WO2015111166A1

WO2015111166A1 - Polymer for positive electrode active material coating of lithium ion batteries

Info

Publication number: WO2015111166A1
Application number: PCT/JP2014/051338
Authority: WO
Inventors: 紀雄岩安
Original assignee: 株式会社日立製作所
Priority date: 2014-01-23
Filing date: 2014-01-23
Publication date: 2015-07-30

Abstract

Provided is a polymer for positive electrode active material coating of lithium ion batteries, which is capable of suppressing gas generation during storage at high temperatures and is also capable of preventing increase of battery resistance. A polymer for positive electrode active material coating of lithium ion batteries, which is represented by formula (1). (In formula (1), x represents a positive number; y represents a number of 0 or more; each of R₁-R₆ independently represents a hydrogen atom or a linear or branched hydrocarbon group; A represents a group represented by formula (1A) (wherein A₁ represents a linear or branched alkylene group, a linear or branched alkenylene group, or a substituted or unsubstituted monocyclic or fused polycyclic arylene group; A₂ represents an alkylene group represented by -(CH₂)_n-, wherein n represents an integer of 0-10; X represents a hydrogen atom or an alkali metal atom; and the wavy line represents a bonding position); and B represents a polar group.)

Description

Polymer for covering positive electrode active material of lithium ion battery

The present invention relates to a polymer for coating a positive electrode active material of a lithium ion battery, and a positive electrode for a lithium ion battery including the positive electrode active material coated thereby. Furthermore, this invention relates to the lithium ion battery provided with the positive electrode for lithium ion batteries of this invention, and the electric power storage system carrying this.

Lithium ion batteries have a high energy density and are widely used in notebook computers and mobile phones by taking advantage of their characteristics. In recent years, interest in electric vehicles has increased from the viewpoint of preventing global warming associated with an increase in carbon dioxide, and the application of lithium ion batteries as a power source has been studied. In particular, in the case of a lithium ion battery used for a portable device such as a notebook personal computer, higher capacity is required.

Under such circumstances, development for increasing the capacity of batteries has been eagerly advanced. For example, in order to increase the capacity, it is known that replacing the transition metal of the positive electrode active material with Ni at a high rate is effective. However, the lithium ion battery using such a positive electrode active material has a problem that when the battery is left at a high temperature, gas is generated mainly due to decomposition of the electrolyte, the battery can expands, and the safety of the battery decreases. . This problem was particularly remarkable in the prismatic battery. In order to suppress the decomposition of the electrolyte, it is necessary to reduce the activity on the surface of the positive electrode active material. As a means for this, it is known to coat the surface of the positive electrode active material with a polymer. In this case, on the surface of the positive electrode active material, lithium ions move through the positive electrode interface during charge / discharge of the battery. Therefore, the polymer to be coated needs to have ion conductivity.

Therefore, attempts have been made to improve the safety of the battery during high temperature storage by coating the positive electrode active material with a polymer. Patent Document 1 discloses a technique for coating a positive electrode active material with a polyethersulfone-based polymer. Patent Document 2 discloses a technique for coating a positive electrode active material with an amide compound or an imide compound. Patent Document 3 discloses a technique for coating a positive electrode active material with an ethylene oxide-based polymer.

However, when the positive electrode active material is coated with the polymer of Patent Documents 1-3, there is a problem that the resistance of the battery increases and the output characteristics deteriorate. The polyethersulfone polymer described in Patent Document 1 is considered to have high resistance because of its high coordination bond with lithium ions. The amide compound and imide compound described in Patent Document 2 are considered to have high battery resistance due to low lithium ion conductivity. The polyethylene oxide polymer described in Patent Document 3 is also considered to have high battery resistance because of its high coordination bond with lithium ions.

Therefore, it was necessary to develop a new polymer capable of suppressing gas generation during high temperature storage and preventing increase in battery resistance.

JP 2011-138732 A JP 2006-351316 A JP-A-2005-19064

Therefore, in view of the above-described conventional situation, the present invention provides a polymer for coating a positive electrode active material of a lithium ion battery that can suppress gas generation during high-temperature storage and can prevent an increase in battery resistance. With the goal.

Thus, as a result of intensive studies by the present inventors, it was found that the above problems can be solved by coating the positive electrode active material with the polymer represented by the formula (1), and the present invention has been completed.

The features of the present invention for solving the above-described problems are as follows.

(1) Formula (1):

[Where:
x is a positive number and y is a number greater than or equal to 0;
R ₁ to R ₆ are each independently hydrogen or a linear or branched hydrocarbon group;
A is the formula (1A):

(Where
A ₁ is a linear or branched alkylene group, a linear or branched alkenylene group, or a substituted or unsubstituted monocyclic or condensed polycyclic arylene group;
A ₂ is an alkylene group represented by — (CH ₂ ) _n —, and n is an integer of 0 to 10;
X is hydrogen or an alkali metal;
(The wavy line represents the coupling position)
A group represented by:
B is a polar group]
The polymer for positive electrode active material coating | cover of a lithium ion battery represented by these.

(2) A is the formula (2):

(Where
R ₇ and R ₈ are each independently hydrogen or a linear or branched hydrocarbon group;
The wavy line represents the coupling position;
A ₂ and X are as defined in claim 1)
The polymer as described in said (1) which is group represented by these.

(3) The above (1) or (2), wherein B is at least one selected from a hydroxyl group, a carboxyl group, a sulfo group, an amino group, a phosphate group, a group containing these groups, and a salt thereof. The polymer described in 1.

(4) The polymer according to any one of (1) to (3), wherein 0.2 ≦ x / (x + y) ≦ 0.9.

(5) The polymer according to any one of (1) to (4) above, which has a number average molecular weight of 1,000 to 1,000,000.

(6) A positive electrode for a lithium ion battery comprising a positive electrode active material coated with the polymer described in any one of (1) to (5) above.

(7) The positive electrode for a lithium ion battery according to the above (6), wherein the positive electrode active material is coated with 0.01% by mass to 10% by mass of polymer with respect to the positive electrode active material.

(8) A lithium ion battery comprising the positive electrode according to (6) or (7).

(9) A power storage system equipped with the lithium ion battery according to (8).

According to the polymer for covering a positive electrode active material of a lithium ion battery of the present invention, gas generation during high temperature storage can be suppressed, and an increase in battery resistance can be prevented. Thereby, the lithium ion battery can maintain excellent output characteristics.

FIG. 1 is a schematic diagram of the internal structure of a battery according to an embodiment of the present invention.

<Polymer of the present invention>
Since the polymer for coating the positive electrode active material of the lithium ion battery of the present invention (hereinafter also referred to as the polymer of the present invention) has a functional group having low coordination bonding with lithium ions, Excellent output characteristics can be maintained without increasing the resistance.

The polymer of the present invention has the formula (1):

It is represented by In this specification, a component derived from a monomer containing A is referred to as an x component, and a component derived from a monomer containing B is referred to as a y component.

In the above formula (1), x is a positive number and y is a number of 0 or more. When y = 0, the polymer represented by the formula (1) is a homopolymer composed of only the x component. In obtaining the effects of the present invention, x / (x + y) is preferably 0.2 ≦ x / (x + y) ≦ 1, and particularly preferably 0.2 ≦ x / (x + y) ≦ 0.9. . In the case of a homopolymer, the value of x / (x + y) is 1. By controlling the copolymer composition ratio defined by x / (x + y), the mobility of ions in the polymer can be adjusted, and the output characteristics are excellent by increasing the mobility of ions in the polymer. A lithium ion battery can be obtained, and the effect of reducing the amount of gas generated is enhanced.

In the above formula (1), R ₁ to R ₆ are each independently hydrogen or a linear or branched hydrocarbon group. The linear or branched hydrocarbon group is preferably a linear or branched hydrocarbon group having 1 to 10 carbon atoms. Examples of the linear or branched hydrocarbon group having 1 to 10 carbon atoms include alkyl groups having 10 or less carbon atoms, alkenyl groups having 10 or less carbon atoms, and aryl groups such as phenyl groups. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group, and a methyl group and an ethyl group are particularly preferable. Examples of the alkenyl group include a vinyl group.

In the above formula (1), A represents the formula (1A):

(The wavy line represents the coupling position).

As shown in the formula (1A), when A has a sulfo group (—SO ₃ X), the dissociation property of lithium ions can be increased, and as a result, the resistance of the battery can be reduced. In addition, by using a sulfo group, the amount of gas generated during high-temperature storage can also be suppressed. As a mechanism for suppressing gas generation, it is considered that a sulfo group is coordinated to a transition metal portion of the positive electrode active material to reduce the decomposition activity of the electrolyte solution by the positive electrode active material. In said formula (1A), X is hydrogen or an alkali metal. As the alkali metal, Li, Na, K, Rb, Cs, Fr and the like can be used, and Li, Na and K are preferably used from the viewpoint of battery performance. Furthermore, as shown in the formula (1A), when A has an amide group (—NHCO—), the electron density in the sulfo group can be reduced, thereby further improving the dissociation property of lithium ions with respect to the sulfo group. Therefore, the resistance of the battery can be reduced.

In the above formula (1A), A ₁ is a linear or branched alkylene group, a linear or branched alkenylene group, or a substituted or unsubstituted monocyclic or condensed polycyclic arylene group, preferably linear Or it is a branched alkylene group. The linear or branched alkylene group preferably has 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms. The linear or branched alkenylene group preferably has 2 to 20 carbon atoms, and particularly preferably 2 to 10 carbon atoms. The substituted or unsubstituted monocyclic or condensed polycyclic arylene group preferably has 6 to 24 carbon atoms, and particularly preferably 6 to 10 carbon atoms. The monocyclic or condensed polycyclic arylene group is a group formed by removing one hydrogen atom from a monocyclic or condensed polycyclic aryl group.

In the divalent groups listed above, one or a plurality of other groups or atoms may be present between the carbon atoms. Examples of other groups or atoms include an etheric oxygen atom, a carbonyl group, an ester group, an amide group, and a sulfide group.

Examples of the linear or branched alkylene group include methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, 1-methylethylene group, 2-methylethylene group, 1-methyltrimethylene group, Examples include 2-methyltrimethylene group, 1,1-dimethylethylene group, 2-ethyltrimethylene group and the like. Examples of the linear or branched alkenylene group include vinylene group, propenylene group, butenylene group, pentenylene group, 1-methylvinylene group, 1-methylpropenylene group, 2-methylpropenylene group, 1- Examples thereof include a methylpentenylene group, a 3-methylpentenylene group, a 1-ethylvinylene group, and a 1-ethylpropenylene group.

Examples of the monocyclic or condensed polycyclic aryl group include phenyl group, 1-naphthyl group, 2-naphthyl group, 1-anthryl group, 9-anthryl group, 2-phenanthryl group, 3-phenanthryl group, and 9-phenanthryl group. Group, 4-biphenyl group and the like. Examples of the substituent of the arylene group include an alkyl group having 1 to 4 carbon atoms such as a methyl group and an ethyl group, an alkoxy group having 1 to 4 carbon atoms such as a hydroxy group, a methoxy group, and an ethoxy group, fluorine, and chlorine. , Halogen atoms such as bromine and iodine. From the viewpoint of lowering the electron density in the sulfo group in the above formula (1A) and thereby further increasing the dissociation property of lithium ions with respect to the sulfo group, it is preferably substituted with an electron-withdrawing substituent.

In the above formula (1A), A ₂ is an alkylene group represented by — (CH ₂ ) _n —. n is an integer of 0 to 10, preferably an integer of 1 to 5.

In the above formula (1), A reduces the electron density in the sulfo group in the above formula (1A), thereby further improving the dissociation property of lithium ions with respect to the sulfo group.

(The wavy line portion represents the bonding position). A ₂ and X are as described above for formula (1A).

In the above formula (2), R ₇ and R ₈ are each independently hydrogen or a linear or branched hydrocarbon group, specifically, an alkyl group having 10 or less carbon atoms, or 10 carbon atoms. Examples include the following alkenyl groups and aryl groups such as phenyl groups. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group, and a methyl group and an ethyl group are particularly preferable. Examples of the alkenyl group include a vinyl group.

In the above formula (1), B is a polar group, specifically selected from a hydroxyl group, a carboxyl group, a sulfo group, an amino group, a phosphate group, a group containing these groups, and salts thereof. It is preferable that it is at least one kind. Among these, from the viewpoint of reducing battery resistance and suppressing gas generation, at least one selected from a hydroxyl group, a carboxyl group, a sulfo group, a salt thereof, a group containing these groups, and a salt thereof It is preferable that The reduction in battery resistance is considered to be based on the high dissociation property with respect to lithium of a polar group such as a hydroxyl group, a carboxyl group, or a sulfo group. In addition, it is considered that the gas generation suppressing effect is caused by the fact that the group having the polarity described above takes a coordination bond at the transition metal portion of the positive electrode active material and reduces the catalytic activity of the electrolytic solution decomposition. The salt of a hydroxyl group, a carboxyl group, a sulfo group, an amino group, or a phosphate group is preferably an alkali metal salt. As the group containing a hydroxyl group, a carboxyl group, a sulfo group, an amino group, or a phosphate group, an alkyl group having 10 or less carbon atoms, an alkenyl group having 10 or less carbon atoms, and an aryl group such as a phenyl group are substituted with the above groups. Those are preferred.

The above formula (1A) is a structure corresponding to a side chain provided in the main chain of the polymer, and has a sulfo group at the end of the side chain. It is considered that the movement of lithium ions is mainly performed through oxygen of the sulfo group. Therefore, by providing the sulfo group at the tip of the side chain away from the main chain, the structure can be moved more flexibly, so that the structure is suitable for transporting lithium ions. For example, when a structure similar to the formula (1A) as shown in the following formula (2-1) is compared with a structure shown in the following formula (2-2) corresponding to the formula (1A), the sulfo group has a main chain. It can be said that the formula (2-2) provided at the tip of the side chain remote from is a structure suitable for transporting lithium ions.

Specific examples of the above B include the following formulas (3) to (6):

In the formula, X is preferably hydrogen or an alkali metal; the wavy line portion represents a bonding position. The groups of the above formulas (3)-(6) are respectively represented by the following formulas (3M)-(6M):

(Wherein X is hydrogen or an alkali metal).

In Formula (3M) and Formula (5M), —SO ₃ X and —OX are arranged in the para position with respect to the main chain from the viewpoint of providing oxygen bonded to the lithium ion at the end of the side chain away from the main chain. It is preferable to do. By providing it in the para position, the lithium ion transport efficiency can be increased.

Preferable specific examples of the polymer represented by formula (1) include formula (7):

(Wherein X is hydrogen or an alkali metal; x and y are as described above for formula (1)).

The number average molecular weight of the polymer of the present invention is not particularly limited, but is preferably 1000 to 1,000,000, particularly preferably 10,000 to 200,000. By adjusting the number average molecular weight, aggregation of the positive electrode active material generated when coating can be suppressed, and as a result, productivity can be improved. The GPC method was used for the measurement of the number average molecular weight. The eluent used was a mixture of 0.2 M NaCl and acetonitrile at a ratio of 90:10 (vol ratio). Pullulan was used for correcting the molecular weight.

When the polymer of the present invention is a copolymer, any of a random copolymer, a block copolymer, and an alternating copolymer may be used. When the monomer corresponding to the x component and the monomer corresponding to the y component are copolymerized, the separation of polymers having different properties can be suppressed as compared to the case where the homopolymers of the respective components are simply mixed. The desired effect of the present invention is also enhanced.

Regardless of whether it is a homopolymer or a copolymer, the polymer of the present invention can be produced by any conventionally known bulk polymerization, solution polymerization, emulsion polymerization, or radical polymerization, and is not particularly limited. However, radical polymerization is preferred from the viewpoint of reducing the residual monomer that lowers battery performance. In the polymerization, a polymerization initiator may or may not be used, and a radical polymerization initiator is preferably used from the viewpoint of easy handling. The polymerization method using a radical polymerization initiator can be carried out in the usual temperature range and polymerization time. The amount of the initiator used is preferably 0.1% by mass to 20% by mass and particularly preferably 0.3% by mass to 5% by mass with respect to the monomer used.

When the polymer of the present invention is a homopolymer (x component alone), the polymer can be used by mixing another polymer, in particular, the homopolymer of the y component represented by the formula (1).

<Positive electrode for lithium ion secondary battery of the present invention>
The present invention also relates to a positive electrode for a lithium ion battery including a positive electrode active material coated with the polymer of the present invention. The positive electrode includes a positive electrode active material, a conductive material, and a binder, and these are applied to a current collector such as aluminum.

(Positive electrode active material)
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 MxO ₂ (however, at least selected from the group consisting of M = Co, Ni, Fe, Cr, Zn, Ti) 1 type, x = 0.01 to 0.2), Li ₂ Mn ₃ MO ₈ (where M = at least one selected from the group consisting of Fe, Co, Ni, Cu, Zn), Li _1-x A _x Mn ₂ O ₄ (where A = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca, at least one selected from the group consisting of x = 0.01 to 0.1), LiNi _{1 -XM} _x O ₂ (where M = Co, Fe, Ga, at least one selected from the group consisting of x, 0.01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _{1 -X} M _x O ₂ (however, M = at least one selected from the group consisting of Ni, Fe and Mn, x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (where M = Mn, Fe, Co, Al, Ga) And 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 , and LiMnPO ₄ .

The particle diameter of the positive electrode active material is usually specified 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.

(Coating method)
The method of coating the polymer of the present invention on the positive electrode active material is not particularly limited as long as the polymer is coated on the positive electrode active material, but the polymer is dissolved in a solvent, the positive electrode active material is added to the solution, and the solvent is dried after stirring. Coating is also preferable from the viewpoint of cost. The solvent is not particularly limited as long as the polymer of the present invention is dissolved, but a protic solvent such as water and ethanol, an aprotic solvent such as N-methylpyrrolidone, a nonpolar solvent such as toluene and hexane, and the like are preferably used. It is done.

The coating amount of the polymer of the present invention is not particularly limited as long as the desired effect of the present invention can be obtained, but is 0.01% by mass to 10% by mass and 0.03% by mass to 1% by mass with respect to the positive electrode active material. It is particularly preferably 0.03% by mass or more and 0.3% by mass or less. The effect of the present invention can be enhanced by adjusting the coating amount.

(Conductive material)
As the conductive material in the positive electrode, any material having conductivity can be applied. For example, carbon blacks such as ketjen black, acetylene black, channel black, furnace black, thermal black, natural graphite, artificial graphite, Examples thereof include graphites such as expanded graphite, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper, aluminum, nickel and silver, and conductive polymers such as polyphenylene derivatives. Any of these may be used alone or in combination.

(binder)
The binder in the positive electrode can be appropriately selected from various thermoplastic resins and thermosetting resins, and is not particularly limited. Specific examples include polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoro. Propylene copolymer, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, fluorine And vinylidene chloride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer and ethylene-acrylic acid copolymer. Any of these may be used alone or in combination.

<Lithium ion battery of the present invention>
The present invention also relates to a lithium ion battery comprising a positive electrode having a positive electrode active material coated with the polymer of the present invention.

(Battery structure)
Hereinafter, an embodiment of the lithium ion battery of the present invention will be described with reference to the drawings and the like. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

A battery 1 according to an embodiment of the present invention shown in FIG. 1 includes a positive electrode 10, a separator 11, a negative electrode 12, a battery container (that is, a battery can) 13, a positive electrode current collecting tab 14, a negative electrode current collecting tab 15, an inner lid 16, It comprises an internal pressure release valve 17, a gasket 18, a positive temperature coefficient (PTC) resistance element 19, a battery lid 20, and an axis 21. 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. A positive electrode 10, a separator 11, and a negative electrode 12 are wound around the shaft center 21.

The separator 11 is inserted between the positive electrode 10 and the negative electrode 12 to produce an electrode group wound around the axis 21. As the axis 21, any known one can be used as long as it can support 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 interior 13 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. The lithium ion battery according to an embodiment of the present invention can be manufactured, for example, by disposing the following negative electrode and positive electrode facing each other via a separator and injecting an electrolyte. The structure of the lithium ion battery according to an embodiment 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 combined. A stacked electrode group can be formed by stacking.

(Positive electrode)
The positive electrode 10 includes a positive electrode active material, a conductive agent, a binder, and a current collector. The positive electrode is coated with the polymer of the present invention.

Since the positive electrode active material is generally oxide-based and has high electrical resistance, a conductive agent made of 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 to bond the powders together and simultaneously adhere to the current collector.

As 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, a foam metal plate, or the like 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.

(Negative electrode)
A negative electrode consists of a negative electrode active material, a binder, and a collector. As the negative electrode active material, an easily graphitized material obtained from natural graphite, petroleum coke, coal pitch coke or the like is heat-treated at a high temperature of 2500 ° C. or higher, and mesophase carbon or amorphous carbon, carbon fiber, and lithium are alloyed. A metal or a material having a metal supported on the surface of carbon particles is used. For example, a metal or alloy selected from lithium, silver, aluminum, tin, silicon, indium, gallium, and magnesium. Further, the metal or the oxide of the metal can be used as a negative electrode active material. Furthermore, lithium titanate can also be used.

(Electrolytes)
As a representative example of an electrolyte solution that can be used in an embodiment of the present invention, a solvent obtained by mixing dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate with ethylene carbonate, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte, Alternatively, there is a solution in which lithium borofluoride (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, fluoroethylene 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- Non-water such as 2-oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, or chloropropylene carbonate There is a medium. 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.

In the case of using a solid polymer electrolyte (polymer electrolyte), ion conductive polymers 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-methylimidazole tetrafluoroborate (EMI-BF4), a lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), a mixed complex of triglyme and tetraglyme, a cyclic quaternary ammonium cation (N-methyl) -N-propylpyrrolidinium is exemplified)) and imide anion (exemplified by bis (fluorosulfonyl) imide) are selected from combinations that do not decompose at the positive electrode 10 and the negative electrode 12, and according to this embodiment. Can be used for batteries.

The shape of the lithium ion battery of the present invention is not particularly limited, but may be, for example, a button type, a sheet type, a laminated type, a cylindrical type, a rectangular type, or the like.

<Power storage system>
The present invention also relates to a power storage system equipped with the positive electrode for a lithium ion battery of the present invention. Since the lithium ion battery of the present invention has a property of low resistance, heat generation due to the internal resistance of the battery can be suppressed when the battery is used. And since the cooling mechanism of a battery can also be simplified, it is useful not only for a small battery for portable equipment but also for a large battery for in-vehicle use. Further, a plurality of such lithium ion batteries can be connected in series to be used as a power source for an electric vehicle.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The results of this example are summarized in Table 1.

<Polymer synthesis method>
Monomer and water as a reaction solvent were added to the reaction vessel. Further, AIBN (azoisobutyronitrile) was added to the solution as a polymerization initiator. The concentration of the polymerization initiator was added so as to be 4% by mass with respect to the total amount of monomers. Then, the polymer was synthesized by heating the reaction solution at 60 ° C. for 3 hours.

<Coating method of positive electrode active material>
A positive electrode active material (LiCoO ₂ ) is added to an aqueous polymer solution prepared in advance and stirred. Then, the coated positive electrode active material was produced by distilling off water. The amount of polymer was 0.1% by mass with respect to the positive electrode active material.

<Method for producing positive electrode>
A positive electrode active material, a conductive agent (SP270: graphite manufactured by Nippon Graphite Co., Ltd.), and a polyvinylidene fluoride binder were mixed at a ratio of 85: 7.5: 7.5 wt%, and charged into N-methyl-2-pyrrolidone. A slurry-like solution was prepared. The slurry was applied to a 20 μm thick aluminum foil by a doctor blade method and dried. The mixture application amount was 200 g / m ² . Then, it pressed and produced the positive electrode.

<Method for producing negative electrode>
Polyvinylidene fluoride was mixed with graphite at a ratio of 95: 5% by weight, and further mixed with N-methyl-2-pyrrolidone to prepare a slurry solution. The slurry was applied to a copper foil having a thickness of 10 μm by a doctor blade method and dried. The mixture was pressed so that the bulk density was 1.5 g / cm ³ to prepare a negative electrode.

<Production method of battery>
A polyolefin separator was inserted between the positive electrode and the negative electrode to form an electrode group. Thereto, an electrolytic solution was injected. Thereafter, the battery was sealed with an aluminum laminate to produce a battery. Then, the battery was initialized by repeating charging / discharging 3 cycles.

<Battery evaluation method>
The battery was charged and discharged with an upper limit voltage of 4.2 V and a lower limit voltage of 2.5 V, with a current density of 0.1 mA / cm ² . Moreover, the battery charged to 4.2V was discharged at a current density of 0.1, 0.5, and 1.0 mA / cm ² for 10 seconds, and the relationship of IV was plotted. DC resistance (R) was obtained from Next, the cell was recharged to 4.2 V, and then placed in a constant temperature bath at 85 ° C. and stored for 24 hours. After storing for 24 hours, the battery was taken out, the battery was cooled to room temperature, the generated gas was collected with a syringe, and the amount of gas generated was measured.

[Example 1]
A polymer was synthesized using the monomer of formula (8) below. Moreover, the positive electrode active material was coat | covered using the said polymer. The initial capacity was 30 mAh, and the DC resistance was 600 mΩ. Moreover, the gas generation amount in the high temperature storage test was 0.062 mL.

[Example 2]
A copolymer was synthesized by mixing X = Li in the formula (8) and the formula (3) so as to be 75:25 (mol%). Moreover, the positive electrode active material was coat | covered using the said polymer. The initial capacity was 30 mAh and the DC resistance was 660 mΩ. The amount of gas generated during the high temperature storage test was 0.059 mL.

[Example 3]
A copolymer was synthesized by mixing X = Li in the formula (8) and the formula (3) so as to be 50:50 (mol%). Moreover, the positive electrode active material was coat | covered using the said polymer. The initial capacity was 30 mAh and the DC resistance was 670 mΩ. Moreover, the gas generation amount in the high temperature storage test was 0.050 mL.

[Example 4]
Copolymer was synthesized by mixing X = Li in the formula (8) and the formula (3) so as to be 25:75 (mol%). Moreover, the positive electrode active material was coat | covered using the said polymer. The initial capacity was 30 mAh and the direct current resistance was 690 mΩ. The amount of gas generated during the high-temperature storage test was 0.048 mL.

[Example 5]
Copolymers were synthesized by mixing X = Li in formula (8) and formula (4) so as to be 75:25 (mol%). Moreover, the positive electrode active material was coat | covered using the said polymer. The initial capacity was 29 mAh, and the DC resistance was 680 mΩ. Moreover, the gas generation amount in the high temperature storage test was 0.050 mL.

[Example 6]
A copolymer was synthesized by mixing X = Li in the formula (8) and the formula (5) so as to be 75:25 (mol%). Moreover, the positive electrode active material was coat | covered using the said polymer. The initial capacity was 29 mAh, and the DC resistance was 673 mΩ. The amount of gas generated during the high-temperature storage test was 0.055 mL.

[Comparative Example 1]
In Example 1, it examined like Example 1 except not adding a polymer. The initial capacity was 29 mAh and the direct current resistance was 698 mΩ. Moreover, the gas generation amount in the high temperature storage test was 0.102 mL.

[Comparative Example 2]
Polymers were synthesized using monomers of formula (3) where X = Li. Moreover, the positive electrode active material was coat | covered using the said polymer. The initial capacity was 29 mAh and the direct current resistance was 690 mΩ. Moreover, the gas generation amount in the high temperature storage test was 0.086 mL.

The polymer of the present invention can be used for small lithium ion batteries for portable devices and large lithium batteries for in-vehicle use.

1. Battery 10. Positive electrode 11. Separator 12. Negative electrode 13. Battery container (ie battery can)
14 Positive electrode current collecting tab 15. Negative electrode current collecting tab 16. Inner lid 17. Internal pressure release valve 18. Gasket 19. Positive temperature coefficient (PTC) resistance element 20. Battery lid 21. Axis

All publications, patents and patent applications cited in this specification shall be incorporated into the present specification as they are.

Claims

Formula (1):

[Where:
x is a positive number and y is a number greater than or equal to 0;
R 1 to R 6 are each independently hydrogen or a linear or branched hydrocarbon group;
A is the formula (1A):

(Where
A 1 is a linear or branched alkylene group, an alkenylene group, or a substituted or unsubstituted monocyclic or condensed polycyclic arylene group;
A 2 is an alkylene group represented by — (CH 2 ) n —, and n is an integer of 0 to 10;
X is hydrogen or an alkali metal;
(The wavy line represents the coupling position)
A group represented by:
B is a polar group]
The polymer for positive electrode active material coating | cover of a lithium ion battery represented by these.
A is the formula (2):

(Where
R 7 and R 8 are each independently hydrogen or a linear or branched hydrocarbon group;
The wavy line represents the coupling position;
A 2 and X are as defined in claim 1)
The polymer of Claim 1 which is group represented by these.
The polymer according to claim 1 or 2, wherein B is at least one selected from a hydroxyl group, a carboxyl group, a sulfo group, an amino group, a phosphate group, a group containing these groups, and a salt thereof.
The polymer according to any one of claims 1 to 3, wherein 0.2≤x / (x + y) ≤0.9.
The polymer according to any one of claims 1 to 4, having a number average molecular weight of 1,000 to 1,000,000.
A positive electrode for a lithium ion battery comprising a positive electrode active material coated with the polymer according to any one of claims 1 to 5.
The positive electrode for a lithium ion battery according to claim 6, wherein the positive electrode active material is coated with 0.01% by mass to 10% by mass of polymer with respect to the positive electrode active material.
A lithium ion battery comprising the positive electrode according to claim 6 or 7.
A power storage system equipped with the lithium ion battery according to claim 8.