KR101701121B1 - Binder for nonaqueous electrolyte secondary cell, binder solution for nonaqueous electrolyte secondary cell, anode mixture for nonaqueous electrolyte secondary cell, and uses thereof - Google Patents

Abstract

An object of the present invention is to provide a nonaqueous electrolyte secondary battery which is excellent in adhesiveness and capable of reducing the initial irreversible capacity of the battery when the nonaqueous electrolyte secondary battery is manufactured and capable of improving the capacity retention ratio at the time of rapid discharge, The present invention relates to a binder for a nonaqueous electrolyte secondary battery, a binder solution for a nonaqueous electrolyte secondary battery, and a negative electrode mixture for a nonaqueous electrolyte secondary battery. The binder for a nonaqueous electrolyte secondary battery of the present invention comprises at least a binder resin for polyvinylidene fluoride having an inherent viscosity of 1.2 to 7 dl / And polyvinyl alcohol having a degree of saponification of 80 to 90 mol%, and the polyvinyl alcohol is contained in an amount of 5 to 90 mass% per 100 mass% of the total of the polyvinylidene fluoride and the polyvinyl alcohol.

Description

Technical Field [0001] The present invention relates to a binder for a nonaqueous electrolyte secondary battery, a binder solution for a nonaqueous electrolyte secondary battery, an anode mixture for a nonaqueous electrolyte secondary battery, and an application thereof. BACKGROUND ART [0002]

The present invention relates to a binder for a nonaqueous electrolyte secondary battery, a binder solution for a nonaqueous electrolyte secondary battery, an anode mixture for a nonaqueous electrolyte secondary battery, and a use thereof.

Recently, the development of electronic technology has been remarkable, and the miniaturization of portable electronic devices has been progressed, and the power source used therefor is required to be small in size and light in weight (high energy density). BACKGROUND ART As a battery having a high energy density, a non-aqueous electrolyte secondary battery typified by a lithium ion secondary battery is widely used. Recently, with the advancement of high performance of small-sized portable devices, it is expected that the non-aqueous electrolyte secondary battery further has high energy density and improved durability.

On the other hand, from the viewpoint of global environmental problems and energy saving, a hybrid vehicle combining a secondary battery and an engine or an electric vehicle powered by a secondary battery has been developed and put into practical use.

A vehicle-mounted power source used as a power source for a hybrid car or an electric car is large and expensive and becomes a main component of a vehicle as compared with a secondary battery used as a power source for a small portable device, . In addition, since the region and season of use of the automobile are various, it is also required to maintain durability and performance at high temperature and low temperature. Also, in these automobiles, it is important to accumulate the braking energy at the time of braking in the battery in order to improve the fuel efficiency, and a high-speed charging is required for this. In order to improve the acceleration of an automobile, the ability to emit energy in a short period of time, that is, high output density is required. As described above, in the nonaqueous electrolyte secondary battery for on-vehicle use, various performance enhancements including safety are required in addition to the performance required for a secondary battery for a small portable device.

In order to obtain a nonaqueous electrolyte secondary battery having such characteristics, various researches and developments have been made on each member constituting the battery. The non-aqueous electrolyte secondary battery is mainly composed of an anode, a cathode, a separator for separating the anode and the cathode, and an electrolyte. The positive electrode and the negative electrode are each formed by adhering a powdery active material to a collecting plate. In order to extract the performance of the active material as a battery performance, it is indispensable to improve the performance of the binder serving as an adhesive for these active materials.

Until now, polyvinylidene fluoride (PVDF) has been widely used as a binder resin for adhering an anode active material of a nonaqueous electrolyte secondary battery because of its excellent electrochemical stability, mechanical properties and slurry characteristics.

The nonaqueous electrolyte secondary battery is preferable as the charge / discharge capacity decreases even if the charge / discharge cycle is repeated. For this purpose, the structure of the active material is required to be stable even if charge and discharge are repeated. It is also important to bond the active material or the active material to the collector plate even if the binder is used for a long period of time in the electrode. Compared with a secondary battery for a small portable device, a large secondary battery for on-vehicle use is required to have high durability, and it is also required to improve the adhesion of a binder in order to improve durability.

In order to improve the adhesiveness, many binders can be used. However, if the amount of the binder used increases, the amount of the active material in the non-aqueous electrolyte secondary battery is reduced, and the charge-discharge capacity of the non-aqueous electrolyte secondary battery is lowered.

In addition, when the amount of the binder used increases, many binders cover the surface of the active material. In the in-vehicle rechargeable battery requiring high input / output characteristics, the binder layer on the surface of the active material becomes a resistance component, Which is undesirable.

On the other hand, it is known that, on the surface of the negative electrode active material, decomposition of the electrolyte solution on the surface of the negative electrode active material is suppressed by forming a surface coating called SEI (Solid Electrolyte Interface) film by reduction decomposition of the electrolyte. However, if the electrolyte becomes excessively thickened, There is a problem in that the film becomes a resistance component to decrease the capacity and deteriorate the input / output characteristics.

As a binder resin, it is desired that a coating capable of improving the adhesiveness without increasing the amount of the binder and capable of suppressing the excessive decomposition of the electrolytic solution effectively coat the surface of the negative electrode.

As the binder resin composition excellent in adhesiveness between the positive electrode active material or the negative electrode active material and the current collector and adhesion between the active materials, a binder resin composition containing (A) a water-soluble resin such as a polyvinyl alcohol derivative and a fluorine- A binder resin composition comprising a resin as an essential component has been proposed (for example, see Patent Document 1). However, the binder resin composition described in Patent Document 1 still has insufficient adhesiveness.

In addition, it is also possible to provide a positive electrode for a lithium ion secondary battery excellent in uniformity, durability and productivity of a positive electrode material mixture layer, wherein the positive electrode material mixture layer contains a first positive electrode active material including a lithium composite oxide, A positive electrode for a lithium ion secondary battery has been proposed (for example, see Patent Document 2). In Patent Document 2, polyvinylidene fluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride maleic acid-modified product and polytetrafluoroethylene are exemplified as the first polymer, and as the second polymer, Polyvinyl alcohol, and polyvinyl pyrrolidone are exemplified. In Patent Document 2, the second polymer is used for securing the fluidity of the positive electrode material mixture slurry used for forming the positive electrode material mixture layer, and when the second polymer is used, the amount of the dispersion medium used in the positive electrode material mixture slurry is excessively increased . It is also disclosed that the amount of the second polymer to be used is preferably 0.01 to 3% with respect to the total solid content, and when the content exceeds 3%, the rigidity of the obtained positive electrode is excessively increased and cracks may occur during winding.

In addition, as a long life lithium secondary battery, it has been proposed to use polyvinylidene fluoride mixed with a thermosetting plasticized polyvinyl alcohol-based resin composition which is a main component of the binder in order to suppress the capacity and the output that accompany the charge- (See, for example, Patent Document 3). However, the polyvinyl alcohol used as the main component can be used only for the thermosetting polyvinyl alcohol (first component) modified with succinic anhydride or the like for the polyvinyl alcohol-based resin. In addition, although the synthesis reaction of the first component is an esterification reaction of polyvinyl alcohol, it is necessary to use a large amount of an organic solvent in order to increase the viscosity of the reaction system and inhibit gelation, and it is difficult to control the water present in the solvent , And the acid anhydride reacts with the residual moisture to lower the esterification rate. In addition, there has been a problem in terms of performance, such as the unreacted product of the cyclic anhydride or the reaction catalyst deteriorating the battery performance. In addition, there has been a problem that the manufacturing cost becomes very high due to the complicated process.

In the examples, there are no examples in which high performance is exhibited only by a thermosetting polyvinyl alcohol-based resin, an example using an acrylic resin-based plasticizer as a second resin component is exemplified, and it is necessary to add a second component . The production of the binder used as the main component in this way requires complicated steps, and addition of additives such as plasticizers and the like require many steps to be carried out. In addition, in the capacity retention rate and the direct current resistance (Patent Document 3, Table 2), the examples do not have particularly excellent effects as compared with the comparative examples, and further improvement has been a problem.

Also, as a binder for an electrode having excellent adhesion to an electrode current collector and an ability to retain an active material, a vinyl alcohol polymer having a constituent unit represented by - (CH ₂ -CHOH) - in a proportion of 30 to 95 wt% A binder for a non-aqueous electrolyte secondary battery electrode has been proposed (for example, see Patent Document 4). As the binder for the nonaqueous electrolyte secondary battery electrode, it is disclosed that the vinyl alcohol polymer may be used alone or in combination with other binder for electrodes. Examples of usable binders include polyvinylidene fluoride, polytetrafluoroethylene, and the like By weight of a fluorine-containing resin.

However, the vinyl alcohol polymer disclosed in Patent Document 4 permits various structures as constituent units other than the constituent units represented by - (CH ₂ -CHOH) -, and other than the constituent units represented by - (CH ₂ -CHOH) - The effect of the constituent unit on the physical properties of the nonaqueous electrolyte secondary battery has not been fully investigated.

Further, even when a nonaqueous electrolyte secondary battery is manufactured using the binder for a nonaqueous electrolyte secondary battery electrode described in Patent Document 4, a battery having a sufficient capacity retention rate at the time of rapid discharge can not be obtained.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2004-95332

[Patent Document 2] JP-A-2009-123463

[Patent Document 3] Japanese Patent Application Laid-Open No. 2004-134367

[Patent Document 4] Japanese Patent Application Laid-Open No. H11-250915

SUMMARY OF THE INVENTION [

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and it is an object of the present invention to provide a nonaqueous electrolyte secondary battery which can reduce the initial irreversible capacity of the battery, A binder solution for a nonaqueous electrolyte secondary battery, and a negative electrode mixture for a nonaqueous electrolyte secondary battery.

[MEANS FOR SOLVING THE PROBLEMS]

The inventors of the present invention have conducted intensive studies in order to achieve the above object, and as a result, they found that the above problems can be solved by using specific polyvinylidene fluoride and specific polyvinyl alcohol in a specific ratio.

That is, the binder for a nonaqueous electrolyte secondary battery of the present invention comprises at least polyvinylidene fluoride having an inherent viscosity of 1.2 to 7 dl / g and polyvinyl alcohol having a saponification degree of 80 to 90 mol%, wherein the polyvinylidene fluoride And 5 to 90 mass% of the polyvinyl alcohol per 100 mass% of the total of the polyvinyl alcohol.

The average degree of polymerization of the polyvinyl alcohol is preferably 100 to 4000.

The binder solution for a nonaqueous electrolyte secondary battery of the present invention comprises a binder and a solvent for the nonaqueous electrolyte secondary battery.

The negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention comprises at least polyvinylidene fluoride having an innervant viscosity of 1.2 to 7 dl / g, polyvinyl alcohol having a saponification degree of 80 to 90 mol%, a negative electrode active material and a solvent, And 5 to 90 mass% of the polyvinyl alcohol per 100 mass% of the total of the polyvinyl alcohol and the polyvinyl alcohol.

The negative electrode active material is preferably made of a carbonaceous material.

The negative electrode for a nonaqueous electrolyte secondary battery of the present invention is obtained by applying the negative electrode mixture for a nonaqueous electrolyte secondary battery to a collector and drying the same.

The nonaqueous electrolyte secondary battery of the present invention has the negative electrode for the nonaqueous electrolyte secondary battery.

The binder for a nonaqueous electrolyte secondary battery, the binder solution for a nonaqueous electrolyte secondary battery, and the negative electrode mixture for a nonaqueous electrolyte secondary battery according to the present invention are excellent in adhesiveness and when a nonaqueous electrolyte secondary battery having a negative electrode for a nonaqueous electrolyte secondary battery formed using the same is manufactured, It is possible to reduce the initial irreversible capacity of the battery and to improve the capacity retention rate at the time of rapid discharge and improve the charge / discharge cycle characteristic.

[Mode for Carrying Out the Invention]

Next, the present invention will be described in detail.

The binder for a nonaqueous electrolyte secondary battery of the present invention comprises at least polyvinylidene fluoride having an innervant viscosity of 1.2 to 7 dl / g and polyvinyl alcohol having a saponification degree of 80 to 90 mol%, wherein the polyvinylidene fluoride and the polyvinyl alcohol Of the polyvinyl alcohol is contained in an amount of 5 to 90 mass% per 100 mass% of the total amount of the polyvinyl alcohol.

The binder solution for a nonaqueous electrolyte secondary battery of the present invention comprises a binder and a solvent for the nonaqueous electrolyte secondary battery.

The negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention comprises at least polyvinylidene fluoride having a viscosity of 1.2 to 7 dl / g, a polyvinyl alcohol having a saponification degree of 80 to 90 mol%, a negative electrode active material and a solvent, Vinylidene fluoride and 5 to 90 mass% of the polyvinyl alcohol per 100 mass% of the total of the polyvinyl alcohol.

In this specification, the negative electrode mixture for a nonaqueous electrolyte secondary battery is also simply referred to as a negative electrode mixture or a combination.

In the present invention, polyvinylidene fluoride having an inherent viscosity of 1.2 to 7 dl / g is used.

The inhaleant viscosity is an index indicating the molecular weight of the polymer. If the inhale viscosity of polyvinylidene fluoride is low, the peeling strength of the mixed layer from the current collector is lowered, which is not preferable. The inherent viscosity of the polyvinylidene fluoride is preferably 1.3 dl / g or more, more preferably 1.5 dl / g or more, and particularly preferably 2.0 dl / g or more. In addition, if the inhalant viscosity is too high, it becomes difficult to dissolve in the solvent, which is not preferable. The inherent viscosity of the polyvinylidene fluoride is preferably 6.0 dl / g or less, more preferably 5.0 dl / g or less, and particularly preferably 4.0 dl / g or less.

The polyvinylidene fluoride used in the present invention is a polymer obtained by using vinylidene fluoride as a monomer, and may be a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and another monomer. As the polyvinylidene fluoride, from the viewpoint of electrochemical stability and good processability, the constituent unit derived from vinylidene fluoride is preferably 90 mol% or more (constituent unit derived from the entire monomer is 100 mol%) or more, more preferably Is 95 mol% or more, particularly preferably vinylidene fluoride homopolymer. As the copolymerizable monomer, a fluorine-based monomer and a hydrocarbon-based monomer can be used. As the fluorine-based monomer, perfluoroalkyl vinyl ether represented by perfluoromethyl vinyl ether, vinyl fluoride, trifluoroethylene, tetrafluoroethylene, Hexafluoropropylene, and the like, and examples of the hydrocarbon-based monomer include ethylene, propylene, 1-butene, and the like. The homopolymer of vinylidene fluoride generally comprises only a constituent unit derived from vinylidene fluoride. In the present invention, the constituent unit derived from another monomer may be contained in an impurity quantity. Specifically, the amount of the impurity means specifically 0 to 0.05 mol% of constitutional units derived from other monomer per 100 mol% of the total of the constitutional units derived from vinylidene fluoride and the other monomer-derived constitutional units.

The method for producing the polyvinylidene fluoride is not particularly limited, but it can be produced by a known production method such as suspension polymerization, emulsion polymerization and solution polymerization. As the production method, suspension polymerization or emulsion polymerization is preferable in view of easiness of post-treatment and the like, and suspension polymerization is particularly preferable because polyvinylidene fluoride having little impurities is not required to use an emulsifier.

In the present invention, polyvinyl alcohol having a degree of saponification of 80 to 90 mol% is used.

The polyvinyl alcohol used in the present invention is soluble in N-methyl-2-pyrrolidone (hereinafter, sometimes abbreviated as NMP), which is a good solvent for polyvinylidene fluoride, and is soluble in non-aqueous electrolyte secondary batteries Is required to have low solubility in an electrolyte solvent constituting the electrolyte membrane. The degree of saponification can be used as an index showing the solubility of polyvinyl alcohol in a solvent. If the degree of saponification is too low, the solubility in an electrolyte solvent becomes undesirably high. If the degree of saponification is too high, And the solubility in a solvent is lowered. The degree of saponification of the polyvinyl alcohol is 80 to 90 mol%, and more preferably 85 to 90 mol%. When the degree of saponification of the polyvinyl alcohol is within the above range, the obtained non-aqueous electrolyte secondary battery is preferable because the capacity retention ratio at the time of rapid discharge is excellent.

The average degree of polymerization of the polyvinyl alcohol is preferably 100 to 4000, more preferably 150 to 3800, and particularly preferably 200 to 3600.

The degree of saponification and the degree of polymerization of the polyvinyl alcohol can be measured in accordance with JIS K 6726: Test Method for Polyvinyl Alcohol.

The polyvinyl alcohol is a kind of thermoplastic resin and is generally obtained by saponifying polyvinyl acetate. Therefore, the polyvinyl alcohol has a structural unit derived from vinyl acetate in addition to the structural unit represented by - (CH ₂ -CHOH) -. The above-mentioned polyvinyl alcohol may have about 0 to 8 mol% of constitutional units other than the constituent units represented by - (CH ₂ -CHOH) - and the constitutional units derived from vinyl acetate (other constitutional units) .

Further, even in the case of having another constituent unit, it is preferable not to have a constituent unit derived from ethylene from the viewpoint of securing solubility in an organic solvent.

Examples of other structural units that may be contained include vinyl propionate, vinyl butyrate, vinyl monochloroacetate, and the like.

The binder for a nonaqueous electrolyte secondary battery of the present invention is characterized by containing at least the polyvinylidene fluoride and the polyvinyl alcohol. The binder is excellent in adhesiveness and can reduce the initial irreversible capacity of the nonaqueous electrolyte secondary battery of the present invention And the capacity retention rate at the time of rapid discharge is also excellent. Although the reason for this is not clear, the present inventors speculate that the polyvinyl alcohol effectively covers the negative electrode active material. More specifically, the polyvinyl alcohol effectively coats the negative electrode active material, thereby exhibiting excellent adhesion and coating, thereby reducing the decomposition reaction of the electrolytic solution on the surface of the negative electrode active material, thereby making it possible to reduce the initial irreversible capacity, The present inventors speculate that the capacity retention ratio at the time of discharge is excellent.

The binder for a non-aqueous electrolyte secondary cell of the present invention may contain the polyvinylidene fluoride and a resin (other resin) other than the polyvinyl alcohol. As the binder for the non-aqueous electrolyte secondary battery of the present invention, the larger the total ratio of the polyvinylidene fluoride and the polyvinyl alcohol to the total binder resin is, the more preferable the polyvinylidene fluoride and the polyvinylidene fluoride per 100 mass% The total amount of the alcohol is preferably 60 mass% or more, more preferably 80 mass% or more, and particularly preferably 90 mass% or more.

In order to manifest the function of the binder for the nonaqueous electrolyte secondary cell of the present invention, it is important to add the polyvinyl alcohol in an appropriate ratio to the polyvinylidene fluoride. The binder for a non-aqueous electrolyte secondary cell of the present invention comprises 5 to 90 mass% of the polyvinyl alcohol per 100 mass% of the total of the polyvinylidene fluoride and the polyvinyl alcohol. If the content of the polyvinyl alcohol is too small, the effect of suppressing the decomposition reaction of the electrolytic solution on the surface of the active material is deteriorated. The content of the polyvinyl alcohol is 5% by mass or more, preferably 6% by mass or more. On the other hand, if the content of the polyvinyl alcohol is excessively large, the coating formed on the surface of the active material is too thick to increase the resistance between the active material and the electrolyte interface, thereby deteriorating the input / output characteristics. The content of the polyvinyl alcohol is 90 mass% or less, preferably 80 mass% or less, more preferably 70 mass% or less, further preferably 50 mass% or less, and most preferably 30 mass% or less . Within the above range, the non-aqueous electrolyte secondary battery is preferable because it has excellent input and output characteristics and adhesion of the binder.

The binder solution for a nonaqueous electrolyte secondary battery of the present invention comprises a binder and a solvent for the nonaqueous electrolyte secondary battery.

As the solvent, an organic solvent is usually used. As the solvent, a solvent having an action to dissolve the polyvinylidene fluoride and polyvinyl alcohol is usually used, and a solvent having a polarity is preferably used. Specific examples of the solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, hexamethylphosphoramide, dioxane, tetrahydrofuran, Urea, triethyl phosphite and trimethyl phosphite. N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and dimethyl sulfoxide are preferable. The organic solvent may be used alone or in combination of two or more.

The binder solution for a nonaqueous electrolyte secondary battery of the present invention may be prepared by dissolving at least a part of the polyvinylidene fluoride and polyvinyl alcohol in a solvent without any particular limitation. Examples of the method for producing the binder solution for a nonaqueous electrolyte secondary battery include a method for producing a binder solution for a nonaqueous electrolyte secondary battery by simultaneously mixing the polyvinylidene fluoride and polyvinyl alcohol with a solvent, A method for producing a binder solution for a nonaqueous electrolyte secondary battery by mixing the obtained mixed liquid and the polyvinyl alcohol, a method for mixing the polyvinyl alcohol with a solvent, A method for producing a binder solution for a battery, a method for preparing a binder solution for polyvinylidene fluoride and a solvent, a method for preparing a binder solution for a non-aqueous electrolyte secondary battery by separately preparing a mixture of the polyvinyl alcohol and a solvent, And the like.

Further, the mixed solution obtained by mixing the polyvinyl alcohol with the solvent in advance is preferably used after filtration, since the negative electrode mixture for the nonaqueous electrolyte secondary battery is applied to the collector and dried to make the mixed layer more uniform.

The binder solution for the nonaqueous electrolyte secondary battery generally contains 100 to 9000 parts by mass, preferably 150 to 4900 parts by mass, more preferably 250 to 3,000 parts by mass of the solvent per 100 parts by mass of the total of the polyvinylidene fluoride and the polyvinyl alcohol. To 3500 parts by mass. Within this range, the stability of the binder solution and the workability at the time of electrode production are preferable.

The negative electrode material mixture for a nonaqueous electrolyte secondary battery of the present invention includes at least the polyvinylidene fluoride, the polyvinyl alcohol (binder for a nonaqueous electrolyte secondary battery), a solvent, and a negative electrode active material. The negative electrode material mixture for a nonaqueous electrolyte secondary battery may contain a conductive auxiliary agent as required. As the solvent, those described as the solvent constituting the binder solution for the above-mentioned nonaqueous electrolyte secondary battery can be used.

The negative electrode material mixture for a nonaqueous electrolyte secondary battery contains 5 to 90 mass% of the polyvinyl alcohol per 100 mass% of the total of the polyvinylidene fluoride and the polyvinyl alcohol. The content of the polyvinyl alcohol is preferably 6 mass% or more. The content of the polyvinyl alcohol is preferably 80 mass% or less, more preferably 70 mass% or less, further preferably 50 mass% or less, and most preferably 30 mass% or less.

The negative electrode active material is not particularly limited as long as it is a material capable of inserting and extracting lithium, but a negative electrode active material made of a carbon-based material, a metal alloy material, a metal oxide, or the like can be used. As the negative electrode active material, it is preferable to use a negative electrode active material composed of a carbonaceous material, that is, a carbon-based negative electrode active material.

The ratio of the active material in the negative electrode mixture for the nonaqueous electrolyte secondary battery is preferably 70 to 99.9 parts by mass, more preferably 75 to 99.5 parts by mass, per 100 parts by mass of the sum of the polyvinylidene fluoride, polyvinyl alcohol and the negative electrode active material And particularly preferably 80 to 99 parts by mass. As the additive, a conductive additive such as carbon black or a dispersant such as polyvinyl pyrrolidone may be included.

The ratio of the solvent in the negative electrode mixture for the nonaqueous electrolyte secondary battery is usually 3 to 300 parts by mass, preferably 4 to 300 parts by mass, per 100 parts by mass of the total amount of the polyvinylidene fluoride, the polyvinyl alcohol and the negative electrode active material. 200 parts by mass. Within the above range, the stability and coating properties of the compound are excellent. The viscosity of the negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention is preferably 2000 to 50000 mPa · s, and more preferably 5000 to 30000 mPa · s.

In the method for producing the negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention, the polyvinylidene fluoride, polyvinyl alcohol, negative electrode active material and solvent are mixed so as to be a uniform slurry, and there is no particular limitation. Examples of the method for producing the negative electrode mixture for a nonaqueous electrolyte secondary battery include a method for preparing a negative electrode mixture for a nonaqueous electrolyte secondary battery by adding and mixing a negative electrode active material to the binder solution for the nonaqueous electrolyte secondary battery, A method for producing a negative electrode mixture for a nonaqueous electrolyte secondary battery by simultaneously mixing all the components, a method for producing a negative electrode mixture for a nonaqueous electrolyte secondary battery by adding and mixing the negative electrode active material and a solvent to a binder for the nonaqueous electrolyte secondary battery, A method of preparing a solution of vinylidene and the solvent, a solution of the polyvinyl alcohol and a solvent, mixing the two kinds of solutions, the negative electrode active material and a solvent to prepare a negative electrode mixture for a nonaqueous electrolyte secondary battery.

The solution obtained by mixing the polyvinyl alcohol with the solvent in advance is preferably used after filtration, since the negative electrode mixture for the nonaqueous electrolyte secondary battery is applied to the collector and dried to make the mixture layer more uniform.

Examples of the carbonaceous anode active material include a graphitic material and a carbonaceous material having a turbostratic structure such as a non-graphitizable carbon or a graphitizable carbon (hereinafter also referred to as a stratified carbon). The use of such a negative electrode active material made of such a carbon-based material is preferable because it makes it possible to manufacture a secondary battery having high durability and high energy density.

Examples of the graphite material include artificial graphite obtained by heat-treating graphitizable carbon at a high temperature (for example, 2000 ° C or higher) and natural graphite produced from nature. Characteristic of the graphite material is that the carbon hexagonal network plane has a three - dimensional regularity and has a laminated structure unlike the carbonaceous material having the egg shell structure. This structure can be found by observing the 100 diffraction line, the 101 diffraction line and the 110 diffraction line and the 112 diffraction line separately from the diffraction line measured by the powder X-ray diffraction method. It is also known that the average layer surface spacing of the hexagonal mesh planes of the carbonaceous material decreases as it approaches the graphite structure and is close to the mean layer plane spacing of the ideal graphite structure, 0.3354 nm. The value is determined by powder X- can do. Since the graphite material has a higher crystal structure, it is possible to store a larger amount of lithium, so that the preferable average value of the average layer surface spacing is 0.345 nm or less, more preferably 0.340 nm or less. Since the graphite material is larger than the true density of the graphitizable carbon having the true density, it can accumulate a large energy in a small volume. Therefore, it is preferable to use a graphite material as the negative electrode active material in order to improve the volume energy density.

In addition, the true density of the graphite material having an ideal structure is 2.26 g / cm < 3 >, and the true density tends to decrease as the crystal structure is disturbed. The true density of the graphite material is preferably 1.9 g / cm3 or more, more preferably 2.0 g / cm3 or more, and still more preferably 2.1 g / cm3 or more.

The carbonaceous material having an egg shell structure is classified into graphitizable carbon and non-graphitizable carbon, and no diffraction line suggesting three-dimensional regularity is observed in the measurement of powder X-ray diffraction, and 10 diffraction lines or 11 diffraction And a diffraction line due to two-dimensional reflection such as a line is observed.

The graphitizable carbon has a property of being changed to a graphitic material by heat treatment at a high temperature (for example, 2000 ° C. or more). A characteristic of graphitizable carbon as a negative electrode active material is that it exhibits a charging / discharging curve in which the voltage changes gently with respect to a charged amount similar to that of non-graphitizable carbon, and it is easy to detect the charged state from the terminal voltage in the battery using the graphitizable carbon. Further, since the potential difference from the charging cut potential is large, it is advantageous for rapid charging. Since graphitizing carbon carries expansion and contraction during charging and discharging, its charging capacity and durability per unit weight are lower than that of non-graphitizable carbon, but it is easy to obtain volume per volume because of the high true density of graphitizable carbon. In addition, since the specific surface area is smaller than that of the non-graphitizable carbon and the absorbability is low, it also has a favorable property that the increase in the irreversible capacity due to oxidation deterioration during storage is small. The graphitizable carbon having a stratified structure can be irradiated by a powder X-ray diffraction method, but the graphitizable carbon differs in electrochemical properties depending on raw materials and conditions of the carbonization reaction. The graphitizable carbon is structurally changed according to the production conditions thereof, and its characteristics can be known by the true density, and when the true density is low, the degree of carbonization is insufficient and the irreversible capacity is increased. In addition, if the true density is too high, the discharge capacity is undesirably reduced. The true density of the graphitizable carbon is preferably 1.8 g / cm3 or more and 2.1 g / cm3 or less.

As the graphitizable carbon, a graphitizable carbon having an average layer spacing (d ₀₀₂ ) of 0.335 to 0.360 nm of (002) planes obtained by an X-ray diffraction method is preferable. The graphitizable carbon preferably is a graphitizable carbon having a crystallite size (Lc ₍₀₀₂₎ ) of 10 nm or more in the c-axis direction. The use of graphitizable carbon having d ₀₀₂ in the above range as the negative electrode active material is preferable because irreversible capacity of the non-aqueous electrolyte secondary battery can be reduced.

On the other hand, the non-graphitizable carbon has a smaller true density than the graphite material and the graphitizable carbon, but it is possible to store a large amount of lithium in the fine space, and since the change of the crystal structure is small even when charging and discharging are repeated, . In addition, even in the case of an electrolytic solution which can be used at a low temperature such as propylene carbonate, the decomposition of the electrolytic solution is small, and therefore, the low temperature characteristics are excellent. In addition, since the terminal voltage has a gentle charging / discharging curve due to the filling rate as in the graphitizable carbon, the charging state can be easily detected from the terminal voltage in the battery using the charging / discharging curve. Further, since the potential difference with the charging cut potential is large, And the like.

The crude graphitizable carbon preferably has a true density of 1.4 g / cm3 or more and less than 1.8 g / cm3. As the non-graphitizable carbon, it is preferable that the average layer spacing (d ₀₀₂ ) of the (002) planes obtained by the X-ray diffraction method is 0.365 to 0.400 nm.

The true density of the non-graphitizable carbon is more preferably 1.4 to 1.7 g / cm 3, and particularly preferably 1.4 to 1.6 g / cm 3.

If the true density exceeds the above range, the charge capacity and the discharge capacity may decrease, which is not preferable.

The average layer surface interval (d ₀₀₂ ) of the non-graphitizable carbon is more preferably 0.370 to 0.395 nm, and particularly preferably 0.375 to 0.390 nm.

The Lc ₍₀₀₂₎ of the non-graphitizable carbon is preferably 10 nm or less, more preferably 5 nm or less, and further preferably 3 nm or less. When Lc ₍₀₀₂₎ is less than 1.0 nm, formation of a carbon skeleton is insufficient, which is not preferable. Therefore, the preferable Lc ₍₀₀₂₎ is 1.0 nm or more and 10 nm or less, more preferably 1.0 nm or more and 5 nm or less, and further preferably 1.0 nm or more and 3 nm or less.

Examples of the carbon-based anode active material include artificial graphite and natural graphite, and graphitizable carbon or non-graphitizable carbon is classified as a stratified carbon. In addition, since the negative electrode active material has a number of different characteristics, it may be used singly or in combination of two or more. As the negative electrode active material, non-graphitizable carbon is more preferable for excellent input / output characteristics and durability of the nonaqueous electrolyte secondary battery. Further, in the case of using non-graphitizable carbon, the initial irreversible capacity of the non-aqueous electrolyte secondary battery is relatively large. However, in the present invention, by using the polyvinylidene fluoride and polyvinyl alcohol as the binder, Can be reduced.

If the average particle diameter of the negative electrode active material is too small, the specific surface area increases and irreversible capacity increases. If the particle diameter is small, the mean free path becomes short and safety during short circuit becomes low. On the other hand, if the average particle diameter is too large, the active material layer of the electrode becomes uneven and the diffusion-free stroke of lithium in the particles increases, which makes it difficult to charge and discharge rapidly. In order to increase the input / output characteristics, it is necessary to widen the electrode area. In order to widen the electrode area within a limited volume, it is necessary to make the active material layer of the electrode thinner. From this viewpoint, the average particle diameter of the negative electrode active material is preferably 1 to 40 m, more preferably 2 to 30 m, and particularly preferably 3 to 15 m.

If the specific surface area of the negative electrode active material is too small, it is difficult to introduce the binder into the active material, and sufficient adhesion can be ensured. In addition, the reaction area for charging and discharging is reduced, which makes charging and discharging difficult, which is not preferable. On the other hand, if the specific surface area is too large, the decomposition amount of the electrolyte increases, and the initial irreversible capacity increases, which is not preferable.

The specific surface area of the negative electrode active material is preferably 0.3 to ²⁵ m ² / g, more preferably 0.5 to ²⁰ m ² / g, and particularly preferably ² to 10 m ² / g.

As the negative electrode active material made of a metal oxide, for example, lithium titanate, lithium vanadium oxide and the like can be used.

The method for producing the carbon-based negative electrode active material is not particularly limited, and for example, it can be produced by firing a decalcified coal obtained by degassing coconut husk and the like.

Examples of commercial products of the carbon-based anode active material include CARBOTRON PS (F) (non-graphitizable carbon), BTR (registered trademark) 918 (BTR NEW ENERGY MATERIALS INC Co., natural graphite), and the like. As the negative electrode active material composed of the metal oxide, ENERMIGHT (registered trademark) LT series LT106 (manufactured by Ishihara Industries, Ltd., lithium titanate) can be used.

The negative electrode for a nonaqueous electrolyte secondary battery of the present invention is obtained by applying and drying an negative electrode mixture for a nonaqueous electrolyte secondary battery to a current collector.

In the present invention, a layer formed from a negative electrode mixture for a nonaqueous electrolyte secondary battery formed by applying and drying a negative electrode mixture for a nonaqueous electrolyte secondary battery to a current collector is referred to as a composite layer.

INDUSTRIAL APPLICABILITY The negative electrode for a nonaqueous electrolyte secondary battery of the present invention has excellent peel strength between a current collector and a mixed layer. The negative electrode for the nonaqueous electrolyte secondary battery is characterized by using the negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention and has excellent peel strength between the current collector and the mixed layer.

The reason why the negative electrode for a nonaqueous electrolyte secondary battery of the present invention is excellent in the peel strength between the collector and the mixture layer is not clear, but it is presumed that the peel strength between the collector and the mixture layer is excellent because the mixture contains the polyvinyl alcohol.

The current collector used in the present invention includes, for example, copper and nickel, and examples of the shape include metal foil and metal nets. A copper foil is preferable as the current collector.

The thickness of the current collector is preferably 5 to 100 mu m, more preferably 5 to 20 mu m.

In addition, the thickness of the composite layer (per one surface) is preferably 10 to 250 mu m, more preferably 20 to 150 mu m.

When manufacturing the negative electrode for a nonaqueous electrolyte secondary battery of the present invention, the negative electrode mixture for a nonaqueous electrolyte secondary battery is applied to at least one surface, preferably both surfaces, of the current collector. The method for application is not particularly limited, and examples of the method include coating with a bar coater, a die coater, and a comma coater. Further, the drying furnace to be carried out after application is usually carried out at a temperature of 50 to 150 DEG C for 1 to 300 minutes. The pressure at the time of drying is not particularly limited, but is usually carried out under atmospheric pressure or reduced pressure. In addition, heat treatment may be performed after drying. When heat treatment is carried out, it is carried out at a temperature of 100 to 160 DEG C for 1 to 300 minutes. Further, although the temperature of the heat treatment is overlapped with the above-mentioned drying, these processes may be separate processes, or may be continuous processes.

Further, a press treatment may be further carried out. In the case of press processing, the press pressure is not particularly limited, but is preferably 1.0 MPa (0.2 t / cm 2) to 52.0 MPa (10 t / cm 2), more preferably 1.6 MPa (0.3 t / 41.6 MPa (8 t / cm 2). The pressing treatment is preferable because the electrode density can be improved.

The negative electrode for a nonaqueous electrolyte secondary battery of the present invention can be produced by the above method. When the negative electrode mixture for a non-aqueous electrolyte secondary battery is applied to one surface of a current collector, the negative electrode mixture for a non-aqueous electrolyte secondary battery is composed of two layers of a mixture layer / current collector, Layer structure of a mixed layer / a collector / a mixed layer.

Since the negative electrode for a nonaqueous electrolyte secondary battery of the present invention uses the negative electrode mixture for a nonaqueous electrolyte secondary battery, cracking or peeling of the electrode easily occurs in processes such as pressing, slitting, and winding, This is preferable because it leads to improvement of productivity.

As described above, the negative electrode for a nonaqueous electrolyte secondary battery of the present invention has excellent peel strength between a collector and a mixture layer. Specifically, the peel strength of the collector and the mixture layer is measured by a 180 deg. Peel test according to JIS K6854 And is generally 0.5 to 20 gf / mm, preferably 1 to 15 gf / mm.

INDUSTRIAL APPLICABILITY The negative electrode for a nonaqueous electrolyte secondary battery of the present invention has excellent peel strength between a current collector and a mixed layer.

The nonaqueous electrolyte secondary battery of the present invention is characterized by having a negative electrode for the nonaqueous electrolyte secondary battery.

The nonaqueous electrolyte secondary battery of the present invention is not particularly limited except that it has the negative electrode for the nonaqueous electrolyte secondary battery. As the nonaqueous electrolyte secondary battery, conventionally well-known materials other than the negative electrode, for example, an anode and a separator may be used as the negative electrode for the nonaqueous electrolyte secondary battery.

The positive electrode is not particularly limited as long as it has a positive electrode active material that is a main component of the positive electrode reaction and has a current collecting function. In most cases, the positive electrode active material layer and the positive electrode material mixture layer function as current collectors, And a positive electrode current collector.

When the nonaqueous electrolyte secondary battery is a lithium ion secondary battery, a lithium-based positive electrode active material containing at least lithium is preferable as the positive electrode active material constituting the positive electrode mixture layer.

Examples of the lithium-based positive electrode active material include transition metals such as LiMY ₂ (M is a transition metal such as Co, Ni, Fe, Mn, Cr, V, etc.) such as LiCoO ₂ , LiNi _x Co _1-x O ₂ A composite metal chalcogenide compound represented by at least one kind of metal: Y is a chalcogen element such as O, S or the like), a composite metal oxide having a spinel structure such as LiMn ₂ O _4, or an olivine-type lithium compound such as LiFePO ₄ have. A commercially available cathode active material may also be used.

The specific surface area of the cathode active material is preferably 0.05 to 50 m ² / g.

The binder resin used when forming the positive electrode material mixture layer is not particularly limited, but those widely used in conventionally known lithium ion secondary batteries can be suitably used. For example, polytetrafluoroethylene, polyvinylidene fluoride , Fluorocarbon resins such as fluorine rubber, acrylonitrile-butadiene copolymers and hydrides thereof, and ethylene-methyl acrylate copolymers. As the above-mentioned fluorocarbon resin, a vinylidene fluoride copolymer may also be used. Vinylidene fluoride-maleic acid monomethyl ester copolymer and the like can be used as the vinylidene fluoride-based copolymer.

In the case where the nonaqueous electrolyte secondary battery is a lithium ion secondary battery, it is preferable that the nonaqueous electrolyte secondary battery is made of aluminum or an alloy thereof as the positive electrode collector, and aluminum foil is particularly preferable. The thickness of the current collector is typically 5 to 100 mu m.

The separator is a separator constituting a nonaqueous electrolyte secondary battery, and functions to electrically insulate the positive electrode from the negative electrode and to hold the electrolyte solution. Examples of the separator include, but are not limited to, polyolefin polymers such as polyethylene and polypropylene, polyester polymers such as polyethylene terephthalate, aromatic polyamide polymers, polyimide polymers such as polyetherimide, polyether sulfone, Single-layer and multilayer porous films and nonwoven fabrics made of polysulfone, polyether ketone, polystyrene, polyethylene oxide, polycarbonate, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, ceramics, have. In particular, it is preferable to use a porous membrane of a polyolefin-based polymer (polyethylene, polypropylene). Examples of the polyolefin-based polymer porous membrane include a single-layer polypropylene separator, a single-layer polyethylene separator, and a polypropylene / polyethylene / polypropylene three-layer separator commercially available as Celgard (registered trademark) of Polyfor.

The nonaqueous electrolyte secondary battery of the present invention can reduce the initial irreversible capacity as compared with the conventional nonaqueous electrolyte secondary battery, and can maintain the capacity retention rate at the time of rapid discharge and improve the charge / discharge cycle characteristic.

The method of analyzing the binder in the present specification will be described below.

[Method of Measuring Intrinsic Viscosity of Polyvinylidene Fluoride]

The above-mentioned inherent viscosity refers to the logarithmic viscosity at 30 ° C of a solution prepared by dissolving 4 g of the resin in 1 liter of N, N-dimethylformamide. The calculation of the intrinsic viscosity η _i can be carried out by dissolving 80 mg of polyvinylidene fluoride in 20 ml of N, N-dimethylformamide and using a Uberode viscometer in a thermostatic chamber at 30 ° C. according to the following equation.

? _i = (1 / C)? ln (? /? ₀ )

Where η is the viscosity of the polymer solution, η ₀ is the viscosity of the solvent, N, N-dimethylformamide alone, and C is 0.4 g / dl.

[Determination of saponification degree of polyvinyl alcohol]

The degree of saponification and the degree of polymerization of the polyvinyl alcohol can be measured in accordance with JIS K 6726: Test Method for Polyvinyl Alcohol.

[Method of measuring viscosity of negative electrode mixture]

Details of the measurement method will be described below. Before measurement, a conical rotor of 3 占 R14 (cone angle of 3 占 and radius of 14 mm) was pushed into the rotor shaft on a detection head of an E-type viscometer (Tokai Sangyo Co., Ltd .; RE550R). In addition, the sample cup with the temperature adjusting function was adjusted to 25 ° C.

The measurement was carried out as follows. A sample cup was detached from the detection head and a homogeneous mixture was injected into the center portion of a 0.55 mL sample cup using a syringe. After the sample injection, the sample cup was mounted on the detection head again. After the sample injection, the sample was allowed to stand for 1 minute, and the sample temperature was set to 25 占 폚, and then the measurement was carried out at a shear rate of 2s- ¹ for 5 minutes. The viscosity after 5 minutes from the start of the measurement was measured to obtain the viscosity of the mixture.

Example

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

The physical properties of the negative electrode active material used in Examples and Comparative Examples are shown in Table 1 below. In the following Table 1, the active material denoted by LT106 is lithium titanate and the other active material is a carbon-based negative electrode active material.

[Table 1]

Each physical property in the above Table 1 was measured by the method described below.

(1) Average particle diameter (Dv50 (占 퐉))

Three drops of a dispersant (cationic surfactant "SN Wet 366" (manufactured by San Nopco)) are added to about 0.1 g of the negative electrode active material, and the dispersant is mixed into the negative electrode active material. Subsequently, 30 ml of pure water was added and dispersed for about 2 minutes by ultrasonic cleaning, and then a particle size distribution in the range of 0.5 to 3000 m in particle diameter was determined with a particle size distribution meter (Shimadzu Corporation "SALD-3000J").

The particle diameter at which the cumulative volume became 50% from the particle diameter distribution was defined as an average particle diameter (Dv50 (占 퐉)).

(2) the average layer surface spacing (d ₀₀₂ ) of the carbon-based negative active material and the crystallite size (Lc ₍₀₀₂₎ ) in the c-

The carbon-based anode active material powder was filled in a sample folder and measured by a symmetric reflection method using X'PertPRO manufactured by PANalytical. An X-ray diffraction pattern was obtained by using a CuK? Ray (wavelength? = 0.15418 nm) monochromated by a Ni filter as a source at an applied current / applied voltage of 45 kV / 40 mA. The correction of the diffraction pattern was carried out according to the Rachinger method only for the correction of the double lines of Kα ₁ and Kα ₂ without correcting for Lorentz polarizing factor, absorption factor, atom scattering factor and the like. (002) diffraction angle was corrected using a (111) diffraction line of a high purity silicon powder for a standard material, d ₀₀₂ was calculated by the following Bragg formula with the wavelength of the CuK? Ray being 0.15418 nm. Further, from the half width of the (002) diffraction line obtained by the integration method and the half width of the (111) diffraction line of the high purity silicon powder for a standard material,? _1/2 is obtained using the Alexander curve, The thickness Lc ₍₀₀₂₎ of the crystallite was calculated. Here, the shape factor K is 0.9.

[Equation 1]

(3) True density by the butanol method (JIS R7212) (ρ _B )

The true density of the carbonaceous anode active material by the butanol method was measured according to the method specified in JIS R7212. The outline is described below.

Weigh accurately the mass (m ₁ ) of the internal volume of 40 ml cigarette lighter. Subsequently, the sample is placed flat on the bottom portion so as to have a thickness of about 10 mm, and then the mass (m ₂ ) is precisely weighed. Add 1-butanol carefully to this to a depth of about 20 mm from the bottom. Subsequently, it is confirmed that the generation of large air bubbles is eliminated by applying a slight vibration to the airbag, and then it is put into a vacuum desiccator and gradually evacuated to 2.0 to 2.7 ㎪. It was kept at that pressure for more than 20 minutes. After the generation of air bubbles ceased, it was taken out, filled with 1-butanol, capped and immersed in a constant temperature water bath (adjusted to 30 ± 0.03 ° C) for 15 minutes or more, To the line. Subsequently, this is taken out, the outside is wiped and cooled to room temperature, and the mass (m ₄ ) is precisely weighed.

Subsequently, the same syringe bottle is filled with 1-butanol, immersed in a constant temperature water bath in the same manner as above, and the mass (m ₃ ) is weighed.

In addition, the distilled water from which the dissolved gas has been removed by boiling immediately before use is taken in a syringe bottle, immersed in a constant temperature water tank as described above, and the mass (m ₅ ) is weighed.

ρ _B is calculated by the following equation.

_{ρ B = (m 2 -m 1} ) (m 3 -m 1) d / [{m 2 -m 1 - (m 4 -m 3)} (m 5 -m 1)]

Here, d is the specific gravity of water at 30 캜 (0.9946 (g / cm 3)).

(4) Specific surface area (SSA)

(Relative pressure x = 0.3) by nitrogen adsorption at liquid nitrogen temperature using the approximate equation vm = 1 / (v (1-x)) derived from the equation of BET, The specific surface area of the sample (negative electrode active material) was calculated.

Specific surface area = 4.35 x vm (m ² / g)

In the approximation formula derived from the equation of BET, vm is an amount of adsorption (cm 3 / g) necessary for forming a monomolecular layer on the surface of a sample, v is a measured adsorption amount (cm 3 / g), and x is a relative pressure.

Specifically, the amount of nitrogen adsorbed to the carbonaceous substance at the liquid nitrogen temperature was measured using "Flow Sorb II2300" manufactured by MICROMERITICS Co., Ltd. as follows.

The sample tube was charged with the negative electrode active material pulverized into particles having a particle diameter of about 5 to 50 mu m and the sample tube was cooled to -196 DEG C while flowing helium gas containing nitrogen at a concentration of 30 mol% to adsorb nitrogen to the negative electrode active material . The test tube is then returned to room temperature. At this time, the amount of nitrogen released from the sample was measured by a thermal conductivity type detector, and the amount of adsorbed gas was determined as v.

The negative electrode active material described as the carbonaceous negative electrode active material derived from coconut shells in Table 1 was prepared by the method described below.

[Production of carbonaceous anode active material derived from coconut shells]

30 g of crushed coconut shell (filipinic acid) having an average particle size of 1 mm or less and 100 g of 35% hydrochloric acid were added and stirred at 150 DEG C for 2 hours. After filtration, the filtration residue was sufficiently washed with ion- Deg.] C for 2 hours to obtain demagnetized coal (Hyper coal).

The thus obtained demineralized carbon was pulverized and classified to obtain carbon precursor fine particles having an average particle diameter of about 10 탆, followed by firing at 1,250 캜 for one hour to obtain a carbon-based negative electrode active material derived from coconut shells. Further, the carbon-based negative electrode active material derived from palm shell-like carbon is non-graphitizable carbon.

In Table 1, commercially available products were used as the negative electrode active materials other than the carbonaceous negative electrode active material derived from the coconut shell carbon.

In Table 1, the negative electrode active material described as CARBOTRON P is CARBOTRON PS (F) (Kureha Co.) (non-graphitizable carbon) and the negative active material described as BTR 918 is BTR (registered trademark) 918 (BTR NEW ENERGY MATERIALS INC., Natural graphite), and the negative active material described as LT106 is ENERMIGHT (registered trademark) LT series LT106 (lithium titanate manufactured by Ishihara Industries, Ltd.).

[Example 1]

(Hereinafter referred to as " PVDF ") (KF # 7200, innert viscosity (η _i ), 2.2 dl / g, manufactured by Kureha Co., 63.8 parts by mass of an NMP solution containing a polyvinylidene fluoride (# 7200) content of 8% by mass and a polyvinyl alcohol (hereinafter also referred to as PVA) (Kuraray POVAL PVA-205 manufactured by Kuraray Co., Ltd.) 9 parts by mass of an NMP solution having a PVA content of 10% by mass, 94 parts by mass of an active material (CARBOTRON P), and further NMP were dissolved in NMP and stirred to prepare an electrode mixture having a solid concentration of 56% by mass. The mass fraction of the active material, PVDF and PVA is 94: 5.1: 0.9.

[Measurement of peel strength]

(Preparation of Electrode for Peeling Strength Measurement)

The electrode mixture was uniformly coated on one surface of a copper foil having a thickness of 10 m with a spacer so as to have a total thickness of 100 탆 and then uniformly coated using a bar coater and heated and dried at 110 캜 for 30 minutes under a nitrogen atmosphere to obtain an electrode structure Electrode for measurement).

(Measurement of Peel Strength of Electrode Composition Layer in Electrode Structure)

The electrode assembly obtained by applying an electrode mixture to a current collector (copper foil) and drying by heating was used as a sample, and the peel strength of the electrode mixture layer from the current collector was measured in accordance with JIS K6854 (measurement of peel strength) .

Specifically, the electrode structure was cut out with a width of 2 cm and a length of 5 cm, a tape (NITTO TAPE) was adhered to the electrode structure surface (electrode mixture layer surface), pressed at 7 mPa-s for 20 seconds, A sample sufficiently adhered to the electrode structure surface was used as a sample.

The copper foil of the sample was peeled off to a depth of 2.7 cm at an angle of 90 ° and then a sample was fixed to a compression tester (STA-1150 manufactured by ORIENTEC Co.) and pulled at 180 ° at 200 mm / min. The value obtained by dividing the average value of the load by the structure width (20 mm) was defined as the peel strength.

[Evaluation of cell performance, measurement of irreversible capacity]

(Preparation of electrode for charging / discharging test)

The electrode mixture was uniformly coated on one side of a copper foil having a thickness of 18 mu m, and then heated and dried at 120 DEG C for 25 minutes. And then pressed to form a negative electrode (this negative electrode was also referred to as a charge / discharge test electrode, a carbon electrode). The mass of the active material in the electrode was adjusted to 10 mg.

(Charge / discharge test method)

The active material (CARBOTRON P) is used as a negative electrode active material constituting the negative electrode of a non-aqueous solvent secondary battery. However, the remaining capacity without de-doping in the battery active material by the additive binder (PVDF or PVA) A lithium ion secondary battery in which a stable lithium metal as a counter electrode (negative electrode) is used and the electrode obtained in the above is used as an anode is constructed in order to evaluate the reduction effect of the lithium ion secondary battery with high precision without being affected by unevenness of the counter electrode performance, The properties were evaluated.

That is, the present invention is an anode mix for a nonaqueous electrolyte secondary battery or a negative electrode for a nonaqueous electrolyte secondary battery. However, when the irreversible capacity and the capacity retention rate at the time of rapid discharge described below are evaluated, the electrode is used as an anode instead of a cathode.

(Preparation of battery for charging / discharging test)

The electrode for charging / discharging test was press-bonded to a stainless steel mesh disk having a diameter of 17 mm and spot-welded on a lid of a can for a coin-type battery having a size of 2016 (diameter 20 mm, thickness 1.6 mm).

The adjustment of the lithium electrode was carried out in a glove box in an Ar atmosphere. A stainless steel mesh disc having a diameter of 17 mm was spot-welded in advance to an outer lid of a can for a coin-type battery of 2016 size, and then a metal lithium thin plate having a thickness of 0.5 mm was punched out in the form of a disk having a diameter of 15 mm. (Main pole).

Using a pair of electrodes thus prepared, LiPF ₆ was added to a mixed solvent of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a volume ratio of 1: 2: 2 as an electrolyte at a ratio of 1.5 mol / L, A coin-shaped nonaqueous electrolyte type lithium secondary battery of 2016 size was assembled in an Ar glove box using a gasket made of polyethylene using a borosilicate glass fiber-made microporous film having a diameter of 19 mm as a separator.

(Measurement of battery capacity)

The lithium secondary battery of the above-described configuration was subjected to a charge-discharge test using a charging / discharging test apparatus (TOSCAT manufactured by Toyo Systems Co., Ltd.). The doping reaction of lithium to the charge / discharge test electrode was carried out according to the constant current constant voltage method, and the undoping reaction was carried out by the low current method. Here, in the battery using the lithium chalcogen compound as the anode, the lithium doping reaction to the carbon electrode is "charged ", and in the battery using the lithium metal as the counter electrode as in the test battery of the present invention, Quot ;, and the nomenclature for the lithium doping reaction to the same carbon pole differs depending on the counter electrode used. Therefore, for convenience, the doping reaction of lithium to the carbon electrode will be described as "charging ".

Conversely, "discharge" means a charging reaction in a test battery, but since it is a de-doping reaction of lithium from a negative electrode active material, it is referred to as "discharge" for convenience. The charging method employed here is a constant current constant voltage method. Specifically, the constant current charging is performed at 0.5 mA / cm 2 until the terminal voltage becomes 0 하고. After the terminal voltage reaches 0 ㎷, a constant voltage Charging was carried out and charging was continued until the current value reached 20 占.. In this case, a value obtained by dividing the supplied electricity quantity by the mass of the carbon material of the electrode is defined as a charging capacity per unit mass of the carbon material (mAh / g).

After completion of charging, the battery circuit was opened for 30 minutes and then discharged. The discharge was performed at a constant current discharge of 0.5 mA / cm 2, and the end voltage was set to 1.5 V. The value obtained by dividing the discharged electricity quantity by the mass of the carbon material of the electrode is defined as the discharge capacity per unit mass of the carbon material (mAh / g). The irreversible capacity is calculated as the charging capacity-discharging capacity.

The charge / discharge capacity and the irreversible capacity were determined by averaging the measured values of the test cells (three in total) prepared using the same sample.

[Evaluation of Battery Performance, Measurement of Capacity Retention Rate at Rapid Discharge]

(Rapid Discharge Test)

The lithium secondary battery (charge / discharge test battery) having the above-described configuration was subjected to charge / discharge as described above (measurement of battery capacity), and then charged / discharged in the same manner again.

Subsequently, constant current charging was performed at 0.5 mA / cm 2 until the terminal voltage became 0 V, and then constant voltage charging was performed at a terminal voltage of 0 하여 to perform charging until the current value was attenuated to 20 ㎂. After completion of charging, the battery circuit was opened for 30 minutes and then discharged. The discharge was carried out at a constant current density of 12.5 mA / cm 2 (corresponding to 5 C) and 25 mA / cm 2 (corresponding to 10 C) until the battery voltage reached 1.5 V, and the respective discharge capacities were determined. The value obtained by dividing each discharge capacity by the discharge capacity at 0.5 mA / cm 2 was defined as a capacity retention rate (%) at the time of rapid discharge.

The measured values for the test cells (three in total) prepared using the same sample were averaged.

The results are shown in Table 3.

[Examples 2 to 4 and Comparative Examples 1 and 2]

Except that the mass ratio of PVDF to PVA was changed as shown in Table 2 by changing the amount of the NMP solution containing 8% by mass of the polyvinylidene fluoride (# 7200) content and the NMP solution containing 10% by mass of the PVA content The procedure of Example 1 was repeated.

The results are shown in Table 3.

[Example 5, Comparative Examples 3 to 6]

The polyvinylidene fluoride (KF # 7200, inherent viscosity (η _i ), 2.2 dl / g) of polyvinylidene fluoride (Kurehaku KF # 1700 manufactured by Kureha Co., Ltd.) (Η _i ) of 1.7 dl / g) or polyvinylidene fluoride (Kurehaku KF # 1100, innervant viscosity (η _i ), 1.1 dl / g) An NMP solution containing polyvinylidene fluoride (# 7200) in an amount of 8 mass% was changed to an NMP solution containing 10 mass% of polyvinylidene fluoride (# 1700), polyvinylidene fluoride (# 1100 ) Was changed to an NMP solution having a content of 12 mass%.

The same procedure as in Example 1 was carried out except that the mass ratio of PVDF to PVA was changed as shown in Table 2 by changing the amount of the NMP solution of the polyvinylidene fluoride and the NMP solution of the PVA content of 10 mass%

The results are shown in Table 3.

[Examples 6 to 8 and Comparative Examples 7 to 11]

(CARBOTRON P) was changed to a carbonaceous anode active material derived from coconut husk, and the polyvinylidene fluoride (Kurena KF # 7200, innert viscosity (? _I ), 2.2 dl / g) was added to polyvinylidene fluoride (Kurena KF # 7300, intrinsic viscosity (? _I ), 3.1 dl / g) or polyvinylidene fluoride (Kure # KF # 1100, by changing to inhibit coherent viscosity (η _i), 1.1dl / g), and changes the amount of the NMP of the polyvinylidene fluoride, and polyvinylidene fluoride (# 7200), an NMP solution of a content of 8% by mass of polyvinylidene fluoride An NMP solution containing 5 mass% of a lidene (# 7300) content, and an NMP solution containing 12 mass% of a polyvinylidene fluoride (# 1100) content.

As shown in Table 2, polyvinyl alcohol (Kuraray POVAL PVA-205 manufactured by Kuraray Co., Ltd.) was mixed with polyvinyl alcohol (Kuraray POVAL PVA-217 manufactured by Kuraray Co., Ltd.) or polyvinyl alcohol Kuraray POVAL PVA-505).

The procedure of Example 1 was repeated except that the amount of the NMP solution of polyvinylidene fluoride and the amount of the NMP solution of 10 mass% of PVA content were changed to change the mass ratio of PVDF and PVA as shown in Table 2.

The results are shown in Table 3.

[Examples 9 to 11 and Comparative Examples 12 to 22]

(CARBOTRON P) was changed to an active material (BTR918) as shown in Table 2, and the polyvinylidene fluoride (Kurena KF # 7200, innervation viscosity (η _i ), 2.2 dl / g) (Η _i ), 3.1 dl / g) or polyvinylidene fluoride (manufactured by Kurehaku KF # 1100, intrinsic viscosity (η _i ) of Kurehai KF # 7300, _i), 1.1dl / g) and a change, by changing the amount of the NMP of the polyvinylidene fluoride, and polyvinylidene fluoride (# 7200), poly vinylidene an NMP solution of a fluoride content of 8% by weight (# 7300) , An NMP solution having a content of 5 mass%, and an NMP solution having a polyvinylidene fluoride (# 1100) content of 12 mass%.

As shown in Table 2, polyvinyl alcohol (Kuraray POVAL PVA-205 manufactured by Kuraray Co., Ltd.) was mixed with polyvinyl alcohol (Kuraray POVAL PVA-217 manufactured by Kuraray Co., Ltd.), polyvinyl alcohol (Kuraray POVAL PVA-105), polyvinyl alcohol (Kuraray POVAL PVA-706 manufactured by Kuraray Co., Ltd.), polyvinyl alcohol (Kuraray POVAL PVA-235 manufactured by Kuraray Co., Ltd.), polyvinyl alcohol Kuraray POVAL PVA -505), polyvinyl alcohol (LM polymer LM10HD manufactured by Kuraray Co., Ltd.), or polyvinyl alcohol (special POVAL JMR150L manufactured by JAPAN VAM & POVAL CO., LTD.).

The procedure of Example 1 was repeated except that the amount of the NMP solution of polyvinylidene fluoride and the amount of the NMP solution of 10 mass% of PVA content were changed to change the mass ratio of PVDF and PVA as shown in Table 2.

The results are shown in Table 3.

[Example 12, Comparative Examples 23 to 26]

(CARBOTRON P) was changed to an active material (LT106), and the polyvinylidene fluoride (Kurena KF # 7200, innert viscosity (η _i ), 2.2 dl / g) (Η _i ), 3.1 dl / g) or polyvinylidene fluoride (manufactured by Kurehaku KF # 1100, intrinsic viscosity (η _i ) of Kurehai KF # 7300, _i), 1.1dl / g) and a change, by changing the amount of the NMP of the polyvinylidene fluoride, and polyvinylidene fluoride (# 7200), poly vinylidene an NMP solution of a fluoride content of 8% by weight (# 7300) , An NMP solution having a content of 5 mass%, and an NMP solution having a polyvinylidene fluoride (# 1100) content of 12 mass%.

The procedure of Example 1 was repeated except that the amount of the NMP solution of polyvinylidene fluoride and the amount of the NMP solution of 10 mass% of PVA content were changed to change the mass ratio of PVDF and PVA as shown in Table 2.

The results are shown in Table 3.

Further, when the nonaqueous electrolyte secondary battery is actually used, various conditions such as productivity, price, as well as characteristics of the battery are examined, and then, what nonaqueous electrolyte secondary battery is to be used is determined. Among the components contained in the negative electrode mixture for a nonaqueous electrolyte secondary battery, the negative active material is a component that greatly affects the characteristics (electrical characteristics) of the nonaqueous electrolyte secondary battery as a battery. Thus, in the examples and comparative examples of the present invention, effects of the present invention were examined in Examples and Comparative Examples using the same active material. When CARBOTRON P is used as an active material, it has a peeling strength of 3.5 gf / mm or more, an irreversible capacity of 70 mAh / g or less, a capacity retention rate of 90% or more at 5 C or a 55% A peel strength of not less than 3.5 gf / mm, an irreversible capacity of not more than 70 mAh / g, a capacity retention ratio of not less than 90% in the case of rapid discharge and not less than 70% in the equivalent of 10 C when the carbonaceous anode active material derived from coconut shells is used When the BTR918 is used as the active material, the solar battery is required to have a peeling strength of 3.5 gf / mm or more, an irreversible capacity of 20 mAh / g or less, a capacity retention rate of 80% or more at the time of rapid discharge and 52% It was judged that the solar cell having a peeling strength of 3.5 gf / mm or more had sufficient performance for practical use.

LT106 is known as a negative electrode active material having a small irreversible capacity and excellent capacity retention ratio at the time of rapid discharge. The technical problem in using this active material is the improvement of the peeling strength, and therefore, the peeling strength is analyzed only.

[Table 2]

[Table 3]

[Example 13]

(Cycle test)

(Fabrication of cathode electrode)

The electrode mixture of Example 7 was uniformly coated on one side of a copper foil having a thickness of 18 mu m and dried by heating at 120 DEG C for 25 minutes. Dried, punched out in the form of a disc having a diameter of 15 mm, and pressed to produce a negative electrode. Further, the mass of the active material contained in the disc-shaped negative electrode was adjusted to be 10 mg.

(Fabrication of anode electrode)

, 94 parts by mass of lithium cobalt oxide ("CELLSEED C-5" manufactured by Japan Chemical Industry Co., Ltd.), 3 parts by mass of carbon black, 3 parts by mass of polyvinylidene (Kurehakai KF # 1300), 3 parts by mass of carbon black NMP was added and mixed to prepare a positive electrode mix. The resultant mixture was uniformly coated on an aluminum foil having a thickness of 50 mu m. After drying, the coated electrodes were punched in the form of a disk having a diameter of 14 mm to prepare a positive electrode. The amount of lithium cobalt oxide in the positive electrode was adjusted so as to be 95% of the charging capacity per unit mass of the active material in Example 7 measured by the method described above (measurement of battery capacity). The capacity of lithium cobalt oxide was calculated to be 150 mAh / g.

Using a pair of electrodes thus prepared, LiPF ₆ was added to a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a volume ratio of 1: 2: 2 as an electrolytic solution at a ratio of 1.5 mol / L, A coin-type nonaqueous electrolyte type lithium secondary battery having a size of 2032 was assembled in an Ar glove box using a gasket made of polyethylene, using a borosilicate glass fiber-made microporous film having a diameter of 19 mm as a separator.

The cycle test was first started after three cycles of charging and discharging were repeated and aging was carried out. The constant-current constant-voltage condition employed in the cycle test was such that charging was performed at a constant current density of 2.5 mA / cm 2 until the battery voltage reached 4.2 V, and then the current value was maintained continuously (while maintaining the constant voltage) And the charging is continued until the current value reaches 50 占.. After completion of charging, the battery circuit was opened for 10 minutes and then discharged. The discharge was performed at a constant current density of 2.5 mA / cm 2 until the battery voltage reached 3.0 V. The charging and discharging were repeated 250 times at 50 캜, and the discharge capacity after 30 cycles and after 250 cycles was divided by the discharge capacity for the first time to obtain the capacity retention rate (%).

The results are shown in Table 4.

[Example 14, Comparative Examples 27 and 28]

The electrode mix of Example 7 was replaced with the electrode mix of Example 9 (Example 14), the electrode mix of Comparative Example 8 (Comparative Example 27), or the electrode mix of Comparative Example 14 (Comparative Example 28) The charging capacity per unit mass of the active material in Example 7 was set to a charging capacity per unit mass of the active material in Example 9 (Example 14), a charging capacity per unit mass of the active material in Comparative Example 8 (Comparative Example 27) Or the charging capacity per unit mass of the active material in Comparative Example 14 (Comparative Example 28), the capacity retention ratio (%) was obtained.

The results are shown in Table 4.

[Example 15]

An electrode mixture having an active material, a mass fraction of PVDF and PVA of 94: 4.5: 1.5 was prepared by changing the amount of NMP solution of polyvinylidene fluoride and the NMP solution of PVA content of 10 mass% from Example 9.

The charge capacity per unit mass of the active material was determined by the same method as described in Example 1 (measurement of battery capacity).

The electrode mix of Example 7 was replaced with the electrode mixture, and the charge capacity per unit mass of the active material in Example 7 was set to be the charge capacity per unit mass of the active material, Retention ratio (%) was obtained.

The results are shown in Table 4.

Among the components contained in the negative electrode mixture for a non-aqueous electrolyte secondary battery, the component having a large influence on the capacity retention rate of the non-aqueous electrolyte secondary battery is the negative active material. Thus, in the examples and comparative examples of the present invention, effects of the present invention were examined in Examples and Comparative Examples using the same active material. When a carbon-based anode active material derived from a coconut shell is used as an active material, a solar cell having a capacity retention rate after 30 times of 91% or more is used. When BTR918 is used as an active material, It was judged that the capacity retention rate was sufficient for practical use.

[Table 4]

Claims (10)

At least a polyvinylidene fluoride having an inherent viscosity of 1.2 to 7 dl / g and a polyvinyl alcohol having a saponification degree of 80 to 90 mol%
Wherein the binder contains 5 to 90% by mass of the polyvinyl alcohol per 100% by mass of the total of the polyvinylidene fluoride and the polyvinyl alcohol. The binder for a nonaqueous electrolyte secondary battery according to claim 1, wherein the polyvinyl alcohol has an average degree of polymerization of 100 to 4,000. A binder solution for a nonaqueous electrolyte secondary battery comprising a binder and a solvent for a nonaqueous electrolyte secondary cell according to any one of claims 1 to 3. Polyvinylidene fluoride having an innervant viscosity of 1.2 to 7 dl / g, polyvinyl alcohol having a saponification degree of 80 to 90 mol%, a negative electrode active material and a solvent,
Wherein the polyvinyl alcohol is contained in an amount of 5 to 90 mass% per 100 mass% of the total of the polyvinylidene fluoride and the polyvinyl alcohol. The negative electrode material mixture for a nonaqueous electrolyte secondary battery according to claim 4, wherein the polyvinyl alcohol has an average degree of polymerization of 100 to 4,000. The negative electrode material mixture for a nonaqueous electrolyte secondary battery according to claim 5, wherein the negative electrode active material is made of a carbonaceous material. The negative electrode material mixture for a nonaqueous electrolyte secondary battery according to claim 5, wherein the negative electrode active material is non-graphitizable carbon. The negative electrode material mixture for a nonaqueous electrolyte secondary battery according to claim 5, wherein the negative active material is graphitizable carbon. A negative electrode for a nonaqueous electrolyte secondary battery obtained by applying a negative electrode mixture for a nonaqueous electrolyte secondary battery according to any one of claims 4 to 8 to a current collector and drying the same. The nonaqueous electrolyte secondary battery having a negative electrode for a nonaqueous electrolyte secondary battery according to claim 9.