JP2004363077A - Nonaqueous electrolytic solution and nonaqueous electrolytic solution secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrolytic solution and a secondary battery wherein deterioration of battery performance is suppressed in high-temperature storage and in high-temperature continuous charging. <P>SOLUTION: In the nonaqueous electrolytic solution for the secondary battery containing a solute, a compound expressed by a general formula (1), and a nonaqueous organic solvent to dissolve these, the compound expressed by the general formula (1) is contained at a concentration of 0.01 wt% or more and 4.5 wt% or less against the total weight of the nonaqueous electrolytic solution. In the formula, R<SB>1</SB>to R<SB>3</SB>independently represent, respectively, either one chosen from a group composed of (i) a chain or cyclic alkyl group with the carbon number of 1 to 8 which may be substituted by halogen atoms, (ii) a phenyl group which may be substituted by the halogen atoms, (iii) a phenyl group which may be substituted by an alkyl group with the carbon number of 1 to 4, and (iv) a phenyl group which may be substituted by halogen atoms and an alkyl group with the carbon number of 1 to 4. Furthermore, in the case R<SB>1</SB>and R<SB>2</SB>or R<SB>2</SB>and R<SB>3</SB>are all alkyl groups, they may be bonded mutually to form a ring structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte for a secondary battery and a non-aqueous electrolyte secondary battery using the same. More specifically, the present invention relates to a highly reliable non-aqueous electrolyte secondary battery that undergoes little deterioration during high-temperature continuous charging and high-temperature storage, and a non-aqueous electrolyte for a secondary battery for providing the same.

2. Description of the Related Art In recent years, lithium secondary batteries having a high energy density have been attracting attention as electric appliances become lighter and smaller.
An electrolyte for a lithium secondary battery includes a solute such as a lithium salt and an organic solvent. The organic solvent is required to have a high dielectric constant, a high oxidation potential, and stability in a battery. Since it is difficult to achieve these requirements with a single solvent, examples of the organic solvent for the electrolyte of the lithium secondary battery include cyclic carbonates such as ethylene carbonate and propylene carbonate and cyclic carboxylate esters such as γ-butyrolactone. And a low-viscosity solvent such as a chain carbonate such as diethyl carbonate or dimethyl carbonate or an ether such as dimethoxyethane.
Further, in order to improve the initial capacity, cycle characteristics, high-temperature storage characteristics, continuous charging characteristics, and the like, it has been proposed to include various compounds in the electrolyte.

  For example, as a method for improving continuous charging characteristics, Patent Document 1 describes that a phosphate ester is contained in an electrolytic solution.

Further, Patent Documents 2 and 3 disclose that a specific phosphonic acid ester or a phosphinic acid ester is contained in an organic solvent in an amount of 5 to 100% by weight, so that the electrolyte solution can be flame-retarded without adversely affecting battery performance. It is described that it has a property. According to the embodiment, an electrolytic solution obtained by dissolving LiPF ₆ in an organic solvent obtained by mixing carbonates or chain ethers and these phosphate compounds at a weight ratio of 2: 1 or 1: 1 is used. The secondary battery used was 10
Although it is shown that the capacity maintenance ratio at the 0th cycle is reduced only to several percent to several tens of percent, there is no description about the high temperature characteristics of the battery.
JP-A-11-233140 JP-A-10-228928 JP-A-11-233141

With the rapid expansion of the application of lithium secondary batteries to portable devices such as notebook computers and mobile phones, demands for higher performance are increasing. In particular, it is an improvement in battery characteristics at high temperatures such as high-temperature continuous charging characteristics and high-temperature storage characteristics.
For example, a notebook computer is almost always used while connected to a power supply via an AC adapter, and the secondary battery in the personal computer is constantly charged even during use. In such a continuous charging state, there is a problem that the electrolytic solution is decomposed due to the influence of heat generation of the main body, and the battery performance is significantly reduced. Decomposition of the electrolytic solution often involves the generation of gas, but when the amount of generated gas is large, there is a problem that the battery is deformed or ruptured, and the battery itself becomes unusable.

In addition, these portable devices may be left at high temperatures such as in a car during the day. Also in this case, the secondary battery is exposed to a high temperature, and there is a problem that the battery characteristics deteriorate due to the decomposition of the electrolytic solution, and the battery can is deformed or ruptured due to generation of gas.
Accordingly, an object of the present invention is to provide an electrolytic solution in which decomposition during high-temperature continuous charging and high-temperature storage is suppressed, and a secondary battery using the electrolytic solution and having excellent high-temperature characteristics.

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by including the phosphinic ester represented by the general formula (1) at a specific concentration in the non-aqueous electrolytic solution, the high-temperature continuous charging characteristics, The present inventors have found that the high-temperature storage characteristics are significantly improved, and have completed the present invention.

  That is, the gist of the present invention is a non-aqueous electrolytic solution containing a solute, a compound represented by the following general formula (1) and a non-aqueous organic solvent for dissolving them, and represented by the following general formula (1). Wherein the content of the compound is 0.01% by weight or more and 4.5% by weight or less with respect to the total weight of the non-aqueous electrolyte.

(Wherein R _{1 to} R ₃ each independently represent (i) a chain or cyclic alkyl group having 1 to 8 carbon atoms which may be substituted with a halogen atom, (ii) (Iii) a phenyl group optionally substituted with an alkyl group having 1 to 4 carbon atoms and (iv) a phenyl group optionally substituted with a halogen atom and an alkyl group having 1 to 4 carbon atoms. And when R ₁ and R ₂ or R ₂ and R ₃ are both alkyl groups, they may be bonded to each other to form a ring structure.)
Another aspect of the present invention resides in a nonaqueous electrolyte secondary battery including a negative electrode and a positive electrode capable of inserting and extracting lithium, and the above-described nonaqueous electrolyte for a secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the electrolyte solution and the secondary battery which suppressed the battery performance degradation at the time of high temperature preservation and high temperature continuous charge can be provided.

Hereinafter, the present invention will be described in detail.
The main components of the non-aqueous electrolytic solution for a secondary battery according to the present invention are a solute and a non-aqueous organic solvent that dissolves the solute, similarly to a conventional non-aqueous electrolytic solution for a secondary battery.
As a solute, a lithium salt is used. The lithium salt is not particularly limited as long as it can be used for this purpose, and examples thereof include the following.
1) Inorganic lithium salts: inorganic fluoride salts such as LiAsF ₆ , LiPF ₆ and LiBF ₄ , LiC
lO _4, perhalogenate such LiBrO _4, LiIO _4.
2) Organic lithium salt: organic lithium borate such as LiB (C ₆ H ₅ ) ₄ , alkane sulfonate such as LiCH ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F _{5) 2} ) Perfluoroalkanesulfonic acid imide salts such as ₂ and perfluoroalkanesulfonic acid salts such as LiCF ₃ SO ₃ .

Among them, LiBF ₄ and LiPF ₆ are preferable. Lithium salts may be used alone or as a mixture of two or more.
The concentration of the lithium salt in the non-aqueous electrolyte is usually 0.5 mol / L or more, preferably 0 mol / L or more.
. It is at least 75 mol / l, usually at most 2.5 mol / l, preferably at most 1.5 mol / l. If the concentration of the lithium salt is too high or too low, the conductivity will decrease, and the battery characteristics may be degraded.

  As the non-aqueous organic solvent, any solvent that has been conventionally proposed as a solvent for a non-aqueous electrolytic solution can be appropriately selected and used. For example, cyclic carbonate (cyclic carbonate), chain carbonate (chain carbonate), cyclic ester (cyclic carboxylate), chain ester (chain carboxylate), cyclic ether and chain Ethers and the like.

As the nonaqueous organic solvent for the electrolytic solution, a mixed solvent of a solvent selected from the group consisting of a chain carbonate and a cyclic ester and a cyclic carbonate is preferable.
When the non-aqueous organic solvent of the electrolytic solution contains a cyclic carbonate, a preferable ratio is 5% by volume to 55% by volume, more preferably 15% by volume to 50% by volume.
When the non-aqueous organic solvent of the electrolytic solution contains a chain carbonate, a preferable ratio is 2% to 85% by volume, more preferably 5% to 85% by volume.
When the cyclic ester is contained in the non-aqueous organic solvent of the electrolytic solution, a preferable ratio is 40% by volume to 100% by volume, more preferably 50% by volume to 98% by volume.

Preferred combinations of organic solvents and their volume ratios include the following.
1. Cyclic carbonate + chain carbonate (15-40: 60-85)
2. Cyclic carbonate + Cyclic ester (20-50: 50-80)
3. Cyclic carbonate + Cyclic ester + Chain carbonate (20-50: 50-80: 2-20)
4. Cyclic ester + chain carbonate (70-98: 2-30)
5. Cyclic ester (single solvent)

Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like. Examples of the cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like. Examples of chain ethers include dimethoxyethane, diethoxyethane, and the like. Examples of the cyclic esters include γ-butyrolactone, γ-valerolactone, and the like. Examples of the chain esters include methyl acetate and methyl propionate.

  These non-aqueous organic solvents may be used alone or as a mixture of two or more, but usually, two or more are used in a mixture so as to exhibit appropriate physical properties. For example, a solvent in which two or more kinds selected from cyclic carbonates, chain carbonates, and cyclic esters are mixed is exemplified. Particularly preferred is a mixture of two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and the like.

  The non-aqueous electrolyte according to the present invention contains the above-mentioned solute and non-aqueous organic solvent as main components, and further contains a compound represented by the following general formula (1).

In the formula, R _{1 to} R ₃ each independently represent (i) a chain or cyclic alkyl group having 1 to 8 carbon atoms which may be substituted with a halogen atom, and (ii) a substituent substituted with a halogen atom. (Iii) a phenyl group optionally substituted with an alkyl group having 1 to 4 carbon atoms and (iv) a phenyl group optionally substituted with a halogen atom and an alkyl group having 1 to 4 carbon atoms. Represents one selected from the group consisting of: Among them, preferred are (i) a chain alkyl group having 1 to 8 carbon atoms which may be substituted with a halogen atom, (ii) a phenyl group which may be substituted with a halogen atom, and (iii) 1 carbon atom. And (iv) a phenyl group optionally substituted with a halogen atom and an alkyl group having 1 to 4 carbon atoms.
Some of the substituents represented by R _{1 to} R ₃ are exemplified.
Examples of the chain alkyl group which may be substituted with a halogen atom include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group and a tert-
Butyl group, n-pentyl group, 2-methylbutyl group, 3-methylbutyl group, 4-methylbutyl group, 2,2-dimethylpropyl group, 2,3-dimethylpropyl group, 3,3-dimethylpropyl group, n-hexyl Groups, n-heptyl group, n-octyl group, 2-ethylhexyl group, trifluoromethyl group, 2,2,2-trifluoroethyl group, pentafluoroethyl group and the like. Among them, preferred are a methyl group, an ethyl group, a n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a trifluoromethyl group, a 2,2,2-trimethyl group. A chain alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom such as a fluoroethyl group and a pentafluoroethyl group. It is more preferable that the number of carbon atoms is 1 to 3.

Examples of the cyclic alkyl group which may be substituted with a halogen atom include a cyclopentyl group, a cyclohexyl group, a 2-fluorocyclohexyl group, a 3-fluorocyclohexyl group, a 4-fluorocyclohexyl group and the like having 4 to 6 carbon atoms, preferably 5-6.
A phenyl group optionally substituted with a halogen atom, a phenyl group optionally substituted with an alkyl group having 1 to 4 carbon atoms, a phenyl group optionally substituted with a halogen atom and an alkyl group having 1 to 4 carbon atoms A phenyl group, a 2-fluorophenyl group, a 3-fluorophenyl group, a 4-fluorophenyl group, a 2-tolyl group, a 3-tolyl group, a 4-tolyl group, a 2,3-
Difluorophenyl group, 2,4-difluorophenyl group, 2,5-difluorophenyl group, 2,6-difluorophenyl group, 3,4-difluorophenyl group, 3,5-difluorophenyl group, 4,5-difluorophenyl Group, 2-fluoro-3-tolyl group, 2-fluoro-4-tolyl group, 2-fluoro-5-tolyl group, 2-fluoro-6-tolyl group, 3-fluoro-2-tolyl group, 3-fluoro -4-tolyl group, 3-fluoro-5-tolyl group, 3-fluoro-6-tolyl group, 4-fluoro-2-tolyl group, 4-fluoro-3-tolyl group and the like. More preferably, the alkyl group to be substituted has 1 to 2 carbon atoms. Of these, a phenyl group, a 2-tolyl group, a 3-tolyl group and a 4-tolyl group are preferred.
The halogen atom to be substituted for the alkyl group or the phenyl group is preferably a fluorine atom as described above, but may be a chlorine atom, a bromine atom, an iodine atom or the like.

When R ₁ and R ₂ or R ₂ and R ₃ are both alkyl groups, they may be bonded to each other to form a ring structure. As a specific example, when R ₁ and R ₂ are linked to form a 5- to 6-membered ring containing a P atom, that is, the P atom is in the 1- and 4-positions of the n-butylene group, or n A case where a ring is formed by bonding to the 1- and 5-positions of the pentylene group, and a case where R ₂ and R ₃ are linked to form a 5- to 6-membered ring containing a P atom and an O atom And the like.

Specific examples of the compound represented by the general formula (1) include the following.
Methyl dialkyl phosphinates: methyl dimethyl phosphinate, methyl ethyl methyl phosphinate, methyl methyl n-propyl phosphinate, methyl n-butyl methyl phosphinate, methyl diethyl phosphinate, methyl ethyl n-propyl phosphinate, n- Methyl butylethyl phosphinate, methyl di-n-propyl phosphinate, methyl n-butyl-n-propyl phosphinate, methyl di-n-butyl phosphinate, methyl bis- (trifluoromethyl) phosphinate, bis- (tri Fluoromethyl) trifluoromethyl, bis- (2,2,2-trifluoroethyl) phosphinic acid methyl, bis- (2,2,2-trifluoroethyl) phosphinic acid trifluoromethyl, bis- (pentafluoro Ethyl) phosphine Methyl, bis - (pentafluoroethyl) phosphinate trifluoromethyl, and the like.

  Ethyl dialkyl phosphinates: ethyl dimethyl phosphinate, ethyl ethyl methyl phosphinate, ethyl methyl-n-propyl phosphinate, ethyl n-butyl methyl phosphinate, ethyl diethyl phosphinate, ethyl ethyl n-propyl phosphinate, n- Ethyl butylethyl phosphinate, ethyl di-n-propylphosphinate, ethyl n-butyl-n-propylphosphinate, ethyl di-n-butylphosphinate, ethyl bis- (trifluoromethyl) phosphinate, bis- (tri Fluoromethyl) phosphinic acid-2,2,2-trifluoroethyl, bis- (trifluoromethyl) phosphinic acid pentafluoroethyl, bis- (2,2,2-trifluoroethyl) phosphinic acid ethyl, bis- (2 , 2,2-trifluoroethyl ) -2,2,2-trifluoroethyl phosphinate, pentafluoroethyl bis- (2,2,2-trifluoroethyl) phosphinate, ethyl bis- (pentafluoroethyl) phosphinate, bis- (pentafluoroethyl) ) -2,2,2-trifluoroethyl phosphinate and pentafluoroethyl bis- (pentafluoroethyl) phosphinate.

  Propyl dialkylphosphinates: n-propyl dimethylphosphinate, n-propyl ethylmethylphosphinate, n-propyl methyl-n-propylphosphinate, n-propyl n-butylmethylphosphinate, diethylphosphinate- n-propyl, ethyl-n-propyl-phosphinic acid-n-propyl, n-butylethylphosphinic acid-n-propyl, di-n-propylphosphinic acid-n-propyl, n-butyl-n-propylphosphinic acid-n -Propyl, -n-propyl di-n-butylphosphinate and the like.

Dialkylphosphinic acid butyls: dimethylphosphinic acid-n-butyl, ethylmethylphosphinic acid-n-butyl, methyl-n-propylphosphinic acid-n-butyl, n-butylmethylphosphinic acid-n-butyl, diethylphosphinic acid- n-butyl, n-butyl ethyl-n-propylphosphinate, n-butyl n-butylethylphosphinate, n-butyl di-n-propylphosphinate, n-butyl-n-propylphosphinate-n -Butyl, -n-butyl di-n-butylphosphinate and the like.
Alkyl diarylphosphinates: methyl diphenylphosphinate, ethyl diphenylphosphinate, n-propyl diphenylphosphinate, n-butyl diphenylphosphinate, methyl bis (2-tolyl) phosphinate, bis (2-tolyl) phosphinic acid Ethyl, n-propyl bis (2-tolyl) phosphinate, n-butyl bis (2-tolyl) phosphinate, methyl bis (3-tolyl) phosphinate, ethyl bis (3-tolyl) phosphinate, bis ( N-propyl 3-tolyl) phosphinate, n-butyl bis (3-tolyl) phosphinate, methyl bis (4-tolyl) phosphinate, ethyl bis (4-tolyl) phosphinate, bis (4-tolyl) N-propyl phosphinate, n-butyl bis (4-tolyl) phosphinate, etc. And the like.
Alkyl alkyl aryl phosphinates: methyl methyl phenyl phosphinate, methyl ethyl phenyl phosphinate, methyl n-propyl phenyl phosphinate, methyl n-butyl phenyl phosphinate, ethyl methyl phenyl phosphinate, ethyl ethyl phenyl phosphinate, n-propyl Ethyl phenylphosphinate, ethyl n-butylphenylphosphinate, n-propyl methylphenylphosphinate, n-propyl ethylphenylphosphinate, n-propyl n-propylphenylphosphinate, n-propyl n-butylphenylphosphinate, methyl N-butyl phenylphosphinate, n-butyl ethylphenylphosphinate, n-butyl n-propylphenylphosphinate, n-butyl n-butylphenylphosphinate, Methyl 2-tolyl phosphinate, methyl ethyl-2-tolyl phosphinate, methyl n-propyl-2-tolyl phosphinate, methyl n-butyl-2-tolyl phosphinate, ethyl methyl-2-tolyl phosphinate, ethyl Ethyl-2-tolylphosphinate, ethyl n-propyl-2-tolylphosphinate, ethyl n-butyl-2-tolylphosphinate, n-propyl methyl-2-tolylphosphinate, n-ethyl-2-tolylphosphinate Propyl, n-propyl n-propyl-2-tolylphosphinate, n-propyl n-butyl-2-tolylphosphinate, n-butyl methyl-2-tolylphosphinate, n-butyl ethyl-2-tolylphosphinate, n-butyl-2-tolylphosphinic acid n-butyl, n-butyl-2-tolylphos N-butyl phosphate, methyl methyl-3-tolylphosphinate, methyl ethyl-3-tolylphosphinate, methyl n-propyl-3-tolylphosphinate, methyl n-butyl-3-tolylphosphinate, methyl-3 -Ethyl tolylphosphinate, ethyl-3-ethyltolylphosphinate, ethyl n-propyl-3-tolylphosphinate, ethyl n-butyl-3-tolylphosphinate, n-propyl methyl-3-tolylphosphinate, ethyl- N-propyl 3-tolylphosphinate, n-propyl n-propyl-3-tolylphosphinate, n-propyl n-butyl-3-tolylphosphinate, n-butyl methyl-3-tolylphosphinate, ethyl-3- N-butyl tolyl phosphinate, n-butyl n-propyl-3-tolyl phosphinate, n-butyl N-butyl tyl-3-tolylphosphinate, methyl methyl-4-tolylphosphinate, methyl ethyl-4-tolylphosphinate, methyl n-propyl-4-tolylphosphinate, methyl n-butyl-4-tolylphosphinate , Ethyl methyl-4-tolylphosphinate, ethyl ethyl-4-tolylphosphinate, ethyl n-propyl-4-tolylphosphinate, ethyl n-butyl-4-tolylphosphinate, n-methyl-4-tolylphosphinate Propyl, n-propyl ethyl-4-tolylphosphinate, n-propyl n-propyl-4-tolylphosphinate, n-propyl n-butyl-4-tolylphosphinate, n-butyl methyl-4-tolylphosphinate, N-butyl ethyl-4-tolylphosphinate, n-propyl-4-tolylphosphite Acid n- butyl, n- butyl-4-tolyl phosphinic acid n- butyl, and the like.
Aryl dialkyl phosphinates: phenyl dimethyl phosphinate, phenyl ethyl methyl phosphinate, phenyl diethyl phosphinate, phenyl methyl-n-propyl phosphinate, phenyl methyl-n-butyl phosphinate, phenyl ethyl-n-propyl phosphinate, ethyl -Phenyl n-butyl phosphinate, phenyl di-n-propyl phosphinate, phenyl n-butyl-n-propyl phosphinate, phenyl di-n-butyl phosphinate, dimethyl phosphinate-2-tolyl, ethyl methyl phosphinate- 2-tolyl, diethyl-2-phosphoric acid-2-tolyl, methyl-n-propylphosphinic acid-2-tolyl, methyl-n-butylphosphinic acid-2-tolyl, ethyl-n-propylphosphinic acid-2-tolyl, ethyl- n- Tylphosphinic acid-2-tolyl, di-n-propylphosphinic acid-2-tolyl, n-butyl-n-propylphosphinic acid-2-tolyl, di-n-butylphosphinic acid-2-tolyl, dimethylphosphinic acid- 3-tolyl, ethyl methylphosphinic acid-3-tolyl, diethylphosphinic acid-3-tolyl, methyl-n-propylphosphinic acid-3-tolyl, methyl-n-butylphosphinic acid-3-tolyl, ethyl-n-propyl Phosphinic acid-3-tolyl, ethyl-n-butylphosphinic acid-3-tolyl, di-n-propylphosphinic acid-3-tolyl, n-butyl-n-propylphosphinic acid-3-tolyl, di-n-butyl Phosphinic acid-3-tolyl, dimethylphosphinic acid-4-tolyl, ethylmethylphosphinic acid-4-tolyl, diethylphosphinic acid 4-tolyl diacid, 4-tolyl methyl-n-propylphosphinate, 4-tolyl methyl-n-butylphosphinate, 4-tolyl ethyl-n-propylphosphinate, ethyl-n-butylphosphine Acid-4-tolyl, di-n-propylphosphinic acid-4-tolyl, n-butyl-n-propylphosphinic acid-4-tolyl, di-n-butylphosphinic acid-4-tolyl and the like.
The molecular weight of the compound represented by the general formula (1) is usually 500 or less, preferably 400 or less, more preferably 350 or less. If the molecular weight is too large, the solubility in the electrolytic solution becomes poor, and the effect of the present invention may not be sufficiently exhibited. The compounds represented by the general formula (1) may be used alone or in combination of two or more. Further, as long as the present invention is satisfied, a mixture with a phosphinic acid ester compound other than the general formula (1) may be used.

The content of the compound represented by the general formula (1) in the nonaqueous electrolyte is usually 0.01% by weight or more, preferably 0.05% by weight or more, based on the total weight of the nonaqueous electrolyte. It is preferably at least 0.1% by weight, usually at most 4.5% by weight, preferably at most 3% by weight, more preferably at most 2.5% by weight. If the concentration of the compound represented by the general formula (1) is too low, a sufficient effect cannot be obtained. If the concentration is too high, battery characteristics such as rate characteristics deteriorate.
The non-aqueous electrolyte according to the present invention contains, if necessary, other conventional auxiliaries, for example, an overcharge inhibitor, a film forming agent for forming a film (SEI) on the surface of the active material of the battery, and the like. It may be. Examples of the overcharge inhibitor include biphenyl and its derivatives, cyclohexylbenzene and its derivatives, dibenzofuran and its derivatives, terphenyl and its derivatives, diphenyl ether and its derivatives, and the like. Examples of the film forming agent include vinylene carbonate and vinyl ethylene carbonate.
The concentration of each auxiliary in the non-aqueous electrolyte is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, based on the total weight of the non-aqueous electrolyte. Usually, it is 10% by weight or less, preferably 8% by weight or less, more preferably 6% by weight or less. The same applies to the case where a plurality of auxiliaries are used in combination.

  The non-aqueous electrolyte for a secondary battery according to the present invention is prepared by dissolving a solute, a compound represented by the general formula (1), and, if necessary, other auxiliaries in the above-mentioned non-aqueous organic solvent. can do. In preparing the non-aqueous electrolyte, each raw material of the non-aqueous electrolyte is preferably dehydrated in advance. Usually, the water is dehydrated to 50 ppm or less, preferably 30 ppm or less. If water is present in the non-aqueous electrolyte, electrolysis of water, hydrolysis of the solute due to the reaction between the water and the solute, and the like may occur. The means for dehydration is not particularly limited. In the case of a liquid such as a solvent, water may be removed by adsorption using a molecular sieve or the like. In the case of a solid such as a solute, drying may be performed at a temperature lower than a temperature at which decomposition occurs.

The non-aqueous electrolyte for a secondary battery according to the present invention is suitable for use as an electrolyte for a lithium secondary battery. Hereinafter, the lithium secondary battery according to the present invention using the electrolytic solution will be described.
The lithium secondary battery according to the present invention is the same as a conventionally known lithium secondary battery except for the electrolytic solution.In general, the positive electrode and the negative electrode are connected to the case via a separator containing the nonaqueous electrolytic solution of the present invention. It is stored. Accordingly, the shape of the secondary battery according to the present invention is not particularly limited, and a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, a pellet electrode and a separator. May be any of coin types in which are stacked.

Examples of the positive electrode active material include transition metal oxides, composite oxides of transition metals and lithium, sulfides of transition metals, inorganic compounds such as metal oxides, lithium metals, and lithium alloys. _{Specifically, MnO, V 2 O 5,} V 6 O 13, TiO transition metal oxides such as _2, lithium-cobalt composite oxide basic composition is LiCoO _2, lithium-nickel composite oxide is LiNiO _2, LiMn Examples thereof include lithium transition metal composite oxides such as lithium manganese composite oxides that are ₂ O _{4 and} LiMnO ₂ , transition metal sulfides such as TiS and FeS, and metal oxides such as SnO ₂ and SiO ₂ . Among them, a lithium transition metal composite oxide, particularly a lithium cobalt composite oxide, a lithium nickel composite oxide, and a lithium cobalt nickel composite oxide are preferably used because they can achieve both high capacity and high cycle characteristics. In addition, the lithium transition metal composite oxide has a part of cobalt, nickel, or manganese which is made of Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, or Zr. Replacement with a metal is preferable because its structure can be stabilized. The positive electrode active materials may be used alone or as a mixture of two or more.

  As the negative electrode active material, any material capable of inserting and extracting lithium may be used, and lithium metal, lithium alloy, and the like can be used. However, a carbonaceous material is preferable in terms of good cycle characteristics and safety. Examples of the carbonaceous material include natural or artificial graphite, carbide of pitch, carbide such as phenol resin and cellulose, pitch-based carbon fiber, PAN-based carbon fiber, graphitized material such as mesophase spherules, furnace black, and acetylene. Black and its graphitized products are exemplified. Further, a material obtained by coating these carbonaceous materials with an organic substance such as pitch and then baking to form amorphous carbon on the surface as compared with these carbonaceous materials can also be suitably used.

  These carbonaceous materials preferably have a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.340 nm, preferably 0.335 to 0.30 nm, determined by X-ray diffraction by the Gakushin method. Those having 337 nm are more preferable. The ash content is preferably at most 1% by weight, more preferably at most 0.5% by weight, particularly preferably at most 0.1% by weight. The crystallite size (Lc) determined by X-ray diffraction according to the Gakushin method is preferably 30 nm or more, more preferably 50 nm or more, and particularly preferably 100 nm or more.

Examples of the binder for binding the active material include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, styrene / butadiene rubber, isoprene rubber, butadiene rubber, polyvinyl acetate, polyethyl methacrylate, polyethylene, and nitrocellulose. Can be mentioned.
The amount of the binder used is usually at least 0.1 part by weight, preferably at least 1 part by weight, and usually at most 30 parts by weight, preferably at most 20 parts by weight, per 100 parts by weight of the active material. If the amount of the binder is too small, the strength of the electrode tends to decrease, and if it is too large, the ion conductivity tends to decrease.

  In the electrode, in order to improve electrical conductivity and mechanical strength, conductive materials, auxiliary agents that express various functions such as reinforcing materials, powders, fillers, and thickeners may be contained. . The conductive material is not particularly limited as long as it can impart conductivity by being mixed in an appropriate amount with the above active material, and usually, fibers and foils of various metals such as copper and nickel, graphite and carbon such as carbon black are used. Quality material. In particular, the positive electrode preferably contains a conductive material. Examples of the thickener include carboxyethyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

The electrode may be formed into a sheet electrode by directly rolling the mixture of the active material with a binder and a conductive material and the like, or may be formed into a pellet electrode by compression molding. It is formed by slurrying a mixture of a conductive material and the like with a solvent, applying the slurry to a current collector, and drying.
The dry thickness of the active material layer formed by coating is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and most preferably 40 μm or more, and usually 200 μm or less, preferably 150 μm or less, and more preferably 100 μm or less. It is as follows. If it is too thin, not only uniform coating becomes difficult, but also the capacity of the battery becomes small. On the other hand, if the thickness is too large, the rate characteristics deteriorate.

  As the current collector, a metal or an alloy is usually used. Specifically, examples of the negative electrode current collector include copper and its alloys, nickel and its alloys, and stainless steel. Among them, copper and its alloys are preferable. Examples of the positive electrode current collector include aluminum, titanium, tantalum, and alloys thereof, and among them, aluminum and alloys thereof are preferable. In order to improve the binding effect with the active material layer formed on the surface, it is preferable that the surface of these current collectors is previously subjected to a roughening treatment. Examples of surface roughening methods include blasting, rolling with a rough roll, and a machine for polishing the current collector surface with a wire cloth equipped with abrasive cloth paper, whetstones, emery buffs, steel wires, etc. to which abrasive particles are fixed. Polishing method, electrolytic polishing method, chemical polishing method and the like.

  Further, in order to reduce the weight of the current collector and improve the energy density per unit weight of the battery, a perforated current collector such as an expanded metal or a punched metal may be used. The weight of this type of current collector can be freely changed by changing its aperture ratio. When an active material layer is formed on both sides of this type of current collector, the active material layer is less likely to peel off due to a rivet effect through this hole. However, when the aperture ratio is too high, the contact area between the active material layer and the current collector is reduced, and the bonding strength may be reduced instead.

The thickness of the current collector is usually 1 μm or more, preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less. If it is too thick, the capacity of the entire battery will be too low, and if it is too thin, handling may be difficult.
The non-aqueous electrolyte may be used in a semi-solid state by gelling it with a gelling agent such as a polymer. The proportion of the non-aqueous electrolyte in the semi-solid electrolyte is usually at least 30% by weight, preferably at least 50% by weight, more preferably at least 75% by weight, and usually at least 99% by weight, based on the total amount of the semi-solid electrolyte. 0.95% by weight or less, preferably 99% by weight or less, more preferably 98% by weight or less. If the ratio of the electrolytic solution is too large, it is difficult to hold the electrolytic solution and the liquid is likely to leak. Conversely, if the ratio is too small, the charge / discharge efficiency and capacity may be insufficient.

  A separator is interposed between the positive electrode and the negative electrode to prevent a short circuit. In this case, the electrolytic solution is used by impregnating the separator. The material and shape of the separator are not particularly limited, but it is preferable to use a porous sheet or a nonwoven fabric formed of a material stable to the electrolytic solution and having excellent liquid retaining properties. As a material of the separator, polyolefin such as polyethylene and polypropylene, polytetrafluoroethylene, polyether sulfone, and the like can be used, and polyolefin is preferable.

  The thickness of the separator is usually at least 1 μm, preferably at least 5 μm, more preferably at least 10 μm, usually at most 50 μm, preferably at most 40 μm, more preferably at most 30 μm. If the separator is too thin, the insulating properties and mechanical strength may be deteriorated. If the separator is too thick, not only the battery performance such as rate characteristics will deteriorate, but also the energy density of the whole battery will decrease.

  The porosity of the separator is usually at least 20%, preferably at least 35%, more preferably at least 45%, usually at most 90%, preferably at most 85%, more preferably at most 75%. If the porosity is too small, the film resistance tends to increase, and the rate characteristics tend to deteriorate. On the other hand, if it is too large, the mechanical strength of the separator tends to decrease, and the insulating property tends to decrease.

The average pore size of the separator is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore size is too large, a short circuit is likely to occur. If the average pore size is too small, the film resistance increases and the rate characteristics may deteriorate.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless departing from the gist of the present invention.
(Manufacture of positive electrode)
90 parts by weight of lithium cobalt oxide (LiCoO ₂ ), 5 parts by weight of acetylene black and 5 parts by weight of polyvinylidene fluoride (hereinafter sometimes referred to as “PVdF”) were mixed, and N-ethylpyrrolidone was added to form a slurry. This was applied to one side of a 20 μm-thick aluminum foil, dried, and further rolled by a press. From this, a 12 mm diameter disk was punched out with a punch to obtain a positive electrode.

(Manufacture of negative electrode)
95 parts by weight of graphite (plane spacing 0.336 nm) and 5 parts by weight of PVdF were mixed, and N-ethylpyrrolidone was added to form a slurry. This was applied to one side of a copper foil having a thickness of 20 μm, dried, and further rolled by a press. From this, a disk having a diameter of 12 mm was punched to obtain a negative electrode.
(Manufacture of lithium secondary batteries)
A lithium secondary battery was prepared in a dry box in an argon atmosphere using a CR2032 type coin cell. That is, the positive electrode was placed in a coin-type cell (positive electrode can), a porous polyethylene film (separator) having a thickness of 25 μm was placed thereon, and pressed with a polypropylene gasket. The negative electrode was placed on the gasket, and a spacer for adjusting the thickness was further placed. After adding an electrolytic solution and sufficiently impregnating the inside of the battery, a coin-type cell (negative electrode can) was placed thereon, and the battery was sealed and closed.

In the following Examples and Comparative Examples, the capacity of the battery was designed to be about 4.0 mAh at a charge upper limit of 4.2 V and a discharge lower limit of 3.0 V.
The ratio of the positive electrode active material weight W (c) to the negative electrode active material weight W (a) was determined such that the capacity ratio Rq between the negative electrode and the positive electrode was 1.1 ≦ Rq ≦ 1.2. . The capacity ratio Rq was determined by the following equation.

  Here, Q (c) (mAh / g) is the electric capacity per weight of the positive electrode active material under conditions corresponding to the initial charging condition of the battery, and Q (a) (mAh / g) is lithium metal deposited. It is the electric capacity per weight of the negative electrode active material which can occlude lithium to the maximum without any problem.

Note that Q (c) and Q (a) were used for the working electrode and the counter electrode using the same electrolyte solution used for assembling the battery, using the positive electrode or the negative electrode as the working electrode and lithium metal as the counter electrode. The positive electrode can be charged (release of lithium ions from the positive electrode) at the lowest possible current density up to the initial charging conditions (upper potential of the positive electrode or lower potential of the negative electrode) by creating a test cell with a separator between them. The capacity was determined as Q (c), and the capacity at which the negative electrode could discharge (occlude lithium ions in the negative electrode) was determined as Q (a).

(Evaluation of battery)
(1) High-temperature storage test The obtained lithium secondary battery was charged at room temperature by 1C (4.0 mA) and a constant current constant voltage method with an upper limit of 4.2 V, and was charged when the current value reached 0.05 mA. Finished. Then, the battery was discharged at 3.0 C to 3.0 V.
Here, 1C represents a current value that can be fully charged in one hour, and 1C = 4.0 mA in the secondary batteries used in the present example and the comparative example. Therefore, 0.2C becomes 0.8mA.
Next, the battery was charged at room temperature by a constant current and constant voltage method having an upper limit of 1 C and 4.2 V, and the charging was terminated when the current value reached 0.05 mA. After maintaining the charged battery at 60 ° C. for 7 days, the battery was cooled to room temperature and the discharge capacity was measured. The larger the value of the discharge capacity after high-temperature storage, the smaller the deterioration in high-temperature storage and the higher the thermal stability.

(2) High-Temperature Continuous Charging Test The obtained lithium secondary battery was charged by a constant current / constant voltage method with an upper limit of 1 C and 4.2 V, and the charging was terminated when the current value reached 0.05 mA. Next, the battery was discharged to 3.0 V at a constant current of 0.2 C. Further, the battery was charged at room temperature by a constant current and constant voltage method having an upper limit of 1 C and 4.2 V, and the charging was terminated when the current value reached 0.05 mA. The charged battery was charged at a constant voltage of 4.2 V (continuous high-temperature charging) at 60 ° C. for 7 days, and the charging capacity was measured. After completion of charging, the battery was cooled to room temperature, and the discharge capacity was measured.

  The charge capacity after high-temperature continuous charging is the amount of current charged to compensate for the voltage reduced by the decomposition of the electrolyte, and a smaller value indicates that the decomposition of the electrolyte is suppressed. The larger the value of the discharge capacity after continuous high-temperature charging, the smaller the deterioration during continuous high-temperature charging and the higher the thermal stability.

(Example 1)
Lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) having a volume ratio of 3: 7 so as to have a concentration of 1 mol / liter.
Was dissolved to obtain a base electrolyte solution, and ethyl diethylphosphinate was added to the base electrolyte solution to a concentration of 1% by weight to obtain an electrolyte solution.
Using the obtained electrolytic solution, a lithium secondary battery was manufactured, and a high-temperature storage test and a high-temperature continuous charging test were performed. The results are shown in Tables 1, 2, and 3.

(Example 2)
A lithium secondary battery was prepared using an electrolyte solution in which ethyl diethylphosphinate was added to a base electrolyte solution at 1% by weight and vinylene carbonate at 2% by weight, and a high-temperature storage test and a high-temperature continuous charge test were performed. . The results are shown in Tables 1 and 2.
(Example 3)
A lithium secondary battery was prepared using an electrolyte solution containing 1% by weight of ethyl diethylphosphinate, 2% by weight of vinylene carbonate, and 2% by weight of cyclohexylbenzene in a base electrolyte solution. A continuous charging test was performed. The results are shown in Tables 1 and 2.
(Example 4)
A lithium secondary battery was prepared using an electrolytic solution obtained by adding 1% by weight of n-butyl di-n-butylphosphinate to a base electrolytic solution, and a high-temperature storage test and a high-temperature continuous charge test were performed. . The results are shown in Tables 1 and 2.
(Example 5)
A lithium secondary battery was prepared using an electrolyte solution in which 1% by weight of n-butyl di-n-butylphosphinate and 2% by weight of vinylene carbonate were added to a base electrolyte solution. A high temperature continuous charge test was performed. The results are shown in Tables 1 and 2.

(Example 6)
A lithium secondary battery was manufactured using an electrolyte solution in which methyl n-butylmethylphosphinate was added to a base electrolyte solution at 1% by weight, and a high-temperature storage test and a high-temperature continuous charge test were performed. The results are shown in Tables 1 and 2.
(Example 7)
A lithium secondary battery was prepared using an electrolyte solution in which 1% by weight of methyl n-butylmethylphosphinate and 2% by weight of vinylene carbonate were added to a base electrolyte solution, and a high-temperature storage test and a high-temperature continuous charge test were performed. Was done. The results are shown in Tables 1 and 2.

(Example 8)
A lithium secondary battery was manufactured using an electrolyte solution in which methyl methylphenylphosphinate was added to the base electrolyte solution so as to be 1% by weight, and a high-temperature storage test and a high-temperature continuous charge test were performed. The results are shown in Tables 1 and 2.
(Example 9)
A lithium secondary battery was prepared using an electrolyte solution in which 1% by weight of methyl methylphenylphosphinate and 2% by weight of vinylene carbonate were added to a base electrolyte solution, and a high-temperature storage test and a high-temperature continuous charge test were performed. Was. The results are shown in Tables 1 and 2.

(Example 10)
A lithium secondary battery was manufactured using an electrolyte solution in which ethyl diethylphosphinate was added to a base electrolyte solution in an amount of 0.1% by weight, and a high-temperature storage test was performed. Table 3 shows the results. (Example 11)
A lithium secondary battery was prepared using an electrolytic solution obtained by adding ethyl diethylphosphinate to the base electrolytic solution to a concentration of 0.25% by weight, and a high-temperature storage test was performed. Table 3 shows the results.
(Example 12)
A lithium secondary battery was manufactured using an electrolyte solution in which ethyl diethylphosphinate was added to the base electrolyte solution in an amount of 0.5% by weight, and a high-temperature storage test was performed. Table 3 shows the results. (Example 13)
A lithium secondary battery was manufactured using an electrolyte solution in which ethyl diethylphosphinate was added to a base electrolyte solution in an amount of 4% by weight, and a high-temperature storage test was performed. Table 3 shows the results.

(Comparative Example 1)
A lithium secondary battery was fabricated using the base electrolyte itself, and a high-temperature storage test and a high-temperature charge test were performed. The results are shown in Tables 1, 2, and 3.
(Comparative Example 2)
A lithium secondary battery was manufactured using an electrolyte solution in which vinylene carbonate was added to a base electrolyte solution to a concentration of 2% by weight, and a high-temperature storage test and a high-temperature charge test were performed. The results are shown in Tables 1 and 2.
(Comparative Example 3)
A lithium secondary battery was manufactured using an electrolyte solution in which vinylene carbonate was added to a base electrolyte solution at 2% by weight and cyclohexylbenzene at 2% by weight, and a high-temperature storage test and a high-temperature continuous charge test were performed. The results are shown in Tables 1 and 2.
(Comparative Example 4)
A lithium secondary battery was prepared using an electrolytic solution obtained by adding ethyl diethylphosphinate to 5 wt% to a base electrolytic solution, and a high-temperature storage test was performed. Table 3 shows the results.

  From Table 1, it can be seen that by adding a small amount of phosphinic acid ester to the electrolytic solution, deterioration of the battery during high-temperature storage can be suppressed. Further, it can be seen that the effect of suppressing this deterioration is exhibited even when a known film forming agent (vinylene carbonate) or an overcharge preventing agent (cyclohexylbenzene) is used in combination.

  From Table 2, it can be seen that by adding a small amount of phosphinic acid ester to the electrolytic solution, decomposition of the electrolytic solution during continuous high-temperature charging can be suppressed, and battery deterioration can be prevented. Further, it can be seen that the expression occurs even when a known film forming agent or an overcharge preventing agent (cyclohexylbenzene) is used in combination.

  Table 3 shows that when the concentration of the phosphinic acid ester in the electrolytic solution is 0.01% by weight or more and 4.5% by weight or less, deterioration of the battery during high-temperature storage can be suppressed.

  The non-aqueous electrolyte for a secondary battery according to the present invention is capable of suppressing decomposition during high-temperature continuous charging and high-temperature storage, and is used as an electrolyte for a lithium secondary battery in secondary batteries of portable devices such as notebook computers and mobile phones. Therefore, its industrial value is extremely large.

Claims (6)

A non-aqueous electrolyte containing a solute, a compound represented by the following general formula (1) and a non-aqueous organic solvent for dissolving them, wherein the content of the compound represented by the following general formula (1) is non-aqueous A non-aqueous electrolyte for a secondary battery, wherein the amount is 0.01% by weight or more and 4.5% by weight or less based on the total weight of the aqueous electrolyte.

(Wherein R _{1 to} R ₃ each independently represent (i) a chain or cyclic alkyl group having 1 to 8 carbon atoms which may be substituted with a halogen atom, (ii) (Iii) a phenyl group optionally substituted with an alkyl group having 1 to 4 carbon atoms and (iv) a phenyl group optionally substituted with a halogen atom and an alkyl group having 1 to 4 carbon atoms. And when R ₁ and R ₂ or R ₂ and R ₃ are both alkyl groups, they may be bonded to each other to form a ring structure.) In the general formula (1), R _{1 to} R ₃ are each independently: (i) a chain alkyl group having 1 to 8 carbon atoms which may be substituted by a halogen atom; (Phenyl) optionally substituted with an alkyl group having 1 to 4 carbon atoms, and (iv) phenyl optionally substituted with a halogen atom and an alkyl group having 1 to 4 carbon atoms. The non-aqueous electrolyte for a secondary battery according to claim 1, wherein the non-aqueous electrolyte is any one selected from the group consisting of groups. 3. The non-aqueous organic solvent according to claim 1, wherein the non-aqueous organic solvent in the non-aqueous electrolytic solution is a mixed solvent of a cyclic carbonate and a cyclic carbonate selected from the group consisting of a chain carbonate and a cyclic ester. 4. Aqueous electrolyte. A non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and the non-aqueous electrolyte for a secondary battery according to claim 1. The non-aqueous electrolyte secondary battery according to claim 4, wherein the positive electrode contains a lithium transition metal composite oxide. The nonaqueous electrolyte secondary solution according to claim 4, wherein the negative electrode is mainly composed of a carbon material having a lattice plane (002 plane) d value of 0.335 to 0.340 nm in X-ray diffraction. battery.