JP2005285492A - Nonaqueous electrolyte solution and lithium secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nonaqueous electrolyte solution for a secondary battery with excellent cycle characteristics, high-temperature preservation characteristics and gas generation restraint as well as a nonaqueous electrolyte solution battery with improved cycle characteristics, high-temperature preservation characteristics or the like. <P>SOLUTION: The nonaqueous electrolyte solution battery is structured by using nonaqueous electrolyte solution with cyclic carbonic acid ester, chained carbonic acid ester, carboxylic acid ester, cyclic carbonic acid ester having unsaturated bond, and lithium salt, prepared with a certain range of volume of addition of ionic metal complex expressed in formula (I). Here in formula (I), M denotes transition metal, metal of III, IV, and V groups of the periodic table, m denotes 1 to 4, n denotes 0 to 8, q is either 0 or 1, R<SP>1</SP>denotes C<SB>1</SB>to C<SB>10</SB>alkylene, C<SB>4</SB>to C<SB>20</SB>arylene or the like, R<SP>2</SP>denotes halogen, C<SB>1</SB>to C<SB>10</SB>alkyl group, and X<SP>1</SP>, X<SP>2</SP>denote O, S or the like. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for improving a non-aqueous electrolyte for a lithium secondary battery, and to a lithium secondary battery using the same. More specifically, a non-aqueous solvent containing a cyclic carboxylic acid ester and a cyclic carbonate having an unsaturated bond, a lithium salt dissolved in the non-aqueous solvent, and a non-aqueous electrolyte solution containing an ionic metal complex, and use thereof The present invention relates to a lithium secondary battery.

  In recent years, with the spread of various small portable electronic devices such as portable electronic terminals typified by mobile phones or notebook personal computers, secondary batteries play an important role as their power source. Secondary batteries for general use include lead-acid batteries, aqueous batteries such as nickel / cadmium batteries, and non-aqueous electrolyte batteries. Among them, positive and negative electrodes capable of occluding and releasing lithium, and non-aqueous electrolytes Non-aqueous electrolyte secondary battery consisting of has various advantages compared to other secondary batteries in terms of high voltage, high energy density, excellent safety, environmental issues, etc. Therefore, research and development are being actively promoted to further improve the characteristics.

  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. Yes. Among such negative electrode active materials, among materials that are currently in practical use, examples of materials having excellent cycle characteristics include carbon materials. 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 non-aqueous electrolyte 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 a non-aqueous electrolyte of the current non-aqueous electrolyte secondary battery, LiBF ₄ , LiPF ₆ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ or LiN (SO ₂ CF ₂ CF ₃ ) are used in an aprotic organic solvent. ) A non-aqueous solution in which a lithium salt such as ₂ is mixed is used (Non-Patent Document 1). Carbonates are known as representatives of such 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).

  That is, at present, a cyclic carbonate having a high dielectric constant such as ethylene carbonate and propylene carbonate and a low-viscosity chain carbonate solvent such as diethyl carbonate, methyl ethyl carbonate and dimethyl carbonate. A solution obtained by mixing the above lithium salt in a mixed solvent is used.

In particular, a non-aqueous electrolyte in which LiBF ₄ and LiPF ₆ are dissolved in a non-aqueous solvent has a high conductivity indicating the transfer of lithium ions and a high oxidative decomposition voltage of LiBF ₄ and LiPF ₆ , so that it is stable at a high voltage. It contributes to drawing out the characteristics of the high voltage and high energy density of the non-aqueous electrolyte secondary battery described above.

However, in the conventional technique in the nonaqueous electrolyte and the nonaqueous electrolyte battery using the nonaqueous electrolyte,
1) Problems with the above lithium salt
2) Problems related to the aprotic organic solvent (non-aqueous solvent) have hindered the provision of a non-aqueous electrolyte having cycle characteristics and high-temperature storage characteristics and a non-aqueous electrolyte battery using the same. there were.

First, 1) The problems regarding the lithium salt are as follows.
That is, the non-aqueous electrolyte composed of the non-aqueous solvent in which LiBF ₄ and LiPF ₆ are dissolved is inferior in thermal stability of these electrolytes. Therefore, the lithium salt is decomposed in a high temperature environment of 60 ° C. or higher, and fluorinated. There is a problem that hydrogen (HF) is generated. Since this hydrogen fluoride decomposes the carbonaceous material of the negative electrode, the secondary battery equipped with the non-aqueous electrolyte has increased internal resistance under a high temperature environment, and battery performance such as charge / discharge cycle life is greatly reduced. There was a problem of doing. In particular, since LiPF ₆ has the lowest thermal stability, the above-described problems tend to be particularly prominent in the non-aqueous electrolyte secondary battery including an electrolyte containing LiPF ₆ .

Therefore, in order to solve the problem, development of a new lithium salt has been intensively studied. As typical examples, lithium bis (trifluoromethanesulfonyl) imide and lithium bis (trifluoromethanesulfonyl) methide have been proposed (Patent Document 3). However, even these lithium salts, and to have no electrical conductivity comparable to LiPF _6, there are problems such as it is corrosive to aluminum current collectors used in batteries, the alternative LiPF ₆ The current situation is not.

Therefore, in view of the drawbacks of the conventional technology, for example, in Japanese Patent Application Laid-Open No. 07-65843 (Patent Document 4), in order to provide an organic electrolyte battery having excellent storage stability, lithium as an electrolyte of the organic electrolyte is used. The use of boron-based alkali metal salts such as boron disalicylate [LiB (—O—C (═O) —C ₆ H ₄ —O—) ₂ ] is described. In addition, Japanese Patent Publication No. 2002-519352 (Patent Document 5) discloses a boron-containing typified by lithium bis (oxalate) borate Li [C ₂ O ₄ ] ₂ B] as a new electrochemically stable lithium salt. Alkali metal salts have been proposed.

  In particular, regarding the latter lithium bis (oxalate) borate, for example, when a graphite negative electrode is used, an electrolyte using propylene carbonate can be used by using lithium bis (oxalate) borate as an electrolyte. It has been shown that lithium bis (oxalate) borate forms a stable film (a film made of a boron-containing compound having a carbonate structure) at the graphite negative electrode / electrolyte interface on the negative electrode surface (Non-patent Document 2). Non-Patent Document 3).

However, regarding the use of lithium bis (oxalate) borate as an electrolyte, for example, according to the study by the present inventors, a single solute has a lithium ion as compared with LiBF ₄ and LiPF ₆ conventionally used. It was in a situation where the conductivity representing the transfer of the water could not be secured in a wide temperature range. In addition, in order to improve the same characteristics, an investigation was made to improve by increasing the amount of lithium bis (oxalate) borate dissolved, but in this case, a chain carbonate generally used as a nonaqueous solvent to be dissolved It was found that there are restrictions such as being difficult to dissolve.

Next, 2) The problems concerning the aprotic organic solvent (nonaqueous solvent) are as follows.
That is, in the non-aqueous electrolyte battery, in order to obtain good battery characteristics, the characteristics of the non-aqueous electrolyte responsible for transferring lithium ions are also important. As the non-aqueous solvent constituting the non-aqueous electrolyte, a mixed solvent combining a high dielectric constant solvent having a high electrolyte solubility and a low viscosity solvent is usually used. Since a high dielectric constant solvent has a high viscosity and ion transfer is very slow, it is necessary to lower its viscosity to increase the ion transfer capability, and a form in which a low viscosity solvent is used in combination with a high dielectric constant solvent is adopted. As shown above, electrolysis comprising a mixed solvent of a cyclic carbonate such as ethylene carbonate or propylene carbonate, which is a high dielectric constant solvent, and a chain carbonate such as dimethyl carbonate, diethyl carbonate or methyl ethyl carbonate, which is a low viscosity solvent. The liquid is generally used because of its high conductivity. However, since ethylene carbonate has a high freezing point of around 38 ° C., when it is used alone, the freezing point can be lowered only to about 0 ° C. even if the freezing point depression due to mixing with the solute is expected. Therefore, low temperature characteristics must be ensured by mixing ethylene carbonate with a solvent having a low viscosity and a low freezing point as described above.

  In addition, when a mixed solvent of cyclic carbonate such as ethylene carbonate and chain carbonate such as dimethyl carbonate or methyl ethyl carbonate is used as the non-aqueous electrolyte as described above, transesterification with chain carbonate on the electrode Reaction occurs, and an alkoxide radical such as a methoxy group or an ethoxy group is generated as an intermediate. In particular, the transesterification reaction of an asymmetric chain carbonate such as methyl ethyl carbonate is easily revealed by analysis, but a symmetrical chain carbonate such as dimethyl carbonate has no structural change. In addition, it is difficult to clarify even if analyzed.

  However, transesterification is also considered to occur in symmetrical chain carbonates such as dimethyl carbonate and diethyl carbonate, and these radicals generated by this transesterification are strong nucleophiles, and therefore cyclic. It promotes ring-opening / decomposition of ethylene carbonate and propylene carbonate, which are carbonic acid esters, to generate gas, or dissolve the metal of the positive electrode active material to destroy the crystal structure, thereby reducing the characteristics.

Furthermore, the thermal stability of LiPF ₆ is the most inferior because as compared with other lithium salts, in the non-aqueous electrolyte battery comprising an electrolytic solution containing LiPF _6, the above-mentioned problems appears particularly remarkably. As a result, there is a problem that the battery capacity is lowered because the charging efficiency in the initial charging is lowered. In addition, the gas generation causes liquid leakage, battery size fluctuation due to swelling, cycle life reduction, and the like.

From the above, in the prior art, as described above, a non-aqueous electrolyte solution that can satisfy all of 1) the problem with the lithium salt and 2) the problem with the aprotic organic solvent (non-aqueous solvent) is as follows. Combinations and formulations that make it difficult to show the negative effects of each non-aqueous electrolyte component (non-aqueous solvent, lithium salt, etc.) are important.
JP-A-4-184872 Japanese Patent Laid-Open No. 10-27625 JP-T-01-501822 Japanese Patent Application Laid-Open No. 07-65843 Special table 2002-519352 gazette Jean-Paul Gabano, "Lithium Battery", ACADEMIC PRESS (1983) Electrochemical and Solid-State Letters, 6 (6) A117-A120 (2003) Electrochemical and Solid-State Letters, 6 (7) A144-A148 (2003)

  As a result of intensive investigations in view of the problems of the prior art, the present inventors have found a novel combination that is not found at all in the conventional system for the purpose of providing a non-aqueous electrolyte excellent in cycle characteristics and high-temperature storage characteristics. And the present invention has been achieved. Another object of the present invention is to provide a non-aqueous electrolyte battery including the excellent non-aqueous electrolyte and having improved cycle characteristics, high-temperature storage characteristics, and the like.

That is, the present invention relates to a non-aqueous electrolyte for a non-aqueous electrolyte battery used in combination with a positive electrode and a negative electrode capable of occluding and releasing lithium, comprising (1) a non-aqueous solvent and (2) the non-aqueous solvent. A non-aqueous electrolyte characterized in that it contains at least a lithium salt to be dissolved and (3) an ionic metal complex represented by the general formula (I),
Formula (I):

Where M is a transition metal, group III, group IV or group V element of the periodic table, m is 1 to 4, n is 0 to 8, q is 0 or 1, and R ¹ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₄ -C ₂₀ arylene, or C ₄ -C ₂₀ halogenated arylene (these alkylenes and arylenes are substituents in the structure) And R ¹ may be bonded to each other.), R ² is halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ halogenated alkyl , C ₄ -C ₂₀ aryl, C ₄ -C ₂₀ aryl halide, or X ³ R ³ (these alkyls and aryls may have substituents, heteroatoms in their structure, and there are n Each R ² is X ¹ , X ² , and X ³ are O, S, or NR ⁴ , R ³ , and R ⁴ are each independently hydrogen, C _{1 to} C ₁₀ Alkyl, C ₁ -C ₁₀ halogenated alkyl, C ₄ -C ₂₀ aryl, C ₄ -C ₂₀ aryl halide (these alkyls and aryls may have substituents, heteroatoms in their structure, A plurality of R ³ and R ⁴ may be bonded to each other to form a ring), and the non-aqueous electrolyte contains 0.01 to 2% by weight of the ionic metal complex. The lithium salt contains 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) _, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), and at least one lithium salt selected from the group consisting of LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), and the non-aqueous solvent is a cyclic carbonate, a chain carbonate, or a cyclic carboxylate And a non-aqueous solvent containing 0.1 to 5% by weight of the cyclic carboxylic acid ester and 0.1 to 5% by weight of the cyclic carbonate having unsaturation. The cyclic carboxylic acid ester is at least one cyclic carboxylic acid ester selected from the group of γ-butyrolactone, γ-valerolactone, γ-caprolactone, and ε-caprolactone, and the cyclic carbonate having unsaturation is A vinylene carbonate derivative represented by the general formula (II),

[In General Formula (II), R ⁵ and R ⁶ represent a hydrogen atom, a halogen atom or an alkyl group which may contain a halogen atom having 1 to 12 carbon atoms, and R ⁵ and R ⁶ are The same case may be used, or they may be different from each other. ],
Or alkenylethylene carbonates represented by the general formula (III)

[In General Formula (III), R ^{7 to} R ¹⁰ are each a hydrogen atom, a halogen atom, a hydrocarbon group which may contain a halogen atom having 1 to 12 carbon atoms, or an alkenyl group having 2 to 12 carbon atoms. And at least one of them is an alkenyl group having 2 to 12 carbon atoms. R ^{7 to} R ¹⁰ may be the same as or different from each other. ],
The present invention provides a non-aqueous electrolyte characterized by the above.

  Furthermore, the present invention is a non-aqueous electrolyte battery comprising the above non-aqueous electrolyte and a positive and negative electrodes capable of occluding and releasing lithium, wherein the positive electrode is a lithium transition metal composite oxide as a positive electrode active material. The negative electrode is made of a material, and the negative electrode is, as a negative electrode active material, (a) a carbonaceous material having a lattice plane (002 plane) d-value of 0.340 nm or less in X-ray diffraction, and / or (b) Sn, Si and It comprises an oxide of at least one metal selected from Al and / or (c) a negative electrode active material containing at least an alloy of at least one metal selected from Sn, Si and Al and lithium. A lithium secondary battery is provided.

  The reason why the battery characteristics can be improved is presumed to be as follows. That is, the ionic metal complex 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 further improved by containing a vinylene carbonate derivative represented by the general formula (II) and an alkenyl ethylene carbonate derivative represented by the general formula (III), which are cyclic carbonates having an unsaturated bond. It becomes. This is presumably because the ionic metal complex and the cyclic carbonate having an unsaturated bond have different decomposition potentials on the surface of the negative electrode, respectively, and a good film is formed stepwise.

  Moreover, in the case of the ionic metal complex represented by the general formula (I), restrictions such as difficulty in dissolving in a chain carbonate generally used as a non-aqueous solvent such as the above-described lithium bis (oxalate) borate In order to show very good solubility in various non-aqueous solvents, there is a problem that the conductivity representing the transfer of lithium ions cannot be secured in a wide temperature range by containing the ionic metal complex. Does not occur.

  According to the present invention, a very suitable non-aqueous electrolyte is provided as a non-aqueous electrolyte for a secondary battery excellent in cycle characteristics, high-temperature storage characteristics, and gas generation suppression. That is, as shown in the present invention, the use of a novel combination of non-aqueous electrolytes that cannot be seen in the conventional system improves the initial capacity, and the non-aqueous electrolyte has stability at high temperatures. Moreover, not only the high-temperature storage characteristics are improved, but also a non-aqueous electrolyte battery capable of suppressing gas generation inside the battery can be provided. In addition, even if the charge / discharge cycle is repeated, the initial capacity can be maintained, and a nonaqueous electrolyte battery having good cycle characteristics can be provided.

The nonaqueous electrolyte solution according to the present invention and a nonaqueous electrolyte battery using the nonaqueous electrolyte solution will be described in detail.

Nonaqueous solvent The nonaqueous solvent used in the present invention includes the following cyclic carbonate ester, chain carbonate ester, cyclic carboxylate ester, and cyclic carbonate ester having an unsaturated bond, as well as conventional secondary battery nonaqueous electrolysis. Various solvents such as those used in the liquid can be used, and these may be used in combination of two or more. In particular, the non-aqueous electrolyte of the present invention always contains any one of propylene carbonate and ethylene carbonate as a non-aqueous solvent, and always contains any one of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. Is preferred.

  Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Among these, ethylene carbonate and propylene carbonate are more preferable, but not particularly limited. Two or more of these cyclic carbonates may be mixed.

  Examples of the cyclic carboxylic acid ester include lactone compounds having 3 to 9 carbon atoms in total. Specific examples 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. The cyclic carboxylic acid ester is preferably in the range of 0.1 to 5% by weight, more preferably in the range of 0.1 to 3% by weight. If it is less than 0.1% by weight, the effect of suppressing gas generation during high-temperature storage at 85 ° C. or higher in a fully charged state of 4.2 V, the improvement effect of high-temperature storage characteristics, particularly the effect of suppressing gas generation is not sufficient. On the other hand, when the amount exceeds 5% by weight, a phenomenon in which the cycle characteristic is remarkably deteriorated is observed. In particular, a phenomenon in which the discharge voltage is lowered during rapid discharge and a curve at the end of discharge is caused to occur. This is not preferable because there is a problem that the flat portion is reduced and the average voltage is lowered.

  Examples of the chain carbonate include chain carbonates having 3 to 9 carbon atoms. 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 Propyl 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.

Cyclic carbonate having an unsaturated bond Next, the cyclic carbonate having an unsaturated bond includes a vinylene carbonate derivative represented by the general formula (II) and an alkenylethylene carbonate represented by the general formula (III). Derivatives.

  Specific examples of the vinylene carbonate derivative include the following compounds. That is, 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. Is not to be done. 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 sort, and it is also possible to be independent or to mix.

  Examples of alkenyl ethylene carbonate derivatives include 4-vinyl ethylene carbonate, 4-vinyl-4-methyl ethylene carbonate, 4-vinyl-4-ethyl ethylene carbonate, 4-vinyl-4-n-propyl ethylene carbonate, 4 -Vinyl-5-methylethylene carbonate, 4-vinyl-5-ethylethylene carbonate, 4-vinyl-5-n-propylethylene carbonate and the like can be mentioned, but are not limited thereto. Among these compounds, 4-vinylethylene carbonate is the cheapest and most effective compound. The alkenylethylene carbonate derivative is at least one, and can be used alone or in combination.

  When the cyclic carbonate having an unsaturated bond of the present invention is used alone or mixed and dissolved in the nonaqueous electrolytic solution, each concentration is in the range of 0.1 to 5% by weight, more preferably 0.1. Desirably, it is ˜3 wt%. If the amount is less than 0.1% by weight, the effect of improving the initial characteristics and charge / discharge characteristics, particularly the effect of improving the cycle characteristics is not sufficient. On the other hand, if the amount exceeds 5% by weight, more gas is generated during the initial charge. When the temperature is higher than 85 ° C. in a fully charged state of 4.2V, the battery characteristics are greatly deteriorated, and at the high temperature, there is a problem that gas is blown out inside the battery.

  Examples of other various solvents include, for example, chain esters having 3 to 9 carbon atoms, chain ethers having 3 to 6 carbon atoms, and benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane. , N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, sulfolane, dichloroethane, chlorobenzene, and nitrobenzene, but are not limited thereto.

  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, methyl propionate, Mention may be made of ethyl propionate, propionate-n-propyl, propionate-isopropyl, propionate-n-butyl, propionate isobutyl, propionate-t-butyl. Among these, ethyl acetate, methyl propionate, and ethyl propionate can be preferable, but are not limited to these.

  Moreover, a C3-C6 chain | strand-shaped ether: Dimethoxymethane, dimethoxyethane, diethoxymethane, diethoxyethane, ethoxymethoxymethane, ethoxymethoxyethane, etc. can be mentioned. Of these, dimethoxyethane and diethoxyethane are more preferable, but are not particularly limited thereto.

Nonaqueous electrolyte solute (lithium salt)
A lithium salt is used as a solute of the nonaqueous electrolytic solution used in the present invention. The lithium salt is not particularly limited as long as it can be used as a solute. Specific examples thereof are as follows.
_A) LiPF _6, LiAsF _6, inorganic fluoride salts LiBF ₄ or the _{like, LiClO 4, LiBrO 4, LiIO} 4, inorganic lithium salts such as perhalogenates equal.
B) The organic lithium salt shown below is mentioned.
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. Among these, 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 ) is more preferable, but it is not particularly limited. Two or more of these lithium salts may be mixed.

  Two or more kinds of these solutes may be mixed and used. It is desirable that the lithium salt molar concentration of the solute in the nonaqueous electrolytic solution is 0.5 to 3 mol / liter. If this concentration is too low, the ionic conductivity of the non-aqueous electrolyte is insufficient due to an absolute lack of concentration. If the concentration is too high, the ionic conductivity decreases due to an increase in viscosity, and precipitation at low temperatures occurs. Since it is likely to occur and causes problems, the performance of the nonaqueous electrolyte battery is undesirably lowered.

Ionic metal complex When the ionic metal complex used in the present invention is singly or mixed and dissolved in the non-aqueous electrolyte, the concentration of each is in the range of 0.01 to 2% by weight, more preferably 0.8. The range of 05 to 1% by weight is desirable. If it is less than 0.01% by weight, the effect of improving the charge / discharge characteristics, particularly the effect of improving the cycle characteristics is not sufficient. On the other hand, if it exceeds 2% by weight, it is 85 ° C. or higher at 4.2V full charge. When the temperature is high, battery characteristics are greatly deteriorated, and at the high temperature, there is a problem that expansion occurs due to gas generation inside the battery.

Examples of the ionic metal complex used in the present invention include those represented by the following formula (IV), formula (V) and formula (VI), but are not limited thereto.
Formula (IV):

Formula (V):

Formula (VI):

The ionic metal complex is at least one, and can be used alone or in combination. The non-aqueous electrolyte of the present invention can be produced, for example, by stirring a non-aqueous solvent and adding and dissolving a lithium compound as an electrolyte therein and adding and dissolving the ionic metal complex. it can.

  In addition, when using a non-aqueous electrolyte containing an ionic metal complex used in the present invention and a cyclic carbonate having an unsaturated bond, there is no particular limitation, but if necessary, in an unsealed 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.

  Examples of the negative electrode active material constituting the negative electrode include 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 ion, silicon oxide, transition metal oxide capable of doping / de-doping lithium ion, doping / desorption of lithium ion 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. The carbon material is preferably a carbon material having a (002) plane spacing (d002) of 0.340 nm or less measured by an X-ray diffraction method, and graphite having a true density of 1.70 g / cm 3 or more or close to it. 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 same 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.

  Also, silicon that can be alloyed with lithium, silicon alloy, tin, tin alloy, tin oxide that can be doped / dedoped with lithium ion, silicon oxide, and doped / dedoped lithium ion In the case of using a transition metal oxide that can be used, the theoretical capacity per weight is higher than that of the above-mentioned carbonaceous material, which 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, LixMO ₂ such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ (where M Is one or more transition metals, and x is a composite oxide of lithium and one or more transition metals represented by: (Lithium transition metal composite oxide), 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 can be used. Most preferably, a lithium transition metal composite oxide material that can be doped and dedoped is used. The positive electrode generally has a configuration in which a positive electrode active material is formed on a current collector such as aluminum, titanium, stainless steel foil, or 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, and the non-aqueous electrolyte is used in a separator in which a porous polyolefin film and a polymer electrolyte are used in combination. May be soaked.

  The shape of the secondary battery using the non-aqueous electrolyte of the present invention is not particularly limited, and can be various shapes such as a cylindrical shape, a square shape, an aluminum laminate type, a coin shape, and a button shape.

  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 1-16
First, as a reference non-aqueous electrolyte 1, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (capacity ratio 1: 2), LiPF ₆ as a lithium salt at a concentration of 1 mol / liter, Prepared by dissolving. Next, a predetermined amount of the compounds described in Table 1 was added to the reference electrolyte solution 1 to prepare various nonaqueous electrolyte solutions.

In addition, among the compounds described in Table 1, the compounds other than the formula (IV), the formula (V), and the formula (VI) shown above are shown by the following abbreviations.
GBL: γ-butyrolactone, GVL; γ-valerolactone,
VC; vinylene carbonate, VEC; 4-vinylethylene carbonate

[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 (Nippon Kagaku Kogyo C-5), 3 parts by weight of acetylene black as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder are mixed and dispersed in N-methylpyrrolidone as a solvent. _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 0.6 mA up to 3.0 V, followed by charging at 1.2 mA up to 4.2 V, then switching 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 at 1.2 mA to 2.75V.
c) 2nd cycle and 3rd cycle charging / discharging conditions: Charging to 4.2 V at 1.2 mA, shifting from 4.2 V to constant voltage charging, and charging was terminated when 6 hours had elapsed in total. Then, it discharged to 2.75V at 1.2mA. This operation was repeated twice.

In addition, regarding the characteristics of the coin-type battery after high-temperature storage, the storage capacity is maintained at 85 ° C. for 24 hours after charging under the same charging conditions as described above, and then discharged at 25 ° C. under the same discharging conditions. Calculated by the formula.
Capacity retention rate = (discharge capacity at the fourth cycle / discharge capacity at the third cycle) × 100 (%)
Further, charge / discharge was performed for 1 cycle under the same conditions as the initial 3 cycles at room temperature, and the capacity recovery rate was calculated by the following equation.
-Capacity recovery rate = (discharge capacity at the fifth cycle / discharge capacity at the third cycle) x 100 (%)

[Production of laminated battery]
Using the same electrode as the coin-type battery described above, a negative electrode having a size of 55 mm × 90 mm and a positive electrode having a size of 50 mm × 80 mm were cut out and faced through a separator made of a microporous polyethylene film to form an electrode group. This electrode group was accommodated in a cylindrical bag made of an aluminum laminate film (manufactured by Sumitomo Electric) so that both the positive and negative lead terminals were drawn out from one open portion. Then, first, the side from which the lead terminal was pulled out was heat-sealed and closed. Next, with the remaining opening facing upward, 1.2 g of the nonaqueous electrolyte solution was injected and impregnated into the electrode group, and then charged for 90 minutes at a constant current of 15 mA.

  Thereafter, with the remaining opening facing up, 0.3 g of non-aqueous electrolyte was further injected and impregnated, and then the opening was heat-sealed to seal the electrode group in a bag. Got.

The laminate battery produced in the above process was allowed to stand for 1 week at room temperature, and the charge / discharge characteristics were measured as follows.
a) Charging after standing for one week at room temperature (charging in the first cycle); charging is performed at 30 mA up to 4.2 V, and after changing from 4.2 V to constant voltage charging for a total of 5 hours I finished charging.
b) First cycle discharge: After the above charge, the battery was discharged at 30 mA to 2.75 V.
c) Charging after the second cycle; after discharging in b), the charging is performed at 30mA up to 4.2V, and then the charging is terminated when the whole of 6 hours elapses from 4.2V to constant voltage charging. did.
d) Discharge after the second cycle;
After charging c), it was discharged to 2.75 V at 30 mA. By the same method, charging / discharging between 2.75V and 4.2V was repeated 3 times.

Regarding the 25 ° C. cycle characteristics, the following charge / discharge test conditions were carried out after the above-described charge / discharge test was performed up to the third cycle. That is, the capacity retention rate after 100 cycles was calculated at 25 ° C. under the following charge / discharge conditions according to the following equation.
-Charging: Charging to 4.2 V at 100 mA, shifting from 4.2 V to constant voltage charging, and finishing charging when 2.5 hours have elapsed as a whole.
-Discharge: After the above-described charging, the battery was discharged to 2.75 V at 100 mA.
・ Capacity maintenance ratio after 100 cycles at 25 ° C. = (Discharge capacity at the 100th cycle / discharge capacity at the third cycle) × 100 (%)

[Comparison of battery characteristics with coin-type battery / laminate battery]
Table 2 shows the characteristic evaluation results after high-temperature storage of the coin-type battery using the various non-aqueous electrolytes shown in Table 1 above and the 25 ° C. cycle characteristic results in the laminated battery.

As shown in Table 2, a coin-type battery using a nonaqueous electrolytic solution containing a predetermined amount of the ionic metal complex of the present invention, a cyclic carboxylic acid ester and a cyclic carbonate having an unsaturated bond (Examples 1 to 2). 16) In any combination, compared with the reference non-aqueous electrolyte (Comparative Example 3), after storage at 85 ° C. for 24 hours, the battery has a clear improvement effect on the capacity retention rate and the capacity recovery rate. It can be seen that On the other hand, in the result of the cycle characteristics in the laminate battery, in the case of using a nonaqueous electrolytic solution containing a predetermined amount of the ionic metal complex of the present invention, a cyclic carboxylic acid ester and a cyclic carbonate having an unsaturated bond, It was confirmed that good characteristics were obtained.

  Further, when the ionic metal complex alone or the cyclic carboxylic acid ester alone is contained in a predetermined amount (Comparative Examples 2 and 3), the high-temperature storage characteristics tend to be inferior as compared with Examples 1 to 16. The combination of the non-aqueous electrolyte constituent elements in the present invention that makes it difficult for the negative effects of each component to appear, and the form of the combination affected.

Examples 17-31
As a reference non-aqueous electrolyte 2, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (capacity ratio 1: 2), LiPF ₆ as a lithium salt, 1.1 mol / liter, LiN (SO ₂ CF ₃ ) Prepared by containing and dissolving ₂ at a concentration of 0.1 mol / liter.

  Next, a predetermined amount of the compounds described in Table 3 was added to the reference electrolyte solution 2 to prepare various nonaqueous electrolyte solutions. In addition, among the compounds described in Table 3, the compounds other than the formula (V) shown above are represented by the same abbreviations as in Table 1.

[Comparison of battery characteristics in laminated batteries]
Table 4 shows the characteristic evaluation results after high-temperature storage of the laminated battery using the various non-aqueous electrolytes shown in Table 3 and the 25 ° C cycle characteristic results.

Regarding the characteristics of the laminated battery after high-temperature storage, the capacity retention rate is expressed by the following equation by discharging the battery at 25 ° C. under the same discharge condition after storage at 85 ° C. for 24 hours under the same charge condition as above. Calculated by
Capacity retention rate = (discharge capacity at the fourth cycle / discharge capacity at the third cycle) × 100 (%)
Further, charge / discharge was performed for 1 cycle under the same conditions as the initial 3 cycles at room temperature, and the capacity recovery rate was calculated by the following equation.
-Capacity recovery rate = (discharge capacity at the fifth cycle / discharge capacity at the third cycle) x 100 (%)

[Evaluation of cell swelling during high-temperature storage]
The method of measuring the swelling of the cell in the laminate battery was measured by the volume change when the cell was immersed in silicone oil. The volume of the laminate battery was measured after cooling to room temperature before and after the high temperature storage test, and the volume change rate was defined as the swelling of the cell during storage.

As shown in Table 4, a non-aqueous electrolyte prepared by adding the ionic metal complex of the present invention, a cyclic carboxylic acid ester, and a cyclic carbonate having an unsaturated bond in an addition amount within a predetermined range of the present invention was used. In any of the combinations of the laminated batteries (Examples 17 to 31), compared to the reference non-aqueous electrolyte (Comparative Examples 4, 5, 6, and 7), after storage at 85 ° C. for 24 hours, It can be seen that the capacity maintenance rate, the capacity recovery rate, and the swelling of the cells show a clear improvement effect. In addition, when the non-aqueous electrolyte containing the above-mentioned ionic metal complex of the present invention, cyclic carboxylic acid ester and cyclic carbonate having an unsaturated bond is added in a predetermined range of the present invention, the cycle characteristics are also used. It was confirmed that good characteristics were obtained.

Claims (7)

A non-aqueous electrolyte for a non-aqueous electrolyte battery used in combination with a positive electrode and a negative electrode capable of occluding and releasing lithium, wherein (1) a non-aqueous solvent and (2) a lithium salt dissolved in the non-aqueous solvent (3) A nonaqueous electrolytic solution comprising at least an ionic metal complex represented by the general formula (I).
Formula (I):
Where M is a transition metal, group III, group IV or group V element of the periodic table, m is 1 to 4, n is 0 to 8, q is 0 or 1, and R ¹ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₄ -C ₂₀ arylene, or C ₄ -C ₂₀ halogenated arylene (these alkylenes and arylenes are substituents in the structure) And R ¹ may be bonded to each other.), R ² is halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ halogenated alkyl , C ₄ -C ₂₀ aryl, C ₄ -C ₂₀ aryl halide, or X ³ R ³ (these alkyls and aryls may have substituents, heteroatoms in their structure, and there are n Each R ² is X ¹ , X ² , and X ³ are O, S, or NR ⁴ , R ³ , and R ⁴ are each independently hydrogen, C _{1 to} C ₁₀ Alkyl, C ₁ -C ₁₀ halogenated alkyl, C ₄ -C ₂₀ aryl, C ₄ -C ₂₀ aryl halide (these alkyls and aryls may have substituents, heteroatoms in their structure, A plurality of R ³ and R ⁴ may be bonded to each other to form a ring). The nonaqueous electrolytic solution according to claim 1, wherein the nonaqueous electrolytic solution contains the ionic metal complex in an amount of 0.01 to 2% by weight. 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 ) _, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), at least one lithium salt selected from the group. The non-aqueous solvent includes a cyclic carbonate ester, a chain carbonate ester, a cyclic carboxylic acid ester, and a cyclic carbonate ester having unsaturation, and the cyclic carboxylic acid ester is 0.1 to 5% by weight and the cyclic group having the unsaturation. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent contains 0.1 to 5% by weight of carbonate. The non-aqueous solution according to claim 4, wherein the cyclic carboxylic acid ester is at least one cyclic carboxylic acid ester selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, and ε-caprolactone. Electrolytic solution. 5. The cyclic carbonic acid ester having unsaturation is a vinylene carbonate derivative represented by the general formula (II) or an alkenyl ethylene carbonate represented by the general formula (III). The non-aqueous electrolyte described.
[In General Formula (II), R ⁵ and R ⁶ represent a hydrogen atom, a halogen atom or an alkyl group which may contain a halogen atom having 1 to 12 carbon atoms, and R ⁵ and R ⁶ are The same case may be used, or they may be different from each other. ]
[In General Formula (III), R ^{7 to} R ¹⁰ are each a hydrogen atom, a halogen atom, a hydrocarbon group which may contain a halogen atom having 1 to 12 carbon atoms, or an alkenyl group having 2 to 12 carbon atoms. And at least one of them is an alkenyl group having 2 to 12 carbon atoms. R ^{7 to} R ¹⁰ may be the same as or different from each other. ] A nonaqueous electrolyte battery comprising the nonaqueous electrolyte solution according to any one of claims 1 to 6, a positive electrode capable of inserting and extracting lithium, and a negative electrode, wherein the positive electrode is lithium as a positive electrode active material. It is made of a transition metal composite oxide material, and the negative electrode is used as a negative electrode active material (a) a carbonaceous material having a d-value of 0.340 nm or less on the lattice plane (002 plane) in X-ray diffraction, and / or (b 1) an oxide of one or more metals selected from Sn, Si and Al, and / or (c) a negative electrode active material containing at least one alloy of at least one metal selected from Sn, Si and Al and lithium. A lithium secondary battery characterized by that.