Specification
SPECIFICATION TITLE OF THE INVENTION: LITHIUM SECONDARY BATTERY, AND NON-AQUEOUS ELECTROLYTIC SOLUTION FOR USE IN THE LITHIUM SECONDARY
BATTERY TECHNICAL FIELD
[0001]
The present invention relates to a lithium secondary-battery which secures good recovery characteristics after low-temperature cycles of the battery even after exposed to high temperatures, and to a nonaqueous electrolytic solution for use in the battery.
BACKGROUND ART
[0002]
In recent years, lithium secondary batteries have been widely used as power supplies for small-size electronic devices such as mobile telephones, notebook-size personal computers and the like, power supplies for electric vehicles, as well as for electric power storage, etc. These electronic devices and vehicles may be used in a broad temperature range, for example, at midsummer high temperatures or at frigid low temperatures, and are therefore required to have well-balanced and improved charging and discharging cycle properties in a broad temperature range.
In this specification, the term of lithium secondary battery is used as a concept including so-called lithium ion secondary batteries.
The lithium secondary battery is mainly constituted of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution containing a lithium salt and a nonaqueous solvent. As the nonaqueous solvent, used are carbonates such as ethylene carbonate (EC) , propylene carbonate (PC), etc.
Lithium secondary batteries, in which a carbon material capable of absorbing and releasing lithium such as coke, artificial graphite, natural graphite or the like is used as the negative electrode, have been widely put into practical use .
[0003]
The lithium secondary battery using a high-crystalline carbon material such as natural graphite, artificial graphite or the like as the negative electrode material therein has some problems in that the solvent in the nonaqueous electrolytic solution is reduced and decomposed on the surface of the negative electrode therein during charging to give a decomposed product, and the decomposed product deposits on the negative electrode to interfere with the Li ion diffusion on the surface of the negative electrode, whereby an active Li metal may irreversibly deposit on the surface of the negative electrode during charging to lower the battery capacity and to lower the battery safety. Such Li metal deposition noticeably occurs at low temperatures at which, in particular, the Li ion diffusion is retarded frequently.
[0004]
On the other hand, lithium secondary batteries using LiCo02 as the positive electrode therein have been most popularized, but the natural resources for Co are hardly available. Accordingly, studies of lithium-containing metal oxides, such as lithium-containing transition metal compounds comprising, as the main constitutive elements, manganese and nickel in place of Co, as well as olivine-type lithium phosphates comprising, as the main constitutive element, iron of which the natural recourses are the most available of all, are being made actively in the art. However, in the batteries using the positive electrode of the type, the main elements to constitute the positive electrode, manganese, nickel and iron, dissolve out as ions in the electrolytic solution and are reduced on the negative electrode; and in particular, in secondary batteries containing a carbon material as the negative electrode active material, the negative electrode resistance may be thereby significantly increased and therefore Li metal may also frequently deposit on the negative electrode therein at low temperatures.
The above-mentioned phenomenon is not a so much serious problem in the case where a positive electrode not containing any of those metal elements of nickel, manganese and iron, such as LJ.C0O2, is used. In addition, the phenomenon is remarkable after the batteries are exposed to high temperatures for long periods, and therefore, it may be considered that, when batteries are stored at high temperatures, metal ion release from the positive electrode active material and reductive decomposition of solvent on the negative electrode would be promoted.
[0005]
Patent Reference 1 shows that, in a lithium secondary battery using LiCoC>2 as the positive electrode active material and using graphite as the negative electrode active material, when a partially hydrogenated naphthalene compound such as 1,2,3,4-tetrahydronaphthalene is added to the nonaqueous electrolytic solution, then the safety of the battery in overcharging could be enhanced as compared with the case where biphenyl is added thereto.
CITATION LIST PATENT REFERENCE
[0006]
Patent Reference 1: JP-A 2003-229171 DISCLOSURE OF THE INVENTION PROBLEMS THAT THE INVENTION IS TO SOLVE
[0007]
An object of the present invention is to provide a nonaqueous electrolytic solution for a lithium secondary battery, which comprises a positive electrode containing, as the positive electrode active material, a lithium-containing metal oxide that contains at least one metal element selected from nickel, manganese and iron, a negative electrode containing, as the negative electrode active material, a carbon material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution of an electrolyte salt dissolved in a nonaqueous solvent, and which secures good recovery characteristics after low-temperature cycles even after exposed to high temperatures; and to provide such a lithium secondary battery using the nonaqueous electrolytic solution.
MEANS FOR SOLVING THE PROBLEMS
[0008]
The present inventors used a nonaqueous electrolytic solution that contains an aromatic compound such as 1, 2, 3, 4-tetrahydronaphthalene, biphenyl or the like described in the above-mentioned Patent Reference 1, singly by itself, for the purpose of enhancing the performance of the lithium secondary battery that comprises a positive electrode containing, as the positive electrode active material, a lithium-containing metal oxide that contains at least one metal element selected from nickel, manganese and iron, a negative electrode containing, as the negative electrode active material, a carbon material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution of an electrolyte salt dissolved in a nonaqueous solvent; however, the electrolytic solution was ineffective for preventing the reduction in the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures.
Consequently, the present inventors further made assiduous studies for the purpose of solving the above-mentioned problems and, as a result, have found that, in the lithium secondary battery having the configuration as above, when at least two types of aromatic compounds are combined for the nonaqueous electrolytic solution, and concretely, when a cyclohexane ring-having aromatic compound, 1,2,3,4-tetrahydronaphthalene, and at least one aromatic compound selected from cyclohexane ring-free biphenyl derivatives and alkylphenol derivatives are contained in the nonaqueous electrolytic solution each in a concentration of from 0.1 to 5% by mass, then the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures can be remarkably increased, and have completed the present invention.
[0009]
Specifically, the present invention provides the following (1) and (2):
(1) A lithium secondary battery comprising a positive electrode containing, as the positive electrode active material, a lithium-containing metal oxide that contains at least one metal element selected from nickel, manganese and iron, a negative electrode containing, as the negative electrode active material, a carbon material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution of an electrolyte salt dissolved in a nonaqueous solvent, wherein the nonaqueous electrolytic solution contains from 0 .1 to 5% by mass of 1, 2, 3, 4-tetrahydronaphthalene, and from 0.1 to 5% by mass of a biphenyl derivative and/or an alkylphenol derivative.
(2) A nonaqueous electrolytic solution for a lithium secondary battery that comprises a positive electrode containing, as the positive electrode active material, a lithium-containing metal oxide that contains at least one metal element selected from nickel, manganese and iron, a negative electrode containing, as the negative electrode active material, a carbon material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution of an electrolyte salt dissolved in a nonaqueous solvent; the nonaqueous electrolytic solution of an electrolyte salt dissolved in a nonaqueous solvent containing from 0.1 to 5% by mass of 1,2, 3, 4-tetrahydronaphthalene, and from 0.1 to 5% by mass of a biphenyl derivative and/or an alkylphenol derivative.
ADVANTAGE OF THE INVENTION [0010]
According to the invention, there are provided a lithium
secondary battery having an increased recovery rate after low-temperature cycles after exposure of the battery to high temperatures, and a nonaqueous electrolytic solution for use in the battery.
BEST MODE FOR CARRYING OUT THE INVENTION
[0011] [Nonaqueous Electrolytic Solution]
The nonaqueous electrolytic solution of the present invention is a nonaqueous electrolytic solution of an electrolyte salt dissolved in a nonaqueous solvent, and contains from 0.1 to 5% by mass of 1, 2, 3, 4-tetrahydronaphthalene and from 0.1 to 5% by mass of a biphenyl derivative and/or an alkylphenol derivative.
Though not always clear, the reason why the lithium secondary battery of the present invention can be greatly improved in point of the recovery rate thereof after low-temperature cycles after exposure to high temperatures would be because of the following:
Basically, 1,2,3,4-tetrahydronaphthalene has an oxidation potential of about 4.3 V to lithium, and even in use at a final charging voltage of not higher than 4.1V, the compound could be oxidized on the. positive electrode in an extremely minor amount to promote proton formation, and therefore has an advantage in that owing to proton reduction, the Li metal on the negative electrode is prevented from depositing thereon.
On the other hand, in case where 1, 2, 3, 4-tetrahydronaphthalene is used alone, the positive electrode active material comprising a lithium-containing metal oxide that contains at least one metal element selected from nickel, manganese and iron is corroded by proton to thereby promote the release of metal ion from the positive electrode, and as a result, the positive electrode resistance is thereby increased or the negative electrode resistance is also increased by deposition of the metal ion on the negative electrode, or that is, the case has a problem in that the recovery rate after low-temperature cycles lowers.
However, the present inventors have found that, when a biphenyl derivative and/or an alkylphenol derivative is combined with 1,2,3,4-tetrahydronaphthalene, then the surface of the positive electrode is protected and there does not occur metal release from the positive electrode, or that is, the combined use brings about such a specific effect that could not be attained by the single use of the individual aromatic compounds, and have reached the present invention.
[0012]
Preferably, the biphenyl derivative for use in the present invention is represented by the following general formula (I):
[0013] [Chemical Formula 1]
[0014]
(In the formula, X represents a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms, a phenyl group, an alkoxy group having from 1 to 6 carbon atoms, or an alkanesulfonyloxy group having from 1 to 6 carbon atoms.)
[0015]
In the formula (I) , the substitution position of the substituent X is preferably an ortho-position or a para-position. As the substituent X, further preferred is a linear or branched alkyl group having from 1 to 6 carbon atoms, a phenyl group, a linear or branched alkoxy group having from 1 to 6 carbon atoms, or a linear or branched alkanesulfonyloxy group having from 1 to 6 carbon atoms, more preferred is a linear or branched alkyl group having from 1 to 6 carbon atoms, or a linear or branched alkanesulf onyloxy group having from 1 to 6 carbon atoms, and even more preferred is a linear or branched alkanesulfonyloxy group having from 1 to 6 carbon atoms.
[0016]
The linear or branched alkyl group having from 1 to 6 carbon atoms for the substituent X includes a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a ) hexyl group, a 2-propyl group, a tert-butyl group, a tert-pentyl group, etc. Of those, preferred are a methyl group, an ethyl group, a tert-butyl group, a tert-pentyl group; and more preferred are a tert-butyl group, a tert-pentyl group.
The linear or branched alkoxy group having from 1 to 6 carbon atoms for the substituent X includes a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, etc. Of those, preferred are a methoxy group, an ethoxy group, and more preferred is a methoxy group.
The linear or branched alkanesulfonyloxy group having from 1 to 6 carbon atoms for the substituent X includes a methanesulfonyloxy group, an ethanesulfonyloxy group, a propanesulfonyloxy group, a butanesulfonyloxy group, a pentanesulfonyloxy group, a hexanesulfonyloxy group, etc. Of those, preferred are a methanesulfonyloxy group, an ethanesulfonyloxy group, a propanesulfonyloxy group; and more preferred is a methanesulfonyloxy group.
At least one hydrogen atom of the alkanesulfonyloxy group may be substituted with a fluorine atom. Concretely, the group is preferably a trifluoromethanesulfonyloxy group or a trifluoroethanesulfonyloxy group.
[0017]
Preferably, the alkylphenol derivative for use in the present invention is represented by the following formula (II) :
[0018]
[Chemical Formula 2]
[0019]
(In the formula, R1 represents an alkyl group having from 1 to 7 carbon atoms; Y represents an alkyl group having from 1 to 6 carbon atoms, an alkanesulfonyl group having from 1 to 6 carbon atoms, an acyl group having from 2 to 6 carbon atoms, an alkoxycarbonyl group having from 2 to 6 carbon atoms, or a formyl group; n indicates 1 or 2.)
In the formula (II), the substituent Y is preferably a linear or branched alkyl group having from 1 to 6 carbon atoms, or a linear or branched alkanesulfonyl group having from 1 to 6 carbon atoms, and is more preferably a linear or branched alkanesulfonyl group having from 1 to 6 carbon atoms. Preferably, n is 2.
The substitution position of the substituent R1 relative to the substituent -OY is preferably an ortho-position and a para-position.
[0020]
In the formula (II), the linear or branched alkyl group having from 1 to 7 carbon atoms for the substituent R1 is preferably a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a 2-propyl group, or a tert-alkyl group represented by the following formula (III) :
[0021]
[Chemical Formula 3]
[0022]
(In the formula, R2, R3 and R4 each independently represent a methyl group or an ethyl group.) Of those, more preferred is a tert-alkyl group (in this case, the compound of the formula (II) is a tert-alkylphenyl derivative) , and even more preferred is a tert-butyl group or a tert-pentyl group.
[0023]
In the formula (II), the linear or branched alkyl group having from 1 to 6 carbon atoms for the substituent Y includes a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a 2-propyl group, a tert-butyl group, etc. Of those, preferred are a methyl group, an ethyl group; and more preferred is a methyl group.
The linear or branched alkanesulfonyl group having from 1 to 6 carbon atoms for the substituent Y includes a methanesulfonyl group, an ethanesulfonyl group, a propanesulfonyl group, a butanesulfonyl group, a pentanesulfonyl group, a hexanesulfonyl group, etc. Of those, preferred are a methanesulfonyl group, an ethanesulf onyl group, a propanesulfonyl group; and more preferred is a methanesulfonyl group.
At least one hydrogen atom of the alkanesulfonyl group may be substituted with a fluorine atom. Concretely, the group is preferably a trifluoromethanesulfonyl group or a trifluoroethanesulfonyl group.
The linear or branched acyl group having from 2 to 6 carbon atoms for the substituent Y includes an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a pivaloyl group, etc. Of those, preferred are an acetyl group, a propionyl group; and more preferred is an acetyl group.
The linear or branched alkoxycarbonyl group having from 2 to 6 carbon atoms for the substituent Y includes a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, an isopropoxycarbonyl group, a butoxycarbonyl group, etc. Of those, preferred is a methoxycarbonyl group, an ethoxycarbonyl group; and more preferred is a methoxycarbonyl group.
[0024]
In the formulae (I), (II), (III), when the substituents are within the above-mentioned ranges, then the compounds are preferred as more effective for increasing the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures.
[0025]
Preferred examples of the biphenyl derivative in the present invention include biphenyl, ortho-terphenyl, meta-terphenyl, para-terphenyl, 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, 2-ethylbiphenyl, 3-ethylbiphenyl, 4-ethylbiphenyl, 2-tert-butylbiphenyl, 3-tert-butylbiphenyl, 4-tert-butylbiphenyl, 2-methoxybiphenyl, 3-methoxybiphenyl, 4-methoxybiphenyl, 2-(methylsulfonyloxy)biphenyl, 3-(methylsulfonyloxy)biphenyl, 4-(methylsulfonyloxy)biphenyl, etc. Of those, preferred is at least one selected from biphenyl, ortho-terphenyl, 4-methylbiphenyl, 4-ethylbiphenyl, 4-tert-butylbiphenyl, 4-methoxybiphenyl and 4-methanesulfonyloxybiphenyl; more preferred is at least one selected from ortho-terphenyl, 4-methylbiphenyl, 4-ethylbiphenyl, 4-tert-butylbiphenyl, 4-methoxybiphenyl and 4-(methylsulfonyloxy)biphenyl; and even more preferred are 4-tert-butylbiphenyl and/or 4-(methylsulfonyloxy)biphenyl.
[0026]
Preferred examples of the alkylphenol derivative in the present invention include 2-tert-butylanisole, 3-tert-butylanisole, 4-tert-butylanisole, 2-tert-pentylanisole, 3-tert-pentylanisole, 4-tert-pentylanisole, 2,3-di-tert-butylanisole, 2,4-di-tert-butylanisole, 2, 5-di-tert-butylanisole, 2,6-di-tert-butylanisole, 3,4-di-tert-butylanisole, 3,5-di-tert-butylanisole, 2-tert-butylphenyl methanesulfonate, 3-tert-butylphenyl methanesulfonate, 4-tert-butylphenyl methanesulfonate, 2-tert-pentylphenyl methanesulfonate, 3-tert-pentylphenyl methanesulfonate, 4-tert-pentylphenylmethanesulfonate, 2,3-di-tert-butylphenyl methanesulfonate, 2,4-di-tert-butylphenylmethanesulfonate, 2,5-di-tert-butylphenyl methanesulfonate, 2,6-di-tert-butylphenyl methanesulfonate, 3,4-di-tert-butylphenyl methanesulfonate, 3,5-di-tert-butylphenyl methanesulfonate, etc. Of those, preferred is at least one selected from 4-tert-butylanisole, 4-tert-pentylanisole, 2,4-di-tert-butylanisole, 2,6-di-tert-butylanisole, 4-tert-butylphenyl methanesulfonate, 4-tert-pentylphenyl methanesulfonate, 2,4-di-tert-butylphenyl methanesulfonate, and 2,6-di-tert-butylphenyl methanesulfonate; more preferred is at least one selected from 4-tert-butylphenyl methanesulfonate, 2,4-di-tert-butylphenyl methanesulfonate, and 2,6-di-tert-butylphenyl methanesulfonate; and even more preferred is at least one selected from 4-tert-butylphenyl methanesulfonate, 4-tert-pentylphenyl methanesulfonate, and 2,4-di-tert-butylphenyl methanesulfonate.
[0027]
In the nonaqueous electrolytic solution of the present invention, when the content of 1,2,3,4-tetrahydronaphthalene is more than 5% by mass, then the compound may be excessively oxidized and decomposed on the positive electrode so that the positive electrode may be greatly deteriorated; but on the other hand, when the content is less than 0.1% by mass, then the electrolytic solution could not be sufficiently effective for increasing the recovery rate after low-temperature cycles after the battery has been exposed to high temperatures . Accordingly, the lower limit of the content of the compound is preferably at least 0.1% by mass relative to the mass of the nonaqueous electrolytic solution, more preferably at least 0.7% by mass, even more preferably at least 1% by mass. The upper limit of the content is preferably at most 5% by mass, more preferably at most 4% by mass, even more preferably at most 3% by mass.
When the content of the biphenyl derivative and/or the alkylphenol derivative is more than 5% by mass, then the derivative (s) may be excessively oxidized and decomposed on the positive electrode to thereby increase the resistance of the positive electrode; but on the other hand, when the content is less than 0.1% by mass, then the electrolytic solution could not be sufficiently effective for increasing the recovery rate after low-temperature cycles after the battery has been exposed to high temperatures. Accordingly, the lower limit of the content of the compound (s) is preferably at least 0.1% by mass relative to the mass of the nonaqueous electrolytic solution, more preferably at least 0.5% by mass, even more preferably at least 0.7% by mass, most preferably at least 1% by mass. The upper limit of the content is preferably at most 5% by mass, more preferably at most 4% by mass, even more preferably at most 3% by mass.
Regarding the ratio of the content of the biphenyl derivative and/or the alkylphenol derivative to that of 1, 2, 3, 4-tetrahydronaphthalene , the lower limit of the ratio is preferably at most 0.1, more preferably at most 0.2, because, when the oxidative decomposition of 1,2,3,4-tetrahydronaphthalene is prevented from being excessively retarded, the electrolytic solution could be more effective for increasing the recovery rate after low-temperature cycles after the battery has been exposed to high temperatures. The upper limit of the ratio is preferably at most 1, more preferably at most 0.5.
[0028]
The nonaqueous electrolytic solution of the present invention can be effective for increasing the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures even though the electrolytic solution contains 1,2,3,4-tetrahydronaphthalene, and a biphenyl derivative and/or an alkylphenol derivative alone; however, when combined with a nonaqueous solvent, an electrolyte salt and other additives to be mentioned below, the above-mentioned effect of the electrolytic solution could be synergistically enhanced. Though not always clear, the reason would be because a mixed surface film having high ionic conductivity could be formed, containing the constitutive elements of 1, 2, 3,4-tetrahydronaphthalene, and the biphenyl derivative and/or the alkylphenol derivative, as combined with the nonaqueous solvent, the electrolyte salt and other additives.
[0029] [Nonaqueous Solvent]
The nonaqueous solvent for use in the nonaqueous electrolytic solution of the present invention includes cyclic carbonates, linear carbonates, linear esters, ethers, amides, phosphates, sulfones, lactones, nitriles, S=0 bond-containing compounds, carboxylic acid anhydrides, aromatic compounds, etc.
The cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), 4-fluoro-l, 3-dioxolan-2-one (FEC), trans or cis-4,5-difluoro-l,3-dioxolan-2-one (hereinafter, the two are collectively referred to as "DFEC"), vinylene carbonate (VC) , vinylethylene carbonate (VEC) , etc. Of those, preferred is use of at least one cyclic carbonate having a carbon-carbon double bond or a fluorine atom, since the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures can be increased further more; and more preferred is use of both a cyclic carbonate containing a carbon-carbon double bond and a cyclic carbonate containing a fluorine atom. As the carbon-carbon double bond-containing cyclic carbonate, preferred are VC and VEC; and as the fluorine-containing cyclic carbonate, preferred are FEC and DFEC.
One kind of those solvents may be used, but using two or more different kinds as combined is preferred as further increasing the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures. Even more preferably, three or more different kinds are combined. Preferred combinations of the cyclic carbonates include EC and PC; EC and VC; PC and VC; FEC and VC; FEC and EC; FEC and PC; FEC and DFEC; DFEC and EC; DFEC and PC; DFEC and VC; DFEC and VEC; EC and PC and VC; EC and FEC and PC; EC and FEC and VC; EC and VC and VEC; FEC and PC and VC; DFEC and EC and VC; DFEC and PC and VC; FEC and EC and PC and VC; DFEC and EC and PC and VC, etc. Of those combinations, more preferred combinations are EC and VC; FEC and PC; DFEC and PC; EC and FEC and PC; EC and FEC and VC; EC and VC and VEC, etc.
Not specifically defined, the content of the cyclic carbonate is preferably within a range of from 10 to 4 0% by volume relative to the total volume of the nonaqueous solvent. When the content is less than 10% by volume, then the electric conductivity of the electrolytic solution may lower, and the internal resistance of the battery may increase; but when more than 40% by volume, then the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures may lower. Consequently, the content preferably falls within the above-mentioned range.
[0030]
The linear carbonates include asymmetric linear carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, etc.; symmetric linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, dibutyl carbonate, etc.
Of those, the nonaqueous electrolytic solution preferably contains a linear carbonate having a methyl group, more preferably at least one of DMC, MEC, MPC, MIPC, even more preferably at least one of DMC and MEC. Also preferably, the nonaqueous electrolytic solution contains both an asymmetric linear carbonate and a symmetric linear carbonate as combined. Preferably, the proportion of the asymmetric linear carbonate in the linear carbonate is at least 50% by volume.
Although one kind of those linear carbonates may be used, two or more kinds of them are preferably used in combination.
The combination and the composition of the linear carbonates falling within the above-mentioned ranges are preferred, since the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures can be increased more. Not specifically defined, the content of the linear carbonate is preferably within a range of from 60 to 90% by volume relative to the total volume of the nonaqueous solvent. When the content is less than 60% by volume, then the viscosity of the electrolytic solution may increase; but when more than 90% by volume, then the electric conductivity of the electrolytic solution may lower and the battery characteristics such as cycle properties and others may worsen. Accordingly, the above range is preferred.
A ratio (volume ratio) "cyclic carbonates:linear carbonates" between the cyclic carbonates and the linear carbonates is preferably from 10:90 to 40:60, more preferably from 15: 85 to 35:65, and particularly preferably from 20:80 to 30:70 from the viewpoints of increasing the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures.
[0031]
As the other nonaqueous solvents, preferably mentioned are linear esters such as methyl propionate, methyl pivalate, butyl pivalate, hexyl pivalate, octyl pivalate, dimethyl' oxalate, ethyl methyl oxalate, diethyl oxalate, etc; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, etc.; linear ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, etc.; amides such as dimethylformamide, etc.; phosphates such as trimethy-1 phosphate, tributyl phosphate, trioctyl phosphate, etc.; sulfones such as sulfolane, etc.; lactones such as y-butyrolactone, Y~valer°lactone, a-angelicalactone, etc.; nitriles such as acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, etc; sultone compounds such as 1,3-butanesultone, 1,4-butanesultone, etc.; cyclic sulfite compounds such as ethylene sulfite, hexahydrobenzo[1,3,2]dioxathiolane-2-oxide (also referred to as 1,2-cyclohexanediol cyclic sulfite), 5-vinyl-hexahydro-l,3,2-benzodioxathiol-2-oxide, etc.; sulfonate compounds such as 1,2-ethanediol dimethanesulfonate, 1,2-propanediol dimethanesulfonate, 1,3-propanediol dimethanesulfonate, 1,4-butanediol dimethanesulfonate, 2-propynyl methanesulfonate, etc.; S=0 bond-containing compounds selected from vinylsulfone compounds such as divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, bis(2-vinylsulfonylethyl) ether, etc.; linear carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, etc. ; cyclic carboxylic acid anhydrides such as succinic anhydride, maleic anhydride, glutaric anhydride, itaconic anhydride, etc.; cyclohexylbenzene, fluorocyclohexylbenzene compounds (l-fluoro-2-cyclohexylbenzene, l-fluoro-3-cyclohexylbenzene, l-fluoro-4-cyclohexylbenzene); branched alkyl group-having aromatic compounds such as tert-butylbenzene, tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, etc.; aromatic compounds such as diphenyl ether, fluorobenzene, difluorobenzene (o-, m-, p-forms), 2,4-difluoroanisole, partially hydrogenated terphenyls (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane), etc.
[0032]
Of the above-mentioned nonaqueous solvents, especially preferred is use of at lest one selected from S=0 bond-containing compounds, since the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures can be increased more. As the S=0 bond-containing compounds, preferred are cyclic sulfite compounds and sulfonate compounds. Among them, more preferred is use of at least one compound selected from ethylene sulfite and 2-propynyl methanesulfonate. When the amount these compounds combined is more than 5% by mass, then the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures may lower; but on the other hand, when less than 0.05% by mass, the electrolytic solution could not be sufficiently effective for enhancing the characteristics .
Accordingly, the content is preferably at least 0.05% by mass of the nonaqueous electrolytic solution, more preferably at least 0 . 5% by mass . The upper limit of the content is preferably at most 5% by mass, more preferably at most 3% by mass.
[0033]
In general, the nonaqueous solvents are used as a mixture thereof for attaining the suitable physical properties. Regarding their combinations, for example, there are mentioned a combination of a cyclic carbonate and a linear carbonate, a combination of a cyclic carbonate, a linear carbonate and a lactone, a combination of a cyclic carbonate, a linear carbonate and a linear ester, a combination of a cyclic carbonate, a linear carbonate and an ether, a combination of a cyclic carbonate, a linear carbonate and an S=0 bond-containing compound, etc.
Of those, preferred is using a nonaqueous solvent of a combination of at least a cyclic carbonate and a linear carbonate, as increasing the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures. More specifically, a combination of one or more kinds of cyclic carbonates selected from EC, PC, VC, VEC, FEC and DFEC, and one or more kinds of linear carbonates selected from DMC, MEC and DEC is preferred.
[0034] [Electrolyte Salt]
The electrolyte salt for use in the present invention includes Li salts such as LiPF6, LiBF4, LiC104, LiN(S02F)2, etc.; linear fluoroalkyl group-containing lithium salts such as LiN(S02CF3)2, LiN(S02C2F5)2, LiCF3S03, LiC (S02CF3) 3, LiPF4(CF3)2, LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3 (iso-C3F7) 3, LiPF5 (iso-C3F7) , etc.; cyclic fluoroalkylene chain-containing lithium salts such as (CF2)2 (S02)2NLi, (CF2) 3 (S02) 2NLi, etc.; and lithium salts with an anion of an oxalate complex such as lithium bis[oxalate-0,01]borate, lithium ifluoro[oxalate-O,0'jborate, etc. Of those, especially preferred is at least one electrolyte salt selected from LiPF6, LiBF4, LiN(S02CF3) 2, and LiN (S02C2F5) 2 One or more of these electrolyte salts may be used herein either singly or as combined.
[0035]
A preferred combination of these electrolyte salts is a combination containing LiPF6 and further containing a lithium salt that contains a nitrogen atom or a boron atom. As the lithium salt that contains a nitrogen atom or a boron atom, at least one kind selected from LiBF4, LiN (S02CF3) 2 and LiN (S02C2F5) 2 is preferred. Even more preferred combinations include a combination of LiPF6 and LiBF4; a combination of LiPF6 and LiN (S02CF3) 2; a combination of LiPF6 and LiN (S02C2F5)2, etc. When the molar ratio LiPF6: [LiBF4 or LiN(S02CF3)2 or LiN (S02C2F5) 2] is smaller than 70:30 in point of the proportion of LiPF6, or when the ratio is larger than 99:1 in point of the proportion of LiPF6, then the effect of increasing the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures may lower. Accordingly, the molar ratio LiPF6: [LiBF4 or LiN(S02CF3)2 or LiN (S02C2F5) 2] is preferably within a range of from 70:30 to 99:1, more preferably from 80:20 to 98:2. The combination falling within the above range is more effective for further increasing the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures.
[0036]
The electrolyte salts can each be mixed at an arbitrary ratio. However, when a ratio (bymol) of the other electrolyte salts except LiBF4, LiN(S02CF3)2 and LiN (S02C2F5) 2 to all the electrolyte salts in the case where LiPF6 is used in combination with those ingredients is less than 0.01%, then the effect of increasing the recovery rate after low-temperature cycles of the battery after exposure thereof may be poor; but when more than 45%, the recovery rate after low-temperature cycles of the battery after exposure thereof may lower. Therefore, the ratio (by mol) is preferably from 0.01 to 45%, more preferably from 0.03 to 20%, still more preferably from 0.05 to 10%, and most preferably from 0.05 to 5%. The concentration of all these electrolyte salts as dissolved in the solution is generally preferably at least 0.3 M relative to the above-mentioned nonaqueous solvent, more preferably at least 0.5 M, most preferably at least 0.7 M. The upper limit of the concentration is preferably at most 2.5 M, more preferably at most 2 . 0 M, even more preferably at most 1. 5 M, most preferably at most 1.2 M.
[0037]
[Production of Nonaqueous Electrolytic Solution]
The nonaqueous electrolytic solution of the present invention can be prepared, for example, by: mixing the nonaqueous solvents; adding the electrolyte salt to the mixture; and adding thereto from 0.1 to 5% by mass of 1, 2, 3, 4-tetrahydronaphthalene and further adding thereto from 0.1 to 5% by mass of a biphenyl derivative and/or an alkylphenol derivative.
In this case, the nonaqueous solvent to be used, and the compounds to be added to the nonaqueous electrolytic solution are preferably previously purified within a range not significantly detracting from the producibility, in which, therefore, the impurity content is preferably as low as possible.
[0038]
In the nonaqueous electrolytic solution of the present invention, usable is not only a liquid one but also a gelled one as the nonaqueous electrolyte. Further in the nonaqueous electrolytic solution of the present invention, also usable is a solid polymer electrolyte.
In the nonaqueous electrolytic solution of the present invention, for example, air and carbon dioxide may be contained.
As the method for introducing (dissolving) air or carbon dioxide in the nonaqueous electrolytic solution, there may be employed (1) a method of bringing the nonaqueous electrolytic solution into contact with air or carbon dioxide-containing gas before the solution is injected into a battery, or (2) a method of introducing air or carbon dioxide-containing gas into a battery after the electrolytic solution has been injected thereinto and before or after the battery is sealed up.
Preferably, the air or the carbon dioxide-containing gas contains water as little as possible and has a dew point of not higher than -40°C, more preferably not higher than -50°C.
In the present invention, using the electrolytic solution with carbon dioxide dissolved therein is especially preferred. The lower limit of the amount of the carbon dioxide dissolved in the nonaqueous electrolytic solution is preferably at least 0.01% by weight of solution, more preferably at least 0.1% by weight, and the upper limit thereof is preferably at most 0.5% by weight, more preferably at most 0.4% by weight.
[0039]
[Lithium Secondary Battery]
The lithium secondary battery of the present invention comprises a positive electrode containing, as the positive electrode active material, a lithium-containing metal oxide that contains at least one metal element selected from nickel, manganese and iron, a negative electrode containing, as the negative electrode active material, a carbon material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution of an electrolyte salt dissolved in a nonaqueous solvent, wherein the nonaqueous electrolytic solution contains from 0.1 to 5% by mass of 1, 2, 3, 4-tetrahydronaphthalene, and from 0.1 to 5% by mass of a biphenyl derivative and/or an alkylphenol derivative.
[0040]
As the positive electrode active material, used here is a lithium-containing metal oxide that contains at least one metal element selected from nickel, manganese and iron. One or more different kinds of such positive electrode active materials may be sued here either singly or as combined.
As the lithium-containing metal oxide, preferred is a lithium-containing transition metal compound that contains at least one metal element of nickel and manganese, or an olivine-type lithium phosphate that contains at least one metal element of nickel, manganese and iron. Above all, more preferred is an olivine-type lithium phosphate that contains at least one metal element of nickel, manganese and iron, since the recovery rate after low-temperature cycles of the battery after exposure thereof to high temperatures can be further increased.
[0041]
(Lithium-Containing Transition Metal Compound) For example, as the lithium-containing transition metal compound that contains at least one metal element of nickel and manganese, preferred are LiMn204, LiNiC>2, LiCoi-xNixC>2 (0.5
Documents
Application Documents
| # |
Name |
Date |
| 1 |
3300-CHENP-2012 PCT 12-04-2012.pdf |
2012-04-12 |
| 1 |
3300-CHENP-2012-AbandonedLetter.pdf |
2018-10-03 |
| 2 |
3300-CHENP-2012-FER.pdf |
2018-03-09 |
| 2 |
3300-CHENP-2012 FORM-5 12-04-2012.pdf |
2012-04-12 |
| 3 |
3300-CHENP-2012 FORM-3 12-04-2012.pdf |
2012-04-12 |
| 3 |
3300-CHENP-2012 FORM-1 01-01-2015.pdf |
2015-01-01 |
| 4 |
3300-CHENP-2012 FORM-2 12-04-2012.pdf |
2012-04-12 |
| 4 |
3300-CHENP-2012 CORRESPONDENCE OTHES 01-01-2015.pdf |
2015-01-01 |
| 5 |
3300-CHENP-2012 FORM-1 12-04-2012.pdf |
2012-04-12 |
| 5 |
3300-CHENP-2012 CORRESPONDENCE OTHERS 08-10-2012.pdf |
2012-10-08 |
| 6 |
3300-CHENP-2012 POWER OF ATTORNEY 08-10-2012.pdf |
2012-10-08 |
| 6 |
3300-CHENP-2012 DESCRIPTION (COMPLETE) 12-04-2012.pdf |
2012-04-12 |
| 7 |
3300-CHENP-2012 CORREPONDENCE OTHERS 12-04-2012.pdf |
2012-04-12 |
| 7 |
3300-CHENP-2012 ABSTRACT 12-04-2012.pdf |
2012-04-12 |
| 8 |
3300-CHENP-2012 CLAIMS 12-04-2012.pdf |
2012-04-12 |
| 9 |
3300-CHENP-2012 CORREPONDENCE OTHERS 12-04-2012.pdf |
2012-04-12 |
| 9 |
3300-CHENP-2012 ABSTRACT 12-04-2012.pdf |
2012-04-12 |
| 10 |
3300-CHENP-2012 DESCRIPTION (COMPLETE) 12-04-2012.pdf |
2012-04-12 |
| 10 |
3300-CHENP-2012 POWER OF ATTORNEY 08-10-2012.pdf |
2012-10-08 |
| 11 |
3300-CHENP-2012 FORM-1 12-04-2012.pdf |
2012-04-12 |
| 11 |
3300-CHENP-2012 CORRESPONDENCE OTHERS 08-10-2012.pdf |
2012-10-08 |
| 12 |
3300-CHENP-2012 FORM-2 12-04-2012.pdf |
2012-04-12 |
| 12 |
3300-CHENP-2012 CORRESPONDENCE OTHES 01-01-2015.pdf |
2015-01-01 |
| 13 |
3300-CHENP-2012 FORM-3 12-04-2012.pdf |
2012-04-12 |
| 13 |
3300-CHENP-2012 FORM-1 01-01-2015.pdf |
2015-01-01 |
| 14 |
3300-CHENP-2012-FER.pdf |
2018-03-09 |
| 14 |
3300-CHENP-2012 FORM-5 12-04-2012.pdf |
2012-04-12 |
| 15 |
3300-CHENP-2012-AbandonedLetter.pdf |
2018-10-03 |
| 15 |
3300-CHENP-2012 PCT 12-04-2012.pdf |
2012-04-12 |
Search Strategy
| 1 |
searchstrat_18-12-2017.pdf |