JP7344874B2 - Non-aqueous electrolyte and power storage device using it - Google Patents

Description

The present invention relates to a non-aqueous electrolyte that can suppress electrochemical properties, particularly a decrease in battery capacity during high-temperature charging and storage, and a power storage device using the same.

In recent years, power storage devices, particularly lithium batteries, have been widely used as power sources for small electronic devices such as mobile phones and notebook computers, and as power sources for electric vehicles and power storage. Note that in this specification, the term lithium battery is used as a concept that also includes so-called lithium ion secondary batteries.

A lithium battery is mainly composed of a positive electrode and a negative electrode containing a material capable of intercalating and deintercalating lithium ions, a lithium salt, and a nonaqueous electrolyte consisting of a nonaqueous solvent. The nonaqueous solvent includes ethylene carbonate (EC), Carbonates such as propylene carbonate (PC) are used.
As negative electrodes for lithium batteries, lithium metal, metal compounds capable of inserting and releasing lithium ions (such as simple metals, metal oxides, alloys with lithium, etc.), carbon materials, and the like are known. In particular, among carbon materials, lithium batteries using carbon materials capable of intercalating and deintercalating lithium ions, such as coke and graphite (artificial graphite, natural graphite), have been widely put into practical use.
Because carbon materials such as coke and graphite store and release lithium ions and electrons at an extremely base potential equivalent to that of lithium metal, many solvents in non-aqueous electrolytes may undergo reductive decomposition. There is. When the solvent in the non-aqueous electrolyte is reductively decomposed on the negative electrode, decomposed products are deposited on the negative electrode surface and gas is generated, which prevents the smooth movement of lithium ions and deteriorates battery characteristics such as high-temperature storage characteristics. There's a problem.
On the other hand, as a positive electrode of a lithium battery, a composite metal oxide containing lithium and one or more selected from the group consisting of cobalt, manganese, and nickel, which is capable of intercalating and deintercalating lithium ions, is used. . Here, heavy metals in the positive electrode active material may be eluted into the non-aqueous electrolyte during high-temperature charging and storage. If the eluted metal is redeposited on the negative electrode, problems such as a decrease in battery capacity, an increase in the amount of gas generated due to decomposition of the non-aqueous electrolyte, and an increase in electrical resistance occur.

Patent Document 1 proposes a non-aqueous electrolyte containing an organic solvent, a lithium salt, and an inner salt having a cation and an anion in the molecule, and utilizes a dissolution precipitation reaction of lithium in the negative electrode. It is disclosed that in a lithium battery using an active material, the charge/discharge cycle characteristics are improved in a 30 cycle test. However, in the lithium battery to which the nonaqueous electrolyte of Patent Document 1 is applied, although there is a description of improving the charge/discharge cycle characteristics in a low-temperature cycle test, there is no description of the effect of improving battery storage characteristics at high temperatures. do not have. In addition, some of the intramolecular salts that have cations and anions in the molecule described in Patent Document 1 dissolve only a small amount in the organic solvent in which the lithium salt is dissolved, and cannot exhibit any effect. It is.
Patent Document 2 proposes a nonaqueous electrolyte containing an organic solvent, a lithium salt, and an inner salt containing anionic SO ₃ or SO ₄ and a cationic triazine in the same molecule. It is disclosed that the high-temperature storage characteristics of the secondary battery and the stability during overcharging are improved.
Patent Document 3 proposes a non-aqueous electrolyte containing an organic solvent such as ethylene carbonate, a lithium salt, and a zwitterionic compound containing a nitrogen or phosphorus atom, which is said to have excellent electrochemical stability. Disclosed.

JP 2003-346897 US Patent Application Publication No. 2017/0125847 International Publication No. 2016/027788

An object of the present invention is to provide a non-aqueous electrolyte that can significantly improve the high-temperature charge storage characteristics of an electricity storage device, and an electricity storage device using the same.
The present invention further provides a non-aqueous electrolyte that can improve the high-temperature charge storage characteristics of an electricity storage device and can also significantly suppress gas generated during storage, and an electricity storage device using the same. The purpose is to

The present inventors have repeatedly conducted research to solve the above problems, and have found that a non-aqueous electrolyte containing zwitterions has the effect of suppressing a decrease in battery capacity during high-temperature charging and storage, and the effect of suppressing generated gas. As a result of further intensive research, the inventors discovered that zwitterions improve solubility in organic solvents and further improve battery characteristics, thereby completing the present invention.
Furthermore, it has been discovered that a zwitterion in which the cationic group contains a phosphorus atom or a nitrogen atom without a heterocycloalkenyl group and the anionic group is -SO ₄ ^- particularly improves battery performance, and the present invention completed.
That is, the present invention provides the following (1) and (2).

(1) A non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous electrolyte being characterized by containing a zwitterion represented by the following general formula (I).

(In formula (I), Q ⁺ is a cationic group represented by the following formula (II) or (III).
L ¹ is an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkenylene group having 2 to 5 carbon atoms, a fluorinated alkenylene group having 2 to 5 carbon atoms, or a fluorinated alkenylene group having 1 to 4 carbon atoms. represents an alkyleneoxy group.
The anionic group represented by A ^- is a sulfonate group or a carboxylate group. )

(In formula (II), R ¹ to R ³ are each independently an alkyl group having 1 to 15 carbon atoms, a fluorinated alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, or an alkenyl group having 2 to 15 carbon atoms. It represents a fluorinated alkenyl group having 2 to 15 carbon atoms, an alkynyl group having 3 to 15 carbon atoms, or a fluorinated alkynyl group having 3 to 15 carbon atoms.
In formula (III), R ⁴ to R ⁶ each independently represent an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms. -5 fluorinated alkoxy group, alkenyl group with 2 to 5 carbon atoms, alkenyloxy group with 2 to 5 carbon atoms, fluorinated alkenyloxy group with 2 to 5 carbon atoms, alkynyl group with 3 to 5 carbon atoms, carbon number It represents an alkynyloxy group having 3 to 5 carbon atoms, a fluorinated alkynyl group having 3 to 5 carbon atoms, a fluorinated alkynyloxy group having 3 to 5 carbon atoms, a dimethylamino group, or a diethylamino group.
* indicates the binding site with ^L1 . )

(2) A power storage device comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous electrolyte being the non-aqueous electrolyte according to (1) above. A power storage device characterized by:

In addition, in this specification, the term "zwitterion" means an inner salt having a positive charge (cationic group) and a negative charge (anionic group) in one molecule.

According to the present invention, it is possible to provide a nonaqueous electrolyte that can significantly suppress a decrease in battery capacity during high-temperature charging and storage of an electricity storage device, and an electricity storage device such as a lithium battery using the nonaqueous electrolyte.
Further, according to the present invention, there is provided a non-aqueous electrolyte capable of suppressing a decrease in battery capacity during high-temperature charging and storage of an electricity storage device and gas generated during high-temperature charging and storage, and an electricity storage device such as a lithium battery using the same. be able to.

<Nonaqueous electrolyte>
The nonaqueous electrolyte of the present invention is a nonaqueous electrolyte in which an electrolyte salt is dissolved in a nonaqueous solvent. It is characterized by containing.

The reason why the non-aqueous electrolyte of the present invention improves the high-temperature charge storage characteristics of an electricity storage device is not necessarily clear, but it is thought to be as follows.
One of the causes of battery capacity reduction when storage devices are stored at high temperatures is that metals such as cobalt, nickel, and manganese are leached from the positive electrode active material and reduced on the negative electrode, resulting in unstable SEI (Solid Electrolyte For example, forming an interphase film. The zwitterion of general formula (I) of the present invention specifically coordinates to the eluted metal. It is thought that the metal coordinated with zwitterions forms a stable SEI film even when reduced on the negative electrode, improving battery characteristics. In addition, since the cationic group in the general formula (I) is chemically stable compared to a heterocycloalkenyl group such as triazine, it improves the zwitterion effect and is an anionic group. The -SO ₄ ^- group exhibits an effective electrode resistance-reducing effect. Therefore, it is considered that the zwitterion of the combination of an anionic group and a cationic group of the general formula (I) particularly promotes improvement of battery characteristics.

[Zwitterion]
The zwitterion according to the present invention is represented by the following general formula (I).

In formula (I), Q ⁺ is a cationic group represented by formula (II) or (III) below.
L ¹ is an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkenylene group having 2 to 5 carbon atoms, a fluorinated alkenylene group having 2 to 5 carbon atoms, or a fluorinated alkenylene group having 1 to 4 carbon atoms. represents an alkyleneoxy group. Among these, L ¹ is preferably an alkylene group having 1 to 3 carbon atoms, an alkenylene group having 2 to 3 carbon atoms, or an alkyleneoxy group having 1 to 4 carbon atoms.
The anionic group represented by A ^- is a sulfonate group (-SO ₃ ^- group) or a carboxylate group (-COO ^- group).

In formula (II), R ¹ to R ³ each independently represent an alkyl group having 1 to 15 carbon atoms, a fluorinated alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, or an alkenyl group having 2 to 15 carbon atoms. -15 fluorinated alkenyl group, C3-15 alkynyl group, or C3-15 fluorinated alkynyl group. Among these, R ¹ to R ³ are each independently an alkyl group having 1 to 15 carbon atoms, a fluorinated alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, or an alkenyl group having 3 to 15 carbon atoms. ~15 alkynyl groups are preferred.
In formula (III), R ⁴ to R ⁶ each independently represent an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms. -5 fluorinated alkoxy group, alkenyl group with 2 to 5 carbon atoms, alkenyloxy group with 2 to 5 carbon atoms, fluorinated alkenyloxy group with 2 to 5 carbon atoms, alkynyl group with 3 to 5 carbon atoms, carbon number It represents an alkynyloxy group having 3 to 5 carbon atoms, a fluorinated alkynyl group having 3 to 5 carbon atoms, a fluorinated alkynyloxy group having 3 to 5 carbon atoms, a dimethylamino group, or a diethylamino group. Among these, R ⁴ to R ⁶ are preferably each independently an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, a dimethylamino group, or a diethylamino group.
* indicates the binding site with ^L1 . That is, L ¹ is bonded to the nitrogen atom or phosphorus atom of Q ⁺ .

In the present invention, the zwitterion is preferably one or more selected from a compound represented by the following general formula (IV) and a compound represented by the following general formula (VII).

In formula (IV), Q ⁺ is a cationic group represented by formula (V) or (VI) below.
L ² represents a fluorinated alkylene group having 1 to 5 carbon atoms, an alkenylene group having 2 to 5 carbon atoms, a fluorinated alkenylene group having 2 to 5 carbon atoms, or an alkyleneoxy group having 1 to 4 carbon atoms.

In formula (V), R ⁷ to R ⁹ each independently represent an alkyl group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkenyl group having 2 to 5 carbon atoms. -5 fluorinated alkenyl group, an alkynyl group having 3 to 5 carbon atoms, or a fluorinated alkynyl group having 3 to 5 carbon atoms.
In formula (VI), R ¹⁰ to R ¹² each independently represent an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms. -5 fluorinated alkoxy group, alkenyl group with 2 to 5 carbon atoms, alkenyloxy group with 2 to 5 carbon atoms, fluorinated alkenyloxy group with 2 to 5 carbon atoms, alkynyl group with 3 to 5 carbon atoms, carbon number It represents an alkynyloxy group having 3 to 5 carbon atoms, a fluorinated alkynyl group having 3 to 5 carbon atoms, a fluorinated alkynyloxy group having 3 to 5 carbon atoms, a dimethylamino group, or a diethylamino group.
* indicates the binding site with ^L2 . That is, L ² is bonded to the nitrogen atom or phosphorus atom of Q ⁺ .

In formula (VII), L ³ represents an alkylene group having 1 to 5 carbon atoms, preferably an alkylene group having 1 to 3 carbon atoms, more preferably an alkylene group having 1 to 2 carbon atoms, and even more preferably a methylene group.
R ¹³ to R ¹⁵ are each independently an alkyl group having 1 to 15 carbon atoms, a fluorinated alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, or a fluorinated alkenyl group having 2 to 15 carbon atoms. group, an alkynyl group having 3 to 15 carbon atoms, or a fluorinated alkynyl group having 3 to 15 carbon atoms. Among these, R ¹³ to R ¹⁵ are preferably each independently an alkyl group having 1 to 15 carbon atoms or an alkenyl group having 2 to 15 carbon atoms.
However, at least one of R ¹³ to R ¹⁵ is an alkyl group having 3 to 15 carbon atoms.

<Zwitterion represented by general formula (IV)>
The zwitterion represented by the general formula (IV) is more preferably a compound represented by the following general formula (VIII).

In formula (VIII), Q ⁺ is a cationic group represented by formula (IX) or (X) below.
L ⁴ represents an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkenylene group having 2 to 5 carbon atoms, or a fluorinated alkenylene group having 2 to 5 carbon atoms. Among these, L ⁴ is preferably an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, or an alkenylene group having 2 to 5 carbon atoms; Alternatively, an alkenylene group having 2 to 3 carbon atoms is more preferable, and an alkylene group having 2 to 3 carbon atoms is even more preferable.

In formula (IX), R ¹⁶ to R ¹⁸ each independently represent an alkyl group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkenyl group having 2 to 5 carbon atoms. -5 fluorinated alkenyl group, an alkynyl group having 3 to 5 carbon atoms, or a fluorinated alkynyl group having 3 to 5 carbon atoms. Among these, R ¹⁶ to R ¹⁸ are each independently an alkyl group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkenyl group having 2 to 5 carbon atoms. A fluorinated alkenyl group having ~5 carbon atoms is preferred, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms is more preferred, an alkyl group having 1 to 3 carbon atoms, or an alkenyl group having 2 to 3 carbon atoms is preferable. More preferred.

In formula (X), R ¹⁹ to R ²¹ each independently represent an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms. -5 fluorinated alkoxy group, alkenyl group with 2 to 5 carbon atoms, alkenyloxy group with 2 to 5 carbon atoms, fluorinated alkenyloxy group with 2 to 5 carbon atoms, alkynyl group with 3 to 5 carbon atoms, carbon number It represents an alkynyloxy group having 3 to 5 carbon atoms, a fluorinated alkynyl group having 3 to 5 carbon atoms, a fluorinated alkynyloxy group having 3 to 5 carbon atoms, a dimethylamino group, or a diethylamino group. Among these, R ¹⁹ to R ²¹ are each independently an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, and a fluorinated alkyl group having 2 to 5 carbon atoms. An alkenyl group having 5 carbon atoms, a dimethylamino group, or a diethylamino group is preferable, and an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, a dimethylamino group, or a diethylamino group is more preferable, and an alkenyl group having 1 to 3 carbon atoms is preferable. An alkyl group, an alkenyl group having 2 to 3 carbon atoms, a dimethylamino group, or a diethylamino group is more preferred, and an alkyl group having 1 to 3 carbon atoms is most preferred.
* indicates the binding site with ^L4 . That is, L ⁴ is bonded to the nitrogen atom or phosphorus atom of Q ⁺ .

In the present invention, the zwitterion represented by the general formula (IV) or (VIII) is selected from a compound represented by the following general formula (XI) and a compound represented by the following general formula (XII). More preferably, it is one or more types.

L ⁵ in formula (XI) and L ⁶ in formula (XII) represent an alkylene group having 2 or 3 carbon atoms.
In formula (XI), R ¹⁶ to R ¹⁸ each independently represent an alkyl group having 1 to 3 carbon atoms.
In formula (XII), R ¹⁹ to R ²¹ each independently represent an alkyl group having 1 to 3 carbon atoms or a dimethylamino group. )

Preferred examples of the zwitterion represented by the general formula (IV), (VIII), (XI) or (XII) include the following compounds.

Among the above compounds, 2-(trimethylammonio)ethyl sulfate (structural formula 1), 2-(triethylammonio)ethyl sulfate (structural formula 4), and 2-(tripropylammonio)ethyl sulfate (structural formula 5), 3-(trimethylammonio)propyl sulfate (structural formula 7), 3-(triethylammonio)propyl sulfate (structural formula 10), 3-(tripropylammonio)propyl sulfate (structural formula 11), 2 -(tributylphosphonio)ethyl sulfate (structural formula 15), 2-(trisdimethylaminophosphonio)ethyl sulfate (structural formula 17), and 3-(tributylphosphonio)propyl sulfate (structural formula 20) More than one type to choose from.

Among the above compounds, 2-(trimethylammonio)ethyl sulfate (structural formula 1), 2-(triethylammonio)ethyl sulfate (structural formula 4), and 2-(tripropylammonio)ethyl sulfate (structure Formula 5), 2-(tributylphosphonio)ethyl sulfate (Structural Formula 15), and 2-(trisdimethylaminophosphonio)ethyl sulfate (Structural Formula 17), and more preferably From the group consisting of 2-(trimethylammonio)ethyl sulfate (structural formula 1), 2-(triethylammonio)ethyl sulfate (structural formula 4), and 2-(tripropylammonio)ethyl sulfate (structural formula 5) More than one type to choose from.

<Zwitterion represented by general formula (VII)>
The zwitterion represented by the general formula (VII) is more preferably a compound represented by the following general formula (VII-I).

In formula (VII-1), L ³ is a methylene group, R ¹³ to R ¹⁵ are each independently an alkyl group having 1 to 15 carbon atoms, and at least one of R ¹³ to R ¹⁵ is an alkyl group having 3 carbon atoms. ~15 alkyl groups.

Preferred examples of the zwitterion represented by general formula (VII) or (VII-1) include the following compounds.

Among the above compounds, 2-butyldimethyl(carboxylatomethyl)ammonium (structural formula 1), 2-butyldimethyl(carboxylatoethyl)ammonium (structural formula 2), 2-butyldimethyl(carboxylatopropyl)ammonium ( Structural formula 3), 2-hexyldimethyl (carboxylatomethyl) ammonium (structural formula 7), 2-hexyldimethyl (carboxylatoethyl) ammonium (structural formula 8), 2-hexyldimethyl (carboxylatopropyl) ammonium (structural formula 9), 2-octyldimethyl(carboxylatomethyl)ammonium (structural formula 10), 2-octyldimethyl(carboxylatoethyl)ammonium (structural formula 11), 2-octyldimethyl(carboxylatopropyl)ammonium (structural formula 12) , 2-decyldimethyl(carboxylatomethyl)ammonium (structural formula 13), 2-decyldimethyl(carboxylatoethyl)ammonium (structural formula 14), 2-decyldimethyl(carboxylatopropyl)ammonium (structural formula 15), 2 -From the group consisting of dodecyldimethyl(carboxylatomethyl)ammonium (structural formula 16), 2-dodecyldimethyl(carboxylatoethyl)ammonium (structural formula 17) and 2-dodecyldimethyl(carboxylatopropyl)ammonium (structural formula 18) More than one type to choose from.

Among the above compounds, 2-butyldimethyl(carboxylatomethyl)ammonium (structural formula 1), 2-hexyldimethyl(carboxylatomethyl)ammonium (structural formula 7), and 2-octyldimethyl(carboxylatomethyl)ammonium (Structural Formula 10), 2-decyldimethyl(carboxylatomethyl)ammonium (Structural Formula 13), and 2-dodecyldimethyl(carboxylatomethyl)ammonium (Structural Formula 16).

In addition, triethyl (sulfopropyl) ammonium, (tributylphosphonio) propyl sulfonate, etc. can be used as the zwitterion, but in this case, a lithium composite metal oxide containing manganese is used as the positive electrode active material, and a negative electrode As the active material, it is preferable to use one or more selected from carbon materials capable of intercalating and deintercalating lithium and titanium composite metal oxides, and as the positive electrode active material, a spinel-type lithium composite containing manganese is used. It is more preferable to use a metal oxide, especially spinel-type lithium manganate (LiMn ₂ O ₄ ), and use a titanium composite metal oxide, especially Li ₄ Ti ₅ O ₁₂ , as the negative electrode active material.

On the other hand, when using a compound represented by the general formula (IV), (VIII), (XI) or (XII), as described later, a lithium composite metal oxide containing manganese is used as the positive electrode active material. is preferable, a manganese lithium composite metal oxide having a spinel type structure is more preferable, and a spinel type lithium manganate is even more preferable. Further, as the negative electrode active material, it is preferable to use one or more selected from carbon materials capable of intercalating and deintercalating lithium, and titanium composite metal oxides.
In addition, when using the compound represented by the general formula (VII) or (VII-1), as described later, a lithium composite metal oxide containing manganese is preferable as the positive electrode active material, and a spinel-type structure is used. A manganese lithium composite metal oxide having the following is more preferable, a spinel-type lithium manganate is even more preferable, and as the negative electrode active material, it is preferable to use a carbon material capable of intercalating and deintercalating lithium.

In the non-aqueous electrolyte of the present invention, each of the compounds represented by the general formula (I), (IV), (VII), (VII-1), (VIII), (XI) or (XII) is contained. The amount is preferably 0.01% by mass or more and saturated amount or less in the nonaqueous electrolyte in order to fully exhibit the effect. Further, in consideration of industrial production, the lower limit is preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more. Further, the upper limit thereof is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 5% by mass or less, and most preferably 2% by mass or less.
Further, the total content of the compounds represented by each of the above general formulas is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.03% by mass or more and 8% by mass or less, and even more preferably 0.05% by mass or less. The content is from 0.1% by mass to 2% by mass, most preferably from 0.1% by mass to 2% by mass.

In the non-aqueous electrolyte of the present invention, by combining the compound represented by the general formula (I) with the non-aqueous solvent, electrolyte salt, and other additives described below, the battery capacity decreases during high-temperature charging and storage. , and the unique effect of synergistically improving the effect of suppressing gas generation during high-temperature charging and storage.

[Non-aqueous solvent]
First, in this specification, "solvent" means a substance for dissolving a solute.
The non-aqueous solvent used in the non-aqueous electrolyte of the present invention is preferably one or more selected from cyclic carbonates, chain esters, lactones, ethers, and amides. Since the electrochemical properties at high temperatures are synergistically improved, it is preferable to include a chain ester, more preferably a chain carbonate, and even more preferably to include both a cyclic carbonate and a chain ester. .

Note that the term "chain ester" is used as a concept including chain carbonates and chain carboxylic acid esters.
Furthermore, "chain carbonate" is defined as a straight chain alkyl carbonate compound.

(cyclic carbonate)
Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans or Cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter collectively referred to as "DFEC"), vinylene carbonate (VC), vinylethylene carbonate (VEC), and 4-ethynyl-1 , 3-dioxolan-2-one (EEC), ethylene carbonate, propylene carbonate, 4-fluoro-1,3-dioxolan-2-one, vinylene, etc. More preferred is one or more selected from the group consisting of carbonate and 4-ethynyl-1,3-dioxolan-2-one (EEC).

The content of the cyclic carbonate is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, based on the total amount of the nonaqueous electrolyte, and the upper limit thereof is preferably The content is 90% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, even more preferably 40% by mass or less, and within this range, the high temperature charge storage characteristics can be further improved without impairing Li ion permeability. This is preferable because it can improve the temperature and suppress gas generation.

In addition, if at least one type of cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond or a fluorine atom is used, the high temperature charge storage characteristics can be further improved and gas generation can be further suppressed. It is preferable to include both a cyclic carbonate containing an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond and a cyclic carbonate having a fluorine atom. As the cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond, VC, VEC, or EEC is more preferable, and as the cyclic carbonate having a fluorine atom, FEC or DFEC is even more preferable.

The content of the cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond is preferably 0.05% by mass or more, more preferably 0.1% by mass based on the total amount of the nonaqueous electrolyte. % or more, more preferably 0.5% by mass or more, and the upper limit thereof is preferably 8% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and within the range. This is preferable because the high temperature charge storage characteristics can be further improved without impairing Li ion permeability and gas generation can be suppressed.

The content of the cyclic carbonate having a fluorine atom is preferably 0.05% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more based on the total amount of the nonaqueous electrolyte, and the upper limit thereof is preferably 40% by mass or less, more preferably 30% by mass or less, further preferably 20% by mass or less, and even more preferably 15% by mass or less, and within this range, Li ion permeability can be further improved without impairing Li ion permeability. This is preferable because it can improve high-temperature charge storage characteristics and suppress gas generation.

These solvents may be used alone, or if two or more are used in combination, it is preferable because the high temperature charge storage characteristics can be improved and gas generation can be suppressed. It is more preferable to use Preferred combinations of these cyclic carbonates include a combination of EC and PC, a combination of EC and VC, a combination of PC and VC, a combination of VC and FEC, a combination of EC and FEC, a combination of PC and FEC, and FEC and DFEC. combination, combination of EC and DFEC, combination of PC and DFEC, combination of VC and DFEC, combination of VEC and DFEC, combination of VC and EEC, combination of EC and EEC, combination of EC, PC and VC, EC and PC and FEC combination, EC, VC and FEC combination, EC, VC and VEC combination, EC, VC and EEC combination, EC, EEC and FEC combination, PC, VC and FEC combination, EC, VC and DFEC A combination of PC, VC, and DFEC, a combination of EC, PC, VC, and FEC, and a combination of EC, PC, VC, and DFEC are preferred. Among the above combinations, a combination of EC and VC, a combination of EC and FEC, a combination of PC and FEC, a combination of EC, PC and VC, a combination of EC, PC and FEC, a combination of EC, VC and FEC, a combination of EC and More preferably, one or more types selected from the group consisting of a combination of VC and EEC, a combination of EC, EEC, and FEC, a combination of PC, VC, and FEC, and a combination of EC, PC, VC, and FEC are more preferable.

(chain ester)
As the chain ester, one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate, methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), and diethyl carbonate (DEC) can be used. ), dipropyl carbonate, and dibutyl carbonate, one or more symmetrical chain carbonates selected from the group consisting of dipropyl carbonate, pivalate esters such as methyl pivalate, ethyl pivalate, and propyl pivalate, methyl propionate, and propionic acid. Preferred examples include one or more chain carboxylic acid esters selected from the group consisting of ethyl, propyl propionate, methyl acetate, and ethyl acetate.

Among the chain esters, methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), A chain ester having a methyl group selected from the group consisting of methyl propyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate, and ethyl acetate is preferred, and a chain carbonate having a methyl group is particularly preferred.

The content of the chain ester in the nonaqueous solvent used in the nonaqueous electrolyte of the present invention is not particularly limited, but it is preferably used in a range of 5 to 90% by mass based on the total amount of the nonaqueous electrolyte. If the content is 5% by mass or more, the viscosity of the nonaqueous electrolyte will not become too high, and it is more preferably 10% by mass or more, still more preferably 30% by mass or more, and even more preferably 50% by mass or more. It is. Further, if it is 90% by mass or less, there is little risk that the electrical conductivity of the non-aqueous electrolyte will decrease and the high-temperature charge storage characteristics will deteriorate, so it is preferably within the above range.

The ratio of cyclic carbonate to chain ester is preferably 10:90 to 50:50, and 30:70 to 40:60, from the viewpoint of improving electrochemical properties at high temperatures. is even more preferable.

(Other non-aqueous solvents)
In the non-aqueous electrolyte of the present invention, other non-aqueous solvents other than those mentioned above can be used.
Other non-aqueous solvents include cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane; Preferred examples include one or more selected from the group consisting of ethers, amides such as dimethylformamide, sulfones such as sulfolane, and lactones such as γ-butyrolactone (GBL), γ-valerolactone, and α-angelicalactone. It will be done.

The other non-aqueous solvents mentioned above are usually used in combination in order to achieve appropriate physical properties. Preferred examples of the combination include a combination of a cyclic carbonate, a chain ester, and a lactone, or a combination of a cyclic carbonate, a chain ester, and an ether, and more preferably a combination of a cyclic carbonate, a chain ester, and a lactone. Among the lactones, it is more preferable to use γ-butyrolactone (GBL).

The content of other nonaqueous solvents is usually preferably 1% by mass or more, more preferably 2% by mass or more, and usually 40% by mass or less, more preferably 30% by mass or more, based on the total amount of the nonaqueous electrolyte. It is not more than 20% by mass, more preferably not more than 20% by mass. If the concentration is within this range, there is little risk that the electrical conductivity will decrease or that the high temperature charge storage characteristics will decrease due to decomposition of the solvent.

(Other additives)
It is preferable to further add other additives to the non-aqueous electrolyte in order to further improve the high-temperature charge storage characteristics and suppress gas generation.
Specific examples of other additives include the following compounds (A) to (J).

(A) One or more nitriles selected from acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, and sebaconitrile.

(B) Aromatic compounds having a branched alkyl group such as cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, or 1-fluoro-4-tert-butylbenzene, biphenyl, terphenyl (o-, m- , p-isomer), fluorobenzene, methylphenyl carbonate, ethylphenyl carbonate, or diphenyl carbonate.

(C) selected from methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate one or more isocyanate compounds.

(D) 2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-(methanesulfonyloxy)propionic acid 2- One or more triple bond-containing compounds selected from propynyl, di(2-propynyl) oxalate, 2-butyne-1,4-diyl dimethanesulfonate, and 2-butyne-1,4-diyl diformate.

(E) 1,3-propanesultone, 1,3-butanesultone, 2,4-butanesultone, 1,4-butanesultone, 1,3-propenesultone, 2,2-dioxide-1,2-oxathiolan-4-yl Sultones such as acetate, cyclic sulfites such as ethylene sulfite, cyclic sulfates such as ethylene sulfate, sulfones such as butane-2,3-diyl dimethane sulfonate, butane-1,4-diyl dimethane sulfonate, methylenemethane disulfonate, etc. One or more S=O group-containing compounds selected from acid esters and vinylsulfone compounds such as divinylsulfone, 1,2-bis(vinylsulfonyl)ethane, and bis(2-vinylsulfonylethyl)ether.

(F) The type of cyclic acetal compound is not particularly limited as long as it is a compound having an "acetal group" in the molecule. Specific examples include cyclic acetal compounds such as 1,3-dioxolane, 1,3-dioxane, or 1,3,5-trioxane.

(G) Trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, ethyl 2-(diethoxyphosphoryl) acetate, and 2-propynyl 2-(diethoxyphosphoryl) ) One or more phosphorus-containing compounds selected from acetate.

The type of carboxylic anhydride (H) is not particularly limited as long as it is a compound having a "C(=O)--O--C(=O) group" in the molecule. Specific examples include chain carboxylic anhydrides such as acetic anhydride and propionic anhydride, succinic anhydride, maleic anhydride, 3-allyl succinic anhydride, glutaric anhydride, itaconic anhydride, and 3-sulfo- Cyclic acid anhydrides such as propionic anhydride.

(J) The type of phosphazene compound is not particularly limited as long as it has an "N=PN group" in the molecule. Specific examples include cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, or ethoxyheptafluorocyclotetraphosphazene.

Among the above, it is preferable to contain at least one selected from the group consisting of (A) nitrile, (B) aromatic compound, and (C) isocyanate compound because the electrochemical properties at high temperatures are further improved.

Among the nitriles (A), one or more selected from the group consisting of succinonitrile, glutaronitrile, adiponitrile, and pimelonitrile are more preferred.

(B) Among the aromatic compounds, one selected from the group consisting of biphenyl, terphenyl (o-, m-, p-form), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-amylbenzene. Or two or more types are more preferable, and one or more types selected from the group consisting of biphenyl, o-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene are even more preferable.

Among the isocyanate compounds (C), one or more compounds selected from the group consisting of hexamethylene diisocyanate, octamethylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate are more preferred.

The content of the compounds (A) to (C) is preferably 0.01 to 7% by mass based on the total amount of the nonaqueous electrolyte. Within this range, the film is sufficiently formed without becoming too thick, the high temperature charge storage characteristics can be improved, and gas generation can be suppressed. The content is more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and more preferably the upper limit is 5% by mass or less based on the total amount of the nonaqueous electrolyte. , more preferably 3% by mass or less.

Further, (D) a triple bond-containing compound, (E) a cyclic or chain S=O group-containing compound selected from the group consisting of sultone, cyclic sulfite, sulfonic acid ester, and vinyl sulfone, (F) a cyclic acetal compound, It is preferable to include (G) a phosphorus-containing compound, (H) a cyclic acid anhydride, and (J) a cyclic phosphazene compound because the high-temperature charge storage characteristics can be improved and gas generation can be suppressed.

(D) Triple bond-containing compounds include 2-propynyl methyl carbonate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl) oxalate, and 2-butyne-1 , 4-diyl dimethane sulfonate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl) oxalate, and 2-butyne-1. , 4-diyl dimethane sulfonate, or more preferably one or more selected from the group consisting of , 4-diyl dimethane sulfonate.

(E) A cyclic or chain S=O group-containing compound selected from the group consisting of sultone, cyclic sulfite, cyclic sulfate, sulfonic acid ester, and vinyl sulfone (provided that triple bond-containing compounds and any of the above general formulas) It is preferable to use compounds (excluding the specific compounds represented by the above).

Examples of the cyclic S=O group-containing compound include 1,3-propanesultone, 1,3-butanesultone, 1,4-butanesultone, 2,4-butanesultone, 1,3-propenesultone, 2,2-dioxide- Preferred examples include one or more selected from the group consisting of 1,2-oxathiolan-4-yl acetate, methylene methanedisulfonate, ethylene sulfite, and ethylene sulfate.

In addition, as the chain S=O group-containing compound, butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, dimethyl methanedisulfonate, pentafluorophenyl methanesulfonate, divinylsulfone, and bis(2-vinylsulfonylethyl) ether.

Among the cyclic or chain S=O group-containing compounds, 1,3-propanesultone, 1,4-butanesultone, 2,4-butanesultone, 2,2-dioxide-1,2-oxathiolan-4-yl acetate More preferred are one or more selected from the group consisting of , ethylene sulfate, pentafluorophenyl methanesulfonate, and divinyl sulfone.

(F) As the cyclic acetal compound, one or more selected from 1,3-dioxolane and 1,3-dioxane are preferred, and 1,3-dioxane is more preferred.

(G) As the phosphorus-containing compound, one or more selected from ethyl 2-(diethoxyphosphoryl) acetate and 2-propynyl 2-(diethoxyphosphoryl) acetate is preferred, and 2-propynyl 2-(diethoxyphosphoryl) acetate is preferred. Acetate is more preferred.

(H) The cyclic acid anhydride is preferably one or more selected from succinic anhydride, maleic anhydride, and 3-allyl succinic anhydride, and one or more selected from succinic anhydride and 3-allyl succinic anhydride. is more preferable.

(J) As the cyclic phosphazene compound, one or more cyclic phosphazene compounds selected from methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and phenoxypentafluorocyclotriphosphazene are preferred, and methoxypentafluorocyclotriphosphazene and More preferably, one or more selected from ethoxypentafluorocyclotriphosphazene.

The content of each of the compounds (D) to (J) is preferably 0.001 to 5% by mass based on the total amount of the nonaqueous electrolyte. Within this range, the film is sufficiently formed without becoming too thick, the high temperature charge storage characteristics can be further improved, and gas generation can be suppressed. The content is more preferably 0.01% by mass or more based on the total amount of the non-aqueous electrolyte, even more preferably 0.1% by mass or more, and the upper limit is 3% by mass based on the total amount of the non-aqueous electrolyte. % or less, more preferably 2% by mass or less.

In addition, in order to further improve the electrochemical properties at high temperatures, a lithium salt (I) having an oxalic acid structure, a lithium salt (II) having a phosphoric acid structure, and an S=O group were added to the nonaqueous electrolyte. It is preferable to include one or more lithium salts selected from among the lithium salts (III).
Specific examples of the lithium salts include lithium bis(oxalato)borate [LiBOB], lithium difluoro(oxalato)borate [LiDFOB], lithium tetrafluoro(oxalato)phosphate [LiTFOP], and lithium difluorobis(oxalato)phosphate [LiDFOP]. ] Lithium salt (I) having at least one oxalic acid structure selected from the group consisting of; lithium salt (II) having a phosphoric acid structure such as LiPO ₂ F ₂ and Li ₂ PO ₃ F; lithium trifluoro (( Methanesulfonyl)oxy)borate [LiTFMSB], Lithium pentafluoro((methanesulfonyl)oxy)phosphate [LiPFMSP], Lithium methylsulfate [LMS], Lithium ethylsulfate [LES], Lithium 2,2,2-trifluoroethylsulfate Lithium salts (III) having one or more S=O groups selected from the group consisting of [LFES] and FSO ₃ Li are preferably mentioned, including LiBOB, LiDFOB, LiTFOP, LiDFOP, LiPO ₂ F ₂ , LiTFMSB, More preferably, it contains a lithium salt selected from the group consisting of LMS, LES, LFES, and FSO ₃ Li.

The proportion of each of the lithium salts in the nonaqueous electrolyte is preferably 0.01% by mass or more and 8% by mass or less based on the total amount of the nonaqueous electrolyte. Within this range, the high temperature charge storage characteristics can be further improved and gas generation can be suppressed. Preferably, it is 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.4% by mass or more, based on the total amount of the nonaqueous electrolyte. The upper limit thereof is preferably 6% by mass or less, more preferably 3% by mass or less based on the total amount of the nonaqueous electrolyte.

(electrolyte salt)
The electrolyte salt used in the present invention is one or more lithium salts selected from inorganic lithium salts, lithium salts containing a fluorinated alkyl group, lithium imide salts having a fluorine atom, and lithium salts having an oxalic acid structure. are preferably mentioned.
Examples of the inorganic lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , and the like.
Lithium salts containing a fluorinated alkyl group include LiCF ₃ SO ₃ , LiC(SO ₂ CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso-C ₃ F ₇ ), and other lithium salts containing a chain fluorinated alkyl group.
As the lithium imide salt having a fluorine atom, a chain having a fluorine atom such as LiN(SO ₂ F) ₂ [LiFSI], LiN(SO ₂ CF ₃ ) ₂ [LiTFSI], LiN(SO ₂ C ₂ F ₅ ) ₂ , etc. Lithium imide salts having a cyclic fluorinated alkylene chain such as (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi, etc. may be mentioned.
The lithium salt having an oxalic acid structure is preferably one or more selected from the group consisting of LiBOB, LiDFOB, LiTFOP, and LiDFOP, and lithium bis(oxalato)borate [LiBOB] is more preferable.
The above lithium salts can be used alone or in combination of two or more.

Among these, one or more inorganic lithium salts selected from LiPF ₆ , LiBF ₄ etc., LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ and LiN(SO ₂ F ) ₂ [LiFSI] A lithium imide salt having one or more fluorine atoms is preferable, and it is preferable to use at least LiPF ₆ .
A suitable combination of these electrolyte salts includes LiPF ₆ and at least one lithium selected from LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ , and LiN(SO ₂ F) ₂ [LiFSI]. It is preferable that the salt is contained in the non-aqueous electrolyte, and it is more preferable to use both LiPF ₆ and LiFSI together.

The respective concentrations and total concentration of the electrolyte salts are generally preferably 4% by mass or more, more preferably 9% by mass or more, and even more preferably 13% by mass or more, based on the total amount of the nonaqueous electrolyte. Further, the upper limit thereof is preferably 28% by mass or less, more preferably 23% by mass or less, and even more preferably 20% by mass or less based on the total amount of the nonaqueous electrolyte.
When the respective concentrations and the total concentration of lithium salts other than LiPF ₆ in the total amount of the non-aqueous electrolyte are 0.01% by mass or more, the high-temperature charge storage characteristics are improved, and the gas generation suppressing effect is also enhanced. It is preferable that the amount is 15% by mass or less, preferably 10% by mass or less, based on the total amount of the non-aqueous electrolyte, since there is little concern that the high temperature charge storage characteristics will deteriorate. The content of lithium salts other than LiPF ₆ is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.46% by mass or more, and most preferably 0.1% by mass or more, based on the total amount of the nonaqueous electrolyte. The upper limit thereof is preferably 13% by mass or less, more preferably 11% by mass or less, still more preferably 9% by mass or less, and most preferably 6% by mass or less.

[Manufacture of non-aqueous electrolyte]
The non-aqueous electrolyte of the present invention can be produced, for example, by mixing the above-mentioned non-aqueous solvent and adding the above-mentioned electrolyte salt and the compound represented by the general formula (I) to the non-aqueous electrolyte. Obtainable.
At this time, it is preferable that the compounds added to the non-aqueous solvent and non-aqueous electrolyte be purified in advance and contain as few impurities as possible within a range that does not significantly reduce productivity.

The non-aqueous electrolyte of the present invention can be used in the following first to fourth electricity storage devices, and as the non-aqueous electrolyte, not only liquid ones but also gelled ones can be used. Furthermore, the non-aqueous electrolyte of the present invention can also be used as a solid polymer electrolyte. Among them, it is preferable to use it for the first electricity storage device (i.e., for lithium batteries) or the fourth electricity storage device (i.e., for lithium ion capacitors) that uses lithium salt as the electrolyte salt, and it is preferable to use it for lithium batteries. More preferably, it is most suitable for use in lithium secondary batteries.

<Electricity storage device>
The electricity storage device of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte in which an electrolyte salt is dissolved in a nonaqueous solvent, and the nonaqueous electrolyte is represented by the general formula (I). It is characterized by containing a zwitterion.

[First electricity storage device (lithium battery)]
In this specification, a lithium battery is a general term for a lithium primary battery and a lithium secondary battery. Furthermore, in this specification, the term lithium secondary battery is used as a concept that also includes so-called lithium ion secondary batteries.
A lithium battery, which is a first power storage device according to the present invention, includes a positive electrode, a negative electrode, and the non-aqueous electrolyte in which an electrolyte salt is dissolved in the non-aqueous solvent. Components other than the nonaqueous electrolyte, such as a positive electrode and a negative electrode, can be used without particular restriction.

(Cathode active material)
For example, as a positive electrode active material for a lithium secondary battery, a composite metal oxide containing lithium and one or more selected from the group consisting of cobalt, manganese, and nickel is used. These positive electrode active materials can be used alone or in combination of two or more.
Examples of such lithium composite metal oxides include LiCoO ₂ , LiCo _1-x M _x O ₂ (where M is Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and One or more elements selected from the group consisting of Cu, 0.001≦x≦0.05), LiMn ₂ O ₄ , LiMn _1.5 Ni _0.5 O _{4 ,} LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01<x<1), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _0.8 Mn _{0 .1} Solid solution of Co _0.1 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , Li ₂ MnO ₃ and LiMO ₂ (M is a transition metal such as Co, Ni, Mn, Fe, etc.) , and LiNi _1/2 Mn _3/2 O ₄ , and two or more kinds are more preferred. Further, they may be used in combination, such as LiCoO ₂ and LiMn ₂ O ₄ , LiCoO ₂ and LiNiO ₂ , and LiMn ₂ O ₄ and LiNiO ₂ .

When a lithium composite metal oxide containing manganese is used as a positive electrode active material, the amount of metal eluted during charging generally increases, and the high-temperature charge storage characteristics tend to deteriorate more easily. However, the lithium secondary battery according to the present invention In this case, deterioration of these electrochemical properties can be particularly suppressed. There is no particular limitation as long as it is a lithium composite metal oxide containing manganese, but preferably a manganese lithium composite metal oxide having a spinel type structure, more preferably a spinel type lithium manganate, to better suppress deterioration of electrochemical properties. do. Specific positive electrode active materials of manganese lithium composite metal oxides include, for example, LiMn ₂ O ₄ , LiMn _1.5 Ni _0.5 O _{4 ,} LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.5 Preferred examples include one or more selected from the group consisting of Mn _0.3 Co _0.2 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O _{2 ,} etc., and particularly LiMn _{1.0 with a spinel structure. 5} Ni _0.5 O _{4 and} LiMn ₂ O ₄ are preferably used.
Further, a part of the manganese sites of the positive electrode active material may be substituted with multiple elements, and other elements that replace the manganese sites include, for example, Sn, Ni, Mg, Fe, Ti, Al, Zr, Cr, Examples include V, Ga, Zn, Co, and Li.

Furthermore, a lithium-containing olivine-type phosphate can also be used as the positive electrode active material. Particularly preferred is a lithium-containing olivine-type phosphate containing at least one selected from iron, cobalt, nickel, and manganese. Specific examples include LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ and the like.
A part of these lithium-containing olivine-type phosphates may be substituted with other elements, and a part of iron, cobalt, nickel, and manganese may be replaced with Co, Mn, Ni, Mg, Al, B, Ti, V, and Nb. , Cu, Zn, Mo, Ca, Sr, W, Zr, etc., or may be coated with a compound or carbon material containing these other elements. You can also do it. Among these, LiFePO ₄ or LiMnPO ₄ is preferred, and LiMnPO ₄ is more preferred.
Moreover, the lithium-containing olivine-type phosphate can also be used, for example, in mixture with the above-mentioned positive electrode active material.

In addition, positive electrode active materials for lithium primary batteries include CuO, Cu ₂ O, Ag ₂ O, Ag ₂ CrO ₄ , CuS, CuSO ₄ , TiO 2 , TiS ₂ , SiO _{2 ,} SnO, V ₂ O ₅ , V _{6 O12} , _VOx , _{Nb2O5 ,} Bi2O3 _{, Bi2Pb2O5 , Sb2O3} , _{CrO3 , Cr2O3} , _{MoO3 , WO3 , SeO2} , _{MnO2 , Mn2 Oxide} or chalcogen compound of one or more metal elements selected from the group consisting of O 3 , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO, etc., SO Examples include sulfur compounds such as ₂ , SOCl ₂ , and fluorinated carbon (fluorinated graphite) represented by the general formula (CF _x ) _n . Among these, MnO ₂ , V ₂ O ₅ , fluorinated graphite, etc. are preferable.

The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not undergo chemical changes. Examples include graphite such as natural graphite (scaly graphite, etc.), artificial graphite, and carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black. Further, graphite and carbon black may be mixed and used as appropriate. The amount of the conductive agent added to the positive electrode mixture is preferably 1 to 10% by mass, more preferably 2 to 5% by mass.

The positive electrode is made of the above-mentioned positive electrode active material, a conductive agent such as acetylene black or carbon black, and polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), or acrylonitrile and butadiene. Mix with a binder such as a copolymer (NBR), carboxymethyl cellulose (CMC), or ethylene propylene diene terpolymer, add a high boiling point solvent such as 1-methyl-2-pyrrolidone, and knead to form a positive electrode mixture. After that, this positive electrode mixture was applied to a current collector such as aluminum foil or stainless steel lath plate, dried and pressure molded, and then vacuumed at a temperature of about 50°C to 250°C for about 2 hours. It can be produced by heat treatment.
The density of the part of the positive electrode excluding the current collector is usually 1.5 g/cm ³ or more, and in order to further increase the battery capacity, it is preferably 2 g/cm ³ or more, more preferably 3 g/cm ³ or more, even more preferably is 3.6 g/cm ³ or more. Note that the upper limit is preferably 4 g/cm ³ or less.

(Negative electrode active material)
As negative electrode active materials for lithium secondary batteries, lithium metal, lithium alloys, and carbon materials capable of intercalating and deintercalating lithium ions [easily graphitizable carbon, and (002) plane spacing of 0.37 nm ( Non-graphitizable carbon of nanometer size or more, graphite with a (002) plane spacing of 0.34 nm or less], tin (single substance), tin compound, silicon (single substance), silicon compound (SiOx: x<2), Silicon alloy (Si-M alloy: M is at least one selected from the group consisting of Al, Ni, Cu, Fe, Ti, and Mn), metal compounds, etc. may be used alone or in combination of two or more. I can do it.
Among these, highly crystalline carbon materials and metal compounds such as artificial graphite and natural graphite are preferably used in terms of their ability to absorb and release lithium ions.

As the highly crystalline carbon material, a carbon material having a graphite-type crystal structure in which the spacing (d ₀₀₂ ) of the lattice plane (002) is 0.340 nm or less, particularly 0.335 to 0.337 nm is preferable.
Repeatedly applying mechanical effects such as compressive force, frictional force, and shearing force to artificial graphite particles having a block structure in which a plurality of flat graphite fine particles are aggregated or combined nonparallelly to each other, or for example, to scaly natural graphite particles, Obtained from X-ray diffraction measurements of the negative electrode sheet when the negative electrode sheet is pressure-molded to a density of 1.5 g/cm3 ^or higher by using graphite particles subjected to spheroidization treatment, excluding the current collector. When the ratio I(110)/I(004) of the peak intensity I(110) of the (110) plane of the graphite crystal to the peak intensity I(004) of the (004) plane becomes 0.01 or more, the amount of light from the positive electrode active material increases. It is preferable because it improves the amount of metal eluted and the charge storage characteristics, more preferably 0.05 or more, and even more preferably 0.1 or more. In addition, excessive treatment may reduce crystallinity and reduce the discharge capacity of the battery, so the upper limit of I(110)/I(004) is preferably 0.5 or less, and more preferably 0.3 or less. preferable.
Further, it is preferable that the highly crystalline carbon material (core material) is coated with a carbon material that is lower in crystallinity than the core material because the high temperature charge storage characteristics will be even better. The crystallinity of the coating carbon material can be confirmed using a transmission electron microscope (TEM).
When a highly crystalline carbon material is used, it generally reacts with a non-aqueous electrolyte during charging and tends to reduce high-temperature charge storage characteristics due to an increase in interfacial resistance. However, the lithium secondary battery according to the present invention In this case, the high-temperature charge storage characteristics are good.

Metal compounds capable of intercalating and deintercalating lithium ions as negative electrode active materials include Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Examples include compounds containing at least one metal element such as Cu, Zn, Ag, Mg, Sr, and Ba. These metal compounds may be used in any form, such as a simple substance, an alloy, an oxide, a nitride, a sulfide, a boride, or an alloy with lithium. This is preferable because it can increase the capacity. Among these, those containing at least one element selected from Si, Ge, and Sn are preferable, and those containing at least one element selected from Si and Sn are particularly preferable because they can increase the capacity of the battery.

Further, a titanium composite metal oxide containing titanium atoms capable of intercalating and deintercalating lithium ions as a negative electrode active material can be mentioned. These titanium composite metal oxides have small expansion and contraction during charging and discharging and are flame retardant, so they are preferable in terms of improving battery safety.
Examples of the titanium composite metal oxide include one or more selected from lithium titanium composite oxide and niobium titanium composite oxide.
As the lithium titanium composite oxide, a lithium titanium composite oxide having a spinel crystal structure represented by the general formula Li ₄ Ti _5-x M _x O ₁₂ is preferable. Here, M is an element substituted at the Ti site, and is at least one element selected from Mn, Fe, V, and Nb.
Examples of the niobium titanium composite oxide include TiNb ₂ O ₇ , Ti ₂ Nb ₁₀ O ₂₉ , TiNb ₁₄ O ₃₇ , and TiNb ₂₄ O ₆₂ , with TiNb ₂ O ₇ being preferred.
Among titanium composite metal oxides, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) is preferred from the viewpoint of improving battery characteristics.

The negative electrode is made by kneading the same conductive agent, binder, and high boiling point solvent as in the preparation of the positive electrode to form a negative electrode mixture, and then applying this negative electrode mixture to a current collector such as copper foil. It can be produced by drying, pressure molding, and then heating under vacuum at a temperature of about 50° C. to 250° C. for about 2 hours.
The density of the part of the negative electrode excluding the current collector is usually 1.1 g/cm ³ or more, and in order to further increase the battery capacity, it is preferably 1.5 g/cm ³ or more, more preferably 1.7 g/cm 3 or more. cm ³ or more. Note that the upper limit is preferably 2 g/cm ³ or less.

To summarize the above, when using triethyl(sulfopropyl)ammonium or (tributylphosphonio)propylsulfonate as the zwitterion, spinel-type lithium manganate (LiMn ₂ O ₄ ) is used as the positive electrode active material, and the negative electrode active material is Preference is given to using a titanium composite metal oxide, especially Li ₄ Ti ₅ O ₁₂ , as the substance.
When using a compound represented by the general formula (IV), (VIII), (XI) or (XII) as the zwitterion, the positive electrode active material is preferably a lithium composite metal oxide containing manganese. , a manganese-lithium composite metal oxide having a spinel-type structure is more preferable, a spinel-type lithium manganate (LiMn ₂ O ₄ ) is even more preferable, and as the negative electrode active material, a carbon material capable of inserting and releasing lithium, It is preferable to use one or more selected from the group consisting of and titanium composite metal oxides.
When using a compound represented by the general formula (VII) or (VII-1) as the zwitterion, the positive electrode active material is preferably a manganese-lithium composite metal oxide having a spinel structure, and a spinel-type manganese Lithium oxide is more preferable, and as the negative electrode active material, it is preferable to use a carbon material capable of intercalating and deintercalating lithium.

Furthermore, examples of the negative electrode active material for lithium primary batteries include lithium metal or lithium alloy.

There is no particular limitation on the structure of the lithium battery, and coin-type batteries, cylindrical batteries, square batteries, laminate batteries, etc. having a single-layer or multi-layer separator can be applied.
As the battery separator, although not particularly limited, single-layer or laminated microporous films, woven fabrics, non-woven fabrics, etc. of polyolefins such as polypropylene and polyethylene can be used.

The lithium secondary battery of the present invention has excellent high-temperature charge storage characteristics even when the end-of-charge voltage is 4.2V or higher, particularly 4.3V or higher, and also has good characteristics even at 4.4V or higher. The discharge end voltage can normally be 2.8V or more, and even 2.5V or more, but the lithium secondary battery in the present invention can have a discharge end voltage of 2.0V or more. The current value is not particularly limited, but is usually used in the range of 0.1 to 30C. Furthermore, the lithium battery of the present invention can be charged and discharged at -40 to 100°C, preferably -10 to 80°C.

In the present invention, as a measure against an increase in the internal pressure of a lithium battery, it is also possible to provide a safety valve on the battery lid or to make a cut in a member such as a battery can or gasket. Further, as a safety measure to prevent overcharging, a current cutoff mechanism that senses the internal pressure of the battery and cuts off the current can be provided on the battery cover.

[Second electricity storage device (electric double layer capacitor)]
A second electricity storage device according to the present invention is an electricity storage device that contains the non-aqueous electrolyte of the invention and stores energy using the electric double layer capacity at the interface between the electrolyte and the electrode. An example of the present invention is an electric double layer capacitor. The most typical electrode active material used in this electricity storage device is activated carbon. The electric double layer capacity increases approximately in proportion to the surface area.

[Third electricity storage device]
A third electricity storage device according to the present invention is an electricity storage device that contains the non-aqueous electrolyte of the invention and stores energy using doping/dedoping reactions of electrodes. Examples of electrode active materials used in this electricity storage device include metal oxides such as ruthenium oxide, iridium oxide, tungsten oxide, molybdenum oxide, and copper oxide, and π-conjugated polymers such as polyacene and polythiophene derivatives. Capacitors using these electrode active materials are capable of storing energy associated with doping/undoping reactions of the electrodes.

[Fourth electricity storage device (lithium ion capacitor)]
A fourth electricity storage device according to the present invention is an electricity storage device that contains the non-aqueous electrolyte of the invention and stores energy using intercalation of lithium ions into a carbon material such as graphite that is a negative electrode. It is called a lithium ion capacitor (LIC). Examples of the positive electrode include those that utilize an electrical double layer between an activated carbon electrode and an electrolyte, and those that utilize a doping/dedoping reaction of a π-conjugated polymer electrode. The electrolyte contains at least a lithium salt such as _LiPF6 .

[Preparation of lithium ion secondary battery 1]
(1) Preparation of Nonaqueous Electrolyte 1 Each solvent and electrolyte salt were mixed in predetermined amounts to prepare the reference electrolytes shown in Tables 1 and 2. The unit M of the concentration of the electrolyte salt described in Tables 1 and 2 indicates mol/L.
The composition of the standard electrolyte is 29.8% by mass of ethylene carbonate (EC), 53.4% by mass of methyl ethyl carbonate (MEC) [EC/MEC=3/7 by volume], and 1% by mass of vinylene carbonate (VC). .0% by mass, LiPF ₆ is 8.4% by mass (0.7M), and LiN(SO ₂ F) ₂ (LiFSI) is 7.4% by mass (0.5M).
In Example 1, 0.5% by mass of 2-(triethylammonio)ethyl sulfate (compound of structural formula 4) was added as a zwitterion to the reference electrolytic solution, stirred for 12 hours or more, and then 0.5% by mass was added as a zwitterion. A non-aqueous electrolyte was prepared by filtration using a 45 μm membrane filter.
In Reference Example 2, 0.43% by mass of 2-dodecyldimethyl(carboxylatomethyl)ammonium was added as a zwitterion to the reference electrolytic solution, and after stirring for 12 hours or more, a 0.45 μm membrane filter was used. and filtered to prepare non-aqueous electrolyte 1.
The contents listed in Tables 1 and 2 are values obtained by analyzing the electrolyte solution prepared above using high performance liquid chromatography.

(2) Preparation of Battery 1 90% by mass of LiMn ₂ O ₄ (positive electrode active material) and 6% by mass of acetylene black were mixed, and 4% by mass of polyvinylidene fluoride (binder) was added to 1-methyl-2-pyrrolidone in advance. It was added to the dissolved solution and mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried, and subjected to pressure treatment and cut into a predetermined size to produce a rectangular positive electrode sheet.
In addition, 98% by mass of natural graphite (negative electrode active material), 1% by mass of carboxymethyl cellulose (thickener), and 1% by mass of styrene-butadiene rubber (binder) were added to a solution dissolved in water and mixed. , a negative electrode mixture paste was prepared. This negative electrode mixture paste was applied to one side of a copper foil (current collector), dried, and subjected to pressure treatment and cut into a predetermined size to produce a negative electrode sheet. Then, the positive electrode sheet, the microporous polyethylene film separator, and the negative electrode sheet were laminated in this order, and the nonaqueous electrolyte prepared in (1) above was added to produce the laminate type battery 1 shown in Tables 1 and 2.

[Preparation of lithium ion secondary battery 2]
(1) Preparation of Nonaqueous Electrolyte 2 Each solvent and electrolyte salt were mixed in fixed amounts to prepare the reference electrolyte shown in Table 3.
The composition shown in mass ratio of the standard electrolyte is 32.2% by mass of propylene carbonate (PC), 52.0% by mass of diethyl carbonate (DEC) [PC/DEC=1/2 by volume], and LiPF ₆ . The content is 15.8% by mass (1.3M).
Add 0.5% by mass of triethyl (sulfopropyl) ammonium as a zwitterion to the standard electrolyte solution, stir for 12 hours or more, and then filter using a 0.45 μm membrane filter to obtain a non-aqueous electrolyte solution. 2 was prepared.

(2) Preparation of Battery 2 Mix 90% by mass of LiMn ₂ O ₄ (positive electrode active material) and 6% by mass of acetylene black, and add 4% by mass of polyvinylidene fluoride (binder) to 1-methyl-2-pyrrolidone in advance. It was added to the dissolved solution and mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried, and subjected to pressure treatment and cut into a predetermined size to produce a rectangular positive electrode sheet.
In addition, 95% by mass of lithium titanate (Li ₄ Ti ₅ O ₁₂ : negative electrode active material) and 2% by mass of a carbon-based conductive agent were mixed, and 3% by mass of polyvinylidene fluoride (binder) was preliminarily mixed with 1-methyl- A negative electrode mixture paste was prepared by adding the mixture to a solution dissolved in 2-pyrrolidone and mixing. This negative electrode mixture paste was applied to one side of an aluminum foil (current collector), dried, and subjected to pressure treatment and cut into a predetermined size to produce a negative electrode sheet. Then, the positive electrode sheet, the microporous polyethylene film separator, and the negative electrode sheet were laminated in this order, and the non-aqueous electrolyte prepared in (1) above was added to produce the laminate type battery 2 shown in Table 3.

[Evaluation of discharge capacity recovery rate, gas generation amount, and AC resistance after high temperature charging and storage]
Using the battery produced by the above method, charging and discharging were performed for 3 cycles at a constant current and constant voltage of 0.2C, a charge end voltage of 4.2V, and a discharge end voltage of 2.7V in a constant temperature bath at 45°C. In this specification, the period up to the three cycles of charging and discharging is defined as pretreatment. Charging was performed for 1 hour at a constant current value of 0.2C in a constant temperature bath at 45℃, and after leaving it for 20 days in a constant temperature bath at 60℃, the battery was charged at a constant current value of 0.2C in a constant temperature bath at 45℃. It was discharged to a voltage of 2.7V. In this specification, the process from charging at a constant current of 0.2C for 1 hour under the 45°C condition to standing at 60°C and discharging at 45°C is defined as a high temperature storage test in this specification. The discharge capacity recovery rate, gas generation amount, and AC resistance value after high temperature charging and storage are shown in Tables 1 and 2.
The discharge capacity recovery rate (%) was calculated using the following formula.
Discharge capacity recovery rate (%) = (Discharge capacity after high temperature storage test/Discharge capacity before high temperature storage test) x 100
The discharge capacity in the above formula means that the battery was charged and discharged at a constant current and voltage of 0.2C in a constant temperature bath at 45℃ before and after the high-temperature storage test, with an end-of-charge voltage of 4.2V and an end-of-discharge voltage of 2.7V. This is the discharge capacity at that time. The discharge capacity recovery rate (%) is an index indicating the degree of battery capacity reduction during high-temperature storage.
The amount of gas generated is a relative value when the amount of gas generated after the high temperature storage test was measured by the Archimedes method, and the amount of gas generated in Comparative Example 1 was set as 100%.
The AC resistance value is determined by measuring the resistance value of the real part of the AC impedance at 100 mHz in a thermostat at 0°C with a charging rate of 50% before and after the high temperature storage test, and taking the value measured in Comparative Example 1 as 100%. It is a relative value.

As is clear from Table 1, in Example 1 using the non-aqueous electrolyte of the present invention, the battery capacity decreased less during high-temperature storage than in Comparative Example 1, and as a result, the discharge capacity after high-temperature storage was It can be seen that the recovery rate is improved and the amount of gas generated and AC resistance can be suppressed.

As is clear from Table 2, in Reference Example 2 using the nonaqueous electrolyte of the present invention, the battery capacity decreased less during high temperature storage than in Comparative Example 1 and Comparative Example 2. It can be seen that the subsequent discharge capacity recovery rate can be improved.

As is clear from Table 3, in Example 3 using the non-aqueous electrolyte of the present invention, the decrease in battery capacity during high-temperature storage was smaller than in Comparative Example 3, and as a result, the discharge capacity after high-temperature storage was It can be seen that the recovery rate can be improved.

The power storage device using the non-aqueous electrolyte of the present invention can significantly improve high-temperature charge storage characteristics, and is therefore useful as a power storage device such as a lithium secondary battery with excellent electrochemical characteristics.

Claims (9)

A non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous electrolyte being characterized by containing a zwitterion represented by the following general formula (VIII) .

(In formula (VIII), Q ⁺ is a cationic group represented by the following formula (IX) or (X).
L ⁴ represents an alkylene group having 1 to 5 carbon atoms, a fluorinated alkylene group having 1 to 5 carbon atoms, an alkenylene group having 2 to 5 carbon atoms, or a fluorinated alkenylene group having 2 to 5 carbon atoms. )

(In formula (IX), R ¹⁶ to R ¹⁸ each independently represent an alkyl group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkenyl group having 2 to 5 carbon atoms. It represents a fluorinated alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 3 to 5 carbon atoms, or a fluorinated alkynyl group having 3 to 5 carbon atoms.
In formula (X), R ¹⁹ to R ²¹ each independently represent an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a fluorinated alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms. -5 fluorinated alkoxy group, alkenyl group with 2 to 5 carbon atoms, alkenyloxy group with 2 to 5 carbon atoms, fluorinated alkenyloxy group with 2 to 5 carbon atoms, alkynyl group with 3 to 5 carbon atoms, carbon number It represents an alkynyloxy group having 3 to 5 carbon atoms, a fluorinated alkynyl group having 3 to 5 carbon atoms, a fluorinated alkynyloxy group having 3 to 5 carbon atoms, a dimethylamino group, or a diethylamino group.
* indicates the binding site with ^L4 . ) The non-aqueous electrolyte according to claim 1 , wherein the zwitterion is one or more types selected from a compound represented by the following general formula (XI) and a compound represented by the following general formula (XII).

(L ⁵ in formula (XI) and L ⁶ in formula (XII) represent an alkylene group having 2 or 3 carbon atoms.
In formula (XI), R ¹⁶ to R ¹⁸ each independently represent an alkyl group having 1 to 3 carbon atoms.
In formula (XII), R ¹⁹ to R ²¹ each independently represent an alkyl group having 1 to 3 carbon atoms or a dimethylamino group. ) The non-aqueous electrolyte according to claim 1 or 2 , wherein the non-aqueous solvent contains a cyclic carbonate and a chain ester. A claim in which the nonaqueous electrolyte contains one or more lithium salts selected from an inorganic lithium salt, a lithium salt containing a fluorinated alkyl group, a lithium imide salt having a fluorine atom, and a lithium salt having an oxalic acid structure. The non-aqueous electrolyte according to any one of 1 to 3 . The nonaqueous electrolyte according to any one of claims 1 to 4 , wherein the nonaqueous electrolyte contains an inorganic lithium salt and a lithium imide salt having a fluorine atom. An electricity storage device comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous electrolyte being the nonaqueous electrolyte according to any one of claims 1 to 5. A power storage device characterized by : The electricity storage device according to claim 6 , wherein the active material of the positive electrode contains a lithium composite metal oxide. The active material of the positive electrode is a lithium composite metal oxide containing manganese,
8. The electricity storage device according to claim 6 , wherein the active material of the negative electrode is one or more selected from a carbon material capable of intercalating and deintercalating lithium, and a titanium composite metal oxide. The electricity storage device according to claim 8 , wherein the active material of the positive electrode is a manganese lithium composite metal oxide having a spinel structure, and the active material of the negative electrode is a titanium composite metal oxide.