WO2020067370A1

WO2020067370A1 - Non-aqueous electrolyte, non-aqueous electrolyte storage element, method for manufacturing non-aqueous electrolyte storage element, and method for using non-aqueous electrolyte storage element

Info

Publication number: WO2020067370A1
Application number: PCT/JP2019/038024
Authority: WO
Inventors: 顕岸本
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2018-09-28
Filing date: 2019-09-26
Publication date: 2020-04-02
Also published as: JPWO2020067370A1

Abstract

One aspect of the present invention, which has an exceptional charge/discharge cycle under low-temperature conditions, is a non-aqueous electrolyte containing a non-aqueous solvent, an electrolytic salt, and an anion in which a dicarboxylate group is bonded to a boron atom, the non-aqueous solvent including a fluorinated cyclic carbonate and a fluorinated carboxylic acid ester having a group that includes a trifluoromethyl group.

Description

Non-aqueous electrolyte, non-aqueous electrolyte storage element, method of manufacturing non-aqueous electrolyte storage element, and method of using non-aqueous electrolyte storage element

The present invention relates to a non-aqueous electrolyte, a non-aqueous electrolyte storage element, a method for manufacturing a non-aqueous electrolyte storage element, and a method for using the non-aqueous electrolyte storage element.

非 Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The nonaqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator, and a nonaqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to be charged and discharged by this. Further, as a non-aqueous electrolyte storage element other than the non-aqueous electrolyte secondary battery, capacitors such as a lithium ion capacitor and an electric double layer capacitor have been widely used.

非 Various studies have been made on non-aqueous electrolytes used in such non-aqueous electrolyte storage elements.

For example, Japanese Patent Application Laid-Open No. 2009-289414 (Patent Document 1) discloses “4-fluoroethylene carbonate (4-FEC), propylene carbonate (PC), and CF ₃ CH that is a fluorinated chain carboxylic acid ester. "A non-aqueous electrolyte secondary battery" using a mixed solvent obtained by mixing ₂ COOCH ₃ at a volume ratio of 20: 5: 75 (paragraph 0063, Example 7). Patent Literature 1 also states that “in the nonaqueous electrolyte secondary battery of Example 7, the capacity remaining rate and the capacity recovery rate after storage were further improved” (paragraph 0077). .

JP-A-2017-168375 (Patent Document 2) discloses a non-aqueous electrolyte for a non-aqueous electrolyte secondary battery containing a non-aqueous solvent and an electrolyte salt, wherein the non-aqueous solvent is 4-fluoroethylene carbonate (FEC) and

methyl

3,3,3-trifluoropropionate (FMP), and further comprising a borate ester. Non-aqueous electrolyte for a secondary battery. " (Claim 1). Patent Document 2 discloses a non-aqueous electrolyte solution “in a non-aqueous solvent in which FEC and FMP of FEC: FMP = 10: 90 are mixed” and “0.5% by mass of triethanolamine borate (BTR) is added”. (Paragraphs 0078 and 0079), "Example battery 1-1 and comparative example battery 1 which are common in that they are non-aqueous electrolytes containing FEC and FMP and differ in the presence or absence of BTR." Comparing with -1, it can be seen that in Example Battery 1-1 to which BTR was added, the DC resistance after high-temperature storage (hereinafter referred to as "resistance after storage") was remarkably low. (Paragraph 0089).

WO 2014/165748 (Patent Document 3) discloses at least one selected from the group consisting of “fluorinated acyclic carboxylate”, “fluorinated acyclic carbonate”, and “fluorinated acyclic ether”. An electrolyte comprising: one fluorinated solvent; at least one cosolvent selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate; a film-forming compound; and an electrolyte salt A composition is described (Claim 1). Patent Document 3 discloses “70% by weight of DFEA / 30% by weight of EC solvent ratio / 1M of LiPF ₆ 2% by weight of FEC, 2% by weight of LiBOB, 96% by weight of a cosolvent and LiPF ₆ ”. The battery used is described (paragraph 0201, Example 51). Here, DFEA is “2,2-difluoroethyl acetate”, and its composition formula is described as “CH ₃ —COO—CH ₂ CF ₂ H” (paragraphs 0085 and 0024).

WO 2016/044088 (Patent Literature 4) discloses that "2,2-difluoroethyl acetate and ... fluoroethylene carbonate are combined .... A 1 M concentration electrolyte composition is prepared. Electrolyte composition B with sufficient LiPF ₆ added to form lithium-bis (oxalato) borate to form electrolyte composition C "(paragraphs 0056 and 0057).

JP 2009-289414 A JP 2017-168375 A International Publication No. 2014/165748 International Publication No. WO 2016/044088

For example, a power storage element using a non-aqueous electrolyte described in Patent Document 1 has a high voltage (for example, 4.4 V (vs. Li ^/ Li ⁺ as a positive electrode potential at the end of charging) under a high temperature environment (for example, 45 ° C.). )) Shows a high discharge capacity retention ratio even when stored. However, the inventors have newly found that such a storage element has a problem that the charge / discharge cycle performance in a low-temperature environment such as 0 ° C. is deteriorated.

The present invention has been made based on the above circumstances, and an object thereof is to provide a non-aqueous electrolyte having excellent charge / discharge cycle performance in a low-temperature environment, and a non-aqueous electrolyte storage device including such a non-aqueous electrolyte. An object of the present invention is to provide a device and a method for manufacturing the same.

One embodiment of the present invention made to solve the above problem includes a non-aqueous solvent, an electrolyte salt, and an anion in which a dicarboxylate group is bonded to a boron atom, and the non-aqueous solvent has a fluorinated cyclic structure. A non-aqueous electrolyte containing carbonate and a fluorinated carboxylic acid ester having a group containing a trifluoromethyl group.

の他 Another embodiment of the present invention is a nonaqueous electrolyte storage element including the nonaqueous electrolyte.

の他 Another embodiment of the present invention is a method for manufacturing a nonaqueous electrolyte storage element including a step of placing the nonaqueous electrolyte in a nonaqueous electrolyte storage element container.

Another embodiment of the present invention is a method for using the nonaqueous electrolyte energy storage device in which the positive electrode potential at the end-of-charge voltage during normal use is 4.4 V (vs. Li ^/ Li ⁺ ) or more.

According to the present invention, a non-aqueous electrolyte having excellent charge-discharge cycle performance in a low-temperature environment, a non-aqueous electrolyte storage element including such a non-aqueous electrolyte, a method for manufacturing a non-aqueous electrolyte storage element, and a non-aqueous electrolyte storage element A method of use can be provided.

FIG. 1 is a perspective view showing a non-aqueous electrolyte storage element according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a power storage device including a plurality of nonaqueous electrolyte power storage elements according to an embodiment of the present invention.

構成 The configuration, operation and effect of the present invention will be described together with technical ideas. However, the mechanism of action includes an estimation, and its correctness is not intended to limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from its main features. Therefore, the embodiments or examples described below are merely examples in all respects, and should not be construed as limiting. Furthermore, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and an anion in which a dicarboxylate group is bonded to a boron atom, and the non-aqueous solvent contains a fluorinated cyclic carbonate, and a group containing a trifluoromethyl group. Is a non-aqueous electrolyte containing a fluorinated carboxylic acid ester having

The non-aqueous electrolyte contains a non-aqueous solvent containing a fluorinated cyclic carbonate and a fluorinated carboxylate having a group containing a trifluoromethyl group, and an anion in which a dicarboxylate group is bonded to a boron atom. Excellent charge / discharge cycle performance can be exhibited in a low temperature environment. The reason for this is not clear, but the following is presumed. The fluorinated cyclic carbonate, the fluorinated carboxylate having a group containing a trifluoromethyl group, and the anion in which a dicarboxylate group is bonded to a boron atom are all decomposed on the negative electrode to form a coating. Here, the fluorinated cyclic carbonate and the anion in which the dicarboxylate group is bonded to the boron atom are decomposed first at a noble potential, and then the fluorinated carboxylate having a group containing a trifluoromethyl group is decomposed to form a coating. To form At this time, first, an anion in which a dicarboxylate group is bonded to a boron atom is suitably adsorbed to a slight bias of electric charge on the negative electrode, and is decomposed to form a good coating. A film containing a fluorine atom is formed thereon. That is, it is considered that the formation of a uniform film in which the boron atoms and the fluorine atoms are close to each other exhibits excellent charge / discharge cycle performance in a low-temperature environment.

Furthermore, the non-aqueous electrolyte exhibits a high capacity retention ratio even when stored in a high-temperature environment. That is, the non-aqueous electrolyte can exhibit excellent charge / discharge cycle performance under a low-temperature environment while maintaining high-temperature storage performance.

The non-aqueous electrolyte storage element is a non-aqueous electrolyte storage element including the above-described non-aqueous electrolyte (hereinafter, also simply referred to as “storage element”). The storage element exhibits excellent charge / discharge cycle performance in a low-temperature environment.

The method for manufacturing a non-aqueous electrolyte storage element is a method for manufacturing a non-aqueous electrolyte storage element including the step of placing the above-described non-aqueous electrolyte in a container for a non-aqueous electrolyte storage element.

According to the manufacturing method, it is possible to manufacture a non-aqueous electrolyte storage element having excellent charge / discharge cycle performance in a low-temperature environment.

In the method of using the nonaqueous electrolyte storage element, the positive electrode potential at the charge end voltage in normal use is 4.4 V (vs. Li ^/ Li ⁺ ) or more. The non-aqueous electrolyte storage element has a high capacity retention rate after storage in a high-temperature environment, and thus is a storage element used under charging conditions in which the positive electrode potential at the charge end voltage during normal use is relatively high. In particular, this effect can be particularly sufficiently exhibited. Here, the normal use is a case where the nonaqueous electrolyte storage element is used by adopting the recommended or specified charging condition for the nonaqueous electrolyte storage element, and is used for the nonaqueous electrolyte storage element. When the non-aqueous electrolyte power storage device is provided, the non-aqueous electrolyte storage element is used by applying the charger. Note that, for example, in a power storage element using graphite as a negative electrode active material, the positive electrode potential is about 5.1 V (vs. Li ^/ Li ⁺ ) when the charge end voltage is 5.0 V, depending on the design.

Hereinafter, the nonaqueous electrolyte, the nonaqueous electrolyte storage element, the method for manufacturing the nonaqueous electrolyte storage element, and the method for using the nonaqueous electrolyte element according to the embodiment of the present invention will be described in detail.

<Non-aqueous electrolyte>
The non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt, and an anion in which a dicarboxylate group is bonded to a boron atom (hereinafter, also simply referred to as “anion”). Hereinafter, each component contained in the nonaqueous electrolyte will be described.

[Non-aqueous solvent]
The non-aqueous solvent includes a fluorinated cyclic carbonate and a fluorinated carboxylate having a group containing a trifluoromethyl group (hereinafter, also simply referred to as “fluorinated carboxylate”).

(Fluorinated cyclic carbonate)
“Fluorinated cyclic carbonate” refers to a compound in which some or all of the hydrogen atoms of the cyclic carbonate have been replaced with fluorine atoms.

Examples of the fluorinated cyclic carbonate include, for example, fluoroethylene carbonate (hereinafter, also referred to as “FEC”), difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, (fluoromethyl) ethylene carbonate, (difluoromethyl) ethylene carbonate, (Trifluoromethyl) ethylene carbonate, bis (fluoromethyl) ethylene carbonate, bis (difluoromethyl) ethylene carbonate, bis (trifluoromethyl) ethylene carbonate, (fluoroethyl) ethylene carbonate, (difluoroethyl) ethylene carbonate, (trifluoro Ethyl) ethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,4-difluoro-5 Chill ethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate. As the fluorinated cyclic carbonate, FEC is preferable. When the fluorinated cyclic carbonate is FEC, a stable film can be formed on the negative electrode particularly under a high voltage, and the charge / discharge cycle performance can be improved. The above fluorinated cyclic carbonates can be used alone or in a combination of two or more.

は The lower limit of the content of the fluorinated cyclic carbonate in the nonaqueous solvent is preferably 1% by volume, more preferably 3% by volume, and still more preferably 5% by volume. When the content ratio of the fluorinated cyclic carbonate is equal to or more than the lower limit, the capacity retention ratio of the storage element after storage in a high-temperature environment can be further increased. On the other hand, the upper limit of the content ratio is, for example, preferably 50% by volume, more preferably 30% by volume, further preferably 20% by volume, and particularly preferably 15% by volume. When the content ratio of the fluorinated cyclic carbonate is equal to or less than the above upper limit, the charge / discharge cycle performance of the non-aqueous electrolyte storage element in a low-temperature environment can be further improved.

(Fluorinated carboxylic acid ester)
The fluorinated carboxylic acid ester is a fluorinated carboxylic acid ester having a group containing a trifluoromethyl group (—CF ₃ ).

Examples of the group containing a trifluoromethyl group include, for example, a trifluoromethyl group itself, a group obtained by substituting a part or all of the hydrogen atoms of a monovalent hydrocarbon group having 1 to 3 carbon atoms with a trifluoromethyl group, or the like. No.

において In the present specification, the “hydrocarbon group” includes a chain hydrocarbon group and a branched chain hydrocarbon group.

Examples of the group obtained by substituting a part or all of the hydrogen atoms of the monovalent hydrocarbon group having 1 to 3 carbon atoms with a trifluoromethyl group include, for example, 2,2,2-trifluoroethyl group, 3,3,3 -Trifluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, 4,4,4-trifluorobutyl group, 2,2,3,3,4,4,4-heptafluorobutyl group And the like.

基 As the group containing a trifluoromethyl group, a 2,2,2-trifluoroethyl group is preferable.

Examples of the fluorinated carboxylic acid ester include a compound represented by the following formula (2).

In the above formula (2), R ⁴ and R ⁵ are each independently a monovalent hydrocarbon group having 1 to 4 carbon atoms or a monovalent fluorinated hydrocarbon group having 1 to 4 carbon atoms. However, at least one of R ⁴ and R ⁵ is a group containing a trifluoromethyl group.

において In this specification, the “fluorinated hydrocarbon group” means a group in which part or all of the hydrogen atoms of a hydrocarbon group are substituted with fluorine atoms. Further, the “fluorinated hydrocarbon group” includes “a group containing a trifluoromethyl group”.

Examples of the monovalent hydrocarbon group having 1 to 4 carbon atoms include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, and t-butyl. And the like. Examples of the monovalent fluorinated hydrocarbon group having 1 to 4 carbon atoms include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2-fluoroethyl group, a 2,2-difluoroethyl group, and a 3-fluoropropyl group. 3,3-difluoropropyl group, 3,3,3-trifluoropropyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, 4, 4,4-trifluorobutyl, 2,2,3,3,4,4-hexafluorobutyl, 2,2,3,3,4,4,4-heptafluorobutyl and the like.

As the above fluorinated carboxylic acid ester, from the viewpoint of charge / discharge cycle performance in a low-temperature environment, -2,2,2-trifluoroethyl acetate (hereinafter, referred to as “FEA”) represented by the following formula (2-1): ),

Methyl

3,3,3-trifluoropropionate (hereinafter, also referred to as “FMP”) represented by the following formula (2-2), or a combination thereof.

下限 The lower limit of the content of the fluorinated carboxylic acid ester in the nonaqueous solvent is preferably 20% by volume, more preferably 30% by volume, and still more preferably 40% by volume. When the content ratio is equal to or more than the lower limit, the charge / discharge cycle performance in a low-temperature environment can be improved. The upper limit of the content ratio is preferably 95% by volume, and more preferably 90% by volume. When the content ratio is equal to or less than the upper limit, an increase in resistance can be suppressed.

(Other non-aqueous solvents)
The non-aqueous electrolyte may include a non-aqueous solvent other than the fluorinated cyclic carbonate and the fluorinated carboxylic acid ester. As the other non-aqueous solvent, a known non-aqueous solvent that is generally used as a non-aqueous solvent for a general non-aqueous electrolyte for a power storage element can be used. Examples of the other non-aqueous solvent include cyclic carbonates other than the fluorinated cyclic carbonate (hereinafter, also simply referred to as “cyclic carbonate”), chain carbonate, fluorinated chain carbonate, ester, ether, amide, sulfone, lactone, Nitriles and the like can be mentioned. Among these, a cyclic carbonate or a chain carbonate is preferable, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2- Diphenylvinylene carbonate and the like. The cyclic carbonate may be one in which some or all of the hydrogen atoms have been substituted with atoms or substituents other than fluorine atoms, but those which are not substituted are preferred. As the cyclic carbonate, EC, PC or BC is preferred, PC or BC is more preferred, and PC is even more preferred.

鎖 Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diphenyl carbonate. The chain carbonate may be one in which some or all of the hydrogen atoms have been substituted with other atoms or substituents, but unsubstituted ones are preferred. As the chain carbonate, DEC, DMC or EMC is preferable, and EMC is more preferable.

When the non-aqueous solvent contains the cyclic carbonate or the chain carbonate, as the upper limit of the total content of the cyclic carbonate and the chain carbonate in the non-aqueous solvent, the ionic conductivity and charge and discharge in a low-temperature environment From the viewpoint of cycle performance, 10% by volume is preferable, and 5% by volume is more preferable.

(4) By setting the composition of the non-aqueous solvent as described above, the dielectric constant, viscosity, and the like become appropriate, so that the capacity retention rate and the like of the electric storage element can be further improved.

[Electrolyte salt]
The non-aqueous electrolyte usually contains an electrolyte salt dissolved in a non-aqueous solvent. Examples of the electrolyte salt include a lithium salt, a sodium salt, a potassium salt, a magnesium salt, and an onium salt. Of these, lithium salts are preferred.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiPF ₂ (C ₂ O ₄ ) ₂ , LiClO ₄ , and LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN ( _{_{_{_{SO 2 CF 3) 2, LiN}}}} (SO 2 C 2 F 5) 2, LiN (SO 2 CF 3) (SO 2 C 4 F 9), LiC (SO 2 CF 3) 3, LiC (SO 2 C 2 F ₅ ) a lithium salt having a fluorinated hydrocarbon group such as ₃ ; Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

As a minimum of content rate of the above-mentioned electrolyte salt in the nonaqueous electrolyte, 0.1 mol / L is preferred, 0.3 mol / L is more preferred, 0.5 mol / L is still more preferred, and 0.8 mol / L is especially preferred. . The upper limit of the content ratio is not particularly limited, but is preferably 2.5 mol / L, more preferably 2 mol / L, and still more preferably 1.5 mol / L.

[Anion]
The anion is an anion in which a dicarboxylate group is bonded to a boron atom.

において In the present specification, the “dicarboxylate group” means a group obtained by removing one hydrogen atom from each of two carboxy groups of a dicarboxylic acid.

Examples of the dicarboxylic acid providing a dicarboxylate group include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid and the like. Among these, oxalic acid or malonic acid is preferred, and oxalic acid is more preferred.

Examples of the dicarboxylate group include groups obtained by removing one hydrogen atom from each of the two carboxy groups of the above-described dicarboxylic acid, such as an oxalate group, a malonate group, a succinate group, a glutarate group, and an adipate group. Can be Among these, an oxalate group or a malonate group is preferred, and an oxalate group is more preferred.

The anion preferably further contains a fluorine atom. When the anion further contains a fluorine atom, a good film can be formed. More specifically, the anion preferably has a fluorine atom bonded to a boron atom.

アニオン The anion is preferably an anion represented by the following formula (1).

In the above formula (1), R ¹ is a single bond or a divalent hydrocarbon group having 1 to 4 carbon atoms. n is 1 or 2. When n is 2, two R ¹ are the same or different from each other. R ² and R ³ are each independently a fluorine atom or a monovalent fluorinated hydrocarbon group having 1 to 3 carbon atoms.

Examples of the divalent hydrocarbon group having 1 to 4 carbon atoms represented by R ¹ include a group obtained by removing two hydrogen atoms from a chain hydrocarbon such as methane, ethane, n-propane, and n-butane. No.

Examples of the monovalent fluorinated hydrocarbon group having 1 to 3 carbon atoms represented by R ² and R ³ include a hydrogen atom of a monovalent hydrocarbon group such as a methyl group, an ethyl group, and an n-propyl group. And a group in which part or all of the group is substituted with a fluorine atom.

As R ¹ , a single bond or a group obtained by removing two hydrogen atoms from a methyl group is preferable, and a single bond is more preferable.

As R ² and R ³ , a fluorine atom is preferable.

N is preferably 1.

Examples of the anion represented by the above formula (1) include a difluorooxalate borate anion represented by the following formula (1-1), a bisoxalate borate anion represented by the following formula (1-2), Difluoromalonate borate anion represented by (1-3), bismalonate borate anion represented by the following formula (1-4), malonate oxalate borate anion represented by the following formula (1-5), etc. Is mentioned.

The anion is preferably a difluorooxalate borate anion represented by the above formula (1-1) or a bis (oxalate) borate anion represented by the above formula (1-2). The represented difluorooxalate borate anion is more preferred. By using these as the above-mentioned anions, a good film can be formed.

The anion is usually contained in the nonaqueous electrolyte in the form of a salt with a cation. Examples of the cation include an alkali metal cation, an alkaline earth metal cation, and an onium cation. Among these, alkali metal cations are preferred, and lithium ions are more preferred.

Examples of the compound providing the anion include lithium difluorooxalate borate (hereinafter, also referred to as “LiDFOB”) represented by the following formula (1-1-1), and the compound represented by the following formula (1-2-1) Lithium bis oxalate borate (hereinafter also referred to as “LiBOB”) and the like.

リチウム As the compound that gives the above-mentioned anion, lithium difluorooxalate represented by the above formula (1-1-1) is preferable.

The lower limit of the content of the anion in the non-aqueous electrolyte in the non-aqueous electrolyte is preferably 0.01% by mass, more preferably 0.05% by mass, and more preferably 0.05% by mass, based on the total mass of the non-aqueous electrolyte. 1% by mass is more preferred, 0.3% by mass is even more preferred, and 0.5% by mass is even more preferred. When the content ratio of the anion is equal to or more than the lower limit, the capacity retention ratio after the charge / discharge cycle of the power storage element in a low-temperature environment can be increased. The upper limit of the content is preferably 5% by mass, more preferably 3% by mass, still more preferably 2% by mass, still more preferably 1% by mass, and particularly preferably 0.8% by mass. When the content of the anion is equal to or less than the upper limit, an increase in resistance can be suppressed.

[Other additives]
The non-aqueous electrolyte may contain other additives other than the non-aqueous solvent, the electrolyte salt and the anion as necessary. Other additives include aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl Partial halides of the aromatic compounds such as, o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole Halogenated anisole compounds such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite , Dimethyl sulfite, dimethyl sulfate, ethylene sulfate, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. Is mentioned. When the nonaqueous electrolyte contains other additives, the upper limit of the content ratio of the other additives is preferably 5% by mass, more preferably 1% by mass, and more preferably 0% by mass relative to the total mass of the nonaqueous electrolyte. 0.1 mass% is more preferred.

<Non-aqueous electrolyte storage element>
A non-aqueous electrolyte storage element according to one embodiment of the present invention includes a non-aqueous electrolyte. Further, the non-aqueous electrolyte storage element usually includes a positive electrode and a negative electrode. Hereinafter, a secondary battery will be described as an example of the nonaqueous electrolyte storage element. The positive electrode and the negative electrode usually form an electrode body that is alternately superimposed by lamination or winding via a separator. This electrode body is housed in a container for a non-aqueous electrolyte storage element, and the container for a non-aqueous electrolyte storage element is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the container for the non-aqueous electrolyte storage element, a known metal container, resin container, or the like which is generally used as a container for a secondary battery can be used.

[Non-aqueous electrolyte]
The non-aqueous electrolyte used in the non-aqueous electrolyte storage element is the above-described non-aqueous electrolyte according to the embodiment of the present invention.

[Positive electrode]
The positive electrode preferably has a positive electrode substrate and a positive electrode mixture layer disposed directly or via an intermediate layer on the positive electrode substrate.

The positive electrode substrate has conductivity. As the material of the base material, a metal such as aluminum, titanium, tantalum, stainless steel or an alloy thereof is used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of the balance between potential resistance, high conductivity, and cost. Examples of the form of forming the positive electrode substrate include a foil and a vapor-deposited film, and a foil is preferable in terms of cost. That is, the positive electrode substrate is preferably an aluminum foil or an aluminum alloy foil. Examples of aluminum or aluminum alloy include A1085P and A3003P specified in JIS-H-4000 (2014).

The intermediate layer is a coating layer on the surface of the positive electrode substrate, and reduces contact resistance between the positive electrode substrate and the positive electrode mixture layer by containing conductive particles such as carbon particles. The configuration of the intermediate layer is not particularly limited. For example, the intermediate layer can be formed of a composition containing a resin binder and conductive particles. Note that “having conductivity” means that the volume resistivity measured according to JIS-H-0505 (1975) is 10 ⁷ Ω · cm or less, and “non-conductive”. Means that the volume resistivity is greater than 10 ⁷ Ω · cm.

The positive electrode mixture layer is a layer formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary.

Usually, a metal oxide is used as the positive electrode active material. Specific positive electrode active materials include, for example, a composite oxide represented by Li _x MO _y (M represents at least one transition metal) (Li _x CoO ₂ , Li having a layered α-NaFeO ₂ type crystal structure) _{_{_{_{x NiO 2, Li x MnO 3}}}} , Li x Ni α Co (1-α) O 2, Li x Ni α Mn β Co (1-α-β) O 2 , etc., _Li x Mn ₂ having a spinel type crystal structure _{_{_{O 4, Li x Ni α Mn}}} (2-α) O 4 , _{_{_{etc.), Li w Me x (AO}}} y) z (Me represents at least one transition metal, a is for example P, Si, B, and V, etc. (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.). You. The elements or polyanions in these compounds may be partially substituted with other elements or anionic species. In the positive electrode mixture layer, one type of these compounds may be used alone, or two or more types may be mixed and used.

The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the performance of the storage element. Examples of such a conductive agent include natural or artificial graphite, furnace black, acetylene black, carbon black such as acetylene black, metal, conductive ceramics, and the like, and acetylene black is preferable. Examples of the shape of the conductive agent include powder, fiber, and the like.

Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, and styrene. Elastomers such as butadiene rubber (SBR) and fluororubber; and polysaccharide polymers.

{Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group which reacts with lithium, it is preferable to inactivate the functional group in advance by methylation or the like.

The filler is not particularly limited as long as it does not adversely affect battery performance. The main components of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

[Negative electrode]
The negative electrode preferably has a negative electrode substrate and a negative electrode mixture layer disposed on the negative electrode substrate directly or via an intermediate layer. The intermediate layer can have the same configuration as the intermediate layer of the positive electrode.

The negative electrode substrate may have the same configuration as the positive electrode substrate, but as the material, copper, nickel, stainless steel, a metal such as nickel-plated steel or an alloy thereof is used, and copper or a copper alloy is used. preferable. That is, a copper foil is preferable as the negative electrode substrate. Examples of the copper foil include a rolled copper foil and an electrolytic copper foil.

The negative electrode mixture layer is formed of a so-called negative electrode mixture containing a negative electrode active material. Further, the negative electrode mixture layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary. As the optional components such as a conductive agent, a binder, a thickener, and a filler, the same components as those of the positive electrode mixture layer can be used.

材質 A material capable of inserting and extracting lithium ions is usually used as the negative electrode active material. Specific negative electrode active materials include, for example, metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxides and Sn oxides; polyphosphate compounds; graphite (graphite); Carbon materials such as carbon (easily graphitizable carbon or hardly graphitizable carbon) are exemplified.

Further, the negative electrode mixture layer is made of a typical nonmetallic element such as B, N, P, F, Cl, Br, or I, or a typical metal element such as Li, Na, Mg, Al, K, Ca, Zn, Ga, or Ge. , Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and other transition metal elements.

[Separator]
As the material of the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of liquid retention of the nonaqueous electrolyte. As a main component of the separator, for example, a polyolefin such as polyethylene or polypropylene is preferable from the viewpoint of strength, and polyimide or aramid is preferable from the viewpoint of resistance to oxidative decomposition. Further, these resins may be combined.

Note that an inorganic layer may be provided between the separator and the electrode (usually, the positive electrode). This inorganic layer is a porous layer also called a heat-resistant layer or the like. Further, a separator in which an inorganic layer is formed on one surface of a porous resin film can also be used. The inorganic layer is usually composed of inorganic particles and a binder, and may contain other components. As the inorganic particles, Al ₂ O ₃ , SiO ₂ , aluminosilicate and the like are preferable.

The secondary battery (electric storage element) has a high capacity retention rate after storage in a high-temperature environment, and thus can be used at a high operating voltage. For example, the positive electrode potential at the end-of-charge voltage during normal use of the secondary battery may be, for example, 4.0 V (vs. Li ^/ Li ⁺ ) or higher, but is 4.4 V (vs. Li ^/ Li ⁺ ). The above is preferred. On the other hand, the upper limit of the positive electrode potential at the end-of-charge voltage during normal use is 5.1 V (vs. Li ^/ Li ⁺ ).

<Non-aqueous electrolyte storage element manufacturing method>
The non-aqueous electrolyte storage element is preferably manufactured by the following method. That is, the method for manufacturing a non-aqueous electrolyte storage element according to one embodiment of the present invention includes a step of placing a non-aqueous electrolyte in a container for a non-aqueous electrolyte storage element (hereinafter, also referred to as “non-aqueous electrolyte injection step”).

(Non-aqueous electrolyte injection step)
The non-aqueous electrolyte injection step can be performed by a known method, except that the non-aqueous electrolyte according to the embodiment of the present invention is used as the non-aqueous electrolyte. That is, the nonaqueous electrolyte may be prepared, and the prepared nonaqueous electrolyte may be injected into the nonaqueous electrolyte storage element container.

The manufacturing method may include the following steps in addition to the nonaqueous electrolyte injection step. That is, the manufacturing method includes, for example, a step of forming a positive electrode, a step of forming a negative electrode, a step of forming an electrode body that is alternately superimposed by stacking or winding the positive electrode and the negative electrode via a separator, and A step of accommodating the positive electrode and the negative electrode (electrode body) in the nonaqueous electrolyte storage element container can be provided. Usually, the non-aqueous electrolyte is injected into the non-aqueous electrolyte storage element container after the electrode body is accommodated in the non-aqueous electrolyte storage element container, but the order may be reversed. After these steps, a secondary battery (non-aqueous electrolyte storage element) can be obtained by sealing the injection port.

<How to use non-aqueous electrolyte storage element>
In the method of using the nonaqueous electrolyte storage element, the positive electrode potential at the charge end voltage in normal use is 4.4 V (vs. Li ^/ Li ⁺ ) or more. The non-aqueous electrolyte storage element has a high capacity retention rate after storage in a high-temperature environment, and thus is a storage element used under charging conditions in which the positive electrode potential at the charge end voltage during normal use is relatively high. In particular, this effect can be particularly sufficiently exhibited. Note that, for example, in a power storage element using graphite as a negative electrode active material, the positive electrode potential is about 5.1 V (vs. Li ^/ Li ⁺ ) when the charge end voltage is 5.0 V, depending on the design.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and can be embodied in modes in which various changes and improvements are made in addition to the above-described modes. For example, it is not necessary to provide an intermediate layer in the positive electrode or the negative electrode. Further, the positive electrode and the negative electrode of the nonaqueous electrolyte energy storage element do not have to have a clear layer structure. For example, the positive electrode may have a structure in which a positive electrode mixture is supported on a mesh-shaped positive electrode base material.

Further, in the above-described embodiment, the description has been given mainly of the embodiment in which the non-aqueous electrolyte storage element is a non-aqueous electrolyte secondary battery, but other non-aqueous electrolyte storage elements may be used. Other non-aqueous electrolyte energy storage devices include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 is a schematic view of a rectangular non-aqueous electrolyte storage element 1 (non-aqueous electrolyte secondary battery) which is one embodiment of the non-aqueous electrolyte storage element according to the present invention. The figure is a view in which the inside of the container is seen through. In the nonaqueous electrolyte storage element 1 shown in FIG. 1, the electrode body 2 is accommodated in a nonaqueous electrolyte storage element container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode mixture layer and a negative electrode having a negative electrode mixture layer via a separator. The positive electrode is electrically connected to the positive terminal 4 via a positive electrode lead 4 ', and the negative electrode is electrically connected to the negative terminal 5 via a negative lead 5'. The nonaqueous electrolyte storage element container 3 is filled with the nonaqueous electrolyte according to one embodiment of the present invention.

構成 The configuration of the nonaqueous electrolyte storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above nonaqueous electrolyte power storage elements. FIG. 2 illustrates an embodiment of a power storage device. 2, power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

非 Abbreviations of non-aqueous solvents and additives used in Examples, Comparative Examples and Reference Examples are shown below.

[Non-aqueous solvent]
EMC: ethyl methyl carbonate FEC: fluoroethylene carbonate FMP:

methyl

3,3,3-trifluoropropionate FEA: 2,2,2-trifluoroethyl acetate DFEA: 2,2,2-difluoroethyl acetate

[Additive]
LiDFOB: lithium difluorooxalate borate LiBOB: lithium bisoxalate borate VEC: vinyl ethylene carbonate

[Example 1]
(Preparation of non-aqueous electrolyte)
FEC and FMP were mixed at a volume ratio of 10:90 to obtain a non-aqueous solvent. Lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was added to this nonaqueous solvent so as to have a content of 1.2 mol / L, and LiDFOB as an additive was added to the total mass of the nonaqueous solvent and the electrolyte. The non-aqueous electrolyte was prepared by dissolving so as to be 0.2% by mass.

(Preparation of positive electrode)
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as a positive electrode active material. A positive electrode paste containing the positive electrode active material: polyvinylidene fluoride (PVdF): acetylene black (AB) at a mass ratio of 94: 3: 3 (in terms of solids) and using N-methylpyrrolidone as a dispersion medium was prepared. . This positive electrode paste is applied to both sides of a strip-shaped aluminum foil as a positive electrode base material so that the positive electrode active material is contained at 18.6 mg / cm ² per unit electrode area, and dried to obtain N-methylpyrrolidone as a dispersion medium. Was removed. This was pressed by a roller press to form a positive electrode mixture layer, and then dried under reduced pressure at 100 ° C. for 14 hours to remove water in the positive electrode mixture layer. Thus, a positive electrode was obtained.

(Preparation of negative electrode)
Graphite was used as the negative electrode active material. By mass ratio, a negative electrode paste containing water as a dispersion medium was prepared, containing a negative electrode active material (graphite): styrene butadiene rubber (SBR): carboxymethyl cellulose (CMC) = 97: 2: 1 (in terms of solid content). . This negative electrode paste is applied to both surfaces of a strip-shaped copper foil current collector as a negative electrode base material so that the negative electrode active material is contained at 9.9 mg / cm ² per unit electrode area, and dried to form a dispersion medium. The water was removed. This was pressed with a roller press to form a negative electrode mixture layer, and then dried under reduced pressure at 100 ° C. for 12 hours to remove moisture in the negative electrode mixture layer. Thus, a negative electrode was obtained.

(Preparation of non-aqueous electrolyte storage element)
As the separator, a microporous polyolefin membrane coated with an inorganic layer was used. The electrode body was manufactured by laminating the positive electrode and the negative electrode via the separator. The electrode body was housed in a rectangular nonaqueous electrolyte storage element container made of aluminum, and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the container for a non-aqueous electrolyte storage element, the container was sealed to obtain a non-aqueous electrolyte storage element (secondary battery) of Example 1.

(Examples 2 to 6 and Comparative Examples 1 to 3)
Example 2 was repeated in the same manner as in Example 1 except that the type and content of the electrolyte salt, the type and volume ratio of the nonaqueous solvent, or the type and amount of the additive were as shown in Tables 1 and 2. 6 and Comparative Examples 1 to 3 were obtained. Note that "-" in the table indicates that the corresponding non-aqueous solvent or additive was not used.

(Example 7)
Same as Example 2 except that the content of lithium hexafluorophosphate (LiPF ₆ ) was 0.4 mol / L and the content of lithium bis (fluorosulfonyl) amide (LiFSA) was 0.8 mol / L as the electrolyte salt. Thus, a non-aqueous electrolyte energy storage device of Example 7 was obtained. Note that "-" in the table indicates that the corresponding non-aqueous solvent or additive was not used.

(Reference Examples 1 to 3)
Except that DFEA was used instead of FMP as the non-aqueous solvent, non-aqueous electrolyte storage elements of Reference Examples 1 to 3 were obtained in the same manner as in Comparative Example 1, Example 5 and Example 2, respectively. Note that "-" in the table indicates that the corresponding non-aqueous solvent or additive was not used. Here, “DFEA” is represented by the following equation (3). “DFEA” has a similar structure to “FEA”, except that the terminal of the group bonded to the oxy oxygen atom of the carbonyloxy group is not a trifluoromethyl group (—CF ₃ ) but a difluoromethyl group (—CF ₂ H ).

Among the non-aqueous electrolyte energy storage devices manufactured by the above-described procedure, a plurality of non-aqueous electrolyte energy storage devices according to Comparative Examples 1 and 2 and Example 2 were prepared and subjected to the following “initial charge / discharge”. Storage test "or" 0 ° C charge / discharge cycle test ". The nonaqueous electrolyte energy storage devices according to Comparative Example 3, Examples 1, 3 to 7, and Reference Examples 1 to 3 were subjected to “initial charge / discharge” and subjected to “0 ° C. charge / discharge cycle test”.

[Evaluation]
<Initial charge / discharge>
The obtained nonaqueous electrolyte energy storage device was initially charged and discharged at 25 ° C. in the following steps (1) to (4).
(1) Charging Step Constant current charging is performed up to 4.3 V at a current value of 0.2 C. After the voltage reaches 4.3 V, the voltage is maintained, and when 8 hours have elapsed from the start of charging, the charging is terminated (so-called constant current constant voltage charging), and a 10-minute pause is performed.
(2) Discharge process A constant current discharge is performed up to 2.75 V at a current value of 0.2 C. When the voltage reaches 2.75 V, the discharge is terminated, and a pause for 10 minutes is performed.
(3) Charging Step Constant current charging is performed up to 4.3 V at a current value of 1C. After reaching 4.3 V, the voltage is maintained, and when 3 hours have passed from the start of charging, the charging is terminated, and a pause of 10 minutes is performed.
(4) Discharge step A constant current discharge is performed up to 2.75 V at a current value of 1C. When the voltage reaches 2.75 V, the discharge is terminated, and a pause for 10 minutes is performed.
The discharge capacity in the above step (4) was recorded as "the second discharge capacity in the initial charge / discharge test".

<45 ° C storage test>
The non-aqueous electrolyte storage element after the initial charge and discharge was subjected to a 45 ° C. storage test in the following steps.
(1 ′) Charging Step The battery is charged at a constant current up to 4.3 V at a current value of 1 C in a thermostat at 25 ° C. After reaching 4.3 V, the voltage is maintained, and when 3 hours have passed from the start of charging, the charging is terminated, and a pause of 10 minutes is performed.
(2 ′) Storage process at 45 ° C. The non-aqueous electrolyte storage element was placed in an open circuit state and left (stored) in a 45 ° C. constant temperature bath. After 30 days from the start of storage, the storage step was terminated, and the storage element was taken out and allowed to stand at room temperature for 5 hours or more.
(3 ′) Discharging Step A constant current discharge is performed at a current value of 1 C to 2.75 V in a constant temperature bath at 25 ° C. When the voltage reaches 2.75 V, the discharge is terminated, and a pause for 10 minutes is performed.
After the steps (1 ′), (2 ′), and (3 ′), the steps (3) and (4) in the above initial charge and discharge are performed in a constant temperature bath at 25 ° C., and the discharge capacity at that time is stored. Later discharge capacity ". The percentage of the discharge capacity after storage relative to the second discharge capacity in the initial charge / discharge test was determined as “capacity retention rate /% after storage test at 45 ° C.”.

<0 ° C charge / discharge cycle test>
The non-aqueous electrolyte storage element after the initial charge / discharge was allowed to stand in a 0 ° C. constant temperature bath for 5 hours, and then subjected to a 0 ° C. charge / discharge cycle test in the following steps.
(1 ″) Charging Step Constant current charging is performed up to 4.3 V at a current value of 1C. After reaching 4.3 V, the voltage is maintained, and when 3 hours have passed from the start of charging, the charging is terminated, and a pause of 10 minutes is performed.
(2 ″) Discharging step A constant current discharging is performed up to 2.75 V at a current value of 1C. When the voltage reaches 2.75 V, the discharge is terminated, and a pause for 10 minutes is performed.
The steps (1 ″) and (2 ″) were defined as one charge / discharge cycle, and 350 charge / discharge cycles were performed. The percentage of the discharge capacity at the 350th cycle relative to the discharge capacity at the first cycle was determined as “capacity retention rate after 0 ° C. cycle test /%”. The difference in the capacity retention after the 0 ° C. cycle test with respect to Comparative Example 1 or Reference Example 1 in which no additive was used was determined as “difference /% of the capacity retention after the 0 ° C. cycle test with the non-added product”. For Reference Examples 2 to 3, the difference from Reference Example 1 was calculated, and for Comparative Example 3 and Examples 1 to 7, the difference from Comparative Example 1 was calculated. That is, this value is an index indicating the magnitude of the effect of improving the charge / discharge cycle performance under a low temperature environment by using the additive.
Before and after the test, the thickness of the nonaqueous electrolyte storage element was measured, and the change in thickness before and after the 0 ° C. charge / discharge cycle test was determined. The difference in thickness change before and after the 0 ° C. charge / discharge cycle test with respect to Comparative Example 1 or Reference Example 1 in which no additive was used was determined as “difference / mm difference between battery thickness change after 0 ° C. cycle test and unadded product”. . For Reference Examples 2 to 3, the difference from Reference Example 1 was calculated, and for Comparative Example 3 and Examples 1 to 7, the difference from Comparative Example 1 was calculated. If this value is a negative value, it means that the increase in the battery thickness after the 0 ° C. cycle test can be suppressed by using the additive.

In the above test, when the voltage of the nonaqueous electrolyte energy storage device was 4.3 V, the potential of the positive electrode was 4.4 V (vs. Li ^/ Li ⁺ ).

Regarding the non-aqueous electrolyte energy storage devices according to Example 2, Comparative Example 1 and Comparative Example 2, the “capacity retention rate /% after 45 ° C. storage test” obtained in the above “45 ° C. storage test” and “0 ° C. Table 1 summarizes the “capacity retention rate /% after the 0 ° C. cycle test” obtained by the “charge / discharge cycle test”.

Comparing Comparative Example 1 with Comparative Example 2, the use of FEC and FMP as the non-aqueous solvent improves the “capacity retention rate after storage test at 45 ° C.” as compared to the case of using FEC and EMC. On the other hand, it is understood that the “capacity retention after the 0 ° C. cycle test” (hereinafter, also referred to as low-temperature characteristics) decreases.
Comparing Example 2 with Comparative Example 1, by adding LiDFOB as an additive, the “capacity retention after 45 ° C. storage test” was improved, and the “capacity retention after 0 ° C. cycle test” was greatly improved. You can see that there is.
From these results, it was found that the non-aqueous electrolyte of the present invention was excellent in charge / discharge cycle performance in a low-temperature environment while maintaining high-temperature storage performance.

Regarding the non-aqueous electrolyte energy storage devices according to Examples 1 to 7, Comparative Examples 1 and 3, and Reference Examples 1 to 3, "No addition of capacity retention rate after 0 ° C cycle test obtained by" 0 ° C charge / discharge cycle test " Table 2 summarizes "difference with product /%" and "difference in battery thickness change after 0 ° C. cycle test with non-added product / mm".

Comparing Examples 1 to 4 with Comparative Example 1, by using LiDFOB as an additive, the low-temperature characteristics are improved and the increase in the battery thickness after the 0 ° C. charge / discharge cycle test is suppressed regardless of the added amount. It was done.

比較 Comparing Example 5 with Comparative Examples 1 and 3, it can be seen that even when LiBOB is used as an additive, the effect of improving low-temperature characteristics can be obtained. However, when using VEC, it turns out that it falls remarkably.

比較 Comparing Example 7 with Comparative Example 1, it can be seen that even when LiFSA is used as the electrolyte salt, the effect of improving low-temperature characteristics can be obtained.

比較 Comparing Example 6 with Comparative Example 1, it can be seen that even when FEA is used as the non-aqueous solvent, an effect of improving low-temperature characteristics can be obtained. Further, the increase in battery thickness after the 0 ° C. charge / discharge cycle test was also suppressed.

Comparing Reference Example 1 with Reference Examples 2 and 3, when DFEA was used as the non-aqueous solvent, the effect of improving the low-temperature characteristics was small even when LiDFOB was added, and the battery after the 0 ° C. charge / discharge cycle test was performed. It can be seen that there is no effect of suppressing the increase in thickness. That is, it is understood that the effect of improving the low-temperature characteristics is more remarkable when FEA or FMP is used as the non-aqueous solvent.
The following reasons can be considered for this mechanism. As a result of the LUMO (Lowest Unoccupied Molecular Orbital) calculation by the PM3 (Parameterized Model number 3) method, the DFEA was the largest among the DFEA, FEA and FMP, and the FMP was the smallest among the LUMOs. It is said that the larger the value of LUMO, the better the reduction resistance. That is, it can be said that FEA and FMP are easily reduced as compared with DFEA, and "fluorinated carboxylic acid ester having a group containing a difluoromethyl group" and "fluorinated carboxylic acid ester having a group containing a trifluoromethyl group" Can be said that the “fluorinated carboxylic acid ester having a group containing a trifluoromethyl group” tends to be more easily reduced. Therefore, a non-aqueous electrolyte storage element using FEA or FMP as a non-aqueous solvent, which is easily reduced as compared with DFEA, is decomposed on a negative electrode together with LiDFOB containing FEA or FMP as an additive, and boron atoms and fluorine atoms are decomposed. It is considered that the formation of a uniform film close to the above exhibits excellent charge / discharge cycle performance in a low-temperature environment.

The present invention is applicable to electronic devices such as personal computers and communication terminals, and non-aqueous electrolyte storage elements used as power sources for automobiles and the like.

DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte storage element 2 Electrode body 3 Container for non-aqueous electrolyte storage element 4 Positive terminal 4 'Positive lead 5 Negative terminal 5' Negative lead 20 Power storage unit 30 Power storage device

Claims

A non-aqueous solvent,
An electrolyte salt;
An anion in which a dicarboxylate group is bonded to a boron atom, and
A nonaqueous electrolyte in which the nonaqueous solvent contains a fluorinated cyclic carbonate and a fluorinated carboxylate having a group containing a trifluoromethyl group.
The non-aqueous electrolyte according to claim 1, wherein the anion further contains a fluorine atom.
The non-aqueous electrolyte according to claim 1, wherein the anion is represented by the following formula (1).

(In the formula (1), R 1 is a divalent hydrocarbon group of a single bond or a carbon atoms of 1 4 .n, when it .n is 2 1 or 2, the two R 1 are each other R 2 and R 3 are each independently a fluorine atom or a monovalent fluorinated hydrocarbon group having 1 to 3 carbon atoms.)
The non-aqueous electrolyte according to claim 3, wherein the anion is a bisoxalate borate anion or a difluorooxalate borate anion.
The non-aqueous electrolyte according to any one of claims 1 to 4, wherein the content of the anion in the total mass of the non-aqueous solvent and the electrolyte salt is 0.01% by mass or more and 5% by mass or less.
The non-aqueous electrolyte according to any one of claims 1 to 5, wherein the fluorinated carboxylic acid ester is represented by the following formula (2).

(In the formula (2), R 4 and R 5 are each independently a monovalent hydrocarbon group having 1 to 4 carbon atoms or a monovalent fluorinated hydrocarbon group having 1 to 4 carbon atoms. , R 4 and R 5 are groups containing a trifluoromethyl group.)
7. The non-aqueous electrolyte according to claim 6, wherein the group containing a trifluoromethyl group is a 2,2,2-trifluoroethyl group.
The non-aqueous electrolyte according to claim 6, wherein the fluorinated carboxylic acid ester is 2,2,2-trifluoroethyl acetate, methyl 3,3,3-trifluoropropionate, or a combination thereof. .
The non-aqueous electrolyte according to any one of claims 1 to 8, wherein the content ratio of the fluorinated carboxylic acid ester in the non-aqueous solvent is from 20% by volume to 95% by volume.
The non-aqueous electrolyte according to any one of claims 1 to 9, wherein the fluorinated cyclic carbonate is fluoroethylene carbonate.
The non-aqueous electrolyte according to any one of claims 1 to 10, wherein the content of the fluorinated cyclic carbonate in the non-aqueous solvent is 1% by volume or more and 50% by volume or less.
A non-aqueous electrolyte energy storage device comprising the non-aqueous electrolyte according to any one of claims 1 to 11.
A method for manufacturing a non-aqueous electrolyte storage element, comprising a step of placing the non-aqueous electrolyte according to any one of claims 1 to 11 in a container for the non-aqueous electrolyte storage element.
The method for using the nonaqueous electrolyte energy storage device according to claim 12, wherein a positive electrode potential at a charge termination voltage in normal use is 4.4 V (vs. Li / Li + ) or more.