WO2015118676A1

WO2015118676A1 - MATERIAL FOR Li BATTERIES

Info

Publication number: WO2015118676A1
Application number: PCT/JP2014/052991
Authority: WO
Inventors: 紀雄岩安
Original assignee: 株式会社日立製作所
Priority date: 2014-02-10
Filing date: 2014-02-10
Publication date: 2015-08-13

Abstract

The present invention provides a novel coating material for negative electrode active materials, having both reduced irreversible capacity and reduced battery resistance. This invention is characterized by being a negative electrode coating material for lithium ion secondary batteries, that is indicated by formula (1). In formula (1), R₃, R₄, and R₅ are C1-10 hydrocarbon groups or H. R₁ and R₂ have at least one functional group having electron-withdrawing properties. n is a repetition count of the structural unit. As a result of the present invention, a negative electrode having little irreversible capacity and little resistance can be provided. Furthermore, a lithium ion secondary battery having high capacity and excellent output characteristics can be provided as a result of applying said negative electrode to the lithium ion secondary battery.

Description

Li battery materials

The present invention relates to a material for a Li battery.

In recent years, materials for Li batteries have been actively developed. It is known that a negative electrode for a Li battery has a high reducing activity of an electrolytic solution and increases an irreversible capacity, thereby causing problems such as a decrease in battery capacity. Therefore, efforts are made to improve the battery performance by covering the negative electrode active material with a polymer.

WO2012 / 132152 Patent Document 1 discloses a technique for coating a negative electrode active material with a polyamideimide resin.

However, when the negative electrode active material is coated with the polymer of Patent Document 1, there is a problem that the resistance of the battery increases and the output characteristics deteriorate. This is presumably because the SEI formed by initializing the negative electrode in which the polymer is present exhibits high resistance.

In the present invention, an object is to provide a novel coating material for a negative electrode active material that achieves both a reduction in irreversible capacity and a reduction in battery resistance.

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

A negative electrode coating material for a lithium ion secondary battery represented by Formula (1).

R ₃ , R ₄ and R ₅ in the formula (1) are each a hydrocarbon group having 1 to 10 carbon atoms or H. R ₁ and R ₂ have at least one electron-withdrawing functional group. n is the number of repeating structural units.

Examples of the negative electrode covering material for a lithium ion secondary battery represented by Formula (1) include Formula (5), Formula (6), Formula (7), and Formula (8).

N in Formula (5), Formula (6), Formula (7), and Formula (8) is the number of repeating structural units.

According to the present invention, a negative electrode having a small irreversible capacity and a low resistance can be provided. In addition, by applying the negative electrode to a lithium ion secondary battery, a lithium ion secondary battery having high capacity and excellent output characteristics can be provided. Problems, configurations, and effects other than those described will be clarified by the following description of embodiments.

The figure which represents typically the internal structure of the battery which concerns on one Embodiment of this invention.

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

FIG. 1 is a diagram schematically showing the internal structure of a battery according to an embodiment of the present invention. 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 a negative electrode and a positive electrode as described below with a separator interposed therebetween 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. 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 (however, 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 -x} M _x O ₂ (however, at least one selected from the group consisting of M = Co, Fe and Ga, x = 0.01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _{1 -x} M _x O ₂ (where little is selected from the group consisting of M = Ni, Fe, Mn Both one, x = 0.01 ~ 0.2), LiNi 1-x M x O 2 ( however, M = Mn, Fe, Co , Al, Ga, Ca, at least one selected from the group consisting of 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 specified so as to be equal to or less than the thickness of the mixture layer formed of 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 electric resistance, a conductive agent made of carbon powder for supplementing electric conductivity is used. 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.

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>
The negative electrode in the present invention comprises a negative electrode active material, a binder, and a current collector. As the negative electrode active material, an easily graphitized material obtained from natural graphite, petroleum coke, coal pitch coke, etc. 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 an oxide of the metal can be used as a negative electrode active material. Furthermore, lithium titanate can also be used.

<Coating material>
The negative electrode active material can be coated with a coating material. By providing the covering material, contact between the negative electrode active material and the electrolyte can be prevented, so that an increase in resistance due to precipitation of the electrolyte component can be suppressed. At the time of charging / discharging of the battery, since lithium ions pass between the electrolyte and the negative electrode active material through the coating material, the coating material preferably has ionicity to the extent that lithium ions are captured and dissociated. When the lithium ion capturing power of the covering material is too strong, the lithium ion conductivity is increased and the output as a battery is inferior. Therefore, it is preferable that the bonding force between the coating material and the lithium ions be adjusted strictly.

It has been found that by using a polymer negative electrode coating material represented by (Formula 1) as a negative electrode active material coating material, it is possible to provide a lithium ion secondary battery with high ion conductivity and high output.

N in the formula (1) is the number of repeating structural units. R3, R3 and R5 in the formula (1) are a hydrocarbon group having 1 to 10 carbon atoms or H. In the present invention, R1 and R2 are important for obtaining the effects of the present application. At least one of R1 and R2 includes an electron-withdrawing functional group. Specifically, a functional group containing halogen is preferably used as the electron-withdrawing functional group. Examples of halogen include F, Cl, Br, I, and At. From the viewpoint of the strength of electron withdrawing and electrochemical stability, F, Cl, Br, and I are preferable, F and Cl are more preferable, and F is particularly preferable. Examples of the functional group containing F include F, CFH ₂ , CF ₂ H, and CF ₃ . From the viewpoint of synthesis, F and CF ₃ are preferably used. In R1 and R2, when there is one electron-withdrawing group, the other functional group is hydrogen or a hydrocarbon group. In formula (1), it is important that R1 and R2 are located adjacent to the sulfo group. When the electron-withdrawing functional group is located adjacent to the sulfo group, the electron density of the sulfo group decreases, and as a result, the degree of dissociation of Li ions increases, and the resistance of the battery can be reduced.

The negative electrode active material is coated with the negative electrode coating material of the present invention. The coating amount is an important value for obtaining the effect of the present application. The coating amount is 0.01 to 10% by weight, preferably 0.1 to 5% by weight, particularly preferably 0.3 to 3% by weight, based on the negative electrode active material.

The polymer having the structure of the formula (1) is produced by polymerizing a monomer having a corresponding structure. The monomer can be synthesized by the following method.

First, the acrylic chloride (2) is dissolved in the solvent tetrahydrofuran. The solution is then heated to 50 ° C. There, the formula (3) dissolved in tetrahydrofuran is gradually added dropwise. After completion of dropping, stirring is continued at 50 ° C. for 10 hours. After completion of the reaction, tetrahydrofuran as a reaction solvent is distilled off with an evaporator to obtain a crude product. The parent product is then purified by column chromatography to obtain the desired product formula (4). In column chromatography, a mixed solvent of hexane and ethyl acetate was used as a solvent.

As the polymer having the structure of the formula (1), for example, structures such as the formulas (5) to (8) are preferable. When F is compared with —CF ₃ , the effect of electron withdrawing is high because F is closer to oxygen bonded to lithium ions. Although the distance between halogen and oxygen is increased by using -CF ₃ , more halogen can be provided via carbon, so that the electron withdrawing effect is high.

It is also possible to use, as a coating material, a copolymer obtained by copolymerizing a first monomer corresponding to a polymer having a structure of formula (1) (for example, formula (4)) with another second monomer. By copolymerization, a higher irreversible capacity reduction effect is exhibited. As the monomer to be copolymerized, a second monomer having the structure of formula (9) to formula (13) is preferably used. X of the monomer is an alkali metal or H, and the alkali metal is preferably used from the viewpoint of electrochemical stability.

(Polymerization method)
As described above, the coating material of the present invention can be produced by polymerizing monomers. The polymerization may be any of conventionally known bulk polymerization, solution polymerization, and emulsion polymerization. The polymerization method is not particularly limited, but radical polymerization is preferably used. 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 a temperature range and a polymerization time which are usually performed. The initiator content in the present invention is 0.1 wt% to 20 wt%, preferably 0.3 wt% or more and 5 wt% with respect to the polymerizable compound.
(Polymer structure)
In the present invention, the polymer structure may be a linear structure, a branched structure, a crosslinked structure, or a dendrimer structure. From the viewpoint of workability at the time of coating, a linear polymer is preferably used. The polymerization mode when monomers are copolymerized is not particularly limited as long as a polymer can be formed, and examples thereof include random copolymerization, alternating copolymerization, block copolymerization, and graft copolymerization.
(Polymer molecular weight)
The number average molecular weight of the polymer used as the negative electrode coating material of the present invention is 1,000 or more and 5,000,000 or less. Preferably it is 1000 or more and 1,000,000 or less. By adjusting the number average molecular weight, aggregation of the negative electrode active material, which tends to occur when coating, can be suppressed.
(Copolymerization composition ratio)
In the present invention, the copolymer composition ratio of the first monomer corresponding to the polymer having the structure of the formula (1) and the second monomer containing the structures of the formulas (9) to (13) is the effect of the present invention. It is important in getting. If the ratio of the first monomer is x and the ratio of the second monomer is y, x / (x + y) is 0 <x / (x + y) ≦ 1, preferably 0.05 ≦ x / (x + y) ≦ 1, particularly preferably 0.1 ≦ x / (x + y) ≦ 1. By controlling x / (x + y), it is possible to provide a Li battery that can achieve both irreversible capacity and low resistance.

In the negative electrode coating material of the present invention, the method of coating the negative electrode active material with the coating material is not particularly limited as long as the negative electrode active material is coated with a polymer, but the polymer is dissolved in a solvent and the negative electrode active material is added to the solution. It is preferable from the viewpoint of cost to dry and coat the solvent after stirring. The solvent is not particularly limited as long as the polymer dissolves, but a protic solvent such as water and ethanol, an aprotic solvent such as N-methylpyrrolidone, and a nonpolar solvent such as toluene and hexane are preferably used.

Formula (9), Formula (10), Formula (11), Formula (12), and Formula (13) can each be homopolymerized, and this polymer and the polymer of Formula (1) are mixed to form a negative electrode The active material can also be coated.

<Separator>
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 allow lithium ions to pass through when charging and discharging the battery, they can be used for lithium ion batteries as long as the pore diameter is generally 0.01 to 10 μm and the porosity is 20 to 90%. .
<Electrolyte>
As a representative example of an electrolyte solution that can be used in an embodiment of the present invention, a solvent obtained by mixing ethylene carbonate with dimethyl carbonate, diethyl carbonate, or ethyl methyl 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, vinylene carbonate, fluoroethylene 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- Non-methyl-2-oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, chloropropylene carbonate, etc. There is a solvent. 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 mixed salt of lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), 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.
<Battery system>
The Li battery using the negative electrode active material found in the present application has an excellent property of low resistance. Therefore, heat generation due to the internal resistance of the battery can be suppressed when the battery is used. Therefore, since the battery cooling mechanism can be simplified, it is useful not only for small batteries for portable devices but also for large batteries for in-vehicle use.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples. The results of this example are summarized in Table 1.
<Synthesis method of monomer and polymer>
In this example, monomers of formula (14) and formula (15) were synthesized according to the reaction scheme shown in the <Coating Material> section of the detailed description of the invention. Moreover, the polymer was synthesize | combined using the monomer. Formula (14) and Formula (15) are monomer structures corresponding to Formula (8) and Formula (6), respectively.

For the synthesis of the polymer, tetrahydrofuran as a monomer and reaction solvent was added to a reaction vessel. Furthermore, AIBN was added to the solution as a polymerization initiator. The concentration of the polymerization initiator was added so as to be 4 wt% with respect to the total amount of monomers. Thereafter, the polymer solutions (8) and (6) were synthesized by heating the reaction solution at 60 ° C. for 3 hours.
<Method for producing positive electrode>
A positive electrode active material (LiCoO ₂ ), a conductive agent (SP270: graphite produced by Nippon Graphite Co., Ltd.), and a polyvinylidene fluoride binder were mixed at a ratio of 85: 7.5: 7.5% by weight, and mixed 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 coating amount of the mixture was 200 g / m ² . Then, it pressed and produced the positive electrode.
<Method for coating negative electrode active material>
A predetermined amount of coating polymer is mixed in water. Thereafter, the negative electrode active material is added to the solution and stirred. After stirring for 20 minutes, the negative electrode active material in the form of a slurry is taken out and placed in a dryer heated to 100 ° C. to remove water. Then, after drying with a vacuum dryer heated to 120 ° C., it was sieved to obtain a coated negative electrode active material. The coating polymer was 0.5 wt% with respect to the negative electrode active material. In addition, graphite was used as the negative electrode active material.
<Method for producing negative electrode>
Polyvinylidene fluoride was mixed with graphite at a weight ratio of 95: 5, and charged into 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.
<Negative electrode evaluation method>
The prepared negative electrode was punched into a circle having a diameter of 15 mm to prepare an electrode. The evaluation cell was configured by using Li metal as a negative electrode and a counter electrode, inserting a separator between the negative electrode and Li metal, and adding an electrolyte thereto. The evaluation cell was charged at a current density of 0.72 mA / cm ² up to a preset lower limit voltage. The discharge was performed at a current density of 0.72 mA / cm ² up to a preset upper limit voltage. The lower limit voltage was 0.01 V and the upper limit voltage was 1.5 V. The irreversible capacity was obtained from the difference between the charge capacity and the discharge capacity.
<Evaluation method of DC resistance>
The positive electrode and the negative electrode were punched into a circle having a diameter of 15 mm to prepare an electrode. The small battery was configured by inserting a separator between the positive electrode and the negative electrode, and adding an electrolytic solution thereto. The small battery was charged at a current density of 0.72 mA / cm ² up to a preset upper limit voltage. The discharge was performed at a current density of 0.72 mA / cm ² up to a preset lower limit voltage. The upper limit voltage was 4.2 V and the lower limit voltage was 3.0 V. The discharge capacity obtained in the first cycle was defined as the initial capacity of the battery. Thereafter, the battery was charged to 50% of the initial capacity, and the direct current resistance was measured.
(Example 1)
A polymer was synthesized using the monomer of formula (14). The synthesized polymer was used to coat the negative electrode active material. A negative electrode single electrode was prepared and the irreversible capacity was measured. The irreversible capacity was 32 mAhg- ¹ . Next, a small battery was produced, and DC resistance was measured. The direct current resistance was 10.6 Ω.
(Example 2)
A polymer was synthesized using the monomer of formula (15). The synthesized polymer was used to coat the negative electrode active material. A negative electrode single electrode was prepared and the irreversible capacity was measured. The irreversible capacity was 33 mAhg- ¹ . Next, a small battery was produced, and DC resistance was measured. The DC resistance was 9.9 Ω.
(Example 3)
A monomer was synthesized by copolymerizing the monomer (x) of the formula (14) and the monomer (y) of the formula (11). The copolymer composition ratio (x / (x + y)) was 0.75. A negative electrode single electrode was prepared and the irreversible capacity was measured. The irreversible capacity was 28 mAhg- ¹ . Next, a small battery was produced, and DC resistance was measured. The DC resistance was 10.9 Ω.
(Example 4)
A monomer was synthesized by copolymerizing the monomer of formula (15) and the monomer (y) of formula (11). The copolymer composition ratio (x / (x + y)) was 0.75. A negative electrode single electrode was prepared and the irreversible capacity was measured. The irreversible capacity was 30 mAhg- ¹ . Next, a small battery was produced, and DC resistance was measured. The DC resistance was 10.2 Ω.
(Example 5)
A monomer was synthesized by copolymerizing the monomer (x) of the formula (14) and the monomer (y) of the formula (11). The copolymer composition ratio (x / (x + y)) was 0.50. A negative electrode single electrode was prepared and the irreversible capacity was measured. The irreversible capacity was 26 mAhg- ¹ . Next, a small battery was produced, and DC resistance was measured. The DC resistance was 11.0 Ω.
(Example 6)
A polymer was synthesized by copolymerizing the monomer (x) of the formula (15) and the monomer (y) of the formula (11). The copolymer composition ratio (x / (x + y)) was 0.50. A negative electrode single electrode was prepared and the irreversible capacity was measured. The irreversible capacity was 24 mAhg- ¹ . Next, a small battery was produced, and DC resistance was measured. The DC resistance was 11.3 Ω.
(Comparative Example 1)
In Example 1, evaluation was performed in the same manner as in Example 1 except that no coating material was used. As a result, the irreversible capacity was 36 mAhg- ¹ . Next, a small battery was produced, and DC resistance was measured. The DC resistance was 12.1Ω.

From Example 1 showing the result of the single polymer of the formula (14), it can be seen that the single polymer of the formula (14) has a low DC resistance and can produce a secondary battery with high output. On the other hand, in Examples 3 and 5 in which the copolymers of the formula (14) and the formula (11) were evaluated, the DC resistance was inferior to that of the example 1, but the irreversible capacity was low. This is considered to be due to the high effect of increasing the affinity with the negative electrode active material and preventing the generation of SEI by copolymerizing with the formula (11).

Claims

A negative electrode coating material for a lithium ion secondary battery represented by (formula 1).

R 3 , R 4 and R 5 in the formula (1) are each a hydrocarbon group having 1 to 10 carbon atoms or H. R 1 and R 2 have at least one electron-withdrawing functional group. n is the number of repeating structural units.
In claim 1,
The electron-withdrawing functional group is a functional group containing a halogen, and the halogen is at least one of F, Cl, Br, I, and At.
3. The negative electrode covering material for a lithium ion secondary battery according to claim 2, wherein the electron-withdrawing functional group is at least one of F, CFH 2 , CF 2 H, and CF 3 .
3. The negative electrode for a lithium ion secondary battery according to claim 2, wherein the negative electrode covering material for a lithium ion secondary battery is at least one of the following formulas (5), (6), (7), and (8): Coating material.

N in Formula (5), Formula (6), Formula (7), and Formula (8) is the number of repeating structural units.
In any one of Claim 1 thru | or 4,
The negative electrode covering material for a lithium ion secondary battery includes a first monomer corresponding to a structural unit of a polymer represented by chemical formula (1),
At least one of the second monomers represented by formula (9), formula (10), formula (11), formula (12), and formula (13);
A negative electrode coating material for a lithium ion secondary battery, which is a copolymer obtained by copolymerization of
In claim 5,
The copolymerization ratio of the first monomer and the second monomer of the copolymer is x / (x, where x is the ratio of the first monomer and y is the ratio of the second monomer. + y) is a negative electrode covering material for lithium ion secondary batteries in the range of 0 <x / (x + y) ≦ 1.
A positive electrode capable of inserting and extracting lithium ions;
In a lithium ion secondary battery having a negative electrode capable of inserting and extracting lithium ions, the negative electrode has a negative electrode active material, and the negative electrode active material is coated with a coating material,
The said coating | covering material is a lithium ion secondary battery which is a coating | coated material in any one of Claim 1 thru | or 6.
In claim 7,
The lithium ion secondary battery, wherein a coating amount of the coating material on the negative electrode active material is 0.01 wt% or more and 10 wt% or less.
Dissolving formula (2) in a solvent to prepare a solution of formula (2);
Adding the formula (3) to the formula (2) solution and reacting the formula (2) and the formula (3) by heating;
Evaporating the solvent to obtain formula (4);
The method for producing a negative electrode coating material for a lithium ion secondary battery represented by the formula (1) according to claim 1, wherein the formula (1) is produced by polymerizing the formula (4).

R 3 , R 4 and R 5 in the formula (1) are H. R 1 and R 2 have at least one electron-withdrawing functional group. n is the number of repeating structural units.