KR20130119447A - Negative electrode active material for lithium ion secondary cell, negative electrode for lithium ion secondary cell, and lithium ion secondary cell - Google Patents

Abstract

The present invention can provide a negative electrode active material for a lithium ion secondary battery having high capacity, high charge and discharge efficiency, and excellent cycle characteristics. In the present invention, including at least the element A consisting primarily of silicon less than 0.05% by mass, and that the element atomic radius (r _A) of A to the atomic radius (r ₀₎ of a silicon _{| (r A -r 0) /} r 0 The negative electrode for lithium ion secondary batteries formed on the electrical power collector by apply | coating or film-forming the negative electrode active material characterized by satisfy | filling the relationship of | <= 0.1 is used.

Description

NEGATIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM ION SECONDARY CELL, NEGATIVE ELECTRODE FOR LITHIUM ION SECONDARY CELL, AND LITHIUM ION SECONDARY CELL}

The present invention relates to a negative electrode active material for a lithium ion secondary battery, a negative electrode and a lithium ion secondary battery using the same, and particularly have high capacity, high charge and discharge efficiency, and do not peel off or drop off from the current collector even after repeated charge and discharge. The negative electrode active material which can implement | achieve this excellent lithium ion secondary battery is related.

Li-ion secondary batteries are used mainly for portable devices, and high capacity is required according to the miniaturization and multifunctionality of the used devices. However, the negative electrode active material used in the current lithium ion secondary battery is a carbon-based material such as artificial graphite or natural graphite, and the theoretical capacity is 372 mAh / g, and further capacity increase cannot be expected.

Therefore, a negative electrode using a metal material such as silicon (Si) or tin (Sn) or an oxide material having a larger theoretical capacity has been proposed (see Patent Document 1, for example). I am getting it. These materials exhibit very high capacities in the first few cycles, but as the charge and discharge are repeated, micronization occurs due to expansion and contraction of the active material, and thus the negative electrode active material is dropped from the current collector. There was a problem that the characteristics are poor and the life is short.

Therefore, a proposal has been disclosed in which carbon nanofibers are grown on the surface of a Si-based active material, and the elastic action is used to mitigate deformation during expansion and contraction of the negative electrode active material particles, thereby improving cycle life (for example, Patent Document 2). Reference).

Further, proposals have been made for hybrid alloying an active material capable of alloying with Li such as Si or Sn, and an element not alloying with Li such as Cu or Fe (see Patent Document 3, for example).

In addition, a method of forming a negative electrode by forming these materials as a thin film on a current collector by CVD, sputtering, vapor deposition, plating or the like has been proposed. According to this thin film type negative electrode, the fineness of a negative electrode active material can be suppressed compared with the conventional coating type negative electrode which apply | coats and produces the slurry which contains a powdery negative electrode active material with a binder etc. on an electrical power collector, Furthermore, adhesiveness of an electrical power collector and an active material is adhesiveness It is known that the electron conductivity at the negative electrode becomes good because it can be integrated integrally.

And by forming the thin film of a negative electrode active material on a foam type electrical power collector, it is proposed to ensure the capacity | capacitance of a battery in the state which maintained the adhesiveness of an electrical power collector and a negative electrode active material higher (for example, refer patent document 4).

Patent Document 1: Japanese Patent Application Laid-Open No. 07-29602 Patent Document 2: Japanese Unexamined Patent Publication No. 2006-244984 Patent Document 3: Japanese Unexamined Patent Publication No. 2005-78999 Patent Document 4: Japanese Unexamined Patent Publication No. 2004-71305

However, the conventional negative electrode which coats the slurry coating liquid of a negative electrode active material, a electrically conductive material, and a binder and forms a negative electrode active material binds the negative electrode active material and an electrical power collector with the resin binder with low electroconductivity, and the usage-amount of resin is high in internal resistance. The binding force is weak because it needs to be kept to a minimum so as not to become large. For this reason, if volume expansion of Si itself cannot be suppressed, problems, such as micronization and peeling of a negative electrode active material, generation | occurrence | production of a negative electrode crack, a fall of electroconductivity between active materials, etc. during charge and discharge generate | occur | produce, and capacity | capacitance will fall. That is, it had the problem that the charging / discharging cycle characteristics were bad and the lifetime of a secondary battery was short.

In addition, the invention described in Patent Literature 2 does not suppress the volume expansion of Si, but binds the negative electrode active material and the current collector to a resin having insufficient bonding force, and thus, the effect of suppressing cycle characteristic deterioration could not be exhibited. In addition, since the production process of carbon nanofibers is required, both productivity and economy are low. Moreover, the technique described in patent document 3 is difficult to disperse | distribute a nanosize component uniformly, and it is a fact that it cannot contribute to the improvement of a charge / discharge cycle characteristic.

As described above, Si, which is expected as a negative electrode active material, has a large volume change during charging and discharging, so that active material particles containing Si are easily cracked, and therefore, current collection in the particles is likely to deteriorate, and thus the cycle life is still short. The flaw remains.

In addition, the thin film-type negative electrode has a great improvement in electrode characteristics. However, when a thin film having an active material amount that satisfies the practical amount required for electronic devices such as a PC or a mobile phone is formed, the charge / discharge cycle characteristics are deteriorated, and thus the life span that can be repeatedly used is shortened. There was this. Therefore, when using it for a lithium ion secondary battery, since it is necessary to reduce an active material amount inevitably, a use is limited and it is difficult to use for universal use.

In addition, in the invention described in Patent Literature 4, the use of the foam-type current collector increases the thickness of the electrode, resulting in lowering the energy density of the electrode and lowering the energy density of the battery. Moreover, since the edge part of the collector foam part was easy to be exposed at the time of electrode processing, there also existed a problem that an internal short circuit was easy to penetrate through a thin separator.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to use a negative electrode active material for a lithium ion secondary battery and a negative electrode active material, which are not easily deteriorated even after repeated charging and discharging, and thus have a long battery life and a high charge and discharge capacity. It is to provide a lithium ion secondary battery having a negative electrode, long life and high energy density.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to achieve the said objective, the negative electrode active material material is introduce | transduced into the negative electrode active material material which has silicon (Si) as a main component by introducing the 2nd element which has an atomic radius about the same size as Si. It is possible to facilitate insertion (charging) and desorption (discharge) between the lattice of silicon active material and the dissociation (discharge) between the lattice of silicon active material during charge and discharge of Li ions having a small ion radius, without giving excessively large deformation between lattice or atoms of It has been found that it is possible to reduce the occurrence of unnecessary irreversible capacity due to the residual Li ions due to discharge after charging. The present invention has been completed based on this finding.

That is, the present invention provides the following invention.

(1) An active material used for a negative electrode for a lithium ion secondary battery, comprising particles of silicon as a main component and containing at least 0.05% by mass of element A, and the atom of the element A with respect to the atomic radius r ₀ of silicon. A radius r _A satisfies the relationship of | (r _A -r ₀ ) / r ₀ | ≤0.1, wherein the negative electrode active material for a lithium ion secondary battery is used.

(2) The negative electrode active material material for lithium ion secondary batteries according to (1), wherein the element A is at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As.

(3) A negative electrode active material for a lithium ion secondary battery, further comprising oxygen or fluorine.

(4) The negative electrode active material material for lithium ion secondary batteries according to (1), wherein the particles have an average particle diameter of the primary particles of 10 nm to 5 m.

(5) The negative electrode for nonaqueous electrolyte secondary batteries which has an active material layer formed by apply | coating and drying the coating liquid containing the negative electrode active material material as described in (1) on one or both surfaces of a negative electrode electrical power collector.

(6) a negative electrode current collector having protrusions on its surface, and a thin film-type negative electrode active material layer having a silicon as a main component formed on the surface of the negative electrode current collector and containing at least 0.05% by mass of element A; is the atomic radius (r ₀₎ atomic radius (r _a) of the element a for the _{| (r a -r 0) /} r 0 | lithium ion secondary battery negative electrode according to the relationship characterized in that an element which satisfies the ≤0.1 .

(7) The negative electrode for lithium ion secondary batteries according to (6), wherein the element A is at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As.

(8) The negative electrode for lithium ion secondary batteries according to (6), wherein the negative electrode active material layer further contains oxygen or fluorine.

(9) The said negative electrode current collector is copper foil, electrolytic roughening process is performed in the surface in which the said active material layer is formed, and a processus | protrusion part is formed and surface roughness Rz is 1 micrometer-6 micrometers, It is characterized by the above-mentioned. The negative electrode for lithium ion secondary batteries as described in (5) or (6) mentioned above.

(10) The negative electrode for lithium ion secondary batteries according to (9), wherein the surface roughness (Rz) of the surface on which the active material layer is formed is 0.5 µm to 3 µm in the copper foil before the electrolytic roughening treatment.

(11) A positive electrode capable of storing and releasing lithium ions, a negative electrode according to (5) or (6), and a separator disposed between the positive electrode and the negative electrode and having a lithium ion conductivity in the positive electrode and the negative electrode. And the separator forming a lithium ion secondary battery.

According to the present invention, it is possible to obtain a negative electrode active material material for realizing a lithium ion secondary battery having high capacity, high charge and discharge efficiency, and no peeling or dropping from the current collector and excellent cycle characteristics even after repeated charging and discharging.

BRIEF DESCRIPTION OF THE DRAWINGS The cross-sectional schematic diagram which shows an example of the negative electrode for lithium ion secondary batteries which concerns on 1st Embodiment.
2 is a view showing an apparatus for producing nano-sized particles.
FIG. 3 is a diagram showing a mixer used for producing a negative electrode according to the first embodiment. FIG.
4 shows a coater used for producing a negative electrode according to the first embodiment.
FIG. 5 is a schematic sectional view illustrating an example of a negative electrode for a lithium ion secondary battery according to the second embodiment. FIG.
6 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail based on drawing.

(1.Negative Electrode for Lithium Ion Secondary Battery According to First Embodiment)

First, the negative electrode for lithium ion secondary batteries which concerns on one Embodiment of this invention is demonstrated with reference to FIG.

The negative electrode 1 for a lithium ion secondary battery of the present invention uses a slurry-like coating liquid containing a negative electrode active material 3, a conductive material 4, and a binder 6 on one or both surfaces of the negative electrode current collector 9. It has the active material layer 5 formed by apply | coating and drying. In the present invention, the negative electrode active material 3 is made of Si-based particles having a characteristic component structure.

(1-1.Configuration of Negative Electrode Active Material)

Then, embodiment of the negative electrode active material material for lithium ion secondary batteries which concerns on this invention is described in detail below.

The negative electrode active material for a lithium ion secondary battery of the present invention has a particulate form, which contains silicon as a main component and contains at least element A as a second element. Since silicon is an element that easily occludes lithium, the particles also have lithium occluding ability. In addition, silicon has an advantage that the cost is relatively low among the elements having lithium storage ability.

The element A is an element whose atomic radius r _A is close to the atomic radius r _{0 of} 0.117 nm of Si, and satisfies the relationship of | (r _A -r ₀ ) / r ₀ | ≤0.1. If the atomic radius (r _A ) of element A and the atomic radius (r ₀ ) of Si satisfy the above relationship, and element A has an atomic radius of the same degree as Si, this element A is mainly composed of Si lattice or Si. In the system, it is highly likely to be substituted at a position substantially equal to the Si atom position of the Si lattice, or it is easy to form a compound with Si, and may exist in a state in which the Si lattice structure is stabilized. On the other hand, when | (r _A -r ₀ ) / r ₀ | exceeds 0.1, an element having an atomic radius too small or too large for the atomic radius of Si is included in the Si lattice or the system mainly comprising Si. do. Excessively large elements penetrate into the lattice positions of Si or create empty lattice points, resulting in excessive strain in the Si lattice, and conversely, excessively small elements become excessively high so that excessive strain due to large amounts of diffusion alloying is caused. . Such an element is likely to generate an unnecessary irreversible capacity that does not inhibit the electrochemical migration of Li ions or breaks into the Si lattice during charging and does not release the alloyed Li ions during discharge and does not contribute to subsequent charge and discharge. In other words, it is not preferable as the negative electrode active material of the present invention.

Element A can be used by selecting one or more from the group of P, Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Se, Br, as shown in Table 1 below. Since these elements A are elements which are not compounded with Li or are compounds which form a compound having a small lithium occlusion even when compounded with Li and which do not produce a large density change compared with silicon, the volume expansion shrinkage of silicon is suppressed during charge and discharge. can do. In addition, element A may form a compound with silicon, and may exist as a single body or a solid solution except Fe. When forming a compound, it does not matter whether it is crystalline or amorphous.

The element A is preferably at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, As. P, Cr, Mn, Fe, Co, Ni, Cu, As are relatively inexpensive economical elements and are practical. In addition, for elements other than P and As, Si and Si ₂ M type or SiM ₂ type compounds can be formed, and the effect of suppressing volume expansion shrinkage is high.

[Table 1]

The above-mentioned element A is contained 0.05 mass% or more in particle | grains. When containing two or more elements A, the sum total of content of these elements shall be 0.05 mass% or more. By setting the content to 0.05% by mass or more, the volume expansion shrinkage of the silicon during charge and discharge can be effectively suppressed. The upper limit of the element A content is not particularly defined, but can be arbitrarily determined in the range of less than 50% by mass in consideration of the lithium storage ability of silicon. Since the element A has an effect of inhibiting volume expansion shrinkage even in a sufficiently small amount compared with Si, it is exemplified to be 30 mass% or less, further 20 mass% or less.

In addition, the particle | grains concerning this invention may further contain oxygen or fluorine as a 3rd element. Oxygen and fluorine have a small atomic radius, but as shown in Table 1, the ion radius r _{A '} is comparable to the atomic radius r ₀ (0.117 nm) of Si. It is possible to further improve the charge and discharge cycle life by suppressing the volume change of silicon without disturbing intrusion and desorption. Oxygen and fluorine also have the effect of stabilizing the active material by dispersing with a part of Li. In addition, although Ag and Cd have an ion radius comparable to the atomic radius r _{0 of} Si, they do not form an ion-bonding compound with Si, which is preferable as the third element constituting the negative electrode active material of the present invention. Not.

However, oxygen and fluorine may be contained uniformly in the whole particle | grain, for example, may be contained in a part of the surface part etc., for example. About content of oxygen and fluorine, in order to maintain charge / discharge characteristic high, it is preferable that it is 0.5 mass% or more, and it is preferable to make the sum total with content of the element A into 50 mass% or less.

The particles according to the present invention may have an average particle diameter of the primary particles having a size of 10 nm to 5 m. Although the negative electrode active material mainly made of conventional silicon reduces the average particle diameter and suppresses the influence of volume expansion shrinkage, the particles constituting the negative electrode active material of the present invention are composed of nanometer orders of primary particles to micrometers of secondary particles. Even if it is used as an order, the effect can fully be exhibited. Therefore, it can be set as the active material material of a suitable size according to a use and various purposes. For example, when the negative electrode active material is composed of nanoscale to submicron particles having an average particle diameter of 10 nm, the path of Li ion conductivity and electron conductivity is short, the current collecting property is good, it is easy to maintain, and the cycle characteristics are also improved. You can. In addition, for example, when the negative electrode active material is composed of particles having a micron order to 5 µm level, the slurry-like coating liquid having excellent coatability on the surface of the current collector can be adjusted, and the thick film can be easily formed to ensure a high practical amount. have. In addition, the particle | grains concerning this invention can also be used as a secondary particle which granulated the primary particle, In this case, considering the practical thickness of the negative electrode active material layer at the time of forming a negative electrode, the average particle diameter of a secondary particle may be 20 micrometers or less. It is preferable to make it, and it is more preferable to set it as about 5 micrometers or less. In addition, it is preferable that average particle diameter shall be 10 nm or more from a particle handling viewpoint.

However, the shape of the particles is not particularly limited, and may be, for example, a substantially spherical body or a linear body. Since the fine particles usually coagulate and exist, the average particle diameter of the particles refers to the average particle diameter of the primary particles here. The measurement of the particle diameter may use the image information of the electron microscope (SEM) together with the volume-based median diameter of the dynamic light scattering photometer (DLS). The average particle size is obtained by confirming the particle shape in advance by SEM image, and obtaining the particle size by image analysis (e.g., "A zokun" (registered trademark) manufactured by Asahi Kasei Engineering Co., Ltd.), or by dispersing the particles in a solvent to obtain DLS (e.g., It is possible to measure by Otsukadenshi DLS-8000). If the fine particles are sufficiently dispersed and aggregated, almost the same measurement results are obtained by SEM and DLS. In addition, even when the particle shape is a highly developed structure shape such as acetylene black, the average particle size can be defined here as the primary particle size, and the average particle size can be obtained by image analysis of the SEM photograph.

In addition, the average particle size of the secondary particles can also be obtained by the image analysis of the SEM photograph.

In addition, in this invention, making silicon as a main component means that content of silicon is the largest among the elements which comprise particle | grains, It shows that content of silicon becomes like this. Preferably it is 50 mass% or more, More preferably, it is 70 mass% or more. . In addition, a 2nd element and a 3rd element are called the 2nd element and the 3rd element about the element group which has a characteristic role other than silicon among the elements which comprise particle | grains, and are not related to both content.

However, the negative electrode active material of the present invention may be any of crystalline, microcrystalline, amorphous, or mixed state thereof. This is because any crystal form is amorphous by alloying with Li ions during charging.

(1-2. Production of Negative Electrode Active Material)

It does not specifically limit about the manufacturing method of the negative electrode active material material of this invention, For example, what has the composition and average particle diameter as mentioned above can be manufactured using a well-known various particle (powder) manufacturing method.

As a manufacture of the nanosize particle | grains which comprise a negative electrode active material material, the gas-phase synthesis method can be illustrated typically. For example, by mixing the raw material powder so as to have a desired composition by the plasma CVD synthesis method, plasma is heated up to 10,000 K, and then cooled, a bone composed of nano-sized particles having an average particle diameter of about 10 nm to about 100 nm. The negative electrode active material of the invention can be produced.

Here, one specific example of the manufacturing apparatus used for manufacture of nanosize particle | grains is demonstrated based on FIG. In the nano-size particle manufacturing apparatus 31 shown in FIG. 2, the high frequency coil 43 for plasma generation is wound by the upper outer wall of the reaction chamber 33. As shown in FIG. An alternating voltage of several MHz is applied to the high frequency coil 43 from the high frequency power supply 45. Preferred frequency is 4 MHz. In addition, the upper outer wall which winds the high frequency coil 43 is a cylindrical double tube made of quartz glass or the like, and coolant is poured into the gap to prevent melting of the quartz glass by the plasma 47.

In addition, the sheath gas supply port 39 is formed in the upper portion of the reaction chamber 33 together with the raw material powder supply port 35. The raw material powder 37 supplied from the raw material powder feeder is supplied into the plasma 47 through the raw material powder supply port 35 together with the carrier gas 42 (rare gas such as helium and argon). In addition, the sheath gas 41 is supplied to the reaction chamber 33 through the sheath gas supply port 39. In addition, the raw material powder supply port 35 is not necessarily provided in the upper portion of the plasma 47, as shown in Figure 2, it is also possible to provide a nozzle in the transverse direction of the plasma 47. In addition, the raw material powder supply port 35 may be cooled with water. Note that the properties of the nano-size particle raw material supplied to the plasma 47 are not limited to the powder, but may be supplied with a slurry-like coating liquid or a gaseous raw material of the raw material powder.

The reaction chamber 33 serves to suppress the pressure maintenance of the plasma reaction part or the dispersion of the manufactured fine powder. The reaction chamber 33 is also water cooled to prevent damage by the plasma 47. A suction pipe is connected to the side of the reaction chamber 33, and a filter 49 for collecting the synthesized fine powder is provided in the middle of the suction pipe. The suction pipe connecting the reaction chamber 33 and the filter 49 is also water cooled with cooling water. The pressure in the reaction chamber 33 is adjusted by the suction capacity of the vacuum pump VP provided on the downstream side of the filter 49.

Since the manufacturing method of nanosize particle | grains is a method of the bottom-up which precipitates nanosize particle | grains from a plasma via a gas and a liquid, and becomes a spherical shape in the droplet stage. On the other hand, in the top-down method of reducing large particles, such as the shredding method or the mechanochemical method, the shape of the particles becomes uneven and the shapes vary greatly.

Moreover, the nanosize particle which comprises the negative electrode active material material which concerns on this invention is obtained by using the mixed powder of Si and each powder of element A as a raw material powder. When the element A is plural, a mixed powder of plural kinds of powders can be used.

As the production of the micron size particles constituting the negative electrode active material material, an atomizing method can be exemplified. For example, an alloy molten alloy blended in a desired composition by a gas atomizing method is supplied into an inert gas stream. By quenching, the negative electrode active material material of this invention which consists of micron size particle | grains of submicron-about 5 micrometers can be manufactured.

The Si-based active material can be oxidized or fluorinated by exposing the obtained negative electrode active material material to oxygen or a fluorine atmosphere, whereby a negative electrode active material material containing oxygen or fluorine as the third element can be produced. In the case of containing oxygen, it may be exposed to a warmed atmosphere.

(1-3. Effect of Negative Electrode Active Material)

According to the negative electrode active material of the present invention, in addition to silicon, it is composed of particles including at least element A having an atomic radius of the same size as silicon, and element A does not exert excessively large deformation between Si lattice or Si atoms. When charging and discharging Li ions having a small ion radius, insertion (charging) and desorption (discharging) between Si-based active material lattice can be easily generated without disturbance, and unnecessary irreversible capacity due to residual Li ions accompanying discharge after charging Occurrence can be reduced.

In addition, silicon occupies lithium when the volume is expanded, whereas element A does not occlude or is difficult to occlude lithium. Therefore, the negative electrode has little volume change and deformation due to expansion and contraction, and the reduction of discharge capacity during cycle characteristics is suppressed. An active material is provided.

Further, by including oxygen or fluorine having an ion radius close to the Si atomic radius as the third element, a negative electrode active material material having more improved charge / discharge cycle characteristics and battery life is provided.

This negative electrode active material can be set in a wide range of 10 nm-5 micrometers in average particle diameter, and can adjust easily the negative electrode active material which has a particle size according to a use.

(1-4. Production of negative electrode by slurry application)

The negative electrode for lithium ion secondary batteries of this invention can be produced by apply | coating and drying the slurry phase coating liquid containing the above-mentioned negative electrode active material material, electrically conductive material, and binder on one side or both sides of a negative electrode electrical power collector. For example, the coating liquid raw materials such as the above-described negative electrode active material material, conductive material, binder, thickener, solvent, etc. of the present invention are added to a mixer and kneaded to form a slurry coating liquid, which is then applied to a current collector. It can manufacture by forming a negative electrode active material layer.

Solid content mix of a coating liquid can be suitably adjusted based on 25-90 mass% of negative electrode active material materials of this invention mentioned above, 0-70 mass% of electrically conductive materials, 1-30 mass% of binders, and 0-25 mass% of thickeners. .

As the mixer, for example, as shown in Fig. 3, a general kneader used for preparing a slurry coating liquid may be used, and an apparatus capable of preparing a coating liquid called a kneader, a stirrer, a disperser, a mixer, a ball mill, or the like may be used. . When adjusting the aqueous coating liquid, latex (rubber dispersion of fine particles) such as styrene, butadiene and rubber (SBR) can be used as a binder, and polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used as the thickener. It is suitable to use as a species or mixture of 2 or more types. Moreover, when preparing an organic coating liquid, polyvinylidene fluoride (PVdF) etc. can be used as a binder, and N-methyl- 2-pyrrolidone can be used as a solvent.

The conductive material is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel and silver. The single powder of carbon, copper, tin, zinc, nickel, and silver may be sufficient, or the powder of each alloy may be sufficient. For example, general carbon black, such as furnace black and acetylene black, can be used. In particular, when silicon is exposed to the surface of the negative electrode active material material of the present invention, the conductivity becomes low. Therefore, carbon nanohorn is preferably added as the conductive material. Here, carbon nanohorn (CNH) has a structure in which the graphene sheet is rolled up in a conical shape, and in actual form, many CNHs face the vertices outward and exist as a radial sea urchin-like aggregate. The outer diameter of the aggregates, such as sea urchins of CNH, is about 50 nm to 250 nm. In particular, it is preferable to use CNH of about 80 nm in average particle diameter.

The average particle diameter of a electrically conductive material also shows the average particle diameter of a primary particle. Even in the case of highly structured shapes such as acetylene black (AB), the average particle diameter can be defined here as the primary particle size, and the average particle size can be obtained by image analysis of the SEM photograph.

Moreover, you may use both a particulate-form electrically conductive material and a wire-shaped electrically conductive material. The wire-shaped conductive material is a wire of a conductive material, and a conductive material exemplified for the particulate conductive material can be used. As the wire-shaped conductive material, a linear body having an outer diameter of 300 nm or less such as carbon fiber, carbon nanotube, copper nanowire, nickel nanowire, or the like can be used. By using a wire-shaped conductive material, it is easy to maintain electrical connection with a negative electrode active material, a current collector, and the like, and the current collecting performance is improved, and a fibrous material increases in the porous membrane-shaped negative electrode, making it difficult to crack the negative electrode. For example, it is possible to use AB or copper powder as the particulate conductive material, and to use Vapor Grown Carbon Fiber (VGCF) as the wire-shaped conductive material. In addition, you may use only a wire-shaped electrically conductive material without adding a particulate electrically conductive material.

The length of the wire-shaped conductive material is preferably 0.1 µm to 2 mm. The outer diameter of the conductive material is preferably 4 nm to 1000 nm, more preferably 25 nm to 200 nm. If the length of the conductive material is 0.1 µm or more, the length is sufficient to increase the productivity of the conductive material. If the length is 2 mm or less, application of the coating liquid is easy. In addition, when the outer diameter of the conductive material is larger than 4 nm, synthesis is easy, and when the outer diameter is thinner than 1000 nm, the coating liquid is easily kneaded. The method of measuring the outer diameter and the length of the conductive material depends on the image analysis by SEM.

The binder is a resin binder, and a fluorine resin such as polyvinylidene fluoride (PVdF), rubber such as styrene butadiene rubber (SBR), or an organic material such as polyimide (PI) or acryl can be used.

Application | coating of the coating liquid to an electrical power collector can apply a coating liquid to one surface of an electrical power collector, for example using a coater. As the coater, a general coating apparatus capable of applying the coating liquid to the current collector can be used. For example, a coater, a comma coater, a die coater, or the like by a roll coater or a doctor blade as shown in FIG. 4.

The current collector can be made of a material that is not alloyed with lithium. For example, a foil made of at least one metal selected from the group consisting of copper, nickel and stainless steel can be used. These metals may be used singly or in their respective alloys. Although thickness differs according to a use, about 4 micrometers-about 35 micrometers are preferable, and it is more preferable that they are about 6 micrometers-20 micrometers. It is preferable to use copper foil from a viewpoint of thinness, strength, electrical conductivity, etc. of foil.

And in this invention, it is preferable that the negative electrode electrical power collector is electrolytically roughened on the surface of copper foil, and the processus | protrusion part was formed. It is preferable that the surface roughness Rz of the electrical power collector which has this protrusion part is 1 micrometer-6 micrometers. Since the negative electrode active material is expanded by alloying with lithium, the surface shape of the current collector is made into an appropriate fine rough surface shape of 1 µm to 6 µm in surface roughness (Rz) by electrolytic roughening treatment to increase the specific surface area and per unit area. When the negative electrode is formed so that the amount of the active material decreases, even when a volume change occurs in the negative electrode active material due to charging and discharging, the stresses caused by expansion and contraction of the negative electrode active material can be alleviated by voids between the protrusions, thereby improving cycle characteristics. . In addition, since the surface area is increased, only the necessary amount of the negative electrode active material layer formed on the surface of the current collector as the negative electrode can be supported with good adhesion.

If the surface roughness (Rz) by electrolytic roughening is less than 1 µm, the surface area of the current collector is not large enough, so the capacity of the negative electrode active material that can be supported is insufficient, and the charge / discharge site per unit area is reduced. It is also unpreferable since the characteristic also falls. When the surface roughness (Rz) by electrolytic roughening treatment exceeds 6 µm, the thickness of the current collector becomes excessively large, which adversely affects the formation of the negative electrode active material layer. For example, the negative electrode collector of a jelly roll-shaped cylindrical or rectangular lithium ion secondary battery It is not preferable because it becomes difficult to put it into practical use as a whole. However, surface roughness Rz in this invention is prescribed | regulated by ten-point average roughness of Japanese Industrial Standard JIS B0601-1994.

These protrusions may be formed on the surface of the metal foil by using a wet method (such as electroplating, electroless plating, chemical etching or electrochemical etching), a dry method (evaporation, pyroion deposition, etc.), and a roughening treatment method such as painting and polishing. Can be. In the present invention, it is proposed as a preferred embodiment to form an electrolytic roughening treatment on a metal foil having a surface roughness Rz of 0.5 µm to 3 µm.

As the metal foil (so-called untreated foil) before the roughening treatment, a double-sided glossy foil or a double-sided smooth foil formed by an electrolytic method or a rolling method can be used. The surface roughness Rz of not less than 0.5 µm is a realistic small roughness in double-sided gloss foil or double-sided smooth foil, and it is not preferable because the surface roughness Rz becomes larger than 3 mu m because the unevenness of the roughness after protrusion formation increases. Although untreated foil may have a surface roughness Rz of 1 µm or more, unevenness formed at the time of manufacture of the foil also includes mild unevenness, and adhesiveness with the active material layer cannot be reliably improved. It is not desirable. It is important to form a concave-convex shape with a complicated shape by the roughening treatment. Further, by roughening the metal foil having the surface roughness in the above range, the protrusions formed on the current collector become uniform in both the same plane and the front and back, and exhibit better adhesion to the negative electrode active material layer, and it is difficult for the negative electrode active material layer to fall off. This can contribute to the long-term life of the negative electrode and to ensure its practical capacity.

In the electrolytic roughening treatment, the surface is roughened by forming a plating film having irregularities on the surface of the untreated foil. For example, a roughening method by plating generally used can be used. In other words, electroplating is performed using an aqueous copper sulfate solution by so-called exposure plating, and a granular copper plating layer is formed on the surface of the foil, and then a normal film-type plating (capsule plating) is performed on the granular copper plating layer to prevent powder from falling off. One projection can be formed. This exposure plating is preferable because the homogeneous control and reproducibility of the plating layer can be ensured and the quality control is excellent. In addition, for example, when the material of the current collector is copper, it is preferable because the projections having a complicated shape can be formed by electroplating. By using an electrolytic copper foil, it is possible to easily form an electrical power collector with few imbalances.

In addition, the anti-rust layer can also be formed in the electrical power collector with a protrusion part by plating of nickel and zinc, chromate treatment, and a silane coupling process. By this rust prevention layer, it can prevent or suppress deterioration with time at the time of manufacture, for example, from stock, and the high temperature atmosphere at the time of negative electrode active material layer formation. It also contributes to preventing overdiffusion of the components of the current collector and the components of the negative electrode active material, thereby maintaining good adhesion. Practically, at least one of electroplating, immersion treatment, substitution plating, or functional surface treatment, antirust treatment, and adhesion enhancement treatment by a known sulfate aqueous solution or the like is performed on the current collector on which protrusions are formed. desirable.

Subsequently, the adjusted coating liquid is uniformly applied to the current collector, then dried at about 50 to 150 ° C., and passed through a roll press to adjust the thickness, thereby obtaining a negative electrode for a lithium ion battery.

(1-5.Effect of negative electrode for lithium ion secondary battery)

According to the present invention, since the negative electrode active material material of the present invention is used, volume expansion during lithium ion occlusion is suppressed, and problems such as micronization and peeling of the negative electrode active material, cracking of the negative electrode, and deterioration in conductivity between the negative electrode active materials are eliminated. A high dose and long life negative electrode is provided.

According to the present invention, since the surface of the current collector is roughened, the bonding force between the negative electrode active material layer and the current collector is high, and the stress due to expansion and contraction of the negative electrode active material can be alleviated and the cycle characteristics of the electrode can be improved. Can be.

(2. The negative electrode for lithium ion secondary batteries which concerns on 2nd Embodiment)

(2-1.Configuration of negative electrode for lithium ion secondary battery)

First, the negative electrode for lithium ion secondary batteries which concerns on one Embodiment of this invention is demonstrated with reference to FIG. The negative electrode 61 for a lithium ion secondary battery of the present invention has a negative electrode current collector 67 having a projection 65 on its surface and a thin film negative electrode active material layer 63 formed on the surface of the negative electrode current collector 67.

In the present invention, the negative electrode active material layer 63 is made of a silicon-based thin film having a characteristic component structure, and the negative electrode current collector 67 having a specific shape is used for the negative electrode active material layer 63.

(2-2. Negative Electrode Active Material Layer)

The negative electrode active material layer 63 of the present invention is a thin film integrally formed on the surface of the negative electrode current collector 67, and contains silicon as a main component and at least element A as a second element. Since silicon is an element which easily occludes lithium, this negative electrode active material layer also has high lithium storage ability. In addition, silicon has an advantage that the cost is relatively low among the elements having lithium storage ability.

The element A is contained 0.05 mass% or more in the negative electrode active material layer. When containing two or more elements A, the sum total of content of these elements shall be 0.05 mass% or more. By setting the content to 0.05% by mass or more, the volume expansion shrinkage of the silicon during charge and discharge can be effectively suppressed. Although it does not specifically limit about the upper limit of content of the element A, It can determine arbitrarily in the range of less than 50 mass% in consideration of the lithium storage ability of silicon | silicone, etc .. Since the effect of suppressing volume expansion contraction is acquired even in a quantity sufficiently small compared with Si, it is illustrated that element A is 30 mass% or less, Furthermore, it is 20 mass% or less.

In addition, the negative electrode active material layer which concerns on this invention may further contain oxygen or fluorine as a 3rd element. Oxygen and fluorine have a small atomic radius, but as shown in Table 1 above, the ion radius r _{A '} is comparable to that of Si (r ₀ ; 0.117 nm). It is possible to further improve the charge and discharge cycle life by suppressing the volume change of silicon without disturbing the intrusion and desorption of ions. Oxygen and fluorine also have the effect of stabilizing the active material by compounding and dispersing part of Li. However, for Ag and Cd, although the ionic radius is comparable to the atomic radius (r ₀ ) of Si, since the ion-bonding compound is difficult to form, it is preferable as the third element constituting the negative electrode active material layer according to the present invention. Not.

In addition, oxygen and fluorine may be uniformly contained in the whole active material layer, for example, may be contained in a part of the surface part, etc., for example. About content of oxygen and fluorine, in order to maintain charge / discharge characteristic high, it is preferable that it is 0.5 mass% or more, and it is preferable to make the sum total with content of the element A into 50 mass% or less.

The negative electrode active material layer according to the present invention needs to have a thickness of at least 1 μm or more practically, and preferably has a thickness of about 1 μm to 6 μm for high energy density applications such as electronic devices.

In addition, in this invention, making silicon as a main component means that silicon content is the largest among the elements which comprise an active material layer, and it shows that content of silicon becomes like this. Preferably it is 50 mass% or more, More preferably, it is 70 mass% or more. have. In addition, a 2nd element and a 3rd element are called the 2nd element and the 3rd element about the element group which has a characteristic role other than silicon among the elements which comprise particle | grains, and are not related to both content.

The negative electrode active material layer of the present invention described above may be any of crystalline, microcrystalline, amorphous, or mixed state thereof. This is because any crystal form is amorphous by alloying with Li ions during charging.

Moreover, the film forming method of the negative electrode active material layer which concerns on this invention is not specifically limited, For example, the thin film which has a composition and thickness as mentioned above can be formed using various well-known film forming methods. Specifically, for example, a sputtering method, a vapor deposition method, a CVD method and the like can be exemplified. Using these methods, it is easy to form a uniform thin film.

(2-3 negative electrode current collector)

The negative electrode collector which concerns on this invention can be comprised from the material which does not alloy with lithium, For example, the foil which consists of at least 1 sort (s) of metal chosen from the group which consists of copper, nickel, and stainless steel can be used. These metals may be used singly or in their respective alloys. It is preferable to use copper foil from a viewpoint of thinness, strength, electrical conductivity, etc. of foil. Although a collector differs according to a use, it is preferable that thickness except a protrusion part is about 4 micrometers-35 micrometers, and it is more preferable that it is about 6 micrometers-20 micrometers.

In addition, the negative electrode current collector in the present invention has a protrusion. It is preferable that this protrusion part is formed by the electrolytic roughening process on the surface of copper foil, and it is preferable that surface roughness Rz is 1 micrometer-6 micrometers. The reason is that since the negative electrode active material is expanded by alloying with lithium, the surface shape of the current collector is made into an appropriate fine rough surface shape of 1 μm to 6 μm in terms of surface roughness (Rz) to increase the specific surface area and increase the negative electrode active material per unit area. This is because by forming the negative electrode so that the amount decreases, even when a volume change occurs in the negative electrode active material layer due to charging and discharging, the stress due to expansion and contraction of the negative electrode active material layer can be alleviated by voids between the protrusions, thereby improving the cycle characteristics. . In addition, since the surface area is increased, only the necessary amount of the negative electrode active material layer formed on the surface of the current collector as the negative electrode can be supported with good adhesion.

When surface roughness Rz by a projection part is less than 1 micrometer, it becomes difficult to carry the negative electrode active material layer formed directly as a thin film on a collector, without peeling. Further, even if the negative electrode active material layer according to the present invention is used, since the surface area of the current collector is not sufficiently large, the capacity of the negative electrode active material that can be supported is insufficient, and the charge / discharge site per unit area is reduced. It is also unpreferable to fall. When surface roughness Rz exceeds 6 micrometers, the micrometer measurement thickness of an electrical power collector will become large too much, and will have a bad influence on the formation of a negative electrode active material layer, for example, it is put to practical use as a negative electrode collector of a jelly roll type cylindrical or square lithium ion secondary battery. It is not preferable because it becomes difficult to do so. However, surface roughness Rz in this invention is prescribed | regulated by ten-point average roughness of Japanese Industrial Standard JIS B0601-1994.

These protrusions use wet (electroplating, electroless plating, chemical etching or electrochemical etching) method, dry method (deposition, pyroion deposition, etc.) and roughening methods such as painting and polishing on the smooth surface of the metal foil. Can be formed. And in this invention, it is shown as a preferable aspect to form and form electrolytic roughening process on copper foil whose surface roughness Rz is 0.5 micrometer-3 micrometers.

As the metal foil (so-called untreated foil) before the roughening treatment, a double-sided glossy foil or a double-sided smooth foil formed by an electrolytic method or a rolling method can be used. The surface roughness Rz of not less than 0.5 µm is a realistic small roughness in double-sided gloss foil or double-sided smooth foil, and it is not preferable because the surface roughness Rz becomes larger than 3 mu m because the unevenness of the roughness after protrusion formation increases. Although untreated foil may have a surface roughness Rz of 1 µm or more, unevenness formed at the time of manufacture of the foil also includes mild unevenness, and adhesiveness with the active material layer cannot be reliably improved. It is not desirable. It is important to form a concave-convex shape with a complicated shape by the roughening treatment. Further, by roughening the surface roughness on both surfaces of the surface roughness, the protrusions formed on the current collector become uniform in both the same plane and the front and back surfaces, and exhibit better adhesion to the negative electrode active material layer and the negative electrode active material layer is eliminated. It is difficult and can contribute to prolonging the life of the negative electrode and securing the practical capacity.

In the electrolytic roughening treatment, the surface is roughened by forming a plating film having irregularities on the surface of the untreated foil. For example, a roughening method by plating generally used can be used. In other words, electroplating is performed using an aqueous copper sulfate solution by so-called exposure plating, and a granular copper plating layer is formed on the foil surface, and then a projection-like plating (capsule plating) is formed on the granular copper plating layer to form a protrusion. have. This exposure plating is preferable because the homogeneous control and reproducibility of the plating layer can be ensured and the quality control is excellent. In addition, for example, when the material of the current collector is copper, it is preferable because the protrusions having a complicated shape can be formed by electroplating. By using an electrolytic copper foil, it is possible to easily form a current collector protrusion with few imbalances.

In addition, the anti-rust layer can also be formed in the electrical power collector with a protrusion part by plating of nickel and zinc, chromate treatment, and a silane coupling process. By this rust prevention layer, it can prevent or suppress deterioration with time at the time of manufacture from the stock period, or deterioration by the high temperature atmosphere at the time of negative electrode active material layer formation, for example. It also contributes to preventing overdiffusion of the components of the current collector and the components of the negative electrode active material, thereby maintaining good adhesion. Practically, at least one of electroplating, immersion treatment, substitution plating, or functional surface treatment, antirust treatment, and adhesion enhancement treatment by a known sulfate aqueous solution or the like is performed on the current collector on which protrusions are formed. desirable.

(2-4.Effect of negative electrode for lithium ion secondary battery)

According to the negative electrode for a lithium ion secondary battery of the present invention, since the negative electrode active material layer contains at least element A having the same atomic radius as that of silicon in addition to silicon, element A exhibits excessively large strain between Si lattice or Si atoms. It is possible to easily insert (charge) and detach (discharge) the silicon active material lattice between the silicon active material lattice during charging and discharging of the Li ion having a small ion radius without giving, and it is unnecessary by the residual Li ion accompanying discharge after charging. It can reduce the occurrence of irreversible capacity.

In addition, since silicon expands in volume when the lithium is occluded, element A does not occlude or is difficult to occlude lithium. Therefore, lithium ion has less volume change and deformation due to expansion and contraction and the discharge capacity is reduced during cycle characteristics. A negative electrode for a secondary battery is provided.

Further, by including oxygen or fluorine having an ion radius close to the Si atomic radius as the third element, a negative electrode for a lithium ion secondary battery with more improved charge / discharge cycle characteristics and battery life is provided.

Further, since the negative electrode current collector has a predetermined surface roughness, a negative electrode for a lithium ion secondary battery in which the effect of the negative electrode active material layer as described above is sufficiently exhibited is provided.

(3. Composition of lithium ion secondary battery)

The lithium ion secondary battery which concerns on one Embodiment of this invention is demonstrated with reference to FIG. The lithium ion secondary battery 11 of the present invention includes a positive electrode 13 capable of storing and releasing lithium ions, a negative electrode 1 for a lithium ion secondary battery according to the present invention, and a positive electrode 13 and a negative electrode 1. The positive electrode 13, the negative electrode 1, and the separator 15 are formed in the electrolyte 17 having the separators 15 arranged thereon and having lithium ion conductivity.

(4.positive electrode)

The positive electrode can be produced by directly applying and drying a composition of the positive electrode active material on a metal current collector such as aluminum foil. The composition of the positive electrode active material can be prepared by mixing a positive electrode active material, a conductive aid, a binder and a solvent.

(4-1.Positive electrode active material)

As the positive electrode active material is generally available both as far as used, and, for example, _{LiCoO 2, LiMn 2 O 4,} LiMnO 2, LiNiO 2, such as _{LiCo 1/3 Ni 1/3} Mn 1/3 O 2, LiFePO 4 Compound.

(4-2.Conductive Preparation)

The conductive aid is a powder made of at least one conductive material selected from the group consisting of carbon, copper, tin, zinc, nickel and silver. The single powder of carbon, copper, tin, zinc, nickel, and silver may be sufficient, or the powder of each alloy may be sufficient. For example, general carbon black, such as furnace black and acetylene black, can be used. Moreover, it is preferable to add carbon nanohorn as a conductive support agent. Here, the carbon nanohorn (CNH) has a structure in which the graphene sheet is rolled up in a conical shape, and in actual form, a plurality of CNHs face the vertices outward and exist as a radial sea urchin-like aggregate. The outer diameter of the aggregates, such as sea urchins of CNH, is about 50 nm to 250 nm. In particular, CNH with an average particle diameter of about 80 nm is preferable.

The average particle diameter of the conductive aid indicates the average particle diameter of the primary particles. Even in the case of highly structured shapes such as acetylene black (AB), the average particle size is defined as the primary particle size. The measurement of the particle diameter may use the image information of the electron microscope (SEM) together with the volume-based median diameter of the dynamic light scattering photometer (DLS). The average particle size is obtained by confirming the particle shape in advance by SEM image, and obtaining the particle size by image analysis (e.g., "A zokun" (registered trademark) manufactured by Asahi Kasei Engineering Co., Ltd.), or by dispersing the particles in a solvent to obtain DLS (e.g., It is possible to measure by Otsukadenshi DLS-8000). If the fine particles are sufficiently dispersed and aggregated, almost the same measurement results are obtained by SEM and DLS.

In addition, you may use both a particulate-form conductive support agent and a wire-shaped conductive support agent. The wire-shaped conductive aid is a wire of a conductive material, and a conductive material exemplified in the particulate conductive aid can be used. The wire-shaped conductive aid may use a linear body having an outer diameter of 300 nm or less, such as carbon fiber, carbon nanotube, copper nanowire, nickel nanowire, or the like. By using a wire-shaped conductive aid, it is easy to maintain electrical connection with a negative electrode active material, a current collector, or the like, and the current collecting performance is improved, and a fibrous material increases in the porous membrane-shaped negative electrode, making it difficult to crack in the negative electrode. For example, it is possible to use AB or copper powder as the particulate conductive aid, and to use Vapor Grown Carbon Fiber (VGCF) as the wire-shaped conductive aid. In addition, you may use only a wire-shaped conductive support agent without adding a particulate conductive support agent.

The length of the wire-shaped conductive aid is preferably 0.1 µm to 2 mm. The outer diameter of the conductive aid is preferably 4 nm to 1000 nm, more preferably 25 nm to 200 nm. If the length of the conductive aid is 0.1 µm or more, the length is sufficient to increase the productivity of the conductive aid. If the length is 2 mm or less, application of the slurry is easy. In addition, when the outer diameter of the conductive aid is greater than 4 nm, the synthesis is easy, and when the outer diameter is thinner than 1000 nm, the slurry is easily kneaded. The method of measuring the outer diameter and length of the conductive material is based on the image analysis by SEM.

(4-3.Binder)

The binder is a resin binder, and organic materials such as fluorine resin such as polyvinylidene fluoride (PVdF), rubber such as styrene butadiene rubber (SBR), and polyimide (PI) or water-soluble acrylic binder can be used.

(4-4.Solvent)

N-methyl-2-pyrrolidone (NMP), water, etc. are used as a solvent. At this time, the content of the positive electrode active material, the conductive aid, the binder, and the solvent can be appropriately adjusted to the level normally used in the lithium ion secondary battery.

(4-5. Production of Positive Electrode)

The composition of the positive electrode active material adjusted as described above is uniformly applied to one surface of the current collector using, for example, a coater. The coater can use a general ceramics device which can apply the composition to the current collector, and is, for example, a coater, a comma coater, a die coater by a roll coater or a doctor blade.

The current collector is a foil made of at least one metal selected from the group consisting of copper, nickel and stainless steel. Each may be used independently and each alloy may be sufficient. Although thickness differs according to a use, 4 micrometers-35 micrometers are preferable, and 6 micrometers-20 micrometers are more preferable.

After apply | coating the composition of a positive electrode active material, it dries to about 50-150 degreeC, and passes through a roll press to adjust thickness, and a positive electrode is obtained.

(5. Separator)

The separator functions to insulate the electron conduction of the positive electrode and the negative electrode, and any separator can be used as long as it is commonly used in a lithium ion secondary battery. For example, a microporous polyolefin film can be used.

(6.electrolyte)

As the electrolyte, various electrolytes and electrolytes having lithium ion conductivity can be used. For example, an organic electrolyte (non-aqueous electrolyte), an inorganic solid electrolyte, a polymer solid electrolyte, or the like can be used.

Specific examples of the organic electrolyte solvent include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate; Ethers such as diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether and diethylene glycol dimethyl ether; Benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butylolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethylchlorobenzene, Aprotic solvents, such as nitrobenzene, or the mixed solvent which mixed 2 or more types of these solvents is mentioned.

The electrolyte of the organic electrolyte is LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAlO ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂₎ alone or in combination of two or more of an electrolyte composed of a lithium salt of _2, and so on it can be used that were mixed.

It is preferable to add the compound which can form an effective solid electrolyte interface film to the surface of a negative electrode active material as an additive to an organic electrolyte solution. For example, a substance having an unsaturated bond in the molecule and capable of reduction polymerization at the time of filling, for example, vinylene carbonate (VC), is added.

In addition, a solid lithium ion conductor may be used instead of the organic electrolyte. For example, a solid polymer electrolyte in which the lithium salt is mixed with a polymer made of polyethylene oxide, polypropylene oxide, polyethyleneimine, or the like, or a polymer gel electrolyte obtained by impregnating an electrolyte solution in a polymer material and processing into a gel can be used.

Lithium nitride, lithium halide, lithium oxyacid, Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₄ SiO ₄ , Li ₂ SiS ₃ , Li ₃ PO ₄ -Li ₂ S Inorganic materials such as -SiS ₂ and phosphorus sulfide compounds may be used as the inorganic solid electrolyte.

(7. Assembly of lithium ion secondary battery)

In the lithium ion secondary battery of the present invention, a separator is disposed between the positive electrode as described above and the negative electrode for lithium ion battery of the present invention to form a battery element. Such battery elements are wound or stacked, placed in a cylindrical or rectangular battery case, and then injected with an electrolyte to form a lithium ion secondary battery.

Specifically, as shown in FIG. 2, the lithium ion secondary battery 11 of the present invention is laminated in the order of separator-negative electrode-separator-positive electrode with the separator 15 interposed between the positive electrode 13 and the negative electrode 1. It arrange | positions and winds so that the positive electrode 13 may become inner, and comprises a pole plate group, and this is inserted in the battery can 19. As shown in FIG. The positive electrode 13 is connected to the positive electrode terminal 25 through the positive electrode lead 23, and the negative electrode 1 is connected to the battery can 19 via the negative electrode lead 21, respectively. The chemical energy generated by the electricity can be excavated to the outside as electrical energy. Subsequently, the electrolyte 17 is charged into the battery can 19 so as to cover the electrode plate group, and then the upper end (opening) of the battery can 19 is composed of a circular cover plate and a positive electrode terminal 25 thereon, and the inside thereof. It can be manufactured by mounting the sealing sphere 27 incorporating a safety valve mechanism through the annular insulating gasket.

(8. Effect of the lithium ion secondary battery according to the present invention)

Lithium ion secondary battery according to the present invention comprises a negative electrode active material material consisting of Si having a larger capacity per unit volume than carbon and particles containing a second element having an atomic radius of the same size as Si and reducing the occurrence of irreversible capacity Since it is used, since the capacity | capacitance is larger than a conventional lithium ion secondary battery, and particle | grains are hard to volume-contract and shrink, and it is hard to micronize, cycling characteristics are good.

Moreover, since the negative electrode for lithium ion secondary batteries of this invention which has a high binding force between a negative electrode active material layer and an electrical power collector, and which can relieve stress by expansion-contraction of a negative electrode active material material is used, it is excellent in cycling characteristics and economical lithium ion A secondary battery is provided.

Example

Hereinafter, the present invention will be described in detail using examples and comparative examples.

[Example 1: A negative electrode active material was coated to prepare a negative electrode]

(Currently made)

Electrolytic plating was carried out on the electrolytic copper foil (NC-WS foil made by Furukawa Denko, 1.5 micrometers in surface roughness (Rz)) of thickness 10micrometer, and the electrical power collector with a protrusion part was produced. Plating conditions are as follows.

(a) Exposure plating of roughening treatment: appropriately selected with an electrolysis time in the range of current density of 10 to 20 A / dm 2 without heating in an electrolytic solution containing copper 30 g / dm 3 and sulfuric acid 150 g / dm 3. Cathodic electrolysis was carried out under the condition of obtaining a predetermined predetermined surface shape.

(b) Smoothing copper plating (capsule plating) of roughening treatment: a current density of 5 to 10 A / dm 2 in an electrolyte solution containing 70 g / dm 3 of copper and 100 g / dm 3 of sulfuric acid as the main component and maintaining the liquid temperature at 40 ° C. Cathode electrolysis was performed under appropriately selected conditions together with an electrolysis time for obtaining a predetermined surface shape determined together with the condition of (a) in the range.

In addition, an inorganic film made of nickel and zinc was formed on the copper foil, and chromate treatment was performed by cathode electrolysis using a known aqueous solution to form a film having a thickness of about nanometers, and then (meth) acryloxy-based silane coupling aqueous solution. It was immersed in and formed each antirust process layer, and it was set as the electrical power collector.

(Production 1 of Negative Electrode Active Material)

As the negative electrode active material, Si, Si-B, Si-P, Si-Fe, and Si-Ni-based nanosize particles were produced using the plasma CVD apparatus of FIG. 2. The raw material was suitably blended with Si powder, B powder having an atomic radius of 0.09 nm, P powder having an atomic radius of 0.11 nm, Fe powder having an atomic radius of 0.12 nm, and Ni powder having an atomic radius of 0.12 nm. These mixed powders were dried and continuously supplied as a carrier gas into a plasma of Ar gas generated in the reaction chamber, thereby producing nanosized particles.

Specifically, after evacuating the inside of the reaction chamber with a vacuum pump, Ar gas was introduced to atmospheric pressure. This exhaust and Ar gas introduction were repeated three times to exhaust residual air in the reaction vessel. Thereafter, Ar gas was introduced into the reaction vessel at a flow rate of 13 L / min, and an alternating voltage was applied to the high frequency coil to generate a high frequency plasma by a high frequency electromagnetic field (frequency 4 MHz). At this time, the plate power was 20 kW. As the carrier gas for supplying the raw material powder, Ar gas having a flow rate of 1.0 L / min was used.

The obtained fine powder was recovered by a filter after the oxidation treatment for preventing dust explosion 12 hours after production.

(Production 2 of Negative Electrode Active Material)

As an anode active material, an alloy molten metal having a predetermined composition of Si-B and Si-P is prepared, and finely powdered by an atomizing method using a known nitrogen gas to form an active material having a micrometer size of Si-P and Si-B. The particles were obtained.

(Production 3 of Negative Electrode Active Material)

The obtained negative electrode active material was subjected to atmospheric oxidation in a thermostat heated at 180 ° C. to contain oxygen.

(Analysis of negative electrode active material composition)

Two to three components of the negative electrode active material were analyzed by ICP (high frequency inductively coupled plasma emission spectroscopy) by an aqueous solution in which the material was dissolved for component quantification. In Table 2, when the mass of the whole material was 100, the mass ratio of the subcomponents was shown as the subcomponent concentration (mass%).

(Production of negative electrode)

10 mass% carbon black was mixed as a electrically conductive material with respect to the negative electrode active material material prepared as mentioned above, and the inside was mixed using the ball mill which carried out the nitrogen substitution. After mixing this mixed powder and the polyimide as a binder at the ratio of mass ratio 95: 5, NMP (N-methyl- 2-pyrrolidone) was added as a solvent, it knead | mixed sufficiently, and the negative electrode coating liquid was obtained.

This negative electrode coating liquid was applied to a current collector at a thickness of 15 μm, and baked at 300 ° C. for 10 minutes. After that, the roll press was rolled to a density of 2 g / cm 3, and punched into a disk shape of 2 cm 2 to obtain a negative electrode.

[Examples 1-1, 1-2]

A negative electrode using two kinds of nano-size Si-P particles having different P concentrations synthesized by the above-described plasma method as an active material was used for evaluation of electrochemical characteristics.

[Examples 1-3 and 1-4]

The electrochemical characteristics were evaluated using the negative electrode which used as the test electrode the Si-P-O particle | grains which introduce | transduced the nanosize Si-P particle | grains of Example 1 and introduce | transduced oxygen as an active material.

[Example 1-5]

The electrochemical characteristics were evaluated using the negative electrode using the Si-P-O particle | grains which introduce | transduced the oxygen | micron size Si-P particle | grains synthesize | combined by said atomization method as an active material as a test electrode.

[Example 1-6]

The electrochemical characteristic was evaluated using the negative electrode using the nanosize Si-Fe particle | grains synthesize | combined by said plasma method as an active material as a test electrode.

[Example 1-7]

The electrochemical characteristic was evaluated using the negative electrode which used the nanosize Si-Ni particle | grains synthesize | combined by said plasma method as an active material material as a test electrode.

[Examples 1-8 and 1-9]

The electrochemical characteristics were evaluated using the negative electrode which used the Si-Fe-O particle and Si-Ni-O particle which oxidized the Si-Fe and Si-Ni particle of Examples 4-5 as active material as a test electrode, respectively.

[Comparative Examples 1-1 to 1-3]

As a comparative example, the negative electrode using nanosize Si single particle | grains, nanosize Si-B particle | grains, and micron size Si-B particle | grains as an active material was used for evaluation of electrochemical characteristics, respectively as a test electrode.

(Production of Electrochemical Characterization Cell of Silicon Electrode)

A beaker cell was produced using a mixed solvent of ethylene carbonate + diethyl carbonate (1: 1 in volume ratio) in which the silicon thin plate, the counter electrode, the lithium metal as the reference electrode, and 1 mol of LiPF ₆ were dissolved as the electrolyte solution.

(Production of Electrochemical Characterization Cell of Silicon Electrode)

The obtained negative electrode was processed into the disk shape of diameter 20mm, and was used as the working electrode in electrochemical characteristic evaluation. In addition, using a mixed solvent of ethylene carbonate and diethyl carbonate (1: 1 in volume ratio) in which lithium metal was dissolved as a counter electrode and a reference electrode, and 1 mol of LiPF ₆ as an electrolyte, they were placed in a beaker together with the working electrode. Made.

(Evaluation of Electrochemical Characteristics of Silicon Electrode)

Next, a test was conducted to evaluate the charge and discharge performance using the electrochemical property evaluation cell. The process of scanning the potential of the working electrode in the direction of high potential (reduction side) is called charging, and the process of scanning the potential of the working electrode in the direction of low potential (oxidation side) is called discharge.

First, the first charge / discharge was performed at 0.1CA until the charge was 0.02V (until the positive potential reached 0.05CA), and the discharge was performed at 1.5V. Charging and discharging after the second cycle were performed by charging at 0.0CA at 0.2CA (until reaching 0.05CA at a positive potential) and discharging at 0.2CA at 1.5V. Evaluation temperature was 25 degreeC. The conditions were evaluated under these conditions, and the capacity retention ratio was determined from the discharge capacity cycle of the first charge and discharge and the discharge capacity of the 50th cycle. In addition, the capacity retention rate was defined as follows.

Capacity maintenance ratio = (discharge capacity of 50th cycle discharge capacity / first cycle) * 100

Table 2 shows the specifications of the negative electrode used as the test electrode and the capacity retention rate of the test evaluation result. The capacity shown in the table is the capacity per mass of silicon.

[Table 2]

From the above result, compared with the active material material which consists only of Si of the comparative example 1-1, the atomic radius of Examples 1-1 to 1-9 is close to the atomic radius of 0.117 nm, and | (r _A -r ₀ ) / It was found that the capacity retention rate of the negative electrode using the active material containing the second element (P, Fe, Ni) that satisfies the relationship of r ₀ | ≤0.1 is about two times or more after the charge / discharge cycle. It can be judged that the current collector has a protrusion having an appropriate shape on the surface, and the adhesion with the active material is good, contributing to the charge / discharge cycle life.

In addition, it was confirmed from the results of Examples 1-3, 1-4, 1-5, 1-8, and 1-9 that the active material material more preferably contained oxygen molecules. In this case, however, the increase in the average particle diameter of the active material by introduction of oxygen atoms does not significantly affect the capacity retention rate.

On the other hand, in the case where an element (B) in which the atomic radiuses of Comparative Examples 1-2 to 1-3 do not satisfy the relationship of | (r _A -r ₀ ) / r ₀ | ≤0.1 is introduced, the capacity retention rate of the negative electrode is large. It was confirmed that it fell.

Although the case where P, Fe, Ni, and oxygen are used as a 2nd element in a negative electrode active material material in this Example was shown, the negative electrode active material material of this invention is not limited to this. As the second element, an element whose atomic radius satisfies the relationship of | (r _A -r ₀ ) / r ₀ | ≤0.1 may be used. For example, Cr, Co, Cu, or the like may be used in addition to P, Fe, and Ni. It is guessed that the same result is obtained even if fluorine is used as a 3rd element.

In this embodiment, exposure plating and capsule plating are performed by the roughening method of the current collector, but the method of forming the current collector protrusion of the present invention is not limited thereto. If it is the method which can form the stable film which has the processus | protrusion part which becomes predetermined surface roughness on the surface of an electrical power collector, it is guessed that the result of the same tendency as this embodiment is obtained.

[Example 2: Film formation on a current collector to produce a negative electrode]

(Preparation 1 of negative electrode for lithium ion secondary battery)

The negative electrode active material layer of Si, Si-P, Si-As, Si-B, and Si-N system composition was formed on the surface of the electrical power collector obtained by the method similar to Example 1, and the negative electrode for lithium ion secondary batteries was produced. Specifically, the formation of a negative electrode active material layer was carried out using a catalytic chemical vapor growth (Cat-CVD) apparatus to form a film under the following conditions. First, a film forming time of Si film was prepared by using monosilane gas as a raw material gas, a flow rate of 20 sccm, a current collector temperature of 250 ° C., and a tungsten wire catalyst body temperature of 1800 ° C. based on the film thickness.

In addition, when P was contained as a 2nd element, the phosphine gas was changed to 10 sccm or 1 sccm in addition to monosilane gas as a source gas, and was supplied. Similarly, when containing As as the second element, 10 sccm of arsine gas was added to monosilane gas as the source gas, 10 sccm of divolane gas when B was included, and 100 sccm of ammonia gas when N was included. .

(Production 2 of negative electrode for lithium ion secondary battery)

When adding oxygen as a 3rd element to the surface of the obtained electrical power collector, the negative electrode active material layer of Si-P-O composition was formed by reactive sputtering of Si containing oxygen, and the negative electrode for lithium ion secondary batteries was produced. Specifically, a substrate of Si and P having different oxygen contents was sputtered to form an active material having a desired ratio.

(Production 3 of negative electrode for lithium ion secondary battery)

The negative electrode obtained using the Cat-CVD apparatus described above was subjected to atmospheric oxidation in a thermostat heated at 180 ° C to contain oxygen.

[Examples 2-1 to 2-3]

Three negative electrode active material layers were formed on the current collector on which the protrusions were formed by changing the P content and thickness by the Cat-CVD method to obtain a negative electrode.

[Example 2-4]

The negative electrode active material layer containing Si and P was formed in the electrical power collector which provided the protrusion part by Cat-CVD method, and it oxidized by the thermostat again to make the negative electrode containing Si, P, and O.

[Example 2-5]

The negative electrode of Example 2-3 was oxidized by a thermostat to form a negative electrode active material layer containing Si, P, and O to form a negative electrode.

[Example 2-6]

The negative electrode active material layer containing Si, P, and O was formed in the current collector in which the protrusion part was formed by reactive sputtering to make a negative electrode.

[Example 2-7]

The negative electrode active material layer containing Si and As was formed in the electrical power collector which provided the protrusion part by the Cat-CVD method, and it was set as the negative electrode.

[Example 2-8]

The negative electrode of Example 2-7 was oxidized by a thermostat to form a negative electrode active material layer containing Si, As, and O to form a negative electrode.

[Example 2-9]

Roughening is performed on the copper foil of the smooth surface different from Example 2-1, and the negative electrode active material layer containing Si and P is formed by the Cat-CVD method on the copper foil which has a protrusion but small surface roughness, The negative electrode I did.

[Comparative Example 2-1]

A negative electrode active material layer made of Si alone was formed on the copper foil on which the protrusions were formed, to form a negative electrode.

[Comparative Example 2-2]

The negative electrode active material layer containing Si and B was formed in the copper foil which formed the protrusion part by Cat-CVD method, and it was set as the negative electrode.

[Comparative Example 2-3]

The negative electrode active material layer containing Si and N was formed in the copper foil which formed the protrusion part by Cat-CVD method, and it was set as the negative electrode.

[Comparative Example 2-4]

A negative electrode active material layer containing Si and P was formed by a Cat-CVD method on a double-sided smooth copper foil (WS foil of Rz 1.5 µm, untreated foil) which did not form a protrusion, thereby forming a negative electrode.

(Analysis of negative electrode active material layer composition)

The cross section of the negative electrode active material layer of the produced negative electrode was analyzed using an X-ray microanalyzer (EPMA), and quantified according to the ZAF correction method for 2-3 components. The results are shown in Table 2 as subcomponent concentrations. However, subcomponent concentration has shown the ratio (mass%) of the subcomponent when the mass of the whole component which comprises a layer is 100.

(Evaluation of Electrochemical Characteristics of Silicon Electrode)

In the same manner as in Example 1, the 50th cycle capacity retention rate was measured.

(Silicon weight measurement)

The obtained negative electrode was obtained by subtracting the current collector (including protrusions) from the weight of the entire negative electrode to obtain the weight of silicon, and the results are shown in Table 3.

[Table 3]

From the above result, compared with the negative electrode which has the active material layer which consists only of Si of the comparative example 2-1, the atomic radius of Examples 2-1-2-8 is close to the atomic radius of 0.1 (0.117 nm), and | (r _A It was found that the capacity retention rate of the negative electrode using the active material layer containing the second element (P, As) satisfying the relationship of -r ₀ ) / r ₀ | ≤0.1 is significantly improved after 50 cycles of charge and discharge.

And from the comparison of Example 2-2 and Example 2-9, when the negative electrode active material layer according to the present invention is combined with a current collector having a sufficiently large surface roughness (Rz), the discharge capacity and the capacity retention rate are remarkably improved. It was confirmed that the charging and discharging cycle characteristics were further improved. In addition, although the negative electrode of Example 2-9 had about half the film thickness and silicon mass compared with Comparative Example 2-1, the negative electrode of Comparative Example 2-1 has a discharging capacity and a capacity maintenance rate intact.

In addition, it was confirmed from the results of Examples 2-4 to 2-6 and 2-8 that the active material layer contains oxygen that the capacity retention rate is further higher. From the result of Example 2-5, it was confirmed that sufficient effect is exhibited even if content of oxygen is 0.7 mass%.

On the other hand, from Comparative Examples 2-2 to 2-3, the capacity of the negative electrode when an element radius (B, N) in which the atomic radius does not satisfy the relationship of | (r _A -r ₀ ) / r ₀ | ≤0.1 is introduced. It was confirmed that the retention rate is greatly reduced.

In addition, it was found from the results of Comparative Example 2-4 that the negative electrode active material layer could not be supported on the current collector unless the protrusions were formed on the surface of the current collector.

Although the case where P and As are used as a 2nd element which comprises a negative electrode active material layer, and oxygen is used as a 3rd element was shown in a present Example, the negative electrode of this invention is not limited to this. As the second element, an element whose atomic radius satisfies the relationship of | (r _A -r ₀ ) / r ₀ | ≤0.1 may be used. In addition to P and As, for example, Fe, Ni, Cr, Co, Cu, or the like may be used. It is guessed that the same result is obtained even if it uses or uses fluorine as a 3rd element.

In this embodiment, exposure plating and capsule plating are performed by the roughening method of the current collector, but the method of forming the current collector protrusion of the present invention is not limited thereto. If it is the method which can form the stable film which has the processus | protrusion part which becomes predetermined surface roughness on the surface of an electrical power collector, it is guessed that the result of the same tendency as this embodiment is obtained.

As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It will be apparent to those skilled in the art that various changes or modifications can be made within the scope of the technical spirit disclosed herein and that naturally belong to the technical scope of the present invention.

1: negative electrode 3: active material
4: conductive material 5: active material layer
6: binder 7: protrusion
9: Current collector 11: Lithium ion secondary battery
13: positive electrode 15: separator
17: electrolyte 19: battery can
21: positive electrode lead 23: negative electrode lead
25: positive electrode terminal 27: sealing sphere
31: nano size particle manufacturing apparatus
33: reaction chamber 35: raw powder supply port
37: raw material powder 39: sheath gas supply port
41: cis gas 42: carrier gas
43: high frequency coil 45: high frequency power supply
47: plasma 49: filter
53: mixer 55: coating liquid
57: coating liquid raw material 59: coater
61: negative electrode 63: negative electrode active material layer
65: projection 67: negative electrode collector

Claims (11)

As an active material used for the negative electrode for lithium ion secondary batteries,
Consists of particles containing silicon as a main component and containing at least 0.05% by mass of element A,
Atomic radius (r _A) of the element A to the silicon atom of the radius (r ₀₎ is | to satisfy the relation of _{≤0.1 | (r A -r 0)} / r 0
The negative electrode active material material for lithium ion secondary batteries characterized by the above-mentioned. The method of claim 1,
Said element A is at least 1 sort (s) of element chosen from the group which consists of P, Cr, Mn, Fe, Co, Ni, Cu, As. The negative electrode active material material for lithium ion secondary batteries. The method of claim 1,
An anode active material material for a lithium ion secondary battery, further comprising oxygen or fluorine. The method of claim 1,
Said particle | grains are the average particle diameters of a primary particle of 10 nm-5 micrometers, The negative electrode active material material for lithium ion secondary batteries characterized by the above-mentioned. The negative electrode for nonaqueous electrolyte secondary batteries which has an active material layer formed by apply | coating and drying the coating liquid containing the negative electrode active material material of Claim 1 on one or both surfaces of a negative electrode electrical power collector. A negative electrode current collector having protrusions on its surface, and a thin film-type negative electrode active material layer having a silicon as a main component and having at least 0.05% by mass of element A formed on the surface of the negative electrode current collector;
In that the element which satisfies the relationship of ≤0.1 | wherein the element A is the element A of the atomic radius (r _A) for the atomic radius (r ₀₎ of a silicon _{| (r A -r 0) /} r 0
A negative electrode for a lithium ion secondary battery characterized by the above-mentioned. The method according to claim 6,
The negative electrode for a lithium ion secondary battery, wherein the element A is at least one element selected from the group consisting of P, Cr, Mn, Fe, Co, Ni, Cu, and As. The method according to claim 6,
Said negative electrode active material layer further contains oxygen or fluorine, The negative electrode for lithium ion secondary batteries characterized by the above-mentioned. The method according to claim 5 or 6,
The negative electrode current collector is copper foil,
An electrolytic roughening treatment is performed on the surface where the active material layer is formed from the copper foil to form a protrusion, and the surface roughness Rz is 1 μm to 6 μm, wherein the negative electrode for a lithium ion secondary battery is used. 10. The method of claim 9,
The surface roughness (Rz) of the surface in which the said active material layer is formed in the said copper foil before electrolytic roughening process is 0.5 micrometer-3 micrometers, The negative electrode for lithium ion secondary batteries characterized by the above-mentioned. A positive electrode capable of storing and releasing lithium ions, a negative electrode according to claim 5 or 6, and a separator disposed between the positive electrode and the negative electrode, the positive electrode, the negative electrode and the separator in an electrolyte having lithium ion conductivity. Lithium-ion secondary battery, characterized in that forming.

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