FIG. 15, when the content of the conductive additive is large, the surface of relatively large particles, SiO _x , is sufficiently covered with the conductive additive, which is fine particles, to form a large number of conductive paths. It is considered to be

The inventors of the present invention have intensively studied based on this assumption, and by setting the compounding amount of the conductive aid to an amount according to the sum of the surface area of SiO _x in the negative electrode material and graphite, the above-mentioned We found that we could solve 4 problems. That is, the negative electrode material for a lithium ion secondary battery of the present invention is a conductive material containing a negative electrode active material comprising a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6) and carbon (C). a negative electrode material for a lithium ion secondary battery comprising a aids, a, BET value of SiO _x a ^(m 2 / g) and a1, the amount of SiO _x (g) of the b1, BET value of the graphite ( Assuming that m ² / g) is a 2, the blending amount (g) of graphite is b 2, and the blending amount (g) of the conductive additive is c, {(a1 × b1) + (a2 × b2)} / It is characterized in that the value of c is 24 or more and 65 or less.

The relationship between the surface area of the negative electrode active material described above and the compounding amount of the conductive aid, that is, the value of {(a1 × b1) + (a2 × b2)} / c is based on the mass of the conductive aid. The negative electrode material for a lithium ion secondary battery of the present invention, which solves the fourth problem described above, based on the volume of the conductive additive, is silicon represented by SiO _x (0.3 ≦ x ≦ 1.6). A negative electrode material for a lithium ion secondary battery comprising a negative electrode active material made of an oxide and a conductive aid containing carbon (C), wherein a BET value (m ² / g) of SiO _x is a 1, The blending amount (g) of SiO _x is b1, the BET value (m ² / g) of graphite is a 2, the blending amount (g) of graphite is b 2, and the blending amount (cm ³ ) of the conductive aid is d When this is done, the value of {(a1 × b1) + (a2 × b2)} / d is 43 or more and 120 or less.

The negative electrode for a lithium ion secondary battery of the present invention for solving the fourth problem is characterized by being made of the above-described negative electrode material for a lithium ion secondary battery of the present invention.

Furthermore, a lithium ion secondary battery of the present invention for solving the fourth problem is characterized by being provided with the above-described lithium ion secondary battery negative electrode of the present invention.

(Fifth means)
The feature of the negative electrode for a lithium ion secondary battery of the present invention to solve the fifth problem is a negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector. there are a carbon-based particles in the anode active material layer includes a storage capable Li occluding particles lithium ions, _D 50 of _{_D} 50 _(D ₁₎ and Li occlusion particles of the carbon-based particles _{(D 2)} the ratio _{_(D} 1 / D ₂₎ is 1/2 or more and 1.3 or less, the ratio of _D 50 of the carbonaceous particles _{(D 1)} the thickness of the negative electrode active material layer _{(t) (D} 1 / t) to be 1/4 or more and 2/3 or less.

The feature of the lithium ion secondary battery of the present invention for solving the fifth problem lies in the use of the negative electrode of the present invention.

(First effect)
The present invention can provide a lithium ion secondary battery having both high capacity and high energy density.

(Second effect)
In the negative electrode active material layer made of a mixture of carbon-based particles and Li storage particles, pores are inevitably contained between the particles. The pores absorb the stress at the time of expansion and contraction, but the larger ones are smaller than the smaller ones, and the larger ones have better stress absorption. Further, it is considered that as the shape of the pores is closer to a true sphere, stress concentration can be avoided and cracks can be prevented.

However, while the D ₅₀ of SiO _x which is typical as Li storage particles is about 6.5 μm in the standard product, the particle diameter of graphite which is typical as carbon-based particles is in the range of 10 μm to 20 μm. Therefore, in the negative electrode material made of a mixture of SiO _x and artificial graphite, the difference in particle size is large, and it has been difficult to have a large number of small pores.

So the negative electrode for a lithium ion secondary battery of the present invention, _D 50 _{(D 1)} and the ratio between _D 50 of Li occlusion particle _{_{(D 2) (D 1 /}} D 2) is greater than 1 and 2 of the carbon-based particles Since the following is assumed, D ₁ and D ₂ are close to each other, and a large number of small pores are contained in the negative electrode active material layer.

On the other hand, the thickness of the negative electrode active material layer is desirably as thin as possible in order to reduce the electrical resistance, but when the thickness of the negative electrode active material layer is reduced, D ₅₀ (D ₁ ) of the carbon-based particles and the negative electrode active material The ratio (D ₁ / t) to the layer thickness (t) also decreases, and the dispersibility of the pores decreases.

Therefore, in the present invention, the ratio (D ₁ / t) of D ₅₀ (D ₁ ) of the carbon-based particles to the thickness (t) of the negative electrode active material layer is 1/4 or more and 5/6 or less. T is sufficiently large relative to _{1 and} the dispersibility of the pores is good.

Therefore, in the lithium ion secondary battery of the present invention using the negative electrode of the present invention, the small and highly dispersible pores contained in the negative electrode active material layer can relieve the stress due to the volume change during charge and discharge. Since peeling can be prevented, cycle characteristics are improved.

(Third effect)
By using the negative electrode for a lithium ion secondary battery of the present invention, it is possible to obtain a lithium ion secondary battery capable of suppressing a volume change of the negative electrode.

(4th effect)
Although the negative electrode material and the negative electrode of the present invention use SiO _x as the negative electrode active material, they are excellent in conductivity and can suppress a decrease in discharge capacity of a lithium ion secondary battery. Moreover, although the lithium ion secondary battery of the present invention uses SiO _x as the negative electrode active material, the conductivity of the negative electrode is excellent and the discharge capacity is unlikely to be reduced.

(5th effect)
The negative electrode for a lithium ion secondary battery of the present invention has a negative electrode active material layer containing carbon-based particles and Li occlusion particles, D _{50 (D} ₂ of _{D 50 (D} ₁₎ and Li occlusion particles of the carbon-based particles The ratio (D ₁ / D ₂ ) to ( ₁ ) is 1/2 or more and 1.3 or less. That is, since the particle size difference between the carbon-based particles and the Li storage particles is small, in the negative electrode active material layer, the carbon-based particles and the Li storage particles are highly dispersed and uniformly mixed.

Therefore, the contact probability between the Li storage particles and the carbon-based particles is increased, and the ion conductivity of Li ions is improved. Therefore, the ratio (D ₁ / t) of D ₅₀ (D ₁ ) of the carbon-based particles to the thickness (t) of the negative electrode active material layer is 1/4 or more and 2/3 or less, and the thickness of the negative electrode active material layer Even if the thickness is reduced, the conductivity of the negative electrode is improved.

That is, in the lithium ion secondary battery of the present invention using the negative electrode of the present invention, since the conductivity of the negative electrode is improved, the output is also improved.

6 is a graph showing the relationship between discharge capacity (mAh) and voltage (V) (VS. Li ^/ Li ⁺ ) in Examples 1 to 3 and Comparative Example 1. FIG. 6 is a graph comparing the graphite ratio and volumetric energy density of Examples 1 to 3 and Comparative Example 1. FIG. It is a SEM image of the cross section of the negative electrode which concerns on Example 5 of this invention. It is a SEM image of the cross section of the negative electrode which concerns on the comparative example 2 of this invention. It is a graph which shows the relationship between cycle number and discharge IR drop. It is a graph which shows the relationship between cycle number and discharge IR drop. FIG. 1 is a schematic view illustrating a negative electrode for a lithium ion secondary battery of the present invention. It is a schematic diagram explaining the volume change of the negative electrode for lithium ion secondary batteries of this invention. Is a schematic view D ₅₀ of SiO _x powder 2 will be described substantially equal or negative electrode for a lithium ion secondary battery using what little smaller and D ₅₀ of the graphite powder 3. It is a schematic diagram explaining the volume change of the negative electrode for lithium ion secondary batteries of FIG. Is a graph comparing the particle size ratio and the electrode density of the SiO _x powder and graphite powder. It is a graph which shows the cycle test result of Examples 8-10. It is a SEM (scanning electron microscope) photograph of the cross section of the negative electrode of Experiment 2. FIG. It is a SEM photograph of the surface of negative electrode material with few amounts of conductive support agents. It is a SEM photograph of the surface of negative electrode material with many amounts of conductive support agents. It is a graph showing the cycling characteristics of the lithium ion secondary battery of the comparative example 5 and Example 11-Example 14, and a vertical axis | shaft is discharge capacity. FIG. 20 is a graph showing the cycle characteristics of the lithium ion secondary batteries of Comparative Example 5 and Examples 11 to 14. The vertical axis is the discharge capacity retention rate. It is a graph showing the cycling characteristics of the lithium ion secondary battery of Examples 15 and 16, and a vertical axis | shaft is discharge capacity. FIG. 20 is a graph showing the cycle characteristics of the lithium ion secondary batteries of Examples 15 to 17, wherein the vertical axis is the discharge capacity retention rate. It is a graph showing the discharge IR drop of the lithium ion secondary battery of Comparative Example 5 and Examples 11 to 14. It is a SEM image of the cross section of the negative electrode concerning Example 18 of this invention. It is a graph which shows initial stage discharge capacity. It is a graph which shows first time discharge IR drop.

1: current collector, 2: SiO _x powder, 3: graphite powder, 4: Binder, 5: active material layer, 6: Graphite, 7: SiO.

First Embodiment
<Lithium ion secondary battery>
The lithium ion secondary battery of the first embodiment of the present invention has a positive electrode, and a negative electrode having a negative electrode active material containing SiO _x (0.5 ≦ x ≦ 1.5) and graphite.

The positive electrode has a current collector and an active material layer formed on the surface of the current collector.

The current collector is a chemically inert electron conductor for keeping current flowing to the electrode during discharge or charge. The current collector may be in the form of a foil, a plate or the like, but the shape is not particularly limited as long as it is suitable for the purpose. As a collector, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably, for example.

The active material layer contains an active material and a binder. You may add a conductive support agent to an active material layer as needed. The active material is a substance that directly contributes to electrode reactions such as charge reactions and discharge reactions.

As an active material of a positive electrode, a lithium containing compound is suitable. As the positive electrode active material, for example, lithium-containing metal composite oxides such as lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide and the like can be used. Other metal compounds or polymer materials can also be used as the positive electrode active material. Other metal compounds include, for example, oxides such as titanium oxide, vanadium oxide or manganese dioxide, or disulfides such as titanium sulfide or molybdenum sulfide. Examples of the polymer material include conductive polymers such as polyaniline or polythiophene.

In particular, the positive electrode active material has a general formula:
It is preferable to include a composite metal oxide represented by LiCo _p Ni _q Mn _r O ₂ (p + q + r = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1). The composite metal oxide is excellent in thermal stability and low in cost. Therefore, by including the composite metal oxide, an inexpensive lithium ion secondary battery with good thermal stability can be obtained.

As the above composite metal oxide, for example, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li _1.0 Ni _0.6 Co _0.2 Mn _0.2 O ₂ , Li _1.0 Ni _0.5 _{_{_{Co 0.2 Mn 0.3 O 2, LiCoO}}} 2, it is possible to use a _{_{_{LiNi 0.8 Co 0.2 O 2, LiCoMnO}}} 2. Among them, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ is preferable in view of thermal stability.

The binder is used as a binder for fixing the active material to the current collector. As a binder, for example, a cured product of polyvinylidene fluoride (PVDF), a cured product of a fluorine-based polymer such as polytetrafluoroethylene (PTFE), a cured product of a rubber such as styrene butadiene rubber (SBR), polyimide, polyamide imide, etc. A cured product of an imide polymer, a cured product of an alkoxysilyl group-containing resin, or a cured product of a thermoplastic resin such as polypropylene or polyethylene can be used.

A conductive support agent is added to the active material layer as needed to enhance the conductivity of the electrode layer. Carbon black fine particles such as carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (Vapor) as conductive support agent
Grown Carbon Fiber (VGCF) etc. can be added singly or in combination of two or more.

The negative electrode has a current collector and an active material layer formed on the surface of the current collector, as in the case of the above-described positive electrode. The active material layer contains an active material and a binder. You may add a conductive support agent to an active material layer as needed. As the current collector, the binder and the conductive aid, those similar to those described for the positive electrode can be used.

The negative electrode active material consists of SiO _x (0.5 ≦ x ≦ 1.5) and graphite.

SiO _x (0.5 ≦ x ≦ 1.5) is a general formula representing an amorphous silicon oxide obtained using silicon dioxide (SiO ₂ ) and metallic silicon (Si) as raw materials. It is known that SiO _x decomposes into Si and SiO ₂ when heat-treated. This is called disproportionation reaction, and in the case of homogeneous solid silicon monoxide SiO which has a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by internal reaction of the solid. . The Si phase obtained by separation is very fine and dispersed in the SiO ₂ phase. In addition, the SiO ₂ phase covering the Si phase has the function of suppressing the decomposition of the electrolytic solution. Therefore, a lithium ion secondary battery using a negative electrode active material composed of SiO _x decomposed into Si phase and SiO ₂ phase is excellent in cycle characteristics.

In SiO _x (0.5 ≦ x ≦ 1.5), if x is less than 0.5, the ratio occupied by the Si phase becomes high, so that the volume change during charge and discharge becomes too large, and lithium ion secondary Battery cycle characteristics are degraded. In addition, when x exceeds 1.5, the ratio of the Si phase decreases to lower the energy density. A further preferable range of x is 0.7 ≦ x ≦ 1.2.

In general, it is said that almost all SiO disproportionate and separate into two phases at 800 ° C. or higher in the oxygen-free state. Specifically, the raw material silicon oxide powder containing non-crystalline SiO powder is heat-treated at 800 ° C. to 1200 ° C. for 1 hour to 5 hours in an inert atmosphere such as vacuum or in an inert gas. Thus, a powder composed of SiO particles including two phases of an amorphous SiO ₂ phase and a crystalline Si phase is obtained.

It is desirable that SiO _x (0.5 ≦ x ≦ 1.5) has a shape that reduces the specific surface area. Here, _if the D _{50 of} SiO _x is large, the disproportionation reaction may occur only on the particle surface and may not occur to the inside of the particle, and the Si phase can not be separated, so the conventional discharge capacity can not be exhibited. Therefore, D ₅₀ of SiO _x is preferably as small as possible.

However, the D ₅₀ of the SiO _x is too small, since the coarse particles by aggregation during the formation of the negative electrode may decrease the charge-discharge characteristics of the lithium ion secondary battery. Further, when the D ₅₀ of the SiO _x is too small, the specific surface area of the SiO _x powder is increased, an increasing number of contact surface with SiO _x powder and the electrolyte, will proceed decomposition of the electrolyte, the cycle of the lithium ion secondary battery The characteristics get worse.

Therefore, _{D 50} of the SiO _x is preferably 1μm or more. Incidentally, it refers to a particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50% and D _50. That is, D ₅₀ refers to the median diameter measured on a volume basis. Further, _{D 50} of the SiO _x is preferably 15μm or less. And D ₅₀ is greater than 15 [mu] m, there is a possibility that disproportionation discharge capacity does not occur until the internal drops than have conventional. In addition, since the SiO _x powder has poor conductivity, the conductivity of the entire electrode becomes nonuniform, and the charge and discharge characteristics of the lithium ion secondary battery are degraded. More preferably, the D _{50 of} SiO _x is 4 μm to 10 μm.

As SiO _x (0.5 ≦ x ≦ 1.5), commercially available SiO _x having a desired D ₅₀ can be used. In addition, SiO _x may be provided with a covering layer made of a carbon material on the surface. Coating layer comprising a carbon material, not only to impart conductivity to the SiO _x, it is possible to prevent the reaction between such SiO _x and hydrofluoric acid, thereby improving the battery characteristics of the lithium ion secondary battery. Natural carbon, artificial graphite, coke, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, etc. can be used as the carbon material constituting the covering layer. Moreover, in order to form a coating layer, it is good to mix and bake a silicon oxide and a carbon material precursor. As the carbon material precursor, organic compounds such as saccharides, glycols, polymers such as polypyrrole, and acetylene black can be used, and organic compounds which can be converted into carbon materials by firing can be used. In addition, the covering layer can be formed even by using a mechanical surface fusion treatment method such as mechanofusion or a vapor deposition method such as CVD.

The formation amount of the covering layer can be 1% by mass to 50% by mass with respect to the total of SiO _x and the covering layer. If the coating layer is less than 1% by mass, the effect of improving conductivity can not be obtained, and if it exceeds 50% by mass, the ratio of SiO _x relatively decreases and the negative electrode capacity decreases. The amount of the coating layer formed is preferably in the range of 5% by mass to 30% by mass, and more preferably in the range of 5% by mass to 20% by mass. Note that in the case of providing a coating layer comprising a carbon material on the surface of the SiO _x, the proportion of SiO _x when the SiO _x and graphite is 100 mass%, including the mass of the coating layer. The carbon material forming the covering layer is distinguished from the negative electrode active material graphite.

As graphite which is a negative electrode active material, natural graphite powder, artificial graphite powder, spherulite graphite powder (graphitized mesophase carbon small spheres), graphite-based carbon material powder, etc. can be used. As the graphite-based carbon material, a pyrolyzate of a condensed polycyclic hydrocarbon compound such as pitch and coke can be used.

_Graphite, it is preferable to use a powder _{D 50} is 4 [mu] m ~ 30 [mu] m. In particular, those having a D ₅₀ of 5 μm to 25 μm are preferable, and those having a D ₅₀ of 8 μm to 20 μm are more preferable.

In the negative electrode active material, the blending ratio of SiO _x is 27 wt% to 51 wt% when SiO _x and graphite are 100 wt%. The lithium ion secondary battery using the negative electrode active material of this compounding ratio has a lithium ion secondary battery compared to the lithium ion secondary battery using only SiO _x (0.5 ≦ x ≦ 1.5) as the negative electrode active material. The discharge voltage of the negative electrode of the secondary battery can be reduced, and a lithium ion secondary battery having a high capacity can be obtained as compared to a lithium ion secondary battery using only graphite as a negative electrode active material. Therefore, a lithium ion secondary battery using the negative electrode active material with the above blending ratio can be a lithium ion secondary battery having high capacity and high energy density.

The energy density decreases even _if the blending ratio of SiO _x is less than 27% by mass and more than 51% by mass. The theoretical capacity decreases as the amount of SiO _x decreases, but the discharge voltage of the negative electrode decreases as the amount of graphite increases, so the ability of the positive electrode can be fully utilized. On the other hand, although the theoretical capacity increases as the amount of SiO _x increases, the discharge voltage of the negative electrode increases as the proportion of graphite decreases, and the positive electrode can not be used well. More preferably, the blending ratio of SiO _x is 27% by mass to 45% by mass.

The said negative electrode and positive electrode can be manufactured by a well-known manufacturing method. For example, the said negative electrode and positive electrode can be manufactured by the manufacturing method which has a slurry preparation process, a slurry application | coating process, a compression molding process, and a heat treatment process. In the slurry preparation step, the active material and the binder resin are mixed to prepare a slurry. If necessary, a solvent and a conductive additive may be added to the slurry.

As the solvent, N-methyl pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK), water and the like can be used.

In order to make active material, binder resin, conductive support agent and solvent mixed and made into slurry, general mixing equipment such as planetary mixer, defoaming kneader, ball mill, paint shaker, vibration mill, lai car, agitator mill etc. You may use it.

In the slurry application step, the slurry is applied to the surface of the current collector. As a method of applying the slurry, a coating method generally used for producing an electrode for a secondary battery, such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method can be used. The coating thickness of the slurry applied to the surface of the current collector is preferably 10 μm to 40 μm.

In the compression molding step, the current collector to which the slurry is applied is compression molded by a roll press. The current collector and the slurry are closely bonded by compression molding. The roll press may be one commonly used. Compression molding can be performed, for example, by press molding at a linear pressure of 10 kg / cm to 2000 kg / cm using a roll press. The linear pressure may be appropriately controlled to be an optimum electrode density from the viewpoint of energy density and battery life.

In the heat treatment step, the binder resin is cured by heating the slurry closely bonded to the surface of the current collector. In the heat treatment step, heating is performed in accordance with the curing temperature of the binder resin to be used. An active material layer is formed on the current collector by this heat treatment step.

The lithium ion secondary battery of the first embodiment of the present invention can use known battery components except using the above-mentioned negative electrode and positive electrode, and can be manufactured by a known method.

The battery components include, in addition to the positive electrode and the negative electrode, a separator and an electrolytic solution.

The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass while preventing the short circuit of the current due to the contact of the both electrodes. For the separator, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene or polyethylene, or a porous film made of ceramic can be used.

The electrolytic solution contains a solvent and an electrolyte dissolved in the solvent.

For example, cyclic esters, linear esters, ethers can be used as a solvent. As cyclic esters, for example, ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, gamma valerolactone and the like can be used. Examples of chain esters that can be used include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester and the like. As the ethers, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane and the like can be used.

Further, as an electrolyte to be dissolved in the above-mentioned electrolytic solution, lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used.

For example, as an electrolytic solution, 0.5 mol / l to 1 lithium salt (electrolyte) such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ and the like in a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate It is possible to use a solution dissolved at a concentration of about 7 mol / l.

The shape of the lithium ion secondary battery according to the first embodiment of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a laminated shape, and a coin shape can be adopted. In any of the shapes, the separator is interposed between the positive electrode and the negative electrode to form an electrode body, and the distance from the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside is for current collection After connection using a lead or the like, the electrode body is sealed in a battery case together with an electrolytic solution to form a battery.

Another lithium ion secondary battery according to the first embodiment of the present invention includes a positive electrode, an element which can be alloyed with lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, It has a negative electrode having a negative electrode active material containing Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi and / or a compound of the above elements, and graphite. The blending ratio of the element and / or the compound of the element when the content of the graphite and the compound of the element and / or the element is 100% by mass is 27% by mass to 51% by mass.

The compounds of lithium can be alloyed _{_{_{_{elements, ZnLiAl, AlSb, SiB 4,}}}} SiB 6, Mg 2 Si, Mg 2 Sn, Ni 2 Si, TiSi 2, MoSi 2, CoSi 2, NiSi 2, CaSi 2, CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _V (0 <V ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO, etc. may be mentioned.

Second Embodiment
The negative electrode for a lithium ion secondary battery according to the second embodiment of the present invention contains carbon-based particles and Li storage particles. Examples of carbon-based particles include natural graphite, artificial graphite, coke, mesophase carbon, vapor grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber and the like, but they have excellent buffer performance and have a D ₅₀ of 1 μm to Graphite in the range of 15 μm is preferred. The D ₅₀ of this carbon-based particle is particularly preferably 1 μm to 10 μm when the following SiO _x is used as the Li storage particle.

As the Li storage particles, silicon, tin, germanium, lead, indium, silicon oxide, tin oxide, etc. can be used, but a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6) It is desirable to use SiO-based particles consisting of The SiO-based particles are composed of SiO _x decomposed into fine Si and SiO ₂ covering Si by disproportionation reaction. When x is less than the lower limit value, the Si ratio increases, so that the volume change at the time of charge and discharge becomes too large, and the cycle characteristics deteriorate. When x exceeds the upper limit value, the Si ratio is lowered and the energy density is lowered. The range of 0.5 ≦ x ≦ 1.5 is preferable, and the range of 0.7 ≦ x ≦ 1.2 is more preferable.

Further, it is preferable that the Li occluding particles be composed of SiO-based particles and a covering layer which is made of a carbon material and covers the surface of the SiO-based particles. By having the covering layer, the reaction between the SiO-based particles and the hydrofluoric acid can be further prevented, and the cycle characteristics of the lithium ion secondary battery can be improved. As the carbon material of the covering layer, natural graphite, artificial graphite, coke, mesophase carbon, vapor grown carbon fiber, pitch carbon fiber, PAN carbon fiber, etc. can be used. Moreover, in order to form a coating layer, mechanical surface fusion treatment methods, such as mechanofusion described in patent document 2, CVD method etc. can be used.

The formation amount of the covering layer can be 1% by mass to 50% by mass with respect to the total of the SiO-based particles and the covering layer. If the coating layer is less than 1% by mass, the effect of improving conductivity can not be obtained, and if it exceeds 50% by mass, the ratio of SiO _x relatively decreases and the negative electrode capacity decreases. The amount of the coating layer formed is preferably in the range of 5% by mass to 30% by mass, and more preferably in the range of 5% by mass to 20% by mass.

Li occlusion particles is _{desirably D 50} in the range of 1 [mu] m ~ 10 [mu] m. D ₅₀ decreases the charge and discharge characteristics of 10μm larger than the lithium ion secondary battery, D ₅₀ is lowered charge-discharge characteristics of the same lithium ion secondary battery for agglomerated with 1μm of less than a coarse grain There is a case.

The mixing ratio of the carbon-based particles to the Li storage particles is preferably in the range of carbon-based particles: Li storage particles = 55: 27 to 45:37 by mass ratio. It is not preferable that the mass ratio of carbon-based particles is larger than that of carbon-based particles: Li storage particles = 55: 27 in mass ratio, since the capacity decreases, and the mass ratio of carbon-based particles: carbon-based particles: Li storage particles = 45: 37 It is not preferable because the cycle characteristics deteriorate if the value of. The carbon-based particles are mixed in the range of 40% by mass or more and 65% by mass or less, where the total mass of the mixture of the carbon-based particles and the Li storage particles, the conductive auxiliary agent, and the binder resin is 100% by mass. Is preferred. If the carbon-based particles are less than 40% by mass, it is difficult to improve the cycle characteristics of the lithium ion secondary battery. Even if the carbon-based particles are mixed at more than 65% by mass, the reason is unknown, but the cycle characteristics of the lithium ion secondary battery are degraded as compared with the case where the carbon-based particles are 65% by mass or less. Furthermore, the mixing amount of the carbon-based particles is more optimally in the range of 45% by mass to 65% by mass.

The ratio of _D 50 _{(D 2)} of the _D 50 _{(D 1)} and Li occlusion particles of the carbon-based particles _(D 1 / _{D 2)} shall be greater than 1 and 2 below. When this ratio exceeds 2, the particle size difference becomes large, and it becomes difficult for the negative electrode active material layer to have many small pores.

The pores preferably have a shape close to a true sphere, and the ratio (a / b) of the minor diameter (a) to the major diameter (b) of the pores is preferably close to 1. By doing so, stress concentration can be prevented, and cracking and peeling can be prevented. The total volume of pores in the negative electrode active material layer is preferably smaller than the total volume of Li storage particles. When the total volume of the pores is larger than the total volume of the Li storage particles, the capacity per volume of the electrode decreases and the capacity retention rate decreases.

The negative electrode of the lithium ion secondary battery of the second embodiment of the present invention has a current collector and a negative electrode active material layer bound on the current collector. The negative electrode active material layer is formed by adding a mixture of carbon-based particles and Li storage particles, a conductive additive, a binder resin, and an appropriate amount of an organic solvent as required, and mixing them to form a slurry by roll coating, dip It can manufacture by apply | coating on a collector by methods, such as a coating method, a doctor blade method, a spray coating method, a curtain coating method, and pressing and hardening binder resin. The thickness (t) of the negative electrode active material layer can be 10 μm to 20 μm as in the conventional case.

The ratio (D ₁ / t) of D ₅₀ (D ₁ ) of the carbon-based particles to the thickness (t) of the negative electrode active material layer is set to 1/4 or more and 5/6 or less. When this ratio (D ₁ / t) is less than 1/4, the electrical resistance of the negative electrode active material layer is increased and the charge / discharge efficiency of the lithium ion secondary battery is decreased. When it exceeds 5/6, the negative electrode active material layer is formed Cracks and peeling are likely to occur. It is particularly desirable that the ratio (D ₁ / t) be 1/2 or more and 2/3 or less.

Further, the ratio (D ₂ / t) of D ₅₀ (D ₂ ) of the Li storage particle to the thickness (t) of the negative electrode active material layer is the D ₅₀ (D ₁ ) of the above-mentioned carbon-based particle and Li storage particle the ratio of _{_D} 50 _(D ₂₎ of _{_(D} 1 / D _2), and the ratio of _{_D} 50 _(D ₁₎ and the anode active material layer thickness of the carbon-based particles _{(t) (D 1 / t} ) From 1/8 to 2/3.

The same current collector as that described in the first embodiment can be used.

As the conductive additive, the same one as described in the first embodiment can be used. The amount of the conductive aid used is not particularly limited. In addition, when using Li occlusion particle | grains which have a coating layer which consists of carbon materials, the addition amount of a conductive support agent can be reduced or there is nothing.

The binder resin is used as a binder for binding the active material and the conductive aid to the current collector. The binder resin is required to bind the active material and the like in a small amount as much as possible, and the amount is 0.5 mass of the total of the mixture of the carbon-based particles and the Li storage particles, the conductive aid and the binder resin. % To 50% by mass is desirable. When the amount of binder resin is less than 0.5% by mass, the formability of the electrode is lowered, and when it is more than 50% by mass, the energy density of the electrode is lowered. As the binder resin, fluorine-based polymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubbers such as styrene butadiene rubber (SBR), and imides such as polyimide, polyamide imide, and polyamide imide silica hybrid Examples thereof include polymers, alkoxysilyl group-containing resins, polyacrylic acids, polymethacrylic acids and polyitaconic acids. Copolymers of acrylic acid and acid monomers such as methacrylic acid, itaconic acid, fumaric acid and maleic acid can also be used. Among them, a high binding binder having excellent binding properties is preferable, and at least one selected from polyamideimide resin, polyamideimide silica hybrid and polyacrylic acid is particularly desirable.

It is desirable that lithium be pre-doped in the negative electrode in the lithium ion secondary battery of the second embodiment of the present invention. In order to dope the negative electrode with lithium, for example, an electrode forming method in which a half cell is assembled using metallic lithium as a counter electrode and electrochemically dope lithium can be used. The doping amount of lithium is not particularly limited.

Represented by Li _x Si _y O _z in the SiO ₂ phase of the SiO-based particles of the negative electrode active material by doping with lithium or after the initial charge of the lithium ion secondary battery of the second embodiment of the present invention It contains oxide compounds. As Li _x Si _y O _z , for example, SiO _{2 with} x = 0, y = 1, z = 2, Li = ₂ SiO ₃ with x = 2, y = 1, z = ₃ , x = 4, y = 1, Examples are Li ₄ SiO _{4 with} z = 4. For example, Li ₄ SiO ₄ of x = 4, y = 1, z = ₄ is produced by the following reaction, and the coulombic efficiency is calculated to be about 77%.
2SiO + 8.6Li + + 8.6e-→ 1.5Li _4.4 Si +
1 / 2Li ₄ SiO ₄

Further, when the reaction is stopped halfway, x = 2, y = 1 , z = 3 of _Li 2 SiO ₃ and x = 4, y = 1, z = 4 in _Li 4 SiO as the following reaction ₄ both generates the coulombic efficiency of this case is calculated to be about 77%.
2SiO + 7.35Li + + 7.35e-→ 1.42Li ₄ Si
+ 1 / 3Li ₂ SiO ₃ + 1 / 4Li ₄ SiO ₄

Li ₄ SiO ₄ produced by the above reaction is an inactive substance not involved in the electrode reaction at the time of charge and discharge, and functions to reduce the volume change of the active material at the time of charge and discharge. Therefore, when the oxide-based compound represented by Li _x Si _y O _z is contained in the SiO ₂ phase of the SiO-based particles, the lithium ion secondary battery of the present invention further improves the cycle characteristics.

The lithium ion secondary battery of the second embodiment of the present invention using the above-mentioned negative electrode can use known positive electrodes, electrolytes and separators which are not particularly limited. The positive electrode may be any one that can be used in a lithium ion secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer contains a positive electrode active material and a binder, and may further contain a conductive aid. The positive electrode active material, the conductive additive and the binder are not particularly limited as long as they can be used in a lithium ion secondary battery.

Examples of the positive electrode active material include metal lithium, LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO ₂ , and sulfur. The current collector may be any one commonly used for a positive electrode of a lithium ion secondary battery, such as aluminum, nickel, stainless steel and the like. As the conductive additive, the same one as described in the above-mentioned negative electrode can be used.

The electrolytic solution is one in which a lithium metal salt which is an electrolyte is dissolved in an organic solvent. The electrolyte is not particularly limited. As an organic solvent, from an aprotic organic solvent such as fluoroethylene carbonate (FEC), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), etc. One or more selected can be used. Further, as an electrolyte to be dissolved, a lithium metal salt soluble in an organic solvent such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiI, LiClO ₄ and LiCF ₃ SO ₃ can be used.

For example, about 0.5 mol / l to about 1.7 mol / l of lithium metal salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 and the} like in an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate Solutions dissolved at concentration can be used.

The separator is not particularly limited as long as it can be used for a lithium ion secondary battery. The separator separates the positive electrode and the negative electrode and holds the electrolytic solution, and a thin microporous film such as polyethylene or polypropylene can be used.

The shape of the lithium ion secondary battery of the second embodiment of the present invention is not particularly limited, and the same shape as that of the first embodiment can be adopted.

Third Embodiment
<Anode for lithium ion secondary battery>
The negative electrode for a lithium ion secondary battery according to the third embodiment of the present invention has a current collector and an active material layer formed on the surface of the current collector.

As the current collector, one similar to that of the first embodiment can be used.

The active material layer contains an active material, a binder and a buffer material. You may add a conductive support agent to an active material layer as needed.

The active material in the third embodiment of the present invention consists of SiO _x powder (0.5 ≦ x ≦ 1.5). SiO _x (0.5 ≦ x ≦ 1.5) is a general formula representing an amorphous silicon oxide obtained using silicon dioxide (SiO ₂ ) and metallic silicon (Si) as raw materials. It is known that SiO _x decomposes into Si and SiO ₂ when heat-treated. This is called disproportionation reaction, and in the case of homogeneous solid silicon monoxide SiO which has a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by internal reaction of the solid. . The Si phase obtained by separation is very fine and dispersed in the SiO ₂ phase. In addition, the SiO ₂ phase covering the Si phase has the function of suppressing the decomposition of the electrolytic solution. Therefore, a lithium ion secondary battery using a negative electrode active material composed of SiO _x decomposed into Si phase and SiO ₂ phase is excellent in cycle characteristics.

In the case of SiO _x powder (0.5 ≦ x ≦ 1.5), if x is less than 0.5, the ratio occupied by the Si phase becomes high, so that the volume change during charge and discharge becomes too large, and the cycle characteristics descend. In addition, when x exceeds 1.5, the ratio of the Si phase decreases to lower the energy density. A further preferable range of x is 0.7 ≦ x ≦ 1.2.

The SiO _x powder preferably consists of substantially spherical particles. From the viewpoint of charge and discharge characteristics of the lithium ion secondary batteries, preferably as D ₅₀ of the SiO _x powder is small. However, if the D ₅₀ is too small, since the coarse particles by aggregation during the formation of the negative electrode may decrease the charge-discharge characteristics of the lithium ion secondary battery. When the D _{50 of the} SiO _x powder is too small, the surface area of the SiO _x powder is increased, the contact surface between the SiO _x powder and the electrolyte is increased, and the decomposition of the electrolyte proceeds, resulting in the lithium ion secondary battery cycle The characteristics get worse. Therefore, _{D 50} of SiO _x powder is preferably 2μm or more. Incidentally, it refers to a particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50% and D _50. That is, D ₅₀ refers to the median diameter measured on a volume basis.

Further, _{D 50} of SiO _x powder is preferably 15μm or less. And D ₅₀ is greater than 15 [mu] m, since SiO _x powder conductivity is poor, the conductivity of the whole electrode becomes uneven, decreases the charge and discharge characteristics of the lithium ion secondary battery.

More preferably, the D _{50 of the} SiO _x powder is 4 μm to 10 μm.

The span of the SiO _x powder is preferably 1.1 to 2.3. In particular, SiO _x powder having a span of 1.3 to 1.4 is preferable. The span is defined as (D ₉₀ -D ₁₀ ), where the particle diameter corresponding to 10%, 50%, 90% in integrated value in particle size distribution measurement by laser diffraction method is D ₁₀ , D ₅₀ , D _90. / D ₅₀ points.

If the span of the SiO _x powder is 1.1 to 2.3, it means that the width of the particle size distribution is narrow and the variation of the particle diameter is small. When the variation of the particle size of the SiO _x powder is small, SiO _x powder does not include those having a large particle size as or extremely having extremely small particle diameter as compared with the D _50. When the SiO _x powder having a particle diameter extremely smaller than D ₅₀ is contained, the surface area of the SiO _x powder is increased, the contact surface between the SiO _x powder and the electrolyte is increased, and the decomposition of the electrolyte progresses. The cycle characteristics of the lithium ion secondary battery deteriorate. Also, if SiO _x powder having a particle diameter extremely larger than D ₅₀ is included, the SiO _x powder may not be filled in the void formed by the buffer material graphite powder.

As SiO _x powder, it can be a commercially available SiO _x powder with desired _{D 50.} In order to adjust the D _{50 of the} SiO _x powder, generally known grinding methods and grinders can be used. For example, a ball mill, a roller mill, a jet mill, a hammer mill or the like can be used. The pulverization may be performed either wet or dry, but the use of wet pulverization in the presence of an organic solvent such as hexane can prevent the surface oxidation of silicon oxide during pulverization. Wet grinding using an organic solvent is desirable because it can prevent the proportion of inert SiO ₂ from increasing.

_{D 50} of the SiO _x powder is 1 / 4-1 / 2 of the _{D 50} of the graphite powder is a cushioning material. If the the above range relation of the graphite powder and SiO _x powder D _50, graphite powder SiO _x powder is placed in the gap to form.

The content of the SiO _x powder is preferably 32% by mass or more and 52% by mass or less when the mass of the entire active material layer is 100% by mass. When the content of the SiO _x powder is less than 32% by mass, the amount of graphite relatively increases, the adhesion of the binder is insufficient, and the cycle characteristics of the lithium ion secondary battery are deteriorated. Cycle characteristics of the content of 52 wt% greater than the SiO _x powder agglomerated lithium ion secondary battery of the SiO _x powder is deteriorated.

The binder is used as a binder for fixing the active material and the buffer material to the current collector. The binder is required to bind the active material and the like in an amount as small as possible. In the case of the present invention, when the mass of the entire active material layer is 100% by mass, the content of the binder is 5% by mass to 25% by mass. The content of the binder is more preferably 8% by mass to 15% by mass.

As the binder, the same one as in the first embodiment can be used.

A conductive support agent is added to the active material layer as needed to enhance the conductivity of the electrode layer. The same conductive aid as that of the first embodiment can be used. The amount of the conductive aid used is not particularly limited, but can be, for example, about 2% by mass to 10% by mass with respect to 100% by mass of the active material.

The buffer material is made of graphite powder. Graphite has a graphite structure (a structure in which hexagonal network planes formed by carbon atoms are regularly stacked). Therefore, graphite has a layered structure, and each layer and each layer are bound by a weak van der Waals force. Therefore, the pressurized graphite powder can absorb the pressure by reducing the distance between the layers. Graphite is also prone to interlayer slippage because of its layered structure, and the pressure applied to the graphite powder is also absorbed by the interlayer slippage. That is, the graphite powder can absorb part of the expansion of SiO _x by the elastic deformation of the graphite powder inside.

As the graphite powder, natural graphite powder, artificial graphite powder, spherulite graphite powder (graphitized mesophase carbon small spheres), graphite-based carbon material powder, etc. can be used. As the graphite-based carbon material, a pyrolyzate of a condensed polycyclic hydrocarbon compound such as pitch and coke can be used. Such a graphite powder has a highly developed graphite structure, and the average interplanar spacing d ₀₀₂ of the (002) plane determined by powder X-ray diffraction, for example, is 0.336 nm or less.

_{D 50} of the graphite powder is 2 to 4 times the _{D 50} of the SiO _x powder, the amount of graphite powder, when the the sum of the mass of the mass and SiO _x powder of the graphite powder is 100 mass% 36% by mass to 61% by mass.

By the D ₅₀ D ₅₀ of the graphite powder SiO _x powder is in the above relationship, SiO _x powder having a small particle diameter voids graphite powder form having a large particle diameter are filled. As the graphite _powder, it is preferable to use a _{D 50} is 4 [mu] m ~ 30 [mu] m. In particular graphite powder preferably has a _{D 50} is 5 [mu] m ~ 25 [mu] _m, and more preferably _{D 50} is 8 [mu] m ~ 20 [mu] m.

When D ₅₀ of the graphite powder decreases, the filling rate of the graphite powder in the active material layer decreases. If this is packed in a container of volume in the powder, although the degree varies depending tap number and the tap pressure, in the same number of taps and the tap pressure, more D ₅₀ is small, the chewing air filling rate falls between by.

Here, the filling rate of the graphite powder in the active material layer is determined by the following equation.
Packing ratio = (mass of graphite per unit volume / true density of graphite) × 100

As the packing ratio of the graphite powder decreases, the packing ratio of the SiO _x powder packed in the voids formed by the graphite powder also necessarily decreases. As the filling rate of the SiO _x powder decreases, the battery capacity of the entire electrode decreases. Therefore, _{D 50} of the graphite powder is preferably not less than 4 [mu] m.

Also it is possible to D ₅₀ of the graphite powder to achieve both power density and energy density by using those 30μm or less. The energy density is the battery weight or the power capacity per battery volume, and the power density is the maximum amount of power that can be provided per battery weight or battery volume. And D ₅₀ is greater than 30μm of the graphite powder, since the time of application of the slurry can not in coating thickness under the maximum particle diameter or less of graphite powder, inevitably coating thickness becomes thick. When the thickness of the coating film is large, streaks may be formed in the finished coating film, and the power density may be reduced depending on the energy density.

The blending amount of the graphite powder is 36% by mass to 61% by mass when the total of the mass of the graphite powder and the mass of the SiO _x powder is 100% by mass.

When the mass of the graphite powder is small, no buffer effect is observed, and when the mass of the graphite powder is large and the mass of the SiO _x powder is small, the electrode capacity is reduced. From the viewpoint of both the electrode capacity and the buffer effect, the blending ratio of the graphite powder and the SiO _x powder is preferably in the above range. Furthermore, the blending amount of the graphite powder is preferably 36% by mass to 49% by mass. When the blending amount of the graphite powder is in this range, the cycle characteristics of the lithium ion secondary battery are less likely to deteriorate.

In the active material layer, SiO _x powder is placed in the gap graphite powder form, and be SiO _x powder is expanded, re-arranged so as SiO _x powder and the graphite powder does not expand in the thickness direction of the active material layer Be done. Therefore, even if the SiO _x powder expands, the volume change in the thickness direction of the negative electrode is suppressed.

Expressing in another form that there is room for such repositioning, the negative electrode for a lithium ion secondary battery is formed through a compression molding process, and has a press pressure higher than the press pressure in the compression molding process. When the negative electrode for a lithium ion secondary battery is compressed, the thickness of the active material layer in the compression direction decreases. If there is no room to rearrange, the thickness of the active material layer can not be reduced even if the negative electrode for a lithium ion secondary battery is compressed at a higher pressing pressure.

When the SiO _x powder is in the state of being filled in the void formed by the graphite powder, the filling efficiency is improved and the amount of the graphite powder and the SiO _x powder contained per unit volume is increased, and thus the electrode Density increases. That electrode density when compared with a constant pressing pressure may be referred to a higher, SiO _x powder is placed in the gap graphite powder and SiO _x powder form graphite powder as described above, and SiO _x powder Even if it expands, it is an index showing that the SiO _x powder and the graphite powder are packed in the state of being rearranged. In addition, when the electrode density is high, the filling rate of the graphite powder in the active material layer is also high.

The electrode density is determined by the following equation: electrode density = (mass of electrode excluding current collector) / (volume of electrode excluding current collector). Although it will be described later in Examples, when the D ₅₀ D ₅₀ of the graphite powder SiO _x powder is in the above relationship, it was confirmed that the electrode density is increased. In addition, since the electrode density is high, the battery capacity per unit volume of the electrode is also high.

Here, the mechanism by which the volume change of the negative electrode is suppressed even if the SiO _x powder is expanded will be described with reference to FIGS. FIG. 7 is a schematic view illustrating the negative electrode for a lithium ion secondary battery of the present invention. In FIG. 7, a state in which the SiO _x powder 2 and the graphite powder 3 are bound on the current collector 1 via the binder 4 and the active material layer 5 is formed on the current collector 1 is schematically shown. Is shown. In FIG. 7, _{D 50} of the SiO _x powder 2 is described as a 1 / 4-1 / 2 of the _{D 50} of the graphite powder 3. FIG. 8 is a schematic view for explaining the volume change of the negative electrode for a lithium ion secondary battery of the present invention. The left view of FIG. 8 is the same as FIG. 7, and the arrangement after the SiO _x powder 2 is expanded by charging is shown in the right view of FIG.

In FIG. 7, the SiO _x powder 2 is disposed in the void formed by the graphite powder 3. In the arrangement state of the SiO _x powder 2 and the graphite powder 3, there is room for further reducing the thickness of the active material layer 5 if pressure is applied to the active material layer from above.

The right side of FIG. 8 shows the state when the SiO _x powder 2 is expanded. This will be described in comparison with the left view of FIG. 8 (the state before expansion, the same as FIG. 7). The SiO _x powder 2 expands about twice in volume upon charging. The fact that the volume of the SiO _x powder 2 expands about twice is illustrated as the D ₅₀ of the SiO _x powder 2 increases by about 10%.

The SiO _x powder 2 contacts the graphite powder 3 disposed nearby by expansion. At the contact surface of the graphite powder 3, the graphite powder 3 is slipped between layers, and part of the expansion of the SiO _x powder 2 is absorbed by elastic deformation of the surface of the graphite powder 3.

In the right view of FIG. 8, when the SiO _x powder 2 expands, the expanded SiO _x powder 2 and the graphite powder 3 disposed near are rearranged so as not to expand in the thickness direction of the active material layer 5. . Therefore, the SiO _x powder 2 is again disposed in the void formed by the graphite powder 3 and the thickness of the active material layer 5 hardly changes.

Figure 9 is a schematic diagram illustrating the SiO _x D ₅₀ of the powder 2 of the graphite powder 3 D ₅₀ substantially equal to or lithium ion secondary battery negative electrode was used slightly smaller, 10, 9 It is a schematic diagram explaining the volume change of the negative electrode for lithium ion secondary batteries described. The left view of FIG. 10 is the same as FIG. 9, and the arrangement after the SiO _x powder 2 is expanded by charging is shown in the right view of FIG.

In Figure 9, _{D 50} of the SiO _x powder 2 is described as a little less than the equivalent _{D 50} of the graphite powder 3. In FIG. 9, as in FIG. 7, SiO _x powder 2 and graphite powder 3 are bound on current collector 1 via binder 4, and active material layer 5 is formed on current collector 1. Although state is shown schematically, _{D 50} of the SiO _x powder 2 is almost equal to _{D 50} of the graphite powder 3, SiO _x powder 2 is filled so as to collide with the graphite powder 3, SiO _x The powder 2 and the graphite powder 3 are stacked to form a thickness of the active material layer 5. In the active material layer 5 of FIG. 9, more voids are found than in the active material layer 5 of FIG. 7, but since the SiO _x powder 2 can not enter into the voids, the active material layer 5 of FIG. Even if pressure is applied from above, the thickness of the active material layer 5 can not be reduced unless the powder is broken.

Therefore, when pressed under the same pressure, the thickness of the active material layer 5 of FIG. 9 is larger than that of the active material layer 5 of FIG. 7.

Description will be made in comparison with the right view of FIG. 10 and the left view of FIG. 10 (state before expansion, the same as FIG. 9). In the right view of FIG. 10, the SiO _x powder 2 contacts the graphite powder 3 disposed nearby by expanding. At the contact surface of the graphite powder 3, the graphite powder 3 is slipped between layers, and part of the expansion of the SiO _x powder 2 is absorbed by elastic deformation of the surface of the graphite powder 3.

Further, in the active material layer 5 of FIG. 10, there is no room where the SiO _x powder 2 and the graphite powder 3 can be rearranged, so the expansion of the SiO _x powder 2 causes the graphite powder 3 and the SiO _x powder 2 to move in the thickness direction. I have no choice. Therefore, the thickness of the active material layer 5 in FIG. 10 is increased.

When the thickness of the active material layer 5 is increased, the binding force between the binder 4 and the SiO _x powder 2 is weakened, the SiO _x powder 2 is peeled off from the binder 4, and the conductive path in the electrode is broken. Further, when such expansion and contraction are repeated, the SiO _x powder 2 is detached from the current collector 1 or the SiO _x powder 2 is distorted to be miniaturized and detached from the current collector 1.

In the case _{D 50} of the SiO _x powder 2 is less than 1/4 of the _{D 50} of the graphite powder 3, aggregation of SiO _x powder 2 with each other occurs. When agglomeration of SiO _x powder 2 together takes place, above 9 and substantially equal to or lithium ion secondary battery using those slightly smaller SiO _x powder 2 _{D 50} described in FIG. 10 is a _{D 50} of the graphite powder 3 The same thing as the negative electrode occurs.

By such a mechanism, the negative electrode for a lithium ion secondary battery according to the third embodiment of the present invention comprises a buffer material in an active material layer containing SiO _x powder (0.5 ≦ x ≦ 1.5) as an active material. By mixing the graphite powder capable of functioning as a predetermined amount and specifying the ratio of the sizes of the two powders, it is possible to largely suppress the volume change of the entire negative electrode.

The negative electrode for a lithium ion secondary battery can be manufactured by a known manufacturing method. For example, it can be manufactured by the same manufacturing method as that of the first embodiment. The coating thickness of the slurry applied to the surface of the current collector is preferably 10 μm to 30 μm.

<Lithium ion secondary battery>
In the lithium ion secondary battery of the third embodiment of the present invention, the negative electrode is the negative electrode for a lithium ion secondary battery of the third embodiment. Since the negative electrode is the negative electrode for a lithium ion secondary battery according to the third embodiment, the volume change of the entire negative electrode during charge and discharge is suppressed. Since the volume change of the whole negative electrode is suppressed, the fall of the initial stage efficiency of a lithium ion secondary battery can be suppressed.

Initial efficiency is the ratio of the discharge capacity to the initial charge capacity of the battery. Lithium ions are stored at the negative electrode during charge and discharged at the time of discharge. When lithium ions are occluded during charging to expand the negative electrode active material and the thickness of the entire negative electrode is increased, the conductive path in the negative electrode is cut and the conductivity of the negative electrode is reduced. When the conductivity of the negative electrode decreases, lithium ions are less likely to be released during discharge. Thereby, the discharge capacity is reduced and the initial efficiency is reduced.

In the lithium ion secondary battery according to the third embodiment of the present invention, since the volume change of the entire negative electrode is suppressed, the decrease in the initial efficiency can be suppressed. In addition, the ability to suppress the decrease in initial efficiency of the battery means that the amount of lithium ions not released is also reduced while being stored in the negative electrode. Therefore, if the decrease in initial efficiency of the battery can be suppressed, lithium moving between the negative electrode and the positive electrode It is possible to suppress an increase in the amount of ions and, as a result, a decrease in the electric capacity of the battery.

Moreover, since the volume change of the whole negative electrode is suppressed, it can suppress that an active material peels or drops off from a collector, and the lithium ion secondary battery of the 3rd Embodiment of this invention can suppress deterioration of cycling characteristics. .

The lithium ion secondary battery of the third embodiment using the above-described lithium ion secondary battery negative electrode of the third embodiment is publicly known except that the above-described lithium ion secondary battery negative electrode of the third embodiment is used. Cell components can be used and can be manufactured according to known techniques.

That is, as a battery component, a positive electrode, a negative electrode, a separator, and an electrolytic solution are used.

Like the negative electrode, the positive electrode has a current collector and an active material layer bonded to the surface of the current collector. The active material layer contains an active material, a binder, and, optionally, a conductive auxiliary. The current collector, the binder, and the conductive additive are the same as those described for the negative electrode.

A lithium-containing compound is suitable as the positive electrode active material. For example, lithium-containing metal composite oxides such as lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide and the like can be used. Other metal compounds or polymer materials can also be used as the positive electrode active material. Other metal compounds include, for example, oxides such as titanium oxide, vanadium oxide or manganese dioxide, or sulfides such as titanium sulfide or molybdenum sulfide. Examples of the polymer material include conductive polymers such as polyaniline or polythiophene.

As a positive electrode active material, xLi ₂ M ¹ O _3. (1-x) LiM ² O ₂ (0 <x ≦ 1, M ¹ is one or more metal elements having a tetravalent Mn essential, M ² is a tetravalent In the case of using a lithium manganese-based oxide represented by two or more kinds of metal elements essential for the Mn), a voltage of 4.5 V is applied to the battery in the activation process of the active material. This is because the above lithium manganese-based oxide has a layered rock salt structure and can not be activated without applying 4.5 V. When a voltage of 4.5 V is applied to the battery, the expansion of the SiO _x powder, which is a negative electrode active material, is twice as large as that of a conventional 4.3 V applied voltage. When the negative electrode of the present invention is used, expansion of the entire thickness of the negative electrode can be suppressed even in the case of such a high voltage. As the lithium manganese _oxide, Li ₂ MnO _{_3,} it is possible to use a _{_{_{_{0.5Li 2 MnO 3 · 0.5LiNi 1/3 Co}}}} 1/3 Mn 1/3 O 2.

As the separator and the electrolytic solution, the same ones as in the first embodiment can be used.

Fourth Embodiment
The negative electrode material for a lithium ion secondary battery according to the fourth embodiment of the present invention contains a negative electrode active material and a conductive additive.

The negative electrode active material is composed of SiO _x (0.3 ≦ x ≦ 1.6) decomposed into fine Si and silicon oxide (SiO ₂ ) covering Si by disproportionation reaction. When x is less than the lower limit value, the Si ratio becomes high, so that the volume change during charge and discharge becomes too large, and the cycle characteristics of the lithium ion secondary battery deteriorate. When x exceeds the upper limit value, the Si ratio is lowered and the energy density is lowered. x is preferably in the range of 0.5 ≦ x ≦ 1.5, and more preferably in the range of 0.7 ≦ x ≦ 1.2.

The negative electrode active material is preferably in the form of particles, and the particle size is not particularly limited. The negative electrode active material may be primary particles or secondary particles. Furthermore, the D ₅₀ of the negative electrode active material is desirably in the range of 1 μm to 10 μm. And D ₅₀ is greater than 10μm of the negative electrode active material, it may decrease the charge-discharge characteristics of the lithium ion secondary battery. Further, a D ₅₀ of 1μm smaller than the negative electrode active material, since the aggregated during electrode fabrication it may become coarse particles, which may be similarly reduced charge and discharge characteristics of the lithium ion secondary battery. Incidentally, D ₅₀ herein refers to a median size measured by volume.

As the SiO _x , in view of charge and discharge characteristics, it is preferable to use one having a large specific surface area. On the other hand, if the specific surface area of SiO _x is too large, the surface film formed on the surface of SiO _x (SEI; Solid
It is not preferable because the Electrolyte Interphase increases. Taking these into consideration, the specific surface area (BET value, so-called BET specific surface area) of SiO _x is preferably 2.5 or more and 7.0 or less, and more preferably 2.5 or more and 3.5 or less. The content of the negative electrode active material of the negative electrode material is preferably 20% by mass to 40% by mass, and 27% by mass to 32% by mass, based on 100% by mass of the entire negative electrode material. More preferable. Furthermore, the sum of the content of the negative electrode active material and the graphite described later is preferably 70% by weight or more and 90% by weight or less, and 70% by weight or more and 85% by weight or less, based on 100% by weight of the entire negative electrode material. Is more preferred. The amount of the binder is preferably 8% by mass or more and 20% by mass or less based on 100% by mass of the entire negative electrode material. The same applies to the amount of the negative electrode active material in the negative electrode.

Graphite is a material that is compounded mainly to buffer the volume change of SiO _x associated with charge and discharge, and it is common to use MAG, SMG, SCMG (registered trademark) or the like. Since these materials are also excellent in conductivity, they may constitute part of the conductive path. The content of the graphite may be set according to the amount of SiO _{x, and when} the content of SiO _x is 100 mass%, it is preferably 120 mass% or more and 210 mass% or less. Further, it is preferable sum of the SiO _x and the graphite when the entire negative electrode material is 100 mass% is less than 90 wt% to 70 wt%, and more preferably not more than 85 wt% to 70 wt%.

As a conductive support agent, carbon black which is a carbonaceous fine particle, acetylene black (AB) which is a type of carbon black, ketjen black (KB), vapor grown carbon fiber (VGCF; Vapor Grown Carbon Fiber), graphite and the like It can be added alone or in combination of two or more. In order to form many conductive paths to improve the conductivity of the negative electrode, it is preferable to increase the blending amount of the conductive aid, but on the other hand, the conductive aid having a large specific surface area is bulky and therefore, in the negative electrode material It is difficult to disperse evenly. Therefore, in view of dispersibility, it is preferable to use one having a small specific surface area as the conductive aid, for example, it is desirable to use AB. Similarly, to use as small a particle size as a conductive additive is preferably, for example, is preferably _{D 50} of the conductive additive is used as a 3nm or 300nm or _less, used as _{D 50} is 10nm or more 100nm or less Is more preferable. D ₅₀ here also refers to a median size measured by volume.

As described above, in the negative electrode material of the present invention, the conductive support agent is blended in an amount corresponding to the sum of the surface area of the negative electrode active material SiO _{x and} the surface area of the graphite. The surface area of the SiO _x ^{(m 2),} specifically, a value obtained by multiplying the amount of SiO _x (g) the BET values of _{^{SiO x (m 2 / g)}} . By blending the conductive auxiliary agent in an amount corresponding to the surface area of SiO _x and graphite, the amount of the conductive auxiliary agent is sufficient to form a conductive path on or near the surface of SiO _x , and lithium ion It is considered that the discharge capacity of the secondary battery can be set to an amount that does not reduce it. In the fourth embodiment of the present invention, the amount of the conductive aid blended into the negative electrode material is the following two arithmetic expressions (the first formula based on the mass of the conductive aid, or the conductive aid It can be calculated based on the second equation based on volume.

The first equation is an arithmetic equation in which the mass of the conductive additive is adopted as the amount of the conductive additive to be added to the negative electrode material, and is represented by {(a1 × b1) + (a2 × b2)} / c. In the formula, a1 is the BET value of SiO _x (m ² / g), a 2 is the BET value of graphite (m ² / g), b 1 is the compounding amount of SiO _{x in} the negative electrode material (g), b 2 is the negative electrode material The blending amount (g) of graphite and c are the blending amount (g) of the conductive auxiliary in the negative electrode material. When the value of {(a1 × b1) + (a2 × b2)} / c is 24 or more and 65 or less, excellent conductivity can be imparted to the negative electrode, and the decrease in discharge capacity of the lithium ion secondary battery is suppressed it can.

The second equation is an arithmetic equation in which the volume of the conductive additive is adopted as the amount of the conductive additive to be added to the negative electrode material, and is represented by {(a1 × b1) + (a2 × b2)} / d. In the formulas, a1, a2, b1 and b2 are the same as above. In formula, d is the compounding quantity (cm < ³ >) of the conductive support agent in negative electrode material. If the value of {(a1 × b1) + (a2 × b2)} / d is 43.2 or more and 117 or less, excellent conductivity can be imparted to the negative electrode, and the discharge capacity of the lithium ion secondary battery is lowered Can be suppressed.

As a conductive support agent, what consists only of the carbonaceous fine particles mentioned above may be used, and a thing containing a dispersing agent etc. may be used. The dispersant is a type of surfactant and is an additive for improving the dispersibility of the carbonaceous fine particles.

The negative electrode material and the negative electrode according to the fourth embodiment of the present invention may further include a binder resin, a dispersant (surfactant), and the like, in addition to the negative electrode active material, the graphite, and the conductive auxiliary agent described above.

Although the type of binder resin is not limited, fluorine-based polymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubbers such as styrene butadiene rubber (SBR), imide-based polymers such as polyimide, alkoxysilyl Examples thereof include group-containing resins, polyacrylic acids, polymethacrylic acids and polyitaconic acids. Among these, it is preferable to use at least one selected from polyamideimide resin, polyamideimide silica hybrid resin, and polyacrylic acid.

The amount of the binder resin is preferably 8% by mass or more and 20% by mass or less, based on 100% by mass of the entire negative electrode material. When the amount of the binder resin is less than 8% by mass, the formability of the electrode decreases, and when it exceeds 20% by mass, the energy density of the electrode decreases and the resistance increases. In the negative electrode for a lithium ion secondary battery of the fourth embodiment of the present invention, at least a part of these binder resins may be contained in a denatured state by thermal decomposition or the like. In addition, the polyamide imide silica hybrid resin refers to that in which a side chain derived from alkoxysilane is formed at the molecular terminal of the polyamide imide resin, and, for example, an alkoxy group-containing silane modified polyamide imide resin (manufactured by Arakawa Chemical Co., Ltd.) It is possible to use commercially available products such as trade name COMPOCELAN, part number H900-2).

The negative electrode according to the fourth embodiment of the present invention is prepared by adding organic solvents to these materials and mixing them into a slurry, such as roll coating, dip coating, doctor blade, spray coating, curtain coating, etc. It can be produced by applying (laminating) to the current collector by a method and heating and curing the binder resin.

As a current collector, a general one may be used as a current collector for a negative electrode of a lithium ion secondary battery. For example, although what formed metals, such as Cu, in shape, such as foil, a board, and a mesh, can be used preferably, if it is the material and shape according to the object, it will not be limited in particular.

The lithium ion secondary battery of the fourth embodiment of the present invention using the above-mentioned negative electrode can use known positive electrodes, electrolytes and separators which are not particularly limited. The positive electrode may be any one that can be used in a lithium ion secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer contains a positive electrode active material and a binder, and may further contain a conductive aid. There is no limitation in particular in a positive electrode active material, a conductive support agent, and a binder, and it should just be a thing which can be used by a lithium ion secondary battery.

As the positive electrode active material, metal lithium, LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO ₂ , S or the like can be used. The current collector for the positive electrode may be any one commonly used for the positive electrode of lithium ion secondary batteries, such as aluminum, nickel, stainless steel and the like. As the conductive support agent, the same one as described for the above-mentioned negative electrode can be used.

The electrolytic solution is one in which an Li metal salt as an electrolyte is dissolved in an organic solvent. The electrolyte is not particularly limited. As an organic solvent, use is made of one or more selected from aprotic organic solvents such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. Can. Further, as an electrolyte to be dissolved, it is possible to use a Li metal salt soluble in an organic solvent such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiI, LiClO ₄ , LiCF ₃ SO _{3 and the} like.

For example, about 0.5 mol / l to 1.7 mol / l of Li metal salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 and the} like in an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate Solutions dissolved at concentration can be used.

Fifth Embodiment
The negative electrode for a lithium ion secondary battery according to the fifth embodiment of the present invention includes carbon-based particles and Li storage particles. Examples of carbon-based particles include natural graphite, artificial graphite, coke, mesophase carbon, vapor grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber and the like, but they have excellent buffer performance and have a D ₅₀ of 1 μm to Graphite in the range of 15 μm is preferred. The D ₅₀ of this carbon-based particle is particularly preferably 1 μm to 10 μm when the following SiO _x is used as the Li storage particle.

As the Li storage particles, those similar to the second embodiment can be used.

The ratio of _D 50 _{(D 2)} of the _D 50 _{(D 1)} and Li occlusion particles of the carbon-based particles _(D 1 / _{D 2)} is a 1/2 or more and 1.3 or less. When this ratio is out of this range, the particle size difference becomes large and the dispersibility is lowered. The ratio (D ₁ / D ₂ ) is particularly preferably 1/2 or more and 1 or less.

The negative electrode of the lithium ion secondary battery of the fifth embodiment of the present invention has a current collector and a negative electrode active material layer bound on the current collector. The negative electrode active material layer is formed by adding a mixture of carbon-based particles and Li storage particles, a conductive additive, a binder resin, and an appropriate amount of an organic solvent as required, and mixing them to form a slurry by roll coating, dip It can manufacture by apply | coating on a collector by methods, such as a coating method, a doctor blade method, a spray coating method, a curtain coating method, and pressing and hardening binder resin. The thickness (t) of the negative electrode active material layer can be 10 μm to 20 μm as in the conventional case.

The ratio (D ₁ / t) of D ₅₀ (D ₁ ) of the carbon-based particles to the thickness (t) of the negative electrode active material layer is 1/4 or more and 2/3 or less. When this ratio (D ₁ / t) is less than 1/4, the electrical resistance of the negative electrode active material layer is increased and the charge and discharge efficiency of the lithium ion secondary battery is decreased. Cracks and peeling are likely to occur. It is particularly desirable that the ratio (D ₁ / t) be 1/2 or more and 2/3 or less.

Further, the ratio (D ₂ / t) of D ₅₀ (D ₂ ) of the Li storage particle to the thickness (t) of the negative electrode active material layer is the D ₅₀ (D ₁ ) of the above-mentioned carbon-based particle and Li storage particle the ratio of _{_D} 50 _(D ₂₎ of _{_(D} 1 / D _2), and the ratio of _{_D} 50 _(D ₁₎ and the anode active material layer thickness of the carbon-based particles _{(t) (D 1 / t} ) And 1/8 or more and 13/15 or less.

As the current collector, one similar to that of the second embodiment can be used.

The same conductive aid as that in the second embodiment can be used. The use amount of the conductive aid is not particularly limited, but can be, for example, about 20 parts by mass to 100 parts by mass with respect to 100 parts by mass of the active material. If the amount of the conductive additive is less than 20 parts by mass, efficient conductive paths can not be formed, and if it exceeds 100 parts by mass, the formability of the electrode is deteriorated and the energy density is lowered. In addition, when using Li occlusion particle | grains which have a coating layer which consists of carbon materials, the addition amount of a conductive support agent can be reduced or there is nothing.

As the binder resin, the same one as in the second embodiment can be used.

It is desirable that lithium be pre-doped in the negative electrode in the lithium ion secondary battery of the fifth embodiment of the present invention. The lithium doping of the negative electrode is the same as that described in the second embodiment.

The lithium ion secondary battery of the fifth embodiment of the present invention using the above-mentioned negative electrode can use known positive electrodes, electrolytes and separators which are not particularly limited. The positive electrode may be one that can be used in a lithium ion secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer contains a positive electrode active material and a binder, and may further contain a conductive aid. The positive electrode active material, the conductive additive and the binder are not particularly limited as long as they can be used in a lithium ion secondary battery.

As the positive electrode active material, the same materials as those described in the second embodiment can be used.

The same electrolytic solution as that described in the second embodiment can be used.

The shape of the lithium ion secondary battery according to the first to fifth embodiments of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a laminated shape, and a coin shape can be adopted. In any of the shapes, the separator is interposed between the positive electrode and the negative electrode to form an electrode body, and the distance from the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside is for current collection After connection using a lead or the like, the electrode body is sealed in a battery case together with an electrolytic solution to form a battery.

The lithium ion secondary batteries of the first to fifth embodiments can be mounted on a vehicle. The vehicle can be equipped with a lithium ion secondary battery having high capacity and high energy density, and can be a high performance vehicle. The vehicle may be any vehicle that uses electric energy from batteries for all or part of the power source, for example, electric vehicles, hybrid vehicles, plug-in hybrid vehicles, hybrid railway vehicles, forklifts, electric wheelchairs, electric assists There are bicycles and electric motorcycles.

The embodiments of the lithium ion secondary battery, the negative electrode for a lithium ion secondary battery, and the negative electrode material for a lithium ion secondary battery according to the present invention have been described above, but the present invention is not limited to the above embodiments. . In the range which does not deviate from the summary of the present invention, it can carry out with various forms which gave change, improvement, etc. which a person skilled in the art can make.

Hereinafter, the present invention will be specifically described by way of examples.

Hereinafter, the present invention will be described in more detail by way of an example.

(Examples 1 to 3 and Comparative Example 1)
<Fabrication of positive electrode>
A 20 μm aluminum foil is prepared as a current collector of the positive electrode, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ (manufactured by Nichia Chemical Co., Ltd.) is prepared as a positive electrode active material, and polyfluorinated as a binder resin of the positive electrode. Vinylidene (PVDF) and acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) were prepared as a conductive aid for the positive electrode.

The active material, the conductive auxiliary agent, and the binder resin were mixed at a mass ratio of active material: conductive auxiliary agent: binder resin = 88: 6: 6. An appropriate amount of N-methylpyrrolidone (NMP) as a solvent was added to the above mixture to prepare a slurry.

The above slurry was placed on an aluminum foil, and the slurry was applied to the aluminum foil in the form of a film using a doctor blade. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then the current collector and the coated product on the current collector were firmly and closely bonded by a roll press. At this time, the electrode density was 2.37 g / cm ³ and the electrode weight per unit area was 12.1 mg / cm ² . The joined product was heated at 120 ° C. for 6 hours in a vacuum dryer, cut into a predetermined shape (25 mm × 30 mm rectangular shape), and used as a positive electrode with a thickness of about 50 μm.

<Fabrication of negative electrode>
As negative electrode active materials, SiO 2 (made by Aldrich) having a D ₅₀ of 4 μm and graphite (natural graphite (made by Hitachi Chemical Co., Ltd.) having a D ₅₀ of 20 μm) were prepared.

Alkoxy group-containing silane-modified polyamideimide resin as a binder resin (Arakawa Chemical Industries, Ltd., trade name Compoceran, product number H900-2, solvent composition: N-methylpyrrolidone (NMP) / xylene (Xyl), cured residue 30%, A viscosity of 8000 mPa · s, silica in the curing residue, 4% by mass, and the curing residue means a solid content obtained by curing the resin and removing volatile components).

A KB (Ketjen black) manufactured by Ketchen Black International Co., Ltd. was prepared as a conduction aid.

The negative electrode was produced as follows.

The active material, the conductive auxiliary agent, and the binder resin were mixed in a mass ratio of SiO: graphite: conductive auxiliary agent: binder resin = 22: 60: 3: 15. At this time, when the sum of the mass of graphite and the mass of SiO is 100% by mass, the blending ratio of SiO is 27% by mass. An appropriate amount of NMP as a solvent was added to the above mixture to prepare a slurry.

The slurry was placed on an electrolytic copper foil having a thickness of 20 μm, and the slurry was applied in a film form on the electrolytic copper foil using a doctor blade. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then the current collector and the coated product on the current collector were firmly and closely bonded by a roll press. The joined product was heated at 200 ° C. for 2 hours in a vacuum dryer, and cut into a predetermined shape (26 mm × 31 mm rectangular shape). It is one.

The compounding ratio of SiO and graphite was changed, and the conditions thereafter were the same. 2 to 4 were made.

Negative electrode No. 2 were mixed in a mass ratio of SiO: graphite: conductive assistant: binder resin = 32: 50: 3: 15. At this time, when the sum of the mass of graphite and the mass of SiO was taken as 100% by mass, the blending ratio of SiO was 39% by mass.

Negative electrode No. 3 were mixed in a mass ratio of SiO: graphite: conductive assistant: binder resin = 42: 40: 3: 15. At this time, when the sum of the mass of graphite and the mass of SiO is 100% by mass, the blending ratio of SiO is 51% by mass.

Negative electrode No. 4 were mixed in a mass ratio of SiO: graphite: conductive assistant: binder resin = 12: 70: 3: 15. At this time, when the sum of the mass of graphite and the mass of SiO is 100% by mass, the blending ratio of SiO is 15% by mass.

<Production of laminate type lithium ion secondary battery>
Example 1
The positive electrode and the negative electrode No. The laminate type lithium ion secondary battery of Example 1 was manufactured using No. 1.
Between the positive electrode and the negative electrode, a rectangular sheet (27 × 32 mm, 25 μm thickness) made of polypropylene resin as a separator was sandwiched to form an electrode plate group. The electrode plate group was covered with a pair of laminate films, the three sides were sealed, and then an electrolytic solution was injected into the bag-like laminate film. A solution in which 1 mole of LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in EC: DEC = 3: 7 (volume ratio) was used as an electrolytic solution. After that, the remaining one side was sealed, and the four sides were airtightly sealed, to obtain a laminate type lithium ion secondary battery in which the electrode plate group and the electrolytic solution were sealed. The positive electrode and the negative electrode are provided with a tab electrically connectable to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. Through the above steps, a laminate-type lithium ion secondary battery using the positive electrode and the negative electrode was obtained. The resulting battery is referred to as the lithium ion secondary battery of Example 1.

(Example 2)
As the negative electrode, the negative electrode No. A laminate-type lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that No. 2 was used.

(Example 3)
As the negative electrode, the negative electrode No. A laminate-type lithium ion secondary battery of Example 3 was produced in the same manner as in Example 1 except that No. 3 was used.

(Comparative example 1)
As the negative electrode, the negative electrode No. A laminate-type lithium ion secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that No. 4 was used.

<Evaluation of charge and discharge test>
About the lithium ion secondary battery of Example 1, Example 2, Example 3, and the comparative example 1, the charging / discharging test was done at 25 degreeC.

The charge / discharge test is a current corresponding to 0.2 C when the charge / discharge current value is calculated assuming that the capacity of the positive electrode is 155 mAh / g, the charge potential is 4.2 V, the discharge potential is 3.0 V, and this is one cycle The discharge capacity (mAh) was examined. At this time, the current for discharging the electric capacity in one hour is represented as 1 C, and the current for discharging in 5 hours is represented as 0.2 C.

A graph showing the relationship between the discharge capacity (mAh) and the voltage (V) (VS. Li ^/ Li ⁺ ) of the lithium ion secondary batteries of Example 1, Example 2, Example 3 and Comparative Example 1 is shown in FIG. .

From FIG. 1, the charge curves showing the discharge potentials of the positive electrodes of Examples 1 to 3 and Comparative Example 1 appeared to overlap because the positive electrodes were the same. From the discharge curve showing the discharge potential of the negative electrode, when the discharge capacity is compared, Comparative Example 1 <Example 3 <Example 1 ≒ Example 2 ≒ 2.

Also, the volumetric energy density was calculated from FIG. The volumetric energy density was determined by the method described above. Specifically, the average voltage was determined from the discharge curve, and the energy (Wh) was determined by multiplying the average value by the discharge capacity value. The thickness was measured by combining the electrode and the separator, and the volume (L) of the cell was obtained. The energy (Wh) was divided by the volume (L) to determine the volumetric energy density (Wh / L).

The graph which compared volume energy density (Wh / L) and a graphite ratio (wt%) in FIG. 2 is shown. Here, the graphite ratio is the mass% of graphite when the total of SiO, graphite, the conductive additive and the binder resin is 100 mass%.

From FIG. 2, it is found that the volumetric energy density is the highest in Example 2 and the volumetric energy density is lowered even if the proportion of graphite increases or decreases according to the proportion of graphite in Example 2. This is considered to be because when the graphite ratio is increased, the SiO ratio relatively decreases and the discharge capacity is decreased, but when the graphite ratio is increased, the discharge potential of the negative electrode is decreased and the average voltage is increased.

Considering from the content of graphite, the graphite ratio is 40% by mass to 60% by mass based on 100% by mass of the total of SiO, graphite, the conductive additive and the binder resin as a range in which the volume energy density increases. It turns out that what is good is good. Here, the ratio of 40% by mass to 60% by mass when the total amount of SiO, graphite, the conductive additive and the binder resin is 100% by mass means that when SiO and graphite are 100% by mass. The composition ratio of is 27% by mass to 51% by mass.

As described above, by using the lithium ion secondary batteries of Examples 1 to 3, it is possible to obtain a lithium ion secondary battery having both high capacity and high energy density.

(Examples 4 to 6 and Comparative Examples 2 to 3)
(Example 4)
<Fabrication of negative electrode for lithium ion secondary battery>
The SiO powder was heat treated at 900 ° C. for 2 hours to prepare an SiO _x powder with a D ₅₀ of 6.5 μm. By this heat treatment, if the ratio of Si to O is a homogeneous solid silicon monoxide (SiO) of approximately 1: 1, the solid is separated into two phases of Si phase and SiO ₂ phase by internal reaction. The Si phase obtained by separation is very fine.

A slurry was prepared by mixing 32 parts by mass of the obtained SiO _x powder, ₅₀ parts by mass of a graphite powder having a D ₅₀ of 9.2 μm, 8 parts by mass of carbon black, and 10 parts by mass of a binder solution. The binder solution was prepared by dissolving a polyamideimide resin in N-methyl-2-pyrrolidone (NMP). The slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of about 20 μm to 30 μm using a doctor blade to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely bonded by a roll press. This was vacuum-dried to form a negative electrode having a thickness of 15 μm of the negative electrode active material layer.

In this negative electrode, the ratio of _{_D} 50 _(D ₂₎ of the _{_D} 50 _(D ₁₎ and SiO _x particles of the graphite particles _{_(D} 1 / D ₂₎ is 1.42, _D 50 of the graphite particles _(D 1) The ratio (D ₁ / t) of the thickness to the thickness (t) of the negative electrode active material layer is 0.61.

<Fabrication of positive electrode>
L333 (Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ ) as a positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder resin Were mixed to prepare a slurry-like positive electrode mixture. The composition ratio of each component (solid content) in the slurry was L333: AB: PVDF = 88: 6: 6 (mass ratio). The slurry was applied to a current collector, and a positive electrode mixture layer was formed on the current collector. Specifically, this slurry was applied to the surface of a 20 μm thick aluminum foil (current collector) using a doctor blade.

Thereafter, the resultant was dried at 80 ° C. for 20 minutes, and the organic solvent was volatilized and removed from the positive electrode mixture. After drying, the electrode density was adjusted by a roll press. The resultant was heat-cured at 200 ° C. for 2 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Fabrication of lithium ion secondary battery>
The positive electrode was cut into a size of 30 mm × 25 mm, and the negative electrode was cut into a size of 31 mm × 26 mm, and the laminate was housed in a laminate film. A rectangular sheet (40 mm × 40 mm square, 30 μm thick) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a pair of laminate films, and the three sides were sealed, and then the above electrolytic solution was injected into the bag-like laminate film. Then, the remaining one side was sealed, and the four sides were airtightly sealed to obtain a laminate cell in which the electrode plate group and the electrolytic solution were sealed. As electrolyte solution, LiPF is mixed with a mixed solution of FEC (fluoro ethylene carbonate), EC (ethylene carbonate), MEC (methyl ethyl carbonate), DMC (dimethyl carbonate) = 0.4: 2.6: 3: 4 (volume ratio) _A solution of ₆ at a concentration of 1 mol / L was used. The positive electrode and the negative electrode were provided with a tab electrically connectable to the outside, and a part of the tab extended to the outside of the laminate cell. Through the above steps, a lithium ion secondary battery in the form of a laminate cell (bipolar pouch cell) was obtained.

(Example 5)
D ₅₀ is _{D 50} in place of the graphite powder of 9.2μm was formed a negative electrode in the same manner as in Example 4 except for the use of graphite powder 12.5 .mu.m. In this negative electrode, the ratio of the _D 50 of the graphite particles _{(D 1)} and _D 50 of the SiO _x particulate _{_{(D 2) (D 1 /}} D 2) is 1.92, the graphite particles _D 50 _{(D 1} The ratio (D ₁ / t) of the thickness of the negative electrode active material layer to the thickness (t) of the negative electrode active material layer is 0.83.

Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 4.

(Example 6)
A slurry was prepared by mixing 42 parts by mass of the same SiO _x powder as in Example 4, 40 parts by mass of a graphite powder having a D ₅₀ of 9.2 μm, 3 parts by mass of carbon black, and 15 parts by mass of a binder solution. The binder solution was prepared by dissolving a polyamideimide resin in N-methyl-2-pyrrolidone (NMP).

A negative electrode was formed in the same manner as in Example 4 except that this slurry was used. In this negative electrode, the ratio of the _D 50 of the graphite particles _{(D 1)} and _D 50 of the SiO _x particulate _{_{(D 2) (D 1 /}} D 2) is 1.92, the graphite particles _D 50 _{(D 1} The ratio (D ₁ / t) of the thickness of the negative electrode active material layer to the thickness (t) of the negative electrode active material layer is 0.61.
Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 4.

(Comparative example 2)
D ₅₀ is _{D 50} in place of the graphite powder of 9.2μm was formed a negative electrode in the same manner as in Example 4 except for the use of graphite powder 20.0 .mu.m. In this negative electrode, the ratio of the _D 50 of the graphite particles _{(D 1)} and _D 50 of the SiO _x particulate _{_{(D 2) (D 1 /}} D 2) is 3.08, the graphite particles _D 50 _{(D 1} The ratio (D ₁ / t) of (A) to the thickness (t) of the negative electrode active material layer is 1.33.
Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 4.

(Comparative example 3)
D ₅₀ is _{D 50} in place of the graphite powder of 9.2μm was formed a negative electrode is in the same manner as in Example 6 except for using graphite powder 20.0 .mu.m. In this negative electrode, the ratio of the _D 50 of the graphite particles _{(D 1)} and _D 50 of the SiO _x particulate _{_{(D 2) (D 1 /}} D 2) is 3.08, the graphite particles _D 50 _{(D 1} The ratio (D ₁ / t) of the thickness of the negative electrode active material layer to the thickness (t) of the negative electrode active material layer is 0.61. Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 6.

<Test>
The cross section of the negative electrode formed in Example 5 and Comparative Example 2 was observed by SEM. The SEM image is shown in FIG. 3 and FIG. It can be seen that small pores are formed more frequently in Example 5 than in Comparative Example 2. The lithium ion secondary batteries of Examples 4 and 5 and Comparative Example 2 are subjected to a constant current charge / discharge test at a charge / discharge current density of 0.2 mA cm ^{−2 in the} first cycle, and the charge / discharge current density after the second cycle. It carried out by 0.5 mAcm- ² . The potential range was 0 V to 3.0 V at lithium reference potential and the test was performed at room temperature. After the first cycle, an oxide-based compound represented by Li _x Si _y O _z containing Li ₄ SiO ₄ is formed in the SiO ₂ phase of SiO _x which is the active material in the negative electrode. In each cycle in the charge and discharge cycle test, the resistance value (discharge IR drop) of the negative electrode 10 seconds after the start of discharge was measured, and the results up to 400 cycles are shown in FIG.

<Evaluation>
From FIG. 5, since the negative electrode of Example 4 and Example 5 has a low discharge IR drop compared with Comparative Example 2, the ratio (D ₁ / D ₂ ) is set to be more than 1 and 2 or less. It can be seen that an excellent negative electrode can be formed. Moreover, since the resistance is lower in Example 5 than in Example 4, it is suggested that the particle diameter of the graphite has an optimum range.

The same constant current charge-discharge test as described above was performed on the lithium ion secondary batteries of Example 6 and Comparative Example 3, and the measurement results of the resistance value (discharge IR drop) of the negative electrode up to 500 cycles are shown in FIG. In Comparative Example 3, it can be seen that the resistance value after exceeding 400 cycles rises more than in Example 6, and increases and decreases significantly from a point near 500 cycles. This indicates that in the negative electrode of Comparative Example 3, a crack was generated in the negative electrode active material layer, or the negative electrode active material layer was peeled off from the current collector to significantly reduce the conductivity.

(Examples 7 to 10 and Comparative Example 4)
<Electrode density measurement>
As an active material, span _{2.0, D} (manufactured by Aldrich) ₅₀ 2μm of SiO, span _{1.1, D} (manufactured by Aldrich) ₅₀ 5μm of SiO, span _{1.2, D 50} is 10μm of SiO ( An Aldrich company, a span 1.2, a SiO 2 with a D ₅₀ of 15 μm (manufactured by Aldrich) and a SiO 2 with a span 1.4 and a D ₅₀ of 20 μm (manufactured by Aldrich) were prepared.

Alkoxy group-containing silane-modified polyamideimide resin (Arakawa Chemical Industries, Ltd., trade name: Compoceran, product number H901-2, solvent composition: N-methylpyrrolidone (NMP) / xylene (Xyl), 30% of curing residue, as a binder resin) A viscosity of 8000 mPa · s, silica in the curing residue, 2% by mass, and the curing residue means solid content obtained by curing the resin and removing volatile components).

Bulk artificial graphite “MAG (Massive) with D ₅₀ of 10 μm as buffer material
Artificial Graphite) (manufactured by Hitachi Chemical Co., Ltd.) and massive artificial graphite “MAG (Massive Artificial Graphite)” (manufactured by Hitachi Chemical Co., Ltd.) having a D ₅₀ of 20 μm were prepared.

The negative electrode for lithium ion secondary batteries was produced as follows.

The active material, the buffer material, the conductive auxiliary agent, and the binder resin were mixed at a mass ratio of SiO powder: graphite powder: conductive auxiliary agent: binder resin = 40: 42: 3: 15. When the sum of the mass of the graphite powder and the mass of the SiO _x powder is 100% by mass, the blending amount of the graphite powder is 44% by mass. An appropriate amount of NMP as a solvent was added to the above mixture to prepare a slurry.

The slurry was placed on an electrolytic copper foil having a thickness of 20 μm, and the slurry was applied in a film form on the electrolytic copper foil using a doctor blade. The obtained sheet is dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then the current collector and the coated product on the current collector are firmly adhered and bonded with a roll press at a linear pressure of 40 kg / cm. I did. The bonded product was heated at 200 ° C. for 2 hours in a vacuum dryer, cut into a predetermined shape (26 mm × 31 mm rectangular shape), and used as an electrode having a thickness of about 18 μm.

The particle size ratio of the SiO powder and the graphite powder was changed, and the conditions thereafter were the same. Negative electrodes of Test Examples 1 to 7 were produced, and the electrode density was measured. The electrode density is determined by measuring the mass and volume of each of the prepared electrodes, and excluding the mass and volume of the current collector, electrode density = (mass of electrode excluding current collector) / (volume of electrode excluding current collector) Calculated by the equation of The filling factor (%) in the active material layer of the graphite powder was determined from the formula: graphite filling factor = (mass of graphite / true density of graphite) / (volume of electrode excluding current collector) × 100. The results are summarized in Table 1.

The graph which compared electrode density and particle size ratio from the result of this Table 1 is shown in FIG. As can be seen from Table 1 and FIG. 11, Test Example 2, Test Example 3 and Test Example 6 in which the particle size ratio is 0.25 to 0.5 have a particle size ratio of 0.1, 0.75, or 1 The electrode density was found to be higher than that of Test Example 1, Test Example 4, Test Example 5 and Test Example 7 that are. In addition, although the particle size ratio of Test Example 3 and Test Example 6 was the same, the electrode density was higher in Test Example 3. This is considered to be because the electrode in the test example 6 and the test example 6 is bulky because the graphite particle diameter D ₅₀ is smaller in the test example 6 and the volume of the electrode in the test example 6 is larger.

When the particle size ratio is as large as 0.75 or 1 as in Test Example 4, Test Example 5 and Test Example 7, the SiO powder is not disposed in the void formed by the graphite powder, and the void is increased. It is considered that the electrode density increased due to an increase in the volume of It is considered that when the particle size ratio is as small as 0.1 as in Test Example 1, the volume of the negative electrode increases and the electrode density decreases because SiO is aggregated.

In Test Examples 1 to 7, since compression molding is performed using the same linear pressure, even if the SiO powder is disposed in the void formed by the graphite powder and the SiO powder is expanded, the electrode density is high, It can be considered that the SiO powder and the graphite powder are displaced in the width direction so as not to expand in the thickness direction of the negative electrode active material layer, and the SiO powder is disposed again in the voids formed by the graphite powder.

Further, in the case where the electrode density is high, the graphite filling rate is also high, and from the results of Test Example 1 to Test Example 7, Test Example 2, Test Example 3, where the particle size ratio is 0.25 to 0.5. Test Example 6 has a graphite packing ratio higher than that of Test Example 1, Test Example 4, Test Example 5 and Test Example 7 having a particle size ratio of 0.1, 0.75, or 1 of 24.2% or more. It turned out that it became.

Comparing the electrode densities of Test Example 1 and Test Example 2 in which the graphite particle size is 20 μm, the electrode density of 0.06 g / cm ³ in Test Example 2 is higher. As the electrode density increases, the energy density (Wh / L), which is the power capacity per battery volume, also increases. Accordingly, it can be said that the energy density (i.e., the electric capacity) of Test Example 2 is about 5% higher than that of Test Example 1. (5 (%) = 0.06 (electrode density difference) / 1.17 (electrode density of Test Example 1) x 100).

Here, the cross section of Test Example 2 was observed with a scanning electron microscope (SEM). The SEM photograph is shown in FIG. It was observed from FIG. 13 that SiO7 was disposed in the void formed by the graphite 6, and the void had room to be relocated. Graphite 6 was observed to be elastically deformed due to its layered structure sliding. Further, it can be observed from FIG. 13 that the space impregnated with the electrolytic solution is sufficiently secured, and the conductive network is also firmly formed.

Next, using the negative electrodes of Test Example 2 and Test Example 4, a laminate-type lithium ion secondary battery was produced, charge and discharge were performed, and the initial efficiency and the expansion ratio of electrode expansion were measured.

<Production of laminate type lithium ion secondary battery>
(Example 7)
The electrode of Test Example 2 was a negative electrode. An aluminum foil of 20 μm was prepared as a current collector of the positive electrode, Li ₂ MnO ₃ was prepared as a positive electrode active material, and polyvinylidene fluoride (PVDF) was prepared as a binder resin of the positive electrode.

Li ₂ MnO ₃ which is a positive electrode active material was produced as follows.

Mix 0.20 mol of lithium hydroxide monohydrate LiOH · H ₂ O (8.4 g) as a molten salt raw material and 0.02 mol of manganese dioxide MnO ₂ (1.74 g) as a metal compound raw material The raw material mixture was prepared. At this time, assuming that all Mn of manganese dioxide is supplied to Li ₂ MnO ₃ , the target product is Li ₂ MnO ₃ , and (Li of target product) / (Li of molten salt raw material) is And 0.04 mol / 0.2 mol = 0.2.

The raw material mixture was poured, transferred into an electric furnace at 700 ° C., and heated at 700 ° C. in vacuum for 2 hours. At this time, the raw material mixture was melted to form a molten salt, and a black product was precipitated.

Next, the crucible containing the molten salt was cooled to room temperature in the electric furnace and then taken out of the electric furnace. After the molten salt was sufficiently cooled and solidified, it was immersed in 200 mL of ion-exchanged water with stirring, whereby the solidified molten salt was dissolved in water. The water became a black suspension because the black product was insoluble in water. The black suspension was filtered to give a clear filtrate and a filter cake of black solid on filter paper. The resulting filtrate was filtered with thorough washing with acetone. The washed black solid was vacuum dried at 120 ° C. for 12 hours and then crushed using a mortar and pestle.

The X-ray diffraction (XRD) measurement using CuK _alpha ray was performed about the obtained black powder. According to XRD, it was found that the obtained black powder had a layered rock salt structure. Further, the composition of the obtained black powder was confirmed to be Li ₂ MnO ₃ from emission spectral analysis (ICP) and mean valence number analysis of Mn by redox titration.

Using the current collector of the positive electrode, the positive electrode active material, and the binder resin of the positive electrode, a positive electrode was prepared in the same manner as the negative electrode.

A laminated lithium ion secondary battery was manufactured using the above positive electrode and negative electrode. Specifically, a rectangular sheet (27 × 32 mm, 25 μm thick) made of polypropylene resin as a separator is sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a pair of laminate films, the three sides were sealed, and then an electrolytic solution was injected into the bag-like laminate film. A solution in which 1 mole of LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in EC: DEC = 3: 7 (volume ratio) was used as an electrolytic solution. After that, the remaining one side was sealed, and the four sides were airtightly sealed, to obtain a laminate type lithium ion secondary battery in which the electrode plate group and the electrolytic solution were sealed. The positive electrode and the negative electrode are provided with a tab electrically connectable to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. Through the above steps, a laminate-type lithium ion secondary battery using the electrode of Test Example 2 was obtained. The resulting battery is referred to as the lithium ion secondary battery of Example 7.

(Comparative example 4)
A lithium ion secondary battery of Comparative Example 4 was obtained in the same manner as Example 7 except that the electrode of Test Example 4 was changed to the negative electrode.

<Evaluation of charge and discharge test>
About the lithium ion secondary battery of Example 7 and Comparative Example 4, the charging / discharging test was done at 25 degreeC. In the charge and discharge test, CCCV charging (constant current constant voltage charging) is performed at 0.1 C to 4.5 V to activate the positive electrode active material, and then charging is performed at a constant voltage of 4.5 V to a current value of 0.01 C The Discharge was done at 1 C up to 2V. At this time, the current for discharging the electric capacity in one hour is represented as 1 C, and the current for discharging in 5 hours is represented as 0.2 C. Therefore, the 1C current value is five times the 0.2C current value.

The electrode thickness before charging was measured, the electrode thickness after charging was measured, and the expansion ratio was calculated. At this time, the thickness of the electrode after charging was obtained by decomposing the battery after charging and measuring the thickness of the electrode. Also, the ratio of the discharge capacity to the initial charge capacity was determined as the initial efficiency.

As a result, while the lithium ion secondary battery of Comparative Example 4 had an initial efficiency of 75% and an electrode expansion ratio of 2.1 times, the lithium ion secondary battery of Example 7 had an initial efficiency of The electrode expansion can be greatly suppressed to 80.5% and the expansion ratio of the electrode is 1.1 times, and deterioration of the initial efficiency could be suppressed.

Further, this battery is operated under the condition that the electrode is expanded by applying a voltage of 4.5 V or more at the time of activation, and it is considered that the same effect can be obtained even at a low voltage. The results of the lithium ion secondary battery of Example 7 using the negative electrode of Test Example 2 are considered to give similar results even when using the negative electrodes of Test Example 3 and Test Example 6.

The expansion ratio of the SiO powder causes peeling of the binder and the SiO powder due to the expansion ratio of the electrode of Comparative Example 4 of 2.1 times, so that the electrolyte solution enters therein and the thickness of the electrode further expands. In addition, the thickness of the electrode is measured after disassembling the battery after charging and taking out the electrode, so the inside of the battery is not expanded so much.

As described above, by using the above-described negative electrode for a lithium ion secondary battery, the expansion of the entire negative electrode can be largely suppressed, and the lithium ion secondary battery of Example 7 can suppress the deterioration of the initial efficiency.

<Cycle test evaluation>
Lithium ion secondary batteries of Examples 8 to 10 below were produced in the same manner as in Example 7 except that the compounding ratio of the SiO powder of the negative electrode and the graphite powder was changed, and the cycle test was conducted.

(Example 8)
A lithium ion secondary battery of Example 8 in the same manner as Example 7 except that the negative electrode was prepared by mixing in a mass ratio of SiO powder: graphite powder: conductive auxiliary agent: binder resin = 32: 50: 3: 15. Was produced. The blending amount of the graphite powder corresponds to 60.9 mass% when the sum of the mass of the graphite powder and the mass of the SiO powder in Example 8 is 100 mass%. The graphite filling rate was 29.3%. The calculation method of the actual graphite filling rate is shown. Since the electrode density is 1.23 g / cm ³ from the results of Test Example 2 in Table 1, the electrode volume is calculated to be 1 cm ³ , 1.23 g (electrode weight) × 50% (mass ratio) = 0.615 g The graphite packing ratio is 0.615 g / 1 cm ³ /(2.1 g / cm ³ ) (graphite true density) × 100 = 29.3%.

(Example 9)
A lithium ion secondary battery of Example 9 in the same manner as Example 7 except that the negative electrode was prepared by mixing in a mass ratio of SiO powder: graphite powder: conductive auxiliary agent: binder resin = 42: 40: 3: 15. Was produced. The blending amount of the graphite powder corresponds to 48.8 mass% when the sum of the mass of the graphite powder and the mass of the SiO powder in Example 9 is 100 mass%. The graphite loading was 23.4%.

(Example 10)
The lithium ion secondary battery of Example 10 was prepared in the same manner as Example 7, except that the negative electrode was prepared by mixing in a mass ratio of SiO powder: graphite powder: conductive auxiliary agent: binder resin = 52: 30: 3: 15. Was produced. In Example 10, when the sum of the mass of the graphite powder and the mass of the SiO powder is 100% by mass, the blending amount of the graphite powder corresponds to 36.6% by mass. The graphite loading was 17.6%.

(Cycle test conditions)
In the cycle test, 150 cycles of CC charging up to 4.2 V at a charge current of 2 C in a constant temperature bath at 60 ° C. and CC discharging up to 2 V at 2 C after 10 minutes of rest were carried out for 150 cycles. The discharge capacity maintenance rate (%) for each cycle was determined. The discharge current capacity retention rate (%) was determined by the following equation.
Discharge current capacity retention rate (%) = (Discharge current capacity of each cycle / Initial discharge current capacity) x 100
The results are described in FIG. FIG. 12 is a graph showing the cycle test results of Examples 8 to 10.

Examples 8 to 10 were all excellent in cycle characteristics with a discharge capacity retention ratio of 85% or more up to about 70 cycles. Examples 8 to 10 had the discharge capacity retention rate of 75% or more until the 100th cycle. At the 150th cycle, the discharge capacity retention rate of Example 8 dropped to 50%, but Examples 9 and 10 maintained the discharge capacity retention rate to about 70%. Accordingly, it can be said that all of Examples 8 to 10 have high discharge capacity retention rates and excellent cycle characteristics up to the 100th cycle.

From the above results, when the total of the mass of the graphite powder and the mass of the SiO powder is 100% by mass, the electrode powder and the cycle characteristic both have to be 36 mass% to 61 mass% of the compounding amount of the graphite powder. It was possible to make a lithium ion secondary battery that Further, when the blending amount of the graphite powder is 36% by mass to 49% by mass, it is possible to obtain an electrode in which deterioration of cycle characteristics is particularly suppressed.

The lithium ion secondary batteries of Examples 7 to 10 of the present invention were able to suppress the expansion of the electrode thickness, and also obtained excellent results regarding the electric capacity and the cycle characteristics.

(Examples 11 to 17 and Comparative Example 5)
(Comparative example 5)
<Fabrication of negative electrode for lithium ion secondary battery>
First, the SiO powder was heat treated at 900 ° C. for 2 hours to prepare a SiO _x powder having a D ₅₀ of 6.5 μm. By this heat treatment, if the ratio of Si to O is a homogeneous solid SiO of about 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by internal reaction of the solid. The Si phase obtained by separation is very fine. That is, the obtained SiO _x powder is an aggregate of SiO _x particles, and the SiO _x particles have a structure in which fine Si particles are dispersed in a matrix of SiO ₂ .

A solution of this SiO _x powder, acetylene black (AB) as a conductive additive, natural graphite, and polyamideimide (PAI) as a binder resin in N-methylpyrrolidone (NMP) as an organic solvent, Were mixed to prepare a slurry-like negative electrode material. At this time, each material was added in the order of AB, SiO and graphite to a solution of PAI in NMP. As AB, one having a true density of 1.8 g / cm ³ , a primary particle diameter (median diameter, D ₅₀ ) of 11 to 18 nm, and a BET value of 180 m ² / g was used. As graphite, one having a particle diameter (median diameter, D ₅₀ ) of 9.2 μm manufactured by Hitachi Chemical Co., Ltd. was used. As PAI, Arakawa Chemical Industries, Ltd. make, brand name Compoceran AI series, and product number AI-301 were used. The composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 22: 60: 3: 15 (mass ratio).

The BET value a1 of SiO _x used in Comparative Example 5 is 6.5574 m ² / g, the BET value a 2 of graphite is 3.8162 m ² / g, the blending amount b 1 of SiO _x is 22 g, the blending amount of graphite The b2 was 60 g, and the compounding amount c of AB as the conduction aid was 3 g. Therefore, values obtained by substituting the respective values into {(a1 × b1) + (a2 × b2)} / c, that is, the mass of the conductive aid, and the surface area of the negative electrode active material and graphite and the conductive aid The value representing the relationship was 124.4.

The true density of AB used in Comparative Example 5 was 1.8 g / cm ³ . The blending amount d of AB converted based on this numerical value is 3 / 1.8 = 1.67 cm ³ . Therefore, the value obtained by substituting each value into {(a1 × b1) + (a2 × b2)} / d, that is, based on the volume of the conductive aid, the sum of the surface area of the negative electrode active material and graphite and the conductive aid The value representing the relationship with was 223.6. The composition of the negative electrode material of Comparative Example 5 and the compositions of the negative electrode materials of Examples 11 to 17 described later are shown in Table 2 below.

The slurry of the negative electrode material obtained by the above procedure was applied to a current collector, and a negative electrode material layer was formed on the current collector. Specifically, this slurry was applied to the surface of a 20 μm-thick electrolytic copper foil (current collector) using a doctor blade.

The resulting laminate was dried at 80 ° C. for 15 minutes to volatilize and remove the organic solvent from the negative electrode material layer. After drying, the electrode density was adjusted by a roll press. After that, heat curing was performed at 200 ° C. for 2 hours in a vacuum drying furnace to form a negative electrode material layer (solid content) having a thickness of about 15 μm on the upper layer of the current collector. After that, the negative electrode of Comparative Example 5 was obtained by natural cooling.

<Fabrication of positive electrode>
L333 (Li ₁ [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ ) as a positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder resin And were mixed to prepare a slurry-like positive electrode material. The composition ratio of each component (solid content) in the slurry was L333: AB: PVDF = 88: 6: 6 (mass ratio). The slurry was applied to a current collector, and a positive electrode material layer was laminated on the current collector. Specifically, this slurry was applied to the surface of a 20 μm thick aluminum foil (current collector) using a doctor blade.

Thereafter, the resultant was dried at 80 ° C. for 20 minutes to volatilize and remove the organic solvent from the positive electrode material layer. After drying, the electrode density was adjusted by a roll press. The resultant was heat-cured at 200 ° C. for 2 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode material layer (solid content) having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Fabrication of lithium ion secondary battery>
The positive electrode was cut into a size of 30 mm × 25 mm, and the negative electrode was cut into a size of 31 mm × 26 mm, and the laminate was housed in a laminate film. A rectangular sheet (40 mm × 40 mm square, 30 μm thick) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a pair of laminate films, and the three sides were sealed, and then the above electrolytic solution was injected into the bag-like laminate film. Then, the remaining one side was sealed, and the four sides were airtightly sealed to obtain a laminate cell in which the electrode plate group and the electrolytic solution were sealed. In the electrolyte solution, LiPF is mixed in a mixed solution of FEC (fluoroethylene carbonate): EC (ethylene carbonate): EMC (ethyl methyl carbonate): DMC (dimethyl carbonate) = 0.4: 2.6: 3: 4 (volume ratio) _A solution of ₆ at a concentration of 1 mol / L was used.

The positive electrode and the negative electrode were provided with a tab electrically connectable to the outside, and a part of the tab extended to the outside of the laminate cell. Through the above steps, a lithium ion secondary battery in the form of a laminate cell (bipolar pouch cell) was obtained.

(Example 11)
The negative electrode material of Example 11 is the same as the negative electrode material of Comparative Example 5 except for the compounding amounts of the conductive additive and the binder resin. In the negative electrode material of Example 11, the composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 22: 60: 6: 12 (mass ratio). The negative electrode and the lithium ion secondary battery of Example 11 were manufactured using the negative electrode material of Example 11 in the same manner as in Comparative Example 5. In addition, in the negative electrode material and the negative electrode of Example 11, a1, a2, b1, and b2 were the same as in Comparative Example 5, and the compounding amount c of AB as a conductive additive was 6 g. Therefore, the value (mass standard) of {(a1 × b1) + (a2 × b2)} / c in Example 11 was 62.2. Further, the compounding amount d of AB was 6 / 1.8 = 3.33 cm ³ , and the value (volume basis) of {(a1 × b1) + (a2 × b2)} / d was 112.1.

(Example 12)
The negative electrode material of Example 12 is the same as the negative electrode material of Comparative Example 5 except for the blending amounts of the conductive additive and the binder resin. In the negative electrode material of Example 12, the composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 22: 60: 8: 10 (mass ratio). The negative electrode and the lithium ion secondary battery of Example 12 are manufactured using the negative electrode material of Example 12 in the same manner as in Comparative Example 5. In the negative electrode material and the negative electrode of Example 12, a1, a2, b1, and b2 were the same as in Comparative Example 5, and the compounding amount c of AB was 8 g. Therefore, the value (mass standard) of {(a1 × b1) + (a2 × b2)} / c in Example 12 was 46.7. Further, the compounding amount d of AB was 8 / 1.8 = 4.44 cm ³ , and the value (volume basis) of {(a1 × b1) + (a2 × b2)} / d was 84.1.

(Example 13)
The negative electrode material of Example 13 is the same as the negative electrode material of Comparative Example 5 except for the compounding amounts of the conductive additive and the binder resin. In the negative electrode material of Example 13, the composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 22: 60: 10: 8 (mass ratio). The negative electrode and the lithium ion secondary battery of Example 13 were manufactured using the negative electrode material of Example 13 in the same manner as in Comparative Example 5. In the negative electrode material and the negative electrode of Example 13, a1, a2, b1, and b2 were the same as in Comparative Example 5, and the compounding amount c of AB was 10 g. Therefore, the value (mass standard) of {(a1 × b1) + (a2 × b2)} / c in Example 13 was 37.3. The compounding amount d of AB was 10 / 1.8 = 5.56 cm ³ , and the value (volume basis) of {(a1 × b1) + (a2 × b2)} / d was 67.1.

(Example 14)
The negative electrode material of Example 14 is the same as the negative electrode material of Comparative Example 5 except for the blending amounts of the conductive additive and the binder resin. In the negative electrode material of Example 14, the composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 22: 60: 12: 6 (mass ratio). The negative electrode and the lithium ion secondary battery of Example 14 were manufactured using the negative electrode material of Example 14 in the same manner as in Comparative Example 5. In the negative electrode material and the negative electrode of Example 14, a1, a2, b1, and b2 were the same as in Comparative Example 5, and the compounding amount c of AB was 12 g. Therefore, the value (mass standard) of {(a1 × b1) + (a2 × b2)} / c in Example 14 was 31.1. The compounding amount d of AB was 12 / 1.8 = 6.67 cm ³ , and the value (volume basis) of {(a1 × b1) + (a2 × b2)} / d was 56.0.

(Example 15)
The negative electrode material of Example 15 is the same as the negative electrode material of Comparative Example 5 except for the types of the negative electrode active material and graphite, the combined amount of the negative electrode active material, artificial graphite, the conductive additive and the binder resin, and the configuration of the electrolytic solution. It is. The negative electrode active material used in the negative electrode material of Example 15 was SiO _X different from Comparative Example 5 and Examples 11 to 14. Specifically, SiO _x used in the negative electrode material of Example 15 was a particle size (median diameter, D ₅₀ ) of 5.0 μm manufactured by the same method as Comparative Example 5. As graphite, as in Comparative Example 5, one manufactured by Hitachi Chemical Co., Ltd. and having a particle diameter (median diameter, D ₅₀ ) of 9.2 μm was used.

In the negative electrode material of Example 15, the composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 32: 50: 6: 12. As an electrolytic solution, EC: EMC: DMC = 3 : 3: Using 4 that at a concentration of the LiPF ₆ is 1 mol / L in a mixed solution (volume ratio). The negative electrode and the lithium ion secondary battery of Example 15 are manufactured using the negative electrode material of Example 15 in the same manner as in Comparative Example 5. In the negative electrode material and the negative electrode of Example 15, the BET value a1 of SiO _x is 2.8029 m ² / g, the BET value a 2 of graphite is 5.9754 m ² / g, the blending amount b 1 of SiO _x is 32 g, The compounding amount b2 was 50 g, and the compounding amount c of AB was 6 g. Therefore, the value (mass standard) of {(a1 × b1) + (a2 × b2)} / c in Example 15 was 64.7. Further, the compounding amount d of AB was 6 / 1.8 = 3.33 cm ³ , and the value (volume basis) of {(a1 × b1) + (a2 × b2)} / d was 116.5.

(Example 16)
The negative electrode material of Example 16 is the same as the negative electrode material of Example 15 except for the blending amounts of the conductive additive and the binder resin. In the negative electrode material of Example 16, the composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 32: 50: 8: 10. The negative electrode and the lithium ion secondary battery of Example 16 are manufactured using the negative electrode material of Example 16 in the same manner as in Comparative Example 5. In the negative electrode material and the negative electrode of Example 16, a1, a2, b1 and b2 were the same as in Example 15, and the compounding amount c of AB was 8 g. Therefore, the value (mass standard) of {(a1 × b1) + (a2 × b2)} / c in Example 16 was 48.6. The compounding amount d of AB was 8 / 1.8 = 4.44 cm ³ , and the value (volume basis) of {(a1 × b1) + (a2 × b2)} / d was 87.4.

(Example 17)
The negative electrode material of Example 17 is the same as the negative electrode material of Example 15 except for the compounding amounts of the conductive additive and the binder resin. In the negative electrode material of Example 17, the composition ratio of each component (solid content) in the negative electrode material was SiO _x : graphite: AB: PAI = 27: 45: 14: 14. The negative electrode and the lithium ion secondary battery of Example 17 are manufactured using the negative electrode material of Example 17 in the same manner as in Comparative Example 5. In the negative electrode material and the negative electrode of Example 17, a1 and a2 were the same as in Example 15, b1 was 27 g, b2 was 45 g, and the blending amount c of AB was 14 g. Therefore, the value (mass standard) of {(a1 × b1) + (a2 × b2)} / c in Example 17 was 24.6. Further, the compounding amount d of AB was 14 / 1.8 = 7.78 cm ³ , and the value (volume basis) of {(a1 × b1) + (a2 × b2)} / d was 44.3.

[Charge and discharge test]
The lithium ion secondary batteries of Comparative Example 5 and Examples 11 to 17 are repeatedly charged and discharged at a current density of 16 mA per 1 cm ² of the negative electrode active material, a discharge termination voltage of 3 V, a charge termination voltage of 4.2 V, and a temperature of 25 ° C. The discharge capacity of the lithium ion secondary battery in each cycle was measured. The load test was performed from the 100th cycle to the 103rd cycle. Graphs showing the cycle characteristics of each lithium ion secondary battery are shown in FIGS. Specifically, FIG. 16 and FIG. 17 are graphs showing the cycle characteristics of the lithium ion secondary batteries of Comparative Example 5 and Examples 11 to 14. FIG. 18 is a graph showing the cycle characteristics of the lithium ion secondary batteries of Examples 15 and 16. FIG. 19 is a graph showing the cycle characteristics of the lithium ion secondary batteries of Examples 15 to 17. The vertical axes in FIG. 16 and FIG. 18 represent the discharge capacity (mAh). The vertical axes in FIG. 17 and FIG. 19 represent the discharge capacity retention rate (%). The discharge capacity retention rate refers to the discharge capacity (%) in each cycle when the discharge capacity in the first cycle is 100%. A lithium ion secondary battery with a low discharge capacity retention rate (%) has a large decrease in discharge capacity due to repeated charge and discharge, and is thus inferior in cycle characteristics.

In addition, for the lithium ion secondary batteries of Comparative Example 5 and Examples 11 to 14, assuming that the amount of voltage change from 10 seconds after the start of discharge when the battery remaining amount is 20% is ΔV (unit: V), I = 3 .4 × 10 ^-3 (unit: A) was used to calculate the amount of decrease in direct current resistance (IR drop) from ΔV / I (unit: Ω). A graph showing the discharge IR drop of the lithium ion secondary batteries of Comparative Example 5 and Examples 11 to 14 is shown in FIG.

As shown in FIG. 16, the discharge capacities (mAh) of the lithium ion secondary batteries of Comparative Example 5 and Examples 11 to 14 are the same as Example 14> Example 13> Example 12> Example 11> Comparative Example 5. It was big in order. This order is in descending order of the amount of conductive additive. However, as shown in FIG. 17, the discharge capacity retention ratio (%) of the lithium ion secondary batteries of Comparative Example 5 and Examples 11 to 14 is that of Example 12> Example 11> Example 13> Comparative Example 5> The sizes were larger in the order of Example 14. In other words, the capacity reduction of the lithium ion secondary battery was suppressed in the order of Example 12> Example 11> Example 13> Comparative Example 5> Example 14. The discharge capacity retention rate of Example 14 was approximately the same as the discharge capacity retention rate of Comparative Example 5. From this result, it can be said that Example 14 can largely improve the discharge capacity of the lithium ion secondary battery by containing a large amount of the conductive aid, and can suppress the capacity reduction to the same extent as Comparative Example 5.

As described above, the value of {(a1 × b1) + (a2 × b2)} / c (that is, based on the mass of the conductive aid, the sum of the surface area of the negative electrode active material and graphite and the conductive aid The values representing the relationship were 124.4 in Comparative Example 5, 62.2 in Example 11, 46.7 in Example 12, 37.3 in Example 13, and 31.1 in Example 14. Therefore, considering the discharge capacity retention rate, the value of {(a1 × b1) + (a2 × b2)} / c is in the range of 24 or more and 65 or less (that is, the range including Examples 11 to 17). It is considered necessary. Further, the value of {(a1 × b1) + (a2 × b2)} / c is preferably 37 or more and 65 or less, and more preferably more than 37.3 and less than 62.2.

In addition, as shown in FIG. 18, the discharge capacity (mAh) of the lithium ion secondary batteries of Examples 15 to 17 is larger in the order of Example 16> Example 15, but the discharge capacity retention ratio (%) Were larger in the order of Example 15> Example 16> Example 17. In other words, the capacity reduction of the lithium ion secondary battery was suppressed in the order of Example 15> Example 16> Example 17. The value of {(a1 × b1) + (a2 × b2)} / c was 64.7 in Example 15, 48.6 in Example 16, and 24.6 in Example 17. In addition, the lithium ion secondary batteries of Examples 15 to 17 in which the value of {(a1 × b1) + (a2 × b2)} / c is included in the range of 24 or more and 65 or less maintain sufficiently large discharge capacity The rate (%) was shown. Also from this result, according to the negative electrode material of the present invention in which the value of {(a1 × b1) + (a2 × b2)} / c is included in the range of 24 or more and 65 or less, the discharge capacity decreases in the lithium ion secondary battery Can be greatly suppressed. Moreover, from this result, the range of the value of {(a1 × b1) + (a2 × b2)} / c that can improve the discharge capacity retention rate depends on the composition ratio of SiO _{x in} the negative electrode material and the composition of the electrolyte. I also know that I am not influenced much.

The discharge capacity retention ratio of the lithium ion secondary batteries of Example 15 and Example 16 was about 95% even after about 180 cycles had passed. That is, in the lithium ion secondary batteries of Example 15 and Example 16, the discharge capacity was particularly difficult to reduce. From this result, it can be said that the value of {(a1 × b1) + (a2 × b2)} / c is preferably 37 or more and 65 or less. Further, it is understood that it is preferable to use SiO _x having a BET value of 6.5 m ² / g or less and graphite having a BET value (m ² / g) of 3.8 or more and 6.0 or less. In addition, about the BET value of graphite, the same tendency is shown, even if it is 3.5 or more and 6.5 or less.

By the way, as described above, the value of {(a1 × b1) + (a2 × b2)} / c needs to be in the range of 24 to 65 (that is, the range including Examples 11 to 17). Conceivable. If the value of {(a1 × b1) + (a2 × b2)} / d is calculated based on the volume of the conductive additive based on this range, {(a1 × b1) + (a2 × b2)} / It can be said that the value of d needs to be 43 or more and 120 or less. Further, it is preferable that the value of {(a1 × b1) + (a2 × b2)} / d is 60 or more and 120 or less.

In addition, as shown in FIG. 20, the discharge IR drop (Ω) increased in the order of Comparative Example 5> Example 11> Example 12> Example 13> Example 14. When the conductivity is high, the discharge IR drop becomes small, so the conductivity can be said to increase in the order of Example 14> Example 13> Example 12> Example 11> Comparative Example 5. Examples 11 to 11 in which the value of {(a1 × b1) + (a2 × b2)} / c and the value of {(a1 × b1) + (a2 × b2)} / d are included in the scope of the present invention described above At the negative electrode of 14, the discharge IR drop is 7 Ω or less, which is sufficiently small. Therefore, it can be said that the negative electrode material and the negative electrode of the present invention are excellent in conductivity.

The lithium ion secondary battery of the present invention is suitable as a vehicle battery.

(Example 18 and Comparative Examples 6 to 7)
(Example 18)
<Fabrication of negative electrode for lithium ion secondary battery>
The SiO powder was heat treated at 900 ° C. for 2 hours to prepare a SiO _x powder with a D ₅₀ of 10 μm. By this heat treatment, if the ratio of Si to O is a homogeneous solid silicon monoxide (SiO) of approximately 1: 1, the solid is separated into two phases of Si phase and SiO ₂ phase by internal reaction. The Si phase obtained by separation is very fine.

A slurry was prepared by mixing 32 parts by mass of the obtained SiO _x powder, 50 parts by mass of graphite powder having a D ₅₀ of 9.2 μm, 8 parts by mass of ketjen black, and 10 parts by mass of a binder solution. The binder solution was prepared by dissolving a polyamideimide resin in N-methyl-2-pyrrolidone (NMP). The slurry was applied to the surface of an electrolytic copper foil (current collector) with a thickness of 15 μm using a doctor blade to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely bonded by a roll press. This was vacuum-dried to form a negative electrode having a thickness of 15 μm of the negative electrode active material layer.

In this negative electrode, the ratio of _{_D} 50 _(D ₂₎ of the _{_D} 50 _(D ₁₎ and SiO _x particles of the graphite particles _{_(D} 1 / D ₂₎ is 0.92, _D 50 of the graphite particles _(D 1) The ratio (D ₁ / t) of the thickness to the thickness (t) of the negative electrode active material layer is 0.61.

<Fabrication of positive electrode>
L333 (Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ ) as a positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder resin Were mixed to prepare a slurry-like positive electrode mixture. The composition ratio of each component (solid content) in the slurry was L333: AB: PVDF = 88: 6: 6 (mass ratio). The slurry was applied to a current collector, and a positive electrode mixture layer was formed on the current collector. Specifically, this slurry was applied to the surface of a 20 μm thick aluminum foil (current collector) using a doctor blade.
Thereafter, the resultant was dried at 80 ° C. for 20 minutes, and the organic solvent was volatilized and removed from the positive electrode mixture. After drying, the electrode density was adjusted by a roll press. The resultant was heat-cured at 200 ° C. for 2 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Fabrication of lithium ion secondary battery>
The positive electrode was cut into a size of 30 mm × 25 mm, and the negative electrode was cut into a size of 31 mm × 26 mm, and the laminate was housed in a laminate film. A rectangular sheet (40 mm × 40 mm square, 30 μm thick) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a pair of laminate films, and the three sides were sealed, and then the above electrolytic solution was injected into the bag-like laminate film. Then, the remaining one side was sealed, and the four sides were airtightly sealed to obtain a laminate cell in which the electrode plate group and the electrolytic solution were sealed. As electrolyte solution, LiPF is mixed with a mixed solution of FEC (fluoro ethylene carbonate), EC (ethylene carbonate), MEC (methyl ethyl carbonate), DMC (dimethyl carbonate) = 0.3: 2.7: 3: 4 (volume ratio) _A solution of ₆ at a concentration of 1 mol / L was used. The positive electrode and the negative electrode were provided with a tab electrically connectable to the outside, and a part of the tab extended to the outside of the laminate cell. Through the above steps, a lithium ion secondary battery in the form of a laminate cell (bipolar pouch cell) was obtained.

(Comparative example 6)
D ₅₀ is D ₅₀ in place of the graphite powder of 9.2μm was formed a negative electrode is in the same manner as in Example 18 except for using graphite powder 20.0 .mu.m. In this negative electrode, the ratio of the _{D 50} of the graphite particles _{(D 1)} and _{D 50} of the SiO _x particulate _{_{(D 2) (D 1 /}} D 2) is 2.00, the graphite particles _{D 50} _{(D 1} The ratio (D ₁ / t) of (A) to the thickness (t) of the negative electrode active material layer is 1.33.
Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 18.

(Comparative example 7)
D ₅₀ is D ₅₀ in place of the graphite powder of 9.2μm was formed a negative electrode is in the same manner as in Example 18 except for using graphite powder 12.5 .mu.m. In this negative electrode, the ratio of the _{D 50} of the graphite particles _{(D 1)} and _{D 50} of the SiO _x particulate _{_{(D 2) (D 1 /}} D 2) is 1.25, the graphite particles _{D 50} _{(D 1} The ratio (D ₁ / t) of the thickness of the negative electrode active material layer to the thickness (t) of the negative electrode active material layer is 0.83. Using this negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 18.

<Test>
The cross sections of the negative electrodes formed in Example 18 and Comparative Example 6 were observed by SEM. When the SEM image of Example 18 and the SEM image of Comparative Example 6 were compared, it was found that Example 18 had higher dispersibility of each particle than Comparative Example 6. The SEM image of the cross section of the negative electrode of Example 18 is shown in FIG. In the figure, whitish particles are SiO _x particles and gray particles are graphite particles.
For the lithium ion secondary batteries of Example 18 and Comparative Examples 6 and 7, while measuring the first discharge capacity at 0.3 C, the first discharge IR drop in 3 C discharge was measured. The first discharge IR drop was measured for the resistance value of the negative electrode 10 seconds after the start of discharge. The results are shown in FIGS. 22 and 23, respectively.

<Evaluation>
From FIG. 22 and FIG. 23, the negative electrode of Example 18 exhibits comparable discharge capacity as compared with Comparative Example 6 and Comparative Example 7, and the discharge IR drop is greatly reduced, and the conductivity is largely improved. it is obvious.

Claims

Positive electrode,
A negative electrode comprising a negative electrode active material comprising SiO x (0.5 ≦ x ≦ 1.5) and graphite,
Have
The blending ratio of SiO x when said SiO x and said graphite are 100% by mass is 27% by mass to 51% by mass.
The positive electrode has a general formula:
2. The positive electrode active material according to claim 1, comprising a composite metal oxide represented by LiCo p Ni q Mn r O 2 (p + q + r = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1). Lithium ion secondary battery as described.
The lithium ion secondary battery according to claim 1, wherein the composite metal oxide is LiCo 1/3 Ni 1/3 Mn 1/3 O 2 .
The mixing ratio of the SiO x when the 100 mass% the SiO x and the graphite, lithium ions according to any one of claims 1 to 3, characterized in that a 27% to 45% by weight Secondary battery.
Positive electrode,
Elements which can be alloyed with lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn And a negative electrode having a negative electrode active material containing a compound of Pb, Sb, Bi and / or the above element, and graphite,
The blending ratio of the element and / or the compound of the element when the graphite and the compound of the element and / or the element are 100% by mass is 27% by mass to 51% by mass. Secondary battery.
A negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector,
And the carbon-based particles in the negative electrode active material layer includes a storage capable Li occluding particles lithium ions, D 50 D 50 of the carbon Motokei particles (D 1) The Li-absorbing particles (D 2) the ratio (D 1 / D 2) is at greater than and 2 below 1, the ratio of the D 50 of the carbon Motokei particles (D 1) the thickness of the negative electrode active material layer and (t) (D 1 / t) A negative electrode for a lithium ion secondary battery characterized by having at least 1/4 and at most 5/6.
The negative electrode for a lithium ion secondary battery according to claim 6, wherein the Li storage particles are SiO-based particles.
The carbonaceous particles D 50 of claim 6 or the negative electrode for a lithium ion secondary battery according to claim 7 is graphite in the range of 1 ~ 15 [mu] m.
The SiO-based particles composed of a SiO 2 phase and the Si phase, the said SiO 2 phase according to Li x Si y O claims oxide-based compound represented by z are in claim 7 or claim 8 Negative electrode for lithium ion secondary battery.
The negative electrode for a lithium ion secondary battery according to any one of claims 6 to 9, wherein the negative electrode active material layer contains a high binding binder.
The negative electrode for a lithium ion secondary battery according to claim 10, wherein the high binding binder is at least one selected from polyamideimide resin, polyamideimide silica hybrid and polyacrylic acid.
A lithium ion secondary battery comprising the negative electrode according to any one of claims 6 to 11.
In a negative electrode for a lithium ion secondary battery having a current collector and an active material layer formed on the surface of the current collector,
The active material layer includes an active material, a binder, and a buffer material,
The active material comprises SiO x powder (0.5 ≦ x ≦ 1.5),
The buffer material is made of graphite powder,
D 50 of the SiO x powder is 1/4 to 1/2 of D 50 of the graphite powder,
The blending amount of the graphite powder is 36% by mass to 61% by mass when the total of the mass of the graphite powder and the mass of the SiO x powder is 100% by mass,
The content of the binder is 5% by mass to 25% by mass when the mass of the entire active material layer is 100% by mass, a negative electrode for a lithium ion secondary battery.
The negative electrode for a lithium ion secondary battery according to claim 13, wherein a blending amount of the graphite powder is 36% by mass to 49% by mass.
The negative electrode for a lithium ion secondary battery according to claim 13 or 14 is formed through a compression molding process,
The lithium ion secondary battery according to claim 13 or 14, wherein the thickness of the active material layer in the compression direction decreases when the negative electrode for lithium ion secondary battery is compressed at a press pressure higher than the press pressure in the compression molding step. Negative electrode.
A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to any one of claims 13 to 15.
xLi 2 M 1 O 3. (1-x) LiM 2 O 2 (0 <x ≦ 1, M 1 is one or more metal elements essential for tetravalent Mn, M 2 is essentially tetravalent Mn The lithium ion secondary battery according to claim 16, comprising a positive electrode including a positive electrode active material having a lithium manganese-based oxide represented by two or more kinds of metal elements) as a basic composition.
A negative electrode for a lithium ion secondary battery, comprising a negative electrode active material comprising a silicon oxide represented by SiO x (0.3 ≦ x ≦ 1.6), graphite, and a conductive additive containing carbonaceous fine particles The material,
BET value of the SiO x to (m 2 / g) and a1, the amount of the SiO x (g) was as b1, and BET value of graphite and (m 2 / g) and a2, said black amount of lead ( When g) is b2 and the amount (g) of the conductive additive is c,
The negative electrode material for a lithium ion secondary battery, wherein the value of {(a1 × b1) + (a2 × b2)} / c is 24 or more and 65 or less.
The negative electrode material for a lithium ion secondary battery according to claim 18, wherein a BET value (m 2 / g) of the SiO x is 2.5 or more and 7.0 or less.
The negative electrode material for a lithium ion secondary battery according to claim 18, wherein a BET value (m 2 / g) of the graphite is 3.5 or more and 6.5 or less.
The total content of the SiO x and the graphite is 70% by mass to 85% by mass, based on 100% by mass of the entire negative electrode material. Negative electrode material for lithium ion secondary batteries.
The negative electrode material for a lithium ion secondary battery according to any one of claims 18 to 21, wherein a value of the {(a1 × b1) + (a2 × b2)} / c is 37 or more and 65 or less.
A negative electrode material for a lithium ion secondary battery, comprising a negative electrode active material comprising a silicon oxide represented by SiO x (0.3 ≦ x ≦ 1.6), and a conductive aid containing carbon (C) There,
BET value of the SiO x to (m 2 / g) and a1, the amount of the SiO x (g) was as b1, and BET value of graphite and (m 2 / g) and a2, said black amount of lead ( When g) is b2 and the compounding amount (cm 3 ) of the conductive additive is d,
The negative electrode material for a lithium ion secondary battery, wherein the value of {(a1 × b1) + (a2 × b2)} / d is 43 or more and 120 or less.
The negative electrode material for a lithium ion secondary battery according to claim 23, wherein a BET value (m 2 / g) of the SiO x is 2.5 or more and 7.0 or less.
The negative electrode material for a lithium ion secondary battery according to claim 22 or 23, wherein a BET value (m 2 / g) of the graphite is 3.5 or more and 6.5 or less.
The total content of the SiO x and the graphite is 70% by mass to 85% by mass, based on 100% by mass of the entire negative electrode material. Negative electrode material for lithium ion secondary batteries.
The negative electrode material for a lithium ion secondary battery according to any one of claims 23 to 26, wherein a value of the {(a1 × b1) + (a2 × b2)} / d is 60 or more and 120 or less.
A negative electrode for a lithium ion secondary battery comprising the negative electrode material for a lithium ion secondary battery according to any one of claims 18 to 27 as a material.
A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 28.
A negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector,
And the carbon-based particles in the negative electrode active material layer includes a storage capable Li occluding particles lithium ions, D 50 D 50 of the carbon Motokei particles (D 1) The Li-absorbing particles (D 2) the ratio (D 1 / D 2) is 1/2 or more and 1.3 or less, the ratio of the D 50 of the carbon Motokei particles (D 1) the thickness of the negative electrode active material layer and (t) ( A negative electrode for a lithium ion secondary battery, wherein D 1 / t) is at least 1/4 and at most 2/3.
Lithium according to D 50 (D 1) and the Li claim 30 the ratio of the D 50 of the occlusion particle (D 2) (D 1 / D 2) is 1/2 or more and 1 or less of the carbon-based particles Negative electrode for ion secondary battery.
The negative electrode for a lithium ion secondary battery according to claim 30, wherein the Li storage particles are SiO-based particles.
The carbonaceous particles a negative electrode for a lithium ion secondary battery according to any one of claims 30 ~ 32 D 50 is graphite in the range of 1 ~ 15 [mu] m.
The SiO-based particles composed of a SiO 2 phase and the Si phase, the said SiO 2 phase according to Li x Si y O claims oxide-based compound represented by z are in claim 32 or claim 33 Negative electrode for lithium ion secondary battery.
The negative electrode for a lithium ion secondary battery according to any one of claims 30 to 34, wherein the negative electrode active material layer contains a high binding binder.
The negative electrode for a lithium ion secondary battery according to claim 35, wherein the high binding binder is at least one selected from a polyamideimide resin, a polyamideimide silica hybrid and a polyacrylic acid.
A lithium ion secondary battery using the negative electrode according to any one of claims 30 to 36.