JP5896154B2 - SOLID ELECTROLYTE FILM FORMING AGENT, ELECTROLYTIC SOLUTION CONTAINING SAME, AND ELECTRIC STORAGE DEVICE - Google Patents

Description

  The present invention relates to a solid electrolyte film forming agent, an electrolytic solution containing the solid electrolyte film forming agent, and an electricity storage device including the electrolytic solution.

  In recent years, there has been a demand for an electricity storage device suitable as a driving power source for electric vehicles, electronic devices, and the like. In particular, lithium ion secondary batteries and lithium ion capacitors are expected as power storage devices having high voltage and high energy density. Here, the lithium ion secondary battery and the lithium ion capacitor have a structure in which an electrolyte solution (electrolyte solution) containing an electrolyte and a solvent is sandwiched between the positive electrode and the negative electrode, and the lithium ions present in the electrolyte It is an electricity storage device using as a medium.

As an electrolytic solution in a lithium ion secondary battery or a lithium ion capacitor, a non-aqueous electrolytic solution that does not substantially contain water is used. In this case, a lithium salt such as LiPF ₆ or LiClO ₄ is generally used as the electrolyte, and an organic solvent such as propylene carbonate or dimethyl carbonate is used as the solvent. These organic solvents may be decomposed on the surface of the electrode (particularly, the negative electrode in the full cell) during the charge / discharge process of the electricity storage device to generate gas such as CO ₂ and impair the battery reaction. In addition, these solvents may irreversibly react with electrode active materials (particularly, negative electrode active materials in full cells) to alter the active materials. As described above, power storage devices using organic solvents such as propylene carbonate and dimethyl carbonate have a problem in durability.

  In order to suppress such deterioration over time of the electricity storage device, a solid electrolyte membrane (Solid Electrolyte Interface Film, commonly referred to as “SEI membrane” in the industry) is obtained by reducing the electrolyte solvent during the initial charge of the electricity storage device. Various methods for forming the above have been proposed. For example, a method of adding a carbonate compound or a sultone compound as an additive (solid electrolyte film forming agent) for forming an SEI film on the surface of an electrode active material has been proposed (see Patent Documents 1 to 4). .

Japanese Patent Application Laid-Open No. 08-45545 JP 2001-006729 A Special table 2011-519133 gazette JP 2004-31100 A

However, according to the conventional solid electrolyte membrane forming agent, the thickness is insufficient and the thickness is not sufficient, and only a part of the surface of the electrode active material may be covered, which is insufficient in terms of quality and quantity. Only a solid electrolyte membrane could be formed. In other words, the conventional solid electrolyte film forming agent is completely lacking in the effect of suppressing problems such as the decomposition of the electrolyte solvent and the alteration of the electrode active material as described above. Moreover, since the solid electrolyte membrane formed by these solid electrolyte membrane forming agents has a large lithium ion migration resistance, there is also a problem that the electrode resistance (impedance) during charging / discharging of the electricity storage device increases. Furthermore, if the amount of addition of these solid electrolyte membrane forming agents is increased in an attempt to improve the effect of suppressing the above-described problems using conventional solid electrolyte membrane forming agents, the electrolyte solution does not participate in the formation of the solid electrolyte membranes. The amount of the remaining agent increases, and this causes a problem that the battery characteristics are impaired due to deterioration over time with charge and discharge.

  Therefore, some aspects according to the present invention provide a solid state storage device that exhibits good charge / discharge characteristics and does not deteriorate over time due to charge / discharge by solving the above-described problems. An electrolyte film forming agent and an electrolytic solution containing the same are provided.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
One aspect of the solid electrolyte membrane forming agent according to the present invention is:
A polymer (A) having a repeating unit (A1) derived from a (meth) acrylate having a chain ether structure;
A liquid medium (B);
It is characterized by containing.

（式（１）中、Ｒ^５は水素原子またはメチル基を表し、Ｒ^６は単結合または２価の有機基を表し、複数存在してもよいＲ^７はそれぞれ独立に２価の炭化水素基を表し、Ｒ^８は水素原子または１価の有機基を表す。ｘは１以上の整数である。） [Application Example 2]
In the solid electrolyte film forming agent of Application Example 1,
The (meth) acrylate having the chain ether structure may be a compound represented by the following general formula (1).

(In the formula (1), R ⁵ represents a hydrogen atom or a methyl group, R ⁶ represents a single bond or a divalent organic group, and a plurality of R ^{7 s} may be independently a divalent hydrocarbon group. R ⁸ represents a hydrogen atom or a monovalent organic group, and x is an integer of 1 or more.)

[Application Example 3]
In the solid electrolyte film forming agent of Application Example 1 or Application Example 2,
The polymer (A) can further contain a repeating unit (A2) derived from (meth) acrylate having a cyclic ether structure.

（式（２）中、Ｒ^１は水素原子またはメチル基を表し、Ｒ^２は２価の連結基を表し、Ｒ^３
は水素原子または１価の有機基を表し、複数存在するＲ^４はそれぞれ独立に水素原子または１価の有機基を表す。ｍおよびｎは０以上の整数であり、ｍ＋ｎ≧１である。） [Application Example 4]
In the solid electrolyte film forming agent of Application Example 3,
The (meth) acrylate having the cyclic ether structure may be a compound represented by the following general formula (2).

(In Formula (2), R ¹ represents a hydrogen atom or a methyl group, R ² represents a divalent linking group, and R ³
Represents a hydrogen atom or a monovalent organic group, and a plurality of R ^{4 s} independently represent a hydrogen atom or a monovalent organic group. m and n are integers of 0 or more, and m + n ≧ 1. )

[Application Example 5]
In the solid electrolyte membrane forming agent of any one of Application Examples 1 to 4,
The number average molecular weight of the polymer (A) may be 1,000 or more and 100,000 or less.

[Application Example 6]
One aspect of the electrolytic solution according to the present invention is:
The solid electrolyte film forming agent according to any one of Application Examples 1 to 5 and the electrolyte (C) are contained.

[Application Example 7]
One aspect of the electricity storage device according to the present invention is:
The electrolytic solution of Application Example 6 is provided.

  According to the solid electrolyte membrane-forming agent of the present invention, it is possible to produce an electricity storage device that exhibits good charge / discharge characteristics and does not deteriorate with time due to charge / discharge. In addition, since the electrolytic solution according to the present invention contains a solid electrolyte membrane forming agent having excellent formation efficiency of the solid electrolyte membrane, a high quality solid electrolyte membrane can be efficiently formed even with a small amount of addition. . This suppresses problems such as decomposition of the electrolyte solvent and alteration of the electrode active material in the prior art. Furthermore, since the solid electrolyte membrane formed from the electrolyte solution according to the present invention has a low lithium ion migration resistance, an electricity storage device with reduced electrode resistance can be obtained.

  Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, and includes various modified examples that are implemented without departing from the scope of the present invention. In the present specification, “(meth) acrylic” is a concept encompassing both “acrylic” and “methacrylic”. Further, “˜ (meth) acrylate” is a concept encompassing both “˜acrylate” and “˜methacrylate”.

1. Solid Electrolyte Film Forming Agent A solid electrolyte film forming agent according to the present embodiment includes a polymer (A) having a repeating unit (A1) derived from (meth) acrylate having a chain ether structure, and a liquid medium (B). And containing. Hereinafter, each component contained in the solid electrolyte membrane forming agent according to the present embodiment will be described in detail.

1.1. Polymer (A)
The polymer (A) contained in the solid electrolyte film forming agent (hereinafter also referred to as “SEI film forming agent”) according to the present embodiment is a repeating unit derived from (meth) acrylate having a chain ether structure ( A1). The polymer (A) has a repeating unit (A1) derived from a (meth) acrylate having a chain ether structure, so that it quickly undergoes electrolytic crosslinking on the active material surface during the initial charging process, and the entire surface of the active material surface It is considered that a dense solid electrolyte membrane (hereinafter also referred to as “SEI membrane”) is formed thereon. And since the SEI film | membrane formed from the polymer (A) becomes a precise | minute and firm film | membrane, it is hard to collapse even if charging / discharging of an electrical storage device is repeated, the lifetime of an electrical storage device improves, and charge / discharge capacity | capacitance is improved. Reduction over time is suppressed. Further, since the SEI film formed from the polymer (A) is dense and firm, the diffusion resistance of lithium ions is low, so that the electrode resistance of the electricity storage device can be maintained at a low value.

1.1.1. Repeating unit (A1)
The repeating unit (A1) is derived from (meth) acrylate having a chain ether structure. The repeating unit (A1) is a main structure for causing the polymer (A) to exhibit the SEI film forming ability as described above. Since the repeating unit (A1) has a (poly) ether-type chain ether structure site, the affinity with the liquid medium (B) used in the electricity storage device can also be improved.

The (meth) acrylate having a chain ether structure is preferably a compound represented by the following general formula (1).

In Formula (1), R ⁵ represents a hydrogen atom or a methyl group, and is preferably a hydrogen atom from the viewpoint of synthesizing a polymer with high yield. In formula (1), R ⁶ represents a single bond or a divalent organic group, and the divalent organic group is preferably an alkylene group having 1 to 10 carbon atoms.

In formula (1), a plurality of R ⁷ which may be present each independently represent a divalent hydrocarbon group, and the divalent hydrocarbon group may be a linear or branched 2 having 1 to 10 carbon atoms. Valent hydrocarbon group. Among these, since the affinity with the liquid medium (B) is high, it is preferred that R ⁷ independently represents an alkylene group having 1 to 3 carbon atoms.

In formula (1), R ⁸ represents a hydrogen atom or a monovalent organic group, and the monovalent organic group is a linear or branched alkyl group having 1 to 4 carbon atoms, or 6 to 12 carbon atoms. An aryl group is preferred. Examples of the linear or branched alkyl group having 1 to 4 carbon atoms include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, 2-methylpropyl group, and 1-methylpropyl group. , T-butyl group and the like. Examples of the aryl group include a phenyl group and a naphthyl group. Since the affinity for the liquid medium (B) is high, it is preferred that R ⁸ is an alkyl group having 1 to 3 carbon atoms. Moreover, in Formula (1), x is an integer greater than or equal to 1, It is preferable that it is 1-30, It is more preferable that it is 1-20, It is especially preferable that it is 1-10.

（式（１−１）中、Ｒ^５は水素原子またはメチル基を表し、Ｒ^１０は単結合または２価の
有機基を表し、複数存在するＲ^１１はそれぞれ独立に水素原子または１価の有機基を表し、Ｒ^８は水素原子または１価の有機基を表す。） The (meth) acrylate having a chain ether structure is more preferably a compound represented by the following general formula (1-1). The repeating unit derived from the compound represented by the following general formula (1-1) has a high affinity with a carbonate-based solvent or a lactone-based solvent that is generally used in a non-aqueous electrolyte, Does not interfere with the movement of lithium ions between active materials. As a result, the electrode resistance of the electricity storage device can be maintained at a low value.

(In the formula (1-1), R ⁵ represents a hydrogen atom or a methyl group, R ¹⁰ represents a single bond or a divalent organic group, and a plurality of R ¹¹ are each independently a hydrogen atom or a monovalent organic group. And R ⁸ represents a hydrogen atom or a monovalent organic group.)

In the formula (1-1), ^{R 5} has the same meaning as ^{R 5} in the general formula (1). R ⁸ has the same meaning as ^{R 8} in formula (1). R ¹⁰ represents a single bond or a divalent organic group, and examples of the divalent organic group include an alkylene group having 1 to 10 carbon atoms. Among these, R ¹⁰ is preferably a single bond.

A plurality of R ¹¹ each independently represent a hydrogen atom or a monovalent organic group, and the monovalent organic group is preferably a linear or branched alkyl group having 1 to 4 carbon atoms. Examples of the linear or branched alkyl group having 1 to 4 carbon atoms include those exemplified and listed in the description of R ⁸ above. Among these, it is preferable that each of R ¹¹ is a hydrogen atom because of its high affinity with the electrolytic solution. Moreover, in Formula (1-1), x is an integer greater than or equal to 1, It is preferable that it is 1-30, It is more preferable that it is 1-20, It is especially preferable that it is 1-10.

  Specific examples of the compound represented by the general formula (1) include 2-methoxyethyl acrylate, methoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, 2-ethylhexyloxydiethylene glycol (meth) acrylate, methoxy Polyethylene glycol (meth) acrylate, 2-ethoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, ethoxytriethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, methoxy Triethylene glycol (meth) acrylate, methoxytetraethylene glycol (meth) acrylate, ethoxydipro Glycol (meth) acrylate, ethoxy tripropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxy diethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate. These compounds may be used alone or in combination of two or more.

  The polymer (A) is not particularly limited as long as it has the above repeating unit (A1), and may be a homopolymer of (meth) acrylate having a chain ether structure or a chain. A copolymer of (meth) acrylate having an ether structure and another monomer may be used. When the polymer (A) is a copolymer, it may have any structure of a random copolymer, an alternating copolymer, a periodic copolymer, and a block copolymer.

  When the polymer (A) is a copolymer, the content ratio of the repeating unit (A1) in the polymer (A) is such that the total amount of the repeating unit (A1) and other repeating units is 100 mol%. The repeating unit (A1) is preferably 60 mol% or more, more preferably 60 to 90 mol%, particularly preferably 65 to 85 mol%. When the content ratio of the repeating unit (A1) in the polymer (A) is in the above range, a dense and firm solid electrolyte membrane can be formed on the active material surface in the initial charging process.

1.1.2. Repeating unit (A2)
When the polymer (A) further has a repeating unit (A2) derived from (meth) acrylate having a cyclic ether structure, the polymer (A) can be used for producing a gel electrolyte. That is, a crosslinked structure can be constructed by opening the cyclic ether structure of the repeating unit (A2), thereby forming a matrix of gel electrolyte.

The (meth) acrylate having a cyclic ether structure is not particularly limited as long as the cyclic ether structure can be opened and crosslinked, but is preferably a compound represented by the following general formula (2). .

In the above formula (2), R ¹ represents a hydrogen atom or a methyl group, and is preferably a methyl group from the viewpoint of the oxidation resistance of the polymer (A).

In the above formula (2), R ² represents a divalent linking group, for example, a single bond, a divalent chain hydrocarbon group having 1 to 20 carbon atoms, a divalent cyclic saturated group having 3 to 20 carbon atoms, or An unsaturated hydrocarbon group, or a divalent group obtained by combining these with an ether group, an ester group, or a carbonyl group can be given. Such a divalent linking group may have a substituent. Is preferably a single bond or an alkylene group having 1 to 4 carbon atoms.

In the above formula (2), R ³ represents a hydrogen atom or a monovalent organic group, and the monovalent organic group is preferably a linear or branched alkyl group having 1 to 8 carbon atoms. Examples of the linear or branched alkyl group having 1 to 8 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a 2-methylpropyl group, and a 1-methylpropyl group. Group, t-butyl group and the like. Among these, R ³ is preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms so that it can be easily crosslinked.

In the above formula (2), a plurality of R ⁴ each independently represents a hydrogen atom or a monovalent organic group, and the monovalent organic group is a linear or branched alkyl group having 1 to 4 carbon atoms. Preferably there is. Examples of the linear or branched alkyl group having 1 to 4 carbon atoms include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, 2-methylpropyl group, and 1-methylpropyl group. , T-butyl group and the like. Among these, it is preferable that each R ⁴ is independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms so that it can be easily crosslinked. M and n are integers of 0 or more and m + n ≧ 1, but they can be easily reacted, and the stability of the polymer is good, so in the above formula (2), m + n is 2 or more. And m + n is more preferably 2.

（式（２−１）中、Ｒ^１は水素原子またはメチル基を表し、Ｒ^９は単結合または２価の有機基を表し、Ｒ^３は水素原子または１価の有機基を表し、複数存在するＲ^４はそれぞれ独立に水素原子または１価の有機基を表す。） The (meth) acrylate having a cyclic ether structure is more preferably a compound represented by the following general formula (2-1). The repeating unit derived from the compound represented by the following general formula (2-1) can be easily ring-opened and cross-linked with lithium ions in a non-aqueous solvent. For this reason, for example, when a gel electrolyte is prepared using an electrolytic solution containing the solid electrolyte membrane-forming agent of the present invention, by using an electrolyte containing lithium ions as an electrolyte (C) described later, ring-opening crosslinking can be easily performed. And the gel electrolyte excellent in electrical conductivity can be produced. In this case, the heat treatment of the electrolytic solution is not essential for producing the gel electrolyte, but from the viewpoint of producing a gel electrolyte with good gel strength, it is preferable to perform the heat treatment at a low temperature that does not deteriorate the active material.

(In Formula (2-1), R ¹ represents a hydrogen atom or a methyl group, R ⁹ represents a single bond or a divalent organic group, R ³ represents a hydrogen atom or a monovalent organic group, and a plurality of them exist. And each R ⁴ independently represents a hydrogen atom or a monovalent organic group.)

In the above formula (2-1), R ¹ , R ³ and R ⁴ have the same meaning as the above formula (2). In the above formula (2-1), R ⁹ represents a single bond or a divalent organic group, and examples of the divalent organic group include an alkylene group having 1 to 10 carbon atoms. Among these, R ⁹ is preferably a methylene group.

  It was prepared by mixing a polymer (A) having a repeating unit (A2) derived from (meth) acrylate having a cyclic ether structure, a liquid medium (B) described later, and an electrolyte (C) described later. The gel electrolyte produced using the electrolytic solution has a cyclic polymer structure of the repeating unit (A2) opened and crosslinked, so that a strong polymer network structure can be constructed and the gel strength is excellent. Gel electrolyte.

  Specific examples of the (meth) acrylate having a cyclic ether structure include glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, caprolactone-modified tetrahydrofurfuryl (meth) acrylate, (3-oxetanyl) methyl (meth) acrylate, (3-Methyl-3-oxetanyl) methyl (meth) acrylate, (3-ethyl-3-oxetanyl) methyl (meth) acrylate, (3-butyl-3-oxetanyl) methyl (meth) acrylate, (3-hexyl- 3-Oxetanyl) methyl (meth) acrylate, (3-ethyl-oxetane-3-yloxy) ethyl (meth) acrylate, (3-ethyl-oxetane-3-yloxy) butyl (meth) acrylate, 3,4-epoxycyclohexyl Methyl ) Acrylate and the like, can be preferably used (3-oxetanyl) methyl (meth) acrylate and (3-alkyl-3-oxetanyl) methyl (meth) acrylate. These compounds may be used alone or in combination of two or more.

  The content of the repeating unit (A2) in the polymer (A) is such that when the total amount of the repeating unit (A1) and the repeating unit (A2) is 100 mol%, the repeating unit (A2) is 10 to 40 mol%. It is preferable that it is 15 to 35 mol%. When the content of the repeating unit (A2) in the polymer (A) is in the above range, a crosslinking reaction can be easily carried out by heating under mild conditions using a metal ion such as lithium ion contained in the electrolytic solution as a catalyst. (Cation polymerization) occurs, and the gel electrolyte can be produced without causing deterioration of the coexisting electrode and the electrolytic solution. Moreover, since it can also fully bridge | crosslink, the mechanical strength of a gel electrolyte can also be ensured.

In general, it is necessary to add an additive such as a thermal acid generator or a photoacid generator for promoting gelation when producing the gel electrolyte. If this additive remains in the gel electrolyte, the charge / discharge characteristics may deteriorate over time in the electricity storage device. However, the electrolytic solution containing the solid electrolyte membrane-forming agent according to the present embodiment does not require such an additive and can be gelled only by heating. It is excellent in that it can suppress deterioration.

1.1.3. Ratio of repeating unit (A1) and repeating unit (A2) The polymer (A) contained in the solid electrolyte membrane-forming agent according to the present embodiment has a total amount of the repeating unit (A1) and the repeating unit (A2). When the amount is 100 mol%, the ratio (M1 / M2) of the amount (M1 [mol%]) of the repeating unit (A1) to the amount (M2 [mol%]) of the repeating unit (A2) is 1 to 10. It is in the range, preferably in the range of 1.5 to 8, and more preferably in the range of 2 to 6. When the value of M1 / M2 is in the above range, a dense SEI film can be formed on the entire surface of the active material, and both good liquid retention and sufficient gelling properties can be achieved.

1.1.4. Production Method The polymer (A) contained in the solid electrolyte membrane-forming agent according to the present embodiment is a (meth) acrylate having the chain ether structure and, if necessary, a (meth) acrylate having the cyclic ether structure. Can be easily prepared by radical (co) polymerization in a reaction solvent in the presence of a radical polymerization initiator and optionally a molecular weight regulator. When the polymer (A) thus obtained is a copolymer, it may have any structure of a random copolymer, an alternating copolymer, a periodic copolymer, and a block copolymer.

Although it does not restrict | limit especially as said reaction solvent, For example, water, alcohol, ester, carbonate, ketone, lactone, ether, sulfoxide, amide etc. can be mentioned.
Examples of the alcohol include methanol, ethanol, isopropanol and the like;
Examples of the ester include ethyl acetate, methyl propionate, and butyl acetate;
Examples of the carbonate include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate;
Examples of the ketone include methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, and diethyl ketone;
Examples of the lactone include γ-butyl lactone;
Examples of the ether include trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran and the like;
Examples of the sulfoxide include dimethyl sulfoxide and the like;
Examples of the amide include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and the like, and one or more selected from these can be used. Is preferred.

  The reaction solvent is preferably at least one solvent that can be contained in the liquid medium (B) exemplified later, and more preferably the same solvent as the solvent actually used for the solid electrolyte film forming agent. By using at least one solvent that can be contained in the liquid medium (B), the solution after polymerizing the polymer (A) can be directly used for the preparation of the solid electrolyte film forming agent, thus simplifying the process. can do. In this case, by performing radical polymerization using a solvent that can be contained in the liquid medium (B) as a reaction solvent, it is possible to produce a gel electrolyte that is superior in liquid retention of the liquid medium (B). In addition, when the same kind of solvent as the solvent actually used for the solid electrolyte film forming agent is used as the reaction solvent, the affinity between the obtained polymer (A) and the liquid medium (B) becomes very good. The preparation of the electrolyte film forming agent is facilitated, and the liquid retention of the gel electrolyte containing this solid electrolyte film forming agent is very good.

The liquid medium (B) will be described later, but as the reaction solvent, carbonate, lactone,
It is preferable to use one or more selected from ethers and sulfoxides, and it is most preferable to use a liquid medium or a mixture thereof actually used for the solid electrolyte film forming agent. Surprisingly, it has been revealed that the effect of improving the liquid retention is maintained even when the solvent is replaced after the polymerization in the reaction solvent.

  The ratio of the solvent used in producing the polymer (A) is preferably 100 to 1,000 parts by mass, and 200 to 500 parts by mass with respect to 100 parts by mass of the total amount of monomers. More preferred.

  In the radical (co) polymerization, a radical polymerization initiator is usually used. Examples of radical polymerization initiators include azo initiators such as N, N′-azobisisobutyronitrile and dimethyl N, N′-azobis (2-methylpropionate); benzoyl peroxide and lauroyl peroxide. And organic peroxide initiators such as The radical polymerization initiator may be added in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of all monomers.

  Examples of the molecular weight regulator include halogenated hydrocarbons such as chloroform and carbon tetrachloride; mercaptan compounds such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dotezyl mercaptan, and thioglycolic acid; dimethyl Examples thereof include xanthogen compounds such as xanthogen disulfide and diisopropylxanthogen disulfide; and other molecular weight regulators such as terpinolene and α-methylstyrene dimer. The use ratio of the molecular weight regulator is preferably 5 parts by mass or less with respect to 100 parts by mass in total of the monomers.

  The number average molecular weight (Mn) of the polymer (A) obtained as described above is preferably 1,000 to 1,000,000, more preferably 1,000 to 100,000, and 10,000 to 100,000. Is particularly preferred. When the number average molecular weight (Mn) of the polymer (A) is 100,000 or less, the impregnation property to the electrode plate is improved, so that the electrical characteristics (charge rate characteristics, DC-IR characteristics, cycle characteristics) of the obtained electricity storage device are obtained. ) Tend to be better. Furthermore, when the number average molecular weight (Mn) of the polymer (A) is 5000 or more and 100,000 or less, the cycle characteristics of the obtained electricity storage device tend to be particularly good. In addition, the number average molecular weight (Mn) of a polymer (A) can be calculated | required by converting from the relationship between the elution time of standard polystyrene measured by GPC (gel permeation chromatography) method, and molecular weight.

1.2. Liquid medium (B)
The liquid medium (B) contained in the solid electrolyte film forming agent according to the present embodiment is not particularly limited as long as it can dissolve the electrolyte described later.

  Examples of the liquid medium (B) include ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), methyl ethyl carbonate (MEC), methyl propyl carbonate (PMC), butylene carbonate (BC), diethyl carbonate ( Carbonates such as DEC; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone; trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, methyltetrahydrofuran, Cyclic ethers such as methyltetrahydrofuran; sulfolane and the like can be used. The liquid medium (B) exemplified above may be used alone or in combination of two or more.

  Among these, ethylene carbonate, diethylene carbonate, propylene carbonate, and γ-butyrolactone are preferable, and a liquid medium in which ethylene carbonate and diethylene carbonate are mixed is particularly preferable.

2. Electrolytic Solution The electrolytic solution according to the present embodiment contains the above-described solid electrolyte membrane forming agent and the electrolyte (C), and further contains additives as necessary.

2.1. Electrolyte (C)
Examples of the electrolyte (C), any conventionally known lithium salts can also be used, and specific examples thereof, for example _{LiClO 4, LiBF 4, LiPF 6} , LiCF 3 CO 2, LiAsF 6, LiSbF 6 , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, lower Examples thereof include lithium fatty acid carboxylate. These electrolytes may be used alone or in combination of two or more.

Moreover, it is also possible to use electrolytes other than Li from a viewpoint of improving the ionic conductivity of the electrolyte solution which concerns on this Embodiment. Examples of such an electrolyte include (FSO ₂ ) ₂ N ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , NO ₃ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , ( _{C 2 F 5 SO 2) 2} N -, (CF 3 SO 2) 3 C -, CF 3 CO 2 -, C 3 F 7 CO 2 -, CH 3 CO 2 -, (CN) 2 N - and the like anions And a salt composed of a combination of cation and cation.

  As the cation, a compound containing any of N, P, S, O, C, Si or two or more elements in the structure and having a chain structure or a cyclic structure such as a 5-membered ring or a 6-membered ring in the skeleton Is mentioned. Examples of the compound having a chain structure in the skeleton include alkyl ammonium. Examples of the compound having a cyclic structure in the skeleton include furan, thiophene, pyrrole, pyridine, oxazole, isoxazole, thiazol, isothiazole, furazane, imidazole, pyrazole, pyrazine, pyrimidine, pyridazine, pyrrolidine, Heterocyclic compounds such as piperidine; and condensed heterocyclic compounds such as benzofuran, isobenzofuran, indole, isoindole, isodridine, and carbazole.

Among the electrolytes (C) exemplified above, when LiPF ₆ or LiBF ₄ is used, lithium ions can act as a cationic polymerization initiator. Therefore, when the polymer (A) has the repeating unit (A2), it is preferable in that a gel electrolyte can be produced without using another cationic polymerization initiator. In addition, when LiPF ₆ is used, it is particularly preferable in that the discharge capacity retention rate at a low temperature of the obtained electricity storage device is good.

  In general, the electrolyte solution according to the present embodiment preferably has an electrolyte concentration of 0.1 to 5 mol / L, and particularly preferably 0.5 to 2 mol / L.

2.2. Additives Examples of the additives include additives that have been used in conventional electrolytes. Specifically, components that improve ionic conductivity or form a protective film on the electrode surface are used. can do. For example, nitrogen-containing and sulfur-containing compounds such as azaindole, benzimidazole, benzodithiol, benzofuran, benzothiazole, 1-benzothiophene, 1H-benzotriazole, benzylcapton, 1-bromo-3-fluorobenzene; vinylene carbonate, Examples thereof include vinyl compounds such as vinyl acrylate and vinyl butyrate; sucrose fatty acid esters, and the addition amount is 10% by mass or less, preferably 3% by mass or less. Moreover, these additives may be used individually by 1 type, and may be used in combination of 2 or more types.

Further, when the polymer (A) has the repeating unit (A2), from the viewpoint of improving the liquid retention of the gel electrolyte obtained and increasing the crosslink density to improve the mechanical strength, A cyclic ether compound can be further added to the electrolytic solution according to the embodiment. As such a cyclic ether compound, those having an alkyl group having 6 to 28 carbon atoms are preferable, an alkyl glycidyl ether having an alkyl group having 6 to 28 carbon atoms, and a fatty acid glycidyl ether having an alkyl group having 6 to 28 carbon atoms. Alkylphenol glycidyl ether having an alkyl group having 6 to 28 carbon atoms is more preferable. Among these, alkyl glycidyl ether having an alkyl group having 6 to 28 carbon atoms is particularly preferable. In addition, these cyclic ether compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  In addition, the cyclic ether compound preferably has two or more cyclic ether groups in the molecule. By adding a cyclic ether compound having two or more cyclic ether groups in the molecule, the crosslink density can be further increased, so that the mechanical strength of the gel electrolyte can be further improved. Examples of such cyclic ether compounds include vinylcyclohexene dioxide, dicyclopentadiene dioxide, alicyclic diepoxy-adipade, 1,6-bis (2,3-epoxypropoxy) naphthalene, and ethylene glycol diglycidyl ether. 3,4-epoxycyclohexenylmethyl-3 ′, 4′-epoxycyclohexenecarboxylate, 1,2: 8,9-diepoxylimonene, 3-ethyl-3 {[(3-ethyloxetane-3-yl) Methoxy] methyl} oxetane, 3-ethyl-3-hydroxymethyloxetane, and the like.

  When a cyclic ether compound is added to the electrolytic solution according to the present embodiment, the cyclic ether compound has a different number of cyclic ether groups from the cyclic ether group contained in the repeating unit (A2) in the polymer (A). It is preferable to have. For example, when the cyclic ether group contained in the repeating unit (A2) is an oxiranyl group, the cyclic ether compound to be added preferably has an oxetanyl group. On the other hand, when the cyclic ether group contained in the repeating unit (A2) is an oxetanyl group, the cyclic ether compound to be added preferably has an oxiranyl group. Since the cyclic ether compound added in this way has a different number of cyclic ether groups from the cyclic ether group contained in the repeating unit (A2), the cyclic ether compound can be more effectively cross-linked, and the gel electrolyte can be produced. The heating temperature can be further reduced. Thereby, deterioration of the electrode and electrolyte solution accompanying heating can be suppressed. Moreover, since a crosslinking density can be improved, the gel electrolyte excellent in mechanical strength can be produced.

  When adding a cyclic ether compound to the electrolyte solution which concerns on this Embodiment, the content rate of a cyclic ether compound may contain in the range of 0-50 mass parts with respect to 100 mass parts of polymers (A). preferable.

2.3. Preparation Method of Electrolytic Solution When preparing the electrolytic solution according to the present embodiment, the above-mentioned solid electrolyte membrane forming agent, electrolyte (C) and, if necessary, additives are added and sufficiently stirred, and the electrolyte ( C) may be completely dissolved in the liquid medium (B). Moreover, when the polymer (A) contained in the above-mentioned solid electrolyte membrane forming agent has the above repeating unit (A2), it may be sufficiently stirred while being heated to about 40 to 60 ° C. Thereby, the polymer (A) can be completely dissolved in the liquid medium (B). In such a case, if the heating temperature is raised to 70 to 100 ° C., a gel electrolyte may be formed, so care must be taken.

  In addition, when the polymer (A) contained in the above-mentioned solid electrolyte membrane forming agent has the repeating unit (A2), the electrolytic solution according to the present embodiment is stable near room temperature and does not gel. . For this reason, since liquid electrolyte can be inject | poured into the housing | casing of an electrical storage device, and it can be set as a gel electrolyte by heating after that, storage stability and the freedom degree of an electrical storage device preparation process can be improved.

  As described above, when the polymer (A) has the repeating unit (A2), the electrolytic solution according to the present embodiment can produce a gel electrolyte only by heating. In contrast, additives such as a thermal acid generator and a photoacid generator used in the preparation of the gel electrolyte can be excluded. For this reason, with the charge / discharge of the electricity storage device, it is possible to suppress the deterioration over time of the charge / discharge characteristics that may be caused by the decomposition of the thermal acid generator or the photoacid generator.

  Moreover, since the heating temperature at the time of gel electrolyte preparation can be 70-100 degreeC (preferably 75-95 degreeC, More preferably, 80-90 degreeC), it suppresses the deterioration of the active material layer of an electrical storage device. Can do. Further, since the ring-opening and crosslinking are performed, the change in the volume of the polymer is small, and damage to the structure of the electricity storage device such as peeling of the active material layer can be suppressed even if the polymer is gelled in a sealed state.

  The gel electrolyte thus obtained is a highly flexible gel and has no thermoreversibility. Therefore, abnormal expansion of the battery due to heating or overcharging can be prevented, and workability such as thin film processing is improved.

3. Electric storage device The electric storage device according to the present embodiment may include known configurations and materials in addition to the above-described electrolyte solution.

  The electrode material is not particularly limited as long as it can insert and desorb lithium ions. As the electrode, for example, an electrode in which a positive electrode / negative electrode active material layer is formed on the surface of a current collector can be used.

Examples of the positive electrode active material include metal oxides such as CuO, Cu ₂ O, MnO ₂ , V ₂ O ₅ , CrO ₃ , MoO ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , and CuO ₃ , and Li _x CO _2. , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , LiFePO ₄ and other complex oxides of lithium and transition metals, TiS ₂ , MoS ₂ , NbSe _{3 and} other metal chalcogenides, polyacene, polyparaphenylene, polypyrrole, Examples thereof include conductive compounds such as polyaniline. In particular, in the present invention, a composite oxide of lithium and one or more kinds selected from transition metals such as cobalt, nickel, manganese, and iron is preferable. Specific examples thereof include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and LiNi. _{x Co (1-x) O} 2, LiMn a Ni b Co c (a + b + c = 1), LiFePO 4 , and the like. These lithium composite oxides may be doped with a small amount of elements such as fluorine, boron, aluminum, chromium, zirconium, molybdenum, and iron.

Examples of the negative electrode active material include lithium storage metals such as lithium metal, Al, Mg, Pt, Sn, Si, Zn, and Bi; Al-based lithium alloys such as Al—Ni, Al—Ag, and Al—Mn; SbSn, Antimony type lithium alloys such as InSb, CoSb ₃ , Mi ₂ MnSb; Sn ₂ M (M = Fe, Co, Mn, V, Ti), Sn ₅ Cu ₆ , Sn ₃ V ₂ , Sn ₁₂ Ag ₁₃ , SnSb _0. Sn-based lithium alloys such as ₄ ; Sn oxides such as SnO ₂ , Sn ₂ P ₂ O ₇ , SNPBO ₆ , SnPO ₄ Cl; Si-based such as Si—C composite, Si—Ti composite, and Si—M thin film Lithium alloys; Nanocomposite materials such as Sn and Si; Amorphous alloy materials such as Sn, Co and Carbon; Sn-based plating alloys such as Sn-Ag and Sn-Cu; Si-based amorphous thin films Examples of carbon materials include amorphous carbon, mesocarbon microbeads, graphite, natural graphite, non-graphitizable carbon, and the like, and surface modified products of these carbon materials are preferable materials.

A conductive agent may be further used for the electrode material. Any conductive material that does not adversely affect battery performance can be used as the conductive agent. Normally, carbon black such as acetylene black and kettin black is used, but carbon fibers such as natural graphite, artificial graphite, carbon whisker, vapor grown carbon, carbon nanotubes, fullerene, conductive ceramic materials, etc. may be used. Often, these can be included as a mixture of two or more.

  The current collector is not particularly limited as long as it is an electronic conductor that does not adversely affect the configured power storage device. For example, as the positive electrode current collector, in addition to aluminum, titanium, stainless steel copper, nickel, baked carbon, conductive polymer, conductive glass, etc., for the purpose of improving adhesion, conductivity, and oxidation resistance, What processed the surface of copper etc. with carbon, nickel, titanium, silver, etc. can be used. As a negative electrode current collector, in addition to copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., the purpose of improving adhesion, conductivity, and oxidation resistance And what processed the surface, such as copper, with carbon, nickel, titanium, silver, etc. can be used. The surface of these current collector materials can be oxidized. As for these shapes, in addition to a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a vitreous body, a porous body, a foamed body and the like are also used.

Examples of the binder for binding the positive electrode / negative electrode active material to the current collector include a copolymer of polyvinylidene fluoride, hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PFMV), and tetrafluoroethylene (TFE). Polymers such as polyvinylidene fluoride copolymer resins, polytetrafluoroethylene (PTFE), fluorine resins such as fluorine rubber, styrene-butadiene rubber (SBR), ethylene-propylene rubber (EPDM), styrene-acrylonitrile copolymer, etc. A polysaccharide such as carboxymethyl cellulose (CMC), a thermoplastic resin such as a polyimide resin, and the like can be used in combination, but the present invention is not limited thereto. Moreover, you may use these in mixture of 2 or more types. The amount added is preferably 0.2 to 30%, more preferably 0.5 to 10%, based on the amount of active material. As for the positive electrode active material whose surface is coated with carbon, such as LiFePO ₄ , a carboxylic acid-modified polyvinylidene fluoride or SBR aqueous binder can be mentioned as a preferable material.

  As the separator, a porous film is used, and usually a porous polymer film or a nonwoven fabric is preferably used. In the present invention, those composed of a non-conductive porous material and electrically insulating particles are particularly suitable. The non-conductive porous material is selected from polyacrylonitrile, polyester (PET), polyimide, polyamide, polytetrafluoroethylene, polyolefin, glass, ceramic and the like. In particular, a nonwoven fabric having an electrically insulating inorganic film on a flat flexible substrate is suitable, and polyester (PET) and polyamide are particularly preferred.

  The insulating particles used in the separator include inorganic materials such as at least one kind of alumina, titania, silicon and / or zirconia, and organic materials such as fluororesin, polystyrene resin and acrylic resin. Particles are used.

  The separator may further have a shutdown mechanism by the presence of a very thin wax particle layer that melts at a desired blocking temperature or a blocking particle of a polymer particle layer in the separator. Materials that are advantageous for forming the barrier particles include low melting polymers such as natural or artificial waxes and polyolefins, which melt at the desired barrier temperature and close the pores of the separator. Further current during the abnormal operation of the battery can be suppressed.

The electricity storage device according to this embodiment can be formed in a cylindrical shape, a coin shape, a square shape, a laminate shape, or any other shape, and the basic configuration of the electricity storage device is the same regardless of the shape, depending on the purpose. The design can be changed.

  As a specific manufacturing method of the electricity storage device according to the present embodiment, for example, a negative electrode formed by applying a negative electrode active material to a negative electrode current collector, and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector Is obtained by storing a wound body wound through a separator in a casing, injecting the above-described composition for forming gel electrolyte, sealing with an insulating plate placed on the top and bottom, and heat-treating it. .

  When producing the electricity storage device according to the present embodiment, if the selected electrode active material generates a large amount of gas during the first charge and affects the cell performance, the above-mentioned gel electrolyte formation After injecting the composition into the pre-battery, a heat treatment may be performed after a charge or charge / discharge treatment as a pretreatment.

4). EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. “Part” and “%” in Examples and Comparative Examples are based on mass unless otherwise specified.

4.1. Example 1
4.1.1. Production of Solid Electrolyte Film Forming Agent In a well-dried container, 52 g of methoxyethyl acrylate (monomer content ratio: 74% by mass, equivalent to 80 mol%), 18 g of (3-ethyl-3-oxetanyl) methyl methacrylate (containing monomer) Ratio: equivalent to 26% by mass and 20 mol%), ethylene carbonate (EC): diethyl carbonate (DEC) = 3: 7 (volume ratio) 211 g as reaction solvent, N, N′-azobisisobutyronitrile 0 0.71 g (1 part by mass with respect to 100 parts by mass of the total monomer mass) was added, heated to 60 ° C. in a dry nitrogen atmosphere, reacted for 6 hours, and then cooled to room temperature. The cooled solution was put into hexane, and the resulting precipitate was collected by filtration. The collected precipitate was dried under reduced pressure at 60 ° C. for 12 hours to obtain a polymer P1 having a number average molecular weight of 200,000. Subsequently, the polymer P1 obtained in ethylene carbonate (EC): diethyl carbonate (DEC) = 3: 7 (volume ratio) is added and stirred, so that the polymer P1 is contained in a solid content concentration of 6% by mass. A solid electrolyte film forming agent was prepared.

4.1.2. Preparation of electrolyte solution In the obtained solid electrolyte membrane forming agent, LiPF ₆ was added to a concentration of 1 mol / L and sufficiently stirred to completely dissolve LiPF ₆ to obtain a solid electrolyte membrane forming agent. An electrolytic solution containing 6% by mass was prepared.

4.1.3. Production and evaluation of electricity storage device (1) Production of positive electrode Binder for electrochemical device electrode (trade name, manufactured by Kureha Co., Ltd., trade name “TK Hibismix 2P-03”, manufactured by PRIMIX Co., Ltd.) “KF polymer # 1120”) 4.0 parts by mass (in terms of solid content), conductive assistant (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name “Denka Black 50% press product”) 3.0 parts by mass, as positive electrode active material 100 parts by mass (converted to solid content) and 36 parts by mass of N-methylpyrrolidone (NMP) with a particle size of 5 μm LiCoO ₂ (manufactured by Hayashi Kasei Co., Ltd.) were added and stirred at 60 rpm for 2 hours. After adding NMP to the obtained paste to adjust the solid content to 65%, using a stirring defoaming machine (trade name “Awatori Netaro”, manufactured by Shinky Co., Ltd.), 2 minutes at 200 rpm, 1800 rpm The mixture was stirred and mixed for 5 minutes at 1,800 rpm for 1.5 minutes under vacuum to prepare a slurry for electrodes. The prepared electrode slurry was uniformly applied to the surface of a current collector made of an aluminum foil having a thickness of 30 μm by a doctor blade method so that the film thickness after drying was 80 μm, followed by drying at 120 ° C. for 20 minutes. Then, the positive electrode was obtained by pressing with a roll press so that the density of an electrode layer might be set to 3.0 g / cm < ³ >.

(2) Manufacture of negative electrode Thickener (trade name “CMC2200”, manufactured by Daicel Chemical Industries, Ltd.) 1 mass in a biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation) Parts (solid content conversion), 100 parts by mass of graphite (manufactured by Hitachi Chemical Co., Ltd., product name “SMG-HE1”) and 68 parts by mass of water were added as the negative electrode active material, and the mixture was stirred at 60 rpm for 1 hour. Thereafter, 2 parts by mass of the SBR binder composition (manufactured by JSR Corporation, trade name “TRD2001”) was added to the polymer, and the mixture was further stirred at 60 rpm for 1 hour to obtain a paste. After adding water to the obtained paste and adjusting the solid content to 50% by mass, the mixture was stirred at 200 rpm for 2 minutes at 200 rpm using a stirring defoamer (trade name “Awatori Nertaro” manufactured by Shinky Co., Ltd.). Then, a negative electrode slurry was prepared by stirring at 1,800 rpm for 5 minutes and further stirring at 1,800 rpm for 1.5 minutes under a reduced pressure of 25 kPa, followed by mixing. The negative electrode slurry prepared above was uniformly applied to the surface of a current collector made of copper foil having a thickness of 20 μm by a doctor blade method so that the film thickness after drying was 150 μm, and dried at 120 ° C. for 20 minutes. . Then, the negative electrode was obtained by pressing using a roll-press machine so that the density of a film | membrane may be 1.5 g / cm < ³ >.

(3) Assembly of lithium ion secondary battery cell A negative electrode terminal was attached to and mounted on the negative electrode cut out to 50 mm × 25 mm on a film-like exterior aluminum seal made of aluminum in a glove box. Next, a separator made of a polypropylene porous film cut out to 54 mm × 27 mm (manufactured by Celgard, trade name “Celguard # 2400”, thickness 25 μm) was placed on the negative electrode, and then cut into 48 mm × 23 mm. A positive electrode terminal was attached to the positive electrode and placed on the separator. And the exterior aluminum seal similar to the said exterior aluminum seal was mounted on this positive electrode. Thus, the laminated body which consists of an exterior aluminum seal, a negative electrode, a separator, a positive electrode, and an exterior aluminum seal was obtained. Thereafter, the outer peripheral aluminum seals on the three sides of this laminate were sealed by bonding the outer peripheral edges of the two outer aluminum seals with a heating sealing device. Then, the electrolyte solution obtained above is further injected so that air does not enter between the layers, and after further degassing under reduced pressure, the negative electrode terminal and the positive electrode terminal are exposed to the outside of the exterior aluminum seal under reduced pressure. Thus, the fourth side was sealed and sealed. The laminated cell thus sealed was heated in an oven at 80 ° C. for 30 minutes to produce a secondary battery (electrochemical device) composed of a bipolar single-layer laminated cell.

(4) Evaluation of discharge rate characteristic The secondary battery cell manufactured above was put into a 25 degreeC thermostat, charge was started with the constant current (0.2C), and it charged until the voltage was set to 4.2V. Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 0.2 C was measured.

  Next, the same cell was charged at 25 ° C. with a constant current (0.2 C), and charged until the voltage reached 4.2V. Next, discharge was started at a constant current (2C), and when the voltage reached 2.7 V, the discharge was completed (cutoff), and the discharge capacity at 2C was measured.

Using the above measured values, the discharge rate (%) was calculated by calculating the ratio (percent%) of the discharge capacity at 2C to the discharge capacity at 0.2C. The discharge rate of the secondary battery cell produced using the above electrolytic solution is “A”, and produced using an electrolytic solution containing EC: DEC = 3: 7 (volume ratio) containing 1 mol / L of LiPF ₆ When the discharge rate of the produced secondary battery cell is “B”, it can be evaluated that the discharge rate characteristic represented by the following formula (3) is 0.7 or more.
Discharge rate characteristics = A / B (3)

  In the measurement conditions, “1C” indicates a current value at which discharge is completed in one hour after constant current discharge of a cell having a certain electric capacity. For example, “0.1 C” is a current value at which discharge is completed over 10 hours, and 10 C is a current value at which discharge is completed over 0.1 hours.

(5) Evaluation of low-temperature characteristic The secondary battery cell manufactured above was put into a 25 degreeC thermostat, charge was started with the constant current (0.2C), and it charged until the voltage was set to 4.2V. Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 25 ° C. was measured.

  Next, the same cell was placed in a thermostatic chamber at 0 ° C., and charging was started at a constant current (0.2 C), and charging was continued until the voltage reached 4.2V. Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 0 ° C. was measured.

Using the measured values, the discharge capacity retention rate (percentage%) at 0 ° C. with respect to the discharge capacity at 25 ° C. was used as an index of low temperature characteristics. Electrolysis of EC: DEC = 3: 7 (volume ratio) containing a discharge capacity retention rate at 0 ° C. of a secondary battery cell produced using the above electrolyte and containing 1 mol / L of LiPF ₆ When the discharge capacity retention rate at 0 ° C. of the secondary battery cell produced using the solution is “D”, the low temperature characteristic represented by the following formula (4) is 0.8 or more. It can be evaluated that there is.
Low temperature characteristics = C / D (4)

(6) Evaluation of internal DC resistance value (DC-IR) The secondary battery cell produced above is placed in a thermostat set at 25 ° C., and 50% DOD (3 at a constant current (0.2 C)). .8V). After that, the voltage change when charging at a constant current (0.5C) for 10 seconds is read, and after a pause for 1 minute, the voltage change when discharging at a constant current (0.5C) for 10 seconds is further performed. I read. The voltage at the time of charging / discharging was read by the same method except having changed the electric current value from 0.5C to 1.0C, 2.0C, 3.0C, 5.0C. A graph was created with the applied current value (A) as the horizontal axis and the voltage value (V) as the vertical axis, and the slope value of the straight line connecting the plot points was calculated at each charge / discharge time. The gradient values were taken as internal DC resistance values (DC-IR) during charging and discharging, respectively. The secondary battery cell produced using the above electrolyte solution has an EC: DEC = 3: 7 (volume ratio) electrolyte solution containing “E” for DC-IR and 1 mol / L of LiPF _6. When the DC-IR of the fabricated secondary battery cell is “F”, it can be evaluated that the DC-IR characteristic represented by the following formula (5) is 2.5 or less.
DC-IR characteristics = E / F (5)

  In the measurement conditions, “DOD” indicates the ratio of the discharge capacity to the charge capacity. For example, “charge to 50% DOD” indicates that only 50% of the capacity is charged when the total capacity is 100%.

(7) Evaluation of 25 ° C. cycle characteristics After the evaluation of “(6) Evaluation of internal direct current resistance (DC-IR)”, the same secondary battery cell is placed in a thermostat set at 25 ° C., and constant current ( 2.0C), charging is continued at a constant voltage (4.2V) when the voltage reaches 4.2V, and charging is completed when the current value reaches 0.01C ( Cut off). Thereafter, discharging was started at a constant current (2.0 C), and the time when the voltage reached 3.0 V was regarded as the completion of discharging (cutoff), and the discharge capacity at the first cycle was calculated. Thus, charging / discharging was repeated 100 times, and the discharge capacity at the 50th cycle was calculated. A value obtained by dividing the discharge capacity at the 50th cycle thus measured by the discharge capacity at the first cycle was defined as the 50th cycle discharge retention rate (%). Electrolysis of EC: DEC = 3: 7 (volume ratio) containing “G” as the discharge capacity maintenance rate at the 50th cycle of the secondary battery cell produced using the above electrolyte and 1 mol / L of LiPF ₆ When the discharge capacity retention rate at the 50th cycle of the secondary battery cell produced using the liquid is “H”, the discharge rate characteristic represented by the following formula (6) is preferably 0.7 or more. Can be evaluated.
Cycle characteristics = G / H (6)

4.2. Examples 2 to 27 , Comparative Examples 1 to 5
P2 to P22 were prepared in the same manner as in Example 1 except that the monomer composition, blending amount, and reaction solvent were changed to those shown in Table 1 or Table 2. Further, Example 2 was performed in the same manner as in Example 1 except that the types and content ratios of the polymer (A), the liquid medium (B) and the electrolyte (C) were changed to those shown in Tables 3 to 4. to prepare an electrolyte solution used in ~ 27 and Comparative examples 1-5. The electricity storage device characteristics produced in Examples 2 to 27 and Comparative Examples 1 to 5 were evaluated in the same manner as in Example 1 except that the electrolytic solution thus obtained was used. In addition, the content rate of the additive in Table 3-Table 4 represents content (mass part) of the additive with respect to 100 mass parts of solid electrolyte membrane forming agents. The monomer compositions, blending amounts and reaction solvents of the produced polymers P1 to P22 are shown in Tables 1 and 2, and the compositions, blending amounts and evaluation results of the solid electrolyte membrane forming agents used in each Example and each Comparative Example are shown. 3 to Table 4.

Abbreviations in Tables 1 to 4 represent the following compounds or product names, respectively.
<(Meth) acrylate having a chain ether structure>
MEA: methoxyethyl acrylate DEGMA: ethoxytriethylene glycol methacrylate TEGA: ethoxytriethylene glycol acrylate MTEGA: methoxytetraethylene glycol acrylate

<(Meth) acrylate having cyclic ether structure>
OXMA: (3-ethyl-3-oxetanyl) methyl methacrylate OXEA: (3-ethyl-oxetane-3-yloxy) ethyl acrylate OXBA: (3-ethyl-oxetane-3-yloxy) butyl acrylate GMA: glycidyl Methacrylate • THFMA: Tetrahydrofurfuryl methacrylate • OXA: (3-Ethyl-3-oxetanyl) methyl acrylate OXEA is described in “Journal of Polymer Science: Part A: Polymer Chemistry, 2003, 41, 469-475.” And OXBA was synthesized in the same manner.

<Polymerization initiator>
AIBN: N, N′-azobisisobutyronitrile

<(Polymerization) solvent>
EC / DEC: mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7 GBL: γ-butyrolactone DG: diglyme (diethylene glycol dimethyl ether)
・ DEC: Diethyl carbonate ・ MEK: Methyl ethyl ketone ・ PC: Propylene carbonate

<Additive (cyclic ether compound)>
CEL: 3,4-epoxycyclohexenylmethyl-3 ′, 4′-epoxycyclohexene carboxylate (product name “Celoxide 2021P” manufactured by Daicel Chemical Industries, Ltd.)
EGDG: ethylene glycol diglycidyl ether DOX: 3-ethyl-3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane OXAL: 3-ethyl-3-hydroxymethyloxetane

<Others>
・ KF: Polyvinylidene fluoride resin (manufactured by Arkema, product name “Kyner Flex 2081”)

4.3. Evaluation Results It is considered that by using the solid electrolyte membrane forming agents of Examples 1 to 27 , a dense and firm solid electrolyte membrane was formed on the entire surface of the active material surface in the initial charging process. Thus, it is considered that a lithium ion secondary battery having a low internal DC resistance value and good discharge rate characteristics, low temperature characteristics, and cycle characteristics could be produced. When the solid electrolyte membrane forming agent of Comparative Examples 2 to 5 containing the polymer (A) obtained by homopolymerizing (meth) acrylate having a chain ether structure is used, the solid electrolyte membrane is used in the initial charging process. It is considered that the electric storage device characteristics are particularly good.

  On the other hand, in Comparative Example 1, since a polyvinylidene fluoride resin is used as the polymer (A), an effective solid electrolyte membrane is not formed on the surface of the active material, and the power storage device characteristics are significantly inferior compared to the Examples. I found out.

  The present invention is not limited to the above embodiment, and various modifications can be made. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). The present invention also includes a configuration in which a non-essential part of the configuration described in the above embodiment is replaced with another configuration. Furthermore, the present invention includes a configuration that achieves the same effects as the configuration described in the above embodiment or a configuration that can achieve the same object. Furthermore, the present invention includes a configuration obtained by adding a known technique to the configuration described in the above embodiment.

Claims (4)

Following general formula (1) repeating unit (A1) derived from a compound represented by, have a repeating unit (A2) derived from a (meth) acrylate having a cyclic ether structure, a number average molecular weight of 1,000 A polymer (A) that is not less than 200,000 ,
A liquid medium (B);
A solid electrolyte film forming agent.

(In the formula (1), R ⁵ represents a hydrogen atom or a methyl group, R ⁶ represents a single bond or a divalent organic group, and R ⁷ which may be present in plural numbers are each independently a divalent hydrocarbon group. R ⁸ represents a hydrogen atom or a monovalent organic group, and x is an integer of 1 or more.) The solid electrolyte membrane forming agent according to claim 1 , wherein the (meth) acrylate having the cyclic ether structure is a compound represented by the following general formula (2).

(In Formula (2), R ¹ represents a hydrogen atom or a methyl group, R ² represents a divalent linking group, R ³ represents a hydrogen atom or a monovalent organic group, and a plurality of R ^{4 s} are each present. Independently represents a hydrogen atom or a monovalent organic group, m and n are integers of 0 or more, and m + n ≧ 1. The electrolyte solution containing the solid electrolyte membrane formation agent of Claim 1 or Claim 2, and electrolyte (C). An electrical storage device provided with the electrolyte solution of Claim 3 .