CN101213689B - Method for preparing lithium secondary battery anode, anode composition and lithium secondary battery - Google Patents

Abstract

The present invention relates to an anode for a lithium secondary battery, which contains a graphite material which itself adopts natural graphite or artificial graphite and has good electrical conductivity and is uniformly distributed without the formation of 10 μm or larger aggregates; the anode's Excellent long-term cycle life and high current characteristics. The composition for producing the anode can be obtained by, for example, mixing a thickener solution containing an anode active material, an aqueous thickener solution, styrene-butadiene rubber as a binder, and carbon fibers dispersed in the thickener having a predetermined viscosity. Composition produced, or prepared by mixing the anode active material with vapor-grown fibers in a dry state and then adding polyvinylidene fluoride.

Description

Method for preparing lithium secondary battery anode, anode composition and lithium secondary battery

Cross References to Related Applications

This application is based on 35 U.S.C. 111(a) and claims the benefit of the filing date of U.S. Provisional Application No. 60/697,960 pursuant to 35 U.S.C. 111(e)(1) pursuant to 35 U.S.C. 111(b ) was lodged on 7 December 2005.

technical field

The present invention relates to a lithium secondary battery excellent in cycle life and high current characteristics, comprising an anode active material which is a graphite material using natural graphite or artificial graphite and carbon fiber having good conductivity in an anode.

Background technique

As the size and weight of high-performance mobile devices increase, the demand for secondary batteries with high capacity and long cycle life continues to increase. In this context, as secondary batteries for small portable devices such as mobile phones and video cameras, lithium secondary batteries such as cylindrical or prismatic lithium ion batteries and lithium polymer batteries using non-aqueous electrolyte solutions are known for their high energy density and high Voltage characteristics have been widely used in many devices.

As for the cathode active material used in these lithium secondary batteries, metal oxides such as lithium cobalt oxide having a high specific charge-discharge capacity are used, and for the anode active material, carbon materials such as lithium cobalt oxide having a high specific charge-discharge capacity are used. Graphite with a charge-discharge capacity close to that of lithium (at low pressure).

Conventionally, regarding anode materials, carbon materials doped with other elements such as boron, natural graphite, artificial graphite, low-crystalline carbon materials, amorphous carbon materials, surface-coated carbon materials, mesophase pitch carbon fibers, and others have been used so far. Material.

Originally, natural graphite attracted attention because of its ability to achieve high battery capacity, but it was difficult to put into practical use due to the important problem of short service life due to strong decomposition reaction of electrolyte.

On the other hand, artificial graphite obtained by heat treatment using raw coke or the like has good cycle characteristics and thus has been widely used as an anode active material.

In order to obtain anode active materials with higher battery capacity and longer cycle life, active research has been ongoing. For example, granular or processed spherical ones obtained by mechanically treating highly crystalline graphite have been suggested, and coating the surface of an anode active material with pitch or resin and heat treatment to control surface activity has been studied.

On the other hand, in order to maintain and enhance electrical conductivity between anode active materials, it is effective to add conductive carbon materials such as carbon black, graphite fine powder, carbon fibers, or vapor-grown carbon fibers. In particular, vapor-grown carbon fiber, which is a fine fiber substance, is effective for forming a conductive path between active materials and passing a large current. Since vapor-grown carbon fiber can reduce the resistance of electrodes, it is presumed that the vapor-grown carbon fiber is used It is beneficial to generate greater energy. Also, in terms of charge-discharge cycle life, it is presumed that thanks to its fibrousness, the conductive path is maintained even when the active material itself swells or shrinks, and therefore research has been conducted on improving the cycle life.

Japanese Patent No. 3033175 describes that the addition of vapor-grown carbon fibers below 5% by weight has no effect on enhancing cycle life. However, an excessively large amount of vapor-grown carbon fibers results in a significant deterioration of wrapability. In addition, the more vapor-grown carbon fibers are added, the lower the proportion of active materials will be, resulting in a decrease in battery capacity. Therefore, a smaller amount of vapor-grown carbon fibers must be used to function.

In Japanese Patent Application Laid-Open No. 2000-133267, cycle life is improved by adding 0.5-22.5 parts by mass of vapor-grown carbon fibers. This document describes the technical feature of including in the electrodes secondary particles comprising vapor-grown carbon fibers with an average particle size of 12-48 μm. However, in the electrodes provided with such conditions, enhancement of cycle life characteristics was not observed (Comparative Example 7). The reason is presumed to be that, when the vapor-grown carbon fibers are localized, the current concentrates on the secondary particles, causing the localized deterioration. Therefore, further improvement is required.

Recently, a material containing carbon fibers grown directly on the surface of an anode active material for the purpose of improving high-current characteristics and cycle life has been reported. (Japanese Patent Application Laid-Open No. 2004-250275). Its role includes improving large current characteristics. However, under the specific condition that the discharge capacity of 5 hours discharge time is 100%, the discharge capacity ratio of 20 minutes discharge time (in the high current condition in which the current density is 15 times more) is 88% (Japanese Patent Application Laid-Open Example 2004-250275), there is room for further improvement. The reason is presumed to be that the degree of crystallinity of carbon fibers produced only by chemical deposition is generally low and insufficient to impart electrical conductivity.

invention disclosure

An object of the present invention is to provide an anode for a lithium secondary battery comprising an anode active material which is a graphite material which is a natural graphite or an artificial graphite material and which has excellent electrical conductivity and is uniformly distributed without aggregation of 10 μm or more a carbon fiber formed from a body; a carbon fiber-containing composition necessary for the production of an anode; an anode composition for a lithium secondary battery and a lithium secondary battery using the anode, the latter having excellent long cycle life and large current characteristic.

In order to achieve the purpose of solving the problems existing in the electrodes of lithium secondary batteries, the present inventors conducted in-depth research, and as a result, they have found a lithium secondary battery with excellent long-term cycle life and high current characteristics, which uses natural and artificial Graphite as an anode active material and carbon fiber with excellent electrical conductivity that is uniformly dispersed and formed without aggregates of 10 μm or larger.

In order to realize an anode in which carbon fibers are uniformly dispersed and no aggregates of 10 μm or larger are formed, a composition satisfying this purpose is required. In the present invention, the composition has been obtained by the following method.

(1) In the case of using styrene-butadiene rubber (hereinafter abbreviated as SBR) as the binder, the liquid in which the vapor-grown carbon fibers are dispersed is an aqueous thickener solution (composition containing carbon fibers) and the anode active material and SBR are in it The dispersed liquid is a pre-prepared aqueous solution of the thickener, and then the two liquids are mixed together in the desired ratio by stirring.

(2) In the case of using polyvinylidene fluoride (hereinafter abbreviated as "PVDF") as a binder, first, the anode active material and carbon fiber are mixed together in a dry state, and then N- PVDF in methyl-2-pyrrolidone was added and mixed by stirring.

In other words, the present invention provides an anode for a lithium secondary battery, a carbon fiber-containing composition for producing the anode, an anode composition for a lithium secondary battery, and a lithium secondary battery using the anode.

[1] A lithium secondary battery anode comprising an anode active material capable of occluding (i.e., absorbing and storing) and releasing lithium, a conductive carbon material, and a binder, wherein the anode active material is a graphite material that Adopt natural graphite or artificial graphite, d(002) measured by X-ray diffraction in its graphite structure, the plane distance between (002) planes is 0.335-0.337nm, wherein the conductive carbon material is a vapor grown carbon fiber, Its average fiber diameter is 1-200nm, each fiber has a hollow structure inside and has a structure in which graphite single-layer (graphene) sheets are laminated in a direction perpendicular to the fiber length direction, and the graphite structure is passed through the powder X-ray diffraction method The measured d(002), the planar distance between the (002) planes is 0.336-0.345nm, and the vapor-grown carbon fiber is contained therein in an amount of 0.1-10% by mass based on the total mass of the anode without 10 μm or more Aggregate formation.

[2] The lithium secondary battery anode according to item 1, wherein the vapor-grown carbon fiber has an average aspect ratio of 20-2000.

[3] The lithium secondary battery anode according to item 1, wherein the vapor-grown carbon fiber has a branched portion.

[4] A carbon fiber-containing composition comprising vapor-grown carbon fibers and an aqueous thickener solution, wherein the vapor-grown carbon fibers have an average fiber diameter of 1 to 200 nm, have a hollow structure inside the fibers and have graphite single-layer sheets along with the fibers A layered structure in a direction perpendicular to the length direction, d(002) measured by powder X-ray diffraction in the graphite structure, the plane distance between the (002) planes is 0.336-0.345nm, wherein the vapor grown carbon fiber Dispersed in an aqueous solution of a thickener, and wherein the viscosity is 5000 mPa·sec or less at 25°C.

[5] The carbon fiber-containing composition as described in item 4, wherein the vapor-grown carbon fiber has an aspect ratio of 20-2000.

[6] The carbon fiber-containing composition as described in item 4, wherein the vapor-grown carbon fiber has a branched portion.

[7] The carbon fiber-containing composition according to item 4, wherein the concentration of the vapor-grown carbon fiber in the composition is in the range of 1 to 20% by mass, and the solid concentration of the thickener aqueous solution is in the range of 0.3 to 3.0% by mass Inside.

[8] The carbon fiber-containing composition as described in item 4, wherein the aqueous thickener solution is an aqueous thickener solution of carboxymethylcellulose.

[9] A method for producing an anode composition for a lithium secondary battery, comprising mixing by stirring an aqueous thickener solution containing an anode material, a thickener solution, water containing styrene-butadiene rubber dispersed therein, and as described in item 4 A carbon fiber-containing composition wherein the anode material-containing thickener aqueous solution comprises an anode active material that employs a natural or artificial graphite whose graphite structure has a d(002) as determined by a powder X-ray diffraction method It is 0.335-0.337nm, and can absorb, store and release lithium.

[10] The production method according to item 9, wherein the thickener solution is an aqueous solution of a carboxymethylcellulose thickener.

[11] A method for producing an anode composition for a lithium secondary battery, which comprises mixing in a dry state an anode active material using natural or artificial graphite whose graphite structure is determined by a powder X-ray diffraction method The d(002) is 0.335-0.337nm, and can absorb, store and release lithium, and such vapor-grown carbon fibers have an internal hollow structure with a structure of graphite single-layer sheets stacked in the direction perpendicular to the fiber axis Also, d(002) in the graphite structure was determined to be 0.336-0.345 nm by powder X-ray diffraction method, and then polyvinylidene fluoride was added thereto, followed by mixing while stirring.

[12] The production method according to item 11, wherein the polyvinylidene fluoride is in a liquid state dissolved in N-methyl-2-pyrrolidone.

[13] A lithium secondary battery anode, which is obtained by the following steps: coating the metal current collector foil with the lithium secondary battery anode composition prepared according to any one of the above-mentioned methods 9-12, drying, Then press-molding.

[14] The lithium secondary battery anode as described in item 13, wherein the metal current collector foil is a Cu or Cu alloy foil having a thickness of 1-50 μm.

[15] A lithium secondary battery comprising the lithium secondary battery anode as described in any one of items 1, 2, 3, 13 and 14 above as a constituent.

[16] The lithium secondary battery as described in item 15, which uses a nonaqueous electrolyte solution and/or a nonaqueous polymer electrolyte, wherein the nonaqueous solvent and/or the nonaqueous polymer electrolyte used for the nonaqueous electrolyte solution Contains at least one substance selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone, and vinylene carbonate.

According to the present invention, a lithium secondary battery anode that does not contain vapor-grown carbon fiber aggregates of 10 μm or more and is used as a conductive carbon material can be obtained. In terms of cycle life under 1C discharge current density, the capacity retention rate can be improved to 74% (embodiment 7) by using the anode of this lithium secondary battery after 300 cycles, while using the disclosed conventional technology (JP 2000-133267A) to produce The retention rate of the lithium secondary battery anode is only 41% (comparative example 7). In addition, in terms of large current characteristics, the present invention achieves a capacity retention rate of 95% or higher, which is significantly improved compared to 88% disclosed in JP 2004-250275A.

Brief description of the drawings

Figure 1 is a flow chart for producing an anode composition for a lithium secondary battery with SBR as a binder.

Fig. 2 is a flow chart for producing an anode composition for a lithium secondary battery with PVDF as a binder.

3 is a SEM photo of the lithium secondary battery anode material (before pressing) of Example 1.

4 is an SEM photo of the lithium secondary battery anode (after pressing) of Example 1.

Fig. 5 is the SEM photo of the lithium secondary battery anode material (before pressing) of Example 6.

6 is a SEM photo of the lithium secondary battery anode (after pressing) of Example 6.

7 is a SEM photo of the lithium secondary battery anode material (before pressing) of Comparative Example 1.

FIG. 8 is a SEM photo of the lithium secondary battery anode (after pressing) of Comparative Example 1. FIG.

FIG. 9 is an enlarged photograph of the raised portion in FIG. 8 .

FIG. 10 is a SEM photo of the lithium secondary battery anode material (before pressing) of Comparative Example 6. FIG.

Best Mode for Carrying Out the Invention

The anode of the lithium secondary battery of the present invention is composed of an anode active material capable of absorbing, storing and releasing lithium, conductive carbon fibers and a binder, wherein graphite materials such as natural graphite or artificial graphite are used as the anode active material, and carbon fibers are used as the conductive carbon material . The carbon fibers used here are required not to form aggregates of 10 μm or larger at the anode.

The anode active material is a graphite material using natural graphite or artificial graphite, and the plane distance d(002) between its (002) planes must be within the range of 0.335-0.337nm measured by powder X-ray diffraction method. If the value is out of this range, the battery capacity decreases. Also, the material preferably satisfies the following powder characteristics.

(1) As the specific surface area becomes larger, the decomposition reaction of the electrolyte solution on the surface of the anode active material is enhanced, especially resulting in an extremely short cycle life. Therefore, the specific surface area measured by the BET method is preferably 1 m ² /g-10 m ² /g Within the range, more preferably 1m ² /g-8m ² /g, even more preferably 1m ² /g-6m ² /g.

(2) Since the particle size is small, the specific surface area increases and because the volume gradually becomes larger, it is difficult to enhance the electrode density. In addition, a larger amount of adhesive is required, which leads to deterioration of wrapability. On the other hand, when the particle size is large, the specific surface area becomes too small, which results in reduced interaction with the binder and further causes peeling of the electrode. In addition, when the current collector is coated with the lithium secondary battery anode composition, large particles seriously affect the performance of the coating film by scratching the coating film, forming grooves, and the like. Therefore, it is preferable that the appropriate particle size is 5 μm to 60 μm as measured by laser diffraction method.

(3) The flatter the shape, the more the graphite crystals become oriented in the molding step of the lithium secondary battery anode production method, which results in a shortened cycle life. Moreover, since many active reaction sites, that is, the edges of graphite single-layer sheets constituting graphite crystals, are exposed on the surface of the anode active material, the reaction to decompose the electrolyte is promoted, which may be the main cause of battery performance deterioration or gas generation inside the battery. The more spherical the shape, the orientation of the graphite crystals can be reduced and there will be less exposed graphite monolayer edges. Thus, the average sphericity of the anode active material is preferably in the range of 0.70-0.99 as measured by a flow particle image analyzer.

The term "natural graphite" refers to graphite material mined from nature as an ore. Natural graphite can be divided into two types according to appearance and performance, one is highly crystalline scaly graphite, and the other is amorphous graphite with low crystallinity. Scale graphite can be subdivided into flake graphite with leaf-like appearance and bulk type according to its appearance. Although natural graphite is produced globally, including China, Brazil, Madagascar, Zimbabwe, India, Sri Lanka, Mexico, and the Korean peninsula, graphite properties vary little by region of production.

Regarding the natural graphite used as the graphite material in the present invention, there are no particular limitations on the production area, performance and type. In addition, natural graphite or particles produced from natural graphite raw materials can be put into use after heat treatment.

In addition, the term "artificial graphite" refers to a graphite material that is produced by various artificial methods and is very close to a perfect graphite crystal. Representative examples include those obtained by calcination treatment at 500 to 1000° C. and graphitization at 2000° C. or higher using coal tar or coke obtained from coal carbonization or the residue of crude oil distillation as a raw material. In addition, primary graphite is also a type of artificial graphite obtained by reprecipitating carbon from molten iron.

As for the conductive carbon material, carbon fiber is used. When the fibers are too thick, the ability to disperse into the anode decreases, and densification of the anode electrode is inhibited. Also, when the fibers are too short, the effect of effectively maintaining electrical conductivity cannot be exhibited. Conversely, when the fibers are too long, the carbon fibers tend to aggregate, resulting in reduced ability to disperse into the anode. Therefore, ideally, the average fiber diameter is in the range of 1-200 nm, more preferably 10-200 nm.

Furthermore, it is preferable that the aspect ratio (average fiber length/average fiber diameter) calculated from the average fiber diameter and the average fiber length is 20-20000 on average, more preferably 20-4000, even more preferably 20-2000.

There is no particular limitation on the carbon fibers used in the present invention, as long as they have good electrical conductivity. However, vapor-grown carbon fibers that are highly crystalline and have graphite single-layer sheets laminated in a direction perpendicular to the fiber axis are preferred.

Vapor-grown carbon fibers can be produced, for example, by blowing into a vaporized organic compound with iron as a catalyst in a high-temperature atmosphere.

Any vapor-grown carbon fibers may be used, such as, for example, those that have been heat-treated at 800-1500°C and those that have been graphitized at about 2000-3000°C. However, those that have been heat-treated or have been further graphitized, have higher carbon crystallinity and high electrical conductivity and high pressure resistance are preferred.

In order to enhance crystallinity, it is effective to add boron as a graphitization accelerator before the graphitization step and then perform graphitization. There is no limitation on the boron source. Crystallization can be easily improved, for example, by adding boron oxide, boron carbide or boron nitride powder to vapor grown carbon fibers prior to graphitization. In this case, the boron concentration kept in the vapor-grown carbon fiber is preferably in the range of 0.1-100000 ppm. If the retained amount of boron is too small, only a small degree of crystallization enhancement can be obtained. If the retained amount of boron is too large, there is no effect on the enhancement of crystallization, and as a result, the conductivity of the vapor-grown carbon fiber decreases as the amount of boron, which is a low-conductivity compound, increases.

In addition, as a preferable form of the vapor-grown carbon fiber, there is a branched fiber. Such bifurcated fibers have a hollow structure in which the hollow space is continuous along the entire fiber including the bifurcated portion, and the carbon layer constituting the cylindrical portion is also continuous. The hollow structure is constituted by rotating carbon layers into a cylindrical shape and includes structures having an imperfect cylindrical shape, having some fractured portions, having layers formed of two layers of carbon laminates, and the like. In addition, the cross section of the cylinder does not have to be perfectly circular and may be elliptical or polygonal.

Many vapor-grown carbon fibers include surface roughness or irregularities, which are beneficial for enhanced adhesion to the anode active material. Through this bonding, a state in which the anode active material and the vapor-grown carbon fiber are mutually bonded and not separated can be maintained, resulting in maintaining anode conductivity and enhancing cycle life.

In the case where the vapor-grown carbon fibers contain a large number of branched fibers, a network can be efficiently formed within the anode. In addition, carbon fibers can be dispersed as wound around the anode active material, which results in enhanced anode strength and maintains good contact between the anode active material particles.

The amount of carbon fiber contained in the anode is in the range of 0.1-20% by mass, preferably 0.1-10% by mass. An excessive amount of the carbon fiber may result in a decrease in electrode density or a decrease in packability in the anode. On the contrary, the amount of less than 0.1% by mass leads to insufficient maintenance effect of anode conductivity and sharp deterioration of cycle life. The amount of carbon fiber can be adjusted to the above specific range by adding carbon fiber according to the corresponding proportion in the production process.

In order for the carbon fibers to exhibit the effect of maintaining electrical conductivity, the carbon fibers must be uniformly dispersed into the anode without aggregation. Due to their filamentous morphology, carbon fibers have an inherent tendency to agglomerate in the production of, for example, anode compositions. However, in the present invention, it is necessary to produce the anode under the condition that at least aggregates of 10 μm or more are not formed. The presence of aggregates of 10 μm or more will lead to non-uniform dispersion of carbon fibers having high conductivity, which will disadvantageously lead to non-uniform distribution of conductivity in the anode and make it difficult to enhance the electrode density in the anode. A lithium secondary battery anode having no aggregates of 10 μm or more can be produced according to the present invention using a carbon fiber-containing composition and a lithium secondary battery anode composition described below.

In the method of the present invention for producing an anode composition for a lithium secondary battery, the order of mixing varies depending on materials used as a binder and a solvent.

In the case where styrene-butadiene rubber (SBR) is used as a binder, examples of thickeners that can be used include polyethylene glycol, cellulose, polyacrylamide, poly-N-vinylamide and poly-N-vinylamide base pyrrolidone. Among them, polyethylene glycol and cellulose such as carboxymethylcellulose (CMC) are preferred, and particularly preferred is carboxymethylcellulose (CMC), which has a high affinity with SBR. Regarding CMC, although there are sodium form and ammonium form, there is no particular limitation thereto.

First, an aqueous solution of a thickener is prepared. In this case, the solid content of the thickener in the aqueous solution is adjusted to be in the range of 0.3-3% by mass. If the solid content is too low, the thickening effect is low and thus a large amount of thickener aqueous solution needs to be used, so that a high-density lithium secondary battery anode cannot be obtained. On the contrary, if the solid content is too high, the viscosity of the anode composition of the lithium secondary battery becomes high, which causes the failure of the coated current collector and causes aggregation of carbon fibers.

Next, carbon fibers are added in portions to the thickener aqueous solution thus prepared while kneading to obtain a carbon fiber-containing composition in which carbon fibers are dispersed to a final concentration of 1 to 20% by mass. If the carbon fiber concentration is too low, a large amount of a thickener solution composition containing an anode active material described below must be added, and therefore, a high-density lithium secondary battery anode cannot be obtained. On the contrary, if the concentration of carbon fiber is too high, it will lead to aggregation of carbon fiber. It is preferable to adjust the concentration of the carbon fiber-containing composition to 5000 mPa·sec or less. If the viscosity is too high, the carbon fibers tend to form aggregates in the lithium secondary battery anode, and more preferably, when the viscosity is adjusted to be in the range of 2000-5000 mPa·sec, the composition is easy to handle.

In the next step, an aqueous thickener solution containing an anode material consisting of an anode active material, an aqueous thickener solution, and SBR is prepared. The above thickener solution was added in portions to the anode active material while kneading to obtain a solution having a final viscosity of 5000 mPa·sec or less. If the viscosity is too high, it is impossible to coat a current collector with the solution. Furthermore, by adding water in which styrene-butadiene rubber is dispersed (for example, BM-400B produced by Nippon Zeon Co., Ltd. can be used) and mixing by stirring, an aqueous thickener solution containing an anode material can be obtained.

In the next step, the above-mentioned carbon fiber-containing composition is added to the above-mentioned thickener aqueous solution containing the anode material so that the concentration of carbon fiber may be 0.1-10% by mass, assuming that the total amount of the anode active material, carbon fiber, SBR and CMC is 100% by mass %, the lithium secondary battery anode composition can be produced.

The kneading in the preparation of the carbon fiber-containing composition and the anode material-containing thickener aqueous solution and the preparation of the lithium secondary battery anode composition can be performed using known equipment. Examples of usable equipment include ribbon mixers, screw kneaders, SPARTAN-RYUZER, Loedige mixers, planetary mixers, universal mixers, and non-bubbling kneaders.

Next, a method of producing an anode composition for a lithium secondary battery using polyvinylidene fluoride (PVDF) as a binder is described.

The anode active material and carbon fiber were weighed so that the concentration of carbon fiber was in the range of 0.1-10% by mass, assuming that the total amount of the anode active material, carbon fiber, and PVDF added in a subsequent step was 100% by mass, and mixed in a dry state. The mixing step here can be performed using known equipment. Examples thereof include ribbon mixers, screw kneaders, SPARTAN-RYUZER, Loedige mixers, planetary mixers, universal mixers and non-foaming kneaders. Although the optimum mixing time in relation to the type of mixing equipment and the size of the container used cannot be determined universally, 5-30 seconds of mixing is usually sufficient.

Next, a predetermined amount of PVDF dissolved in N-methyl-2-pyrrolidone (for example, KF-polymer produced by KUREHA CORPORATION can be used) is added to the previously prepared mixture and mixed by stirring, and an anode for a lithium secondary battery can be obtained combination. Also in this case, mixing by stirring can be performed using known equipment. Examples of usable equipment include ribbon mixers, screw kneaders, SPARTAN-RYUZER, Loedige mixers, planetary mixers, universal mixers, and non-foaming kneaders.

By using the lithium secondary battery anode composition of the present invention, a lithium secondary battery anode can be produced. The lithium secondary battery anode material can be obtained by applying the above lithium secondary battery anode composition on a Cu or Cu-alloy foil with a thickness of 1-50 μm, drying and pressing. If the foil is too thin, the mechanical strength decreases, while if it is too thick, the rigidity increases. Therefore, in both cases, it is difficult to produce batteries.

The above-mentioned coating step can be performed by a known method. For example, a scalpel or stick applicator can be used. In the subsequent molding step, a roll press or the like may be used.

The lithium secondary battery of the present invention can be realized by combining the lithium secondary battery anode as a component, wherein the lithium secondary battery anode is obtained by using the lithium secondary battery anode composition of the present invention as a raw material. A production method of the lithium secondary battery is described below.

Examples of raw materials of cathode active materials suitable for the cathode and capable of absorbing, storing and releasing lithium include cobalt-based oxides such as lithium cobaltate, manganese-based oxides such as lithium manganate, nickel-based oxides such as lithium nickelate, vanadium-based oxides substances such as vanadium pentoxide and composite oxides and mixtures of these compounds, but are not limited thereto.

The particle size of the cathode active material is not particularly limited. Generally, the particle size is preferably 0.1-50 μm. The specific surface area is also not particularly limited, and the value of the specific surface area measured by the BET method is preferably 0.2 m ² /g to 10 m ² /g.

The method of preparing the cathode is not particularly limited. Generally, a cathode can be obtained by mixing the above-mentioned cathode active material, conductive carbon material and binder material, applying the mixture to a carrier substrate such as a metal current collector, drying and pressing.

Examples of conductive carbon materials that can be used include carbon black, acetylene black, carbon fibers, vapor-grown carbon fibers, and carbon nanotubes. As a binder, PVDF can be used.

The mixing of the cathode active material, the conductive carbon material and the binder material can be performed by, for example, stirring with a stirrer or the like. The stirring method is not particularly limited and can be used, for example, a ribbon mixer, a screw kneader, SPARTAN-RYUZER, a Loedige mixer, a planetary mixer, a universal mixer, and a foamless kneader.

The usage amount of the binder is preferably adjusted in the range of 1-15% by mass, assuming that the total amount of the cathode active material, conductive carbon material and PVDF is 100% by mass.

Coating on the current collector can be performed by known methods, examples of which are methods of coating with a scalpel or bar coater, drying, and molding with a roller press. As the current collector, known materials such as aluminum, stainless steel, nickel, titanium, alloys of these metals, platinum or carbon sheets can be used.

A lithium secondary battery can be produced by a known method. Representative examples of producing lithium ion batteries and/or lithium ion polymer batteries are described below, however, are not limited to these methods.

The anode prepared above was machined into a desired shape, and then formed a laminate consisting of cathode/separator/anode together with the cathode so that the anode was not in contact with the cathode. The laminate thus prepared is put into a container having a button shape, a rectangle, a cylinder or a sheet shape. The product was dried again under reduced pressure and/or under an inert atmosphere at the dew point (-50°C) and then transferred at the dew point (-50°C), possibly absorbing some moisture and oxygen during the layering and laying steps into an inert atmosphere. After that, the electrolytic solution was poured into the container and the container was sealed, thereby obtaining a lithium ion battery or a lithium polymer battery.

As the separator, known separators can be used. From the standpoint of thinning and high strength, microporous membranes made of polyethylene and polypropylene are preferred. From the viewpoint of ion conduction, the higher the porosity, the more preferable. However, if the porosity is too high, the strength decreases or causes a short circuit between the cathode and anode. Therefore, the porosity is controlled to be 30-90%, preferably 50-80%. In addition, the thinner the film thickness, the more preferable it is from the viewpoint of ion conduction and battery capacity. However, if it is too thin, the strength decreases or it causes a short circuit between the cathode and anode. Therefore, the thickness is usually 5-100 μm, preferably 5-50 μm. The microporous film can be combined with two or more kinds or combined with non-woven fabric.

As the electrolyte solution and the electrolyte in the non-aqueous secondary battery, especially lithium ion battery and/or lithium polymer battery, known organic electrolyte solution, inorganic solid electrolyte or solid polymer electrolyte can be used.

Preferable examples of the organic electrolytic solution include ethers such as diethyl ether, butyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, Diethylene glycol monobutyl ether, diglyme, and ethylene glycol phenyl ether; amides, such as formamide, N-methylformamide, N,N-dimethylformamide, N-ethyl Formamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, N,N -Dimethylpropionamide and hexamethylphosphoramide; sulfur compounds such as dimethyl sulfoxide and sulfolane; dialkyl ketones such as methyl ethyl ketone and methyl isobutyl ketone; cyclic ethers such as ethylene oxide, propylene oxide , tetrahydrofuran, 2-methoxytetrahydrofuran, 1,2-dimethoxyethane and 1,3-dioxane; carbonates such as ethylene carbonate and propylene carbonate; gamma-butyrolactone; pyrrolidone; and organic solvents such as acetonitrile and nitromethane. More preferred are esters such as ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, vinylene carbonate, gamma-butyrolactone, ethers such as dioxane, diethyl ether and diethyl ether Ethoxyethane, Dimethyl Sulfoxide, Acetonitrile and Tetrahydrofuran. Particularly preferably, carbonate-based non-aqueous solvents such as ethylene carbonate and propylene carbonate can be used. One of these solvents may be used alone or a mixture of two or more thereof may be used. As the solute (electrolyte) in these solvents, lithium salts are used. Examples of commonly known lithium salts include: LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , and LiN(CF ₃ SO ₂ ) ₂ .

Examples of solid polymer electrolytes include polyethylene oxide derivatives, polymers containing the derivatives, polypropylene oxide derivatives, polymers containing the derivatives, phosphate polymers, polycarbonate derivatives, and polymers containing the derivatives. Derivative polymers.

In addition to the materials mentioned above, there is no restriction on the choice of other elements needed to construct the battery.

Example

The present invention will be described in detail with reference to representative embodiments of the present invention described below. The shown embodiments are only for illustrating the invention, and the invention is therefore not limited thereto.

The properties and the like described in the Examples were measured by the methods and equipment described below.

[1] Average particle size: Measured with a particle size analyzer using a laser diffraction and scattering method, Microtrack HRA (manufactured by NIKKISO CO., LTD.).

[2] Specific surface area: Using a specific surface area measuring device, NOVA-1200 (manufactured by Yuasa Ionics), it was measured by the BET method using liquid nitrogen, which is a common method for measuring the specific surface area.

[3] Sphericity: Evaluated by the following evaluation method using a flow particle image analyzer, FPIA-2100 (manufactured by SYSMEX Co., Ltd).

A graphite fine powder sample was dispersed in water containing a surfactant and introduced into a flow particle image analyzer via a syringe. A photo of the sample (liquid in which fine powder is dispersed) flowing in the core part of the flow cell is taken every 1/30 second by a CCD camera and the still photo is processed in real time. The sphericity was calculated by the following formula.

Sphericity = (perimeter calculated from the diameter of the corresponding ring)/(perimeter of the projected image of the particle)

The "diameter of the corresponding ring" is the diameter of a perfect ring having an area corresponding to the perimeter of the projected image of the particle actually taken. The sphericity is a value obtained by dividing it by the perimeter of the projected image of the particle actually taken. For example, in the case of an ideal circle, the sphericity is 1, and the more complex the shape of the particle image, the smaller the value of the sphericity. The average sphericity is calculated for each individual particle.

[4] Viscosity: Measured with an LV-series B-type rotational viscometer (manufactured by Brookfield Engineering laboratories, Inc). First, the sample to be measured is placed in a stainless steel container and placed on the measuring device. In order to keep the sample temperature constant, the container was immersed in a constant temperature bath set at 25°C. The spindle was then turned and after 3 minutes of turning, the viscosity was measured. Each sample was measured twice and averaged. As for the rotor, a No. 4 rotor was used and the rotational speed was 6 rpm.

[5] Methods of evaluating batteries:

(1) Preparation of anode

According to the procedure for preparing the anode, the preparation of the anode composition, coating, drying and molding were carried out in sequence. The following is the procedure including coating and subsequent steps.

The anode compositions prepared according to the various methods were each applied to a predetermined thickness on a flat roll-pressed copper foil (thickness 18 µm, manufactured by Nippon Foil Mfg. Co., Ltd) with a scalpel. Vacuum dried at 120° C. for 1 hour and the foil was cut to a diameter of 18 mm by punching. Further, the electrodes thus cut out were sandwiched between super-steel extruded plates at about 1×10 ² -3×10 ² N/mm ² (1×10 ³ -3×10 ³ kg/ cm ² ) pressed to form an electrode. The coating weight is 7-9 mg/cm ² , the thickness is 40-60 μm, and the electrode density is 1.6 g/cm ³ . It was then dried in a vacuum desiccator at 120°C and used for evaluation.

(2) Preparation of cathode

A cathode to be combined with the anode obtained in (1) above was prepared as follows.

LiCoO ₄ Cellseed C-10 (manufactured by Nippon Chemical Industrial Co., Ltd.) and acetylene black (manufactured by DENKI KAGAKU KOGYO KABUSHIKI KAISHA) were each mixed in a dry state at a mass ratio of 95:5 using a small high-speed scraper A mixer IKA (manufactured by IKA-Labotechnik Staufen (Janke & Kunkel GmbH)) was mixed at a rotation speed of 10000 rpm for 10 seconds to prepare a cathode material mixture. A solution of N-methyl 2-pyrrolidone (NMP) containing 12% by mass of KF-polymer L#1320 (polyvinylidene fluoride (PVDF), manufactured by KUREHA Corporation) was added thereto so that the mass of the cathode material mixture and PVDF The ratio is 95:3. The obtained mixture was kneaded using a non-bubble kneader NBK-1 (NISSEI Corporation) kneader at a rotation speed of 500 rpm for 5 minutes. During the operation, stirring balls (12 mm in diameter) were added to the kneader, thereby obtaining a pasty cathode composition.

The above cathode composition was applied to a rolled aluminum foil (thickness 25 µm) produced by SHOWA DENKOK.K. using a scalpel to a predetermined thickness. Vacuum dried at 120° C. for 1 hour and then cut by punching to a diameter of 18 mm. Further, the electrodes thus trimmed were sandwiched between super steel extruded plates and under a pressure of about 1×10 ² -3×10 ² N/mm ² (1×10 ³ -3×10 ³ kg/cm ² ) pressed into electrodes. The electrodes were then dried in a vacuum desiccator at °C for 12 hours and used for evaluation. The thickness is about 80 μm and the electrode density is about 3.5 g/cm ³ .

(3) Prepare a three-electrode battery for lithium-ion battery testing

A three-electrode cell was prepared as follows. The following procedures were carried out in a glove box under a dry argon atmosphere at a dew point of -80°C or lower.

In a battery (inner diameter about 18 mm) made of polypropylene with a screw cap, the anode with copper foil obtained in (1) above and the metal lithium foil as the counter electrode pass through a separator (polypropylene microporous) sandwiching them. film, manufactured by Tonen Corporation) was laminated. Further, metal lithium foil (50 μm) used as a comparison was also laminated thereon. An electrolytic solution was added, whereby a test battery was obtained.

(4) Preparation of button cells for testing lithium-ion batteries

A coin cell was prepared as follows. The following procedures were carried out in a glove box under a dry argon atmosphere at a dew point of -80°C or lower.

In a cylindrical type case made of SUS304-, the spacer, the leaf spring, the anode with copper foil obtained in the above (1) and the cathode with aluminum foil obtained in the above (2) are used by sandwiching them (polypropylene microporous membrane, Cell Guard 2400 manufactured by Tonen Corporation) was laminated. Further, the top was covered with a cylindrical casing made of SUS304 as a top cover.

In the next step, vacuum immersion was performed by immersing it in the dielectric solution for 5 minutes. Then, the button battery was caulked with a caulking device, thereby obtaining a test button battery.

(5) Dielectric solution

LiPF ₆ was dissolved as a solute in a mixture of 8 parts by mass of EC (ethylene carbonate) and 12 parts by mass of SEMC (ethyl methyl carbonate), and the obtained solution with a LiPF ₆ concentration of 1.0 mol/1 was used as a dielectric solution.

(6) Tests to evaluate the performance of high-rate batteries

By using the three-electrode battery used for the evaluation, a constant-voltage constant-current discharge test was performed.

CC (constant current) discharge was performed at 0.2 mA/cm ² to a quiescent voltage of 2 mV. Subsequently, the charging was shifted to 2 mVCV (constant voltage), and the discharging was stopped at the point when the current value dropped to 12.0 μA.

CC discharge was performed at each current density (0.2 mA/cm ² (corresponding to 0.1C) 4.0 mA/cm ² (corresponding to 2.0C)) and cut off at a voltage of 1.5V.

The ratio of the discharge capacity at 2.0C to the discharge capacity at 0.1C was defined as the capacity retention ratio of high-rate discharge and evaluated.

(7) Charge-discharge cycle life test

A constant voltage and constant current charge-discharge test was performed using a coin cell battery used for evaluation.

During the first two charge/discharge cycles, CC (constant current) charging was performed from quiescent voltage to 4.2V at 0.2mA/ ^cm2 , then shifted to CV (constant voltage) charging at 4.2V and the current value It stops when it drops to 25.4μA. Subsequently, CC discharge was performed at 0.2 mA/ ^cm and stopped at a voltage of 2.7 V.

In the third cycle and subsequent cycles, CC (constant current) charge from quiescent voltage to 4.2V at 1.0mA/ ^cm2 (equivalent to 0.5C), and then shift to CV (constant voltage) charge at 4.2V, And it stops when the current value drops to 25.4 μA. Subsequently, CC discharge was performed at a current density of 2.0 mA/cm ² (corresponding to 1.0 C) and cut off at a voltage of 2.7 V. The ratio of the discharge capacity in the 300th cycle to the discharge capacity in the second cycle was defined as the cycle charge capacity retention rate and evaluated.

[6] Method for observing the state of carbon fiber aggregation:

Carbon fibers were observed by the following method using a scanning electron microscope T-20 (manufactured by JEOL Ltd.).

Electrode samples were pressed with a pressure of 1 t/cm ² and placed on a microscope stage. The microscope stage was tilted at an angle of 30-60° from the horizontal state in order to adjust the observation range to such an extent that the entire electrode surface could be observed at the minimum magnification (×35). During the observation, it was determined whether there were protrusions (protrusions) on the surface of the sample. In the case where aggregates of carbon fibers occur, the presence of protrusions can be known by judging whether the portion appears more prominent than other portions.

[7] Materials used for anode:

(1) Anode active material

LB-CG: spherical natural graphite (Nippon Graphite Industries, Ltd.)

X-ray d(002): 0.3359nm

Specific surface area: 6m ² /g

Average particle size: 20μm

Sphericity: 0.90

MCMB (25-28): mesophase spherical artificial graphite (manufactured by OSAKA GAS Co., Ltd)

X-ray d(002): 0.3363nm

Specific surface area: 0.9m ² /g

Average particle size: 25μm

Sphericity: 0.93

SCMG-A: Large block artificial graphite (manufactured by SHOWA DENKO K.K.)

X-ray d(002): 0.3367nm

Specific surface area: 2.2m ² /g

Average particle size: 20μm

Sphericity: 0.86

(2) carbon fiber

VGCF: Vapor-grown graphite fiber (manufactured by SHOWA DENKO K.K.)

Average fiber diameter (by SEM image analysis): 150nm,

Average fiber length (by SEM image analysis): 8 μm,

Average aspect ratio: 53

Bifurcation degree: about 0.1 bifurcation/μm (the number of bifurcation points per 1 μm fiber length is analyzed by SEM photos; the same applies below)

X-ray d(002): 0.3384nm,

Lc (crystallite size): 48 nm.

VGCF-H: Vapor-grown graphite nanofibers (manufactured by SHOWADENKO K.K.)

Average fiber diameter (by SEM photo analysis): 150nm,

Average fiber diameter (by SEM photo analysis): 6μm,

Average aspect ratio: 40

Fork degree: 0.05 fork/μm,

X-ray d(002): 0.3384nm,

Lc: 35nm.

VGCF-S: Vapor-grown graphite fiber (manufactured by SHOWA DENKO K.K.)

Average fiber diameter (by SEM photo analysis): 120nm,

Average fiber length (by SEM photo analysis): 12μm,

Average aspect ratio: 100

Bifurcation degree: about 0.02 bifurcation/μm,

X-ray d(002): 0.3385nm, Lc: 48nm

VGNT: Vapor-grown graphite nanotubes (manufactured by SHOWA DENKO K.K.)

Average fiber diameter (by SEM photo analysis): 25nm,

Average fiber length (by SEM photo analysis): 5μm,

Average aspect ratio: 200,

Bifurcation degree: 0.1 bifurcation/μm,

X-ray d(002): 0.3449nm, Lc: 30nm.

(3) Adhesive

Styrene-butadiene rubber (SBR): BM-400B (manufactured by ZEON CORPORATION)

Polyvinylidene fluoride (PVDF): KF-Polymer L#9210 (manufactured by KUREHACORPORATION)

(4) Thickener

Carboxymethylcellulose (CMC): WS-C (manufactured by DAI-ICHI KOGYO SEIYAKU CO., LTD.)

(5) Solvent

N-methyl 2-pyrrolidone (NMP): EP-II (manufactured by SHOWA DENKO K.K.)

Example 1

The 1% by mass CMC aqueous solution prepared in advance was added in portions to 20 g of VGCF, while using a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (manufactured by PRIMIX) kneaded for 90 minutes. As a result, a carbon fiber-containing composition containing 8.5% by mass of VGCF was produced. The viscosity of this solution was 4000 mPa·sec.

The 1% by mass CMC aqueous solution prepared in advance was added in portions to 70g spherical natural graphite LB-CG, while using a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) kneaded for 2 hours. As a result, a CMC solution containing 50% by mass of spherical natural graphite LB-CG was produced. To this solution, SBR-dispersed water BM-400B was added so that the SBR solid content was 1.5% by mass, and kneaded for 1 hour. The viscosity of this thickener solution containing the anode material was 3500 mPa·sec.

Next, the carbon fiber-containing composition was mixed with the anode material-containing thickener solution so that the VGCF content was 2% by mass, assuming that the total amount of LB-CG, VGCF, SBR, and CMC was 100% by mass, and the mixture was kneaded 15 minutes.

The lithium secondary battery anode was prepared by using the thus obtained lithium secondary battery anode composition according to the above-mentioned "anode preparation" method.

Figure 3 shows an enlarged SEM photo of the state of the anode material before pressing, and Figure 4 shows the SEM photo of the state of the anode surface after pressing. It can be clearly seen from Figure 3 that the carbon fibers present in the anode material are well dispersed, and no aggregates with a diameter exceeding 10 μm were observed on the surface of the anode shown in Figure 4 .

Example 2

The 1% by mass CMC aqueous solution prepared in advance was added in portions to 70 g of bulk artificial graphite SCMG-A, and kneaded for 2 hours with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX). As a result, a CMC solution containing 60% by mass of bulk artificial graphite SCMG-A was obtained. To this solution, SBR-dispersed water BM-400B was added so that the SBR solid content was 1.5% by mass, and kneaded for 1 hour. The viscosity of this thickener solution containing the anode material was 3000 mPa·sec.

Other procedures were carried out in the same manner, thereby preparing an anode for a lithium secondary battery.

The obtained anode was observed with a scanning electron microscope in the same manner as in Example 1, and it was observed that carbon fibers were well dispersed in the anode material and there were no carbon fiber aggregates with a diameter exceeding 10 μm.

Example 3

1% by mass of B ₄ C was added to VGCF and heat treatment was performed in an argon flow at 2800° C. using a small graphitization furnace (manufactured by KABUSHIKIKAISHA SAN RIKO DENKI). After cooling and collecting, d(002) was determined to be 0.3376 nm by X-ray powder diffraction method. Using this boron-treated VGCF, a lithium secondary battery anode was prepared in a manner similar to that of Example 1.

The obtained anode was observed with a scanning electron microscope in the same manner as in Example 1, and it was observed that carbon fibers were well dispersed in the anode material and there were no carbon fiber aggregates with a diameter exceeding 10 μm.

Example 4

Add 20 g of VGCF-H to 1% by mass of CMC aqueous solution prepared in advance, and knead with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX) for 90 minutes to obtain the concentration of VGCF-H 14.0% by mass of a carbon fiber-containing composition. The viscosity of this solution was 3000 mPa·sec.

Subsequent procedures were carried out in the same manner as in Example 1, thereby obtaining an anode for a lithium secondary battery.

The obtained anode was observed with a scanning electron microscope in the same manner as in Example 1, and it was observed that carbon fibers were well dispersed in the anode material and there were no carbon fiber aggregates with a diameter exceeding 10 μm.

Example 5

Add the 1 mass % CMC aqueous solution prepared in advance to 20g VGCF-S in portions, knead with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) for 90 minutes, so as to obtain the concentration of VGCF-S 5.3% by mass of a carbon fiber-containing composition. The viscosity of this solution was 4900 mPa·sec.

Subsequent procedures were carried out in the same manner as in Example 1, thereby obtaining an anode for a lithium secondary battery.

The obtained anode was observed with a scanning electron microscope in the same manner as in Example 1, and it was observed that carbon fibers were well dispersed in the anode material and there were no carbon fiber aggregates with a diameter exceeding 10 μm.

Example 6

The 1 mass % CMC aqueous solution prepared in advance was added to 20 g VGNT in portions, and kneaded with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) for 90 minutes, so as to obtain a VGNT concentration of 5.3 mass % carbon fiber composition. The viscosity of this solution was 4800 mPa·sec.

Subsequent procedures were carried out in the same manner as in Example 1, thereby obtaining an anode for a lithium secondary battery.

Fig. 5 shows an enlarged SEM photo of the state of the anode material before pressing, and Fig. 6 shows an SEM photo of the state of the anode surface after pressing. It is clearly seen from Fig. 5 that the carbon fibers present in the anode material are well dispersed, and on the surface of the anode shown in Fig. 6, no carbon fiber aggregates with a diameter exceeding 10 μm were observed.

Example 7

Spherical artificial graphite MCMB (25-28) and VGCF were mixed using a small, high-speed scraper mixer IKA (manufactured by IKA-Labotechnik Staufen (Janke & Kunkel GmbH)) in a dry state at a rotation speed of 10000 rpm for 10 seconds. Then, a solution of PVDF (KF-polymer) in NMP was added. The addition was performed after calculation so that the mass ratio of MCMB, VGCF and PVDF was 93:2:5.

Next, NMP was added thereto in portions to adjust the viscosity of the anode composition. Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

The obtained anode was observed with a scanning electron microscope in the same manner as in Example 1, and it was observed that carbon fibers were well dispersed in the anode material and there were no carbon fiber aggregates with a diameter exceeding 10 μm.

Comparative example 1

20 g of spherical artificial graphite LB-CG and 0.4 g of VGCF were mixed in a dry state at 10000 rpm for 10 seconds using a small, high-speed scraper mixer IKA (manufactured by IKA-Labotechnik Staufen (Janke & Kunkel GmbH)). A 1% by mass CMC aqueous solution prepared in advance was added to the mixture in portions, and kneaded for 90 minutes with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (manufactured by PRIMIX Corporation). In this solution, SBR-dispersed water BM-400B was added so that the SBR solid content was 1.5% by mass, and kneading was performed for 1 hour. The final viscosity of this solution was 4600 mPa·sec.

Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Fig. 7 shows an enlarged SEM photo of the state of the anode material before pressing, and Fig. 8 shows a SEM photo of the state of the anode surface after pressing. As can be seen from FIG. 7, the carbon fibers present in the anode material have aggregated, and from the surface of the pressed anode shown in FIG. 8, there are many prominent protrusions. Figure 9 shows a magnified image of the raised portion. It can be found from Figure 9 that these protrusions are carbon fiber aggregates with a diameter of about 20 μm.

Comparative example 2

The 1 mass % CMC aqueous solution prepared in advance is added in 20 g VGCF in portions, and kneaded with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) for 90 minutes, so as to obtain a VGCF concentration of 25 mass % of carbon fiber-containing composition. The viscosity of this solution was 12000 mPa·sec.

The 1 mass % CMC aqueous solution prepared in advance will be added in gradations in 70g spherical natural graphite LB-CG, with multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) kneading 2 hours, thus obtain Spherical natural graphite LB-CG concentration is 50% by mass of CMC solution. To this solution, SBR-dispersed water BM-400B was added so that the SBR solid content was 1.5% by mass, and kneading was performed for 1 hour. The final viscosity of this thickener solution containing the anode material was 3500 mPa·sec.

Then, the carbon fiber-containing composition and the thickener solution containing the anode material were mixed together so that the VGCF content was 2% by mass, assuming that the total amount of LB-CG, VGCF, SBR and CMC was 100% by mass, and stirred The mixture was left for 15 minutes.

Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Observing the obtained anode with a scanning electron microscope, it is found that carbon fibers exist in the anode material in an aggregated state, and many carbon fiber aggregates with a diameter of more than 20 μm are discretely distributed on the surface of the pressed anode.

Comparative example 3

Add the 1 mass % CMC aqueous solution prepared in advance in 20 g VGCF in portions, and knead with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) for 90 minutes, so as to obtain a VGCF concentration of 8.5 mass % of carbon fiber-containing composition. The viscosity of this solution was 4000 mPa·sec.

Add 1% by mass of CMC aqueous solution prepared in advance to 70g spherical natural graphite LB-CG in portions, and knead with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) for 2 hours, thereby preparing CMC solution with 60% by mass of spherical natural graphite LB-CG. To this solution, SBR-dispersed water BM-400B was added so that the SBR solid content was 1.5% by mass, and kneaded for 1 hour. The final viscosity of this anode material-containing thickener solution was 10000 mPa·sec.

Then, the carbon fiber-containing composition was mixed with the anode material-containing thickener solution so that the VGCF content was 2% by mass, assuming that the total amount of LB-CG, VGCF, SBR, and CMC was 100% by mass, and the mixture was kneaded for 15 minute.

Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Observing the obtained anode with a scanning electron microscope, it is found that carbon fibers exist in the anode material in an aggregated state, and many carbon fiber aggregates with a diameter of more than 20 μm are discretely distributed on the surface of the pressed anode.

Comparative example 4

The 1 mass % CMC aqueous solution that will be prepared in advance is added in 20g VGCF in gradations, with multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) is kneaded 90 minutes, thereby prepares VGCF with 8.5 mass % A carbon fiber-containing composition of carbon fibers. The viscosity of this solution was 4000 mPa·sec.

The carbon fiber-containing composition was added to 70 g of spherical natural graphite LB-CG so that the VGCF concentration was 2% by mass. Kneading was carried out for 2 hours with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (manufactured by PRIMIX Corporation). In this case, a 1% by mass CMC solution was further added thereto to adjust the viscosity. Then, SBR-dispersed water BM-400B was added to the solution so that the SBR solid content was 1.5% by mass, and kneaded for 1 hour. The viscosity of this lithium secondary battery anode composition was 4000 mPa·sec.

Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Observing the obtained anode with a scanning electron microscope, it is found that carbon fibers exist in the anode material in an aggregated state, and many carbon fiber aggregates with a diameter of more than 20 μm are discretely distributed on the surface of the pressed anode.

Comparative example 5

The 1 mass % CMC aqueous solution prepared in advance will be added in portions to 70g spherical natural graphite LB-CG, with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) kneading for 2 hours, thereby preparing 50 mass% CMC solution of spherical natural graphite LB-CG.

VGCF and a 1% by mass CMC solution were added thereto to adjust the viscosity, and kneading was performed for 2 hours. Then, SBR-dispersed water BM-400B was added so that the SBR solid content was 1.5% by mass, and kneaded for 1 hour. The viscosity of this lithium secondary battery anode composition was 4000 mPa·sec.

Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Observing the obtained anode with a scanning electron microscope, it is found that carbon fibers exist in the anode material in an aggregated state, and many carbon fiber aggregates with a diameter of more than 20 μm are discretely distributed on the surface of the pressed anode.

Comparative example 6

KF-polymer was added in spherical artificial graphite MCMB (25-28), and kneaded for 15 hours with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company). VGCF was then added to the mixture and further kneaded. The addition was performed after calculation so that the mass ratio of MCMB, VGCF and PVDF was 93:2:5.

Then, the viscosity of the anode composition was adjusted with the addition of NMP in portions. Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Figure 10 shows an enlarged SEM photograph of the state of the anode material before pressing. It can be seen from Figure 10 that carbon fibers exist in the anode material in an aggregated state, and many carbon fiber aggregates with diameters exceeding 20 μm are discretely distributed on the surface of the pressed anode.

Comparative example 7

KF-polymer was added to VGCF, and kneaded for 15 hours with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company). Spherical artificial graphite MCMB (25-28) was then added to the mixture and further kneaded. The addition was performed after calculation so that the mass ratio of MCMB, VGCF and PVDF was 93:2:5.

Then, the viscosity of the anode composition was adjusted with the addition of NMP in portions. Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Observing the obtained anode with a scanning electron microscope, it is found that carbon fibers exist in the anode material in an aggregated state, and many carbon fiber aggregates with a diameter of more than 20 μm are discretely distributed on the surface of the pressed anode.

Comparative example 8

The 1 mass % CMC solution that will be prepared in advance is added in gradation in 70g spherical natural graphite LB-CG, with multi-functional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) kneading 2 hours, thereby prepares containing 50% by mass of a CMC solution of spherical natural graphite LB-CG, followed by adding SBR-dispersed water BM-400B to the solution so that the SBR solid content was 1.5% by mass, and kneading for 1 hour. The viscosity of the CMC solution was 3500 mPa·sec.

Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Comparative example 9

1% by mass of CMC prepared in advance was added in portions of 70g of bulk artificial graphite SCMG-A, and kneaded with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company) for 2 hours, thereby preparing CMC solution containing 60% by mass of bulk artificial graphite SCMG-A. Then, SBR-dispersed water BM-400B was added to the solution so that the SBR solid content was 1.5% by mass, and kneaded for 1 hour. The viscosity of this CMC solution was 3000 mPa·sec.

Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Comparative example 10

KF-polymer was added in spherical artificial graphite MCMB (25-28), and kneaded for 15 hours with a multifunctional mixer, T.K.HIVIS MIX (registered trademark) f-type 03 (produced by PRIMIX company). The addition was performed after calculation so that the mass ratio of MCMB(25-28) to PVDF was 93:5.

Then, the viscosity of the anode composition was adjusted with the addition of NMP in portions. Using the lithium secondary battery anode composition thus obtained, the lithium secondary battery anode was prepared according to the above-mentioned "anode preparation" method.

Table 1

Battery Performance Evaluation Results

High rate (high rate) discharge capacity retention rate (%)  Cyclic discharge capacity retention (%) Example-1 97.2 75 Example-2 95.0 78 Example-3 98.2 80 Example-4 97.2 76 Example-5 97.0 75 Example-6 97.3 73 Example-7 95.1 74 Comparative example-1 79.1 45 Comparative example-2 78.0 43 Comparative example-3 77.9 39 Comparative example-4 78.2 42 Comparative example-5 77.4 46 Comparative example-6 73.3 43 Comparative example-7 74.6 41 Comparative example-8 83.2 20 Comparative example-9 90.0 60 Comparative example-10 75.0 48

Industrial adaptability

The present invention is applicable to any lithium secondary battery having any shape and any type, and the lithium secondary battery can be used as a power source for portable phones and mobile electronic devices, a car battery or an electric tool battery.

Claims (16)

1. A lithium secondary battery anode, which comprises an anode active material, a conductive carbon material and a binding agent capable of absorbing and storing and releasing lithium, wherein the anode active material is such a graphite material, which adopts natural graphite Or artificial graphite, d(002) measured by X-ray diffraction in its graphite structure, the plane distance between (002) planes is 0.335-0.337nm, wherein the conductive carbon material is vapor grown carbon fiber, and its average fiber The diameter is 1-200nm, each fiber has a hollow structure inside, and has a structure in which graphite single-layer sheets are stacked in a direction perpendicular to the fiber length direction, and the graphite structure of the vapor-grown carbon fiber is determined by powder X-ray diffraction The d(002) measured by the method, the plane distance between the (002) planes is 0.336-0.345nm, and the vapor-grown carbon fiber is contained therein in an amount of 0.1-10% by mass based on the total mass of the anode, and no 10 μm or more Large aggregates are formed. 2. The lithium secondary battery anode according to claim 1, wherein the average aspect ratio of the vapor-grown carbon fibers is 20-2000. 3. The lithium secondary battery anode according to claim 1, wherein said vapor-grown carbon fiber has a branched portion. 4. A carbon-fiber-containing composition, which comprises steam-grown carbon fiber and thickener aqueous solution, wherein the average fiber diameter of the steam-grown carbon fiber is 1-200nm, the inside of the fiber has a hollow structure and has a graphite single-layer sheet along the length of the fiber A layered structure in a direction perpendicular to the direction, d(002) measured by powder X-ray diffraction in the graphite structure, the plane distance between the (002) planes is 0.336-0.345nm, wherein the vapor-grown carbon fibers are dispersed In an aqueous solution of a thickener, and wherein the viscosity is 5000 mPa·sec or less at 25°C. 5. The carbon fiber-containing composition of claim 4, wherein the vapor-grown carbon fibers have an aspect ratio of 20-2000. 6. The carbon fiber-containing composition of claim 4, wherein the vapor-grown carbon fibers have branched portions. 7. The carbon fiber-containing composition of claim 4, wherein the concentration of the vapor-grown carbon fiber in the composition is in the range of 1-20% by mass, and the concentration of solids in the thickener aqueous solution is in the range of 0.3-3.0% by mass. 8. The carbon fiber-containing composition of claim 4, wherein the thickener aqueous solution is an aqueous thickener solution of carboxymethylcellulose. 9. A method for producing lithium secondary battery anode composition, comprising by stirring and mixing the thickener aqueous solution containing anode material, the thickener solution and the water comprising the styrene-butadiene rubber dispersed therein and the carbon fiber-containing combination of claim 4 Article wherein the aqueous thickener solution containing the anode material comprises an anode active material using natural or artificial graphite whose graphite structure has a d(002) of 0.335-0.337 as determined by a powder X-ray diffraction method nm, and can absorb, store and release lithium. 10. The production method according to claim 9, wherein said thickener solution is an aqueous solution of carboxymethylcellulose thickener. 11. A method for producing an anode composition for a lithium secondary battery, comprising mixing such an anode active material in a dry state, which employs such natural or artificial graphite whose graphite structure is determined by powder X-ray diffraction method d(002) is 0.335-0.337nm, and can absorb, store and release lithium, and such a vapor-grown carbon fiber, which has an internal hollow structure, has a structure of graphite single-layer sheets stacked in a direction perpendicular to the fiber axis, And d(002) in the graphite structure of the vapor-grown carbon fiber was measured by powder X-ray diffraction method to be 0.336-0.345nm, and then polyvinylidene fluoride was added thereto, followed by mixing while stirring. 12. The production method according to claim 11, wherein the polyvinylidene fluoride is in a liquid state dissolved in N-methyl-2-pyrrolidone. 13. A lithium secondary battery anode, which is obtained by the following steps: coating a metal current collector foil with the lithium secondary battery anode composition prepared by the method according to any one of claims 9-12, drying and then molding. 14. The lithium secondary battery anode according to claim 13, wherein the metal current collector foil is Cu or Cu alloy foil with a thickness of 1-50 μm. 15. A lithium secondary battery comprising the lithium secondary battery anode according to claims 1, 2, 3, 13 and 14 as a constituent. 16. The lithium secondary battery of claim 15, which uses a nonaqueous electrolyte solution and/or a nonaqueous polymer electrolyte, wherein the nonaqueous solvent and/or the nonaqueous polymer electrolyte for the nonaqueous electrolyte solution contains at least one A substance selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone and vinylene carbonate.

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