JP2006164759A - Nonaqueous electrolyte for electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery capable of keeping an initial capacity even if a charge-discharge cycle is repeated and having an excellent cycle characteristic. <P>SOLUTION: This nonaqueous electrolyte for an electrochemical device is produced by dissolving an electrolyte in a nonaqueous solvent. (1) The nonaqueous solvent is a mixture of chain carbonic ester, saturated cyclic carbonate, and unsaturated cyclic carbonate; (2) the electrolyte is lithium salt dissolving in the nonaqueous solvent; and (3) the electrolyte contains a chain isocyanato compound represented by a general formula (I) and/or a formula (II). In the formulas, X is hydrogen, halogen, an isocyanato group or 1-20C aliphatic hydrocarbon; Y is O, SO<SB>2</SB>or 1-20C aliphatic hydrocarbon; and Z is hydrogen, halogen, an isocyanato group, 1-20C aliphatic hydrocarbon or 6-20C aromatic hydrocarbon. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte for electrochemical devices such as lithium secondary batteries.

  In recent years, with the widespread use of various portable electronic devices such as portable electronic terminals typified by mobile phones and notebook personal computers, secondary batteries play an important role as their power source. These secondary batteries include aqueous batteries such as lead storage batteries and nickel / cadmium batteries, and non-aqueous electrolyte batteries. Among these, positive and negative electrodes capable of occluding and releasing lithium and the like, and non-aqueous electrolytes. The resulting non-aqueous electrolyte secondary battery has various advantages over other secondary batteries in terms of high voltage, high energy density, excellent safety, environmental issues, and the like.

  As non-aqueous electrolyte secondary batteries currently in practical use, for example, a composite oxide of lithium and a transition metal is used as a positive electrode active material, and a material capable of doping and dedoping lithium is used as a negative electrode active material. A lithium secondary battery is mentioned. In the negative electrode active material of a lithium secondary battery, a carbon material is an example of a material having excellent cycle characteristics. Among carbon materials, graphite materials are expected as materials that can improve the energy density per unit volume.

Further, in order to improve the characteristics of the lithium secondary battery, not only the characteristics of the negative electrode / positive electrode but also the characteristics of the non-aqueous electrolyte responsible for transferring lithium ions are required. As such a non-aqueous electrolyte, a lithium salt such as LiBF ₄ , LiPF ₆ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ was mixed in an aprotic organic solvent. A non-aqueous solution is used (Non-Patent Document 1). Carbonates are known as typical examples of aprotic organic solvents, and the use of various carbonate compounds such as ethylene carbonate, propylene carbonate, and dimethyl carbonate has been proposed (Patent Documents 1 and 2).

  As these carbonate compounds, in a mixed solvent of a cyclic carbonate having a high dielectric constant such as ethylene carbonate and propylene carbonate, and a chain carbonate solvent of low viscosity such as diethyl carbonate, methyl ethyl carbonate, and methyl carbonate, A solution in which the above lithium salt is mixed is used.

In addition, the non-aqueous electrolyte in which LiBF ₄ and LiPF ₆ are dissolved as an electrolyte has high conductivity indicating the transfer of lithium ions, and is stable at a high voltage because of the high oxidative decomposition voltage of LiBF ₄ and LiPF _6. This contributes to drawing out the high voltage and high energy density characteristics of the lithium secondary battery.

  On the other hand, when a non-aqueous electrolyte secondary battery such as a lithium secondary battery is used as each power source, there is a demand for a long battery life. One of the factors governing the battery life is an adverse effect on the negative electrode surface. For example, in a lithium secondary battery, generation of lithium dentlite on the negative electrode accompanying charge / discharge cycles, current concentration caused by the state of the negative electrode surface, side reaction between the nonaqueous electrolyte and the negative electrode, and the like. That is, the negative electrode surface state has a large influence on these factors, and it is necessary to control the negative electrode surface coating in order to extend the life of the battery.

In order to improve the battery life of these lithium secondary batteries and to provide an organic electrolyte battery having excellent high-temperature storage stability, for example, Patent Document 4 discloses a non-aqueous solvent of a carbonate compound containing an isocyanate compound, and an electrolyte. A non-aqueous electrolyte consisting of As an isocyanato compound in Patent Document 4, a cyclic isocyanato compound in which an isocyanato group is bonded to an aromatic hydrocarbon is described as being particularly preferable. Examples of the cyclic isocyanato compound include 1,3-diisocyanato-4-methylbenzene, isocyanatobenzene, diisocyanatobenzene, methylisocyanatobenzene, ethylisocyanatobenzene, methyldiisocyanatobenzene, and ethyldiisocyanatobenzene. , Trimethyldiisocyanatobenzene, and the like.
JP-A-4-184872 Japanese Patent Laid-Open No. 10-27625 Japanese translation of PCT publication No. 01-501822 JP 2002-8719 A Jean-Paul Gabano, "Lithium Battery", ACADEMIC PRESS (1983)

  The inventors have studied the above-described problems of the prior art, particularly electrochemical devices such as a lithium secondary battery having good cycle characteristics that can maintain the initial capacity even after repeated charge / discharge cycles. As a result, for example, it was confirmed that the nonaqueous electrolyte solution containing a cyclic isocyanate compound in which an isocyanato group is bonded to an aromatic hydrocarbon described in Patent Document 4 has an excellent effect for this purpose.

  However, many of these cyclic isocyanate compounds have a low decomposition potential. In non-aqueous electrolyte batteries, this triggers the cyclic isocyanate compound to decompose on the positive electrode, resulting in long-term cycle characteristics and cycle characteristics at high temperatures. It was found to adversely affect Further, some cyclic isocyanato compounds, which are said to exhibit excellent characteristics, are suspected to be mutagenic, such as 1,3-diisocyanato-4-methylbenzene. Therefore, when using an electrolytic solution containing these cyclic isocyanate compounds in a non-aqueous electrolyte battery, it is necessary to take measures in the manufacturing process when the cyclic isocyanate compound is scattered during the injection of the electrolytic solution. There is also a problem that sufficient consideration is necessary.

  Furthermore, in the non-aqueous electrolyte battery containing these cyclic isocyanate compounds, if the battery's safety valve is activated and the electrolyte comes out of the battery, there is a possibility of harming the health of consumers.

  Thus, the present invention provides a non-aqueous electrolyte solution for an electrochemical device such as a lithium secondary battery having improved cycle characteristics and an electrochemical device using the non-aqueous electrolyte solution, without these conventional problems. For the purpose of provision.

The present invention achieves the above object and has the following gist.
(1) A nonaqueous electrolytic solution for an electrochemical device obtained by dissolving an electrolyte in a nonaqueous solvent, wherein (1) the nonaqueous solvent is a chain carbonate ester, a saturated cyclic carbonate ester, or an unsaturated cyclic carbonate ester It is a mixture, (2) the electrolyte is a lithium salt that dissolves in a non-aqueous solvent, and (3) contains a chain isocyanato compound represented by the general formula (I) and / or (II) Non-aqueous electrolyte.

However, X is hydrogen, halogen, isocyanato group, or a C ₁ to -C ₂₀ aliphatic hydrocarbons (which may have a hetero atom). Y represents O, SO ₂ , or a C _{1 to} C ₂₀ aliphatic hydrocarbon (which may have a hetero atom). Z is hydrogen, halogen, isocyanato group, C _{1 to} C ₂₀ aliphatic hydrocarbon (which may have a hetero atom), or C _{6 to} C ₂₀ aromatic hydrocarbon (which has a hetero atom). May be).
(2) The nonaqueous electrolytic solution according to (1), wherein the chain isocyanato compound is contained in an amount of 0.01 to 3% by weight.
(3) (1) or (1) above, wherein 30 to 80% by weight, 10 to 50% by weight, and 0.01 to 5% by weight of chain carbonate, saturated cyclic carbonate, and unsaturated cyclic carbonate, respectively, are contained (2) Nonaqueous electrolyte solution.
(4) The unsaturated cyclic carbonate ester is any one of the above (1) to (3), which is a vinylene carbonate derivative represented by the general formula (III) or an alkenylethylene carbonate represented by the general formula (V). Non-aqueous electrolyte

(However, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, or an alkyl group that may contain a halogen atom having 1 to 12 carbon atoms.)

(However, R < ₃ > -R < ₆ > is respectively independently a hydrogen atom, a halogen atom, the hydrocarbon group which may contain the C1-C12 halogen atom, or a C2-C12 alkenyl group. And at least one of them is an alkenyl group having 2 to 12 carbon atoms.)
(5) The lithium salt is LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO _2), a non-aqueous electrolyte according to any one of LiN _(CF 3 SO _2), and _{(C 4} F 9 SO above is at least one lithium salt selected from the group of ₂₎ (1) to (4) liquid.
(6) An electrochemical device using the nonaqueous electrolytic solution according to any one of (1) to (5) above.
(7) The electrochemical device is a lithium secondary battery, the positive electrode active material is made of a lithium transition metal composite oxide material, and the negative electrode active material is (d) d value of the lattice plane (002 plane) in X-ray diffraction Is a carbonaceous material having a thickness of 0.340 nm or less, and / or (b) one or more metal oxides selected from Sn, Si and Al, and / or (c) one type selected from Sn, Si and Al The electrochemical device according to (6), which is an alloy of the above metal and lithium.

  The nonaqueous electrolytic solution according to the present invention provides a nonaqueous electrolytic solution for electrochemical devices such as a lithium secondary battery excellent in good initial characteristics and cycle characteristics.

  The reason why such excellent characteristics are obtained is not necessarily clear, but is presumed to be as follows. The non-aqueous electrolyte of the present invention, which is a non-aqueous solvent containing a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester, can maintain a stable liquid state over a wide temperature range. Good low temperature characteristics. And the non-aqueous electrolyte of the present invention contains a chain isocyanato compound represented by the above general formulas (I) and (II), thereby exfoliating the carbonaceous material and increasing the load reverse capacity, It becomes possible to suppress decomposition of the cyclic carbonate.

  Further, the chain isocyanato compound is decomposed at the interface between the non-aqueous electrolyte and the negative electrode to form a reaction coating layer having a lower resistance. This is considered to reduce the internal resistance of the battery and contribute to the improvement of cycle characteristics. This effect is presumably because the chain isocyanate compound and the cyclic carbonate having an unsaturated bond have different decomposition potentials on the negative electrode surface, and a good film is formed stepwise.

  In addition, the chain isocyanato compound contained in the non-aqueous electrolyte in the present invention is different from the cyclic isocyanate compound in that the oxidative decomposition potential is more than the practical range in the non-aqueous electrolyte battery, and during normal charge / discharge Further, there is no problem that the chain isocyanato compound is decomposed on the positive electrode, and as described above, long-term cycle characteristics and high-temperature cycle characteristics can be secured.

  Furthermore, when using an electrolytic solution containing a chain isocyanato compound in a non-aqueous electrolyte battery, the problem in the manufacturing process at the time of injecting the electrolytic solution as in the case of an electrolytic solution containing a cyclic isocyanate compound is considered. There is also an advantage that it is not necessary.

Hereinafter, the nonaqueous electrolytic solution of the present invention and the electrochemical device using the same will be described in detail.
Nonaqueous solvent The nonaqueous solvent used in the nonaqueous electrolytic solution of the present invention contains a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester. In the present invention, it is necessary to contain these three types of carbonic acid esters, and when any of them is not included, the non-aqueous electrolyte solution having excellent characteristics according to the present invention cannot be obtained.

  In the nonaqueous solvent used in the present invention, the chain carbonate ester, the saturated cyclic carbonate ester, and the unsaturated cyclic carbonate ester are 30 to 80% by weight, 10 to 50% by weight, respectively, in the nonaqueous electrolytic solution. And 0.01 to 5% by weight is preferably contained. When each carbonate ester is contained outside the above range, the non-aqueous electrolyte having excellent characteristics according to the present invention cannot be obtained satisfactorily. For example, when the chain carbonate ester is smaller than 30% by weight, the viscosity of the electrolytic solution increases, and in addition, it solidifies at a low temperature, so that sufficient characteristics cannot be obtained. When the value is large, the dissociation / solubility of the lithium salt is lowered, and the ionic conductivity of the electrolytic solution is lowered. When the saturated cyclic carbonate is smaller than 10% by weight, the dissociation / solubility of the lithium salt is lowered, and the ionic conductivity of the electrolytic solution is lowered. Conversely, when the saturated cyclic carbonate is larger than 50% by weight, the electrolytic solution In addition, the viscosity of the resin increases and, at the same time, solidifies at a low temperature, so that sufficient characteristics cannot be obtained. In addition, when the unsaturated cyclic carbonate is smaller than 0.01% by weight, a good film is not formed on the negative electrode surface, so that the cycle characteristics are deteriorated. Conversely, when the unsaturated cyclic carbonate is larger than 5% by weight, for example, When stored at a high temperature, the electrolyte solution is likely to generate gas, and the pressure in the battery is increased, which is undesirable in practice.

  Examples of the chain carbonate used in the present invention include a chain carbonate having 3 to 9 carbon atoms in total. Specifically, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, di-n-butyl carbonate, di-t-butyl carbonate, n-butyl isobutyl carbonate, n-butyl-t-butyl carbonate, isobutyl-t-butyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, n-butyl methyl carbonate, isobutyl methyl carbonate, t-butyl methyl carbonate, ethyl-n-propyl carbonate, n-butyl ethyl carbonate, isobutyl ethyl carbonate, t-butyl ethyl carbonate, n-butyl-n-propyl carbonate, isobutyl-n- B pills carbonate, t- butyl -n- propyl carbonate, n- butyl isopropyl carbonate, isobutyl isopropyl carbonate, and t-butyl isopropyl carbonate. Among these, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable, but are not particularly limited. Two or more of these chain carbonates may be mixed.

  Examples of the saturated cyclic carbonate used in the present invention include ethylene carbonate, propylene carbonate, butylene carbonate and the like. Among these, ethylene carbonate and propylene carbonate are more preferable. By using propylene carbonate, a stable nonaqueous electrolytic solution can be provided in a wide temperature range. Two or more of these saturated cyclic carbonates may be mixed.

  Examples of the unsaturated cyclic carbonate used in the present invention include vinylene carbonate derivatives represented by the following general formula (III).

In the general formula (III), R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, or an alkyl group that may contain a halogen atom having 1 to 12 carbon atoms. Of these, R ₁ and R ₂ are preferably hydrogen (the compound of (III) is vinylene carbonate).
Specific examples of the vinylene carbonate derivative include the following compounds. Vinylene carbonate, fluorovinylene carbonate, methyl vinylene carbonate, fluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, etc. are limited thereto. It is not a thing.

Among these compounds, vinylene carbonate is the cheapest and most effective compound. In addition, regarding the said vinylene carbonate derivative, it is at least 1 type, and it is also possible to be independent or to mix.
Moreover, as another unsaturated cyclic carbonate used by this invention, the alkenyl ethylene carbonate represented by the following general formula (IV) is mentioned.

In the above formula (IV), R _{3 to} R ₆ each independently represent a hydrogen atom, a halogen atom, a hydrocarbon group that may contain a halogen atom having 1 to 12 carbon atoms, or a carbon number of 2 to 2. 12 alkenyl groups, at least one of which is an alkenyl group having 2 to 12 carbon atoms. Especially, when one of R < ₃ > -R < ₆ > is a vinyl group and the remainder is hydrogen (the compound of (IV) is 4-vinyl ethylene carbonate), it is preferable.

  Specific examples of the alkenylethylene carbonate include compounds such as 4-vinylethylene carbonate, 4-vinyl-4-methylethylene carbonate, 4-vinyl-4-ethylethylene carbonate, 4-vinyl-4-n-propylethylene carbonate, and the like. Can be mentioned.

  The nonaqueous solvent used in the present invention may contain other various solvents in addition to the above components. Examples of these other various solvents include cyclic carboxylic acid esters, chain esters having 3 to 9 carbon atoms, and chain ethers having 3 to 6 carbon atoms. These various other solvents are preferably contained in the nonaqueous electrolytic solution in an amount of 0.2 to 10% by weight, particularly preferably 0.5 to 5% by weight.

  Examples of the cyclic carboxylic acid ester (lactone compound having 3 to 9 total carbon atoms) include γ-butyrolactone, γ-valerolactone, γ-caprolactone, ε-caprolactone, and the like. Among these, γ-butyrolactone and γ-valerolactone are more preferable, but not particularly limited. Two or more of these cyclic carboxylic acid esters may be mixed.

  Examples of the chain ester having 3 to 9 carbon atoms include methyl acetate, ethyl acetate, acetic acid-n-propyl, acetic acid-isopropyl, acetic acid-n-butyl, acetic acid isobutyl, acetic acid-t-butyl, propionic acid. Mention may be made of methyl, ethyl propionate, propionate-n-propyl, propionate-isopropyl, propionate-n-butyl, propionate isobutyl, propionate-t-butyl. Of these, ethyl acetate, methyl propionate, and ethyl propionate are preferred.

  Examples of the chain ether having 3 to 6 carbon atoms include dimethoxymethane, dimethoxyethane, diethoxymethane, diethoxyethane, ethoxymethoxymethane, and ethoxymethoxyethane. Of these, dimethoxyethane and diethoxyethane are more preferable.

  Further, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene and the like can be used. .

Nonaqueous electrolyte solute (lithium salt)
A lithium salt is used as the solute of the nonaqueous electrolytic solution of the present invention. The lithium salt is not particularly limited as long as it can be dissolved in the non-aqueous solvent. Specific examples thereof are as follows.
(A) Inorganic lithium salt:
LiPF _6, LiAsF _6, inorganic fluoride salts LiBF ₄ or the _{like, LiClO 4, LiBrO 4, LiIO} 4, perhalogenate etc. like.
(B) Organic lithium salt:
Organic sulfonates such as LiCF ₃ SO ₃ , perfluoro such as LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) Alkylsulfonic acid imide salts, perfluoroalkylsulfonic acid methide salts such as LiC (CF ₃ SO ₂ ) ₃ , LiPF (CF ₃ ) ₅ , LiPF ₂ (CF ₃ ) ₄ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₂ ( _{C 2 F 5) 4, LiPF} 3 (C 2 F 5) 3, LiPF (n-C 3 F 7) 5, LiPF 2 (n-C 3 F 7) 4, LiPF 3 (n-C 3 F 7) _{3, LiPF (iso-C 3} F 7) 5, LiPF 2 (iso-C 3 F 7) 4, LiPF 3 (iso-C 3 F 7) 3, LiB (CF 3) 4, LiBF (CF 3 _{3, LiBF 2 (CF 3)} 2, LiBF 3 (CF 3), LiB (C 2 F 5) 4, LiBF (C 2 F 5) 3, LiBF 2 (C 2 F 5) 2, LiBF 3 (C 2 _{F 5), LiB (n-} C 3 F 7) 4, LiBF (n-C 3 F 7) 3, LiBF 2 (n-C 3 F 7) 2, LiBF 3 (n-C 3 F 7), LiB Some fluorine such as (iso-C ₃ F ₇ ) ₄ , LiBF (iso-C ₃ F ₇ ) ₃ , LiBF ₂ (iso-C ₃ F ₇ ) ₂ , LiBF ₃ (iso-C ₃ F ₇ ) Examples thereof include inorganic fluoride salt fluorophosphate substituted with a perfluoroalkyl group and fluorine-containing organic lithium salt of perfluoroalkyl.

In the present invention, among the above, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN
(C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ), LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) are more preferable. Two or more of these lithium salts may be mixed.

  The concentration of the lithium salt, which is the solute of the nonaqueous electrolytic solution of the present invention, is preferably 0.5 to 3 mol / liter, particularly 0.7 to 2 mol / liter. If this concentration is too low, the ionic conductivity of the non-aqueous electrolyte is insufficient due to an absolute concentration shortage. If the concentration is too high, the ionic conductivity decreases due to an increase in viscosity, and precipitation at a low temperature occurs. Since it is likely to occur and causes problems, the performance of the nonaqueous electrolyte battery is undesirably lowered.

Chain isocyanato compound The chain isocyanato compound contained in the non-aqueous electrolyte of the present invention has a concentration of preferably 0.01 to 3 wt%, more preferably 0.05 to 2 wt% in the non-aqueous electrolyte. % Is preferred. If the concentration is less than 0.01% by weight, the effect of improving charge / discharge characteristics, particularly the improvement of cycle characteristics, is not sufficient. On the other hand, if the concentration exceeds 2% by weight, the cycle characteristics are significantly reduced, and the temperature is high. Occasionally, swelling may occur due to gas generation inside the battery, which is not preferable.

As the chain isocyanato compound used in the present invention, the compound represented by the above general formula (I) or (II) is used, and specific examples thereof include the following. Diisocyanato sulfone, diisocyanato ether, trifluoromethane isocyanate, pentafluoroethane isocyanate, trifluoromethanesulfonyl isocyanate, pentafluoroethanesulfonyl isocyanate, benzenesulfonyl isocyanate, 4-fluorobenzenesulfonyl isocyanate, 1,3-diisocyanatopropane, 1,3-diisocyanato-2-fluoropropane, 1,4-diisocyanatobutane, 1,4-diisocyanato-2-butene, 1,4-diisocyanato-2-fluorobutane, 1,4-diisocyanato-2,3 -Difluorobutane, 1,5-diisocyanatopentane, 1,5-diisocyanato-2-pentene, 1,5-diisocyanato-2-methylpentane, 1,6-diisocyanate Natohexane, 1,6-diisocyanato-2-hexene, 1,6-diisocyanato-3-hexene, 1,6-diisocyanato-3-fluorohexane, 1,6-diisocyanato-3,4-difluorohexane, 1,7- Diisocyanatoheptane, 1,8-diisocyanatooctane, 1,12-diisocyanatodecane, 1-isocyanatoethylene, isocyanatomethane, 1-isocyanatoethane, 1-isocyanato-2-methoxyethane, 3- Isocyanato-1-propene, isocyanatocyclopropane, 2-isocyanatopropane, 1-isocyanatopropane, 1-isocyanato-3-methoxypropane, 1-isocyanato-3-ethoxypropane, 2-isocyanato-2-methylpropane, 1-isocyanatobutane, 2-isocyanatobutane 1-isocyanato-4-methoxybutane, 1-isocyanato-4-ethoxybutane, methyl isocyanatoformate, isoanatocyclopentane, 1-isocyanatopentane, 1-isocyanato-5-methoxypentane, 1-isocyanato-5 -Ethoxypentane, 2- (isocyanatomethyl) furan, isocyanatocyclohexane, 1-isocyanatohexane, 1-isocyanato-6-methoxyhexane, 1-isocyanato-6-ethoxyhexane, ethyl isocyanatoacetate, isocyanatocyclopentane , Isocyanatomethyl (cyclohexane), 1-isocyanatoheptane, ethyl 3-isocyanatopropanoate, isocyanatocyclooctane, 2-isocyanatoethyl-2-methyl acrylate, 1-isocyanatooctane 2-isocyanato-2,4,4-trimethylpentane, butylisocyanatoacetate, ethyl 4-isocyanatobutanoate, 1-isocyanatononane, 1-isocyanatoadamantane, 1-isocyanatodecane, ethyl 6- Isocyanatohexanoate, 1,3-bis (isocyanatomethyl) cyclohexane, 1-isocyanatoundecane.
In the present invention, a chain isocyanato compound represented by the following formula (V), formula (VI) or formula (VII) is preferred.

  In the present invention, the chain isocyanato compound represented by the above formula (II) and the chain isocyanato compound represented by the formula (VI) are particularly preferable. Specifically, 1,3-diisocyanatopropane, 1 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, or 1,7-diisocyanatoheptane is preferred.

  In obtaining the nonaqueous electrolytic solution of the present invention, one or more chain isocyanato compounds are used. For example, the lithium compound as an electrolyte is added to the nonaqueous solvent while stirring the nonaqueous solvent. And the chain isocyanato compound is added and dissolved.

In addition, when using the non-aqueous electrolyte containing the chain isocyanate compound used in the present invention and a cyclic carbonate having an unsaturated bond, there is no particular limitation, but if necessary, the non-sealed state in a dry atmosphere. It is also possible to precharge the non-aqueous electrolyte battery and remove the gas generated during the initial charge from the battery. By implementing this formulation, it becomes possible to provide a non-aqueous electrolyte battery with more stable quality, and to prevent deterioration of battery characteristics when left at high temperature.

Electrochemical devices such as lithium ion secondary batteries The non-aqueous electrolyte of the present invention includes various types such as lithium ion secondary batteries, electric double layer capacitors, hybrid batteries in which one of the positive and negative electrodes is a battery and the other is a double layer. Although it can be used in an electrochemical device, a lithium ion secondary battery as a typical example will be described below.

  As the negative electrode active material constituting the negative electrode, carbon materials capable of doping / de-doping lithium ions, metallic lithium, lithium-containing alloys, silicon capable of being alloyed with lithium, silicon alloys, tin, Tin alloy, tin oxide capable of doping / de-doping lithium ions, silicon oxide, transition metal oxide capable of doping / de-doping lithium ions, doping / desorption of lithium ions Any of the transition metal nitrogen compounds which can be doped, or a mixture thereof can be used. The negative electrode generally has a configuration in which a negative electrode active material is formed on a current collector such as a copper foil or expanded metal. In order to improve the adhesion of the negative electrode active material to the current collector, for example, it may contain a polyvinylidene fluoride binder, a latex binder, etc., and carbon black, amorphous whisker carbon, etc. are added as a conductive aid. May be used.

As the carbon material constituting the negative electrode active material, for example, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, organic polymer compound fired bodies (phenol resin, furan resin, etc.) are suitable. And carbonized by firing at a suitable temperature), carbon fiber, activated carbon and the like. The carbon material may be graphitized. As the carbon material, a carbon material having a (002) plane spacing (d002) of 0.340 nm or less, particularly measured by X-ray diffraction, is preferable, or a graphite having a true density of 1.70 g / cm ³ or more or close thereto. A highly crystalline carbon material having properties is desirable. When such a carbon material is used, the energy density of the nonaqueous electrolyte battery can be increased.

  Further, those containing boron in the carbon material, those coated with a metal such as gold, platinum, silver, copper, Sn, Si, or those coated with amorphous carbon can be used. One type of these carbon materials may be used, or two or more types may be used in combination as appropriate.

  Silicon, silicon alloy, tin, tin alloy that can be alloyed with lithium, tin oxide that can be doped / undoped with lithium ions, silicon oxide, transition metals that can be doped / undoped with lithium ions In the case of using an oxide, any of the above-described carbonaceous materials has a higher theoretical capacity per weight and is a suitable material.

On the other hand, the positive electrode active material constituting the positive electrode can be formed from various materials that can be charged and discharged. For _example, in _{LiCoO 2, LiNiO 2, LiMn 2} O 4, LixMO 2 such as LiMnO ₂ (where, M is one or more transition metals, x is different according to the charge and discharge state of the battery, usually 0.05 ≦ x ≦ 1.20), a composite oxide of lithium and one or more transition metals (lithium transition metal composite oxide),
Lithium transition metals that can be doped and dedoped with Li can be used, such as chalcogenides of transition elements such as FeS ₂ , TiS ₂ , V ₂ 0 ₅ , MoO ₃ , MoS _2, or polymers such as polyacetylene and polypyrrole. Most preferably, a composite oxide material is used.

  The positive electrode generally has a configuration in which a positive electrode active material is formed on a current collector such as an aluminum, titanium, or stainless steel foil, or an expanded metal. In order to improve the adhesion of the positive electrode active material to the current collector, for example, polyvinylidene fluoride binder and latex binder, carbon black, amorphous whisker, graphite etc. to improve the electron conductivity in the positive electrode It may contain.

  The separator is preferably a membrane that electrically insulates the positive electrode from the negative electrode and is permeable to lithium ions. For example, a porous membrane such as a microporous polymer film is used. As the microporous polymer film, a porous polyolefin film is particularly preferable, and more specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film is preferable. Furthermore, a polymer electrolyte can also be used as a separator. As the polymer electrolyte, for example, a polymer material in which a lithium salt is dissolved, a polymer material swollen with an electrolytic solution, and the like can be used, but the polymer electrolyte is not limited thereto.

The non-aqueous electrolyte of the present invention may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer substance with the non-aqueous electrolyte, or a separator having a combination of a porous polyolefin film and a polymer electrolyte. A non-aqueous electrolyte may be soaked in the liquid.
The shape of the lithium ion secondary battery using the non-aqueous electrolyte of the present invention is not particularly limited, and may be various shapes such as a cylindrical shape, a square shape, an aluminum laminate type, a coin shape, and a button shape. it can.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
Examples 1-6
First, as a standard non-aqueous electrolyte, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (the former: latter weight ratio is 40:60), and LiPF ₆ as a lithium salt at a concentration of 1 mol / liter. And dissolved and prepared. Next, predetermined amounts of the compounds described in Table 1 were added to this reference electrolyte solution to prepare various nonaqueous electrolyte solutions.
In Table 1, VC is vinylene carbonate, 1,3-diisocyanato-4-methylbenzene (cyclic isocyanate compound) represented by the following formula (VIII), and is a comparative example.

[Preparation of negative electrode]
93 parts by weight of MCMB25-28 (manufactured by Osaka Gas Chemical) and 6 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed and dispersed in N-methylpyrrolidone as a solvent to prepare a negative electrode mixture slurry. Then, this negative electrode mixture slurry was applied to a negative electrode current collector made of copper foil having a thickness of 18 μm, dried, compression molded, and punched into a disk shape having a diameter of 18 mm to obtain a coin-shaped negative electrode. It was. The negative electrode mixture had a thickness of 95 μm and a weight of 68 mg in the form of a disk having a diameter of 18 mm.
[Preparation of positive electrode]
94 parts by weight of LiCoO ₂ (C-5 manufactured by Nippon Kagaku Kogyo Co., Ltd.), 3 parts by weight of acetylene black as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder are mixed, dispersed in N-methylpyrrolidone as a solvent, and LiCoO _Two mixture slurries were prepared. This LiCoO ₂ mixture slurry was applied to an aluminum foil having a thickness of 20 μm, dried, compression molded, and punched out to a diameter of 16.5 mm to produce a positive electrode. The LiCoO ₂ mixture had a thickness of 105 μm and a weight of 65 mg in a circle with a diameter of 16.5 mm.

[Production of coin-type battery]
A separator made of a negative electrode having a diameter of 18 mm, a positive electrode having a diameter of 16.5 mm, a microporous polyethylene film having a thickness of 25 μm and a diameter of 18.5 mm is placed in a stainless steel 2032 size battery can in the order of the negative electrode, the separator and the positive electrode. Laminated and arranged. Thereafter, 1000 μL of a non-aqueous solution was injected into the negative electrode, separator, and positive electrode in a vacuum, and then an aluminum plate (thickness 1.1 mm, diameter 16.5 mm) and a spring were housed. Finally, the battery can lid is caulked with a special coin cell caulking machine through a polypropylene gasket, thereby maintaining the airtightness in the battery, and a coin-type battery having a diameter of 20 mm and a height of 3.2 mm. Was made.

[Measurement conditions for charge / discharge characteristics of coin-type battery]
Using the coin-type battery produced by the method described above, charge / discharge characteristics were measured as follows.
a) Charging in the first cycle: At 25 ° C., charging at 3.0 mA to 3.0 V, followed by charging at 1.4 mA to 4.2 V, shifting from 4.2 V to constant voltage charging, totaling 6 Charging was terminated when time passed.
b) First cycle discharge: After the above charge, the battery was discharged to 2.75 V at 1.4 mA.

Regarding the 25 ° C. cycle characteristics, the following charge / discharge test conditions were carried out after carrying out the above-described charge / discharge test up to the first cycle. That is, the capacity retention rate after 50 cycles under the following charge / discharge conditions at 25 ° C. was calculated by the formula (1). Further, after the above test was completed, the capacity maintenance rate after 50 cycles was calculated at 45 ° C. under the following charge / discharge conditions using the formula (2). Charging; charging to 4.2 V at 3.5 mA. The charging is finished when 3 hours have passed since the transition from 2V to constant voltage charging.
-Discharge: After the above-described charging, the battery was discharged to 2.75 V at 3.5 mA.
Capacity retention after 50 ° C. 50 cycles = (discharge capacity at 50 ° C. at 25 ° C./discharge capacity at 2nd cycle at 25 ° C.) × 100 (%) (1)
Capacity retention after 50 ° C. at 50 ° C. = (25 ° C. 50 cycles + 45 ° C. 50th cycle discharge capacity / 25 ° C. 50 cycles + 45 ° C. first cycle discharge capacity) × 100 (%) (2) )
[Battery characteristics of coin-type battery]
Table 2 shows the results of cycle characteristics at 25 ° C. and 45 ° C. in laminated batteries using various non-aqueous electrolytes shown in Table 1 above.

  As shown in Table 2, coin-type batteries (Examples 1 to 6) using a non-aqueous electrolyte solution containing a predetermined amount of the chain isocyanate compound of the present invention and a cyclic carbonate having an unsaturated bond, It can also be seen that even in the combination, a clear improvement effect is exhibited in the 25 ° C. and 45 ° C. cycle characteristics as compared with the reference non-aqueous electrolyte (Comparative Examples 1 and 2).

  Further, 1,3-diisocyanato-4-methylbenzene (Comparative Examples 3 and 4), which is a cyclic isocyanato compound, was inferior in cycle characteristics at 45 ° C. as compared with Examples 1 to 6.

Examples 7-12
As a standard non-aqueous electrolyte, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (the former: the weight ratio of the latter: 40:60 ) contains LiPF ₆ as a lithium salt at a concentration of 1 mol / liter. And dissolved.
Next, a predetermined amount of the compounds shown in Table 3 was added to this reference electrolyte solution to prepare various nonaqueous electrolyte solutions. Of the compounds described in Table 3, the compounds other than the formula (VII) shown above are represented by the same abbreviations as in Table 1.

[Evaluation of charge / discharge characteristics of coin-cell battery]
Table 4 shows the characteristic evaluation results of the coin-type battery using the various non-aqueous electrolytes shown in Table 3 above after cycle high temperature storage.

  As shown in Table 4, a cycle of a coin-type battery using a non-aqueous electrolyte prepared by adding the above-mentioned chain isocyanate compound of the present invention and a cyclic carbonate having an unsaturated bond in an addition amount within a predetermined range of the present invention. In the characteristic evaluation (Examples 7 to 12), the cyclic carbonate having an unsaturated bond and the chain isocyanato compound of the present invention is compared with the reference nonaqueous electrolytic solution (Comparative Examples 5 and 6) in any combination. It was confirmed that good characteristics were obtained when a non-aqueous electrolyte containing an addition amount in a predetermined range of the present invention was used.

  According to the present invention, there is provided a non-aqueous electrolyte for an electrochemical device such as a lithium ion secondary battery that can maintain the initial capacity even after repeated charge / discharge cycles and has good cycle characteristics. The electrochemical device using the above plays an important role as a power source for various portable electronic devices typified by mobile phones or notebook personal computers.

Claims (7)

A nonaqueous electrolytic solution for an electrochemical device obtained by dissolving an electrolyte in a nonaqueous solvent, wherein (1) the nonaqueous solvent is a mixture of a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester (2) a non-aqueous electrolyte characterized in that the electrolyte is a lithium salt that dissolves in a non-aqueous solvent and (3) contains a chain isocyanato compound represented by the general formula (I) and / or (II) Electrolytic solution.

However, X is hydrogen, halogen, isocyanato group, or a C ₁ to -C ₂₀ aliphatic hydrocarbons (which may have a hetero atom). Y represents O, SO ₂ , or a C _{1 to} C ₂₀ aliphatic hydrocarbon (which may have a hetero atom). Z is hydrogen, halogen, isocyanato group, C _{1 to} C ₂₀ aliphatic hydrocarbon (which may have a hetero atom), or C _{6 to} C ₂₀ aromatic hydrocarbon (which has a hetero atom). May be).   The nonaqueous electrolytic solution according to claim 1, wherein the chain isocyanato compound is contained in an amount of 0.01 to 3% by weight.   The chain carbonate ester, saturated cyclic carbonate ester, and unsaturated cyclic carbonate ester are contained in 30 to 80% by weight, 10 to 50% by weight, and 0.01 to 5% by weight, respectively. Non-aqueous electrolyte. The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the unsaturated cyclic carbonate is a vinylene carbonate derivative represented by the general formula (III) or an alkenyl ethylene carbonate represented by the general formula (IV).

(However, R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, or an alkyl group that may contain a halogen atom having 1 to 12 carbon atoms.)

(However, R < ₃ > -R < ₆ > is respectively independently a hydrogen atom, a halogen atom, the hydrocarbon group which may contain the C1-C12 halogen atom, or a C2-C12 alkenyl group. And at least one of them is an alkenyl group having 2 to 12 carbon atoms.) Lithium _{salt, LiPF 6, LiBF 4, LiCF} 3 SO 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 2 F 5 SO 2) The nonaqueous electrolytic solution according to claim 1, which is at least one lithium salt selected from the group consisting of LiN (CF ₃ SO ₂ ) and (C ₄ F ₉ SO ₂ ).   The electrochemical device which uses the non-aqueous electrolyte in any one of Claims 1-5.   The electrochemical device is a lithium secondary battery, the positive electrode active material is made of a lithium transition metal composite oxide material, and the negative electrode active material is (a) the d value of the lattice plane (002 plane) in X-ray diffraction Carbonaceous material of 0.340 nm or less and / or (b) one or more metal oxides selected from Sn, Si and Al, and / or (c) one or more metals selected from Sn, Si and Al The electrochemical device according to claim 6, which is an alloy of lithium and lithium.