KR20030057321A - Non-aqueous electrolytic solutions and lithium secondary battery containing the same - Google Patents

Abstract

It is an object of the present invention to provide a non-aqueous electrolyte having a high overcharge preventing effect and excellent high temperature storage characteristics and suitable for lithium secondary batteries.

A fluorine-substituted aromatic compound, an aromatic hydrocarbon compound composed only of carbon and hydrogen, a nonaqueous solvent and an electrolyte containing a lithium-containing electrolyte. The fluorine atom-substituted aromatic compound contains 0.1 to 20% by weight in the electrolyte, and 0.1 to 3% by weight of the aromatic hydrocarbon compound. As an example of a fluorine-substituted aromatic compound, cyclohexylbenzene and biphenyl are mentioned as a fluorine-substituted naphthalene, fluorene, or a biphenyl compound, and an aromatic hydrocarbon compound. The non-aqueous electrolyte is further at least one member selected from the group consisting of vinylene carbonates, alkenylethylene carbonates, sultones having an unsaturated hydrocarbon group, sulfonic acid esters having an aryl group, sultones having an unsaturated hydrocarbon group, and sulfonic acid imides. By adding a compound of the high temperature storage characteristics can be improved.

Description

Non-aqueous electrolyte and lithium secondary battery using same {NON-AQUEOUS ELECTROLYTIC SOLUTIONS AND LITHIUM SECONDARY BATTERY CONTAINING THE SAME}

The present invention relates to a non-aqueous electrolyte having an overcharge preventing effect and excellent high temperature storage characteristics, and a lithium secondary battery having excellent safety during overcharging using the same.

Batteries using nonaqueous electrolyte have high voltage and high energy density, and have high reliability such as storage property and are widely used as power sources for consumer electronic devices.

Such batteries are also manufactured as secondary batteries, and a representative example thereof is a lithium ion secondary battery. This battery is composed of a negative electrode containing an active material capable of occluding and releasing lithium, a positive electrode containing a composite oxide of lithium and a transition metal, an electrolyte solution and the like. The electrolyte solution is a solution obtained by mixing lithium electrolytes such as LiBF ₄ and LiPF ₆ with a mixed solvent of high dielectric constant carbonate solvents such as propylene carbonate and ethylene carbonate and low viscosity carbonate solvents such as diethyl carbonate, methylethyl carbonate and dimethyl carbonate. It is used.

By the way, it has been reported that the thermal stability of a lithium ion secondary battery is related to the state of charge of the battery. When the battery is charged above the specified voltage value, i.e., overcharged, metal lithium precipitates on the negative electrode, or the oxidation degree of the positive electrode is increased, so that a chemical reaction with the electrolyte is likely to occur, and the thermal stability of the battery is lowered. When the battery with low thermal stability is placed under high temperature conditions, it is considered that thermal runaway occurs due to self-heating reaction, so it is important not to overcharge the battery.

For this reason, Japanese Unexamined Patent Application Publication No. 9-171840, Japanese Patent Application Laid-Open No. 2000-58116, Japanese Patent Application Laid-Open No. 2001-15155 and the like have proposed the use of an electrolyte solution containing biphenyls and alkylbenzenes. In Japanese Patent Laid-Open No. 11-162512, an alkyl compound substituted with two aromatic groups, a fluorine atom-substituted aromatic compound, and the like have been proposed as an overcharge preventing agent having improved high temperature characteristics.

Alkyl compounds substituted with biphenyls, alkylbenzenes, aromatic groups, and fluorine atom-substituted aromatic compounds have lower oxidation potentials than common solvents used in lithium batteries, so that the electrolyte solution to which they are added is likely to be electrolyzed. For this reason, instead of overcharging the battery, the electrolytic solution is electrolyzed, thereby preventing the overcharge. Hereinafter, the compound which has such a function is called an overcharge inhibitor.

On the other hand, since the overcharge inhibitor has a low oxidation potential, even in a high temperature condition in a normal use state, electrolysis occurs in a small amount and the high temperature storage characteristics may be lowered. That is, in the electrolyte solution to which the overcharge inhibitor is added, the overcharge prevention action and the high temperature storage characteristic have a trade-off relationship.

For example, according to the studies by the present inventors, the above-described biphenyls and alkylbenzenes have little effect on battery characteristics at room temperature, but when the temperature is higher than 85 ° C. at a voltage of 4.2V, the battery characteristics are greatly reduced. Experimental results have been obtained. For example, according to the present inventors' investigation, the fluorine atom-substituted aromatic compounds have slightly improved high temperature storage characteristics compared to biphenyl, but experimental results have been obtained in which the action of preventing overcharge is lowered. This is because fluorine atom-substituted aromatic compounds have a slightly higher oxidation potential than biphenyls and alkylbenzenes, so that electrolysis is unlikely to occur under high temperature conditions, but even when the battery is in an overcharged state, electrolysis is less likely to occur, thereby preventing overcharging. I think it's lowered.

In addition, Japanese Patent Application Laid-open No. Hei 11-162512 describes that the amount of the fluorine-substituted aromatic compound added is 2.5% by weight. However, according to the investigation by the present inventors, as described above, the fluorine atom-substituted aromatic compounds have a slightly lower action of preventing overcharging as compared to biphenyl, so that only the fluorine atom-substituted aromatic compounds can increase the safety of the battery during overcharge. It is necessary to make the addition amount 3 weight% or more, and in that case, even if a fluorine-substituted aromatic compound is used, deterioration of battery characteristics under high temperature will become large.

Moreover, as a method of improving the high temperature storage property of batteries, vinylene carbonates (Japanese Patent No. 3066126), alkenylethylene carbonates (Japanese Patent Laid-Open No. 2001-57232) and sultones (Japanese Patent Laid-Open No. 10-50342) It is reported to add aromatic sulfonic acid esters (Japanese Patent Laid-Open No. 2002-158035) to an electrolyte solution. It is conceivable to improve the high temperature storage characteristics of the overcharge inhibitor by applying these methods to the electrolyte solution to which the overcharge inhibitor is added. However, according to the investigation by the present inventors, even when these additives were used in a battery using biphenyl as an overcharge inhibitor, there was little improvement in the high temperature storage characteristics.

As mentioned above, the nonaqueous electrolyte and the lithium secondary battery which are excellent in the overcharge prevention characteristic and excellent in the high temperature storage characteristic have not been obtained yet. Therefore, an object of the present invention is to provide a nonaqueous electrolyte having high overcharge preventing effect and excellent high temperature storage characteristics. In addition, an object of the present invention is to provide a secondary battery containing such a nonaqueous electrolyte and improving safety during overcharging.

In other words, the present invention is an electrolyte solution consisting of a fluorine atom-substituted aromatic compound, an aromatic hydrocarbon compound containing only carbon atoms and hydrogen atoms, other non-aqueous solvents, and a lithium-containing electrolyte, wherein the fluorine atom-substituted aromatic compound is 0.1 to 20% by weight in the electrolyte, The aromatic hydrocarbon compound provides a nonaqueous electrolyte containing 0.1 to 3% by weight of the electrolyte. Such a non-aqueous electrolyte exhibits an excellent overcharge preventing effect and can suppress a decrease in high temperature storage characteristics as much as possible.

As said fluorine-substituted aromatic compound, it is preferable that it is at least 1 sort (s) of compound chosen from the group which consists of a fluorine-substituted naphthalene, a fluorine-substituted fluorene, and a fluorine-substituted biphenyl. Especially, it is preferable that it is at least 1 sort (s) of compound chosen from the group which consists of 2-fluoro biphenyl, 4-fluoro biphenyl, and 4,4'- difluoro biphenyl. Moreover, as said aromatic hydrocarbon compound, cycloalkyl group substituted benzene and / or biphenyl are preferable.

In addition, the present invention, the above electrolyte solution also has a vinylene carbonate represented by the general formula (1), alkenylethylene carbonates represented by the general formula (2), and an unsaturated hydrocarbon group represented by the general formula (3) 0.01-10% by weight of an electrolyte containing at least one compound selected from the group consisting of sultones, sulfonic acid esters having an aryl group represented by the general formula (4), sultones having a saturated hydrocarbon group and sulfonic acid imides Provide a nonaqueous electrolyte. When these are used together with the fluorine atom substituted aromatic compound and the mixture of the aromatic hydrocarbon compound which consists only of a carbon atom and a hydrogen atom, high temperature storage characteristic can be improved significantly.

In Formula (1), R <^1> and R <^2> may mutually be same or different, and represents the alkyl group which may contain a hydrogen atom, a halogen atom, or the halogen atom of 1 to 12 carbon atoms.

In Formula (2), R <^3> -R <^6> may mutually be same or different, and may be a hydrogen group, a halogen atom, the hydrocarbon group which may contain the C1-C12 halogen atom, or C2-C12 An alkenyl group, at least one of which is an alkenyl group having 2 to 12 carbon atoms.

In formula (3), R <^7> -R <^10> may mutually be same or different, and is an alkyl group which may contain the hydrogen atom, the halogen atom, or the halogen atom of C1-C12, n is 0-3 Is an integer,

In formula (4), R <^11> -R <^16> may mutually be same or different, and is a hydrogen atom, a lithium atom, a halogen atom, a sulfonic acid ester group, a carboxylic acid ester group, a lithium sulfonate group, and C1-C12 It is an atom or group chosen from the alkyl group which may contain the halogen atom of.

The present invention also provides a lithium secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, wherein the electrolyte is the nonaqueous electrolyte described above.

In addition, the lithium secondary battery according to the present invention may further include a current interruption mechanism that cuts off the charge when the gas pressure inside the battery reaches a predetermined value or more. In addition, a current interruption mechanism for interrupting charging when the temperature of the battery reaches a predetermined value or more may be provided. Thereby, the safety at the time of overcharge can be improved further.

Next, the structure is demonstrated concretely about the nonaqueous electrolyte which concerns on this invention, and the lithium secondary battery using this nonaqueous electrolyte.

Fluorine atom substituted aromatic compound

The fluorine atom-substituted aromatic compound which is one component of the nonaqueous electrolyte according to the present invention is a substance which functions as an overcharge preventing agent, in which part or all of hydrogen atoms bonded to the aromatic ring are substituted with fluorine atoms. Here, the compound having an aromatic ring represents a cyclic compound which is substantially stabilized by delocalization of π electrons.

Examples of such compounds include fluorine-substituted benzenes, fluorine-substituted naphthalenes, fluorine-substituted decalins, fluorine-substituted fluorenes, fluorine-substituted biphenyls, fluorine-substituted diphenylmethanes, and fluorine. Atom-substituted anthracene, fluorine-substituted terphenyl, fluorine-substituted phenyl ether, fluorine-substituted thiophene, fluorine-substituted furan, fluorine-substituted pyrrole, fluorine-substituted indole, fluorine-substituted pyridine, etc. Can be mentioned. Among these, fluorine-substituted naphthalenes, fluorine-substituted fluorenes, and fluorine-substituted biphenyls are preferable because of their high overcharge protection effect and relatively low deterioration of battery characteristics even under high temperature conditions. Particularly, fluorine-substituted biphenyls are preferable. More preferred. These compounds may be used independently and may be used in combination of 2 or more type.

Next, the specific example of fluorine-substituted naphthalene is given.

(1) Fluorine-substituted naphthalenes:

1-fluoronaphthalene, 2-fluoronaphthalene, 3-fluoronaphthalene, 1,2-difluoronaphthalene, 1,3-difluoronaphthalene, 1,4-difluoronaphthalene, 1,5-di Fluoronaphthalene, 1,6-difluoronaphthalene, 1,7-difluoronaphthalene, 1,8-difluoronaphthalene, 2,3-difluoronaphthalene, 2,6-difluoronaphthalene, 2 , 7-difluoronaphthalene, 1,3,5-trifluoronaphthalene, 1,3,7-trifluoronaphthalene, 1,3,5,7-tetrafluoronaphthalene, pentafluoronaphthalene, hexafluoro Ronaphthalene, heptafluoronaphthalene, perfluoronaphthalene

(2) Alkyl group and fluorine-substituted naphthalenes:

1-fluoro-3-methylnaphthalene

(3) Alkyloxy groups and fluorine-substituted naphthalenes:

1-fluoro-3-methoxynaphthalene

(4) Chlorine and fluorine-substituted naphthalenes:

1-fluoro-3-chloronaphthalene

In these fluorine-substituted naphthalenes, the number of fluorine atom-substituted atoms per molecule is preferably 2 to 4. When the fluorine atom substitution is within the above range, an excellent overcharge preventing effect is obtained and the deterioration of battery characteristics under high temperature storage is reduced.

Next, the specific example of fluorine atom substituted fluorene is given.

(1) Fluorine atom substituted fluorenes

1-fluorofluorene, 2-fluorofluorene, 3-fluorofluorene, 4-fluorofluorene, 9-fluorofluorene, 1,2-difluorofluorene, 1,3-di Fluorofluorene, 1,4-difluorofluorene, 1,5-difluorofluorene, 1,6-difluorofluorene, 1,7-difluorofluorene, 1,8-di Fluorofluorene, 2,3-difluorofluorene, 2,6-difluorofluorene, 2,7-difluorofluorene, 2,8-difluorofluorene, 3,4-di Fluorofluorene, 3,5-difluorofluorene, 3,6-difluorofluorene, 4,5-difluorofluorene, 9,9-difluorofluorene, 1,3,5 -Trifluorofluorene, 2,3,7-trifluorofluorene, 1,3,5,7-tetrafluorofluorene, pentafluorofluorene, hexafluorofluorene, heptafluorofluorene , Perfluorofluorene

(2) Alkyl group and fluorine-substituted fluorenes:

1-fluoro-3-methylfluorene

(3) Alkyloxy groups and fluorine-substituted fluorenes:

1-fluoro-3-methoxyfluorene

(4) Chlorine and fluorine-substituted fluorenes:

1-fluoro-3-chlorofluorene

In these fluorine-substituted fluorenes, 2-4 pieces of the fluorine atom-substituted number per molecule are preferable. When the number of fluorine atoms is in this range, excellent overcharge preventing effect is obtained and deterioration of battery characteristics under high temperature storage is reduced.

Next, the specific example of fluorine atom substituted biphenyls is given.

(1) Fluorine-substituted biphenyls:

2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 2,3-difluorobiphenyl, 2,4-difluorobiphenyl, 2,5-difluorobiphenyl, 2,6-di Fluorobiphenyl, 2,2'-difluorobiphenyl, 2,3'-difluorobiphenyl, 2,4'-difluorobiphenyl, 2,5'-difluorobiphenyl, 2,6'-di Fluorobiphenyl, 3,3'-difluorobiphenyl, 3,4'-difluorobiphenyl, 3,5'-difluorobiphenyl, 3,6'-difluorobiphenyl, 4,4'-di Fluorobiphenyl, trifluorobiphenyl, tetrafluorobiphenyl, pentafluorobiphenyl, hexafluorobiphenyl, heptafluorobiphenyl, octafluorobiphenyl, nonafluorobiphenyl, perfluorobiphenyl

(2) Alkyl group and fluorine atom substituted biphenyls

2-fluoro-4-methylbiphenyl, 4-fluoro-2-methylbiphenyl, 2-fluoro-2'-methylbiphenyl

(3) Alkyloxy groups and fluorine-substituted biphenyls

2-fluoro-4-methoxybiphenyl, 4-fluoro-2-methoxybiphenyl, 2-fluoro-2'-methoxybiphenyl

(4) Chlorine and fluorine-substituted biphenyls

2-fluoro-4-chlorobiphenyl

In these fluorine-substituted biphenyls, 1-3 are preferable, as for the molecule | numerator, 1 or 3 are more preferable, 1 or 2 are more preferable, and 1 is more preferable. When the fluorine atom substitution is in the above range, excellent overcharge prevention effect can be obtained.

In the case of a fluorine atom monosubstituted biphenyl, the fluorine atom substitution position is preferably 2 or 4, and more preferably 2 position. When the 2-position is substituted, the electrolysis voltage of biphenyl is controlled not only by the electron withdrawing effect but also by the steric effect of the fluorine atom, and the deterioration of the battery characteristics under high temperature storage can be suppressed as much as possible, and the overcharge prevention effect can be enhanced.

In the case of a fluorine atom disubstituted biphenyl, the fluorine atom substituted position is preferably 2 or 4 positions of two rings, more preferably 4 and 4 'positions. When the fluorine atom is bonded at the above substitution position, the electrolysis voltage of biphenyl can be controlled to an appropriate level, the degradation of battery characteristics under high temperature storage can be suppressed, and the overcharge prevention effect can be enhanced.

Among the above-described fluorine-substituted biphenyls, 2-fluorobiphenyl, 4-fluorobiphenyl, 4,4'-difluorobiphenyl are preferable, and 2-fluorobiphenyl is particularly preferable.

Aromatic hydrocarbon compounds

In the nonaqueous electrolyte according to the present invention, an aromatic hydrocarbon compound composed of only carbon atoms and hydrogen atoms is added as one of its components. As a result, the effect of further increasing the overcharge prevention effect of the fluorine-substituted aromatic compound can be obtained. Examples of such aromatic hydrocarbon compounds include benzenes, biphenyls, terphenyls, naphthalenes, and the like, and they may be used in one kind or in combination of two or more kinds.

Next, the specific example of these aromatic hydrocarbon compounds is given.

(1) benzenes:

Benzene, toluene, xylene, cumene, cyclohexylbenzene, tetralin

(2) biphenyls:

Biphenyl, 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, 2-ethylbiphenyl, 2,2'-dimethylbiphenyl

(3) Terphenyls:

Orthoterphenyl, metaterphenyl, paraterphenyl, methylterphenyl

(4) Naphthalenes:

Naphthalene, 1-methylnaphthalene, 2-methylnaphthalene

Among these aromatic hydrocarbon compounds, alkyl groups or cycloalkyl group-substituted benzenes and biphenyls are preferable, cyclohexyl benzene and biphenyl are more preferable, and biphenyl is most preferred. When a small amount of these compounds is added, the effect of preventing overcharge of the fluorine atom-substituted aromatic compound can be enhanced while minimizing the deterioration of battery characteristics during high temperature storage.

Other compounds

In the nonaqueous electrolyte according to the present invention, in addition to the two components described above, vinylene carbonates represented by the general formula (1), alkenylethylene carbonates represented by the general formula (2), and general formula (3) It is preferable to add at least 1 sort (s) of compound chosen from the group which consists of a sultone which has an unsaturated hydrocarbon group represented, a sulfonic acid ester which has an aryl group represented by General formula (4), a sultone which has a saturated hydrocarbon group, and a sulfonic acid imide. .

In the case where the overcharge inhibitor is the two components described above, the deterioration in battery characteristics at the time of high temperature storage caused by the addition of the overcharge inhibitor can be significantly suppressed.

As a compound mentioned above, the compound described next can be illustrated. They may be used independently and may be used in combination of 2 or more type.

(1) Vinylene carbonates represented by the general formula (1)

(2) Alkenylethylene carbonates represented by General formula (2)

(3) Sultones having an unsaturated hydrocarbon group represented by the general formula (3)

(4) sulfonic acid ester having an aryl group represented by General Formula (4)

(5) Sultones having saturated hydrocarbon groups

(6) sulfonic acid imides

Vinylene carbonate is represented by General formula (1) shown next.

In Formula (1), R <^1> and R <^2> may mutually be same or different, and represents the alkyl group which may contain a hydrogen atom, a halogen atom, or the halogen atom of 1 to 12 carbon atoms. The halogen atom is preferably a fluorine atom or a chlorine atom, and more preferably a fluorine atom.

As specific examples of the vinylene carbonates represented by the formula (1), the following compounds may be mentioned. That is, vinylene carbonate, fluorovinylene carbonate, methylvinylene carbonate, fluoromethylvinylene carbonate, ethylvinylene carbonate, propylvinylene carbonate, butylvinylene carbonate, dimethylvinylene carbonate, diethylvinylene carbonate, Dipropylvinylene carbonate. Of these compounds, vinylene carbonate is most preferred.

Alkenyl ethylene carbonates are represented by General formula (2) shown next.

In Formula (2), R <^3> -R <^6> may mutually be same or different, and may be a hydrogen group, a halogen atom, the hydrocarbon group which may contain the C1-C12 halogen atom, or C2-C12 As the alkenyl group, at least one of R ³ to R ⁶ is an alkenyl group having 2 to 12 carbon atoms. As an example of an alkenyl group, a vinyl group, a propenyl group, an aryl group, butenyl group, etc. are mentioned.

The following compound is mentioned as a specific example of alkenylethylene carbonate represented by Formula (2). That is, vinyl ethylene carbonate, propenyl ethylene carbonate, 4,4-divinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-4-vinyl ethylene carbonate, 4-fluoro-4-vinyl ethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, 4-ethyl-4-vinylethylene carbonate. Among these compounds, vinyl ethylene carbonate and divinyl ethylene carbonate are most preferred.

Sultones having an unsaturated hydrocarbon group are represented by the following general formula (3).

In formula (3), R <^7> -R <^10> may mutually be same or different, and is an alkyl group which may contain the hydrogen atom, the halogen atom, or the halogen atom of C1-C12, n is 0-3 Is an integer.

The following compound is mentioned as a specific example of the sultone which has an unsaturated hydrocarbon group represented by Formula (3). Ie ethylsultone, 1,3-propenesultone, 1,4-butenesultone, 1,5-pentenesultone, 1-methyl-1,3-propenesultone, 1-fluoro-1,3-propene Sultone, 2-methyl-1,3-propenesultone, 3-methyl-1,3-propenesultone, 1-trifluoromethyl-1,3-propenesultone. Among these compounds, 1,3-propenesultone and 1,4-butenesultone are most preferred.

As sulfonic acid ester which has an aryl group, the thing of General formula (4) shown next can be illustrated.

In formula (4), R <^11> -R <^16> may mutually be same or different, and is a hydrogen atom, a lithium atom, a halogen atom, a sulfonic acid ester group, a carboxylic acid ester group, a lithium sulfonate group, and C1-C12 It is an atom or group chosen from the group which consists of an alkyl group which may contain the halogen atom of.

The following compound is mentioned as a specific example of sulfonic acid ester which has an aryl group represented by Formula (4). Namely, ethyl benzene sulfonate, benzenedi (methyl sulfonate), benzenedi (ethyl sulfonate), benzenedi (propyl sulfonate), benzene (methyl sulfonate) (ethyl sulfonate), benzene (aryl sulfonate), Benzene di (vinyl sulfonate), benzenedi (ethynyl sulfonate), benzene tri (methyl sulfonate), sulfo benzoic anhydride, dimethyl sulfo benzoic acid, methyl toluene sulfonate, toluene di (ethyl sulfonate), toluene Propyl phosphate), methyl trifluoromethylbenzenesulfonate, trifluoromethylbenzenedi (methylsulfonate), trifluoromethylbenzenetri (ethylsulfonate), lithium naphthalenesulfonate salt, lithium benzenesulfonate salt, tri Fluoromethylbenzenesulfonic acid lithium salt, benzenedisulfonic acid lithium salt, trifluoromethylbenzenedisulfonic acid lithium salt, benzenetrisulfonic acid trilithium salt, sulfobenzoic acid dilithium salt, toluene sulfonic acid lithium salt, toluene disulfone Sandylithium salt.

Among these compounds, benzene di (sulfonic acid ester) is preferable, and benzene di (sulfonic acid ester) of meta-substituted is particularly preferable.

The following compound can be illustrated as a sultone which has a saturated hydrocarbon group.

1,3-propanesultone, 1,4-butanesultone, 1,5-pentanesultone, 1,6-hexanesultone, 1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone, 1-methyl-1,4-butanesultone, 2-methyl-1,4-butanesultone, 3-methyl-1,4-butanesultone, 4-methyl-1, 4-butanesultone.

Of these, 1,3-propanesultone and 1,4-butanesultone are preferred.

The following compound can be illustrated as sulfonic acid imide.

N-methyl-di (methanesulfonic acid) imide, N, N-dimethyl-methanesulfonic acid imide, tris (trifluoromethanesulfonic acid) imide, N-methyl-di (trifluoromethanesulfonic acid) imide De, di (trifluoromethanesulfonic acid) imide lithium salt, N, N-dimethyl-trifluoromethanesulfonic acid imide, N-ethyl-di (trifluoromethanesulfonic acid) imide, N, N- Diethyl-trifluoromethanesulfonic acidimide, N-methyl-di (pentafluoroethanesulfonic acid) imide, di (pentafluoroethanesulfonic acid) imide lithium salt, N, N-dimethyl-pentafluoro Ethanesulfonic acid imide, N-methyl-di (perfluoropropanesulfonic acid) imide, N, N-dimethyl-perfluoropropanesulfonic acid imide, N-methyl-di (perfluorobutanesulfonic acid) imide , N, N-dimethyl-perfluorobutanesulfonic acid imide.

Among these compounds, di (trifluoromethanesulfonic acid) imides and di (pentafluoroethanesulfonic acid) imides are preferable, and in particular, di (trifluoromethanesulfonic acid) imide lithium salts and di (pentafluoro) The sulfonic acid) imide lithium salt is preferable because it also acts as an electrolyte and improves the ion conductivity of the electrolyte solution.

Among the above compounds, vinylene carbonates represented by the general formula (1) and alkenesultones having an unsaturated hydrocarbon group represented by the general formula (3) are preferable. Specifically, vinylene carbonate and 1,3-propenesultone are preferable.

In addition, when the vinylene carbonates represented by the general formula (1) and the sultones having an unsaturated hydrocarbon group represented by the general formula (3) are added at the same time, the effect of high temperature preservation increases and is preferable. And a combination of ethylene carbonate and 1,3-propenesultone.

Other non-aqueous solvents

The nonaqueous electrolyte according to the present invention is basically composed of a nonaqueous solvent and an electrolyte, and the nonaqueous solvent is a nonaqueous solvent which is usually used in addition to the aforementioned fluorine-substituted aromatic compounds and aromatic hydrocarbon compounds composed only of carbon atoms and hydrogen atoms. Here, "normally used nonaqueous solvent" is called "other nonaqueous solvent", and it demonstrates concretely next.

Other nonaqueous solvents that can be used include cyclic aprotic solvents and / or linear aprotic solvents. Among them, examples of the cyclic aprotic solvent include cyclic carbonates such as ethylene carbonate, cyclic esters such as γ-butyrolactone, cyclic sulfones such as sulfolane, and cyclic ethers such as dioxolane. Examples of the chain aprotic solvent include chain carbonates such as dimethyl carbonate, chain carboxylic acid esters such as methyl propionate, and chain ethers such as dimethoxyethane.

When the load characteristic and low temperature characteristic of a battery are especially improved, it is preferable to mix and use a cyclic aprotic solvent and a linear aprotic solvent. In addition, when the electrochemical stability of electrolyte solution is important, it is preferable to mix and use cyclic carbonate as a cyclic aprotic solvent, and to select a linear carbonate as a linear aprotic solvent.

Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate. High dielectric constant ethylene carbonate and propylene carbonate are suitable. When graphite is used for a negative electrode active material, ethylene carbonate is especially preferable. You may use these cyclic carbonates in mixture of 2 or more types.

Examples of the chain carbonates include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and methyl trifluoroethyl carbonate. Can be. Dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate with low viscosity can be used suitably. You may use these linear carbonates in mixture of 2 or more types.

The mixing ratio (cyclic carbonate: chain carbonate) of the cyclic carbonate and the linear carbonate is expressed in a weight ratio, preferably 1:99 to 99: 1, more preferably 5:95 to 70:30, and even more preferably 10:90 60:40. If it is in the range of such a mixing ratio, since the viscosity rise of electrolyte solution can be suppressed and the dissociation degree of electrolyte can be improved, the conductivity of the electrolyte solution related to the charge / discharge characteristic of a battery can be improved.

On the other hand, when the flash point of a solvent is made high from the viewpoint of the fire safety improvement of a battery, cyclic aprotic solvent is used independently as another nonaqueous solvent, or the mixing ratio of a chain | strand-shaped aprotic solvent is other nonaqueous. It is preferable to adjust to 20 weight% or less with respect to the whole solvent.

As the cyclic aprotic solvent in this case, it is particularly preferable to use one or a combination of ethylene carbonate, propylene carbonate, sulfolane, γ-butyrolactone and N-methyloxazolinone.

Examples of the specific solvent combination include ethylene carbonate and sulfolane, ethylene carbonate and propylene carbonate, ethylene carbonate and γ-butyrolactone, ethylene carbonate and propylene carbonate and γ butyrolactone.

When using a chain | strand aprotic solvent in the ratio of 20 weight% or less with respect to the whole other nonaqueous solvent, chain | strand carbonate, a chain carbonate, and a chain phosphate ester can be used as chain | strand aprotic solvent. Particularly, chain carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diheptyl carbonate, dioctyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, methyl heptyl carbonate and methyl octyl carbonate are preferable. Do. The mixing ratio of the cyclic carbonate and the linear carbonate (cyclic carbonate: chain carbonate) is preferably 80:20 to 99.5: 0.5, more preferably 90:10 to 99: 1.

The other nonaqueous solvent may contain the solvent of that excepting the above within the range which does not deviate from the objective of this invention. Specific examples of such a solvent include amides such as dimethylformamide, chain carbamates such as methyl-N, N-dimethyl carbamate, and cyclic amides such as N-methylpyrrolidone, and N, N-dimethyl. Cyclic ureas such as imidazolidinone, trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, borate esters such as triborate tri (trimethylsilyl), trimethyl phosphate, triethyl phosphate, and tris (trimethylsilyl) Linear phosphate esters such as and ethylene glycol derivatives such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, and the like.

Lithium-containing electrolyte

As the electrolyte containing lithium usable in the nonaqueous electrolyte of the present invention, any electrolyte can be used without particular limitation as long as it is usually used as an electrolyte for the nonaqueous electrolyte.

Specific examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (an integer from k = 1 to 8), LiPF _n {C _k F _{( 2k + 1)} } _(6-n) Lithium salt, such as (an integer of n = 1-5, the integer of k = 1-8), etc. are mentioned.

Moreover, the lithium salt represented with the following general formula can also be used. That is, LiC (SO ₂ R ¹⁷ ) (SO ₂ R ¹⁸ ) (SO ₂ R ¹⁹ ), LiN (SO ₂ OR ²⁰ ) (SO ₂ OR ²¹ ), LiN (SO ₂ R ²² ) (SO ₂ OR ²³ ), LiN (SO ₂ R ²⁴ ) (SO ₂ R ²⁵ ). Here, R <^17> -R <^25> may mutually be same or different and is a C1-C8 perfluoroalkyl group.

Among these, LiPF ₆ , LiBF ₄ and LiN (SO ₂ R ²⁴ ) (SO ₂ R ²⁵ ) are preferred.

In addition, some of the compounds exemplified herein partially overlap with the above-mentioned sulfonic acid imides, but these compounds act as an electrolyte and also have an effect of suppressing deterioration of battery characteristics under high temperature conditions of the nonaqueous electrolyte. It may be used for any purpose and is preferably used as a lithium-containing electrolyte.

These lithium salts may be used alone or in combination of two or more kinds thereof. As a combination used by mixing two or more kinds, LiPF ₆ and LiBF _4, LiPF ₆ and LiN (SO ₂ R ²⁴ ) (SO ₂ R ²⁵ ), LiBF ₄ and LiN (SO ₂ R ²⁴ ) (SO ₂ R ²⁵ ) And LiPF ₆ and LiBF ₄ and LiN (SO ₂ R ²⁴ ) (SO ₂ R ²⁵ ) are illustrated.

Non-aqueous electrolyte

The nonaqueous electrolyte according to the present invention contains at least a nonaqueous solvent and a lithium-containing electrolyte containing a fluorine atom-substituted aromatic compound, an aromatic hydrocarbon compound comprising only carbon atoms and hydrogen atoms, and other non-aqueous solvents.

The content of the fluorine-substituted aromatic compound is preferably 0.1 to 20% by weight, preferably 0.5 to 20% by weight, more preferably 3 to 20% by weight, and more preferably 3 to 10% by weight based on the total electrolyte. Within this range, a high overcharge prevention effect can be obtained, and a decrease in high temperature storage characteristics can be suppressed to a minimum, and a decrease in lithium ion conductivity of the electrolyte solution can be maintained. Thus, the load characteristics of the battery can be maintained satisfactorily.

As for content of the aromatic hydrocarbon compound which consists only of a carbon atom and a hydrogen atom, 0.1-3 weight% with respect to the whole electrolyte solution, Preferably it is 0.1-2 weight%, More preferably, 0.1-1 weight% is preferable. Within this range, an excellent overcharge prevention effect can be obtained by synergistic effect with the fluorine atom-substituted aromatic compound, and the deterioration of battery characteristics at high temperature storage is also minimized.

The lithium-containing electrolyte is preferably contained in the nonaqueous electrolyte at a concentration of preferably 0.1 to 3 mol / liter, more preferably 0.5 to 2 mol / liter. Thereby, electrical characteristics, such as a favorable load characteristic and low temperature characteristic, can be acquired.

In one aspect of the nonaqueous electrolyte according to the present invention, in addition to the above-described basic structure including the above-described fluorine atom-substituted aromatic compound, aromatic hydrocarbon compound composed only of carbon atoms and hydrogen atoms, other non-aqueous solvents and electrolytes, Can be changed to a configuration in which is added. The content is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, still more preferably 0.1 to 3% by weight based on the entire electrolyte solution. If the addition amount is in this range, the fall of the battery characteristic at the time of high temperature storage which arises when the above-mentioned overcharge inhibitor is added can be suppressed significantly.

The nonaqueous electrolyte according to the present invention having the above-described configuration is not only suitable as a nonaqueous electrolyte for lithium secondary batteries, but also for nonaqueous electrolyte for primary batteries, nonaqueous electrolyte for electrochemical capacitors, electric double layer capacitors and aluminum electrolytic capacitors. It can also be used as a nonaqueous electrolyte solution.

Rechargeable battery

The lithium secondary battery according to the present invention is basically composed of a negative electrode, a positive electrode, a separator separating them from each other, and the nonaqueous electrolyte.

Examples of the negative electrode active material constituting the negative electrode include metal lithium, a lithium-containing alloy, or a silicon, a silicon alloy, tin, tin alloy, and a tin oxide which can be doped and dedoped of lithium ions, which can be alloyed with lithium, Of a transition metal oxide capable of doping and dedoping lithium ions, a transition metal nitrogen compound capable of doping and undoping lithium ions, a carbon material capable of dope and dedoping lithium ions, or a mixture thereof Any can be used.

Examples of the carbon material include carbon black, activated carbon, artificial graphite, natural graphite, and amorphous carbon materials. The form may be any of fibrous, spherical, potted and flake shaped. Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers (MCF), and the like that are calcined at 1500 ° C or lower. Examples of the graphite material include natural graphite, graphitized coke, graphitized MCMB, graphitized MCF, and boron-containing materials, and those coated with metals such as gold, platinum, silver, copper, Sn, and Si, or amorphous carbon. Coated ones can be used. One kind of these carbon materials may be used, or two or more kinds thereof may be used in combination. Moreover, carbon black, amorphous whisker carbon, etc. may be added and used as a conductive support agent.

As the carbon material, a carbon material having a plane angle (d002) of the (002) plane measured by X-ray diffraction is particularly 0.340 nm or less, and a graphite having a true density of 1.70 g / cm ³ or more or a high crystallinity having properties close thereto. Carbon materials are preferred. By using such a carbon material, the energy density of a battery can be made high.

Examples of the positive electrode active material constituting the positive electrode include transition metal sulfides or transition metal oxides such as FeS ₂ , MoS ₂ , TiS ₂ , MnO ₂ , V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , A composite oxide of lithium and a transition metal such as LiNi _x Co _(1-x) O ₂ , LiNi _x Co _y Mn _(1-xy) O ₂ , polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothia Conductive polymer materials, such as a diazole polyaniline composite, carbon materials, such as a fluorocarbon and activated carbon, etc. are mentioned.

Among these, especially the composite oxide of lithium and a transition metal is preferable because it is easy to electrolyze an overcharge inhibitor, since the increase of the battery voltage at the time of overcharge is large. One type of positive electrode active material may be used, and two or more types may be mixed and used for it. Since the positive electrode active material usually does not have sufficient conductivity, a positive electrode is used together with a conductive assistant. As such a conductive support agent, carbon materials, such as carbon black, amorphous whisker carbon, and graphite, can be illustrated.

The separator may be a membrane that electrically insulates the positive electrode and the negative electrode, and is capable of transmitting lithium ions, and a porous membrane or a polymer electrolyte is used. As the porous membrane, a microporous polymer film is suitably used, and examples thereof include polyolefin, polyimide, polyvinylidene fluoride, polyester and the like. In particular, a porous polyolefin film is preferable, and specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film can be illustrated. On these porous polyolefin films, other resins excellent in thermal stability may be coated.

As a polymer electrolyte, the polymer material which melt | dissolved lithium salt, the polymer material swelled with electrolyte solution, etc. are mentioned. The nonaqueous electrolyte of the present invention may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer material.

The lithium secondary battery of such a structure can be formed in cylindrical shape, coin shape, square shape, film shape, and other arbitrary shapes. However, the basic structure of the battery is almost the same regardless of the shape, and the design can be changed according to the purpose.

In the lithium secondary battery according to the present invention, in order to exert the overcharge prevention effect of the nonaqueous electrolyte, the current cut-off mechanism and / or the temperature of the battery which cuts off the charge when the gas pressure inside the battery reaches a predetermined value or more, It is desirable to have a current cut-off mechanism to cut off the charge.

In general, when the battery is overcharged, the electrolyte is electrolyzed to generate gas and heat. The current interruption mechanism is a mechanism that detects this gas and / or heat and cuts off the charge of the battery, thereby preventing the battery from being overcharged. The nonaqueous electrolyte according to the present invention is electrolyzed when the voltage of the battery rises above a certain value, and in addition to the function of not progressing the charge of the battery any more, the current blocking mechanism is operated quickly because gas and heat are generated during the electrolysis. You can. Therefore, the safety at the time of overcharging of a battery can further be improved.

As the current cut-off mechanism that cuts off the charge when the gas pressure inside the battery is higher than the predetermined value, it is deformed as the internal pressure of the battery rises and the charge-current contact breaks. Examples include a circuit, an external circuit that detects deformation of the battery due to the internal voltage of the battery with a sensor, and stops charging, and a mechanism for deforming as the internal pressure of the battery increases to short the positive and negative electrodes to prevent the battery from being charged. can do. Of these, the mechanism that deforms as the internal pressure of the battery increases and the contact point of the charging current is broken is preferable because of its simple structure and high effect.

As a current cut-off mechanism that cuts off the charge when the battery temperature is higher than a predetermined value, an external circuit that detects the temperature rise of the battery by using a sensor to stop charging, and melts when the temperature of the battery rises, causing a blockage and passing ions. Separator that prevents the battery from rising, capsules dissipating the deactivation material of the battery when the temperature rises, device whose electrical resistance rises when the temperature rises, and melts when the temperature rises Examples thereof include an electrode including a conductive material in which electrical resistance increases when the temperature of the mechanism and the battery rises.

Next, although an example of the structure of a cylindrical and coin type battery is demonstrated, the negative electrode active material, the positive electrode active material, and the separator which comprise each battery can be used common to the above.

In the cylindrical lithium secondary battery, a non-aqueous electrolyte is injected with a negative electrode coated with a negative electrode active material on a negative electrode current collector such as copper foil, and a positive electrode coated with a positive electrode active material on a positive electrode current collector such as aluminum foil. It winds through a separator and is stored in the battery can in the state which mounted the insulating plate on the upper and lower sides of the winding body. Then, the battery can is closed by using a sealing body with a current contact that is deformed and broken when the internal pressure of the battery rises or an element whose electrical resistance increases when the temperature of the battery rises. It is a closed structure.

In a coin-type lithium secondary battery, a disc-shaped negative electrode, a separator into which a nonaqueous electrolyte is injected, a disc-shaped positive electrode, and spacer plates such as stainless or aluminum are stacked in this order, if necessary, in a coin-type battery can. In addition, a strain gauge or the like for detecting the deformation of the battery due to the internal pressure of the battery may be attached.

Example

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited at all by these Examples.

1. Fabrication of batteries

<Preparation of nonaqueous electrolyte amount>

As the non-aqueous solvent, ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a ratio of EC: MEC = 4: 6 (weight ratio), and then LiPF ₆ , an electrolyte, was dissolved in the above non-aqueous solvent to give an electrolyte concentration. A nonaqueous electrolyte was prepared so that it became 0.1 mol / liter.

Next, predetermined amounts of the various compounds listed in Table 1 were added to this nonaqueous electrolyte to prepare 19 kinds of electrolyte solutions.

In addition, in Table 1, the kind of additive was abbreviated and described as follows.

FBP: 2-fluorobiphenyl, BP: biphenyl,

VC: vinylene carbonate, PES: 1,3-propenesultone,

DPM: diphenylmethane, CHB: cyclohexylbenzene,

BD: metabenzene disulfonic acid dimethyl ester,

TF: di (trifluoromethanesulfonic acid) imide lithium

PS: 1,3-propanesultone

In addition, the numerical value in parentheses is the value which showed content in the electrolyte solution of each compound by weight%.

<Production of negative drama>

74 parts by weight of mesocarbon microbeads (MCMB10-28 manufactured by Osaka Gas Co., Ltd.), 20 parts by weight of natural graphite (LF18A manufactured by Nagakoshi Graphite Co., Ltd.) and 6 parts by weight of polyvinylidene fluoride (PVDF) as a binder It disperse | distributed to N-methylpyrrolidinone which is a solvent, and prepared the negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to a negative electrode current collector made of a band-like copper foil having a thickness of 18 μm, and dried.

<Production of plus play>

82 parts by weight of LiCoO ₂ (HLC-22 manufactured by Honso FMC Energy Systems Co., Ltd.), 7 parts by weight of graphite as a conductive agent, 3 parts by weight of acetylene black, and 8 parts by weight of polyvinylidene fluoride as a binder, are mixed with N-methylpi Dispersed in rollidone to prepare a LiCoO ₂ mixture slurry. This LiCoO ₂ mixture slurry was applied to an aluminum foil having a thickness of 20 μm and dried.

<Production of coin type battery>

The negative electrode for a coin-type battery was subjected to compression molding of the negative electrode described above, and a hole was formed in a disk shape having a diameter of 14 mm to obtain a coin-shaped negative electrode. The thickness of the negative electrode mixture was 70 µm, and the weight was 20 mg / 14 mmφ.

In the positive electrode for a coin battery, the positive electrode was compression molded, and a hole was formed in a disk shape having a diameter of 13.5 mm to obtain a coin-shaped LiCoO ₂ plus electrode. The LiCoO ₂ mixture had a thickness of 70 μm and a weight of 42 mg / 13.5 mmφ.

Separator completed with a negative pole of 14 mm in diameter, a plus pole of 13.5 mm in diameter, and a microporous polypropylene film of 16 mm in diameter with a thickness of 25 μm, in the order of minus pole, separator, plus pole in a 2032 battery can made of stainless steel. Laminated. Then, 0.04 ml of said nonaqueous electrolyte was inject | poured into the separator, Furthermore, the aluminum plate (thickness 1.2mm, diameter 16mm) and the spring were accommodated. Finally, a coin-type battery having a diameter of 20 mm and a height of 3.2 mm was produced by maintaining the airtightness in the battery by covering the lid of the battery can through a gasket made of polypropylene.

<Production of laminate battery>

Using the same electrode as described above, the negative electrode having a dimension of 21 mm x 21 mm and the positive electrode having a size of 20 mm x 20 mm were cut out, and the electrode body was made to face each other via a separator completed with a microporous polypropylene film having a width of 25 mm x 50 mm in length. . The electrode body was housed in a cylindrical bag made of an aluminum laminate film (manufactured by Showa Laminate Kogyo Co., Ltd.) so that both lead wires of the positive electrode and the negative electrode were taken out from the opening of one side, and the lead wire was taken out. The gin side was closed by heat fusion. Next, 0.15 ml of the electrolyte solution was injected into the electrode body to be impregnated, and then the remaining open portion was heat-sealed to seal the electrode body in a bag to obtain a laminate battery.

2. Evaluation of Battery Characteristics

<Evaluation method of overcharge prevention effect 1: Measurement of gas generation amount during overcharge>

The laminate battery described above was charged to 4.1 V, and stored at 45 ° C. for 24 hours, and then charged and discharged at 4.2 V to 3.0 V to confirm the battery capacity. The capacity of the battery at this time was 10 mAh. The battery was charged at a constant current of 5 mA for 5 hours to overcharge the battery.

The volume of the battery during overcharging and the volume of the battery after overcharging were measured, and the amount of gas generated during overcharging was measured from the difference. Table 2 shows the measurement results of the type of electrolyte solution used for the measurement and the amount of gas generated during overcharge.

<Method 2: Evaluation of the Overcharge Prevention Effect> Measurement of Oxidation Pressure of Electrolyte Solution

The oxidation pressure of the electrolyte solution is 10 mV / sec in the range of 3V to 5V, with the working electrode as the glossy carbon and the counter electrode and the reference electrode as the metal lithium while the electrolyte is heated to 80 ° C in the glove box. Measured by doing a tree. The measurement was performed at 80 ° C because the battery generates heat due to the heat of electrolysis of the electrolyte when the battery is overcharged, and therefore the oxidation pressure of the electrolyte at a high temperature is effectively important. Table 3 shows the kind of electrolyte solution used for the measurement and the oxidation current value at 4.65V.

〈Evaluation Method of High Temperature Storage Characteristics〉

The coin-type battery described above was charged at 4.1 V, and stored at 45 ° C. for 7 days, and then charged and discharged at 4.2 V to 3.0 V to confirm the battery capacity. The battery capacity at this time was 5 mAh. The storage test of coin-type battery was conducted in the same battery for 4.1 days after charging the battery at 4.1V (referred to as "aging") for 7 days, and after the battery was charged at 4.2V for 3 days at 85 ° C. It carried out continuously in 2 conditions of conditions (called "high temperature storage").

The "5 mA discharge capacity" of the battery before and after storage was measured, then the "discharge capacity ratio" was calculated, and the high temperature storage characteristics were evaluated from the result. Table 4 shows the evaluation results of the type of electrolyte solution and the high temperature storage characteristics used for the measurement.

The "discharge capacity ratio" represents the 5 mA discharge capacity after storage (after aging or after high temperature storage) as a ratio with respect to the 5 mA discharge capacity when not preserved, and was taken as the discharge capacity ratio after aging and the discharge capacity ratio after high temperature storage, respectively.

Discharge capacity ratio = (C / D) × 100 (%)

C = 5mA discharge capacity after storage

D = 5mA discharge capacity without preservation

Here, the "5 mA discharge capacity" of the battery is a discharge capacity when the coin-type battery is discharged at a current of 5 mA after charging at 4.2V.

<result>

From the results of Table 2 and Table 3, the electrolyte solution to which both compounds of the fluorine-substituted aromatic compound (2-fluorobiphenyl) and the aromatic hydrocarbon compound (biphenyl, cyclohexylbenzene) which consist only of a carbon atom and a hydrogen atom was added at the time of overcharge The amount of gas generated was large (Examples 1 to 4), and the oxidation current value was significantly higher than that of the fluorine atom-substituted aromatic compound alone (Comparative Example 5) (Examples 5 to 9). Therefore, when this electrolyte is applied to a battery equipped with a mechanism for stopping charging in conjunction with the pressure in the battery, it indicates that a battery having a high safety during overcharging can be obtained.

In addition, the experiments of Examples 1 to 3 were carried out in a calorimeter (Cetrometer C-80), and the calorific value from the battery was measured. It was confirmed that more heat generation occurred than the electrolyte solution (Comparative Example 1) containing no additives. . Therefore, this electrolyte solution, in particular, is applied to a battery having a mechanism that stops charging in association with the temperature in the battery, thereby improving the safety at the time of overcharging and obtaining a battery with little deterioration at high temperature storage.

From the results in Table 4, the electrolyte solution (Examples 10, 11, and 12) containing both a fluorine-substituted aromatic compound and an aromatic hydrocarbon compound composed only of carbon atoms and hydrogen atoms (Examples 10, 11, and 12) was prepared by adding an electrolyte solution ( Compared with the comparative example 8, it turned out that the fall of high temperature storage characteristic is suppressed to the minimum. On the other hand, the electrolyte solution (comparative example 9) containing only the aromatic hydrocarbon compound which consists only of a carbon atom and a hydrogen atom (comparative example 9) drastically deteriorated high temperature storage characteristic.

Moreover, the electrolyte solution (Examples 13-20) which further added the "other compound" mentioned above has the further high temperature storage characteristic, and is excellent in high temperature storage compared with the electrolyte solution (Comparative example 7) which does not contain an overcharge inhibitor. Characteristics. On the other hand, when the overcharge inhibitor is only an aromatic hydrocarbon compound composed of only carbon atoms and hydrogen atoms, the improvement of high temperature storage characteristics is low even in the electrolyte solution to which "other compounds" are added (Comparative Example 12) or no improvement at all. (Comparative Examples 10, 11).

The nonaqueous electrolyte according to the present invention has a large amount of gas generated during overcharging, and a high overcharge preventing effect can be obtained because a large amount of oxidizing current flows. Moreover, the high temperature storage characteristic is excellent from the high temperature storage test result of a coin battery. Therefore, the lithium secondary battery containing this non-aqueous electrolyte has high safety when overcharged, and is also excellent in high temperature storage characteristics. In addition, when the nonaqueous electrolyte is applied to a battery having a mechanism for stopping charging in conjunction with the internal pressure and / or temperature of the battery, a battery having high safety during overcharging of the battery and less degradation at high temperature can be obtained.

Claims (7)

A fluorine-substituted aromatic compound, an aromatic hydrocarbon compound containing only carbon atoms and hydrogen atoms, other nonaqueous solvents, and an electrolyte containing a lithium-containing electrolyte, wherein the fluorine-substituted aromatic compound is 0.1 to 20% by weight in the electrolyte, and the aromatic hydrocarbon compound is an electrolyte solution. 0.1-3 weight% in the nonaqueous electrolyte characterized by the above-mentioned. A non-aqueous electrolyte solution according to claim 1, wherein the fluorine-substituted aromatic compound is at least one compound selected from fluorine-substituted biphenyls. The nonaqueous electrolyte solution according to claim 1, wherein the aromatic hydrocarbon compound is at least one compound selected from the group consisting of alkyl groups or cycloalkyl group substituted benzenes and biphenyls. The electrolyte solution according to claim 1, wherein the electrolyte solution further includes vinylene carbonates represented by the general formula (1), alkenylethylene carbonates represented by the general formula (2), and sultones having an unsaturated hydrocarbon group represented by the general formula (3). At least one compound selected from the group consisting of a sulfonic acid ester having an aryl group represented by the general formula (4), a sulfonic acid having a saturated hydrocarbon group, and a sulfonic acid imide, in an electrolyte solution, containing 0.01 to 10% by weight Nonaqueous Electrolyte: In formula (1), R <^1> and R <^2> may mutually be same or different, and represents the alkyl group which may contain the hydrogen atom, the halogen atom, or the halogen atom of 1-12 carbon atoms, In Formula (2), R <^3> -R <^6> may mutually be same or different, and may be a hydrogen group, a halogen atom, the hydrocarbon group which may contain the C1-C12 halogen atom, or C2-C12 An alkenyl group, at least one of which is an alkenyl group having 2 to 12 carbon atoms, In formula (3), R <^7> -R <^10> may mutually be same or different, and is an alkyl group which may contain the hydrogen atom, the halogen atom, or the halogen atom of C1-C12, n is 0-3 Is an integer, In formula (4), R <^11> -R <^16> may mutually be same or different, and is a hydrogen atom, a lithium atom, a halogen atom, a sulfonic acid ester group, a carboxylic acid ester group, a lithium sulfonate group, and C1-C12 It is an atom or group chosen from the group which consists of an alkyl group which may contain the halogen atom of. A secondary battery comprising a negative electrode, a positive electrode, and an electrolyte solution, wherein the electrolyte solution is the nonaqueous electrolyte solution according to any one of claims 1 to 4. 6. The lithium secondary battery according to claim 5, wherein the secondary battery is further provided with a current interruption mechanism for interrupting charging when the gas pressure inside the battery is above a predetermined value. 6. The lithium secondary battery according to claim 5, wherein the secondary battery is further provided with a current interrupting mechanism for interrupting charging when the temperature of the battery is above a predetermined value.