JP2016066529A - Negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode which enables the rise in battery capacity, and the enhancement in cycle characteristics and initial charge and discharge characteristics.SOLUTION: A negative electrode 10 for a nonaqueous electrolyte secondary battery comprises: a silicon compound (SiO: 0.5≤x≤1.6) containing a Li compound as a negative electrode active material 12; and polyacrylic acid or its metal salt. In the negative electrode 10 for a nonaqueous electrolyte secondary battery, the polyacrylic acid or its metal salt has a basic skeleton represented by the formula (1) below, and has peaks in ranges of 4-4.5 ppm and 1-2 ppm as chemical shift values determined fromH-NMR spectra. (M represents H, Li, Na or K.)SELECTED DRAWING: Figure 1

Description

  The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

  In recent years, small electronic devices typified by mobile terminals have been widely used, and further downsizing, weight reduction, and long life have been strongly demanded. In response to such market demands, development of secondary batteries capable of obtaining a high energy density, in particular, being small and light is underway. This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.

  Among them, lithium ion secondary batteries are highly expected because they are small and easy to increase in capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.

  Said lithium ion secondary battery is equipped with the electrolyte solution with the positive electrode, the negative electrode, and the separator, and the negative electrode contains the negative electrode active material in connection with charging / discharging reaction.

  As a negative electrode active material, while carbon materials are widely used, further improvement in battery capacity is required due to recent market demand. As an element for improving battery capacity, the use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected. The development of a siliceous material as a negative electrode active material has been examined not only for silicon itself but also for compounds represented by alloys and oxides. The shape of the active material has been studied from a standard coating type using a carbon material to an integrated type directly deposited on a current collector.

  However, when silicon is used as the negative electrode active material as the main raw material, the negative electrode active material expands and contracts during charge / discharge, and therefore, it tends to break mainly near the surface of the negative electrode active material. Further, an ionic material is generated inside the active material, and the negative electrode active material is easily broken. When the negative electrode active material surface layer is cracked, a new surface is generated thereby increasing the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating that is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.

  To date, various studies have been made on negative electrode materials and electrode configurations for lithium ion secondary batteries mainly composed of a siliceous material in order to improve battery initial efficiency and cycle characteristics.

  Specifically, for the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are deposited simultaneously using a vapor phase method (see, for example, Patent Document 1). Further, in order to obtain a high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of the silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed ( For example, see Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, refer to Patent Document 4).

Further, Si phase, (for example, see Patent Document 5) by using a nanocomposite containing SiO 2, _M y _O metal oxide in order to improve the initial charge and discharge efficiency. In order to improve cycle characteristics, SiO _x (0.8 ≦ x ≦ 1.5, particle size range = 1 μm to 50 μm) and a carbon material are mixed and fired at a high temperature (see, for example, Patent Document 6).

  Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the difference between the maximum value and the minimum value of the molar ratio in the vicinity of the active material and current collector interface The active material is controlled within a range of 0.4 or less (see, for example, Patent Document 7). Further, in order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Further, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the siliceous material (see, for example, Patent Document 9).

Further, in order to improve cycle characteristics, conductivity is imparted by using silicon oxide and forming a graphite film on the surface layer (see, for example, Patent Document 10). In Patent Document 10, with respect to the shift value obtained from the Raman spectra for graphite coating, with broad peaks appearing at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio _I 1330 _{/ I 1580} is _{1.5 <I 1330} / _{I 1580} <3.

  In addition, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used in order to improve high battery capacity and cycle characteristics (see, for example, Patent Document 11). Further, in order to improve overcharge and overdischarge characteristics, silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (see, for example, Patent Document 12). In addition, in order to improve high battery capacity and cycle characteristics, a mixed electrode of silicon and carbon is prepared and the silicon ratio is designed to be 5 wt% or more and 13 wt% or less (see, for example, Patent Document 13).

JP 2001-185127 A JP 2002-042806 A JP 2006-164955 A JP 2006-114454 A JP 2009-070825 A JP 2008-282819 A JP 2008-251369 A JP 2008-177346 A JP 2007-234255 A JP 2009-212074 A JP 2009-205950 A Japanese Patent No. 2,997,741 JP 2010-092830 A

  As described above, in recent years, small mobile devices typified by electronic devices have been improved in performance and multifunction, and the lithium ion secondary battery as the main power source is required to have an increased battery capacity. Yes. As one method for solving this problem, development of a lithium ion secondary battery composed of a negative electrode using a siliceous material as a main material is desired. Moreover, the lithium ion secondary battery using a siliceous material is desired to have a cycle characteristic close to that of a lithium ion secondary battery using a carbon material. However, a negative electrode having cycle stability equivalent to that of a lithium ion secondary battery using a carbon material as a main material has not been proposed.

  The present invention has been made in view of the above-described problems, and is a negative electrode capable of improving battery capacity, improving cycle characteristics and initial charge / discharge characteristics, and a non-aqueous electrolyte secondary having this negative electrode. An object is to provide a battery.

（式中、Ｍは、水素原子、リチウム原子、ナトリウム原子、又はカリウム原子のいずれかを表し、ｎは、２以上の整数を表す。） In order to achieve the above object, the present invention provides a negative electrode for a non-aqueous electrolyte secondary battery including a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) containing a Li compound therein as a negative electrode active material. The negative electrode for a non-aqueous electrolyte secondary battery includes polyacrylic acid or a metal salt thereof, and the polyacrylic acid or the metal salt thereof has a basic skeleton represented by the following formula (1): A chemical shift value obtained from a ¹ H-NMR spectrum and having tetramethylsilane as a reference substance has a peak at at least one place in the range of 4 to 4.5 ppm and 1 to 2 ppm. A negative electrode for a non-aqueous electrolyte secondary battery is provided.

(In the formula, M represents one of a hydrogen atom, a lithium atom, a sodium atom, and a potassium atom, and n represents an integer of 2 or more.)

  Such a negative electrode for a non-aqueous electrolyte secondary battery can improve the battery capacity and initial charge / discharge efficiency (initial efficiency), which are problems of the silicon compound, by including a silicon compound subjected to Li doping. At this time, as in the present invention, by including the polyacrylic acid or the metal salt thereof as described above, the silicon compound subjected to Li doping can be stably slurried and turned into an electrode. Battery characteristics such as characteristics and initial charge / discharge efficiency (initial efficiency) can be improved.

At this time, the peak in the range of 4 to 4.5 ppm is attributed to —O—CH ₂ —, and the peak in the range of 1 to ₂ ppm is − in the region near the end of the polyacrylic acid or a metal salt thereof. CH 2 _- is preferably one attributed to.

  If it is such, stabilization of a slurry and stability of aqueous solution can be improved more, and a battery characteristic can be improved.

At this time, the polyacrylic acid or a metal salt thereof is obtained from a ¹³ C-NMR spectrum, as a chemical shift value using tetramethylsilane as a reference substance, except for a peak attributed to the basic skeleton in a range of 20 to 60 ppm. In addition, it is preferable to have a plurality of peaks that are weaker than the peaks attributed to the basic skeleton.

  If it is such, stabilization of a slurry and stability of aqueous solution can be improved more, and a battery characteristic can be improved.

At this time, it is preferable that the plurality of peaks obtained in the range of 20 to 60 ppm belong to part of the acrylate as chemical shift values obtained from the ¹³ C-NMR spectrum.

  The presence of a structure in which a part of polyacrylic acid is substituted with a metal salt makes it possible to stabilize aqueous solutions and slurries, and to improve battery characteristics.

  At this time, the molecular weight of the polyacrylic acid or a metal salt thereof is preferably in the range of 500,000 to 1,250,000.

  If the molecular weight is 500,000 or more, sufficient binding properties can be obtained, so that the electrode structure is not easily broken and the battery characteristics are improved. Moreover, if molecular weight is 1.25 million or less, it will be easy to make aqueous solution and the fall of the solid content of the slurry used for negative electrode material preparation can be suppressed. As a result, sufficient binding properties are obtained, and battery characteristics are improved.

  In addition to the polyacrylic acid or a metal salt thereof, the negative electrode of the present invention may further contain at least one of styrene butadiene rubber, carboxymethyl cellulose or a metal salt thereof, and polyvinylidene fluoride as a binder. preferable.

  When the binder contains polyacrylic acid or a metal salt thereof and at least one of styrene butadiene rubber, carboxymethyl cellulose or a metal salt thereof, and polyvinylidene fluoride, a total of two or more compounds, a negative electrode material is produced. Therefore, the stability of the slurry can be further improved, and the battery characteristics can be improved.

  At this time, the carboxymethyl cellulose or the metal salt thereof preferably has a degree of etherification in the range of 0.7 to 1.5.

  Carboxymethyl cellulose having a degree of etherification of 0.7 or more or a metal salt thereof has high alkali resistance, so that the stability of the slurry is improved and the cycle characteristics are improved. Moreover, if the degree of etherification is 1.5 or less, the average degree of polymerization does not become too high, and it is easy to make an aqueous solution. As a result, the stability of the slurry is improved and the cycle characteristics are improved.

  Moreover, it is preferable that the ratio of the said silicon compound with respect to the total amount of the said negative electrode active material is a thing whose negative electrode of this invention is 6 mass% or more.

  With such a negative electrode, the volume energy density of the battery can be improved.

  At this time, the negative electrode for a nonaqueous electrolyte secondary battery has a negative electrode active material layer containing the negative electrode active material, and the negative electrode active material layer contains 0.1% by mass of the polyacrylic acid or a metal salt thereof. It is preferable that it is contained at a ratio of 2.5% by mass or less.

  Even if the polyacrylic acid or its metal salt contained in the negative electrode active material layer of the present invention is in a small amount, an effect is obtained for the silicon active material having alkalinity. If it is 0.1 mass% or more, a slurry can be stabilized more and a battery characteristic can be improved. Further, when the ratio is 2.5% or less, the binding property does not decrease when the slurry is applied to a current collector or the like and pressed after drying. Can be improved.

  At this time, it is preferable that the silicon compound has a carbon film, and at least a part of the surface layer contains lithium carbonate.

  Conductivity improves because the silicon compound is coated with the carbon film. Moreover, if at least a part of the surface layer of the silicon compound is covered with lithium carbonate, the initial efficiency of the battery can be greatly improved.

  The silicon compound is preferably such that carbon particles are attached to the surface layer via a binder having a carboxyl group.

  If the carbon particles contain a silicon compound adhering to the surface layer, contact between the negative electrode active material particles can be made smoothly. The carbon particles can be firmly attached by using a binder having a carboxyl group.

  At this time, it is preferable that the carbon particles attached to the surface layer of the silicon compound have a median diameter of 20 nm to 200 nm.

  If the median diameter of the carbon particles is 20 nm or more, sufficient contact between the negative electrode active material particles can be obtained. If the median diameter of the carbon particles is 200 nm or less, the proportion of the carbon particles that can be contacted between the negative electrode active material particles is increased, and the amount of carbon particles necessary for making contact is reduced. It is not necessary to add a large amount to the battery, and a sufficient battery capacity can be secured.

  Moreover, at this time, it is preferable that the binder which has the said carboxyl group contains at least 1 sort (s) among carboxymethylcellulose or its metal salt, and polyacrylic acid or its metal salt.

  Such binders are suitable as the binder for attaching the carbon particles to the surface layer of the silicon compound.

  At this time, it is preferable that the silicon compound is produced in a process including an electrochemical method.

By producing a silicon compound using such a modification (in-bulk modification) method, it is possible to reduce or avoid the formation of a Li compound in the Si region. In the atmosphere or in an aqueous slurry, a solvent slurry It becomes a stable substance. In addition, if the SiO ₂ component part of the silicon compound is modified by an electrochemical method, it is modified by a random compounding method such as thermal modification (thermal doping method) or vapor deposition Li method. It becomes a more stable substance than anything.

  At this time, the half width (2θ) of the diffraction peak due to the (111) crystal plane obtained by X-ray diffraction of the silicon compound is 1.2 ° or more, and the crystallite size due to the crystal plane Is preferably 7.5 nm or less.

  The lower the crystallinity of the Si component of the silicon compound, the better. The half width (2θ) of the diffraction peak attributed to the Si (111) crystal plane obtained by X-ray diffraction, and the crystallite size attributed to the crystal plane are in the above range. It is desirable that Battery characteristics can be improved by reducing the crystallinity of the Si component.

  At this time, the negative electrode of the present invention preferably further contains carbon nanotubes.

  Carbon nanotubes (CNT) are suitable for obtaining electrical contact between a silicon compound having a high expansion rate and shrinkage rate and another active material such as a carbon-based active material, and can impart good conductivity to the negative electrode. Battery characteristics are improved.

  Moreover, according to this invention, the negative electrode for nonaqueous electrolyte secondary batteries characterized by using any one of said negative electrode for nonaqueous electrolyte secondary batteries is provided.

  Such a non-aqueous electrolyte secondary battery has a high capacity and good cycle characteristics and initial charge / discharge characteristics.

The silicon compound in the negative electrode for a non-aqueous electrolyte secondary battery of the present invention is generated at the time of charging because the SiO ₂ component part that is destabilized at the time of lithium insertion / extraction is previously modified to another compound. The irreversible capacity can be reduced. Moreover, as a structure of the negative electrode binder (negative electrode binder) suitable for using the silicon compound particles, polyacrylic acid or a metal salt thereof is included, and the basic skeleton of the polyacrylic acid or the metal salt thereof is represented by the above formula (1). Cycle characteristics obtained by ¹ H-NMR spectrum and having a peak in at least one of 4 to 4.5 ppm or 1 to 2 ppm as chemical shift values, and high initial efficiency Can be obtained. Moreover, the negative electrode for nonaqueous electrolyte secondary batteries of this invention and the nonaqueous electrolyte secondary battery using this negative electrode can improve battery capacity, cycling characteristics, and initial charge / discharge characteristics. Moreover, the same effect can be acquired also in the electronic device, electric tool, electric vehicle, electric power storage system, etc. which used the secondary battery of this invention.

It is sectional drawing which shows the structure of the negative electrode for nonaqueous electrolyte secondary batteries of this invention. It is the reformer in a bulk used when manufacturing the negative electrode active material contained in the negative electrode for nonaqueous electrolyte secondary batteries of this invention. It is a figure showing the structural example (laminate film type) of the lithium secondary battery containing the negative electrode for nonaqueous electrolyte secondary batteries of this invention. Were measured in Example 1-2 and Comparative Example 2-1 is a diagram showing the ^{1 H-NMR} spectrum of a polyacrylic acid contained in the non-aqueous electrolyte secondary battery negative electrode. It is a figure which shows the ¹³ C-NMR spectrum of the polyacrylic acid contained in the nonaqueous electrolyte secondary battery negative electrode measured in Example 1-2 and Example 2-2. It is a figure which shows the increase rate of battery capacity at the time of increasing the phase which the silicon compound in a negative electrode active material cracks.

  As described above, as one method for increasing the battery capacity of a lithium ion secondary battery, the use of a negative electrode using a silicon material as a main material as a negative electrode of a lithium ion secondary battery has been studied. The lithium ion secondary battery using this silicon material is expected to have cycle characteristics similar to those of a lithium ion secondary battery using a carbon material, but the cycle is equivalent to that of a lithium ion secondary battery using a carbon material. A negative electrode that exhibits stability has not been proposed.

  Accordingly, the present inventors have made extensive studies on a negative electrode capable of obtaining a high battery capacity, good cycle characteristics, and initial efficiency as a negative electrode of a lithium ion secondary battery, and reached the present invention.

（式中、Ｍは、水素原子、リチウム原子、ナトリウム原子、又はカリウム原子のいずれかを表し、ｎは、２以上の整数を表す。） The negative electrode for a non-aqueous electrolyte secondary battery of the present invention contains a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) containing a Li compound therein as a negative electrode active material. Furthermore, the negative electrode of the present invention contains polyacrylic acid or a metal salt thereof. This polyacrylic acid or a metal salt thereof has a basic skeleton represented by the following formula (1), and is obtained from a ¹ H-NMR spectrum and has a chemical shift value of 4 to 4 using tetramethylsilane as a reference substance. It has a peak in at least one place in the range of 0.5 ppm and 1-2 ppm.

(In the formula, M represents one of a hydrogen atom, a lithium atom, a sodium atom, and a potassium atom, and n represents an integer of 2 or more.)

The hydrogen atom, lithium atom, sodium atom, and potassium atom represented by M in the above formula (1) may exist in an ionized state. Moreover, the apparatus used for < ¹ > H-NMR measurement should just use a commercial item, and is not specifically limited. Further, as described above, the reference substance for the chemical shift is tetramethylsilane (TMS), and the chemical shift of TMS is set to 0 ppm. In actual measurement, TMS is not necessarily used as a reference substance.

  Such a negative electrode for a non-aqueous electrolyte secondary battery can improve the initial charge / discharge efficiency (initial efficiency), which is a problem of the silicon compound, by using a Li-doped silicon compound. Moreover, since the irreversible Li component inserted from a positive electrode can be removed by producing | generating Li compound inside the bulk of a silicon compound, it leads to the improvement of battery capacity.

Moreover, as a binder contained in the negative electrode using such a silicon compound, for example, as a main binder, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), a secondary binder, and a thickener as carboxy. Methyl cellulose (CMC) can be used. However, a slurry using a silicon compound that is closer to alkali like a silicon compound that has been doped with Li reduces the binding properties and viscosity increase of CMC, and causes the slurry to become unstable. Therefore, in the present invention, polyacrylic acid capable of suppressing the binding property and viscosity increase of the slurry is included. That is, in addition to the basic skeleton represented by the formula (1), as a chemical shift value obtained from a ¹ H-NMR spectrum, polyacrylic acid having a peak in at least one place in the above range is used, and a slurry Increase stability. Thus, by including polyacrylic acid having a structure capable of enhancing slurry stability, it becomes possible to stabilize the slurry without lowering the binding property and viscosity increase. The effect of improving the binding property can be obtained.

  Such a negative electrode for a nonaqueous electrolyte secondary battery of the present invention will be described. FIG. 1 shows a cross-sectional configuration of a negative electrode for a nonaqueous electrolyte secondary battery (hereinafter sometimes simply referred to as “negative electrode”) according to an embodiment of the present invention.

[Configuration of negative electrode]
As shown in FIG. 1, the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. Furthermore, the negative electrode current collector 11 may not be provided in the negative electrode for a nonaqueous electrolyte secondary battery of the present invention.

[Negative electrode current collector]
The negative electrode current collector 11 is an excellent conductive material and is made of a material that is excellent in mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

  The negative electrode current collector 11 preferably contains carbon (C) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved. In particular, in the case of having an active material layer that expands during charging, if the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector. Although content of said content element is not specifically limited, Especially, it is preferable that it is 100 ppm or less. This is because a higher deformation suppressing effect can be obtained.

  The surface of the negative electrode current collector 11 may be roughened or not roughened. The roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching. The non-roughened negative electrode current collector is, for example, a rolled metal foil.

[Negative electrode active material layer]
The negative electrode active material layer 12 includes a particulate negative electrode active material capable of occluding and releasing lithium ions (hereinafter also referred to as negative electrode active material particles) and a binder (negative electrode binder). Other materials such as auxiliaries may be included.

The negative electrode of this invention contains the silicon compound (SiOx: 0.5 <= x <= 1.6) in which Li compound is contained inside as a negative electrode active material. Of course, as the negative electrode active material, a carbon-based active material may be included in addition to the silicon compound. Moreover, the silicon compound used for the negative electrode of the present invention is a silicon oxide material (SiO _x : 0.5 ≦ x ≦ 1.6), and the composition is preferably such that x is close to 1. This is because high cycle characteristics can be obtained. The composition of the silicon compound in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements.

  The negative electrode of the present invention contains polyacrylic acid or a metal salt thereof as a part of the negative electrode binder. The basic skeleton of polyacrylic acid or a metal salt thereof is represented by the following formula (1).

Furthermore, polyacrylic acid or a metal salt thereof has a peak at least in one of the ranges of 4 to 4.5 ppm and 1 to 2 ppm as a chemical shift value obtained from ¹ H-NMR spectrum using TMS as a reference substance. It has the structure which has. By including such polyacrylic acid or a metal salt thereof, it is possible to improve the stability of the slurry in which the alkali-like silicon compound containing the Li compound is mixed, so that the cycle characteristics of the negative electrode can be improved.

In addition, the chemical shift value in the range of 4 to 4.5 ppm has a peak attributed to —O—CH ₂ —, in the range of 1 to ₂ ppm, —CH ₂ in a region near the end of polyacrylic acid or a metal salt thereof. It is desirable to have a peak attributed to-. Thus, the peak in the range of 4 to 4.5 ppm is substantially attributable to —O—CH ₂ —, and the peak in the range of 1 to ₂ ppm is substantially close to the end of the molecule. -CH 2 region _- as long as due to, it is possible to further improve the stability of the stabilization and aqueous slurries.

Furthermore, the polyacrylic acid or its metal salt that constitutes the negative electrode of the present invention is obtained from the ¹³ C-NMR spectrum, as a chemical shift value using TMS as a reference substance, within the range of 20 to 60 ppm by the above formula (1). It is more desirable to have a plurality of peaks other than the peaks attributed to the basic skeleton represented. In addition, it is preferable that the plurality of peaks that are weaker than the peak attributed to the basic skeleton substantially originate from a structure in which a part of the carboxyl group of polyacrylic acid is substituted with a metal salt. By containing such polyacrylic acid or a metal salt thereof, the aqueous solution and the slurry can be stabilized.

Moreover, the apparatus used for < ¹³ > C-NMR measurement should just use a commercial item, and is not specifically limited. The reference substance for the chemical shift of ¹³ C-NMR is TMS. In the actual measurement, other reference materials may be used.

  Furthermore, it is desirable that the polyacrylic acid or the metal salt constituting the negative electrode of the present invention has a molecular weight of 500,000 to 1.25 million. When the molecular weight is 500,000 or more, sufficient binding properties can be obtained, so that the electrode structure is not easily broken and the battery characteristics are improved. Moreover, if molecular weight is 1.25 million or less, it will be easy to make aqueous solution and the fall of the solid content of the slurry used for negative electrode material preparation can be suppressed. As a result, sufficient binding properties are obtained, and battery characteristics are improved. A more preferable molecular weight is around 1 million.

  In the negative electrode of the present invention, in addition to polyacrylic acid or a metal salt thereof, it is preferable that the binder further contains at least one of styrene butadiene rubber, carboxymethyl cellulose or a metal salt thereof, and polyvinylidene fluoride as a binder. . In addition to polyacrylic acid or a metal salt thereof, the stability of the slurry can be further improved by including at least one of these, or a total of two or more compounds, as a binder.

  Carboxymethylcellulose or a metal salt thereof preferably has a degree of etherification of 0.7 to 1.5. If the degree of etherification of carboxymethylcellulose or a metal salt thereof is 0.7 or more, the alkali resistance is high, so that the stability of the slurry is improved and the cycle characteristics are improved. Moreover, if the degree of etherification is 1.5 or less, the average degree of polymerization does not become too high, and it is easy to make an aqueous solution. As a result, the stability of the slurry is improved and the cycle characteristics are improved.

  At this time, the ratio of the silicon compound to the total amount of the negative electrode active material is preferably 6% by mass or more.

  If it is such, the volume energy density of a battery can be improved. In addition, for example, when a carbon-based active material is included in addition to the silicon compound as the negative electrode active material, the carbon-based active material can be discharged at a lower potential than the silicon compound. The volume energy density of the battery can be improved by mixing. Furthermore, at this time, if the ratio of the silicon-based active material in the negative electrode active material is 6% by mass or more, the volume energy density of the battery is improved even if the silicon compound is high-potential discharge with respect to the carbon material. be able to.

  Furthermore, the negative electrode for a non-aqueous electrolyte secondary battery desirably contains the polyacrylic acid or a metal salt thereof in a proportion of 0.1% by mass to 2.5% by mass. Even if the polyacrylic acid or its metal salt contained in the negative electrode active material layer of the present invention is in a small amount, an effect is obtained for the silicon active material having alkalinity. If it is 0.1 mass% or more, a slurry can be stabilized more and a battery characteristic can be improved. Further, when the ratio is 2.5% or less, the binding property does not decrease during application of the slurry to the electrode and pressing after drying, so that a stable negative electrode active material layer can be obtained and battery characteristics can be improved. .

  Moreover, it is preferable that the silicon compound contained in the negative electrode for nonaqueous electrolyte secondary batteries of this invention has a carbon film, and lithium carbonate is included in at least one part of the surface layer. Conductivity improves because the silicon compound is coated with the carbon film. Moreover, if at least a part of the surface layer of the silicon compound is covered with lithium carbonate, the initial efficiency of the battery can be greatly improved.

  In addition, it is preferable that the coating amount of a carbon film is 0.1 mass%-15 mass% with respect to the sum total of a silicon compound and a carbon film. If the coating amount of the carbon coating is 0.1% by mass or more, sufficient conductivity can be obtained. Moreover, if the coating amount is 15% by mass or less, a sufficient battery capacity can be secured.

  It is preferable that lithium carbonate is contained in the range of 0.5 mass% or more and 4 mass% or less with respect to the silicon compound. If lithium carbonate is contained in an amount of 0.5% by mass or more based on the silicon compound, the effect of improving the initial efficiency can be sufficiently obtained. Moreover, if lithium carbonate is 4 mass% or less, slurry stability can be maintained.

  Furthermore, the negative electrode of the present invention is preferably such that the silicon compound has carbon particles attached to the surface layer via a binder having a carboxyl group. The carbon particles can be firmly attached by using a binder having a carboxyl group. Further, if the carbon particles are attached to the silicon compound, it becomes easy to make contact between the negative electrode active material particles, and stable battery characteristics can be obtained. Furthermore, the carbon particles are desirably in the range of 20 nm to 200 nm. If the median diameter of the carbon particles is 20 nm or more, sufficient contact between the negative electrode active material particles can be obtained. If the median diameter of the carbon particles is 200 nm or less, the proportion of the carbon particles that can be contacted between the negative electrode active material particles is increased, and the amount of carbon particles necessary for making contact is reduced. It is not necessary to add a large amount to the battery, and a sufficient battery capacity can be secured.

  The binder having a carboxyl group for adhering carbon particles to the silicon compound preferably contains at least one of carboxymethyl cellulose or a metal salt thereof and polyacrylic acid or a metal salt thereof. If it is such a thing, carbon particles can be made to adhere especially firmly.

In the negative electrode of the present invention, the silicon compound containing a Li compound therein can be obtained by selectively changing a part of the SiO ₂ component generated inside to a Li compound. If the SiO ₂ component part that destabilizes the silicon compound at the time of insertion or desorption of lithium is modified in advance to another Li compound, the irreversible capacity generated during charging can be reduced. Among them, in the interior of the silicon compound, as a Li _{compound, Li 4 SiO 4, Li 2} SiO 3, Li 6 Si 2 _{if O 7} are included, they show particularly good cell characteristics. This makes it possible to produce a selective compound by performing potential regulation or current regulation on the lithium counter electrode and changing the conditions. Li compounds can be quantified by NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy). The XPS and NMR measurements can be performed, for example, under the following conditions.
XPS
・ Device: X-ray photoelectron spectrometer,
・ X-ray source: Monochromatic Al Kα ray,
・ X-ray spot diameter: 100 μm,
Ar ion gun sputtering conditions: 0.5 kV 2 mm × 2 mm.
²⁹ Si MAS NMR (magic angle rotating nuclear magnetic resonance)
Apparatus: 700 NMR spectrometer manufactured by Bruker,
Probe: 4 mm HR-MAS rotor 50 μL,
Sample rotation speed: 10 kHz,
-Measurement environment temperature: 25 ° C.

  The method for producing the selective compound, that is, the modification of the silicon-based active material is preferably performed by an electrochemical method.

  By producing a silicon compound using such a modification (in-bulk modification) method, it is possible to reduce or avoid the formation of a Li compound in the Si region. In the atmosphere or in an aqueous slurry, a solvent slurry It becomes a stable substance. Further, by performing the modification by an electrochemical method, it is possible to produce a more stable material with respect to the thermal modification (thermal doping method) and vapor deposition method in which compounds are randomly formed.

The presence of at least one of Li ₄ SiO ₄ , Li ₂ SiO ₃ , and Li ₆ Si ₂ O ₇ generated in the bulk of the silicon-based active material improves the characteristics, but these characteristics are more improved. Species coexistence.

  Moreover, the preservation | save characteristic of powder can be improved greatly by producing | generating reaction-suppressing substances, such as lithium carbonate, in at least a part of the outermost layer of the silicon-based active material. A method for generating the reaction inhibitor is not particularly limited, but an electrochemical method is most preferable.

  Moreover, the lower the crystallinity of the silicon-based active material contained in the negative electrode material of the present invention, the better. Specifically, the full width at half maximum (2θ) of the diffraction peak attributed to the Si (111) crystal plane obtained by X-ray diffraction of the silicon compound is 1.2 ° or more, and the crystallite size attributed to the crystal plane Is preferably 7.5 nm or less. As described above, since the crystallinity is low and the amount of Si crystals present is small, not only the battery characteristics are improved, but also a stable Li compound can be generated.

  The median diameter of the silicon-based active material is not particularly limited, but is preferably 0.5 μm to 20 μm. This is because, within this range, lithium ions are easily occluded and released during charging and discharging, and the particles are difficult to break. If the median diameter is 0.5 μm or more, the surface area is not too large, so that the battery irreversible capacity can be reduced. On the other hand, a median diameter of 20 μm or less is preferable because the particles are difficult to break and a new surface is difficult to appear.

  Examples of the negative electrode conductive assistant include one or more carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotube (CNT), and carbon nanofiber. In particular, carbon nanotubes are suitable for obtaining electrical contacts between a silicon material and a carbon material having a high expansion / contraction rate.

[Production method of negative electrode]
First, a method for producing a silicon compound contained in the negative electrode for a nonaqueous electrolyte secondary battery of the present invention will be described. First, a silicon compound represented by SiO _x (0.5 ≦ x ≦ 1.6) is prepared, and then Li is inserted into the silicon-based active material to generate a Li compound inside the silicon compound. be able to. More specifically, the silicon compound is produced by the following procedure, for example.

First, a raw material (vaporization starting material) that generates silicon oxide gas is heated in the temperature range of 900 ° C. to 1600 ° C. in the presence of an inert gas or under reduced pressure to generate silicon oxide gas. In this case, the raw material is a mixture of metal silicon powder and silicon dioxide powder, and considering the surface oxygen of the metal silicon powder and the presence of trace amounts of oxygen in the reactor, the mixing molar ratio is 0.8 <metal silicon powder / It is desirable that the silicon dioxide powder is in the range of <1.3. The Si crystallites in the particles are controlled by changing the preparation range and vaporization temperature, and by heat treatment after generation. The generated gas is deposited on the adsorption plate. The deposit is taken out with the temperature in the reactor lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like. In this way, a silicon compound represented by SiO _x (0.5 ≦ x ≦ 1.6) is produced.

  Next, a carbon film can be coated on the surface layer of the obtained powder material, but this step is not essential. However, it is effective for improving battery characteristics.

  Pyrolysis CVD is desirable as a technique for coating the surface layer of the obtained powder material with a carbon film. Thermal decomposition CVD fills the silicon oxide powder set in the furnace and the hydrocarbon gas into the furnace to raise the temperature in the furnace. The decomposition temperature is not particularly limited, but is preferably 1200 ° C. or lower. More desirably, the temperature is 950 ° C. or lower, which can suppress disproportionation of particles. The hydrocarbon gas is not particularly limited, but 3 ≧ n is desirable in the CnHm composition. This is because the manufacturing cost is low and the physical properties of the decomposition product are improved.

  Next, modification in the bulk of the powder material is performed. It is desirable that in-bulk modification can electrochemically insert and desorb Li. Although the apparatus structure is not particularly limited, for example, the bulk reforming can be performed using the bulk reforming apparatus 20 shown in FIG. The in-bulk reformer 20 includes a bathtub 27 filled with an organic solvent 23, a positive electrode (lithium source, reforming source) 21 disposed in the bathtub 27 and connected to one of the power sources 26, And a separator 24 provided between the positive electrode 21 and the powder storage container 25. The powder storage container 25 is connected to the other side of the power source 26. The powder storage container 25 stores silicon oxide powder 22. At this time, smooth modification can be obtained by adhering the carbon particles to the silicon oxide powder 22 via polyacrylic acid.

  As described above, the obtained modified particles may not include the carbon layer. However, when more uniform control is required in the reforming process in the bulk, it is necessary to reduce the potential distribution, and it is desirable that a carbon layer exists.

As the organic solvent 23 in the bathtub 27, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, or the like can be used. As the electrolyte salt contained in the organic solvent 23, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or the like can be used.

  The positive electrode 21 may use a Li foil or a Li-containing compound. Examples of the Li-containing compound include lithium carbonate, lithium oxide, lithium cobaltate, lithium olivine, lithium nickelate, and lithium vanadium phosphate.

  Subsequently, the silicon-based active material is mixed with the carbon-based active material as necessary, and the negative-electrode active material particles are mixed with other materials such as a binder (negative-electrode binder) and a conductive auxiliary agent. After preparing an agent, an organic solvent or water is added to form a slurry.

  At this time, in the present invention, it is essential to contain polyacrylic acid or a metal salt thereof as a binder. Further, as the binder, at least one of polyacrylic acid or a metal salt thereof, styrene butadiene rubber, and polyvinylidene fluoride can be added.

Here, the polyacrylic acid or metal salt thereof contained in the negative electrode of the present invention is at least one of 4 to 4.5 ppm or 1 to 2 ppm in terms of chemical shift value (TMS standard) obtained from the ¹ H-NMR spectrum. It has a peak as described above. If the slurry for forming the negative electrode includes such a binder as a binder, the slurry is suitable for the silicon compound after modification. That is, even in an alkaline slurry in which a silicon compound containing a Li compound is mixed, the thickening and binding properties can be improved.

  Next, the negative electrode mixture slurry is applied to the surface of the negative electrode current collector 11 and dried to form the negative electrode active material layer 12 shown in FIG. At this time, a heating press or the like may be performed as necessary.

<2. Lithium ion secondary battery>
Next, a lithium ion secondary battery will be described as a specific example of the nonaqueous electrolyte secondary battery using the negative electrode of the present invention.

[Configuration of laminated film type secondary battery]
A laminated film type secondary battery 30 shown in FIG. 3 is one in which a wound electrode body 31 is accommodated mainly in a sheet-like exterior member 35. The wound electrode body 31 has a separator between a positive electrode and a negative electrode, and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated. In both electrode bodies, the positive electrode lead 32 is attached to the positive electrode, and the negative electrode lead 33 is attached to the negative electrode. The outermost peripheral part of the electrode body is protected by a protective tape.

  The positive and negative leads 32 and 33 are led out in one direction from the inside of the exterior member 35 to the outside, for example. The positive electrode lead 32 is formed of a conductive material such as aluminum, and the negative electrode lead 33 is formed of a conductive material such as nickel or copper.

  The exterior member 35 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order. This laminate film is formed of two films so that the fusion layer faces the electrode body 31. The outer peripheral edges of the fusion layer are bonded together with an adhesive or an adhesive. The fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like. The protective layer is, for example, nylon.

  An adhesion film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent intrusion of outside air. This material is, for example, polyethylene, polypropylene, or polyolefin resin.

[Positive electrode]
The positive electrode has, for example, a positive electrode active material layer on both sides or one side of the positive electrode current collector, similarly to the negative electrode 10 of FIG.

  The positive electrode current collector is formed of, for example, a conductive material such as aluminum.

  The positive electrode active material layer includes any one or more of positive electrode materials capable of occluding and releasing lithium ions, and other materials such as a positive electrode binder, a positive electrode conductive additive, and a dispersant depending on the design. May be included. In this case, details regarding the positive electrode binder and the positive electrode conductive additive are the same as, for example, the negative electrode binder and negative electrode conductive additive already described.

As the positive electrode material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element. Among these described positive electrode materials, compounds having at least one of nickel, iron, manganese, and cobalt are preferable. These chemical formulas are represented by, for example, Li _x M ₁ O ₂ or Li _y M ₂ PO ₄ . In the formula, M ₁ and M ₂ represent at least one transition metal element. The values of x and y vary depending on the battery charge / discharge state, but are generally expressed as 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium nickel cobalt composite oxide. . Examples of the lithium nickel cobalt composite oxide include lithium nickel cobalt aluminum composite oxide (NCA) and lithium nickel cobalt manganese composite oxide (NCM). Examples of the phosphate compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). Is mentioned. If these positive electrode materials are used, a high battery capacity can be obtained, and excellent cycle characteristics can also be obtained.

[Negative electrode]
The negative electrode has the same configuration as the negative electrode 10 for lithium ion secondary battery in FIG. 1 described above, and has, for example, a negative electrode active material layer on both sides of the current collector. This negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

  The positive electrode active material layer is provided on part of both surfaces of the positive electrode current collector, and similarly, the negative electrode active material layer is provided on part of both surfaces of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is to perform a stable battery design.

  In the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is, so that the composition and the like of the negative electrode active material can be accurately examined with good reproducibility without depending on the presence or absence of charge / discharge.

[Separator]
The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing current short-circuiting due to bipolar contact. This separator is formed of, for example, a porous film made of synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution). This electrolytic solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.

  For example, a non-aqueous solvent can be used as the solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran. Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because better characteristics can be obtained. In this case, more advantageous characteristics can be obtained by combining a high viscosity solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

  The solvent additive preferably contains an unsaturated carbon bond cyclic carbonate. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed. Examples of the unsaturated carbon bond cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.

  The solvent additive preferably contains sultone (cyclic sulfonic acid ester). This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone and propene sultone.

  Furthermore, it is preferable that the solvent contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propanedisulfonic acid anhydride.

The electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ).

  The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent. This is because high ion conductivity is obtained.

[Production method of laminated film type secondary battery]

  First, a positive electrode is manufactured using the positive electrode material described above. First, a positive electrode active material and, if necessary, a positive electrode binder and a positive electrode conductive additive are mixed to form a positive electrode mixture, which is then dispersed in an organic solvent to form a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector with a coating apparatus such as a die coater having a knife roll or a die head, and dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compression molded with a roll press or the like. At this time, heating may be performed or compression may be repeated a plurality of times.

  Next, a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector, using the same operation procedure as the production of the negative electrode 10 for a lithium ion secondary battery described above.

  When producing the positive electrode and the negative electrode, respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, the active material application length of both surface portions may be shifted in either electrode (see FIG. 1).

  Subsequently, the electrolytic solution is adjusted. Subsequently, the positive electrode lead 32 is attached to the positive electrode current collector and the negative electrode lead 33 is attached to the negative electrode current collector by ultrasonic welding or the like. Subsequently, the positive electrode and the negative electrode are laminated or wound via a separator to produce a wound electrode body 31, and a protective tape is bonded to the outermost periphery. Next, the wound body is molded so as to have a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior member 35, the insulating portions of the exterior member are bonded to each other by a thermal fusion method, and the wound electrode body is released in only one direction. Enclose. Subsequently, an adhesion film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. Subsequently, a predetermined amount of the adjusted electrolytic solution is introduced from the release portion, and vacuum impregnation is performed. After impregnation, the release part is bonded by a vacuum heat fusion method. The laminated film type secondary battery 30 can be manufactured as described above.

  In the non-aqueous electrolyte secondary battery of the present invention such as the laminated film type secondary battery 30 produced as described above, the negative electrode utilization rate during charge / discharge is preferably 93% or more and 99% or less. If the negative electrode utilization rate is in the range of 93% or more, the initial charge efficiency does not decrease, and the battery capacity can be greatly improved. Moreover, if the negative electrode utilization rate is in the range of 99% or less, Li is not precipitated and safety can be ensured.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these. The NMR measurement chemical shift values in the following description are based on tetramethylsilane as a reference substance.

(Example 1-1)
The laminate film type secondary battery 30 shown in FIG. 3 was produced by the following procedure.

First, a positive electrode was produced. The positive electrode active material was prepared by mixing 95 parts by mass of lithium cobaltate (LiCoO ₂ ), 2.5 parts by mass of the positive electrode conductive additive and 2.5 parts by mass of the positive electrode binder (polyvinylidene fluoride, Pvdf). An agent was used. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone, NMP) to obtain a paste slurry. Then, the slurry was apply | coated to both surfaces of the positive electrode electrical power collector with the coating device which has a die head, and it dried with the hot air type drying apparatus. At this time, a positive electrode current collector having a thickness of 15 μm was used. Finally, compression molding was performed with a roll press.

Next, a negative electrode was produced. The silicon compound was produced as follows. First, a raw material in which metallic silicon and silicon dioxide are mixed is placed in a reaction furnace, and vaporized in a 10 Pa vacuum atmosphere is deposited on an adsorption plate. After sufficiently cooling, the deposit is taken out by a ball mill. Crushed. After adjusting the particle diameter, pyrolytic CVD was performed to coat the carbon coating so that the total amount of the silicon compound and the carbon coating was 5% by mass. Next, carbon particles having a median diameter of 35 nm were adhered to the silicon oxide powder via polyacrylic acid. Thereafter, bulk reforming was performed using an electrochemical method in a mixed solvent having a volume ratio of ethylene carbonate and dimethyl carbonate of 3: 7 (containing an electrolyte salt at a concentration of LiPF ₆ 1.3 mol / kg).

The silicon compound after bulk modification contained Li ₂ SiO ₃ and Li ₄ SiO ₄ inside, and lithium carbonate was contained in the surface layer thereof. Moreover, lithium carbonate was contained in the ratio of 1.0 mass% with respect to the silicon compound. The silicon compound represented by SiO _x has an x value of 0.5, a median diameter D ₅₀ of 4 μm, and a half of the diffraction peak due to the (111) crystal plane obtained by X-ray diffraction. The value width (2θ) was 2.593 °, and the crystallite size attributable to the crystal plane was 3.29 nm.

  Subsequently, the produced silicon compound and natural graphite having a median diameter of 20 μm as a carbon-based active material were mixed to obtain a negative electrode active material. At this time, the negative electrode active material was produced by mixing at a mass ratio such that the ratio of the silicon compound to the total amount of the negative electrode active material was 10% by mass.

Next, the produced negative electrode active material, conductive additive 1 (carbon nanotube, CNT), conductive additive 2 (carbon fine particles having a median diameter of about 50 nm), styrene butadiene rubber (styrene butadiene copolymer, hereinafter referred to as SBR), After mixing polyacrylic acid (hereinafter referred to as PAA) carbomethylcellulose (hereinafter referred to as CMC) at a dry mass ratio of 91.65: 1: 1.25: 2.5: 0.6: 3, pure water Was diluted with a negative electrode mixture slurry. In addition, said SBR, CMC, and PAA are negative electrode binders (negative electrode binder). The polyacrylic acid added here has a basic skeleton represented by the above formula (1), and is attributed to —O—CH ₂ — in the range of 4 to 4.5 ppm as a chemical shift value obtained from a ¹ H-NMR spectrum. The peak attributed to —CH ₂ — in the region near the end of polyacrylic acid or its metal salt was in the range of 1 to 2 ppm. Furthermore, this polyacrylic acid has a plurality of peaks that are weaker than the peak attributed to the basic skeleton in addition to the peak attributed to the basic skeleton in the range of 20 to 60 ppm as the chemical shift value obtained from the ¹³ C-NMR spectrum. Had. The polyacrylic acid having an average molecular weight of about 1 million was used. CMC having a degree of etherification of 0.85 was used.

Further, as the negative electrode current collector, an electrolytic copper foil (thickness 15 μm) was used. Finally, a slurry of the negative electrode mixture was applied to the negative electrode current collector and dried at 100 ° C. to 180 ° C. for 1 hour in a vacuum atmosphere. The amount of deposition (area density) of the negative electrode active material layer per unit area on one side of the negative electrode after drying was 5 mg / cm ² . The negative electrode active material layer contained polyacrylic acid at a ratio of 0.6% by mass.

Next, after mixing a solvent (4-fluoro-1,3-dioxolan-2-one (FEC)), ethylene carbonate (EC) and dimethyl carbonate (DMC)), an electrolyte salt (lithium hexafluorophosphate: LiPF ₆ ) was dissolved to prepare an electrolytic solution. In this case, the composition of the solvent was FEC: EC: DMC = 10: 20: 70 as a deposition ratio, and the content of the electrolyte salt was 1.2 mol / kg with respect to the solvent.

  Next, a secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to the negative electrode current collector. Subsequently, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order and wound in the longitudinal direction to obtain a wound electrode body. The end portion was fixed with a PET protective tape. As the separator, a laminated film of 12 μm sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges except for one side were heat-sealed, and the electrode body was housed inside. As the exterior member, a nylon film, an aluminum foil, and an aluminum laminate film in which a polypropylene film was laminated were used. Subsequently, the prepared electrolyte was injected from the opening, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

(Example 1-2, Example 1-3, Comparative example 1-1, Comparative example 1-2)
A secondary battery was manufactured in the same manner as Example 1-1 except that the amount of oxygen in the bulk of the silicon compound was adjusted. In this case, the amount of oxygen deposited was adjusted by changing the ratio and temperature of the vaporized starting material. The values of x of the silicon compounds represented by SiO _x in Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 are shown in Table 1.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 were examined, the results shown in Table 1 were obtained.

The cycle characteristics were examined as follows. First, in order to stabilize the battery, charge / discharge was performed for 2 cycles in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 100, and the discharge capacity was measured each time. Finally, the discharge capacity at the 100th cycle was divided by the discharge capacity at the 2nd cycle and multiplied by 100 for% display, and the capacity maintenance rate (hereinafter, sometimes simply referred to as the maintenance rate) was calculated. As cycling conditions, a constant current density until reaching 4.2V, and charged at 2.5 mA / cm ^2, current density 4.2V constant voltage at the stage of reaching the voltage of 4.2V is to 0.25 mA / cm ² Charged until it reached. During discharging, discharging was performed at a constant current density of 2.5 mA / cm ² until the voltage reached 2.5V.

When examining the initial charge / discharge characteristics, the initial efficiency (hereinafter sometimes referred to as initial efficiency) was calculated. The initial efficiency was calculated from an equation represented by initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100. The ambient temperature was the same as when the cycle characteristics were examined. The charge / discharge conditions were 0.2 times the cycle characteristics. That is, a constant current density until reaching 4.2V, and charged at 0.5 mA / cm ^2, at 4.2V constant voltage at the stage where the voltage reaches 4.2V until the current density reached 0.05 mA / cm ² The battery was charged and discharged at a constant current density of 0.5 mA / cm ² until the voltage reached 2.5V.

  As can be seen from Table 1, when there is not enough oxygen (Comparative Example 1-1, x = 0.3), although the initial efficiency is improved, the capacity retention rate is remarkably deteriorated. Moreover, when there was too much oxygen amount (Comparative Example 1-2, x = 1.8), the electroconductivity fell and the capacity | capacitance of SiO material was not expressed.

(Examples 2-1 and 2-2, Comparative Examples 2-1 and 2-2)
A secondary battery was manufactured in the same manner as in Example 1-2 except that the molecular structure of polyacrylic acid was changed. There is no change in the basic skeleton of polyacrylic acid. The polyacrylic acid contained in the negative electrode in Example 2-1 has a peak attributed to —O—CH ₂ — in the range of 4 to 4.5 ppm as a chemical shift value obtained from the ¹ H-NMR spectrum. Furthermore, the chemical shift value obtained from the ¹³ C-NMR spectrum had a plurality of peaks that were weaker than the peak attributed to the basic skeleton in the range of 20 to 60 ppm. The polyacrylic acid contained in the negative electrode in Example 2-2 has a peak attributed to —O—CH ₂ — in the range of 4 to 4.5 ppm as the chemical shift value obtained from the ¹ H-NMR spectrum. It had a peak attributed to —CH ₂ — in a region near the end of polyacrylic acid or a metal salt thereof in the range of ˜2 ppm. Example 2-2 did not have a plurality of peaks weaker than the peak attributed to the basic skeleton in the range of 20 to 60 ppm as the chemical shift value obtained from the ¹³ C-NMR spectrum. Comparative Examples 2-1 and 2-2 did not have peaks in either the range of 4 to 4.5 ppm or ^{1 to} 2 ppm as the chemical shift value obtained from the ¹ H-NMR spectrum. However, Comparative Example 2-1 had a plurality of peaks that were weaker than the peaks attributed to the basic skeleton in the range of 20 to 60 ppm as chemical shift values obtained from the ¹³ C-NMR spectrum.

Figure 4 shows the ^{1 H-NMR} spectrum of the polyacrylic acid contained in the measured non-aqueous electrolyte secondary battery negative electrode in Examples 1-2 and Comparative Examples 2-1. In Example 1-2, peaks are observed in the range of 4 to 4.5 ppm and in the range of 1 to 2 ppm as chemical shift values (portions indicated by arrows in the left diagram of FIG. 4). On the other hand, in Comparative Example 2-1, no peak is observed in any of these ranges (the right diagram in FIG. 4). In addition, the attribution of the peak in the ¹ H-NMR spectrum is as follows: Reference: 11th JAI Seminar (October 22, 1991) “Analysis of chain distribution of acrylic acid / acrylic acid ester copolymer by pyrolysis GC” ( Relying on Analytical Center of Lion Co., Ltd. Satoshi Yamada, Yoshihisa Endo, Haruo Yoshimura)

FIG. 5 shows the ¹³ C-NMR spectrum of polyacrylic acid contained in the negative electrode of the nonaqueous electrolyte secondary battery measured in Example 1-2 and Example 2-2. As shown in FIG. 5, the ¹³ C-NMR spectrum of Example 1-2 shows a chemical shift value from a peak attributed to the basic skeleton in addition to a peak attributed to the basic skeleton in the range of 20 to 60 ppm. Also have a plurality of weak peaks (upper figure in FIG. 5). On the other hand, in Example 2-2, a plurality of peaks weaker than the peak attributed to the basic skeleton other than the peak attributed to the basic skeleton are not observed in any of these ranges (FIG. 5). (Figure below). In addition, the attribution of the peak in a ¹³ C-NMR spectrum is literature: ARCHIVES OF METALLURGY AND MATERIALS, Volume 54 (2009) Issue 2, “STRUCTURAL EXAMINATION OF THE CROSSING LIGATION RECHION OF GOLD REGION REACTION. GRABOWSKA, M.M. Rely on HOLTZER.

  Regarding Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2, the cycle characteristics and initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Example 1-2. Table 2 shows the measurement results of Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2.

As can be seen from Table 2, when polyacrylic acid having a peak at least at one or more sites in the range of 4 to 4.5 ppm and ¹ to 2 ppm as a chemical shift value obtained from a ¹ H-NMR spectrum is included (Examples) 1-2, 2-1, 2-2), it was found that the maintenance rate and the initial efficiency were improved. In particular, it was found that by having peaks attributed to —O—CH ₂ — and —CH ₂ —, the stabilization of the slurry proceeds. Furthermore, as the chemical shift value obtained from the ¹³ C-NMR spectrum, in addition to the peak attributed to the basic skeleton in the range of 20 to 60 ppm, polyacrylic acid having a plurality of peaks weaker than the peak attributed to the basic skeleton. When included (Examples 1-2, 2-1), it was found that the slurry was further stabilized, and the maintenance rate and the initial efficiency were further improved.

(Examples 3-1 to 3-4)
A secondary battery was manufactured in the same manner as in Example 1-2 except that the molecular weight of polyacrylic acid was changed. For Examples 3-1 to 3-4, the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Example 1-2. Table 3 shows the measurement results of Examples 3-1 to 3-4.

  When the molecular weight is 500,000 or more and 1.25 million or less, particularly good maintenance ratio and initial efficiency are obtained. If the molecular weight is 500,000 or more, the electrode structure can be reliably prevented from being destroyed. Further, when the molecular weight is 1.25 million or less, the slurry viscosity does not become too high, and as a result, the solid content can be increased, so that an optimum slurry can be obtained.

(Examples 4-1 to 4-3)
A secondary battery was fabricated in the same manner as in Example 1-2 except that the main binder and the secondary binder other than polyacrylic acid (PAA) were changed. In Example 4-1, the negative electrode binder (binder) to be added is SBR, CMC, and CMC-Li (lithium salt of carboxymethyl cellulose) in Example 4-1, and in Example 4-2, in addition to PAA, Polyvinylidene fluoride (hereinafter referred to as Pvdf) and CMC. In Example 4-3, Pvdf, CMC, and CMC-Li were used in addition to PAA. SBR and Pvdf are main binders. Pvdf used was a particulate material. When particulate Pvdf is used, the binding property is improved by using Pvdf dispersed in water and drying at 180 ° C. after forming the electrode. Moreover, although the sodium salt is generally used for CMC, Li salt was prepared and used in Examples 4-1 and 4-3. Li salt can be prepared, for example, by titrating LiOH to prepare a lithium salt, or using a CMC solution in which a silicon compound contained in the negative electrode of the present invention is washed. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 4-1 to 4-3 were examined, the results shown in Table 4 were obtained.

  As can be seen from Table 4, all the examples have good maintenance ratio and initial efficiency, and in the present invention, SBR, CMC, and particulate Pvdf are polyacrylic acid or a metal salt thereof as a negative electrode binder. It turned out that it is suitable for using together.

(Examples 5-1 to 5-7)
A secondary battery was fabricated in the same manner as in Example 1-2 except that the degree of etherification of CMC was changed. When the cycle characteristics and initial charge / discharge characteristics of the secondary batteries of Examples 5-1 to 5-7 were examined, the results shown in Table 5 were obtained.

  As can be seen from Table 5, when the degree of etherification includes CMC having a degree of etherification of 0.7 or more and 1.5 or less, the maintenance ratio and the initial efficiency are further improved. This is because CMC having an etherification degree of 0.7 or more and 1.5 or less has particularly strong alkali resistance, and the slurry for preparing the negative electrode material is stabilized.

(Examples 6-1 to 6-5)
A secondary battery was manufactured in the same manner as in Example 1-2, except that the ratio of the silicon compound to the total amount of the negative electrode active material was changed. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 6-1 to 6-5 were examined, the results shown in Table 6 were obtained.

  As can be seen from Table 6, as the ratio of the silicon compound decreases and the ratio of the carbon-based active material increases, the characteristics of the carbon-based active material are easily obtained and the battery characteristics are improved. However, a reversible capacity of a general carbon material is about 330 mAh / g, and a reversible capacity of 1500 mAh / g (0V-1.2V) is sufficiently high. Although the battery capacity retention rate is reduced by adding, the battery capacity is greatly improved. In particular, the siliceous material has a higher discharge potential than the carbon material, and when considering the battery capacity, it is difficult to substantially improve the capacity. Therefore, from which region the capacity improvement can be obtained with the actually obtained siliceous material was calculated, it was found that the capacity improvement was obtained when about 6% by mass was added.

  FIG. 6 is a graph showing the relationship between the ratio of the silicon compound to the total amount of the negative electrode active material and the increase rate of the battery capacity of the secondary battery. The graph shown by A in FIG. 6 shows the rate of increase in battery capacity when the proportion of the silicon compound is increased in the negative electrode active material of the negative electrode of the present invention. On the other hand, the graph indicated by B in FIG. 6 shows the increase rate of the battery capacity when the proportion of the silicon compound not doped with Li is increased. As can be seen from FIG. 6, when the ratio of the silicon compound is 6% by mass or more, the increase rate of the battery capacity is increased as compared with the conventional case, and the volume energy density is particularly remarkably increased.

(Examples 7-1 to 7-6, Comparative example 7-1)
A secondary battery was manufactured in the same manner as in Example 1-2 except that the ratio of polyacrylic acid contained in the negative electrode active material layer was changed. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 7-1 to 7-6 and Comparative Example 7-1 were examined, the results shown in Table 7 were obtained.

  As can be seen from Table 7, when polyacrylic acid is contained in the negative electrode active material layer at a ratio of 0.1% by mass or more and 2.5% by mass or less, cycle characteristics and initial efficiency are improved. Thus, even if the polyacrylic acid or its metal salt contained in the negative electrode active material layer is a small amount, an effect is obtained for a material such as a silicon compound having alkalinity. Also, if polyacrylic acid is contained in the negative electrode active material layer in a proportion of 2.5% or less, the binding property may be reduced during pressing after applying the slurry to the electrode and drying it. Absent. Further, as in Comparative Example 7-1, when the polyacrylic acid was not included as the negative electrode binder, the slurry became unstable, and the maintenance rate, that is, the cycle characteristics were greatly deteriorated.

(Examples 8-1 to 8-8)
Secondary as in Example 1-2, except that the median diameter of the carbon particles attached to the silicon compound and the type of binder for attaching the carbon particles to the silicon compound were changed as shown in Table 8. The battery was manufactured. In Table 8, PAA represents polyacrylic acid and CMC represents carboxymethylcellulose. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 8-1 to 8-8 were examined, the results shown in Table 8 were obtained.

  As can be seen from Table 8, when the median diameter of the carbon particles is 20 nm or more and 200 nm or less, a better maintenance ratio and initial efficiency can be obtained. Thus, when the median diameter of the carbon particles is 20 nm or more, contact between the negative electrode active material particles can be more sufficiently obtained as compared with the case where the median diameter is less than 20 nm (Example 8-1). If the median diameter of the carbon particles is 200 nm or less, compared to the case where the median diameter is larger than 200 nm (Example 8-6), the proportion of particles that can be contacted between the negative electrode active material particles is increased, and contact is made. Since the amount of carbon particles required for the process is small, it is not necessary to add more carbon particles than necessary, and a sufficient battery capacity can be secured. Especially as a binder, polyacrylic acid or its metal salt, carboxymethylcellulose, or its metal salt can be used conveniently.

(Examples 9-1 and 9-2)
A secondary battery was fabricated in the same manner as in Example 1-2, except that modification in the bulk of the silicon compound was performed by thermal doping method in Example 9-1 and by Li deposition method in Example 9-2. did. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Example 9-1 and Example 9-2 were examined, the results shown in Table 9 were obtained.

  In any of the reforming methods, good battery characteristics were obtained. In particular, when the electrochemical method was used, better battery characteristics were obtained than other methods. Further, it is more desirable to insert and desorb Li several times during reforming.

(Example 10-1 to Example 10-9)
A secondary battery was manufactured in the same manner as in Example 1-2 except that the crystallinity of the silicon compound was changed. The change in crystallinity can be controlled by heat treatment in a non-atmospheric atmosphere after Li insertion and desorption. Table 10 shows the half widths of the silicon-based active materials of Examples 10-1 to 10-9. In Example 10-9, the half width is calculated to be 20 ° or more, but it is a result of fitting using analysis software, and a peak is not substantially obtained. Therefore, it can be said that the silicon-based active material of Example 10-9 is substantially amorphous. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Example 10-1 to Example 10-9 were examined, the results shown in Table 10 were obtained.

  As shown in Table 10, the capacity retention ratio and the initial efficiency changed according to their crystallinity. In particular, a high capacity retention ratio and initial efficiency were obtained with a low crystalline material having a half width (2θ) of 1.2 ° or more and a crystallite size attributable to the Si (111) plane of 7.5 nm or less. In particular, the best battery characteristics were obtained in the non-crystalline region.

(Example 11-1)
Although a secondary battery was basically manufactured in the same manner as in Example 1-2, in Example 11-1, carbon nanotubes (CNT) were not added as a conductive additive when the negative electrode mixture slurry was prepared. It was. When the cycle characteristics and initial charge / discharge characteristics of the secondary battery of Example 11-1 were examined, the results shown in Table 11 were obtained.

  As can be seen from Table 11, it was confirmed that the capacity retention ratio and the initial efficiency were both improved by adding CNT. Thus, it was found that by adding CNT to the negative electrode, an electronic contact between the silicon-based active material (SiO material) and the carbon-based active material can be obtained, so that the battery characteristics are improved.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

10 ... negative electrode, 11 ... negative electrode current collector, 12 ... negative electrode active material layer,
20 ... reformer in bulk, 21 ... positive electrode (lithium source, reforming source),
22 ... Silicon oxide powder, 23 ... Organic solvent, 24 ... Separator,
25 ... Powder storage container, 26 ... Power supply, 27 ... Bathtub,
30 ... lithium secondary battery (laminated film type), 31 ... wound electrode body,
32 ... Positive electrode lead, 33 ... Negative electrode lead, 34 ... Adhesion film,
35 ... exterior member.

Claims (17)

A negative electrode for a non-aqueous electrolyte secondary battery including a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) containing a Li compound therein as a negative electrode active material,
The negative electrode for a non-aqueous electrolyte secondary battery includes polyacrylic acid or a metal salt thereof,
The polyacrylic acid or a metal salt thereof has a basic skeleton represented by the following formula (1), and is obtained from a ¹ H-NMR spectrum and has a chemical shift value of 4 to 4 using tetramethylsilane as a reference substance. A negative electrode for a non-aqueous electrolyte secondary battery, having a peak at at least one place in the range of 0.5 ppm and 1-2 ppm.

(In the formula, M represents one of a hydrogen atom, a lithium atom, a sodium atom, and a potassium atom, and n represents an integer of 2 or more.) The peak in the range of 4 to 4.5 ppm is attributed to —O—CH ₂ —, and the peak in the range of 1 to ₂ ppm is —CH ₂ — in a region near the end of the polyacrylic acid or a metal salt thereof. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein The polyacrylic acid or a metal salt thereof is obtained from a ¹³ C-NMR spectrum, as a chemical shift value using tetramethylsilane as a reference substance, in addition to the peak attributed to the basic skeleton in the range of 20 to 60 ppm. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode has a plurality of peaks that are weaker than the peaks attributed to the skeleton. The chemical shift value obtained from the ¹³ C-NMR spectrum, wherein the plurality of peaks obtained in a range of 20 to 60 ppm belong to a part of the acrylate. Negative electrode for non-aqueous electrolyte secondary battery.   5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polyacrylic acid or a metal salt thereof has a molecular weight in the range of 500,000 to 1,250,000. Negative electrode.   In addition to the polyacrylic acid or a metal salt thereof, the binder further comprises at least one of styrene butadiene rubber, carboxymethyl cellulose or a metal salt thereof, and polyvinylidene fluoride as a binder. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 5.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 6, wherein the carboxymethyl cellulose or a metal salt thereof has an etherification degree of 0.7 or more and 1.5 or less.   The ratio of the said silicon compound with respect to the total amount of the said negative electrode active material is a thing of 6 mass% or more, The negative electrode for nonaqueous electrolyte secondary batteries of any one of Claims 1-7 characterized by the above-mentioned.   The negative electrode for a non-aqueous electrolyte secondary battery has a negative electrode active material layer containing the negative electrode active material, and the negative electrode active material layer contains 0.1% by mass or more of the polyacrylic acid or a metal salt thereof. The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 8, wherein the negative electrode is contained at a ratio of 5% by mass or less.   The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 9, wherein the silicon compound has a carbon coating, and lithium carbonate is included in at least a part of a surface layer thereof.   11. The non-aqueous electrolyte 2 according to claim 1, wherein the silicon compound has carbon particles attached to a surface layer thereof through a binder having a carboxyl group. Negative electrode for secondary battery.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 11, wherein the carbon particles attached to the surface layer of the silicon compound have a median diameter of 20 nm to 200 nm.   The non-aqueous electrolyte according to claim 11 or 12, wherein the binder having a carboxyl group includes at least one of carboxymethyl cellulose or a metal salt thereof and polyacrylic acid or a metal salt thereof. Negative electrode for secondary battery.   The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 13, wherein the silicon compound is produced by a process including an electrochemical technique.   The silicon compound has a half-width (2θ) of a diffraction peak due to the (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more and a crystallite size due to the crystal plane of 7.5 nm. The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 14, wherein:   Furthermore, the negative electrode for nonaqueous electrolyte secondary batteries of any one of Claims 1-15 characterized by including a carbon nanotube.   A non-aqueous electrolyte secondary battery using the negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 16.

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