Nonaqueous electrolyte batteries typified by a lithium ion secondary battery have been used widely in recent years as power sources for mobile appliances typified by a mobile phone since these batteries have high energy densities.
In the present common lithium ion secondary batteries, transition metal oxides such as lithium cobaltate are used as a positive active material and carbonaceous materials such as graphite are used as a negative active material. With respect to a negative electrode using graphite or the like for the negative active material, the insertion/extraction reaction of the lithium ion is carried out in a potential region range of about 0.2 V or lower relative to the lithium potential. As described above, since the negative electrode using graphite or the like as the negative active material has a low operating potential, a lithium ion secondary battery using the negative electrode is enabled to reliably have high battery voltage and high energy density.
To stably operate such a negative electrode with a low operating potential, it is indispensable to add a cyclic carbonate compound such as ethylene carbonate or propylene carbonate to a nonaqueous solvent to be used for a nonaqueous electrolyte. It is because the cyclic carbonate compound has a high dielectric property required to dissociate an electrolytic salt and exhibit high ion conductivity and at the same time has a property to form a protection film on a surface of the negative electrode, which is necessary for reliably retaining chemical stability and electrochemical stability between the negative electrode and an electrolyte. In a lithium ion secondary battery using graphite or the like for the negative active material, the characteristics of the protection film changes according to the type of a solvent and an additive to be used for an electrolyte solution and is known as a main factor in determining battery performance by affecting the ion migration or charge transfer (e.g., refer to Non-Patent Document 1).
However, a lithium ion secondary battery using graphite or the like as a negative active material has an issue of stability in relation to an electrolyte solution particularly at a high temperature and a problem of lowering the battery performance because of the low operating potential of the negative electrode. When quick charge is carried out at a low temperature, because of low operating potential of the negative electrode, there is a problem that metal lithium is precipitated to form dendrite on the negative electrode and it also leads to deterioration of the battery performance.
Recently, it has been expected that a nonaqueous electrolyte battery would be employed not only for power sources for small appliances but also for power sources for power storage equipment and middle to large scale industrial uses such as motive power sources for vehicles, e.g., HEV and therefore, technological development have been actively addressed. Particularly, a battery for hybrid automobiles is required to have a high output performance for instantaneously driving a motor for assisting the engine power and a high input performance for regenerating the energy when automobiles stop, especially at a low temperature, which is a severe condition. Further, since the battery is to be exposed at a high temperature in the case of driving automobiles or parking automobiles under the boiling sun, it is required to keep the low-temperature-input/output performances even after storage at high temperature. On the other hand, in such a use, a large number of batteries are often assembled and used and exchange of batteries costs labor cost and the like and therefore, a long life in terms of charge-discharge cycle performance is required rather than the properties such as high voltage and high energy density.
Consequently, a material typified by lithium titanate is proposed as a negative active material, which has a nobler operating potential about 1.5 V to the lithium potential as compared with a carbon material and arises a stable insertion/extraction reaction of the lithium ion.
Patent Document 1 discloses an invention of an electrolyte solution for a capacitor consisting of an electrolyte and an electrolytic solvent containing a compound having a Si-containing group. Patent Document 1 describes that a capacitor using an active carbon electrode and an electrolytic solvent containing a Si compound as a nonaqueous electrolyte solution has decreased electric current leakage and that the apparent deformation degree of a product is suppressed in a 70° C. load test.
However, even if the gas emission at a high temperature is suppressed, it does not mean that the retention rate of the low-temperature-output performance after storage at high temperature would be improved and as shown in the examples given later, no correlation between the thickness and the output power performance of the battery after high-temperature-storage is found. Further, Patent Document 1 does not describe or suggest how the low-temperature-output performance would be after high-temperature-storage in the case of a nonaqueous electrolyte battery equipped with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher and it cannot be derived from Patent Document 1 that the low-temperature-output performance would be improved after high-temperature-storage by adding at least one kind of compound selected from a group of compounds defined by general formulas (1) to (3) described later to a nonaqueous electrolyte of a nonaqueous electrolyte battery provided with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher.
Patent Document 2 describes an invention characterized in that a nonaqueous solvent containing a compound having a (metal element, phosphorus, or boron)-(oxygen)-(silicon) bond is used for a nonaqueous electrolyte solution for a lithium secondary battery. In Table 1 of Patent Document 2, it is shown that the leakage current in charging, which shows the electric decomposition amount of an electrolyte solution on graphite, is lowered by adding tri(trimethylsilyl)borate, tri(trimethylsilyl)phosphate, or titanium tetra(trimethylsiloxide) as the compound having a (metal element, phosphorus, or boron)-(oxygen)-(silicon) bond to a solvent containing EC and DMC at 40:60 in a coin type battery having a graphite negative electrode and a metal lithium foil.
However, Patent Document 2 does not describe or suggest how the low-temperature-output performance would be after storage at high temperature in the case of a nonaqueous electrolyte battery equipped with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher and it cannot be derived from Patent Document 2 that the low-temperature-output performance would be improved after high-temperature-storage by adding at least one kind of compound selected from a group of compounds defined by general formulas (1) to (3) described later to a nonaqueous electrolyte of a nonaqueous electrolyte battery provided with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher.
Patent Document 3 proposes a nonaqueous electrolyte battery characterized in that a compound containing at least B and S is contained in the inside of the nonaqueous electrolyte battery. There is a description in Patent Document 3 that “addition of at least one kind of compound containing B and Si to a nonaqueous electrolyte battery suppresses contact of an electrolyte solution and a negative electrode by formation of a film on the negative electrode surface by the compound and thus the decomposition reaction of the electrolyte solution on the negative electrode is decreased and accordingly, a battery with high reliability and an excellent preservation property can be obtained” (paragraph 0034). Patent Document 3 describes that the capacity recovery ratio (capacity after storage/capacity before storage×100(%)) after storage at 80° C. for 5 days was improved by using LiCoO2 for a positive electrode and meso-phase graphite for a negative electrode and adding tris(trimethylsilyl)borate to a nonaqueous electrolyte.
However, there is neither a description of how the output performance at low temperature would be after storage at high temperature storage in the case of a nonaqueous electrolyte battery equipped with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher nor a description of a nonaqueous electrolyte battery having more than 70 volume % of a chain carbonate and less than 30 volume % of a cyclic carbonate ester in a nonaqueous solvent composing a nonaqueous electrolyte. Consequently, the fact that the output performance at low temperature after storage at high temperature is made excellent by using a negative electrode containing a negative active material capable of inserting/extracting the lithium ion at a potential of 1.2 V or higher relative to the lithium potential and containing at least one kind of compound selected from a group of compounds defined by the general formulas (1) to (3) in the nonaqueous electrolyte is not derived from Patent Document 3. Particularly, it cannot be derived from Patent Document 3 that it is preferable to keep the volume ratio of the cyclic carbonate be 10 volume % or lower in the entire volume of carbonates contained in the nonaqueous solvent composing the nonaqueous electrolyte.
Patent Document 4 describes that the initial discharge capacity is increased in a nonaqueous lithium secondary battery characterized in that a nonaqueous electrolyte solution contains lithium oxalate and a Lewis acid compound, and there is a description that “the Lewis acid compound is at least one kind of compound selected from (CH3(CH2)2O)3B, (CH3(CH2)3O)3B, ((CH3)3SiO)3B, ((CF3)2CHO)3B, ((CH3)3SiO)3P, and ((CF3)2CHO)3P” (claim 2). Patent Document 4 describes that “since addition of a Lewis acid compound, that is, a compound soluble in an organic solvent and having an electron-accepting property in addition to lithium oxalate, improves the solubility of lithium oxalate” (paragraph 0006): and that dissolution of lithium oxalate in a nonaqueous electrolyte solution is important to provide a battery with a large initial discharge capacity.
However, there is neither a description of how the low-temperature-output performance would be after storage at high temperature in the case of a nonaqueous electrolyte battery equipped with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher nor a description of a nonaqueous electrolyte battery having more than 70 volume % of a chain carbonate and less than 30 volume % of a cyclic carbonate in a nonaqueous solvent composing a nonaqueous electrolyte. Consequently, the fact that the output performance at low temperature after high-temperature-storage is made excellent by using a negative electrode containing a negative active material capable of inserting/extracting the lithium ion at a potential of 1.2 V or higher relative to the lithium potential and containing at least one kind of compound selected from a group of compounds defined by the general formulas (1) to (3) in the nonaqueous electrolyte is not derived from Patent Document 4. Particularly, it cannot be derived from Patent Document 4 that it is preferable to keep the volume ratio of the cyclic carbonate ester be 10 volume % or lower in the entire volume of carbonates contained in the nonaqueous solvent composing the nonaqueous electrolyte.
Patent Document 5 proposes an invention characterized by adding a first additive having a reduction potential with a LUMO level between 0.3 and 0.5 eV calculated by the AM1 method among the quantum chemical calculation methods and a second additive having a reduction potential with a LUMO level between −0.2 and 0.3 eV or between 0.5 and 1 eV calculated by the AM1 method among the quantum chemical calculation methods. In Table 2 of Patent Document 5, there is a description that the discharge capacity at −20° C., suppression of swelling after storage at 85° C., and the cycle life in a range of 10 to 60° C. are improved in the case of using trimethylsilyl phosphate or a mixture of LiBF4 and trimethylsilyl phosphate as the first additive and fluoroethylene carbonate, vinylene carbonate, or a mixture thereof as the second additive.
However, there is neither a description of how the low-temperature-output performance would be after high-temperature-storage in the case of a nonaqueous electrolyte battery equipped with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher nor a description of a nonaqueous electrolyte battery having more than 70 volume % of a chain carbonate and less than 30 volume % of a cyclic ester in a nonaqueous solvent composing a nonaqueous electrolyte. Consequently, the fact that the output performance at low temperature after storage at high temperature is made excellent by using a negative electrode containing a negative active material capable of inserting/extracting the lithium ion at a potential of 1.2 V or higher relative to the lithium potential and containing at least one kind of compound selected from a group of compounds defined by the general formulas (1) to (3) in the nonaqueous electrolyte is not derived from Patent Document 5. Particularly, it cannot be derived from Patent Document 5 that it is preferable to keep the volume ratio of the cyclic carbonate be 10 volume % or lower in the entire volume of carbonates contained in the nonaqueous solvent composing the nonaqueous electrolyte.
Claims 1 of Patent Documents 6 to 8 describe the general formula (3) which include a compound defined by the general formula (1) characterizing the present invention as a narrower concept. In examples of Patent Documents 6 to 8, batteries using electrolyte solutions containing trimethylsilyl methanesulfonate as a compound corresponding to the general formula (3) are described.
Patent Document 6 describes an invention characterized in that a nonaqueous electrolyte solution contains a chain carboxylatecarboxylate as an indispensable component and also a compound containing Si—O-A (A is a group consisting of H, C, N, O, F, S, Si and/or P) in a molecule in order to improve the low-temperature-output performance and also describes that the output performance at −30° C. is improved by adding trimethylsilyl methanesulfonate to a nonaqueous electrolyte battery having a positive electrode containing LiCoO2, a negative electrode containing graphite, and a nonaqueous electrolyte solution obtained by mixing 1 mol/L of LiPF6 with a mixture of ethylene carbonate (EC), methyl ethyl carbonate (MEC) and one of methyl propionate (MP), ethyl acetate (EA), and methyl acetate (MA) at 3:6:1 in volume ratio.
However, there is no description of how the low-temperature-output performance would be after high-temperature-storage in the case of a nonaqueous electrolyte battery equipped with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher. Further, as shown in examples provided later, in the case of using trimethylsilyl methanesulfonate, with which it is proved that the output performance is improved at low temperature, for a nonaqueous electrolyte battery having a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher, the low-temperature-output performance is surely improved immediately after production of the battery; however, the output retention rate after the high temperature storage test is comparative to that in the case of using no additive and thus the problems of the invention cannot be solved. Further, also in the case a compound encompassed by the general formula described in Patent Document 6 is added to a nonaqueous electrolyte battery containing a negative electrode of a carbon material with an operating potential lower than 1.2 V (vs. Li/Li+) and a chain carboxylate (methyl acetate or the like) and a cyclic carbonate (ethylene carbonate) as nonaqueous electrolytes, the low-temperature-output performance is improved immediately after production of the battery; however, the output retention rate after the high temperature storage test is comparative to that in the case of using no additive and thus the problems of the invention cannot be solved. Consequently, the fact that the output performance at low temperature after storage at high temperature is made excellent by using a negative electrode containing a negative active material capable of inserting/extracting the lithium ion at a potential of 1.2 V or higher relative to the lithium potential and containing at least one kind of compound selected from a group of compounds defined by the general formulas (1) to (3) in the nonaqueous electrolyte is not derived from Patent Document 6.
Patent Document 7 describes an invention characterized in that the ratio of ethylene carbonate in a nonaqueous solvent is adjusted to be 1 to 25 volume % and a nonaqueous electrolyte solution contains a compound containing Si—O-A (A is a group consisting of H, C, N, O, F, S, Si and/or P) in a molecule in order to improve the low-temperature-output performance and also describes that the output performance at −30° C. is improved by adding trimethylsilyl methanesulfonate to a nonaqueous electrolyte battery having a positive electrode containing LiCoO2, a negative electrode containing graphite, and a nonaqueous electrolyte solution obtained by mixing 1 mol/L of LiPF6 with a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (MEC).
However, there is no description of how the low-temperature-output performance would be after high-temperature-storage in the case of a nonaqueous electrolyte battery equipped with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher. Further, as shown in examples provided later, in the case of using trimethylsilyl methanesulfonate, with which it is proved that the output performance is improved at low temperature, for a nonaqueous electrolyte battery having a negative electrode with an operating potential of 1.2 V (vs. Li/Li+) or higher, the low-temperature-output performance is surely improved immediately after production of the battery; however, the output retention rate after the high-temperature-storage test is comparative to that in the case of using no additive and thus the problems of the invention cannot be solved. Consequently, the fact that the output performance at low temperature after storage at high temperature is made excellent by using a negative electrode containing a negative active material capable of inserting/extracting the lithium ion at a potential of 1.2 V or higher relative to the lithium potential and containing at least one kind of compound selected from a group of compounds defined by the general formulas (1) to (3) in the nonaqueous electrolyte is not derived from Patent Document 7.
Patent Document 8 describes an invention characterized in that a negative active material contains a metal oxide containing titanium, which is capable of absorbing and desorbing lithium and also a compound containing the following formula Si—O-A (A is a group consisting of H, C, N, O, F, S, Si and/or P) in a molecule in order to improve the low-temperature-output performance and in Examples 4 to 6, there is a description that the output resistance is lowered by using a lithium-titanium composite oxide for a negative electrode and using, as a solvent for a nonaqueous electrolyte solution, a solvent obtained by mixing trimethylsilyl methanesulfonate with a mixture of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate (volume ratio 3:3:4).
However, as shown in examples provided later, in the case of using trimethylsilyl methanesulfonate, with which it is proved that the output performance is improved at low temperature, for a nonaqueous electrolyte battery with a negative electrode having an operating potential of 1.2 V (vs. Li/Li+) or higher, the low-temperature-output performance is surely improved immediately after production of the battery; however, the output retention rate after the high-temperature-storage test is comparative to that in the case of using no additive and thus the problems of the invention cannot be solved. Consequently, the fact that the output performance at low temperature after storage at high temperature is made excellent by using a negative electrode containing a negative active material capable of inserting/extracting the lithium ion at a potential of 1.2 V or higher relative to the lithium potential and containing at least one kind of compound selected from a group of compounds defined by the general formulas (1) to (3) in the nonaqueous electrolyte is not derived from Patent Document 8.    Non-Patent Document 1: J. Power Source, 68 (1997) 59-64    Patent Document 1: JP-A No. 2001-52965    Patent Document 2: JP-A No. 2001-57237    Patent Document 3: JP-A No. 2001-283908    Patent Document 4: JP-A No. 2004-259682    Patent Document 5: JP-A No. 2006-12806    Patent Document 6: JP-A No. 2007-141831    Patent Document 7: JP-A No. 2007-149656    Patent Document 8: JP-A No. 2007-214120
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