JP5455889B2 - Non-aqueous electrolyte and secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte and a secondary battery.

In a lithium ion battery, when overcharge is performed to exceed the normal working voltage (for example, LiCoO ₂ , 4.2 V when fully charged), excess lithium is released from the positive electrode. At the same time, excessive lithium deposition occurs in the negative electrode, resulting in dendrite. Therefore, both the positive and negative electrodes become chemically unstable and eventually react with carbonates in the nonaqueous electrolytic solution, which may cause a rapid exothermic reaction due to decomposition or the like. This causes a problem that the entire battery generates heat abnormally and the safety of the battery is impaired.

  Therefore, various techniques for improving the safety during overcharging of the nonaqueous electrolyte secondary battery have been studied. Usually, since a countermeasure is taken to prevent overcharging by a protection circuit or the like so as not to cause an internal short circuit, an abnormal situation does not occur. However, it is necessary to take measures to maintain the safety of the battery itself even in the case of overcharging, assuming a failure of the charger or the protection circuit.

  Patent Documents 1 to 4 and Non-Patent Document 1 disclose a technique for ensuring safety during overcharge by adding an aromatic compound as an additive to an electrolytic solution.

  In Patent Documents 1 to 3, a solution in which cyclohexylbenzene, biphenyl, 3-R-thiophene, 3-chlorothiophene, furan, or the like is dissolved in an electrolytic solution is used, and gas is generated in the battery at the time of overcharge to generate internal electricity. A technique for suppressing overcharge of a battery by a method such as operating a cutting device or generating a conductive polymer is disclosed.

  Patent Document 4 discloses an organic compound having an electron orbital (anisole derivative, etc.) having a molecular weight of 500 or less and a reversible redox potential at a potential nobler than a positive electrode potential at the time of full charge. ) Containing a non-aqueous electrolyte secondary battery.

  Non-Patent Document 1 also discloses an electrically active thiophene-based polymer having a molecular weight of about several thousand, for example, poly (3-butylthiophene) (poly (3-butylthiophene)), poly (3-phenylthiophene) (poly ( It is disclosed that overcharge can be suppressed by adding 3-phenylthiophene)) to the electrolyte.

JP-A-10-275632 JP-A-9-171840 JP-A-10-32258 JP-A-7-302614

Electrochemical and Solid-State Letters, 9 (1), A24-A26 (2006)

Although the low molecular weight compound has an effect of suppressing overcharge by electrolytic polymerization, a large amount of addition is necessary to realize a sufficient overcharge suppression effect. In this case, there were many side reactions such as gas generation and potential decrease. Further, since the polymer of thiophene is electropolymerized even at 4.0 V or less on the basis of lithium metal, it cannot be applied to a lithium ion battery having an operating voltage of 4.0 V or more such as current LiCoO ₂ .

  An object of the present invention is to solve the above-described problems and provide a non-aqueous electrolyte secondary battery having high safety.

  The electrolyte of the non-aqueous electrolyte secondary battery of the present invention includes a solution of a non-aqueous solvent and an electrolyte salt, and a low molecular compound that electropolymerizes to the above solution at least 4.3 V to 5.5 V based on lithium metal And a polymer that is electrolytically polymerized at 4.3 V or more and 5.5 V or less on the basis of lithium metal.

  Another aspect of the present invention is a non-aqueous electrolyte secondary battery using the above electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the overcharge can be suppressed and the secondary battery excellent in safety can be provided.

It is a schematic diagram which shows an example of a non-aqueous-electrolyte secondary battery, (a) Top view, (b) Partial longitudinal cross-sectional view. It is an external appearance perspective view of FIG. It is a graph which shows the change of the battery surface temperature at the time of the overcharge test of Example 1 and Comparative Examples 1-3.

  Lithium ion batteries containing non-aqueous electrolytes are characterized by high voltage (operating voltage 4.2V) and high energy density, so they are widely used in the field of portable information devices, and the demand is rapidly expanding. . Currently, it has established a position as a standard battery for mobile information devices such as mobile phones and notebook computers.

This lithium ion battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and in particular, LiMO ₂ (M includes one or more metal elements selected from the group consisting of Co, Ni, and Mn). And a non-aqueous solution in which an electrolyte salt is dissolved in a non-aqueous solvent (organic solvent) is used as an electrolytic solution. Lithium ion batteries are commonly used.

  As the non-aqueous solvent, generally, carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are used.

In a lithium ion battery, when overcharge is performed to exceed the normal working voltage (for example, LiCoO ₂ , 4.2 V when fully charged), excess lithium is released from the positive electrode. At the same time, excessive lithium deposition occurs in the negative electrode, resulting in dendrite. Therefore, both the positive and negative electrodes become chemically unstable and eventually react with carbonates in the nonaqueous electrolytic solution, which may cause a rapid exothermic reaction due to decomposition or the like. This causes a problem that the entire battery generates heat abnormally and the safety of the battery is impaired.

  As described above, measures are usually taken to prevent overcharging by a protection circuit, etc., so as not to cause an internal short circuit, so an abnormal situation does not occur, but measures are taken to maintain the safety of the battery itself. It has been. In particular, this problem becomes more important as the energy density and capacity of lithium ion batteries increase.

  Therefore, it is effective to dissolve in the electrolyte an overcharge inhibitor that reacts with the positive electrode having a high potential during overcharge and electrolytically polymerizes to suppress overcharge. As the overcharge inhibitor, the present inventors include a low-molecular compound that is electrolytically polymerized at 4.3 V to 5.5 V based on lithium metal, and a polymer that is electropolymerized at 4.3 V to 5.5 V based on lithium metal. As a result, the safety of the lithium ion battery was improved. When the secondary battery is overcharged, such a mixed type overcharge inhibitor reacts with the positive electrode having a high potential, and the overcharge additive is polymerized to suppress overcharge. There are few side effects. In addition, since the electropolymerization is performed at a high potential, it can be applied to a secondary battery having a high operating voltage, and the safety when the battery is overcharged can be enhanced.

  The mixed-type overcharge inhibitor of the present invention is composed of two chemical compounds of low molecular weight and polymer which react at a specific potential. Hereinafter, the mixed-type overcharge inhibitor, which is a feature of the present invention, will be described.

  The low molecular weight overcharge inhibitor reacts rapidly with the polymer overcharge inhibitor to form a high molecular weight compound. As a result, it is easy to form a film on the electrode surface, and it is possible to quickly increase the internal resistance and cut off the current. Further, the low molecular weight overcharge inhibitor preferably includes a plurality of reaction sites. It becomes possible to form a higher molecular weight compound by crosslinking the polymer type overcharge inhibitor.

  The low molecular weight overcharge inhibitor is a compound that can be electropolymerized under a condition of 4.3 to 5.5 V based on lithium metal. Considering the solubility in the electrolytic solution, the chemical stability, and the electrochemical stability, an aromatic compound having an aromatic functional group having 7 to 18 total carbon atoms in the molecule that satisfies the Huckle rule is preferable. Specific examples of aromatic compounds include biphenyl and derivatives thereof; partially hydrogenated terphenyl; aliphatic compounds and alicyclic compounds having a benzene ring represented by cyclohexylbenzene and t-butylbenzene; anisole and derivatives thereof; Examples thereof include partially fluorinated aromatic compounds typified by fluorobenzene. Biphenyl, cyclohexylbenzene and fluorobenzene are particularly preferred.

  A part of hydrogen of these aromatic compounds may be substituted. Moreover, elements other than carbon may be contained in the aromatic ring (aromatic ring). Specifically, elements such as S, N, Si, and O are used.

  The polymers represented by the chemical formulas (1) to (3) have a functional group that can be electrolytically polymerized at 4.3 V or more and 5.5 V or less on a lithium metal basis. Even with this polymer overcharge inhibitor alone, there is a possibility that a secondary battery excellent in safety as compared with the previous example can be realized. However, when such a polymer is added in a large amount, there is a high possibility that the rate characteristics of the battery will deteriorate. Therefore, it is preferable to use a mixture with a low molecular weight overcharge inhibitor. Moreover, it is preferable that a polymer type overcharge inhibitor is equipped with a hydrophilic ether bond or ester bond as a functional group for improving solubility, as represented by chemical formulas (1) to (3).

  The polymer overcharge inhibitor having the aromatic functional group in the molecule is represented by the following chemical formulas (1) to (3).

In the formula, A is a functional group that undergoes electropolymerization at 4.3 V or more and 5.5 V or less on a lithium metal basis, and has a hydrophilic ether bond or ester bond. R and R 'are hydrogen or a methyl group. R ¹ and R ⁴ are functional groups having an aromatic ring that is electropolymerized at 4.3 V or more and 5.5 V or less based on lithium metal, and R ² and R ⁵ are hydrogen or an alkyl group having 1 to 3 carbon atoms. The hydrogen of this alkyl group may be substituted with fluorine. R ³ is a group having an alkyl group having 1 to 6 carbon atoms or an aromatic functional group, wherein hydrogen of the alkyl group or aromatic functional group may be substituted with fluorine, and the number of carbon atoms via the alkoxy group It may be an alkyl group of 1 to 6 or an aromatic functional group. R ⁶ is a functional group having an alkyl group having 1 to 6 carbon atoms or an aromatic ring, and hydrogen of the functional group having an alkyl group or an aromatic ring may be substituted with fluorine. c and e are integers of 1 or more, and d and f are integers of 0 or 1 or more.

  As described above, the polymer overcharge inhibitor has a repeating unit, and the compound has a functional group that undergoes electropolymerization under a condition where the potential based on the lithium metal is 4.3 to 5.5V.

  The content of the polymer overcharge inhibitor and the low molecular weight overcharge inhibitor in the non-aqueous electrolyte takes into account the overcharge suppression effect, and the battery type, capacity, total amount of overcharge inhibitor added, and molecule It is determined in accordance with the ratio of the electropolymerization unit in the inside and the molecular structure of the functional group.

  The addition amount of the low molecular weight overcharge inhibitor is preferably 0.1 wt% or more and 5 wt% or less, more preferably 0.5 wt% or more and 4 wt% or less, in order to reduce side reactions and manifest the overcharge effect. 1 wt% or more and 3.5 wt% or less are particularly preferable.

  The polymer overcharge inhibitor is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, based on the total amount of the non-aqueous electrolyte, from the viewpoint of more effectively exerting the overcharge suppression effect. More preferred. In addition, when there is too much content of said polymer in a non-aqueous electrolyte, the viscosity of a non-aqueous electrolyte will become high too much and the load characteristic of a battery may fall. Moreover, since the cost of a nonaqueous electrolyte solution also becomes high, it is preferable that the content is 5 mass% or less.

  The number average molecular weight (Mn) of the polymer represented by the chemical formulas (1) to (3) is not particularly limited because it depends on the solubility of the polymer in the electrolytic solution and the viscosity after dissolution. A quantified oligomer may be used, but 3000 to 1000000 is preferable. When the molecular weight is too large, the solubility in the electrolytic solution decreases. As a result, the above polymer does not dissolve in the electrolytic solution or the viscosity of the electrolytic solution increases, so that the battery performance is lowered. On the other hand, if the molecular weight is too low, purification may be difficult, or the rate of increase in internal resistance after the battery is overcharged may be slow.

In the above chemical formulas (1) to (3), the functional groups A, R ¹ and R ⁴ that can be electropolymerized at 4.3 to 5.5 V based on the lithium metal are aromatic functional groups. It functions as an overcharge inhibitor by electrolytic polymerization of this aromatic functional group, reacts at a predetermined voltage, and suppresses overcharge. The reaction is a voltage higher than the operating voltage of the battery. Specifically, it is 4.3 to 5.5 V on the basis of lithium metal.

  Here, the aromatic functional group is an aromatic functional group having a total carbon number of 7 to 18 that satisfies the Huckle rule. A part of the aromatic functional group may be substituted. Further, the aromatic functional group may contain an element other than carbon in the aromatic ring (aromatic ring). Specifically, elements such as S, N, Si, and O are used.

  Specifically, alkylbiphenyl such as biphenyl, 2-methylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, naphthalene, dibenzofuran, etc. Functional groups derived from aromatic compounds; derived from aromatic compounds such as 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4'-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene Partially fluorinated functional groups such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, functional groups derived from fluorinated anisole compounds such as 3,5-difluoroanisole, etc. It is.

  Among these, from the viewpoint of improvement in safety during overcharge and battery characteristics, alkylbiphenyl such as biphenyl and 2-methylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, t- Aromatic functional groups derived from butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, etc .; 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4'-difluorobiphenyl, o-cyclohexylfluorobenzene, p -Partially fluorinated functional groups and naphthyl groups derived from aromatic compounds such as cyclohexylfluorobenzene are preferred.

Further, in the above formula (2) (3), and R ² or R ^5, characterized in that it has a functional group consisting of an ether bond or an ester bond. These functional groups are not intended to cause electropolymerization. Such a polymer having an ether bond or an ester bond in the molecule has a high affinity for a non-aqueous solvent and an electrolyte salt, so that it can be easily dissolved in the electrolyte and can suppress an increase in the viscosity of the electrolyte. .

  In the chemical formulas (2) and (3), c and e of the electropolymerization unit are integers of 1 or more, and d and f of the unit that is not electropolymerized are 0 or an integer of 1 or more. Moreover, in order to improve the overcharge suppression characteristic, it is desirable that c and e in the polymer molecule be as large as possible if the solubility of the polymer in the electrolytic solution can be secured. However, if it is too large, the solubility of the polymer in the electrolytic solution may be lowered. Therefore, the balance of molecular weight, solubility, overcharge performance, etc. is important. In addition, the electropolymerization unit in the polymer molecule or between the molecules and the unit that does not perform the electropolymerization may be bonded while forming a block, or may be bonded at random. That is, it may have a distribution similar to general polymers.

  The polymer type overcharge inhibitor represented by the above chemical formulas (1) to (3) is a compound obtained by polymerizing a polymerizable monomer. The polymer-type overcharge inhibitor is obtained by polymerizing a polymerizable monomer having a C═C unsaturated bond. It is not impossible to react the polymerizable monomer in the battery to form a polymer, but from the viewpoint of electrochemical stability, the polymerizable monomer is polymerized in advance and the polymer is prepared, and then the polymer is purified. And preferably used.

  The method for synthesizing the polymer is not particularly limited, and any conventionally known bulk polymerization, solution polymerization, or emulsion polymerization may be used. In particular, solution polymerization is preferable. The polymerization method is not particularly limited, but radical polymerization is preferably used. In the polymerization, a polymerization initiator may or may not be used. From the viewpoint of ease of handling, it is preferable to use a radical polymerization initiator. The blending amount of the radical polymerization initiator is 0.1 to 5 wt%, preferably 0.3 to 2 wt% with respect to the polymerizable compound. The polymerization method using a radical polymerization initiator can be carried out in the usual temperature range and polymerization time.

  For the purpose of not damaging members used in electrochemical devices, it is preferable to use a radical polymerization initiator in the range of 30 to 90 ° C. as the 10-hour half-life temperature, which is an indicator of the decomposition temperature and rate. The 10-hour half-life temperature is a temperature required for the amount of undecomposed radical polymerization initiator to be halved in 10 hours at a concentration of 0.01 mol / liter in a radical inert solvent such as benzene. It points to.

  As radical polymerization initiators, t-butyl peroxypivalate, t-hexyl peroxypivalate, methyl ethyl ketone peroxide, cyclohexanone peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2, 2-bis (t-butylperoxy) octane, n-butyl-4,4-bis (t-butylperoxy) valerate, t-butyl hydroperoxide, cumene hydroperoxide, 2,5-dimethylhexane-2,5-di Hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α'-bis (t-butylperoxy m-isopropyl) benzene, 2,5-dimethyl-2,5-di ( t-butylperoxy) hexane, 2,5 -Organic peroxides such as dimethyl-2,5-di (t-butylperoxy) hexane, benzoyl peroxide, t-butylperoxypropyl carbonate, 2,2'-azobis [2- (2-imidazolin-2-yl) Propane], 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis {2-methyl-N- [ 1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2′-azobis (2-methylpropionamide) ) Dihydrate, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (2-methylpropane), dimethyl, 2,2'-azobisisobutyrate, 4,4'-azobis (4-cyanovaleric acid), 2,2'-azobis [2- (hydroxymethyl) propionitrile], azobisisobutyronitrile, etc. An azo compound is mentioned.

  The polymerizable monomer of the chemical formula (1) is not particularly limited as long as it has a functional group that can be electrolytically polymerized at 4.3 V to 5.5 V on the basis of lithium metal and has at least one ether bond or ester bond. A polymerizable monomer having an organic group having a C═C unsaturated bond such as a vinyl group, an allyl group, an acryloyl group or a methacryloyl group is preferably used. Further, by having an ether bond or an ester bond in this monomer molecule, the dissolution in the electrolytic solution is promoted. A case where there is one C═C unsaturated bond is desirable. This is because when there are two or more C═C unsaturated bonds, it may become insoluble in the electrolyte due to an intramolecular crosslinking reaction.

Similarly, the polymers in the chemical formulas (2) and (3) are obtained by copolymerization from a polymerizable monomer. The monomer having R ¹ or R ⁴ is not particularly limited as long as it has a C═C unsaturated bond and a functional group that can be electropolymerized at 4.3 to 5.5 V based on lithium metal. A polymerizable monomer having an organic group having a C═C unsaturated bond such as a vinyl group, an allyl group, an acryloyl group, or a methacryloyl group is preferably used. Further, it is desirable that there is one C═C unsaturated bond.

Further, the polymerizable monomer having R ² or R ⁵ in the chemical formulas (2) and (3) has an ether bond or an ester bond. These polymerizable monomers are not particularly limited as long as they have a C═C unsaturated bond because they increase the solubility in an electrolytic solution. Further, it is desirable that there is one C═C unsaturated bond.

  For example, ethoxylated phenyl acrylate (EO = 1 to 10 mol) having ethylene oxide (EO), methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, diethylene glycol mono 2-ethylhexyl ether acrylate, diethylene glycol monophenyl ether acrylate, tetra Ethylene glycol monophenyl ether acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, lauryl methacrylate, isobornyl acrylate, isobornyl methacrylate, 2-phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxypropyl acrylate, benzyl acrylate, ethoxy Phenylmetac Acrylate-based monomers represented by rate (EO = 1 to 10 mol), tetrahydrofurfuryl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, 2- (2,4,6-tribromophenoxy) ethyl acrylate, etc .; allyl benzyl ether, allyl Allyl ethers typified by alkyl ethers, allyl acetate, allyl benzoate, allyl octyl oxalate, allyl propyl phthalate, allyl alkyl carbonate, allyl alkyl fumarate, allyl alkyl isophthalate, allyl alkyl malonate, allyl alkyl oxalate, allyl Alkyl phthalate, allyl alkyl sebacate, diallyl succinate, allyl alkyl terephthalate, allyl alkyl tartrate, allyl alcohol Organic acid esters or inorganic acid esters such as carboxylic acid having an allyl functional group represented by ruphthalate, ethyl allyl malate, methyl allyl fumarate, methyl metaallyl malate, allyl metasulfonate, methyl allyl sulfate, etc .; and vinyl acetate, Examples thereof include vinyl monomers represented by vinyl propionate, vinyl trifluoroacetate, vinyl propionate, vinyl pivalate and the like.

  Among these, alkyl acrylate (methacrylate) having 1 to 3 carbon atoms, allyl alkyl ether, ethoxylated phenyl acrylate (EO = 0 to 5 mol), ethoxylated methyl acrylate (EO = 0 to 5 mol), vinyl acetate and the like. Particularly desirable.

  The operation of the present invention will be described by taking as an example a nonaqueous electrolytic solution containing a polymer having an aromatic functional group in the molecule and a low molecular compound having an aromatic functional group. When a mixture of a low molecular weight overcharge inhibitor and an overcharge inhibitor of a polymer having an aromatic functional group is used, the overcharge inhibitor of the polymer first becomes an electric charge between the aromatic functional groups in the molecule during overcharge. Crosslinks by chemical polymerization to rapidly form higher molecular weight compounds. As a result, it is easy to form a film on the electrode surface, and the internal resistance is easily increased.

  A low molecular weight overcharge inhibitor has the effect of suppressing overcharge at a constant rate. A high molecular weight polymer quickly suppresses overcharge in the initial stage of overcharge, and crosslinks between polymer overcharge inhibitors reduce the reactivity of aromatic functional groups in the molecule. Can be suppressed for a long time.

  Next, a non-aqueous electrolyte using the above-described overcharge inhibitor will be described. The nonaqueous electrolytic solution includes a mixture of a nonaqueous solvent, an electrolyte salt, a low molecular weight (molecular weight is about 200 or less) overcharge inhibitor, and a polymer type overcharge inhibitor having an aromatic functional group.

  As the non-aqueous solvent (organic solvent) used for the non-aqueous electrolyte, those having a high dielectric constant are preferable, and esters containing carbonates are more preferable. Among them, it is recommended to use an ester having a dielectric constant of 30 or more.

  Examples of such high dielectric constant esters include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfur-based esters (ethylene glycol sulfite, etc.), and the like. Among these, cyclic esters are preferable, and cyclic carbonates such as ethylene carbonate, vinylene carbonate, propylene carbonate, and butylene carbonate are particularly preferable. In addition to the above solvents, low-viscosity polar linear carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, and aliphatic branched carbonate compounds can be used. A mixed solvent of a cyclic carbonate (particularly ethylene carbonate) and a chain carbonate is particularly preferred.

  In addition to the above non-aqueous solvents, chain alkyl esters such as methyl propionate; chain phosphate triesters such as trimethyl phosphate; nitrile solvents such as 3-methoxypropionitrile; dendrimers and dendrons A non-aqueous solvent (organic solvent) such as a branched compound having an ether bond represented by the above can be used.

A fluorine-based solvent can also be used. Examples of the fluorine-based solvent include H (CF ₂ ) ₂ OCH ₃ , C ₄ F ₉ OCH ₃ , H (CF ₂ ) ₂ OCH ₂ CH ₃ , H (CF ₂ ) ₂ OCH ₂ CF ₃ , H (CF ₂ ) ₂ CH ₂ O (CF ₂ ) ₂ H, etc., or (perfluoroalkyl) alkyl ether having a linear structure such as CF ₃ CHFCF ₂ OCH ₃ , CF ₃ CHFCF ₂ OCH ₂ CH ₃ , or iso (par Fluoroalkyl) alkyl ether, that is, 2-trifluoromethyl hexafluoropropyl methyl ether, 2-trifluoromethyl hexafluoropropyl ethyl ether, 2-trifluoromethyl hexafluoropropylpropyl ether, 3-trifluorooctafluorobutyl methyl ether , 3-trifluorooctafluorobutyl ethyl ether, 3-trifluorooctafluorobutylpropyl ether Ter, 4-trifluorodecafluoropentyl methyl ether, 4-trifluorodecafluoropentyl ethyl ether, 4-trifluorodecafluoropentyl propyl ether, 5-trifluorododecafluorohexyl methyl ether, 5-trifluorododecafluorohexyl ethyl Ether, 5-trifluorododecafluorohexyl propyl ether, 6-trifluorotetradecafluoroheptyl methyl ether, 6-trifluorotetradecafluoroheptyl ethyl ether, 6-trifluorotetradecafluoroheptylpropyl ether, 7-trifluorohexa Examples include decafluorooctyl methyl ether, 7-trifluorohexadecafluorooctyl ethyl ether, and 7-trifluorohexadecafluorohexyl octyl ether. Furthermore, the above iso (perfluoroalkyl) alkyl ether can be used in combination with the above-described (perfluoroalkyl) alkyl ether having a linear structure.

  As the electrolyte salt used for the non-aqueous electrolyte, a lithium salt is used in the case of a lithium ion battery. Preference is given to lithium perchlorate, organic boron lithium salts, lithium salts of lithium-containing compounds, lithium imide salts and the like.

Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCnF _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ (where Rf is a fluoroalkyl group). Of these lithium salts, fluorine-containing organic lithium salts are particularly preferred. This is because the fluorine-containing organic lithium salt has a large anionic property and is easily separated into ions, so that it is easily dissolved in the non-aqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is, for example, preferably 0.3 mol / L (mol / liter) or more, more preferably 0.7 mol / L or more, and preferably 1.7 mol / L or less. Preferably it is 1.2 mol / L or less. If the electrolyte salt concentration is too low, the ionic conductivity may be reduced, and if it is too high, an electrolyte salt that cannot be completely dissolved may be deposited.

In addition, various additives for improving battery performance may be added to the nonaqueous electrolytic solution, and there is no particular limitation. For example, in a non-aqueous electrolyte solution to which a compound having a C═C unsaturated bond in the molecule is added, deterioration in charge / discharge cycle characteristics of the battery can be suppressed. Examples of the compound having such a C═C unsaturated bond in the molecule include aromatic compounds such as C ₆ H ₅ C ₆ H ₁₁ (cyclohexylbenzene); H (CF ₂ ) ₄ CH ₂ OOCCH═CH ₂ , F (CF ₂ ) ₈ CH ₂ CH ₂ OOCCH═CH _2, etc., fluorinated aliphatic compounds; fluorine-containing aromatic compounds, and the like. In addition, compounds having a sulfur element such as 1,3-propane sultone and 1,2-propadiol sulfate (for example, chain or cyclic sulfonate, chain or cyclic sulfate, etc.), vinylene carbonate, Vinyl ethylene carbonate, fluorinated ethylene carbonate, etc. can also be used and may be very effective.

  In particular, when a highly crystalline carbon material is used as the negative electrode active material, the combined use with vinylene carbonate, vinyl ethylene carbonate, fluorinated ethylene carbonate, or the like is more effective. When vinylene carbonate, vinyl ethylene carbonate, or fluorinated ethylene carbonate is added to the non-aqueous electrolyte, the battery is charged to form a protective film on the negative electrode surface, and the reaction caused by the contact between the negative electrode active material and the non-aqueous electrolyte is caused. It suppresses and has the effect | action which suppresses decomposition | disassembly etc. of the non-aqueous electrolyte by such reaction. The addition amount of these various additives is preferably 0.05 to 5% by mass in the total amount of the non-aqueous electrolyte.

  In addition, an acid anhydride may be added to the non-aqueous electrolyte in order to achieve improvement in the high temperature characteristics of the non-aqueous electrolyte secondary battery. The acid anhydride is involved in the formation of a composite film on the negative electrode surface as a surface modifier for the negative electrode, and has a function of further improving the storage characteristics of the battery at high temperatures. Moreover, since the amount of water in the non-aqueous electrolyte can be reduced by adding acid anhydride to the non-aqueous electrolyte, the amount of gas generated in the battery using this non-aqueous electrolyte is also reduced. be able to. The acid anhydride added to the non-aqueous electrolyte is a compound having at least one acid anhydride structure in the molecule, and may be a compound having a plurality of acid anhydride structures. The amount of acid anhydride added is preferably 0.05 to 1% by mass in the total amount of the non-aqueous electrolyte.

  Specific examples of the acid anhydride include, for example, mellitic anhydride, malonic anhydride, maleic anhydride, butyric anhydride, propionic anhydride, puruvic anhydride, phthalonic anhydride, phthalic anhydride, pyromellitic anhydride, lactic anhydride, anhydrous Naphthalic acid, toluic anhydride, thiobenzoic anhydride, diphenic anhydride, citraconic anhydride, diglycolamide anhydride, acetic anhydride, succinic anhydride, cinnamic anhydride, glutaric anhydride, glutaconic anhydride, valeric anhydride, anhydrous Itaconic acid, isobutyric anhydride, isovaleric anhydride, benzoic anhydride and the like can be mentioned, and one or more of them can be used.

  Next, the structure of the non-aqueous electrolyte secondary battery using the above-described overcharge inhibitor will be described. The non-aqueous electrolyte secondary battery only needs to have the above-described non-aqueous electrolyte, and there are no particular restrictions on the other components, and the same as the conventionally known non-aqueous electrolyte secondary battery is adopted. it can. 1 and 2 show an example of a non-aqueous electrolyte secondary battery. FIG. 1 is a schematic view of a nonaqueous electrolyte secondary battery, in which (a) is a plan view and (b) is a partial cross-sectional view thereof. The battery of FIG. 1 is formed by stacking a separator 4 between a positive electrode 2 and a negative electrode 3 to form an electrode laminate, winding the electrode in a spiral shape, and then forming an electrode winding body 1. After loading, the positive and negative electrodes and the positive and negative terminals of the outer package are connected via lead bodies (lead pieces) 7, 8 and the like, and after the nonaqueous electrolyte is injected into the outer package, the outer package is sealed. Is done. FIG. 2 is an external perspective view of FIG.

  As shown in FIG. 1 (b), the positive electrode 2 and the negative electrode 3 are spirally wound through a separator 4 and crushed into a flat shape so that the cross section is flat and the bottom is covered with tape 6. The electrode winding body 1 is accommodated together with an electrolyte in a square (square tube) outer can 5. The positive electrode lead of the flat electrode winding body is connected to the positive electrode terminal and the negative electrode lead is connected to the negative electrode terminal according to a conventional method, and after the electrolyte is injected, the outer can is sealed. However, in FIG. 1, in order to avoid complication, a metal foil, an electrolyte, or the like as a current collector used for manufacturing the positive electrode 2 or the negative electrode 3 is not illustrated, and the inner circumference of the flat electrode winding body 1 is not illustrated. The side portion is not cross-sectioned. Further, the tape 6 on the bottom surface of the flat electrode winding body 1 does not distinguish between the base material and the adhesive material, and the tape 6 is disposed only on the bottom surface of the flat electrode winding body 1. Is shown.

  The outer can 5 is made of aluminum or aluminum alloy, and the outer can 5 also serves as a positive electrode terminal. From the flat electrode winding body 1, a positive electrode lead 7 and a negative electrode lead 8 connected to one end of each of the positive electrode 2 and the negative electrode 3 are drawn out. In addition, a stainless steel terminal 11 is attached to a battery lid 9 (battery lid made of aluminum alloy or the like) for sealing the opening of the outer can 5 via a PP insulating packing 10. A stainless steel lead plate 13 is attached via the body 12.

  And this battery cover 9 is inserted in the opening part of the armored can 5, and the opening part of the armored can 5 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery shown in FIG. 6, an electrolytic solution inlet 14 is provided in the battery lid 9, and a sealing member is inserted into the electrolytic solution inlet 14 by, for example, laser welding or the like. The sealing of the battery is ensured (therefore, in the batteries of FIGS. 6 and 7, the electrolyte inlet 14 is actually the electrolyte inlet and the sealing member. For ease of illustration, shown as electrolyte inlet 14). Further, the battery cover 9 is provided with an explosion-proof vent 15.

  In the battery shown in FIG. 1, the outer can 5 and the battery lid 9 function as a positive electrode terminal by directly welding the positive electrode lead 7 to the battery lid 9, and the negative electrode lead 8 is welded to the lead plate 13. By connecting the negative electrode lead 8 and the terminal 11 through the terminal 11, the terminal 11 functions as a negative electrode terminal. However, depending on the material of the outer can 5, the sign may be reversed.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown.

  Furthermore, FIG. 1 and FIG. 2 are for facilitating understanding of the shape and structure of the nonaqueous electrolyte secondary battery, and the size of each component of the battery shown in these figures is not necessarily accurate.

  Further, as the battery outer package, in addition to the metal square as shown in FIG. 1, a cylindrical outer package, a laminate outer package formed of a metal (aluminum, etc.) laminate film, or the like can be used.

  The configuration of the non-aqueous electrolyte secondary battery will be described in more detail using a lithium ion battery as an example. The lithium ion battery includes a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte.

As the positive electrode active material for the positive electrode, a compound capable of occluding and releasing lithium ions can be used. For example, Li _x MO ₂ or Li _y M ₂ O ₄ (where M is a transition metal, and 0 ≦ x ≦ 1, And lithium-containing composite oxides represented by 0 ≦ y ≦ 2), spinel oxides, layered metal chalcogenides, and olivine structures.

Specific examples thereof include lithium cobalt oxides such as LiCoO ₂ , lithium manganese oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , and lithium titanium oxides such as Li _4/3 Ti _5/3 O _4. Metal oxides such as lithium oxide, lithium manganese / nickel composite oxide, lithium manganese / nickel / cobalt composite oxide, manganese dioxide, vanadium pentoxide, chromium oxide, LiMPO ₄ (M = Fe, Mn, Ni), etc. Materials having an olivine type crystal structure; metal sulfides such as titanium disulfide and molybdenum disulfide;

In particular, a lithium-containing composite oxide having a layered structure or a spinel structure is preferably used, and lithium manganese / nickel composite oxidation represented by LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1/2 Mn _1/2 O _2, etc. LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.6 Mn _0.2 Co _0.2 O ₂ typified by lithium manganese / nickel / cobalt composite oxide, or LiNi _1-xy-z Co _x Al _y Mg _z O ₂ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 0.1, 0 ≦ z ≦ 0.1, 0 ≦ 1-xyz ≦ 1) Lithium composite oxide in which the open circuit voltage during charging is 4 V or more on the basis of Li, such as lithium-containing composite oxide substituted with an additive element selected from Ge, Ti, Zr, Mg, Al, Mo, Sn, etc. When used as an active material, the characteristics of the non-aqueous electrolyte of the example Can take advantage of, it is possible to obtain a non-aqueous electrolyte secondary battery having high safety.

  These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together. For example, by using both a lithium-containing composite oxide having a layered structure and a lithium-containing composite oxide having a spinel structure, both capacity increase and safety improvement can be achieved.

  As a method for producing the positive electrode, for example, a conductive additive (carbon black, acetylene black, etc.), a binder (polyvinylidene fluoride, polyethylene oxide, etc.) and the like are appropriately added to the positive electrode active material described above to form a positive electrode mixture. Is prepared, and a current collecting material (aluminum foil or the like) is applied as a core material to finish it into a strip-shaped molded body.

  Examples of the negative electrode active material related to the negative electrode include compounds capable of occluding and releasing lithium ions (lithium metal alone, an alloy such as Al, Si, Sn, In, etc., or oxidation that can be charged and discharged at a low potential close to lithium (Li). Materials, various materials such as carbon materials).

  In particular, a carbon material capable of electrochemically taking in and out lithium ions is preferable. Examples of such carbon materials include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, and the like. When a carbon material is used for the negative electrode active material, the interlayer distance d002 of the (002) plane of the carbon material is preferably 0.37 nm or less. In order to realize a high capacity of the battery, d002 is more preferably 0.35 nm or less, and further preferably 0.34 nm or less. The lower limit of d002 is not particularly limited, but is theoretically about 0.335 nm.

  The crystallite size Lc in the c-axis direction of the carbon material is preferably 3 nm or more, more preferably 8 nm or more, and further preferably 25 nm or more. The upper limit of Lc is not particularly limited, but is usually about 200 nm. And the average particle diameter becomes like this. Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more, Preferably it is 15 micrometers or less, More preferably, it is 13 micrometers or less. Further, the purity is desirably 99.9% or more.

  As a method for producing the negative electrode, for example, a conductive additive (carbon black, acetylene black, etc.), a binder (polyvinylidene fluoride, styrene butadiene rubber, etc.), etc. are appropriately added to the negative electrode active material as necessary. Then, a method is used in which a negative electrode mixture is prepared, and a current collector material such as copper foil is applied as a core material to finish the molded body.

  The separator arrange | positioned between a positive electrode and a negative electrode can use suitably the various separators employ | adopted in the conventionally well-known nonaqueous electrolyte secondary battery. For example, a microporous separator formed of a polyolefin resin such as polyethylene or polypropylene or a polyester resin such as polybutylene terephthalate is preferably used. Moreover, even if those microporous separators (microporous film) are overlapped or an inorganic layer such as alumina is provided on the surface thereof, the separator can also be used.

  Although there is no restriction | limiting in particular in the thickness of a separator, It is preferable to set it as 5-30 micrometers in consideration of both the safety | security of a battery and high capacity | capacitance. Further, the air permeability (second / 100 mL) of the separator is not particularly limited, but is preferably 10 to 1000 (second / 100 mL), more preferably 50 to 800 (second / 100 mL), and particularly preferably 90 to 700 ( Sec / 100 mL).

〔Example〕
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to such examples. In the following description, “%” is based on mass unless otherwise specified.

  First, a method for measuring the molecular weight of a synthesized product and a method for identifying a compound will be described.

(1) Molecular weight measurement Gel permeation chromatography (GPC) measurement was performed on the following conditions on the basis of polystyrene, and the molecular weight and distribution of the synthesized product were measured.

〔Measurement condition〕
Apparatus: Liquid chromatograph "L-6000 type" (manufactured by Hitachi High-Technologies Corporation)
Detector: Differential refractometer (RI) detector “L-3300” (manufactured by Hitachi High-Technologies Corporation)
Column: Gelpack GL-R440 + R450 + R400M
Sample concentration: 120 mg / 5 mL (milligram / milliliter)
Column temperature: 25 ° C
Mobile phase: Tetrahydrofuran (THF)
Flow rate: 2.05 ml / min (ml / min)
Sample injection volume: 200 microliters

(2) Compound identification ¹ H-NMR and ¹³ C-NMR spectra were measured using the following nuclear magnetic resonance spectroscopy (NMR, Nuclear Magnetic Resonance) to identify the compound and analyze the composition of the copolymer. It was.
Device: BRUKER AV400M
¹ H: 400.13MHz
Solvent: deuterated chloroform (CDCl ₃ )

[Example 1]
A copolymer having a biphenyl functional group represented by the following chemical formula (4) and electropolymerized at about 4.5 V based on lithium metal was synthesized. This copolymer is referred to as polymer (I).

  First, diethylene glycol monophenyl ether acrylate (42.5 g), which is ethoxylated phenyl acrylate (EO = 2 mol), and 4 are added to a 500 mL (milliliter) two-necked eggplant type flask equipped with a thermometer, a reflux condenser, and a stirring device. -Vinyl biphenyl (7.5 g) was mixed, and 500 mg of azobisisobutyronitrile (AIBN) was added as a polymerization initiator.

  200 g of dimethyl carbonate (DMC) was added thereto, and oxygen in the container was removed with argon gas. Thereafter, while bubbling with argon gas, the reaction was carried out in an oil bath at 60 ° C. for 3 hours and further at 70 ° C. for 2 hours.

  After completion of the reaction, 300 mL of cold methanol was gradually added to the reaction mixture and stirred to precipitate. Thereafter, the precipitate was washed several times with cold methanol to remove unreacted monomers and additives to obtain a solid polymer.

  The polymer after washing was dried under reduced pressure at 60 ° C. to remove methanol, and then vacuum-dried overnight at 80 ° C. to obtain about 37 g of a transparent, viscoelastic light yellow solid polymer (I). It was. The yield was 74%.

The structure of the polymer (I) was confirmed by ¹ H-NMR and ¹³ C-NMR. Moreover, when the ratio of diethylene glycol monophenyl ether acrylate and 4-vinylbiphenyl in the polymer (I) molecule was determined from the area ratio of each proton peak in the 1H-NMR spectrum, it was almost as charged. When the molecular weight was measured by GPC, the number average molecular weight was 21,000.

<Preparation of non-aqueous electrolyte>
10 mol / L of LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) at a volume ratio of 1: 1: 1, and about 4.5 V on the basis of lithium metal. A non-aqueous electrolyte was prepared by adding 0.5 wt% of the polymer (I) to be electropolymerized and 2 wt% of cyclhexylbenzene (CHB) to be electropolymerized at about 4.7 V based on the lithium metal. The non-aqueous electrolyte was prepared in an Ar atmosphere.

<Production of electrode>
The positive electrode was produced as follows. First, 92 parts by mass of LiCoO ₂ (positive electrode active material) was mixed with 5 parts by mass of flake graphite as a conductive additive, and 3 parts by mass of polyvinylidene fluoride was dissolved in N-methylpyrrolidone in this mixture. And mixed to obtain a positive electrode mixture slurry. This positive electrode mixture slurry was passed through a 70 mesh net to remove the large particle size, and then this positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm. Then, after compression molding with a roll press machine to a total thickness of 165 μm, cutting was performed and a nickel lead body was welded to produce a belt-like positive electrode.

The negative electrode was produced as follows. As the negative electrode active material, high crystal artificial graphite synthesized by the following method was used. That is, 100 parts by mass of coke powder, 40 parts by mass of tar pitch, 14 parts by mass of silicon carbide, and 20 parts by mass of coal tar were mixed in air at 200 ° C. and then pulverized, and heat treated at 1000 ° C. in a nitrogen atmosphere Artificial graphite was obtained by heat treatment at 3000 ° C. in a nitrogen atmosphere and graphitization. The obtained artificial graphite had a BET specific surface area of 4.0 m ² / g, a (002) plane distance d002 measured by X-ray diffraction of 0.336 nm, and the crystallite size Lc in the c-axis direction was 48 nm, the total pore volume was 1 × 10 ⁻³ m ³ / kg.

  Using this artificial graphite, using styrene butadiene rubber as a binder, using carboxymethyl cellulose as a thickener, mixing them in a mass ratio of 98: 1: 1, adding water and mixing them, and mixing the negative electrode mixture It was a strike. This negative electrode mixture paste was uniformly applied to both sides of a negative electrode current collector made of copper foil having a thickness of 10 μm, dried, and then compression-molded by a roll press machine to a total thickness of 145 μm, followed by cutting. And the lead body made from nickel was welded, and the strip | belt-shaped negative electrode was produced.

<Production of battery>
The belt-like positive electrode is stacked on the belt-like negative electrode via a microporous polyethylene separator (porosity: 41%) having a thickness of 20 μm, wound in a spiral shape, and then pressed so as to be flat. An electrode winding body having a flat winding structure was formed, and the electrode winding body was fixed with an insulating tape made of polypropylene. Next, the electrode winding body is inserted into a rectangular battery case made of aluminum alloy having outer dimensions of 4.4 mm (thickness), 34 mm (width), and 50 mm (height), and the lead body is welded. The lid plate was welded to the open end of the battery case. Then, the nonaqueous electrolyte containing said polymer (I) and CHB was inject | poured from the electrolyte solution injection port provided in the cover board, and the battery was created through chemical conversion etc. In addition, the design electric capacity of the nonaqueous electrolyte secondary battery of the present example was 840 mAh.

[Comparative Examples 1-5]
As Comparative Example 1, a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that no overcharge additive was added.

  As Comparative Example 2, a nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that only the low molecular overcharge additive CHB was added so as to be 2% by mass with respect to the total mass of the nonaqueous electrolyte. Obtained.

  As Comparative Example 3, a non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that only the polymer (I) was added to 2% by mass with respect to the total mass of the non-aqueous electrolyte.

  As Comparative Example 4, a non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that only polymer (I) was added to 5.0% by mass with respect to the total mass of the non-aqueous electrolyte. It was.

  As Comparative Example 5, the non-aqueous electrolyte solution 2 was added in the same manner as in Example 1 except that only CHB of the low molecular weight overcharge additive was added so as to be 4.0% by mass with respect to the total mass of the non-aqueous electrolyte solution. The next battery was obtained.

[Example 2]
A polymer (II) having a biphenyl structure represented by the following chemical formula (5) and electropolymerized at about 4.5 V (based on lithium metal) was synthesized. The synthesis of polymer (II) was the same as the synthesis of polymer (I) in Example 1 except that 4-vinylcyclohexylbenzene (40 wt%) and diethylene glycol monomethyl ether methacrylate (60 wt%) were used as starting materials. went.

  A nonaqueous electrolytic solution having 0.5 wt% polymer (III) and 2 wt% CHB was prepared in the same manner as in Example 1 except that the above polymer (II) was used instead of the polymer (I). In addition, an evaluation battery was produced and evaluated in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used.

Example 3
A polymer (III) having a 4-cyclhexylphenyl structure represented by the following chemical formula (6) and electropolymerized at about 4.7 V (lithium metal standard) was synthesized. The synthesis of polymer (III) was carried out in the same manner as the synthesis of polymer (I) in Example 1, except that diethylene glycol monocyclohexyl phenyl ether methacrylate was used.

  A non-aqueous electrolyte solution containing 0.5 wt% polymer (III) and 2 wt% CHB was prepared in the same manner as in Example 1 except that the polymer (III) was used instead of the polymer (I). An evaluation battery was prepared and evaluated in the same manner as in Example 1 except that the water electrolyte was used.

Example 4
A non-aqueous electrolyte having 1 wt% of polymer (II) that is electropolymerized at about 4.5 V (lithium metal standard) and 2 wt% of CHB that is electropolymerized at about 4.7 V (lithium metal standard) is prepared. An evaluation battery was prepared and evaluated in the same manner as in Example 1 except that the water electrolyte was used.

<High temperature storage characteristics test>
The batteries of Examples 1 to 4 and Comparative Examples 1 to 5 were charged at 20 ° C. at 840 mA (1C) to 4.2 V, and further charged at a constant voltage of 4.2 V for 2.5 hours to be fully charged. Then, the discharge capacity before storage was measured by discharging to 20V at 0.2C to 3V. This capacity was defined as the capacity of the battery.

  Next, each battery was charged in the same manner as described above, and then stored in a thermostatic bath at 60 ° C. for 20 days. The battery after storage was naturally cooled to 20 ° C., the thicknesses of the battery cases of Example 1, Comparative Examples 1 and 2 were measured, and the swelling of the battery was determined from the comparison with the thickness of the battery case before storage. Thereafter, all the batteries were discharged at 20 ° C. to 3 V at 0.2 C, and the discharge capacity after storage was measured. Again, a constant voltage charge was performed in the same manner, and a constant current discharge was performed up to 3.0 V at 0.2 CmA to obtain a recovery capacity.

Subsequently, using the discharge capacity before storage, the discharge capacity after storage, and the recovery capacity after storage, the capacity retention rate and the capacity recovery rate are calculated by the following formula, and the battery swelling, capacity retention rate and capacity recovery rate are calculated. High temperature storage characteristics were evaluated.
(Equation 1)
Capacity retention (%) = (discharge capacity after storage / discharge capacity before storage) × 100
(Equation 2)
Capacity recovery rate (%) = (discharge capacity after storage / discharge capacity before storage) × 100

<Overcharge characteristics>
5 fully charged batteries are put in a box made of separate thermosetting phenolic resin plates, charged to 5.0V with 1A current at 20 ° C under no air convection, and a constant voltage of 5.0V The battery was charged for 3.5 hours and overcharged. The safety of the battery was determined from the presence and number of ignition batteries after overcharging. In addition, the battery voltage, current, and surface temperature during overcharge were measured simultaneously.

  FIG. 3 shows changes in the surface temperature of the batteries used in Example 1 and Comparative Examples 1 to 3 during overcharging. From FIG. 3, the battery having the polymer (I) and CHB of Example 1 was safe with the maximum temperature of the battery surface at overcharge being 100 ° C. or less, and the batteries of Comparative Examples 1 to 3 were all ignited. You can see that

  Table 1 shows the overcharge inhibitor used in each battery and the battery characteristics. It can be seen that the battery of Example 1 using polymer (I) and CHB is also excellent in storage characteristics at 60 ° C. Further, from Table 1, the nonaqueous electrolyte secondary batteries of Examples 2 to 4 have no ignition at the time of overcharge, have higher safety than Comparative Examples 1 to 3, and the battery swells at 60 ° C. It can be seen that the storage characteristics are excellent as compared with Comparative Examples 4 and 5.

  From the above points, the mixed overcharge inhibitor comprising the polymer overcharge inhibitor and the low molecular overcharge inhibitor of the present invention is effective in ensuring high safety while maintaining the basic characteristics of the battery. . Thus, the non-aqueous electrolyte secondary battery of the example is excellent in safety and has good battery characteristics. Therefore, taking advantage of these characteristics, it can be applied to mobile information devices such as mobile phones and notebook computers. It can be widely used not only as a secondary battery for a driving power source but also as a power source for various devices such as an electric vehicle and a hybrid electric vehicle.

DESCRIPTION OF SYMBOLS 1 Flat electrode winding body 2 Positive electrode 3 Negative electrode 4 Separator 5 Exterior can 6 Tape 7 Positive electrode lead 8 Negative electrode lead 9 Battery lid 10 Insulation packing 11 Terminal 12 Insulator 13 Lead plate 14 Electrolyte injection hole 15 Explosion-proof vent

Claims (8)

A non-aqueous solvent, an electrolyte salt, a low-molecular compound that is electropolymerized at 4.3 V to 5.5 V based on lithium metal, and a polymer that is electropolymerized at 4.3 V to 5.5 V based on lithium metal Contains ,
The polymer is a compound represented by the general formula (1),
The low molecular weight compound includes at least one of biphenyl, cyclohexylbenzene, t-butylbenzene, and fluorobenzene,
The polymer 0.1 mass% or more, less than 1 wt%, and the low molecular compound is 0.1 wt% or more, a non-aqueous electrolyte, wherein Rukoto included below 5 wt%.
[In the above formula, A is a functional group that undergoes electrolytic polymerization at 4.3 V or more and 5.5 V or less based on lithium metal, and has an ether bond or an ester bond. R and R 'are hydrogen or a methyl group. A is biphenyl, 2-methylbiphenyl, cyclopentylbenzene, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, naphthalene, dibenzofuran, 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4, 4'-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, or 3,5-difluoroanisole . ] The non-aqueous electrolyte according to claim 1,
The non-aqueous electrolyte characterized in that the polymer is a compound represented by the general formula (2) or (3).
(In the formula, R ¹ and R ⁴ are functional groups having an aromatic ring that is electrolytically polymerized at 4.3 V to 5.5 V on the basis of lithium metal, and include biphenyl, 2-methylbiphenyl, cyclopentylbenzene, cyclohexylbenzene, t -Butylbenzene, t-amylbenzene, diphenyl ether, naphthalene, dibenzofuran, 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4'-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, Any one of 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole R ² and R ⁵ are hydrogen or an alkyl group having 1 to 3 carbon atoms. And the hydrogen of this alkyl group Tsu optionally substituted with iodine .R ³ is a group having an alkyl group or an aromatic group having 1 to 6 carbon atoms, hydrogen of the alkyl group or aromatic group is optionally substituted with fluorine It may be an alkyl group having 1 to 6 carbon atoms or an aromatic functional group via an alkoxy group, and R ⁶ is a functional group having an alkyl group having 1 to 6 carbon atoms or an aromatic ring, The hydrogen of the functional group having an alkyl group or aromatic ring may be substituted with fluorine, c and e are integers of 1 or more, and d and f are 0 or an integer of 1 or more. The non-aqueous electrolyte according to claim 1,
The polymer has a number average molecular weight (Mn) of 3,000 to 1,000,000. The non-aqueous electrolyte according to claim 1,
The low molecular weight compound has a molecular weight of 200 or less. The non-aqueous electrolyte according to claim 1,
The non-aqueous electrolyte characterized in that the electrolyte is a lithium salt. The non-aqueous electrolyte according to claim 1,
The nonaqueous solvent includes a cyclic carbonate and a chain carbonate. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The non-aqueous electrolyte non-aqueous electrolyte secondary battery which is a nonaqueous electrolyte solution according to any of claims 1 to 6. The non-aqueous electrolyte secondary battery according to claim 7 ,
The non-aqueous electrolyte secondary battery, wherein the positive electrode and the negative electrode are a positive electrode and a negative electrode capable of inserting and extracting lithium, and the electrolyte contains a lithium salt.