JP6801167B2 - Electrodes for non-aqueous electrolyte secondary batteries - Google Patents

Description

The present invention relates to an electrode for a non-aqueous electrolyte secondary battery, and more specifically, an electrode for a non-aqueous electrolyte secondary battery capable of improving cycle characteristics.

In recent years, Li (lithium) ion secondary batteries have been attracting attention as rechargeable and dischargeable secondary batteries with the aim of reducing oil consumption and greenhouse gases, and further diversifying and improving the efficiency of energy infrastructure. In particular, it is expected to be applied to electric vehicles, hybrid electric vehicles and fuel cell vehicles. In electric vehicles, improvement in cruising range is required, and in the future, higher energy density of secondary batteries will be further required. Focusing on the current negative electrode, graphite electrodes are generally used. The theoretical capacity of graphite is 372 mAh / g. On the other hand, Si and Sn have been attracting attention in recent years as active materials having a capacity higher than 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 due to occlusion and release of Li is also large. Specifically, the storage of Li increases the volume by about 4 times.

Electrodes using active materials, which have a larger capacity than graphite, undergo large volume changes due to charging and discharging, desorption from the electrodes due to cutting of the conductive path of the electrodes and pulverization, current collectors and active material layers. There is a risk of peeling. This may be a factor that deteriorates the cycle characteristics of the battery. On the other hand, Patent Document 1 discloses that sodium alginate is used as the binder resin.

Further, in Patent Document 2, sodium alginate is used as a binder resin conventionally used, such as PVdF (Poly Vinylidene diFluoride: polyvinylidene fluoride), CMC (Carboxy Metyl Cellulose: Carboxymethyl Cellulose) and SBR (Styrene-Budai). It is described that it has better cycle characteristics than styrene-butadiene rubber). Further, in Patent Document 2, as the viscosity of alginate used as a binder resin, the viscosity of a 1% (W / V = Weight / Volume%) aqueous solution at 20 ° C. is within the range of 1000 mPa · s or more and 2000 mPa · s or less. It is stated that the use of a binder resin exhibits excellent output characteristics.

WO2011-140150 Japanese Unexamined Patent Publication No. 2013-161832

However, as a binder resin, as described in the prior literature, a fluorine-based binder resin such as PVdF tends to have a weak intermolecular force with an active material, so that it tends to be difficult to obtain an adhesive force. Target resistance increases and it works against you. Further, 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, the adhesion is poor, the cycle performance is poor, and the battery performance is affected. Further, although SBR can obtain a strong adhesive force, it is disadvantageous for cycle identification because the double bond of butadiene is easily oxidized. In addition, although the use of sodium alginate in the binder resin improves the cycle characteristics, the continuous SEI (Solid Electrolyte Interface: between the electrolyte and the electrode, which has low electrical conductivity and ionic conductivity) due to cycle charging and discharging is still observed. The problem arises that the cycle maintenance rate associated with the production of the substance) decreases. An object of the present invention is to solve such a problem, and an object of the present invention is to provide an electrode for a non-aqueous electrolyte secondary battery having excellent output characteristics and cycle characteristics.

As a result of diligent studies aimed at further improving the cycle characteristics, the present inventor used an acrylic resin limited to a certain molecular weight range or a salt thereof as the binder resin to apply the binder resin to the surface of the active material or the like. We have found that it is possible to improve the cycle characteristics by providing a partially coated layer, containing vapor-phase carbon fibers therein, and examining the mixing order, etc. Obtained.

The invention according to claim 1 of the present invention is an electrode for a non-aqueous electrolyte secondary battery in which a coating film containing an electrode-forming composition is formed on the surface of a current collector, and the electrode-forming composition is , Active material, conductive auxiliary agent, binder resin, the active material contains SiOx (x is 1.5 or less), the conductive auxiliary agent contains acetylene black and vapor phase carbon fiber, and the acetylene black. The mass is in the range of 12 to 20% by mass with respect to the active material, the mass of the vapor phase carbon fiber is in the range of 2 to 6% by mass with respect to the active material, and the binder resin has a weight average molecular weight of 20. The binder resin containing at least a polyacrylic acid or polyacrylic acid salt in the range of 10,000 or more and less than 1 million and a polyacrylic acid or polyacrylic acid salt having a weight average molecular weight in the range of 5 million or more and less than 10 million. The electrode for a non-aqueous electrolyte secondary battery is characterized in that the mass is in the range of 10 to 25% by mass with respect to the active material.

In the invention according to claim 2 of the present invention, the binder resin comprises a polyacrylic acid or polyacrylic acid salt having a weight average molecular weight in the range of 200,000 or more and less than 1 million, and a weight average molecular weight of 5 million or more and less than 10 million. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode is mixed with polyacrylic acid or polyacrylate in the range of.

The invention according to claim 3 of the present invention is a non-aqueous electrolyte secondary battery according to claim 1 or 2 before fang inductor resin is characterized in that it is crosslinked.

According to the present invention, in a non-aqueous electrolyte secondary battery electrode formed of an active material, a conductive auxiliary agent, and a binder resin on the surface of the current collector, the weight average molecular weight of the binder resin is in the range of 200 to 10 million. A strong binder resin network can be formed by selecting from at least one of a certain polyacrylic acid and polyacrylic acid salt, and expansion and contraction at the time of insertion / removal of lithium ions can be suppressed. Further, by containing SiOx as an active material, there is an effect of reducing expansion and contraction at the time of insertion / detachment of lithium ions, and the synergistic effect of this SiOx and the binder resin keeps the capacity retention rate of cycle characteristics high. be able to.

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

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

The present invention is an electrode for a non-aqueous electrolyte secondary battery in which a coating film composed of an electrode-forming composition containing an active material, a conductive auxiliary agent, a binder resin, and a diluting solvent is formed on the surface of a current collector. Specifically, as shown in FIG. 1, the surface of the active material 1 is coated with the conductive auxiliary agent containing the binder resin 2, acetylene black, and the vapor phase carbon fiber 3, and the electrode is attached to the current collector. It is an electrode for a non-aqueous electrolyte secondary battery, which is formed by applying a forming composition and drying it.

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

As the active material 1, a known material, for example, a carbon-based material such as graphite can be used, but it is preferable that the active material 1 contains SiOx. Although Si has a high initial capacity, it has a large expansion and contraction due to the insertion / removal of lithium ions, and has a problem of deterioration of cycle characteristics. On the other hand, SiOx is a little inferior to Si in the initial capacity, but is preferable because the capacity retention rate with the cycle tends to be high. That is, since SiOx has a smaller expansion and contraction at the time of insertion / removal of lithium ions than other active materials, the capacity retention rate associated with the cycle can be increased by the synergistic effect with the binder resin described later.

Further, the smaller the particle size of SiOx, the higher the capacity and cycle retention rate. On the other hand, since the aggregation of SiOx progresses with charging and discharging, graphite may be added to SiOx as an active material. In this case, by supporting the SiOx nanoparticles on the graphite, it is possible to suppress the aggregation of the SiOx particles.

The conductive auxiliary agent contains acetylene black and the vapor phase 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 the active material 1. If it is less than 12% by mass, the conductive path is cut due to the volume fluctuation of the electrode due to charging and discharging, and the cycle maintenance rate 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 required for binding, and as a result, the cycle maintenance rate is lowered. In order to prevent such a problem, it is necessary to mix the vapor phase carbon fiber 3 which makes it easy to efficiently and three-dimensionally construct a network.

Gas phase method carbon fiber 3 is fibrous carbon produced from a gas phase represented by carbon nanofibers (CNFs) and carbon nanotubes (CNTs), and has an average fiber diameter of several tens to several hundreds of nao orders. Fiber lengths of several tens of microns or less are preferable. Such a vapor phase carbon fiber 3 can form a three-dimensional network by coexisting with the binder resin, which has an effect of alleviating expansion and contraction due to insertion / detachment of tium ions.

The mass ratio of the vapor phase carbon fiber 3 is preferably in the range of 2 to 6% by mass with respect to the mass of the active material 1. If it is less than 2% by mass, the relative amount of the vapor phase carbon fiber 3 is small and the three-dimensional network effect cannot be obtained. In addition, it is difficult to form a network because the number of stirring contacts during dispersion is large and the vapor phase growth portion is lost. Further, when the mass ratio of the vapor phase 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 deteriorates for the same reason as when a large amount of acetylene black is added. This is because the paint has a high viscosity and many streaks are drawn, making it difficult to apply.

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 or more and 25% by mass or less with respect to the mass of the active material 1. This is because if 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 decreases, but the aggregation and flexibility are lacking, and the cycle maintenance rate becomes low. Is. Further, if 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 decreases, and the electric resistance of the coating film increases, resulting in loss. ..

In particular, as the binder resin 2, an acrylic resin is preferable, and examples thereof include polyacrylic acid and polyacrylic acid salt (for example, sodium polyacrylate). These have a higher ratio of carboxylic acid groups per repeating unit than the conventionally used CMC, and for this reason, the acrylic acid resin is localized (partially coated) on the surface of SiOx of the active material 1. When an acrylic acid-based resin is mixed, a good ionic conductive film can be formed.

Further, since the coating layer is mechanically reinforced by adding the vapor phase carbon fiber 3 to the conductive auxiliary agent described above, it is possible to form a coating layer in which cracks are unlikely to occur even if charging and discharging are repeated. It will be possible. That is, the surface of the active material 1 is coated with an acrylic resin, or the vapor phase carbon fiber 3 is contained or adhered to the mixed portion. This makes it possible to provide a polycarboxylic acid-coated Si-based active material 1 containing the vapor phase carbon fiber 3 and an electrode for a non-aqueous electrolyte secondary battery using the active material 1, and thus has cycle characteristics. It becomes possible to provide an electrode for a non-aqueous electrolyte secondary battery capable of improving the above.

Further, by using polyacrylic acid or polyacrylic acid salt as the acrylic resin, an acid state can be easily obtained, so that the binder resin itself is flexible in the exchange of electrons. Furthermore, by setting the weight average molecular weight of this acrylic acid-based resin to 200 to 10 million, stability and flexibility can coexist. If the weight average molecular weight is less than 200,000, it becomes familiar with active materials and conductive auxiliaries and is easy to coat, but lacks flexibility in expansion and contraction of charge and discharge. In addition, when the weight average molecular weight exceeds 10 million, the coating film can flexibly respond to expansion and contraction, but cannot be uniformly scattered on the active material and the conductive auxiliary agent, and localization causes adhesion and the like. Will fall. Preferably, by mixing an acrylic resin having a weight average molecular weight of 200 to 1 million and an acrylic resin having a weight average molecular weight of 5 to 10 million, the above-mentioned stabilization is further increased. In particular, the acrylic acid-based resin on the low molecular weight side is hard and brittle with a relatively high Young's modulus, while the acrylic acid-based resin on the high molecular weight side has a low Young's modulus and high rigidity.

Further, when the paint is prepared, the binder resin on the low molecular weight side is mixed with the active material or the conductive auxiliary agent first, so that the binder resin is present on the surface of the powders, and then the binder resin on the high molecular weight side is dispersed. It can also be mixed and dispersed well with the binder resin. Further, in some cases, when the paint is produced as described above, the binder resin is crosslinked to obtain a flexible rigid film, and the film structure changes while absorbing expansion and contraction in the charge / discharge cycle. Can be minimized. In addition, copolymerization or mixing with a divalent or higher polyvalent carboxylic acid for increasing the absolute amount of carboxylic acid, promoting the dehydration reaction of acid-base, increasing the acid value and increasing the conductivity of the film. Is also possible.

Solvents of the electrolytic solution used for the non-aqueous electrolyte secondary battery include 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, and γ. -Butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, 1,3-dioxolane, methyl acetate, methyl propionate, vinylene carbonate, dimethylformamide, sulfolane and a mixed solvent 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, etc., and their It is possible to use a mixture or the like. Preferably, a lithium salt obtained by mixing one or more of LiBF ₄ and LiPF ₆ is preferable.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to Examples.

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

Further, the obtained positive electrode slurry was applied to the 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 . Subsequently, after drying with hot air at 120 ° C. for 10 minutes, a positive electrode was obtained by pressing so that the density was 2.5 g / cm ³ .

Next, as the negative electrode side, SiO (manufactured by Osaka Titanium Co., Ltd.) having an active material of 5.39 g and a median diameter (d50) of 6.6 μm, and graphite (Gr: Graphite, high-rate SMG for SBR, Hitachi Chemical) of 2.16 g. Weighed 1.07 g of acetylene black, 0.27 g of vapor phase carbon fiber (Showa Denko: VGCF), and 1.62 g of polyacrylic acid (Nippon Catalyst: Weight). In addition to (average molecular weight: 1 million) and 49.50 g of water, the mixed solution pre-dispersed with a disperser (manufactured by SMT) is fully dispersed with Philmix (registered trademark) (manufactured by Primix) to form a negative electrode slurry. Obtained. Then, the obtained negative electrode slurry was applied to the current collector. A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Subsequently, after drying with hot air at 80 ° C. for 10 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ .

<Example 2>
The positive electrode side was produced in the same manner as in Example 1.
The same method is used for the negative electrode side halfway, but the active material is 5.39 g of SiO (manufactured by Osaka Titanium) with a median diameter (d50) of 6.6 μm and 2.16 g of graphite (Gr: Graphite, SBR). High-rate SMG for use, manufactured by Hitachi Kasei Co., Ltd.) Weighed, 1.07 g of acetylene black, 0.27 g of vapor phase carbon fiber (VGCF), and 0.30 g of polyacrylic acid (manufactured by Nippon Catalyst Co., Ltd .: Add 49.50 g of water to 49.50 g of water (weight average molecular weight: 800,000), pre-disperse with a disperser (manufactured by SMT), and then add 1.32 g of sodium acrylate (manufactured by Nippon Catalyst: weight average molecular weight: 5 million). In addition, it was redispersed, and the liquid was mainly dispersed with Fillmix (registered trademark) (manufactured by Primix) to obtain a negative electrode slurry. Then, the obtained negative electrode slurry was applied to the current collector. A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Subsequently, after drying with hot air at 80 ° C. for 10 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ .

<Example 3>
The positive electrode side was produced in the same manner as in Example 1.
The same method is used for the negative side, but the active material is 5.39 g of SiO (manufactured by Osaka Titanium) with a median diameter (d50) of 6.6 μm and 2.16 g of graphite (Gr: Graphite, SBR). High-rate SMG for use, manufactured by Hitachi Kasei Co., Ltd.) was selected and weighed, and 1.07 g of acetylene black, 0.27 g of vapor phase carbon fiber (VGCF), and 0.3 g of a copolymer of acrylic acid and maleic acid were selected. (Made by Nippon Catalyst: Weight average molecular weight: 800,000), add 49.50 g of water, pre-disperse with a disperser (manufactured by SMT), and then 1.32 g of sodium acrylic acid salt (manufactured by Nippon Catalyst). : Weight average molecular weight: 5 million) was added and redispersed, and the mixed solution was main-dispersed with Fillmix (registered trademark) (manufactured by Primix) to obtain a negative electrode slurry. Then, the obtained negative electrode slurry was applied to the current collector. A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Subsequently, after drying with hot air at 80 ° C. for 10 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ .

<Comparative example 1>
The positive electrode side was produced in the same manner as in Example 1.
On the negative electrode side, as active materials, 5.39 g of SiO (manufactured by Osaka Titanium) with a median diameter (d50) of 6.6 μm and 2.16 g of graphite (Gr, high-rate SMG for SBR, manufactured by Hitachi Kasei). , 1.07 g of acetylene black (AB), 0.27 g of vapor phase carbon fiber (VGCF), and 0.68 g of polyacrylic acid (manufactured by Nippon Catalyst Co., Ltd .: weight average molecular weight 1 million), 49.50 g. The mixed solution pre-dispersed with a disperser (manufactured by SMT) was mainly dispersed with a fill mix (manufactured by Primex) in addition to the water of No. Then, the obtained negative electrode slurry was applied to the current collector. A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.40 mg / cm ² . Subsequently, after drying at 80 ° C. for 30 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ . A coin cell was prepared using the electrodes obtained as described above, 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, as active materials, 5.39 g of SiO (manufactured by Osaka Titanium) with a median diameter (d50) of 6.6 μm and 2.16 g of graphite (Gr, high-rate SMG for SBR, manufactured by Hitachi Kasei). , 1.07 g of acetylene black (AB), 0.27 g of vapor phase carbon fiber (VGCF) and 2.27 g of polyacrylic acid (manufactured by Nippon Catalyst Co., Ltd .: weight average molecular weight: 1 million), 49.50 g. The mixed solution pre-dispersed with a disperser (manufactured by SMT) was mainly dispersed with a fill mix (manufactured by Primex) in addition to the water of No. Then, the obtained negative electrode slurry was applied to the current collector. A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.40 mg / cm ² . Subsequently, after drying at 80 ° C. for 30 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ . A coin cell was prepared using the electrodes obtained as described above, 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, SiO (manufactured by Osaka Titanium Co., Ltd.) having an active material of 5.39 g and a median diameter (d50) of 6.6 μm, and graphite (Gr: Graphite, high-rate SMG for SBR, Hitachi Chemical) of 2.16 g. Weighed 1.07 g of acetylene black, 0.27 g of vapor phase carbon fiber (VGCF), and 1.62 g of polyacrylic acid (manufactured by Nippon Catalyst Co., Ltd .: weight average molecular weight: 50,000). ) Was added to 49.50 g of water, and the mixed solution pre-dispersed with a disperser (manufactured by SMT) was mainly dispersed with Fillmix (registered trademark) (manufactured by Primix) to obtain a negative electrode slurry. Then, the obtained negative electrode slurry was applied to the current collector.
A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Subsequently, after drying with hot air at 80 ° C. for 10 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ .

<Comparative example 4>
The positive electrode side was produced in the same manner as in Example 1.
Next, as the negative electrode side, SiO (manufactured by Osaka Titanium Co., Ltd.) having an active material of 5.39 g and a median diameter (d50) of 6.6 μm, and graphite (Gr: Graphite, high-rate SMG for SBR, Hitachi Chemical) of 2.16 g. Weighed 1.07 g of acetylene black, 0.27 g of vapor phase carbon fiber (VGCF), and 1.62 g of polyacrylic acid (manufactured by Nippon Catalyst Co., Ltd .: weight average molecular weight: 15 million). ) Was added to 49.50 g of water, and the mixed solution pre-dispersed with a disperser (manufactured by SMT) was mainly dispersed with Fillmix (registered trademark) (manufactured by Primix) to obtain a negative electrode slurry. Then, the obtained negative electrode slurry was applied to the current collector. A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Subsequently, after drying with hot air at 80 ° C. for 10 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ .

<Comparative example 5>
The positive electrode side was produced in the same manner as in Example 1.
The same method is used for the negative side, but the active material is 5.39 g of SiO (manufactured by Osaka Titanium) with a median diameter (d50) of 6.6 μm and 2.16 g of graphite (Gr: Graphite, SBR). High-rate SMG for use, manufactured by Hitachi Kasei Co., Ltd.) Weighed, 1.07 g of acetylene black, 0.27 g of vapor phase carbon fiber (VGCF), and 1.32 g of sodium acrylate (manufactured by Nippon Catalyst: Co., Ltd .: (Weight average molecular weight: 5 million) is pre-dispersed by adding 9.50 g of water, and then 0.3 g of a copolymer of acrylic acid and maleic acid (manufactured by Nippon Catalyst Co., Ltd .: weight average molecular weight: 800,000) is added and re-dispersed. The dispersed product was further dispersed and further dispersed by Fillmix (registered trademark) (manufactured by Primix Co., Ltd.) to obtain a negative electrode slurry. Then, the obtained negative electrode slurry was applied to the current collector. A copper foil having a thickness of 12 μm was used as the current collector. The negative electrode slurry was applied with a doctor blade so as to have a basis weight of 1.32 mg / cm ² . Subsequently, after drying with hot air at 80 ° C. for 10 minutes, a negative electrode was obtained by pressing so that the density was 1.2 g / cm ³ .

The conditions for the active material, the conductive auxiliary agent, and the binder resin in the negative electrode (electrode for non-aqueous electrolyte secondary battery) forming composition used in Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1 below.

<Making coin cells>
A coin cell was produced using the negative electrode and the positive electrode obtained in Examples 1 to 3 and Comparative Examples 1 to 5.
A 2032 type coin cell was used, and the negative electrode had an electrode and a separator (manufactured by Cellguard: model number 2200) punched into a disk having a diameter of 15 mm and a positive electrode having a diameter of 13.5 mm. As the electrolytic solution, 1 Mol of LiPF6 was mixed with a solution of ethylene carbonate (EC) containing 2 wt% VC (Vinylene Carbonate) and diethyl carbonate (DMC) at a ratio of 3: 7 (v / v). I used the one added so that.
<Cycle test>
The coin cell produced above was subjected to a cycle test under the following charge / discharge conditions.
Charging: 366 mAg / (active material weight), discharging: 1829 mAg / (active material weight), and charging / discharging was 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 example products obtained in Comparative Examples 1 to 5 were all in the range of 60 to 80%, especially in the capacity retention rate after the cycle test, and showed a level of practicality problematic results. Among them, the product of the present invention of Example 3 is
The best values were shown for the initial capacity and the capacity retention rate after the cycle test. From this, it can be confirmed that the conductive material contains acetylene black and vapor phase carbon fiber, 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 Examples 1 to 3, when the electrode surface before the cycle was observed by SEM, as shown in FIG. 1, the surface of the active material was covered with the binder resin, and the vapor phase method carbon fiber 3 was obtained. 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 with the cycle and the cycle maintenance rate is improved.

The electrodes for non-aqueous electrolyte secondary batteries obtained by the present invention are power sources for various portable electronic devices, storage batteries for driving electric vehicles and the like that require high energy density, and various energies such as solar energy and wind power generation. It is used as an electrode for a power storage device or a storage power source for household electric appliances.

1 ... Active material, 2 ... Binder resin, 3 ... Vapor phase carbon fiber

Claims (3)

An electrode for a non-aqueous electrolyte secondary battery in which a coating film containing an electrode-forming composition is formed on the surface of a current collector .
The electrode-forming composition contains an active material, a conductive additive, and a binder resin.
The active material contains SiOx (x is 1.5 or less).
The conductive auxiliary agent contains acetylene black and vapor phase carbon fiber, and the mass of acetylene black is in the range of 12 to 20% by mass with respect to the active material, and the mass of the vapor phase carbon fiber is with respect to the active material. In the range of 2 to 6% by mass
The binder resin includes polyacrylic acid or polyacrylic acid salt having a weight average molecular weight in the range of 200,000 or more and less than 1 million, and polyacrylic acid or polyacrylic acid having a weight average molecular weight in the range of 5 million or more and less than 10 million. An electrode for a non-aqueous electrolyte secondary battery, which contains at least a salt and has a molecular weight of the binder resin in the range of 10 to 25% by mass with respect to the active material. The binder resin includes polyacrylic acid or polyacrylic acid salt having a weight average molecular weight in the range of 200,000 or more and less than 1 million, and polyacrylic acid or polyacrylic acid having a weight average molecular weight in the range of 5 million or more and less than 10 million. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode is mixed with a salt. The non-aqueous electrolyte secondary battery according to claim 1 or 2 before fang inductor resin is characterized in that it is crosslinked.

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