JP5855737B2 - Lithium ion battery - Google Patents

Description

  The present invention relates to a negative electrode for a lithium ion battery, and a lithium ion battery including the negative electrode.

  Lithium-ion batteries have a high energy density, so they are attracting attention as batteries used for on-board applications such as railways and automobiles, or for applications that store electric power generated by solar power generation or wind power generation and supply it to an electric power system. Has been. For example, automobiles equipped with lithium-ion batteries (hereinafter referred to as “batteries” where appropriate) include zero-emission electric cars equipped with no engine, hybrid electric cars equipped with both an engine and a secondary battery, and system power supplies. There are plug-in hybrid electric vehicles that charge directly. In addition, it is expected to be used as a stationary power storage system that supplies power in an emergency when the power system is cut off.

  Among such various uses, lithium ion batteries having high output characteristics and high energy density are required.

  Also, excellent durability is required for the battery. For example, even if the environmental temperature becomes high or the charge / discharge cycle is repeated, the reduction rate of the rechargeable battery capacity (that is, battery capacity) is low, and the battery capacity maintenance rate is required to be high over a long period of time. Further, because of radiant heat from the road surface or heat conduction from the inside of the vehicle, for example, storage characteristics and cycle life in a high temperature environment of 60 ° C. or higher are important required performances. However, the battery capacity of a lithium ion battery is reduced by being left in a high temperature environment or performing a charge / discharge cycle.

  In view of such circumstances, Patent Document 1 discloses a technique using a binder for a lithium ion battery electrode comprising a lithium salt of poly (meth) acrylic acid and a sodium salt of carboxymethyl cellulose (hereinafter referred to as “CMC” as appropriate). doing. An object of the present invention is to obtain a battery that easily removes moisture in the drying stage and has excellent charge / discharge cycle characteristics.

  Patent Document 2 contains a polyacrylate and a water-soluble polymer (including CMC), and the addition amount of the polyacrylate is 0.1% by weight or more to the total weight of the negative electrode mixture. Disclosed is a non-aqueous electrolyte secondary battery, wherein the water-soluble polymer is added in an amount of 5% by weight or less and 0.3% by weight or more and 0.5% by weight or less based on the total weight of the negative electrode mixture. ing. An object of the present invention is to provide a battery having high output characteristics by reducing the total amount of water-soluble polymer (CMC) using this technique.

  Further, Patent Document 3 discloses a lithium secondary battery characterized in that the surface of carbon for negative electrode is coated with a water-soluble polymer. An object of the present invention is to provide a battery having a high energy density by reducing the irreversible capacity generated by the decomposition of the solvent on the negative electrode surface during the initial charge / discharge.

  Patent Document 4 discloses a technique using polyacrylic acid as a binder for a graphite negative electrode. By using this technique, a battery that can operate even in a propylene carbonate (PC) electrolyte can be provided.

JP 2002-50360 A JP 2002-304986 A JP-A-11-129992 JP 2002-134171 A

  In a lithium ion battery, the battery capacity decreases due to initial charge / discharge, standing in a high temperature environment, and charge / discharge cycles. This decrease in battery capacity occurs remarkably when the binding force of the negative electrode is small or when the electrolyte solution is easily decomposed on the graphite surface.

  The present invention is for solving the above-described problems, and an object thereof is to provide a lithium ion battery having high energy density, excellent high-temperature storage stability, and durability during cycle driving.

  The polymer polycarboxylic acid was excellent in covering the surface of the negative electrode active material such as graphite and suppressing the decomposition of the electrolytic solution. However, as in Patent Document 4, the graphite is coated only with the polymer polycarboxylic acid. Then, a hard film is formed. Since graphite expands and contracts during charge and discharge, if the formed film is hard, it cannot follow expansion and contraction, and cycle characteristics deteriorate.

  In order to solve this problem, water-soluble polysaccharides were used in addition to the high-molecular polycarboxylic acid, but good results could be obtained even if the amounts shown in Patent Documents 1 and 2 were used. There wasn't. As a result of detailed investigation of this cause by the present inventors, it has been found that a coating structure is not sufficiently formed on graphite. Moreover, it discovered that the coating | coated structure of a graphite produced a big difference with the usage-amount and usage-amount of high molecular polycarboxylic acid and water-soluble polysaccharide.

  Therefore, as a result of intensive studies by the present inventors, a sufficient coating structure can be formed by coating the negative electrode active material with a specific amount and ratio of a high molecular weight polycarboxylic acid and a water-soluble polysaccharide. As a result, it was found that high temperature storage stability and durability during cycle driving can be improved.

  That is, the present invention includes the following inventions.

(1) a negative electrode current collector; and a negative electrode mixture layer comprising a negative electrode active material, a water-soluble polysaccharide, and a polymer polycarboxylic acid or a derivative thereof disposed on the negative electrode current collector;
A negative electrode for a lithium ion battery comprising:
The negative electrode mixture layer includes the water-soluble polysaccharide and the polymer polycarboxylic acid or a derivative thereof in a total amount of 0.9 to 1.7% by weight,
The negative electrode for a lithium ion battery, wherein a ratio of the weight of the polymer polycarboxylic acid or its derivative to the weight of the water-soluble polysaccharide is 0.02 to 0.25.

(2) The negative electrode for a lithium ion battery according to (1), wherein the negative electrode mixture layer further contains a non-fluorine organic polymer.

(3) The lithium according to (2), wherein the ratio of the weight of the non-fluorinated organic polymer to the total weight of the water-soluble polysaccharide and the polymer polycarboxylic acid or derivative thereof is 0.55 to 1.45. Negative electrode for ion battery.

(4) The negative electrode for a lithium ion battery according to any one of (1) to (3), wherein the polymer polycarboxylic acid or a derivative thereof is polyacrylic acid, polymethacrylic acid, or a salt or ester thereof.

(5) The negative electrode for a lithium ion battery according to any one of (1) to (4), wherein the polymer polycarboxylic acid or a derivative thereof is a salt of polyacrylic acid.

(6) The negative electrode for a lithium ion battery according to any one of (1) to (5), wherein the negative electrode active material is graphite having an interlayer distance (d ₀₀₂ ) of 0.3345 to 0.338 nm.

(7) The negative electrode mixture layer contains 1.0 to 1.3% by weight in total of the water-soluble polysaccharide and the polymer polycarboxylic acid or a derivative thereof, and the polymer polycarboxylic acid or its weight relative to the weight of the water-soluble polysaccharide The negative electrode for a lithium ion battery according to any one of (1) to (6), wherein the weight ratio of the derivative is 0.1 to 0.15.

(8) A lithium ion battery comprising the negative electrode for a lithium ion battery according to any one of (1) to (7).

  According to the present invention, it is possible to provide a negative electrode for a lithium ion battery and a lithium ion battery excellent in high temperature storage and durability during cycle driving.

It is sectional drawing of the lithium ion battery produced in the Example of this invention.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment” as appropriate) will be described in detail. However, the present embodiment is not limited to the following contents and does not depart from the gist of the present invention. It can carry out by changing arbitrarily within.

  The present invention relates to a negative electrode for a lithium ion battery including a negative electrode mixture layer including a negative electrode active material, a water-soluble polysaccharide, and a polymer polycarboxylic acid or a derivative thereof (for example, a salt and an ester).

  The total amount of the water-soluble polysaccharide and the polymer polycarboxylic acid is 0.9% by weight or more and 1.7% by weight or less based on the total weight of the negative electrode mixture. Within this numerical range, the surface of the negative electrode active material is sufficiently composite-coated with the water-soluble polysaccharide and the polymer polycarboxylic acid. The total weight of the negative electrode mixture means the total weight of solids contained in the dried negative electrode mixture layer, and does not include the weight of the solvent used at the time of slurry preparation. If the amount is less than 0.9% by weight, the surface of the negative electrode active material cannot be satisfactorily covered because the amount is small. Therefore, the coating structure cannot be maintained when the negative electrode active material expands and contracts, and the high-temperature storage characteristics and cycle characteristics deteriorate. On the other hand, if it exceeds 1.7% by weight, the water-soluble polysaccharide and the high-molecular polycarboxylic acid aggregate and remarkably thicken, so that the high-temperature storage characteristics and cycle characteristics deteriorate. The total addition amount of the water-soluble polysaccharide and the polymer polycarboxylic acid is preferably 0.95% by weight or more and 1.5% by weight or less, and particularly preferably 1.0% by weight or more and 1.3% by weight or less.

  The ratio of the weight of the polymer polycarboxylic acid to the weight of the water-soluble polysaccharide (polymer polycarboxylic acid / water-soluble polysaccharide) is 0.02 or more and 0.25 or less. Within this numerical range, the surface of the negative electrode active material is sufficiently composite-coated with the water-soluble polysaccharide and the polymer polycarboxylic acid. When the polymer polycarboxylic acid / water-soluble polysaccharide exceeds 0.25, the water-soluble polysaccharide and the polymer polycarboxylic acid are aggregated, or the polymer polycarboxylic acid is precipitated during kneading. The reason for this is not clear, but is thought to be due to the interaction between the water-soluble polysaccharide and the high-molecular polycarboxylic acid. The polymer polycarboxylic acid / water-soluble polysaccharide is preferably from 0.05 to 0.2, particularly preferably from 0.1 to 0.15.

  The amounts and ratios of the water-soluble polysaccharide and the high-molecular polycarboxylic acid need to be within the above ranges. If either one is out of the above range, the surface of the negative electrode active material is not well coated, and the coating structure cannot be maintained when the negative electrode active material expands and contracts. Thereby, a high temperature storage characteristic and cycling characteristics fall.

  Examples of the water-soluble polysaccharide in the present invention include methylcellulose, ethylcellulose, acetylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch, carrageenan, pullulan, guar gum, xanthan gum (xanthan gum), hydroxypropylcellulose, hydroxypropylmethylcellulose and the like. Some of these may be salted. Among these, a sodium salt of carboxymethyl cellulose is particularly preferable. These compounds may be used alone or in combination of two or more.

  The polymer polycarboxylic acid in the present invention is a polymer obtained by polymerizing a monomer having a carboxyl group. Examples of the polymer polycarboxylic acid and derivatives thereof include polyacrylic acid, polyacrylate, polyacrylate, polymethacrylic acid, polymethacrylate, and polymethacrylate. These polymers have a strong polar carboxyl group or a derivative thereof in the repeating unit and have a strong binding force. Although it does not specifically limit, polyacrylic acid, polymethacrylic acid, and those sodium salt, potassium salt, ammonium salt, methyl ester, ethyl ester, butyl ester, etc. are mentioned. These may be used alone or in combination of two or more. Moreover, in a salt or ester, all the carboxyl groups may be neutralized or esterified, or the carboxyl groups may partially remain. In this, a polyacrylate is preferable and especially a sodium salt is preferable.

  The weight average molecular weight of the polymeric polycarboxylic acid is preferably 1,000 to 1,000,000. More preferably, it is 100,000-1 million. The molecular weight is a weight average molecular weight value measured by liquid chromatography.

  The negative electrode of the present invention includes a negative electrode active material, a water-soluble polysaccharide, a polymer polycarboxylic acid, and a current collector. When high rate charge / discharge is required, a conductive agent may be added. As the negative electrode active material that can be used in the present invention, graphite, non-graphite carbon, or the like can be selected.

The negative electrode active material preferably contains graphite. The graphite preferably has a graphite interlayer distance (d ₀₀₂ ) of 0.3345 nm or more and 0.338 nm or less. Such graphite has good wettability to water-soluble polysaccharides and high-molecular polycarboxylic acids, and can easily be combined with water-soluble polysaccharides and high-molecular polycarboxylic acids, improving the high-temperature storage characteristics and cycle characteristics of lithium-ion batteries. Can be made larger.

Graphite as the negative electrode active material is natural graphite, artificial graphite, mesophase carbon, expanded graphite, carbon fiber, vapor grown carbon fiber, pitch-based carbonaceous material, needle capable of chemically occluding and releasing lithium ions. Manufactured from coke, petroleum coke, polyacrylonitrile-based carbon fiber and the like. The graphite interlayer distance (d ₀₀₂ ) can be measured by using XRD (X-Ray Diffraction Method) or the like.

As the negative electrode active material, a material that forms an alloy with lithium or a material that forms an intermetallic compound may be used. For example, metals such as aluminum, silicon and tin and alloys thereof, lithium-containing transition metal nitrides Li _(3-x) M _x N, lower oxides of silicon Li _x SiO _y (0 ≦ x, 0 <y < 2), and a lower oxide of tin, Li _x SnO _y (0 ≦ x, 0 <y <2). Materials other than the above materials can also be used as the negative electrode active material.

  The particle size of the negative electrode active material is desirably set to be equal to or smaller than the thickness of the mixture layer formed of the negative electrode active material and the binder. If there are coarse particles in the negative electrode active material powder having a size larger than the thickness of the mixture layer, remove the coarse particles in advance by sieving, airflow classification, etc., and use particles less than the thickness of the mixture layer Is preferred.

  The specific particle size is preferably 3 μm or more and 30 μm or less, more preferably 3 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. preferable. When the average particle size exceeds 30 μm, the electrode is likely to be uneven, and the battery characteristics may be deteriorated. On the other hand, when the thickness is less than 3 μm, graphite is not easily crushed, so that the density tends to be difficult to increase. The particle size distribution can be measured by dispersing a sample in purified water containing a surfactant and measuring with a laser diffraction / scattering type particle size distribution measuring device, and the average particle size is 50% cumulative (50% D). Calculated.

Further, the graphite of the negative electrode active material in the present invention has a specific surface area determined using the BET (Brunauer-Emmet-Teller) method from an adsorption isotherm obtained from the 77K nitrogen adsorption measurements, 0.1 m ² / g or more 10 m ² / G or less is preferable. If it is less than 0.1 m ² / g, the reaction area between the active material and lithium ions decreases, and the charge / discharge characteristics may deteriorate. On the other hand, if it exceeds 10 m ² / g, the reaction with the electrolyte is likely to occur, so that the irreversible capacity increases and the life characteristics may be deteriorated.

  The method for producing the negative electrode is not particularly limited. For example, a negative electrode active material, a water-soluble polysaccharide, and a polymer polycarboxylic acid are placed in a solvent, and a general mixture such as a ball mill or a planetary mixer is used. A negative electrode mixture slurry is prepared by thoroughly kneading and dispersing using a smelting and dispersing method. Subsequently, this negative electrode mixture slurry is applied onto a current collector made of a metal foil such as copper using an applicator, vacuum dried at an appropriate temperature of, for example, about 100 ° C., and compression molded using a press. Then, the desired negative electrode can be produced by cutting or punching into a desired size.

  Although it does not specifically limit as a solvent at the time of preparing a negative mix slurry, For example, a pure water, N-methyl-2-pyrrolidone (NMP), ethylene glycol, toluene, xylene etc. are mentioned. Among these, pure water is particularly preferable.

  Further, a non-fluorinated organic polymer such as acrylonitrile-butadiene rubber (NBR) or styrene-butadiene rubber (SBR) may be added to the negative electrode mixture as a binder. The ratio of the weight of the non-fluorine organic polymer to the total weight of the polymer polycarboxylic acid and the water-soluble polysaccharide is (non-fluorine organic polymer / polymer polycarboxylic acid + water-soluble polysaccharide) is 0.55 or more. It is preferable that it is 1.45 or less. 0.7 to 1.4 is more preferable, and 0.8 to 1.2 is particularly preferable. If it is less than 0.55, since the binding force cannot be ensured, cycle deterioration may be reduced. On the other hand, if it exceeds 1.45, the growth of the coating structure may be inhibited, and the high-temperature storage characteristics and cycle characteristics may be deteriorated.

  For the current collector of the negative electrode, a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to copper, materials such as stainless steel, titanium, or nickel are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

  A negative electrode slurry in which a negative electrode active material, a binder, and an organic solvent are mixed is attached to a current collector by a doctor blade method, a dipping method, a spray method, or the like, and then the organic solvent is dried and pressure-molded by a roll press. Thereby, a negative electrode can be produced. Moreover, it is also possible to form a multilayer mixture layer on a current collector by carrying out a plurality of times from application to drying.

  Next, a battery to which the negative electrode of the present invention can be applied will be described. Hereinafter, a battery to which the negative electrode according to this embodiment can be applied (hereinafter, referred to as “battery according to this embodiment” as appropriate) will be described with reference to FIG. However, the configuration of the battery shown in FIG. 1 is merely an example of the internal structure of the lithium ion battery to which the negative electrode according to this embodiment can be applied.

  FIG. 1 is a diagram schematically illustrating the internal structure of the battery according to the present embodiment. A battery according to this embodiment shown in FIG. 1 includes a positive electrode 10, a separator 11, a negative electrode 12, a battery container (battery can) 13, a positive electrode current collecting tab 14, a negative electrode current collecting tab 15, an inner lid 16, an internal pressure release valve 17, A gasket 18, a positive temperature coefficient (PTC) resistance element 19, a battery lid 20, and an axial center are included. The battery lid 20 is an integrated part composed of the inner lid 16, the internal pressure release valve 17, the gasket 18, and the PTC resistance element 19. Moreover, the positive electrode 10, the separator 11, and the negative electrode 12 are wound by the shaft center.

The positive electrode 10 includes a positive electrode active material, a conductive agent, a binder, and a current collector. Illustrative examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . In addition, LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2−x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn, Ti are selected. Li ₂ Mn ₃ MO ₈ (provided that M = at least one selected from the group consisting of Fe, Co, Ni, Cu, Zn), Li _{1 − x} A _x Mn ₂ O ₄ (provided that, A = Mg, B, Al , Fe, Co, Ni, Cr, Zn, at least one selected from the group consisting of Ca, x = 0.01~0.1), _{LiNi 1-x M x O 2} ( however, M = Co, Fe, at least one selected from the group consisting of _{Ga, x = 0.01~0.2), LiFeO} 2, Fe 2 (SO 4) 3, _{LiCo 1-x M x O 2} ( where M = Ni, Fe, at least one selected from the group consisting of _{Mn, x = 0.01~0.2), LiNi} 1-x M x O 2 ( however, M = Mn, Fe, Co , Al, Ga , At least one selected from the group consisting of Ca, Mg, x = 0.01 to 0.2), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO ₄ , and the like.

  The particle size of the positive electrode active material is usually defined so as to be equal to or less than the thickness of the mixture layer formed from the positive electrode active material, the conductive agent, and the binder. When there are coarse particles having a size equal to or greater than the thickness of the mixture layer in the positive electrode active material powder, the coarse particles can be removed in advance by sieving classification or wind classification to produce particles having a thickness of the mixture layer thickness or less. preferable.

  In addition, since the positive electrode active material is generally oxide-based and has high electrical resistance, a conductive agent such as carbon powder is used to supplement electrical conductivity. Since both the positive electrode active material and the conductive agent are usually powders, a binder can be mixed with the powders, and the powders can be bonded together and simultaneously bonded to the current collector.

  For the current collector of the positive electrode 10, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, or a metal foam plate is used. . In addition to aluminum, materials such as stainless steel and titanium are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

  A positive electrode slurry in which a positive electrode active material, a conductive agent, a binder, and an organic solvent are mixed is attached to a current collector by a doctor blade method, a dipping method, or a spray method, and then the organic solvent is dried and applied by a roll press. The positive electrode 10 can be produced by pressure forming. In addition, a plurality of mixture layers can be laminated on the current collector by performing a plurality of times from application to drying.

  As the negative electrode 12, the negative electrode described above is used.

  The separator 11 is inserted between the positive electrode 10 and the negative electrode 12 produced by the above method to prevent a short circuit between the positive electrode 10 and the negative electrode 12. The separator 11 can be a polyolefin polymer sheet made of polyethylene, polypropylene, or the like, or a two-layer structure in which a polyolefin polymer and a fluorine polymer sheet typified by tetrafluoropolyethylene are welded. It is. A mixture of ceramics and a binder may be formed in a thin layer on the surface of the separator 11 so that the separator 11 does not shrink when the battery temperature increases. Since these separators 11 need to permeate lithium ions during charging / discharging of the battery, they can generally be used for lithium ion batteries if the pore diameter is 0.01 to 10 μm and the porosity is 20 to 90%.

  Such a separator 11 is inserted between the positive electrode 10 and the negative electrode 12 to produce an electrode group wound around an axis. As the axis, any known one can be used as long as it can carry the positive electrode 10, the separator 11, and the negative electrode 12. In addition to the cylindrical shape shown in FIG. 1, the electrode group has various shapes such as a laminate of strip electrodes, or a positive electrode 10 and a negative electrode 12 wound in an arbitrary shape such as a flat shape. Can do. The shape of the battery case 13 may be selected from shapes such as a cylindrical shape, a flat oval shape, a flat oval shape, and a square shape according to the shape of the electrode group.

  The material of the battery container 13 is selected from materials that are corrosion resistant to non-aqueous electrolytes, such as aluminum, stainless steel, and nickel-plated steel. Further, when the battery container 13 is electrically connected to the positive electrode 10 or the negative electrode 12, the material is not deteriorated due to corrosion of the battery container 13 or alloying with lithium ions in the portion in contact with the nonaqueous electrolyte. Thus, the material of the battery container 13 is selected.

  The electrode group is housed in the battery container 13, the negative electrode current collecting tab 15 is connected to the inner wall of the battery container 13, and the positive electrode current collecting tab 14 is connected to the bottom surface of the battery lid 20. The electrolyte is injected into the battery container before the battery is sealed. As a method for injecting the electrolyte, there are a method of adding directly to the electrode group in a state where the battery cover 20 is released, or a method of adding from an injection port installed in the battery cover 20.

  Thereafter, the battery lid 20 is brought into close contact with the battery container 13 to seal the entire battery. If there is an electrolyte inlet, seal it as well. As a method for sealing the battery, there are known techniques such as welding and caulking.

As a typical example of the electrolytic solution that can be used in the present invention, lithium hexafluorophosphate (LiPF ₆ ) or lithium borofluoride as an electrolyte in a solvent obtained by mixing dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate with ethylene carbonate There is a solution in which (LiBF ₄ ) is dissolved. The present invention is not limited to the type of solvent and electrolyte, and the mixing ratio of solvents, and other electrolytes can be used.

  Examples of non-aqueous solvents that can be used for the electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2 -Methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphate triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, Tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, chloropropylene carbonate, and the like can be given. Other solvents may be used as long as they do not decompose on the positive electrode 10 or the negative electrode 12 incorporated in the battery of the present invention.

In addition, examples of the _{electrolyte, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, or imide salts such as lithium represented by lithium trifluoromethane sulfonimide, multi There are different types of lithium salts. A nonaqueous electrolytic solution obtained by dissolving these salts in the above-mentioned solvent can be used as a battery electrolytic solution. An electrolyte other than this may be used as long as it does not decompose on the positive electrode 10 and the negative electrode 12 included in the battery according to the present embodiment.

  When a solid polymer electrolyte (polymer electrolyte) is used, an ion conductive polymer such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, polyhexafluoropropylene, and polyethylene oxide can be used for the electrolyte. When these solid polymer electrolytes are used, there is an advantage that the separator 11 can be omitted.

Furthermore, an ionic liquid can be used. For example, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF ₄ ), a lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), a mixed complex of triglyme and tetraglyme, a cyclic quaternary ammonium-based positive ion This combination is selected by selecting a combination that does not decompose at the positive electrode 10 and the negative electrode 12 from an ion (for example, N-methyl-N-propylpyrrolidinium) and an imide anion (for example, bis (fluorosulfonyl) imide). It can use for the battery which concerns on a form.

  The lithium ion battery of the present invention can be manufactured by, for example, disposing the negative electrode and the positive electrode as described above with a separator interposed therebetween and injecting an electrolyte. The structure of the lithium ion battery of the present invention is not particularly limited. Usually, the positive electrode and the negative electrode and the separator separating them are wound into a wound electrode group, or the positive electrode, the negative electrode and the separator are stacked to form a stacked type. Electrode group.

  By using the battery described above, it is possible to provide a battery having excellent high-temperature storage characteristics and cycle characteristics.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, the following Examples are examples and are not limited to these.

Example 1
A negative electrode active material was synthesized according to the following procedure. First, coal-based coal tar was heat-treated at 400 ° C. using an autoclave to obtain raw coke. The raw coke was pulverized and calcined at 2800 ° C. in an inert atmosphere to obtain graphite having a graphite interlayer distance (d ₀₀₂ ) of 0.3350 nm. This graphite was pulverized using an impact crusher equipped with a classifier, and coarse particles were removed with a 300 mesh sieve to obtain graphite particles. At that time, the average particle diameter was 17.2 μm and the specific surface area was 1.6 m ² / g.

  Subsequently, a positive electrode active material was synthesized according to the following procedure. Nickel oxide, manganese oxide, and cobalt oxide were used as raw materials, weighed so that the Ni: Mn: Co ratio was 1: 1: 1 by atomic ratio, and pulverized and mixed with a wet pulverizer. Next, the pulverized mixed powder to which polyvinyl alcohol (PVA) was added as a binder was granulated with a spray dryer. The obtained granulated powder was put in a high-purity alumina container, pre-baked at 600 ° C. for 12 hours to evaporate PVA, crushed after air cooling. Further, lithium hydroxide monohydrate was added to the pulverized powder so that the atomic ratio of Li: transition metal (Ni, Mn, Co) was 1: 1 and mixed well. This mixed powder was put into a high-purity alumina container and subjected to main firing at 900 ° C. for 6 hours. The obtained positive electrode active material was pulverized and classified with a ball mill. The average particle diameter of this positive electrode active material was 6 μm.

In this embodiment, the surface spacing _{d 002} of (002) plane of graphite was measured using an X-ray diffraction apparatus RU200B manufactured by Rigaku Corporation. CuKα rays (λ = 0.15418 nm) were used as the X-ray source, and the diffraction angle was corrected using Si. By performing profile fitting on the peak obtained by measurement, it can be calculated using the Bragg equation.

  The particle size (50% D) of the material in the examples was examined using a laser diffraction / scattering particle size distribution measuring apparatus LA-920 manufactured by Horiba, Ltd. A He—Ne laser 1 mW was used as a light source, and a dispersion medium of graphite particles was obtained by adding two drops of a surfactant to ion exchange water. The ultrasonic treatment was performed for 5 minutes or more in advance, and the ultrasonic treatment was also performed during the measurement, and the measurement was performed while preventing aggregation. The cumulative 50% particle size (50% D) of the measurement results was taken as the average particle size.

  The specific surface area of graphite, which is the negative electrode active material of the lithium ion battery in the examples, was equilibrated using nitrogen adsorption at 77K using BELSORP-mini manufactured by Nippon Bell Co., Ltd. after vacuum drying of graphite at 120 ° C. for 3 hours. The adsorption isotherm measured at 300 seconds was obtained by analyzing by the BET method.

  Next, a lithium ion battery was produced as follows. FIG. 1 is a cross-sectional view of the lithium ion battery of this example. In FIG. 1, 10 is a positive electrode, 11 is a separator, 12 is a negative electrode, 13 is a battery can, 14 is a positive electrode tab, 15 is a negative electrode tab, 16 is an inner lid, 17 is an internal pressure release valve, 18 is a gasket, and 19 is a PTC element. , 20 represents a battery lid.

  First, a positive electrode was produced. Add 6.0 parts by weight and 2.0 parts by weight of powdered carbon and acetylene black as conductive materials to 86.0 parts by weight of the positive electrode active material, respectively, and pre-dissolve 6.0 parts by weight of PVDF in NMP as a binder. The prepared solution was added and further mixed with a planetary mixer to prepare a positive electrode mixture slurry. This slurry was uniformly and evenly applied to both surfaces of a current collector made of an aluminum foil having a thickness of 20 μm by a coating machine. After the application, compression molding was performed with a roll press to obtain a positive electrode.

  Next, a negative electrode was produced. 97.9 parts by weight of graphite as a negative electrode active material, 0.1 part by weight of solid content of 3% aqueous solution of polyacrylic acid (weight average molecular weight 500,000), and 1.0% solid content of 1% aqueous solution of CMC An equivalent amount by weight and an equivalent amount of 1 part by weight of a solid content of a 40% aqueous solution of SBR were added and further mixed by a planetary mixer to prepare a negative electrode mixture slurry. This slurry was uniformly and evenly applied to both surfaces of a current collector made of a rolled copper foil having a thickness of 10 μm by a coating machine. After the application, it was compression molded with a roll press to obtain a negative electrode.

And the positive electrode and the negative electrode were cut | judged to the desired magnitude | size, and the current collection tab was ultrasonically welded to the uncoated part of the mixture layer, respectively. As the current collecting tab, an aluminum lead piece was used for the positive electrode and a nickel lead piece was used for the negative electrode. Thereafter, a separator having a thickness of 30 μm made of a porous polyethylene film was wound while being sandwiched between the positive electrode and the negative electrode. The wound body was inserted into the battery can, the negative electrode tab was connected to the bottom of the battery can by resistance welding, and the positive electrode lid was connected to the positive electrode tab by ultrasonic welding. Next, an electrolyte in which 1 mol / l LiPF ₆ was dissolved in a mixed solvent of volume ratio ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1: 1: 1 was injected, and then The positive electrode lid was caulked and sealed in a battery can to obtain the target lithium ion battery.

  The manufactured battery was charged to 4.20 V at a current equivalent to 0.3 CA at around normal temperature (25 ° C.), and then constant voltage charging was performed until the current reached 0.03 C at 4.20 V. After a 30-minute pause, constant current discharge was performed up to 3.0 V with a constant current corresponding to 0.3 CA. This was initialized by performing 4 cycles, and the battery capacity at the 4th cycle was measured, and the measured battery capacity was defined as the initial battery capacity. The initial battery capacity was 1.15 Ah.

  Next, 500 charge / discharge cycles were performed at 25 ° C. In each cycle, the battery was charged to 4.20 V with a current corresponding to 1 C, and then constant voltage charging was performed until the current became 0.03 C at 4.20 V. Discharge was discharged to 2.7 V with a current corresponding to 1 C. During charging and discharging, a pause was performed for 30 minutes. The battery capacity was measured as described above.

  The cycle capacity retention rate was calculated according to the following formula using the obtained results. The results are shown in Table 1.

Cycle capacity retention rate (%) = (battery capacity after 500 cycles) / (initial battery capacity)
Moreover, the storage test was done at 50 degreeC. The battery was charged to 4.20 V with a current corresponding to 0.3 CA, and then constant voltage charging was performed until the current became 0.03 C at 4.20 V. After a 30-minute rest, it was stored in a 50 ° C. constant temperature bath for 3 months. After storage, the sample was taken out from the thermostat and allowed to stand at around 25 ° C. for 3 hours, and then the capacity was measured. The battery capacity was measured as described above.

  The storage capacity retention rate was calculated according to the following formula using the results obtained above. The results are shown in Table 1.

Storage capacity retention rate (%) = (Battery capacity after 3 months storage) / (Initial battery capacity)
(Example 2)
The cycle capacity retention ratio and storage capacity retention ratio were calculated in the same manner as in Example 1 except that the graphite mixing amount was changed to 97.95 parts by weight and the polyacrylic acid mixing amount was changed to 0.05 parts by weight. did. The results are shown in Table 1.

(Example 3)
The cycle capacity retention ratio and the storage capacity retention ratio were calculated in the same manner as in Example 1 except that the amount of graphite was changed to 97.8 parts by weight and the amount of polyacrylic acid was changed to 0.2 parts by weight. did. The results are shown in Table 1.

Example 4
The cycle capacity retention ratio and the storage capacity retention ratio were calculated in the same manner as in Example 1 except that the graphite mixing amount was changed to 98.1 parts by weight and the CMC mixing amount was changed to 0.8 parts by weight. The results are shown in Table 1.

(Example 5)
Except that the mixing amount of graphite was changed to 97.4 parts by weight, the mixing amount of polyacrylic acid was changed to 0.2 parts by weight, and the mixing amount of CMC was changed to 1.4 parts by weight, the same as in Example 1. The cycle capacity maintenance rate and the storage capacity maintenance rate were calculated. The results are shown in Table 1.

(Example 6)
Except that the mixing amount of graphite was changed to 97.3 parts by weight, the mixing amount of polyacrylic acid was changed to 0.3 parts by weight, and the mixing amount of CMC was changed to 1.4 parts by weight, the same as in Example 1. The cycle capacity maintenance rate and the storage capacity maintenance rate were calculated. The results are shown in Table 1.

(Comparative Example 1)
The cycle capacity retention ratio and the storage capacity retention ratio were calculated in the same manner as in Example 1 except that the amount of graphite was changed to 98.0 parts by weight and the amount of polyacrylic acid was changed to 0 parts by weight. The results are shown in Table 1.

(Comparative Example 2)
The cycle capacity retention ratio and the storage capacity retention ratio were calculated in the same manner as in Example 1 except that the amount of graphite was changed to 97.9 parts by weight and the amount of polyacrylic acid was changed to 0.01 parts by weight. did. The results are shown in Table 1.

(Comparative Example 3)
The cycle capacity retention ratio and the storage capacity retention ratio were calculated in the same manner as in Example 1 except that the graphite mixing amount was changed to 97.5 parts by weight and the polyacrylic acid mixing amount was changed to 0.5 parts by weight. did. The results are shown in Table 1.

(Comparative Example 4)
The cycle capacity retention ratio and the storage capacity retention ratio were calculated in the same manner as in Example 1 except that the amount of graphite was changed to 97.0 parts by weight and the amount of polyacrylic acid was changed to 1.0 parts by weight. did. The results are shown in Table 1.

(Comparative Example 5)
Except that the mixing amount of graphite was changed to 97.2 parts by weight, the mixing amount of polyacrylic acid was changed to 0.4 parts by weight, and the mixing amount of CMC was changed to 1.4 parts by weight, the same as in Example 1. The cycle capacity maintenance rate and the storage capacity maintenance rate were calculated. The results are shown in Table 1.

(Comparative Example 6)
Except for changing the mixing amount of graphite to 98.4 parts by weight, the mixing amount of polyacrylic acid to 0.1 parts by weight, and the mixing amount of CMC to 0.5 parts by weight, the same as in Example 1. The cycle capacity maintenance rate and the storage capacity maintenance rate were calculated. The results are shown in Table 1.

(Comparative Example 7)
The same procedure as in Example 1 except that the amount of graphite was changed to 98.3 parts by weight, the amount of polyacrylic acid was changed to 0.2 parts by weight, and the amount of CMC was changed to 0.5 parts by weight. The cycle capacity maintenance rate and the storage capacity maintenance rate were calculated. The results are shown in Table 1.

(Comparative Example 8)
The cycle capacity retention ratio and the storage capacity retention ratio were calculated in the same manner as in Example 1 except that the polyacrylic acid mixing amount was changed to 0.5 parts by weight and the CMC mixing amount was changed to 0.5 parts by weight. did. The results are shown in Table 1.

(Comparative Example 9)
The cycle capacity retention rate and the storage capacity retention rate were calculated in the same manner as in Example 1 except that the polyacrylic acid mixing amount was changed to 1.0 part by weight and the CMC mixing amount was changed to 0 part by weight. The results are shown in Table 1.

  As shown in Table 1, the weight ratio of polyacrylic acid to CMC is in the range of 0.02 to 0.25, and the total amount of polyacrylic acid and CMC is in the range of 0.9 to 1.7% by weight. Within the range, the cycle capacity retention ratio (cycle characteristics) and the storage capacity retention ratio (high temperature storage characteristics) were improved.

(Example 7)
The same procedure as in Example 1 was conducted except that the negative electrode was produced by changing polyacrylic acid to a sodium salt of polyacrylic acid.

  As shown in Table 2, both the cycle capacity retention rate and the storage capacity retention rate were improved by using polyacrylic acid sodium salt instead of polyacrylic acid.

  As described above, the lithium ion battery of the present invention is superior in high-temperature storage characteristics and cycle characteristics as compared with the prior art.

  All publications, patents and patent applications cited herein are incorporated herein by reference in their entirety.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Separator 12 Negative electrode 13 Battery can 14 Positive electrode tab 15 Negative electrode tab 16 Inner cover 17 Internal pressure release valve 18 Gasket 19 PTC element 20 Battery cover

Claims (6)

A negative electrode current collector; and a negative electrode mixture layer comprising a negative electrode active material, a water-soluble polysaccharide, a high-molecular polycarboxylic acid or a derivative thereof, and a non-fluorine organic polymer disposed on the negative electrode current collector;
A negative electrode for a lithium ion battery comprising:
The negative electrode mixture layer includes the water-soluble polysaccharide and the polymer polycarboxylic acid or a derivative thereof in a total amount of 0.9 to 1.7% by weight,
The ratio of the weight of the relative weight of the water-soluble polysaccharide polymer polycarboxylic acid or derivative thereof Ri der 0.02-0.25,
The negative electrode for a lithium ion battery , wherein a ratio of the weight of the non-fluorinated organic polymer to the total weight of the water-soluble polysaccharide and the high-molecular polycarboxylic acid or derivative thereof is 0.55 to 1.45 . The negative electrode for a lithium ion battery according to claim 1, wherein the polymer polycarboxylic acid or a derivative thereof is polyacrylic acid, polymethacrylic acid, or a salt or ester thereof. The negative electrode for a lithium ion battery according to claim 1 or 2 , wherein the polymer polycarboxylic acid or a derivative thereof is a salt of polyacrylic acid. Negative electrode active material is graphite having a interlayer distance 0.3345~0.338nm _{(d 002),} a negative electrode for a lithium-ion battery according to any one of claims 1-3. The negative electrode mixture layer contains 1.0 to 1.3% by weight of the water-soluble polysaccharide and the polymer polycarboxylic acid or a derivative thereof in total, and the weight of the polymer polycarboxylic acid or the derivative thereof with respect to the weight of the water-soluble polysaccharide The negative electrode for a lithium ion battery according to any one of claims 1 to 4 , wherein the ratio of is 0.1 to 0.15. The lithium ion battery containing the negative electrode for lithium ion batteries in any one of Claims 1-5 .

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