JP2011040311A - Electrolyte for secondary battery, and lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for a secondary battery capable of showing excellent cycle characteristics, and a lithium ion secondary battery using the electrolyte for the secondary battery. <P>SOLUTION: The electrolyte for the secondary battery includes a compound, which is a compound having a frame expressed with -(O-C<SB>m</SB>)<SB>n</SB>-O-, having at least one electron attracting group selected from a group of a monovalent electron attracting group (A) combined with a carbon atom, an electron attracting group (B) formed together with two or more carbon atoms in the compound, an electron attracting group (C) wherein -CH<SB>2</SB>- in the compound is replaced, and a monovalent electron attracting group (D) combined with an oxygen atom in the compound. The lithium ion secondary battery uses the electrolyte for the secondary battery. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrolytic solution for a secondary battery and a lithium ion secondary battery.

  Since secondary batteries such as lithium secondary batteries and lithium ion secondary batteries use a flammable organic solvent as an electrolyte, there is a risk of ignition or rupture during battery runaway. Therefore, attempts have been made to make the electrolyte nonflammable by using specific hydrofluoroethers. However, electrolytes containing hydrofluoroethers do not have sufficient lithium salt solubility, or can easily separate into two phases when used in combination with a high dielectric constant solvent in order to increase the solubility of the lithium salt, and are nonflammable. Sometimes it was enough.

Therefore, an electrolytic solution containing a glyme-based solvent has been proposed as an electrolytic solution that ensures nonflammability more stably.
An electrolytic solution containing LiN (CF ₃ SO ₂ ) ₂ and a glyme solvent as a solvent (Patent Document 1).
An electrolytic solution containing LiBF ₄ and tetraglyme as a solvent (Patent Document 2).

On the other hand, lithium salts such as CF ₃ SO ₂ N (Li) SO ₂ CF ₃ and FSO ₂ N (Li) SO ₂ F form a stable 1: 1 by forming a strong interaction with ether oxygen of the glyme solvent. From the results of formation of a complex and thermal analysis, it has been reported that the complex behaves as a single ionic species and was not ignited by heating with a burner. (Non-Patent Documents 1 and 2).
Moreover, an organic electrolyte battery using an electrolyte mainly composed of tetraglyme and lithium borofluoride is shown (Patent Document 3).
Further, lithium and glyme type solvent, an alkyl (fluoroalkyl) ether, a cyclic _{carbonate, LiN (SO 2 (CF 2} ) c F) 2 ( However, c is the is an integer of 1-5.) Represented by An electrolyte containing a salt is disclosed (Patent Document 4).

JP 2004-87136 A Japanese Patent Laid-Open No. 2004-234983 JP 2001-273926 A JP 2001-93572 A

Proceedings of the 47th Battery Symposium 2006 1F06 Abstracts of the 75th Annual Meeting of the Electrochemical Society of Japan 3D09

  However, the present inventor has noticed that a secondary battery using a glyme-based solvent as an electrolytic solution has a problem that cycle characteristics are deteriorated as compared with a secondary battery not using a glyme-based solvent. An object of the present invention is to solve the problem and to provide an electrolyte solution for a secondary battery exhibiting excellent cycle characteristics and a lithium ion secondary battery using the electrolyte solution for the secondary battery.

In order to achieve the above object, the present invention employs the following configuration.
[1] An electrolytic solution for a secondary battery comprising a lithium salt and the following compound (1).
Compound (1): a monovalent electron-withdrawing group (A) in which a hydrogen atom bonded to a carbon atom of the compound (1H) represented by the following formula (1H) is substituted, two or more in the compound (1H) An electron-withdrawing group (B) formed with a carbon atom, an electron-withdrawing group (C) in which —CH ₂ — in the compound (1H) is substituted, and R ^H1 or R ^H2 in the compound (1H) are A compound having one or more electron-withdrawing groups selected from the group consisting of substituted monovalent electron-withdrawing groups (D).

However, the symbol in Formula (1H) shows the following meaning.
m: an integer of 1 to 4.
n: An integer of 2 to 10.
R ^H1 and R ^H2 : each independently an alkyl group having 1 to 8 carbon atoms or a group having one or more oxygen atoms inserted between carbon-carbon atoms of the alkyl group. Alternatively, R ^H1 and R ^H2 are linked to each other, and are an alkylene group having 1 to 5 carbon atoms, or a group in which one or more oxygen atoms are inserted between carbon-carbon atoms of the alkylene group.
[2] The electrolyte solution for a secondary battery according to [1], wherein the compound (1H) is a compound (1H-1) represented by the following formula (1H-1).

However, the symbol in Formula (1H-1) shows the following meaning.
n: Same as the compound (1H).
R ^H10 and R ^H20 : each independently an alkyl group having 1 to 8 carbon atoms or an alkylene group having 1 to 5 carbon atoms formed by linking each other.
[3] The electron withdrawing group (A) is a nitro group, a nitroso group, a cyano group, a monovalent aromatic group lacking π electrons, or a monovalent aromatic heterocyclic group lacking π electrons. The electrolytic solution for a secondary battery according to [1] or [2].
[4] The above [1] to [3], wherein the electron withdrawing group (B) is a divalent aromatic group lacking π electrons or a divalent aromatic heterocyclic group lacking π electrons. The electrolyte solution for secondary batteries in any one of.
[5] For the secondary battery according to any one of [1] to [4], wherein the electron-withdrawing group (C) is —C (═O) —, —SO ₂ — or —PO ₂ —. Electrolytic solution.
[6] a group in which the electron-withdrawing group (D) has —C (═O) —, —SO ₂ —, or —PO ₂ — at the bond end; a monovalent aromatic group lacking π electrons; and The electrolyte solution for secondary batteries according to any one of [1] to [5], which is a group selected from monovalent aromatic heterocyclic groups lacking π electrons.
[7] The lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , Li (C ₂ O ₄ ) ₂ , LiN (SO ₂ (CF ₂ ) _p F) ₂ (where p is an integer of 1 to 5) ), FSO ₂ N (Li) SO ₂ F, CF ₃ SO ₃ Li, and a compound represented by the following formula (2) (wherein q is an integer of 1 to 5). The electrolyte solution for secondary batteries according to any one of [1] to [6], wherein the electrolyte solution is one or more lithium salts selected from:

[8] The secondary battery according to any one of [1] to [7], wherein the content of the compound (1) is 0.2 to 8.0 times moles of the total amount of the lithium salt. Electrolyte.
[9] The electrolyte solution for a secondary battery according to any one of [1] to [8], including a hydrofluoroether.
[10] The electrolyte solution for a secondary battery according to any one of [1] to [9], including a carbonate solvent.
[11] The electrolyte solution for a secondary battery according to [10], wherein the amount of the carbonate-based solvent is 10% by volume or less when the total amount of the solvent in the electrolyte solution is 100% by volume.
[12] A material that can electrochemically occlude / release lithium ions or a negative electrode made of metallic lithium or a lithium alloy, a positive electrode made of a material that can electrochemically occlude / release lithium ions, and [1] to [11] A secondary battery electrolyte solution according to any one of the above.
[13] The lithium ion secondary battery according to [12], wherein the charging voltage is 3.4 V or higher (potential based on lithium metal).

The electrolyte solution for secondary batteries of the present invention exhibits excellent cycle characteristics by using an ether solvent into which a specific electron-withdrawing group is introduced as the electrolyte solution.
Moreover, this invention provides the lithium ion secondary battery using this electrolyte solution for secondary batteries.

In the present specification, a compound represented by the formula (1) is referred to as a compound (1). The same applies to compounds represented by other numbers.
[Electrolyte for secondary battery]
The electrolytic solution for a secondary battery of the present invention (hereinafter simply referred to as “electrolytic solution”) is an electrolytic solution containing a lithium salt and a compound (1) that dissolves the lithium salt. The electrolytic solution is preferably a non-aqueous electrolytic solution. The nonaqueous electrolytic solution includes a solvent and an electrolyte that are substantially free of water. Even if the solvent in the non-aqueous electrolyte contains water, the amount of water is such that the performance of the secondary battery using the non-aqueous electrolyte is not deteriorated. The amount of water contained in the non-aqueous electrolyte is preferably 0 to 500 ppm by mass, more preferably 0 to 100 ppm by mass, and 0 to 50 ppm by mass with respect to the total mass of the electrolyte. It is particularly preferred.

(Lithium salt)
The lithium salt in the present invention is an electrolyte that dissociates in an electrolytic solution and supplies lithium ions.
Lithium salt includes LiPF ₆ , LiBF ₄ , LiClO ₄ , Li (C ₂ O ₄ ) ₂ , Li (C ₂ O ₄ ) F ₂ , LiN (SO ₂ (CF ₂ ) _p F) ₂ (where p is indicates an integer of 1 to _{5.), FSO 2 N (Li} ) SO 2 F, CF 3 SO 3 Li and the following compound (2) (wherein, q is selected from the group consisting of indicating.) an integer from 1 to 5 1 type or more to be mentioned. These lithium salts are compounds known as lithium salts for lithium ion secondary batteries.
The lithium salt is preferably at least one selected from the group consisting of LiPF ₆ and compound (2) (where q represents an integer of 1 to 5).

  Examples of the compound (2) include the following compounds (2-1) to (2-5).

As the lithium salt, use of LiPF ₆ alone, use of one or more compounds (2), and combined use of LiPF ₆ and compound (2) are preferable. When LiPF ₆ and the compound (2) are used in combination, the molar ratio (Mb / Ma) between the molar amount (Ma) of LiPF ₆ and the molar amount (Mb) of the compound (2) increases the nonflammable electrolyte. From the point of being able to make conductivity and the point of being able to make a chemically stable electrolytic solution, (Mb / Ma) is preferably 0.01 to 10, and preferably 0.05 to 2.0. More preferred.
Examples of combinations with other lithium salts are 1 selected from the group consisting of LiPF ₆ and LiN (SO ₂ (CF ₂ ) _p F) ₂ , FSO ₂ N (Li) SO ₂ F and CF ₃ SO ₃ Li. The combined use with more than a seed is mentioned. In addition, LiBF ₄ or LiClO ₄ , Li (C ₂ O ₄ ) ₂ , LiN (SO ₂ (CF ₂ ) _p F) ₂ , FSO ₂ N (Li) SO ₂ F, CF ₃ SO ₃ Li and a compound (2 Examples of combinations with one or more selected from the group consisting of:
LiPF ₆ and _FSO 2 N (Li) moles of LiPF ₆ in the case of using the SO ₂ F (Ma) and the molar amount of _{FSO 2 N (Li) SO 2} F (Mc) and the molar ratio of (Mc / Ma) Is preferably (Mc / Ma) from 0.01 to 10 because the non-flammable electrolyte can be made highly conductive and can be made a chemically stable electrolyte. It is more preferable that it is 05-2.0.

As the compound (2), a compound (2-2) in which q is 2 is preferable from the viewpoint that an electrolytic solution having high conductivity is easily obtained.
As LiN (SO ₂ (CF ₂ ) _p F) ₂ , LiN (SO ₂ (CF ₃ ) ₂ (a compound in which p is 1), LiN (SO ₂ (C ₂ F ₅ ) ₂ (p is 2) Compound) is preferred.

  The lithium salt content in the electrolytic solution is preferably 0.1 to 3.0 mol / L, and preferably 0.5 to 2.0 mol / L, based on the total amount of solvent used in the electrolytic solution. Particularly preferred. When the content of the lithium salt is 0.1 mol / L or more, an electrolytic solution with high conductivity is easily obtained. Moreover, if content of lithium salt is 3.0 mol / L or less, it will be easy to dissolve lithium salt in the below-mentioned hydrofluoroether used in the compound (1) in electrolyte solution and as needed.

(Compound (1))
The compound (1) of the present invention is a compound in which a part of the following compound (1H) is substituted with electron-withdrawing groups (A) to (D) described later. Compound (1) is a compound that can improve cycle characteristics and oxidation resistance in a battery using the electrolytic solution of the present invention by having electron-withdrawing groups (A) to (D). In the electrolytic solution of the present invention, the compound (1) is considered that part or all of the compound forms a complex with a lithium salt and expresses the action of the present invention. In the formula, n is preferably 2 or more.

However, the symbol in a compound (1H) shows the following meaning.
m: an integer of 1 to 4.
n: An integer of 2 to 10.
R ^H1 and R ^H2 : each independently an alkyl group having 1 to 8 carbon atoms or a group having one or more oxygen atoms inserted between carbon-carbon atoms of the alkyl group. Alternatively, R ^H1 and R ^H2 are linked to each other, and are an alkylene group having 1 to 5 carbon atoms, or a group in which one or more oxygen atoms are inserted between carbon-carbon atoms of the alkylene group.

m is preferably 2 or 3, and 2 is particularly preferred.
n is preferably an integer of 2 to 6, more preferably an integer of 2 to 5, and particularly preferably an integer of 2 to 4.
In compound (1H), two or more (—O— (CH ₂ ) _m —) structures exist. In that case, the number of m in each (—O— (CH ₂ ) _m —) structure may be the same or different. Compound (1H) is preferably compound (1H) in which 2 to 6 (—O— (CH ₂ ) _m —) structures in which m is 1 and / or 2 are connected, and m is only 2 (IH), or, m is _{1 (-O- (CH 2) m} -) structure is one, and, m is _{2 (-O- (CH 2) m} -) structures 1 More preferably, it is ˜5 compounds (1H), and particularly preferred is compound (1H) wherein m is only 2.

Examples of the group formed by linking R ^H1 and R ^H2 include an alkylene group having 1 to 5 carbon atoms, or a group in which one or more oxygen atoms are inserted between carbon-carbon atoms of the alkylene group. , Methylene group, ethylene group, and triethylene group are particularly preferable.
R ^H1 and R ^H2 include an alkyl group having 1 to 3 carbon atoms, a group in which one or more oxygen atoms are inserted between carbon-carbon atoms of the alkyl group, or R ^H1 and R ^H2 are connected to each other. The methylene group, ethylene group and triethylene group formed are preferred. Further, these groups are preferably groups having no branching.

  As the compound (1H), the following compound (1H-1) is preferable.

However, the symbol in a compound (1H-1) shows the following meaning.
n: The same meaning as the compound (1H).
R ^H10 and R ^H20 : each independently an alkyl group having 1 to 8 carbon atoms or an alkylene group having 1 to 5 carbon atoms formed by linking each other (for example, a methylene group, an ethylene group, or a triethylene group is preferable. ).

(Compound (1-A))
Among the compounds (1), a compound having an electron withdrawing group (A) is a compound having a monovalent electron withdrawing group (A) substituted with a hydrogen atom bonded to a carbon atom of the compound (1H) ( Hereinafter, the compound (1) having the electron-withdrawing group (A) is referred to as “compound (1-A)”.
Examples of the monovalent electron withdrawing group (A) include a nitro group, a nitroso group, a cyano group, a monovalent aromatic group lacking π electrons, and a monovalent aromatic heterocyclic group lacking π electrons. And a nitro group, a cyano group, or a (2- or 3-) nitrofuryl group is preferred.
Here, the monovalent aromatic group lacking π electrons refers to a group having one or more electron-withdrawing groups that attract π electrons of the ring. Examples of the electron withdrawing group include the same group as the electron withdrawing group (A), the same group as Y ¹ described later, and the groups shown in the specific examples of the compound (1-A) and the compound (1-B). It is done. Examples of the aromatic ring lacking π electrons include a benzene ring to which one or more electron-withdrawing groups are bonded.
A monovalent aromatic heterocyclic group lacking π electrons is an aromatic group bonded with a group having a hetero atom (for example, a nitrogen atom) that attracts π electrons of the ring or an electron-withdrawing group that attracts π electrons. This refers to the group heterocyclic group.
Examples of the group having a hetero atom (for example, a nitrogen atom) that attracts π electrons of the ring include a pyridyl group, a pyrazyl group, a pyrimidyl group, and a pyridazyl group. One or more hydrogen atoms of these groups may be substituted, and the substituent may or may not be an electron-withdrawing group.
The monovalent aromatic heterocyclic group lacking π electrons is preferably an aromatic heterocyclic group having an electron-withdrawing group and an oxygen atom as a hetero atom. The electron withdrawing group is preferably a nitro group, and the aromatic heterocyclic ring is preferably a furyl group.

  The electron withdrawing group (A) is preferably a group having a property of attracting electrons from an oxygen atom in the compound (1-A). Therefore, the substitution position of the electron withdrawing group (A) is preferably bonded to a carbon atom adjacent to the oxygen atom. The number of electron-withdrawing groups (A) is preferably 1 or 2 in the compound (1-A).

  As the compound (1-A), the following compound (1-A1) is preferable.

However, in the compound (1-A1), n has the same meaning as described above. In R ^A , two R ^A may be the same or different, and the hydrogen atom bonded to the carbon atom at the non-bonding terminal of the alkyl group having 1 to 8 carbon atoms is a monovalent electron withdrawing group (A ) Represents a substituted group or a hydrogen atom, at least one of which is a monovalent electron-withdrawing group (A).
Specific examples of the compound (1-A) include the following compounds. However, d shows the integer of 2-9.

(Compound (1-B))
Among the compounds (1), the compound having an electron withdrawing group (B) is a compound having an electron withdrawing group (B) formed together with two or more carbon atoms in the carbon skeleton of the compound (1H) (hereinafter referred to as “compound (1H)”). Compound (1) having an electron-withdrawing group (B) is referred to as “compound (1-B)”.
Examples of the electron-withdrawing group (B) include a structure in which a skeleton that forms part of a structure that exhibits electron-withdrawing properties is shared with the carbon skeleton of the compound (1H). Examples of the structure that exhibits electron withdrawing include aromatic rings lacking π electrons or aromatic heterocycles lacking π electrons.

As the electron attractive group (B), a divalent group is preferable, and a divalent aromatic group lacking π electrons and a divalent aromatic heterocyclic group lacking π electrons are particularly preferable.
Examples of the divalent aromatic group lacking π electrons include groups in which one or more hydrogen atoms of the phenylene group are substituted with electron withdrawing groups. Among them, a phenylene group substituted with an electron-withdrawing group (the phenylene group may be any of 1,2-, 1,3-, and 1,4-phenylene groups, and a 1,2-phenylene group is preferable. Is particularly preferred.
Examples of the divalent aromatic heterocyclic group lacking π electrons include a pyridylene group, a pyrazylene group, a pyrimidylene group, a pyridazylene group, and a group in which one or more hydrogen atoms of those rings are substituted. The substituent may or may not be an electron-withdrawing group, and is preferably an electron-withdrawing group.
Examples of the electron-withdrawing group as a substituent include groups described in specific examples.
The number of electron withdrawing groups (B) in the compound (1-B) is preferably one.

Examples of compound (1-B) include compounds in which part or all of the structure of the — (CH ₂ ) _m — moiety in compound (1H) is changed to any one or more of the following groups.
A group in which two hydrogen atoms bonded to a ring selected from a benzene ring, a naphthalene ring, an anthracene ring, and a pyrene ring serve as a bond, and at least one of the remaining hydrogen atoms is substituted with a monovalent electron-withdrawing group.
A group in which two hydrogen atoms of a ring selected from a pyridine ring, a pyrazine ring, a pyrimidine ring, and a pyridazine ring serve as a bond.
A group in which two hydrogen atoms in a ring selected from a pyridine ring, a pyrazine ring, a pyrimidine ring, and a pyridazine ring serve as a bond, and one or more of the hydrogen atoms in the ring are substituted with a monovalent electron-withdrawing group.
Examples of the monovalent electron withdrawing group include the same groups as the monovalent electron withdrawing group (A).

The compound (1-B) is preferably a compound in which the compound (1H) has a —CH ₂ CH ₂ — structure, and the —CH ₂ CH ₂ — is changed to a group represented by the following formula (b-1). .

Y ¹ represents a monovalent electron-withdrawing group, and —C (═O) —R ¹ , —O—C (═O) —OR ² , —C (═O) OR ³ , —O—C ( ═O) —R ⁴ (wherein R ¹ and R ⁴ are each independently a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, an aryl group, an amino group, an alkylamino group, or a halogenated alkoxy group. ² and R ³ are each independently an alkyl group, a halogenated alkyl group, or an aryl group.), Cyano group, nitro group, nitroso group, —SO ₂ X ^a , —P (═O) (X ^a ) ₂ ( ^Xa is a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a halogenated alkoxy group) or a halogenated alkyl group having 1 to 10 carbon atoms.
r represents the number of ^{Y 1,} preferably an integer of 0 to 4, particularly preferably 1 to 2 integer.

  As the compound (1-B) having a group represented by the formula (b-1), the following compound (1-B1) is particularly preferable.

However, in the compound (1-B1), R ^H1 and R ^H2 have the same meaning as the compound (1H), Q represents a group represented by the formula (b-1), and a and b are each independently Represents an integer of 0 to 5, and a + b is an integer of 1 to 9.
Specific examples of the divalent aromatic group lacking π electrons in the compound (1-B1) include the following compounds. However, Et in a formula shows an ethyl group.

  Specific examples of the compound (1-B) when the electron-withdrawing group (B) is a divalent aromatic hetero ring lacking π electrons include, for example, the following compounds.

(Compound (1-C))
Among the compounds (1), a compound having an electron withdrawing group (C) is a compound having an electron withdrawing group (C) in which —CH ₂ — in the carbon skeleton of the compound (1H) is substituted (hereinafter referred to as “compound (1H)”). Compound (1) having an electron-withdrawing group (C) is referred to as “compound (1-C)”.
The electron-withdrawing group (C) is preferably a group selected from —C (═O) —, —SO ₂ —, and —PO ₂ — in terms of a balance between oxidation resistance and reduction resistance. . The position of the electron withdrawing group (C) is preferably a — (CH ₂ ) _m — moiety in the compound (1H). The number of electron withdrawing groups (C) is preferably 1 or 2.

As the electron-withdrawing group (C), —C (═O) — is preferable, —O—C (═O) —CH ₂ — structure, or —O—C (═O) —C (═O). When it exists as a —O— structure, an electron on an oxygen atom to which the electron-withdrawing group (C) is bonded is particularly preferable.
In the linear compound (1H), examples of the compound (1-C) in which a part of CH ₂ is substituted with the electron-withdrawing group (C) include the following compounds.

Further, in the compound (1H) in which R ^H1 and R ^H2 of the compound (1H) form a ring, a compound in which a part of CH ₂ is substituted with an electron-withdrawing group (C) (1- Examples of C) include the following compounds.

(Compound (1-D))
Among the compounds (1), the compound having an electron withdrawing group (D) is a compound in which R ^H1 or R ^H2 of the compound (1H) is substituted with the electron withdrawing group (D) (hereinafter referred to as an electron withdrawing group). Compound (1) having (D) is referred to as “compound (1-D)”. The compound (1-D) may be a compound in which one of R ^H1 and R ^H2 is substituted with an electron withdrawing group (D), and both R ^H1 and R ^H2 are substituted with an electron withdrawing group (D). It may be a substituted compound.

The electron-withdrawing group (D) is a group having —C (═O) —, —SO ₂ —, or —PO ₂ — at the bond end; a monovalent aromatic group lacking π electrons; A group selected from a deficient monovalent aromatic heterocyclic group is preferred. Examples of the monovalent aromatic group lacking π electrons and the monovalent aromatic hetero group lacking π electrons include the same groups as those described for the electron-withdrawing group (A).
The monovalent aromatic group lacking π electrons is preferably a phenyl group in which one or more hydrogen atoms are substituted with an electron-withdrawing group. The monovalent aromatic hetero group lacking π electrons is preferably a pyridyl group, a pyrazyl group, a pyridazyl group, or a furyl group substituted with an electron-withdrawing group.

As the electron-withdrawing group (D), —C (═O) —H, —COX (where X is an alkyl group having 1 to 10 carbon atoms, or carbon-carbon of an alkyl group having 1 to 10 carbon atoms) Represents a group having an etheric oxygen atom inserted between the bonds.), —SO ₂ X ^b , —P (═O) (X ^b ) ₂ (X ^b is a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group) Group, aryl group, amino group, alkylamino group, or halogenated alkoxy group), o-nitrophenyl group, p-nitrophenyl group, m-nitrophenyl group (hereinafter, o-, m-, and p). -Substituted nitrophenyl groups are collectively referred to as mononitrophenyl groups, and the same applies to other substituted phenyl groups.), Mononitrosophenyl groups, monotrifluoromethylphenyl groups, mono (halogenosulphates) ) Phenyl group, a mono (alkyl) phenyl group, mono-cyanophenyl group, a pyridyl group, pyrazyl group, pyrimidyl group, pyridazyl group, and a nitro-furyl group.

  The electron-withdrawing group (D) is particularly preferably a group represented by —COX (where X represents the same meaning as described above). That is, as the compound (1-D), the following compound (1-D1) and compound (1-D2) are particularly preferable.

However, n, ^RH2, and X in the compound (1-D1) and the compound (1-D2) have the same meaning as described above.
Specific examples of the compound (1-D) include the following compounds. However, d shows the integer of 2-9.

  Further, the compound (1) may be a compound having two or more groups selected from the electron-withdrawing groups (A), (B), (C), and (D). Examples of the compound include the following compounds.

A compound (1) may be used individually by 1 type, and may use 2 or more types together.
The content of the compound (1) in the non-electrolytic solution is preferably 0.2 to 8.0 times mol, and 0.2 to 4.0 times the total amount of the lithium salt in the electrolytic solution. More preferably, it is a mole, and particularly preferably 0.5 to 2.0 times mole.
If the compound (1) is 0.5 times mol or more with respect to the lithium salt, it is easy to form a complex of the lithium salt and the compound (1) and to uniformly dissolve the lithium salt in the electrolytic solution. Become. Moreover, if a compound (1) is 8.0 times mole or less with respect to the said lithium salt, the electrolyte solution excellent in the nonflammability will be easy to be obtained.

Conventionally, in a lithium ion secondary battery using a glyme-based solvent as an electrolytic solution (hereinafter simply referred to as “secondary battery”), cycle characteristics sometimes deteriorated when charging and discharging are repeated. Thus, when the cause of the decrease in the cycle characteristics was examined, it was found that the cause was that the glyme solvent was deteriorated by being electrically oxidized on the electrode surface.
The electrolytic solution of the present invention is characterized by using a compound (1) having any one or more of electron withdrawing groups (A) to (D) in order to suppress the electrical oxidation. That is, in the compound (1), electrons are attracted from the oxygen atoms in the skeleton by any one or more of the electron-withdrawing groups (A) to (D), so that the HOMO of the oxygen atoms Since the (maximum occupied level) is lowered, the oxidation potential is increased and the oxidation resistance is improved. Therefore, electrical oxidation of compound (1) on the electrode surface is suppressed, and an electrolytic solution having excellent cycle characteristics can be obtained.

(Hydrofluoroether)
The electrolyte solution of the present invention preferably contains hydrofluoroether (HFE).
Hydrofluoroether is a solvent that imparts incombustibility to an electrolytic solution, and has a structure in which some of the hydrogen atoms of the ether are replaced with fluorine atoms.
As hydrofluoroether, the following compound (3) is mentioned, for example.
R ⁵ —O—R ⁶ (3)

R ⁵ and R ⁶ in the compound (3) are each independently a fluorinated alkyl group having 1 to 10 carbon atoms or a fluorinated alkyl group having 1 to 10 carbon atoms having an etheric oxygen atom between carbon atoms and carbon atoms. And one or both of R ⁵ and R ⁶ is a partially fluorinated group. R ⁵ and R ⁶ may be the same or different. In the present specification, the fluorinated alkyl group is a group in which part or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms. The partially fluorinated group refers to a group in which a part of hydrogen atoms of an alkyl group which may have an etheric oxygen atom between carbon atoms and carbon atoms is substituted with a fluorine atom. A hydrogen atom is present in the partially fluorinated group. In the present invention, the alkyl group and the structure of the alkyl group having an etheric oxygen atom between a carbon atom and a carbon atom are each a linear structure, a branched structure, a cyclic structure, or a group having a partial cyclic structure (for example, A cycloalkylalkyl group.).
As the compound (3), R ⁵ and R ⁶ are both a compound (3-A) having a C 1-10 partially fluorinated alkyl group, and R ⁵ is an etheric oxygen atom between the carbon atom and the carbon atom. A C 1-10 partially fluorinated alkyl group having an atom, and R ⁶ is a C 1-10 partially fluorinated alkyl group or a C 1-10 carbon atom having an etheric oxygen atom between carbon atoms. The compound (3-B) which is a partially fluorinated alkyl group is preferable.

  When the compound (3) has too few carbon atoms, the boiling point is too low, and when it is too much, the viscosity is increased, so that the compound having a total carbon number of 4 to 10 is preferable, and the compound of 4 to 8 is particularly preferable. The molecular weight of the compound (3) is preferably from 200 to 800, particularly preferably from 200 to 500. Since the number of etheric oxygen atoms in the compound (3) affects flammability, the number of etheric oxygen atoms in the case of the compound (3) having an etheric oxygen atom is preferably 1 to 2, or 1 or 2 Is particularly preferred. Further, since the nonflammability is improved when the fluorine content in the compound (3) is increased, the ratio of the molecular weight of the fluorine atom to the molecular weight of the compound (3) is preferably 50% or more, particularly preferably 60% or more.

As the compound (3), a compound (3-A) in which R ⁵ and R ⁶ are a partially fluorinated alkyl group having 1 to 10 carbon atoms is preferable, and CF ₃ CH ₂ OCF ₂ CF ₂ H (trade name) : AE-3000, manufactured by Asahi Glass Co., Ltd.), CHF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, and CF ₃ CH ₂ OCF ₂ CHFCF ₃ are preferred, and CF ₃ CH ₂ OCF ₂ CF ₂ H is particularly preferred.

  Moreover, as hydrofluoroethers other than compound (3), the following compound (4) is mentioned, for example.

In the formula, X _A represents an alkylene group having 1 to 5 carbon atoms, partially fluorinated alkylene group having 1 to 5 carbon atoms, carbon atoms - alkylene of 1 to 5 carbon atoms having an etheric oxygen atom between carbon atoms Or any one of a C 1-5 partially fluorinated alkylene group having an etheric oxygen atom between a carbon atom and a carbon atom. The partially fluorinated alkylene group refers to a group in which a part of hydrogen atoms of the alkylene group is substituted with fluorine atoms.

In the compound (4), the lithium salt is uniformly dissolved, and an electrolyte having high non-flammability and high conductivity is easily obtained. Therefore, X _{A in the} formula (4) is CH ₂ , CH ₂ CH ₂ , It is preferably a hydrofluoroether that is one type selected from the group consisting of CH (CH ₃ ) CH ₂ and CH ₂ CH ₂ CH ₂ .
As the hydrofluoroether, it is preferable to use one or more selected from the group consisting of the compound (3) and the compound (4).

The content of the hydrofluoroether in the electrolytic solution is preferably 20 to 95% by volume, particularly preferably 50 to 90% by volume, when the total amount of solvent used in the electrolytic solution is 100% by volume.
Moreover, when using together compound (3) (capacity | capacitance: Va) and compound (4) (capacity | capacitance: Vb) as hydrofluoroether, those capacity ratios (Vb / Va) are 0.01-0.99. It is preferably 0.1 to 0.9.

(Carbonate)
Moreover, the electrolyte solution of this invention may contain carbonate other than the above-mentioned lithium salt, hydrofluoroether, and a compound (1). As the carbonate, one or more carbonates selected from the group consisting of the following compound (5-1), the following compound (5-2), and the following (5-3) are preferable, and the compound (5-2) is more preferable. .

R ^{7 to} R ¹² in the compound (5-1) are each independently a hydrogen atom, a halogen atom, an alkyl group, or a halogenated alkyl group.
Compound (5-1) is dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, di-n-propyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, methyl isopropyl carbonate, ethyl-n-propyl carbonate, It is preferably at least one compound selected from the group consisting of ethyl isopropyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, and 3-fluoropropyl methyl carbonate, and dimethyl carbonate from the standpoint of availability and properties of the electrolytic solution. Diethyl carbonate and methyl ethyl carbonate are particularly preferred.

R ^{13 to} R ¹⁶ in the compound (5-2) are each independently a hydrogen atom, a halogen atom, an alkyl group, or a halogenated alkyl group.
Compound (5-2) is propylene carbonate, ethylene carbonate, butylene carbonate, 4-chloro-1,3-dioxolan-2-one, 4-fluoro-1,3-dioxolan-2-one, 4-trifluoromethyl. It is preferably one or more cyclic carbonates selected from the group consisting of -1,3-dioxolan-2-one, and ethylene carbonate, propylene carbonate, and fluoroethylene carbonate are particularly preferred from the viewpoints of availability and properties of the electrolytic solution. preferable.
R ¹⁷ and R ¹⁸ in the compound (5-3) are each independently a hydrogen atom, a halogen atom, an alkyl group, or a halogenated alkyl group.
As the compound (5-3), vinylene carbonate and dimethyl vinylene carbonate are preferable, and vinylene carbonate is particularly preferable.

By adding the compound (5), the solubility of the lithium salt in the hydrofluoroether is improved.
In addition, the compound (5) decomposes on the surface of the negative electrode (for example, a carbon electrode) to form a stable coating when charging is performed with a secondary battery using an electrolytic solution containing the compound (5). Since the film formed of the compound (5) can reduce the resistance at the electrode interface, the effect of promoting the intercalation of lithium ions into the negative electrode can be obtained. That is, the intercalation of lithium ions into the negative electrode is promoted by reducing the impedance at the negative electrode interface due to the film formed of the compound (5) in the electrolytic solution.

The content of the compound (5) in the electrolytic solution is that the phase separation in the electrolytic solution and the suppression of a large amount of carbon dioxide gas generation and the improvement of the solubility of the lithium salt can be easily achieved. The total amount of solvent is preferably 10% by volume or less, more preferably 0.01 to 10% by volume, and particularly preferably 0.1 to 5% by volume.
The compound (5) is preferably used in a small amount because the higher the relative dielectric constant, the higher the possibility of causing phase separation in the electrolytic solution. Moreover, when there is too much compound (5), there exists a possibility of a large amount of carbon dioxide generation by decomposition | disassembly, and it will be difficult to maintain nonflammability.
When the chain carbonate of the compound (5-1) and the cyclic carbonate of the compound (5-2) and / or the compound (5-3) are used in combination, the chain carbonate (volume V ₁ ) and the cyclic carbonate (volume V ₂ ) The volume ratio (volume ratio V ₁ : V ₂ ) is preferably 1:10 to 10: 1.

(Other solvents)
The electrolyte solution of the present invention may contain other solvents in addition to the hydrofluoroether, the compound (1), and the compound (5) as long as the electrolyte solution is within a range where phase separation does not occur.
Other solvents include, for example, propionic acid alkyl esters, malonic acid dialkyl esters, carboxylic acid esters such as acetic acid alkyl esters, cyclic esters such as γ-butyrolactone, cyclic sulfonic acid esters such as propane sultone, sulfonic acid alkyl esters, Examples include phosphoric acid alkyl esters.
The content of the other solvent is preferably 10% by volume or less, and more preferably 5% by volume or less, when the total amount of solvent used in the electrolytic solution is 100% by volume.

  Moreover, in order to improve a function, the electrolyte solution of this invention may contain the other component as needed. Examples of the other components include conventionally known overcharge inhibitors, dehydrating agents, deoxidizing agents, capacity maintenance characteristics after high-temperature storage, and property improvement aids for improving cycle characteristics.

Examples of the overcharge inhibitor include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; 2-fluoro Partially fluorinated products of the above aromatic compounds such as biphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; fluorinated anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole and 2,6-difluoroaniol Compounds. An overcharge inhibitor may be used individually by 1 type, and may use 2 or more types together.
When electrolyte solution contains an overcharge inhibitor, it is preferable that content of the overcharge inhibitor in electrolyte solution is 0.1-5 mass%. By containing 0.1% by mass or more of the overcharge inhibitor in the electrolytic solution, it becomes easier to suppress the rupture / ignition of the secondary battery due to overcharge, and the secondary battery can be used more stably.

  Examples of the dehydrating agent include molecular sieves, mirabilite, magnesium sulfate, calcium hydride, potassium hydride, sodium hydride, lithium aluminum hydride, calcium chloride, sodium metal, and the like. As the solvent used in the electrolytic solution of the present invention, it is preferable to use a solvent obtained by performing rectification after dehydrating with the dehydrating agent. Moreover, you may use the solvent which performed only the dehydration by the said dehydrating agent, without performing rectification.

Examples of the property improving aid include carbonate compounds such as fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate, erythritan carbonate, spiro-bis-dimethylene carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, Carboxylic acid anhydrides such as citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinic anhydride; ethylene sulfite, 1, 3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, diphenyl sulfone, methylphenyl sulfone, dibutyl disulfide Sulfur-containing compounds such as dicyclohexyl disulfide, tetramethylthiuram monosulfide, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3- Nitrogen-containing compounds such as methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide; hydrocarbon compounds such as heptane, octane, cycloheptane, fluorobenzene, difluorobenzene, hexafluoro Examples thereof include fluorine-containing aromatic compounds such as benzene and benzotrifluoride. These characteristic improvement aids may be used alone or in combination of two or more.
When the electrolytic solution contains a characteristic improving aid, the content of the characteristic improving auxiliary in the electrolytic solution is preferably 0.1 to 5% by mass.

In addition, the electrolytic solution of the present invention preferably has a conductivity of 0.25 S · m ⁻¹ or more from the viewpoint of obtaining practically sufficient conductivity. Moreover, it is preferable that the viscosity (20 degreeC) measured with the rotary viscometer is 0.1-20 cP.
Further, the electrolyte solution of the present invention preferably has a flash point of 70 ° C. or higher in the Cleveland open type flash point test (based on JIS-K2265), and does not exhibit a flash point. Particularly preferred. The flash point of the electrolytic solution can be adjusted by adjusting the type or content of the hydrofluoroether and the compound (1). For example, if the amount of hydrofluoroether is 20% by volume or more based on the total amount of solvent, there is a tendency not to show a flash point, and if n in the compound is 3 or more, the flash point is 70 ° C. or more. Although there is a tendency, these types and contents can be changed as appropriate in consideration of the balance with other required performance as an electrolytic solution.

Moreover, the electrolytic solution of the present invention is preferably an electrolytic solution in which a potential region (potential window) at which a decomposition current value reaches 0.05 mA / cm ² is in a region wider than a range of 0.2 V to 4.2 V. . The value of the potential window is a value expressed in terms of a lithium metal reference potential. It said potential window, Compound (1) (molar amount: _{M G)} and a lithium salt (molar _{amount: M Li)} and the molar ratio of _{(M G: M Li)} of 0.5: 1 to 4: 1 to Can be achieved. The potential window can be measured by the method described in the examples. Further, when the compound (1) is a compound in which a part of the compound (H1) in which R ^H1 and R ^H2 are methyl groups is changed to electron withdrawing groups (A) to (C), the molar ratio ( _MG : M _Li ) is preferably 0.5: 1 to 4: 1.

The electrolytic solution of the present invention described above uses the compound (1) excellent in oxidation resistance, so that the compound (1) is electrically oxidized and deteriorates even if the secondary battery is repeatedly charged and discharged. Is suppressed and has excellent cycle characteristics.
In addition, when the compound (3) or the compound (4) is used as the hydrofluoroether in the electrolytic solution of the present invention, further excellent nonflammability can be obtained. Furthermore, in this case, since the compound (1) is coordinated to the lithium salt, the lithium salt can be uniformly dissolved in the hydrofluoroether having a low dielectric constant and low viscosity, and the obtained electrolytic solution is practically sufficient. Indicates conductivity. Moreover, since a large amount of carbonate is not required, there is no fear of generation of carbon dioxide, and nonflammability can be maintained for a long time.
Further, in the electrolytic solution of the present invention, corrosion of the electrode can be prevented by using LiPF ₆ which is a non-imide lithium salt, compound (2) which is a cyclic lithium salt, or the like.

[Lithium ion secondary battery]
The secondary battery of this invention is a secondary battery which has a negative electrode and a positive electrode, and the electrolyte solution of this invention.
Examples of the negative electrode include an electrode including a negative electrode active material capable of electrochemically inserting and extracting lithium ions. As the negative electrode active material, known negative electrode active materials for lithium ion secondary batteries can be used. Graphite (graphite) capable of occluding and releasing lithium ions, carbonaceous materials such as amorphous carbon, metallic lithium, lithium alloys And the like, and metal compounds. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

Especially, as a negative electrode active material, a carbonaceous material is preferable. Further, as the carbonaceous material, graphite and a carbonaceous material in which the surface of graphite is coated with amorphous carbon as compared with the graphite are particularly preferable.
Graphite preferably has a lattice plane (002 plane) d value (interlayer distance, hereinafter simply referred to as d value) of 0.335 to 0.338 nm determined by X-ray diffraction using the Gakushin method. More preferably, it is -0.337 nm. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is preferably 30 nm or more, more preferably 50 nm or more, and further preferably 100 nm or more. The ash content of graphite is preferably 1% by mass or less, more preferably 0.5% by mass or less, and further preferably 0.1% by mass or less.

Further, as a carbonaceous material in which the surface of graphite is coated with amorphous carbon, graphite having a d value of 0.335 to 0.338 nm is used as a core material, and the d value of the graphite surface is larger than that of the graphite. The ratio of graphite (mass W _A ), which is coated with amorphous carbon, and amorphous carbon (mass W _B ) covering the graphite is 80 / weight ratio (W _A / W _B ). It is preferable that it is 20-99 / 1. By using this carbonaceous material, it becomes easy to produce a negative electrode having a high capacity and hardly reacting with the electrolytic solution.

  The particle size of the carbonaceous material is preferably 1 μm or more, more preferably 3 μm or more, further preferably 5 μm or more, and more preferably 7 μm or more in terms of the median diameter by a laser diffraction / scattering method. Particularly preferred. Further, the upper limit of the particle size of the carbonaceous material is preferably 100 μm or less, more preferably 50 μm or less, further preferably 40 μm or less, and particularly preferably 30 μm or less.

The specific surface area according to the BET method of the carbonaceous material is preferably 0.3 m ² / g or more, more preferably 0.5 m ² / g or more, and further preferably 0.7 m ² / g or more. Preferably, it is particularly preferably 0.8 m ² / g or more. The upper limit of the specific surface area of the carbonaceous material is preferably at 25.0 m ² / g or less, more preferably 20.0 m ² / g or less, more preferably at most 15.0 m ² / g It is more preferable that it is 10.0 m < ² > / g or less.

Carbonaceous material, when analyzed by Raman spectrum using argon ion laser light, the peak P in the peak intensity _{I A} of the peak _{P A} in the range of 1570～1620Cm ^-1, in the range of 1300～1400Cm ^-1 R value expressed by the ratio of the peak intensity _{I B} of _{B (= I B / I a} ) is preferably a 0.01 to 0.7. Further, the half width of the peak _{P A} is, it is particularly preferable is preferably 26cm ^-1 or less, and 25 cm ^-1 or less.

Examples of metals that can be used as the negative electrode active material other than metallic lithium include Ag, Zn, Al, Ga, In, Si, Ti, Ge, Sn, Pb, P, Sb, Bi, Cu, Ni, Sr, and Ba. It is done. Moreover, as a lithium alloy, the alloy of lithium and the said metal is mentioned. Moreover, as a metal compound, the said metal oxide etc. are mentioned.
Among these, at least one metal selected from the group consisting of Si, Sn, Ge, Ti and Al, a metal compound containing the metal, a metal oxide and a lithium alloy are preferable, and selected from the group consisting of Si, Sn and Al. One or more kinds of metals, a metal compound containing the metal, a lithium alloy, and lithium titanate are more preferable.
A metal capable of inserting and extracting lithium ions, a metal compound containing the metal, and a lithium alloy generally have a larger capacity per unit mass than a carbonaceous material typified by graphite, so a higher energy density is required. It is suitable for a secondary battery.

Examples of the positive electrode include an electrode including a positive electrode active material that can electrochemically occlude and release lithium ions.
As the positive electrode active material, known positive electrode active materials for lithium ion secondary batteries can be used. For example, lithium-containing transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide, Examples thereof include lithium-containing transition metal composite oxides, transition metal oxides, transition metal sulfides, metal oxides, and olivine type metal lithium salts using the above transition metals.

The transition metal of the lithium-containing transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, for example, lithium cobalt composite oxide such as LiCoO ₂ or lithium nickel composite such as LiNiO _2. Lithium manganese composite oxides such as oxides, LiMnO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , and some of the transition metal atoms that are the main components of these lithium transition metal composite oxides are Al, Ti, V, Cr, Mn, Examples include those substituted with other metals such as Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, and Yb. Examples of those substituted with other metals include LiMn _0.5 Ni _0.5 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiMn _{1 .5 Ni 0.5 O 4, LiNi 1/3} Co 1/3 Mn 1/3 O 2, LiMn 1.8 Al 0.2 O 4 and the like.
Examples of transition metal oxides include TiO ₂ , MnO ₂ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ , transition metal sulfides TiS ₂ , FeS, MoS ₂ , metal oxides SnO ₂ , Examples thereof include SiO ₂ .
The olivine-type metal lithium salt is represented by (formula) Li _L X _x Y _y O _z F _g (where X is Fe (II), Co (II), Mn (II), Ni (II), V (II), Or Cu (II), Y represents P or S, and each represents a number satisfying 0 ≦ L ≦ 3, 1 ≦ x ≦ 2, 1 ≦ y ≦ 3, 4 ≦ z ≦ 12, 0 ≦ g ≦ 1 ) Or a complex thereof. For example, LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ) ₃ , LiFeP ₂ O ₇ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₂ FePO ₄ F, Li ₂ MnPO ₄ F, Li ₂ NiPO ₄ F, Li ₂ CoPO Examples thereof include ₄ F, Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ NiSiO ₄ , and Li ₂ CoSiO ₄ . These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.
In addition, a material in which a substance having a composition different from that of the main constituent of the positive electrode active material is attached to the surface of the positive electrode active material can be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate and carbonates such as lithium carbonate, calcium carbonate and magnesium carbonate.
As the amount of the surface adhering substance, the lower limit of the mass with respect to the positive electrode active material is preferably 0.1 ppm, more preferably 1 ppm, and still more preferably 10 ppm. The upper limit is preferably 20%, more preferably 10%, still more preferably 5%. The surface adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte on the surface of the positive electrode active material, and can improve the battery life.

As the positive electrode active material, a lithium-containing composite oxide based on an α-NaCrO ₂ structure such as LiCoO ₂ , LiNiO ₂ , LiMnO _2, or the like, LiMn ₂ O, because of its high discharge voltage and high electrochemical stability A lithium-containing composite oxide based on a spinel structure such as ₄ is preferred.
The secondary battery of the present invention has a negative electrode and a positive electrode in which either one or both of the negative electrode and / or the positive electrode are polarizable electrodes, and the non-aqueous electrolyte of the present invention. The polarizable electrode is preferably composed mainly of a material having a high specific surface area that is electrochemically inactive, and particularly preferably composed of activated carbon, carbon black, metal fine particles, and conductive oxide fine particles. In particular, it is preferable that an electrode layer made of a carbon material powder having a high specific surface area such as activated carbon is formed on the surface of the metal current collector. The nonaqueous electrolytic solution of the present invention can be used for other charging devices because it dissolves lithium salt well and is excellent in nonflammability. Examples of other charging devices include an electric double layer capacitor and a lithium ion capacitor.

For the production of the electrode, a binder that binds the negative electrode active material or the positive electrode active material is used.
As the binder for binding the negative electrode active material and the positive electrode active material, any binder can be used as long as it is a material that is stable with respect to the solvent and the electrolytic solution used during electrode production. The binder is, for example, a fluororesin such as polyvinylidene fluoride or polytetrafluoroethylene, a polyolefin such as polyethylene or polypropylene, a polymer having an unsaturated bond such as styrene / butadiene rubber, isoprene rubber or butadiene rubber, and a copolymer thereof. Examples thereof include acrylic polymers such as polymers, acrylic acid copolymers, and methacrylic acid copolymers, and copolymers thereof. These binders may be used individually by 1 type, and may use 2 or more types together.

The electrode may contain a thickener, a conductive material, a filler and the like in order to increase mechanical strength and electrical conductivity.
Examples of the thickener include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and polyvinylpyrrolidone. These thickeners may be used individually by 1 type, and may use 2 or more types together.

  Examples of the conductive material include a metal material such as copper or nickel, and a carbonaceous material such as graphite or carbon black. These electrically conductive materials may be used individually by 1 type, and may use 2 or more types together.

As an electrode manufacturing method, a binder, a thickener, a conductive material, a solvent, etc. are added to a negative electrode active material or a positive electrode active material to form a slurry, which is then applied to a current collector and dried. it can. In this case, the electrode is preferably consolidated by pressing after drying.
If the density of the positive electrode active material layer is too low, the capacity of the secondary battery may be insufficient.

  As the current collector, various current collectors can be used, but usually a metal or an alloy is used. Examples of the negative electrode current collector include copper, nickel, and stainless steel, with copper being preferred. Moreover, examples of the current collector for the positive electrode include metals such as aluminum, titanium, and tantalum, and alloys thereof. Aluminum or an alloy thereof is preferable, and aluminum is particularly preferable.

The shape of the secondary battery may be selected according to the application, and may be a coin type, a cylindrical type, a square type or a laminate type. Further, the shapes of the positive electrode and the negative electrode can be appropriately selected according to the shape of the secondary battery.
The charging voltage of the secondary battery of the present invention is preferably 3.4 V or higher, particularly preferably 4.0 V or higher, and particularly preferably 4.2 V or higher. When the positive electrode active material of the secondary battery is a lithium-containing transition metal oxide, a lithium-containing transition metal composite oxide, a transition metal oxide, a transition metal sulfide, or a metal oxide, the charging voltage is preferably 4.0 V or more, 4.2V is particularly preferred. In addition, when the positive electrode active material is an olivine-type metal lithium salt, the charging voltage is preferably 3.2 V and particularly preferably 3.4 V or more. Since the nonaqueous electrolytic solution of the present invention has an oxidation resistance of 4.2 V or higher and a reduction resistance of 0.2 V or lower, the electrolytic solution of the present invention is used for any electrode having an operating potential in the range. I can do it.
Furthermore, the secondary battery of the present invention is particularly preferably a secondary battery that is used at a charging voltage of 4.2 V or higher (potential based on lithium metal). For example, a secondary battery having the nonaqueous electrolytic solution of the present invention having a potential window wider than the range of 0V to 4.2V can be given.

In order to prevent a short circuit, a porous film is usually interposed as a separator between the positive electrode and the negative electrode of the secondary battery. In this case, the nonaqueous electrolytic solution is used by impregnating the porous membrane. The material and shape of the porous membrane are not particularly limited as long as it is stable with respect to the non-aqueous electrolyte and has excellent liquid retention properties, such as polyvinylidene fluoride, polytetrafluoroethylene, a copolymer of ethylene and tetrafluoroethylene, etc. A porous sheet or non-woven fabric made of a polyolefin resin such as polyethylene or polypropylene is preferred, and a material such as polyethylene or polypropylene is preferred. Moreover, you may use what made these porous membranes impregnate electrolyte solution and gelatinize it as a gel electrolyte.
The battery case used in the non-aqueous electrolyte of the present invention may be made of any material that is usually used for secondary batteries. Nickel-plated iron, stainless steel, aluminum or alloys thereof, nickel, titanium, and resin materials And film materials.

Since the secondary battery of the present invention uses the non-aqueous electrolyte described above, there is no risk of ignition even if an excessive load is generated on the secondary battery, such as overheating, overcharging, internal short circuit, external short circuit, etc. Excellent in properties. Therefore, it is not necessary to provide a complicated monitoring system for monitoring the excessive load as described above in the secondary battery.
Therefore, the secondary battery of the present invention includes a mobile phone, a portable game machine, a digital camera, a digital video camera, an electric tool, a notebook computer, a portable information terminal, a portable music player, an electric vehicle, a hybrid vehicle, a train, an aircraft, an artificial It can be used for various applications such as satellites, submarines, ships, uninterruptible power supplies, robots, and power storage systems. Further, since the secondary battery of the present invention is particularly excellent in safety, large-scale electric vehicles, hybrid vehicles, trains, aircraft, satellites, submarines, ships, uninterruptible power supply devices, robots, power storage systems, etc. The secondary battery has particularly preferable characteristics.

  As described above, the secondary battery electrolyte solution of the present invention uses the secondary battery electrolyte solution to suppress deterioration of the electrolyte solution, and has excellent cycle characteristics, long-term incombustibility, and practically sufficient. It has a good electrical conductivity.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited by the following description.

[Production Example 1]
Triethylene glycol monomethyl ether (287 g, 1.75 mol) was charged into a 500 ml four-necked flask equipped with a dropping funnel, thermometer and condenser, and acetyl chloride (165 g, 2.1 mol) while maintaining the internal temperature within 30 ° C. Was gradually added dropwise. After completion of dropping, the reaction was continued at 60 ° C. for 4 hours. It was confirmed by GC analysis that triethylene glycol monomethyl ether had disappeared, and the resulting crude liquid was purified with a multi-stage rectification column. As a result, 99.9% purity target product, triethylene glycol monomethyl ether monoacetate was obtained. 170 g was obtained.
The triethylene glycol monomethyl ether monoacetate (3.09 g, 15.0 mmol) and a lithium salt LiPF ₆ (1.51 g, 10.0 mmol) are mixed to form a complex, and the complex is hydrofluoroether HFE347 (CF ₃ CH ₂ OCF ₂ CF ₂ H, 10 mL) is added and mixed to obtain an electrolytic solution 1.

[Production Example 2]
Triethylene glycol (150 g, 1.00 mol) was charged into a 500 ml four-necked flask equipped with a dropping funnel, thermometer and condenser, and acetyl chloride (165 g, 2.1 mol) was gradually added while maintaining the internal temperature within 30 ° C. Dripping. After completion of dropping, the reaction is continued at 60 ° C. for 4 hours. It is confirmed by GC analysis that triethylene glycol has disappeared, and the resulting crude liquid is purified by a multistage rectification column to obtain a 99.9% pure target product, triethylene glycol diacetate.
The triethylene glycol diacetate (4.68 g, 20.0 mmol) and the lithium salt LiPF ₆ (1.51 g, 10.0 mmol) are mixed to form a complex, and the complex is a hydrofluoroether. _{HFE347 (CF 3 CH 2 OCF 2} CF 2 H, 10mL) added and mixed to the electrolyte 2.

[Production Example 3]
Diethylene glycol monomethyl ether (210 g, 1.75 mol) was charged into a 500 ml four-necked flask equipped with a dropping funnel, thermometer and condenser, and acetyl chloride (165 g, 2.1 mol) was gradually added while maintaining the internal temperature within 30 ° C. Dripping. After completion of dropping, the reaction is continued at 60 ° C. for 4 hours. It is confirmed by GC analysis that diethylene glycol monomethyl ether has disappeared, and the obtained crude liquid is purified by a multistage rectification column to obtain a 99.9% pure target product, diethylene glycol monomethyl ether monoacetate.
The diethylene glycol monomethyl ether monoacetate (3.24 g, 20.0 mmol) and a lithium salt LiPF ₆ (1.51 g, 10.0 mmol) are mixed to form a complex, and the complex is a hydrofluoroether. _{HFE347 (CF 3 CH 2 OCF 2} CF 2 H, 10mL) added and mixed to the electrolyte 3.

[Production Example 4]
Diethylene glycol monomethyl ether (180 g, 1.50 mol) and oil-impregnated sodium hydride (10 g, purity 55%) are charged into a 500 ml four-necked flask equipped with a dropping funnel, thermometer and condenser. The condenser is supplied with 65 ° C. warm water to raise the internal temperature to 140 ° C. The dropping funnel is charged with hexachloroacetone (132 g, 0.5 mol). From the dropping funnel, with stirring, the chloroform by-produced hexachloroacetone is distilled off and charged over 2 hours. After completion of the dropwise addition, heating is continued until no distillation of chloroform is confirmed. After cooling, purification by silica gel column chromatography yields the target product, bis (2- (2-methoxyethoxy) ethoxy) carbonate, having a purity of 99.9%.
The bis (2- (2-methoxyethoxy) ethoxy) carbonate (3.99 g, 15.0 mmol) and the lithium salt LiPF ₆ (1.51 g, 10.0 mmol) were mixed to form a complex, To this complex, HFE347 (CF ₃ CH ₂ OCF ₂ CF ₂ H, 10 mL), which is a hydrofluoroether, is added and mixed to obtain an electrolytic solution 4.

[Production Example 5]
2-Methoxyethanol (114 g, 1.50 mol) and oil impregnated sodium hydride (10 g, purity 55%) are charged into a 500 ml four-necked flask equipped with a dropping funnel, thermometer and condenser. The condenser is refluxed by passing hot water of 65 ° C. The dropping funnel is charged with hexachloroacetone (132 g, 0.5 mol). From the dropping funnel, hexachloroacetone is charged over 2 hours with stirring while distilling off by-produced chloroform. After completion of the dropwise addition, heating is continued until no distillation of chloroform is confirmed. After cooling, purification by silica gel column chromatography yields the desired product, bis (2-methoxyethoxy) carbonate, having a purity of 99.9%.
The bis (2-methoxyethoxy) carbonate (3.56 g, 20.0 mmol) and the lithium salt LiPF ₆ (1.51 g, 10.0 mmol) are mixed to form a complex. HFE347 (CF ₃ CH ₂ OCF ₂ CF ₂ H, 10 mL) which is ether is added and mixed to obtain an electrolytic solution 5.

[Production Example 6]
The following compound (1-B1-1) (2.41 g, 6.7 mmol) and LiPF ₆ (1.51 g, 10.0 mmol) which is a lithium salt are mixed to form a complex. HFE347 (CF ₃ CH ₂ OCF ₂ CF ₂ H, 10 mL) which is ether is added and mixed to obtain an electrolyte solution 6.

[Production Example 7]
The following compound (1-A-1) (2.68 g, 6.7 mmol) and LiPF ₆ (1.51 g, 10.0 mmol) which is a lithium salt are mixed to form a complex. HFE347 (CF ₃ CH ₂ OCF ₂ CF ₂ H, 10 mL) which is ether is added and mixed to obtain an electrolyte solution 7.

[Production Example 8] (Reference Example)
Diglyme (manufactured by Tokyo Chemical Industry Co., Ltd.) is refined by 10-stage multi-stage distillation so that the content of hydroxyl group-containing impurities (impurities in which diglyme ends are hydroxyl groups) is less than the detection limit (detection limit: 10 mg / kg) of GC analysis. The diglyme (1.78 g, 13.3 mmol) and the lithium salt LiPF ₆ (1.51 g, 10.0 mmol) were mixed to form a complex. HFE347 (CF ₃ CH ₂ OCF ₂ CF ₂ H, 10 mL) which is ether is added and mixed to obtain an electrolytic solution A.

<Evaluation of sheet-shaped lithium ion secondary battery of single electrode cell made of LiCoO ₂ positive electrode-lithium metal foil>
[Example 1]
90 parts by mass of LiCoO ₂ (manufactured by AGC Seimi Chemical Co., Ltd., trade name “Selion C”), 5 parts by mass of carbon black (trade name “Denka Black”, manufactured by Denki Kagaku Kogyo Co., Ltd.), and 5 parts by mass of polyvinylidene fluoride were mixed. , N-methyl-2-pyrrolidone is added to form a slurry, and the slurry is uniformly applied to one side of an aluminum foil having a thickness of 20 μm and dried. Thereafter, the density of the positive electrode active material layer becomes 3.0 g / cm ³ . The positive electrode is manufactured by pressing as described above.
Next, the LiCoO ₂ positive electrode, a lithium metal foil having the same area as the LiCoO ₂ positive electrode, and a polyethylene separator are laminated in the order of the lithium metal foil, the separator, and the LiCoO ₂ positive electrode to produce a battery element. Next, the battery element is placed in a bag made of a laminate film in which both surfaces of aluminum (thickness 40 μm) are coated with a resin layer (polyethylene resin), and terminals of the LiCoO ₂ positive electrode and negative electrode (lithium metal foil) of the battery element are provided. The bag is stored outside the bag. Next, the electrolytic solution 1 prepared in Production Example 1 is injected into the bag and vacuum-sealed to produce a sheet-like secondary battery 1 (secondary battery 1).

[Examples 2 to 7]
Sheet-like secondary batteries 2 to 7 (secondary batteries 2 to 7) are produced in the same manner as in Example 1 except that the electrolytic solution used is changed as shown in Table 1.

[Comparative Example 1]
A sheet-like secondary battery 8 (secondary battery 8) is produced in the same manner as in Example 1 except that the electrolytic solution A prepared in Production Example 8 is used.

[Evaluation methods]
Evaluation of the cycle characteristics of the secondary batteries 1 to 8 of Examples 1 to 7 and Comparative Example 1 is performed by the following method.
With a constant current corresponding to 0.1 C at 25 ° C. in a state where a sheet-like secondary battery of a single electrode cell made of LiCoO ₂ positive electrode-lithium metal foil is sandwiched between glass plates in order to enhance the adhesion between the electrodes. Charge the battery to 4.2V and perform 5 cycles of discharging to 3V with a constant current corresponding to 0.1C to stabilize the secondary battery. After the 5th cycle, the battery is charged to 4.2V with a constant current of 0.2C, and further charged to a current value of 0.02C with a constant voltage of 4.2V, and up to 3V with a constant current of 0.2C. The discharge cycle is repeated, and the maintenance rate of the discharge capacity at the 80th cycle relative to the first discharge capacity is taken as the evaluation result. However, 1C represents a current value for discharging the reference capacity of the battery in 1 hour, and 0.2C represents a current value of 1/5 thereof.
In addition, the cycle characteristics similar to those described above are also evaluated under the condition where the charging voltage is changed from 4.2 V to 4.3 V and 4.4 V.

The evaluation criteria for cycle characteristics are as follows.
○: The charge capacity maintenance rate is 90% or more.
Δ: The charge capacity retention rate is 85% or more and less than 90%.
X: The charge capacity maintenance rate is less than 85%.
Table 1 shows the evaluation of the cycle characteristics of the secondary batteries 1 to 8 of Examples 1 to 7 and Comparative Example 1. “Vc” in Table 1 means a charging voltage.

  As shown in Table 1, the secondary batteries of Examples 1 to 7 including the electrolytic solution containing the compound (1) of the present invention were charged under the conditions of a charging voltage of 4.2 V, 4.3 V, and 4.4 V. The cycle characteristics are superior to those of the secondary battery of Comparative Example 1 using diglyme.

  The electrolyte for a lithium ion secondary battery and the lithium ion secondary battery of the present invention are excellent in cycle characteristics, have long-term nonflammability and practically sufficient conductivity. Therefore, it can be suitably used for a secondary battery for various uses such as a mobile phone, a notebook computer, and an electric vehicle.

Claims (13)

An electrolytic solution for a secondary battery comprising a lithium salt and the following compound (1).
Compound (1): a monovalent electron-withdrawing group (A) in which a hydrogen atom bonded to a carbon atom of the compound (1H) represented by the following formula (1H) is substituted, two or more in the compound (1H) An electron-withdrawing group (B) formed with a carbon atom, an electron-withdrawing group (C) in which —CH ₂ — in the compound (1H) is substituted, and R ^H1 or R ^H2 in the compound (1H) are A compound having one or more electron-withdrawing groups selected from the group consisting of substituted monovalent electron-withdrawing groups (D).

However, the symbol in a formula shows the following meaning.
m: an integer of 1 to 4.
n: An integer of 2 to 10.
R ^H1 and R ^H2 : each independently an alkyl group having 1 to 8 carbon atoms or a group having one or more oxygen atoms inserted between carbon-carbon atoms of the alkyl group. Alternatively, R ^H1 and R ^H2 are linked to each other, and are an alkylene group having 1 to 5 carbon atoms, or a group in which one or more oxygen atoms are inserted between carbon-carbon atoms of the alkylene group. The electrolyte solution for secondary batteries of Claim 1 whose said compound (1H) is a compound (1H-1) represented by the following Formula (1H-1).

However, the symbol in a formula shows the following meaning.
n: Same as the compound (1H).
R ^H10 and R ^H20 : each independently an alkyl group having 1 to 8 carbon atoms or an alkylene group having 1 to 5 carbon atoms formed by linking each other.   The electron-withdrawing group (A) is a nitro group, a nitroso group, a cyano group, a monovalent aromatic group lacking π electrons, or a monovalent aromatic heterocyclic group lacking π electrons. The electrolyte solution for secondary batteries as described in 1 or 2.   The electron-withdrawing group (B) is a divalent aromatic group lacking π electrons or a divalent aromatic heterocyclic group lacking π electrons. Secondary battery electrolyte. Electron-withdrawing group (C) is, -C (= O) -, - SO 2 - or -PO ₂ - a is, the electrolyte solution for a secondary battery according to any one of claims 1 to 4. A group in which the electron-withdrawing group (D) has —C (═O) —, —SO ₂ —, or —PO ₂ — at the bond end; a monovalent aromatic group lacking π electrons; The electrolytic solution for a secondary battery according to any one of claims 1 to 5, which is a group selected from a deficient monovalent aromatic heterocyclic group. The lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , Li (C ₂ O ₄ ) ₂ , LiN (SO ₂ (CF ₂ ) _p F) ₂ (where p is an integer of 1 to 5), It is selected from the group consisting of FSO ₂ N (Li) SO ₂ F, CF ₃ SO ₃ Li, and a compound represented by the following formula (2) (wherein q is an integer of 1 to 5). The electrolyte solution for secondary batteries in any one of Claims 1-6 which is 1 or more types of lithium salts.

  The electrolyte solution for secondary batteries in any one of Claims 1-7 whose content of the said compound (1) is 0.2-8.0 times mole with respect to the total amount of the said lithium salt.   The electrolyte solution for secondary batteries in any one of Claims 1-8 containing hydrofluoro ether.   The electrolyte solution for secondary batteries in any one of Claims 1-9 containing a carbonate type solvent.   The electrolyte solution for secondary batteries of Claim 10 whose quantity of the said carbonate type solvent is 10 volume% or less when the total amount of solvent in electrolyte solution is 100 volume%.   The negative electrode which consists of a material which can occlude / release lithium ion electrochemically, or metal lithium or a lithium alloy, and the positive electrode which consists of a material which can electrochemically occlude / release lithium ion, A lithium ion secondary battery.   The lithium ion secondary battery according to claim 12, wherein the charging voltage is 3.4 V or higher (potential based on lithium metal).