JP2016219370A - Electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a nonaqueous electrolyte secondary battery, which has superior output and cycle characteristics.SOLUTION: An electrode for a nonaqueous electrolyte secondary battery comprises: a current collector; and a coating film including a composition for electrode formation and formed on the surface of the current collector, provided that the composition contains an active material 1, a conductive assistant, a binder resin 2, and a diluted solvent. The conductive assistant contains acetylene black and vapor-grown carbon fiber 3; the mass of the acetylene black is in a range of 12-20 mass% to that of the active material 1; the mass of the vapor grown carbon fiber 3 is in a range of 2-6 mass% to that of the active material 1; and the mass of the binder resin 2 is in a range of 10-25 mass% to that of the active material 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nonaqueous electrolyte secondary battery electrode, and more particularly to a nonaqueous electrolyte secondary battery electrode capable of improving cycle characteristics.

  In recent years, attention has been focused on Li (lithium) ion secondary batteries as secondary batteries that can be repeatedly charged and discharged with the aim of reducing the amount of oil used and greenhouse gases, and further diversifying and improving the efficiency of the energy base. In particular, application development to electric vehicles, hybrid electric vehicles, and fuel cell vehicles is expected. In an electric vehicle, an improvement in the cruising distance is required, and a higher energy density of the secondary battery will be further required in the future. When attention is paid to the current negative electrode, a graphite electrode is generally used. The theoretical capacity of graphite is 372 mAh / g. On the other hand, Si and Sn have attracted attention in recent years as an active material having a capacity exceeding that of graphite. The theoretical capacity of Si is 4200 mAh / g, and the theoretical capacity of Sn is 990 mAh / g. On the other hand, since Si has a capacity about 11 times that of graphite, the volume change associated with insertion and extraction of Li increases. Specifically, the volume increases by about 4 times due to the occlusion of Li.

  Compared with graphite, an electrode using an active material having a large capacity has a large volume change accompanying charging / discharging, detachment from the electrode due to cutting or pulverization of the conductive path of the electrode, current collector and active material layer There is a risk of peeling. This can be a factor that degrades the cycle characteristics of the battery. On the other hand, Patent Document 1 discloses using sodium alginate as a binder resin.

  Patent Document 2 discloses that sodium alginate is a binder resin that has been conventionally used, such as PVdF (Poly Vinylidene diFluoride), CMC (Carboxy Methyl Cellulose: Carboxymethyl Cellulose) and SBR (Styrene-Butadiene: It is described that it has excellent cycle characteristics compared to (styrene-butadiene rubber). Patent Document 2 discloses that the viscosity of an alginate used as a binder resin is 1% (W / V = Weight / Volume%) aqueous solution having a viscosity at 20 ° C. of 1000 mPa · s to 2000 mPa · s. It is described that excellent output characteristics are exhibited by using a binder resin.

WO2011-140150 Publication JP 2013-161832 A

However, as described in the prior art, as a binder resin, a fluorine-based binder resin such as PVdF has a tendency that it is difficult to obtain an adhesive force due to a weak intermolecular force with an active material. The resistance increases and it works disadvantageously. In addition, in a water-soluble binder resin such as CMC, since the solvent is water, the active material and the conductive material tend to be non-uniformly dispersed, resulting in poor adhesion and poor cycleability, which affects battery performance. In addition, although SBR can provide a strong adhesive force, the double bond of butadiene is easily oxidized, which is disadvantageous for cycle identification. In addition, when sodium alginate is used as the binder resin, the cycle characteristics are improved, but the continuous SEI (Solid Electrolyte Interface) associated with the cycle charge / discharge is still between the electrolyte and the electrode with low electrical conductivity and ion conductivity. The problem is that the cycle maintenance rate accompanying the (substance) generation decreases. The present invention is intended to solve such problems, and an object thereof is to provide a nonaqueous electrolyte secondary battery electrode having excellent output characteristics and cycle characteristics.

  As a result of intensive studies aimed at further improving the cycle characteristics, the present inventor used a binder resin on the surface of an active material or the like by using an acrylic resin or a salt thereof limited to a certain molecular weight region as the binder resin. It has been found that the cycle characteristics can be improved by providing a partially coated layer, incorporating vapor grown carbon fiber therein, and studying the mixing order. Obtained.

In the invention according to claim 1 of the present invention, the surface of the current collector is a non-aqueous electrolyte 2 in which a coating film made of an electrode forming composition containing an active material, a conductive additive, a binder resin, and a diluent solvent is formed. A secondary battery electrode,
The conductive auxiliary agent includes acetylene black and vapor grown carbon fiber,
The mass of acetylene black is in the range of 12 to 20% by mass relative to the active material,
The mass of the vapor grown carbon fiber is in the range of 2 to 6% by mass with respect to the active material,
The binder resin is an electrode for a nonaqueous electrolyte secondary battery, wherein the mass of the binder resin is in the range of 10 to 25% by mass with respect to the active material.

  A second aspect of the present invention is the electrode for a non-aqueous electrolyte secondary battery according to the first aspect, wherein the active material contains SiOx (x is 1.5 or less).

  3. The binder resin according to claim 1 or 2, wherein the binder resin is selected from at least one of polyacrylic acid and polyacrylate having a weight average molecular weight in the range of 20 to 10 million. This is an electrode for a non-aqueous electrolyte secondary battery.

  According to a fourth aspect of the present invention, the binder resin includes a polyacrylic acid or polyacrylate having a weight average molecular weight of less than 1 million and a polyacrylic acid or polyacrylate having a weight average molecular weight of 5 million or more. The electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the electrode is a mixture of

  A fifth aspect of the present invention is the electrode for a nonaqueous electrolyte secondary battery according to any one of the first to fourth aspects, wherein the binder resin constituting the coating film is crosslinked.

  According to the present invention, the surface of the current collector is a nonaqueous electrolyte secondary battery electrode formed of an active material, a conductive additive, and a binder resin, and the binder resin has a weight average molecular weight in the range of 20 to 10 million. By selecting from at least one of polyacrylic acid and polyacrylic acid salt, a strong binder resin network can be formed, and expansion / contraction upon insertion / extraction of lithium ions can be suppressed. In addition, by containing SiOx as an active material, there is an effect of reducing expansion and contraction at the time of lithium ion insertion / extraction, and the capacity retention rate of cycle characteristics is kept high by the synergistic effect of this SiOx and the binder resin. be able to.

It is a schematic diagram which shows the structure of the active material layer with which the electrode of 1st embodiment of this invention is provided.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

  The present invention is an electrode for a nonaqueous electrolyte secondary battery in which a coating film made of an electrode forming composition containing an active material, a conductive auxiliary agent, a binder resin, and a diluent solvent is formed on the surface of a current collector. Specifically, as shown in FIG. 1, an electrode is applied to the current collector in a state where the surface of the active material 1 is coated with a conductive additive containing a binder resin 2, acetylene black, and vapor grown carbon fiber 3. An electrode for a nonaqueous electrolyte secondary battery, which is formed by applying and drying a forming composition.

  The current collector used in the present invention is not particularly limited, and for example, a known copper foil can be used.

  The active material 1 may be a known material, for example, a carbon-based material such as graphite, but preferably contains SiOx. Although Si has a high initial capacity, it has a large expansion / contraction caused by insertion / extraction of lithium ions, and there is a problem in deterioration of cycle characteristics. In contrast, SiOx is preferred because it has a slightly lower initial capacity than Si, but tends to have a higher capacity retention rate associated with the cycle. That is, since SiOx has a smaller expansion / contraction during insertion / extraction of lithium ions than other active materials, the capacity maintenance rate accompanying the cycle can be increased by a synergistic effect with the binder resin described later.

  Moreover, the capacity | capacitance and a cycle maintenance factor become high, so that SiOx is small in a particle size. On the other hand, since aggregation of SiOx accompanying charge / discharge proceeds, graphite (graphite) may be added to SiOx as an active material. In this case, it is possible to suppress aggregation of SiOx particles by supporting SiOx nanoparticles on graphite.

  The conductive auxiliary agent includes acetylene black and vapor grown carbon fiber 3, and the mass ratio of acetylene black is preferably in the range of 12 to 20% by mass with respect to the mass of active material 1. When the amount is less than 12% by mass, the conductive path is cut due to the volume change of the electrode accompanying charging and discharging, and the cycle maintenance ratio is lowered. On the other hand, if it exceeds 20% by mass, the surface area of all the particles in the active material layer increases, so that it is necessary to increase the amount of binder resin necessary for binding, resulting in a decrease in cycle retention. In order to prevent such a problem, it is necessary to mix the vapor grown carbon fiber 3 that can efficiently construct a three-dimensional network.

  The vapor grown carbon fiber 3 is fibrous carbon generated from the vapor phase represented by carbon nanofiber (CNF) and carbon nanotube (CNT), and the average fiber diameter is on the order of several tens to several hundreds Nao. The fiber length is preferably several tens of microns or less. Such a vapor grown carbon fiber 3 can form a three-dimensional network by coexistence with a binder resin, and has the effect of relaxing expansion and contraction associated with insertion / extraction of thium ions.

  The mass ratio of the vapor grown carbon fiber 3 is preferably in the range of 2 to 6% by mass with respect to the mass of the active material 1. When the amount is less than 2% by mass, the relative amount of vapor grown carbon fiber 3 is small and a three-dimensional network effect cannot be obtained. Another reason is that it is difficult to form a network because the number of stirring contacts during dispersion is large and the vapor phase growth part is lost. Further, when the mass ratio of the vapor grown carbon fiber 3 is more than 6% by mass with respect to the mass of the active material 1, the performance such as the cycle maintenance rate is lowered for the same reason as when a large amount of acetylene black is added. This is because the viscosity of the paint is high and it is difficult to apply a lot of streaks.

The mass ratio of the binder resin 2, which is one of the features of the present invention, is in the range of 10% by mass to 25% by mass with respect to the mass of the active material 1. This is because when the mass ratio of the binder resin 2 is less than 15% by mass with respect to the mass of the active material 1, the resistance value of the coating film is lowered but lacks aggregation and flexibility, resulting in a low cycle maintenance rate. It is. Furthermore, when the mass ratio of the binder resin 2 is more than 25% by mass with respect to the mass of the active material 1, the capacity per electrode mass is reduced, or the electric resistance of the coating film is increased, resulting in a loss. .

  In particular, the binder resin 2 is preferably an acrylic resin, and examples thereof include polyacrylic acid and polyacrylic acid salts (for example, polyacrylic acid sodium salt). These have a higher proportion of carboxylic acid groups per repeating unit than conventional CMCs. For this reason, an acrylic resin is localized (partially covered) on the surface of SiOx of the active material 1. When an acrylic resin is mixed, a good ion conductive film can be formed.

  Furthermore, since the coating layer is mechanically reinforced by adding the vapor grown carbon fiber 3 to the conductive aid described above, it is possible to form a coating layer that does not easily crack even after repeated charge and discharge. It becomes possible. That is, the surface of the active material 1 is coated with an acrylic resin, or the vapor grown carbon fiber 3 is contained or adhered to the mixed portion. As a result, it becomes possible to provide a polycarboxylic acid-coated Si-based active material 1 containing vapor grown carbon fiber 3 and a non-aqueous electrolyte secondary battery electrode using this active material 1. It becomes possible to provide the electrode for nonaqueous electrolyte secondary batteries which can improve this.

  Further, by using polyacrylic acid or polyacrylic acid salt as the acrylic resin, the acid state can be easily obtained, so that the binder resin itself is flexible in the travel of electrons. Furthermore, stability and a softness | flexibility can be made to coexist by making the weight average molecular weight of this acrylic resin into 20-10 million. When the weight average molecular weight is less than 200,000, the material is familiar with the active material and the conductive additive, and is easy to coat, but lacks flexibility in charge and discharge expansion and contraction. In addition, if the weight average molecular weight exceeds 10 million, it can flexibly cope with the expansion and contraction of the coating film, but it cannot be evenly dispersed in the active material and the conductive auxiliary agent, and can be localized to adhere. Will fall. Preferably, the above-mentioned stabilization is further increased by mixing an acrylic resin having a weight average molecular weight of 200 to 1,000,000 and an acrylic resin having 5 to 10 million. In particular, the acrylic resin on the low molecular weight side is hard and brittle with a relatively high Young's modulus, whereas the acrylic resin on the high molecular weight side has a low Young's modulus and high rigidity.

  Furthermore, when the coating material is prepared, the binder resin on the surface of the powder is present by mixing the low molecular weight binder resin with the active material and the conductive auxiliary agent first. The binder resin can be well mixed and dispersed. In some cases, when preparing the coating as described above, the binder resin is cross-linked to obtain a flexible and rigid film, and the film structure changes while absorbing expansion and contraction in the charge / discharge cycle. Can be minimized. Also, increase the absolute amount of carboxylic acid, promote the dehydration reaction of acid-base, etc., copolymerize and mix with divalent or higher polyvalent carboxylic acid to increase the acid value and increase the conductivity of the film Is also possible.

  The solvent of the electrolyte used for the non-aqueous electrolyte secondary battery includes low-viscosity chain carbonates such as dimethyl carbonate and diethyl carbonate, and cyclic carbonates having a high dielectric constant such as ethylene carbonate, propylene carbonate, and butylene carbonate, γ -Butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, methyl propionate, vinylene carbonate, dimethylformamide, sulfolane, and mixed solvents thereof can be used. is there.

The electrolyte contained in the electrolytic solution is not particularly limited, and LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiI, LiAlCl ₄ , and the like. Mixtures and the like can be used. Preferably, a lithium salt obtained by mixing one or more of LiBF ₄ and LiPF ₆ is preferable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited by an Example.

<Example 1>
As a binder resin, 120 g of PVdF in NMP (N-methylpyrrolidone, N-methyl-2-pyrrolidone) solution (manufactured by Kureha, # 7208), 24 g of acetylene black (AB: Acetylene Black, manufactured by Denki Kagaku Kogyo, HS −100) and 41 g of NMP were added, and the mixture was stirred with Hibismix for 10 minutes.
Subsequently, 144 g of NCM (nickel / manganese / cobalt ternary material, manufactured by Nippon Kagaku Sangyo) and 337 g of LMO (lithium manganate Type-F, manufactured by Mitsui Mining & Smelting) were added as active materials and stirred for 10 minutes. did. After confirming that the ink was in a kneaded state, it was further kneaded for 10 minutes. Then, NMP was added and diluted so that NV (solid content ratio) might be 60%, and the positive electrode slurry was obtained.

Further, the obtained positive electrode slurry was applied to a current collector. As the current collector, an Al foil having a thickness of 15 μm was used. The positive electrode slurry was applied with a doctor blade so as to have a basis weight of 18.8 mg / cm ² . Then, after drying with 120 degreeC hot air for 10 minutes, it pressed so that a density might be set to 2.5 g / cm < ³ >, and the positive electrode was obtained.

Next, as the negative electrode side, the active material, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium Co., Ltd.), 2.16 g of graphite (Gr: Graphite, high rate SMG for SBR, Hitachi Chemical) Selected weight, 1.07 g of acetylene black, 0.27 g of vapor grown carbon fiber (Showa Denko KK: VGCF), 1.62 g of polyacrylic acid (made by Nippon Shokubai Co., Ltd .: weight) In addition to water with an average molecular weight of 1 million) and 49.50 g, the mixture pre-dispersed with a disperser (manufactured by SMT) is main-dispersed with Filmix (registered trademark) (manufactured by Primics) to form a negative electrode slurry Obtained. And the obtained negative electrode slurry was apply | coated to the electrical power collector. The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Then, after drying with 80 degreeC hot air for 10 minutes, it pressed so that a density might be set to 1.2 g / cm < ³ >, and the negative electrode was obtained.

<Example 2>
About the positive electrode side, it produced similarly to Example 1. FIG.
On the negative electrode side, a similar production method is used, but the active material, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium) and 2.16 g of graphite (Gr: Graphite, SBR) High-rate SMG, manufactured by Hitachi Chemical Co., Ltd., weighed 1.07 g of acetylene black, 0.27 g of vapor grown carbon fiber (VGCF), and 0.30 g of polyacrylic acid (manufactured by Nippon Shokubai Co., Ltd .: In addition to 49.50 g of water (weight average molecular weight: 800,000) and pre-dispersed with a disperser (manufactured by SMT), 1.32 g of sodium acrylate (manufactured by Nippon Shokubai: weight average molecular weight: 5 million) In addition, the mixture was redispersed, and the liquid was main-dispersed with Filmix (registered trademark) (manufactured by Primex) to obtain a negative electrode slurry. And the obtained negative electrode slurry was apply | coated to the electrical power collector. The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Then, after drying with 80 degreeC hot air for 10 minutes, it pressed so that a density might be set to 1.2 g / cm < ³ >, and the negative electrode was obtained.

<Example 3>
About the positive electrode side, it produced similarly to Example 1. FIG.
On the negative electrode side, a similar production method is used, but the active material, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium) and 2.16 g of graphite (Gr: Graphite, SBR) High-rate SMG, manufactured by Hitachi Chemical Co., Ltd.), 1.07 g of acetylene black, 0.27 g of vapor grown carbon fiber (VGCF), 0.3 g of acrylic acid and maleic acid copolymer In addition to 49.50 g of water (manufactured by Nippon Shokubai Co., Ltd .: weight average molecular weight: 800,000), pre-dispersed with a disperser (manufactured by SMT), followed by 1.32 g of sodium acrylate (manufactured by Nippon Shokubai) : The weight average molecular weight: 5 million) was added and re-dispersed, and this mixture was main-dispersed with Filmix (registered trademark) (manufactured by Primex) to obtain a negative electrode slurry. And the obtained negative electrode slurry was apply | coated to the electrical power collector. The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Then, after drying with 80 degreeC hot air for 10 minutes, it pressed so that a density might be set to 1.2 g / cm < ³ >, and the negative electrode was obtained.

<Comparative Example 1>
The positive electrode side was produced in the same manner as in Example 1.
On the negative electrode side, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium) and 2.16 g of graphite (Gr, high rate SMG for SBR, manufactured by Hitachi Chemical Co., Ltd.) 49.50 g of 1.07 g of acetylene black (AB), 0.27 g of vapor grown carbon fiber (VGCF), and 0.68 g of polyacrylic acid (manufactured by Nippon Shokubai Co., Ltd .: weight average molecular weight 1 million). In addition to the above water, the mixed liquid pre-dispersed with a disperser (manufactured by SMT) was main-dispersed with a fill mix (manufactured by Primics) to obtain a negative electrode slurry. And the obtained negative electrode slurry was apply | coated to the electrical power collector. The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.40 mg / cm ² . Then, after drying at 80 degreeC for 30 minutes, it pressed so that a density might be 1.2 g / cm < ³ >, and the negative electrode was obtained. Using the electrode obtained as described above, a coin cell was prepared, and a cycle evaluation similar to that of the example of the present invention was performed.

<Comparative example 2>
The positive electrode side was produced in the same manner as in Example 1.
On the negative electrode side, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium) and 2.16 g of graphite (Gr, high rate SMG for SBR, manufactured by Hitachi Chemical Co., Ltd.) 49.50 g of 1.07 g of acetylene black (AB), 0.27 g of vapor grown carbon fiber (VGCF) and 2.27 g of polyacrylic acid (manufactured by Nippon Shokubai Co., Ltd .: weight average molecular weight: 1,000,000) In addition to the above water, the mixed liquid pre-dispersed with a disperser (manufactured by SMT) was main-dispersed with a fill mix (manufactured by Primics) to obtain a negative electrode slurry. And the obtained negative electrode slurry was apply | coated to the electrical power collector. The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.40 mg / cm ² . Then, after drying at 80 degreeC for 30 minutes, it pressed so that a density might be 1.2 g / cm < ³ >, and the negative electrode was obtained. Using the electrode obtained as described above, a coin cell was prepared, and a cycle evaluation similar to that of the example of the present invention was performed.

<Comparative Example 3>
The positive electrode side was produced in the same manner as in Example 1.
Next, as the negative electrode side, the active material, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium Co., Ltd.), 2.16 g of graphite (Gr: Graphite, high rate SMG for SBR, Hitachi Chemical) Selected weight, 1.07 g of acetylene black, 0.27 g of vapor grown carbon fiber (VGCF), 1.62 g of polyacrylic acid (manufactured by Nippon Shokubai Co., Ltd .: weight average molecular weight: 50,000) ) Was added to 49.50 g of water and the pre-dispersed liquid mixture with a disperser (manufactured by SMT) was main-dispersed with Filmix (registered trademark) (manufactured by Primix) to obtain a negative electrode slurry. And the obtained negative electrode slurry was apply | coated to the electrical power collector.
The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Then, after drying with 80 degreeC hot air for 10 minutes, it pressed so that a density might be set to 1.2 g / cm < ³ >, and the negative electrode was obtained.

<Comparative example 4>
The positive electrode side was produced in the same manner as in Example 1.
Next, as the negative electrode side, the active material, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium Co., Ltd.), 2.16 g of graphite (Gr: Graphite, high rate SMG for SBR, Hitachi Chemical) Selected weight, 1.07 g of acetylene black, 0.27 g of vapor grown carbon fiber (VGCF), and 1.62 g of polyacrylic acid (manufactured by Nippon Shokubai Co., Ltd .: weight average molecular weight: 15 million) ) Was added to 49.50 g of water and the pre-dispersed liquid mixture with a disperser (manufactured by SMT) was main-dispersed with Filmix (registered trademark) (manufactured by Primix) to obtain a negative electrode slurry. And the obtained negative electrode slurry was apply | coated to the electrical power collector. The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Then, after drying with 80 degreeC hot air for 10 minutes, it pressed so that a density might be set to 1.2 g / cm < ³ >, and the negative electrode was obtained.

<Comparative Example 5>
The positive electrode side was produced in the same manner as in Example 1.
On the negative electrode side, a similar production method is used, but the active material, 5.39 g of median diameter (d50) of 6.6 μm SiO (manufactured by Osaka Titanium) and 2.16 g of graphite (Gr: Graphite, SBR) High-rate SMG, manufactured by Hitachi Chemical Co., Ltd., weighed 1.07 g of acetylene black, 0.27 g of vapor grown carbon fiber (VGCF), and 1.32 g of sodium acrylate (manufactured by Nippon Shokubai Co., Ltd .: (Weight-average molecular weight: 5 million) and 9.50 g of water and pre-dispersed, then 0.3 g of a copolymer of acrylic acid and maleic acid (manufactured by Nippon Shokubai Co., Ltd .: weight-average molecular weight: 800,000) is added again. Dispersed, and further mixed and dispersed, was finally dispersed with Filmix (registered trademark) (manufactured by Primex) to obtain a negative electrode slurry. And the obtained negative electrode slurry was apply | coated to the electrical power collector. The current collector was a copper foil having a thickness of 12 μm. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Then, after drying with 80 degreeC hot air for 10 minutes, it pressed so that a density might be set to 1.2 g / cm < ³ >, and the negative electrode was obtained.

  The conditions relating to the active material, the conductive additive, and the binder resin in the negative electrode (nonaqueous electrolyte secondary battery electrode) forming compositions used in Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1 below.

<Production of coin cell>
Coin cells were produced using the negative electrodes and positive electrodes obtained in Examples 1 to 3 and Comparative Examples 1 to 5.
The coin cell was a 2032 type, and the basic configuration was an electrode and a separator (manufactured by Cellguard: Model No. 2200) punched into a disk having a diameter of 15 mm and a positive electrode having a diameter of 13.5 mm, respectively. The electrolytic solution was prepared by mixing 1 mol of LiPF6 into a solution obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DMC) containing 2 wt% of VC (Vinylene Carbonate, vinylene carbonate) at a ratio of 3: 7 (v / v). What was added so that it might become was used.
<Cycle test>
A cycle test was performed on the coin cell produced above under the following charge / discharge conditions.
Charging: 366 mAg / (active material weight), discharging: 1829 mAg / (active material weight), charging and discharging were repeated 100 times in a voltage range of 3 V to 4.25 V. The evaluation results are shown in Table 2 below.

<Comparison result>
The products of the present invention obtained in Examples 1 to 3 showed good results of 80% or more in the initial capacity, particularly the capacity retention rate after the cycle test. On the other hand, the comparative products obtained in Comparative Examples 1 to 5 were in the range of 60 to 80%, especially in the capacity retention ratio after the cycle test, and showed a result of a level having a problem in practicality. Among them, the product of the present invention of Example 3 is
The best values were shown in the initial capacity and the capacity maintenance ratio after the cycle test. From this, it can be confirmed that the conductive material contains acetylene black and vapor grown carbon fiber, and the mixing ratio of the binder resin, the weight average molecular weight of the binder resin, etc. are optimized, and the present invention is appropriate. It was confirmed that there was.

  Further, in Example 1 to Example 3, when the surface of the electrode before the cycle was observed by SEM, the surface of the active material was covered with a binder resin as shown in FIG. It was confirmed that the binder resin 2 was mixed. From this, it is considered that the shape of FIG. 1 suppresses the continuous generation of SEI accompanying the cycle and improves the cycle maintenance rate.

  The electrode for a non-aqueous electrolyte secondary battery obtained by the present invention is a power source for various portable electronic devices, a storage battery for driving an electric vehicle or the like that requires a high energy density, and various energy such as solar energy and wind power generation. It is used for an electrode of a power storage device or a storage power source of a household electric appliance.

  DESCRIPTION OF SYMBOLS 1 ... Active material, 2 ... Binder resin, 3 ... Vapor grown carbon fiber

Claims (5)

The surface of the current collector is an electrode for a nonaqueous electrolyte secondary battery in which a coating film made of an electrode forming composition containing an active material, a conductive additive, a binder resin, and a diluent solvent is formed,
The conductive auxiliary agent includes acetylene black and vapor grown carbon fiber,
The mass of acetylene black is in the range of 12 to 20% by mass relative to the active material,
The mass of the vapor grown carbon fiber is in the range of 2 to 6% by mass with respect to the active material,
The electrode for a non-aqueous electrolyte secondary battery, wherein the mass of the binder resin is in the range of 10 to 25 mass% with respect to the active material.   The electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the active material contains SiOx (x is 1.5 or less).   3. The non-aqueous electrolyte according to claim 1, wherein the binder resin is selected from at least one of polyacrylic acid and polyacrylic acid salt having a weight average molecular weight in the range of 200 to 10 million. Secondary battery electrode.   The binder resin comprises a mixture of polyacrylic acid or polyacrylate having a weight average molecular weight of less than 1 million and polyacrylic acid or polyacrylate having a weight average molecular weight of 5 million or more. The electrode for nonaqueous electrolyte secondary batteries according to any one of claims 1 to 3.   The electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein a binder resin constituting the coating film is crosslinked.

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