JP2010027610A - Nonaqueous electrolyte solution, and nonaqueous electrolyte solution battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nonaqueous electrolyte solution capable of achieving a nonaqueous electrolyte solution battery of high capacity and excellent in high-temperature preservation characteristics with safety at overcharging fully enhanced, as well as a nonaqueous electrolyte solution battery produced with the use of the same. <P>SOLUTION: The nonaqueous electrolyte solution contains electrolyte and a nonaqueous solvent, and further, (a) diphenyl carbonate, and (b) at least one kind of compound selected from a group consisting of vinylene carbonate, cyclic carbonate compound having a fluorine atom, monofluoro phosphate and difluoro phosphate, and further, ethylene carbonate and dialkyl carbonate as a nonaqueous solvent. A ratio of (a) the diphenyl carbonate occupied in the nonaqueous electrolyte solution is 0.001 wt.% or more and less than 5 wt.%, a ratio of (b) the total compound is 0.001 to 20 wt.%, and a ratio of the ethylene carbonate to a sum of the ethylene carbonate and dialkyl carbonate in the nonaqueous solution is 5 to 50 vol.%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte battery using the same.

  Non-aqueous electrolyte batteries such as lithium secondary batteries are being put to practical use in a wide range of applications from so-called consumer power sources such as mobile phones and laptop computers to in-vehicle power sources for automobiles and the like. However, the demand for higher performance of non-aqueous electrolyte batteries in recent years is increasing, and there is a demand for improvement in battery characteristics.

  The electrolyte used for a non-aqueous electrolyte battery is usually composed mainly of an electrolyte and a non-aqueous solvent. The main components of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone. It is used.

  In addition, in order to improve battery characteristics such as load characteristics, cycle characteristics, and storage characteristics of such nonaqueous electrolyte batteries, and to improve battery safety during overcharge, various studies have been made on nonaqueous solvents and electrolytes. ing.

  Patent Document 1 proposes to protect the battery by increasing the internal resistance of the battery by mixing an additive that is polymerized at a battery voltage equal to or higher than the maximum operating voltage of the battery in the electrolyte. In 2 the internal electrical disconnection device provided for overcharge protection is ensured by mixing gas and an additive that generates pressure by polymerizing at a battery voltage above the maximum operating voltage of the battery in the electrolyte. It has been proposed to work. Moreover, aromatic compounds, such as biphenyl, thiophene, and furan, are disclosed as those additives.

  Furthermore, Patent Document 3 discloses a non-aqueous system in which phenylcyclohexane is added in a range of 0.1 to 20% by weight in a non-aqueous electrolyte solution in order to suppress deterioration of battery characteristics when biphenyl or thiophene is used. A non-aqueous electrolyte secondary battery system including an electrolyte secondary battery and a charge control system that senses an increase in battery temperature and disconnects a charging circuit has been proposed.

  Patent Document 4 discloses that diphenyl carbonate is contained in an amount of 0.5% by mass to 10% by mass and unsaturated compounds in order to suppress swelling of the battery during high temperature storage while suppressing a decrease in initial charge / discharge efficiency. There has been proposed an electrolyte characterized by containing a solvent containing a cyclic carbonate in a range of 0.5% by mass or more and 5% by mass or less, and vinyl ethylene carbonate is preferred as the cyclic carbonate of the unsaturated compound. It is said that.

JP-A-9-106835 JP-A-9-171840 JP 2002-50398 A JP 2005-322634 A

  However, the demand for higher performance of batteries in recent years is increasing, and it is required to achieve high capacity, high temperature storage characteristics, and cycle characteristics at a high level.

  As a method of increasing the capacity of a battery, it has been studied to pack as many active materials as possible in a limited battery volume. For example, a method of pressurizing an active material layer of an electrode to increase the density, a battery In general, the design is such that the volume (for example, the amount of electrolytic solution) occupied other than the internal active material is minimized. However, if the active material layer of the electrode is pressed to increase the density or the amount of the electrolytic solution is reduced, the active material cannot be used uniformly. Thereby, a part of lithium precipitates due to a non-uniform reaction, or deterioration of the active material is promoted, so that a problem that sufficient characteristics cannot be obtained easily occurs.

  Furthermore, since the voids inside the battery are reduced due to the increase in capacity, there is a problem that the internal pressure of the battery is remarkably increased when a small amount of gas is generated due to decomposition of the electrolytic solution. In particular, in non-aqueous electrolyte secondary batteries, in most cases used as a backup power source in the event of a power failure or as a power source for portable equipment, a weak current is always supplied to make up for the self-discharge of the battery, and it is continuously charged. . In such a continuously charged state, the activity of the electrode active material is always high, and at the same time, due to the heat generated by the device, the capacity of the battery is reduced, or the electrolyte is decomposed and gas is easily generated. If a large amount of gas is generated, a safety valve may be activated in a battery that senses this when the internal pressure is abnormally increased due to an abnormality such as overcharge and activates the safety valve. Further, in a battery without a safety valve, the battery may expand due to the pressure of the generated gas, and the battery itself may become unusable.

  In the non-aqueous electrolyte secondary battery using the electrolyte solution described in Patent Documents 1 to 4, the high-temperature storage characteristics are deteriorated in the above cases, and it is not yet satisfactory.

  The present invention has been made in view of the above-described conventional situation, and it is possible to realize a non-aqueous electrolyte battery having high capacity and excellent high-temperature storage characteristics while sufficiently enhancing safety during overcharge. It is an object of the present invention to provide a non-aqueous electrolyte solution and a high-performance non-aqueous electrolyte battery that can be miniaturized using the non-aqueous electrolyte solution.

  As a result of various studies to achieve the above object, the present inventors have found that the above-mentioned problems can be solved by incorporating a specific compound in the electrolytic solution, and the present invention has been completed. It was.

  That is, the gist of the present invention is as follows.

[1] A group consisting of (a) diphenyl carbonate, (b) vinylene carbonate, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate in a nonaqueous electrolytic solution containing an electrolyte and a nonaqueous solvent At least one compound selected from the group consisting of: (a) the proportion of diphenyl carbonate in the non-aqueous electrolyte is 0.001 wt% or more and less than 5 wt%; (b) vinylene carbonate, cyclic having a fluorine atom The total proportion of at least one compound selected from the group consisting of carbonate compounds, monofluorophosphates and difluorophosphates is 0.001 to 20% by weight, and the nonaqueous solvent contains ethylene carbonate and dialkyl carbonate Ethylene carbonate and dial in non-aqueous solvents Nonaqueous electrolyte, wherein the ratio of ethylene carbonate is less than 50 volume% 5 volume% or more to the sum of the Le carbonate.

[2] A non-aqueous electrolyte battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is the non-aqueous electrolyte solution described in [1] above. A non-aqueous electrolyte battery characterized by the above.

  According to the present invention, it is possible to provide a non-aqueous electrolyte battery with high capacity and excellent high-temperature storage characteristics while sufficiently enhancing safety during overcharging, and miniaturization of the non-aqueous electrolyte battery. High performance can be achieved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not specified by these contents.

[Non-aqueous electrolyte]
The non-aqueous electrolyte solution of the present invention contains an electrolyte and a non-aqueous solvent that dissolves the electrolyte, as in the case of a conventional non-aqueous electrolyte solution.

<Electrolyte>
As the electrolyte, a lithium salt is usually used. The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any lithium salt can be used. Specific examples include the following.

For example, inorganic lithium salts such as LiPF ₆ and LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-perfluoroethanedisulfonylimide , Lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ ( C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ ( _{CF 3 SO 2) 2, LiBF} 2 (C 2 F 5 SO 2) fluorine-containing organic lithium salt and lithium bis _2, etc. (oxalate) volley , And lithium difluoro (oxalato) borate and the like.

Of these, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ are preferable from the viewpoint of improving battery performance, and LiPF ₆ or LiBF ₄ is particularly preferable. preferable.

  These lithium salts may be used alone or in combination of two or more.

A preferable example in the case of using two or more lithium salts in combination is a combination of LiPF ₆ and LiBF ₄ , which has an effect of improving cycle characteristics. In this case, the lower limit of the proportion of LiBF _{4 in} the total of both is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and particularly preferably 0.2% by weight or more. The upper limit is preferably 20% by weight or less, more preferably 5% by weight or less, and particularly preferably 3% by weight or less. If the lower limit is not reached, the desired effect may be difficult to obtain. If the upper limit is exceeded, battery characteristics after high-temperature storage may be deteriorated.

Another example is the combined use of an inorganic lithium salt and a fluorine-containing organic lithium salt. In this case, the proportion of the inorganic lithium salt in the total of both is 70% by weight or more and 99% by weight or less. It is desirable. Examples of the fluorine-containing organic lithium salt include LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropane. It is preferably any of disulfonylimide. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

Further, when the non-aqueous solvent is intended to include γ- butyrolactone 55 volume% or more, as the lithium salt, LiBF ₄ or LiBF ₄ and combined with others are preferred. In this case, LiBF ₄ preferably accounts for 40 mol% or more of the lithium salt. Particularly preferably, the proportion of LiBF _{4 in} the lithium salt is 40 mol% or more and 95 mol% or less, and the remainder is LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ is a combination selected from the group consisting of ₂ .

  The concentration of these electrolytes in the non-aqueous electrolytic solution is not particularly limited in order to exhibit the effects of the present invention, but is usually 0.5 mol / liter or more, preferably 0.6 mol / liter or more, more Preferably it is 0.7 mol / liter or more. The upper limit is usually 3 mol / liter or less, preferably 2 mol / liter or less, more preferably 1.8 mol / liter or less, and still more preferably 1.5 mol / liter or less. If the concentration of the electrolyte in the non-aqueous electrolyte is too low, the electrical conductivity of the electrolyte may be insufficient, whereas if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity. Battery performance may be reduced.

<Nonaqueous solvent>
Among these, the nonaqueous solvent according to the present invention contains ethylene carbonate and dialkyl carbonate, and the ratio of ethylene carbonate to the total of ethylene carbonate and dialkyl carbonate in the nonaqueous solvent is 5% by volume or more and 50% by volume or less. It is characterized by being. Other nonaqueous solvents can be appropriately selected from conventionally known solvents for nonaqueous electrolyte solutions. For example, cyclic carbonates having no fluorine atom, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylic acid esters, chain carboxylic acid esters, sulfur-containing organic solvents, phosphorus-containing organic solvents, etc. Can be mentioned.

  Examples of the cyclic carbonates having no fluorine atom include alkylene carbonates having 2 to 4 carbon atoms such as ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate and propylene carbonate are exemplified. From the viewpoint of improving battery characteristics, ethylene carbonate is particularly essential in the present invention.

  In the present invention, dialkyl carbonate is essential among the chain carbonates. As for carbon number of the alkyl group which comprises a dialkyl carbonate, 1-5 are preferable about each of two alkyl groups, Most preferably, it is 1-4. Specific examples of the dialkyl carbonate include symmetrical chain alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; ethyl methyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and the like. And dialkyl carbonates such as asymmetric chain alkyl carbonates. Among these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable from the viewpoint of improving battery characteristics.

  Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran.

  Examples of chain ethers include dimethoxyethane and dimethoxymethane.

  Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone.

  Examples of the chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

  Examples of the sulfur-containing organic solvent include sulfolane, 2-methylsulfolane, 3-methylsulfolane, and diethylsulfone.

  Examples of the phosphorus-containing organic solvent include trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, and the like.

  These non-aqueous solvents may be used alone or in combination of two or more, but it is preferable to use in combination of two or more compounds. For example, it is preferable to use a high dielectric constant solvent such as alkylene carbonates or cyclic carboxylic acid esters in combination with a low viscosity solvent such as dialkyl carbonates or chain carboxylic acid esters. In the present invention, at least one of ethylene carbonate and dialkyl carbonate is used in combination.

  One preferable combination of the non-aqueous solvents is a combination mainly composed of one or more of ethylene carbonate and dialkyl carbonate. Among them, the total of ethylene carbonate and dialkyl carbonate in the nonaqueous solvent is 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more, and relative to the total of ethylene carbonate and dialkyl carbonate. The proportion of ethylene carbonate is 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, 50% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less, still more preferably 25% by volume or less. Use of a combination of these non-aqueous solvents is preferable because the balance between cycle characteristics and high-temperature storage characteristics (particularly, remaining capacity and high-load discharge capacity after high-temperature storage) of a battery produced using the non-aqueous solvent is improved.

  Specific examples of preferred combinations of ethylene carbonate and dialkyl carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and ethyl methyl. Examples thereof include carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

  A combination in which propylene carbonate is further added to such a combination of ethylene carbonate and dialkyl carbonate is also a preferable combination.

  When the non-aqueous solvent contains propylene carbonate, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99: 1 to 40:60, and particularly preferably 95: 5 to 50:50. Furthermore, the lower limit of the proportion of propylene carbonate in the entire non-aqueous solvent is usually 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, and the upper limit is usually 20% by volume or less. Preferably it is 8 volume% or less, More preferably, it is 5 volume% or less. When the nonaqueous solvent contains propylene carbonate in this concentration range, it is preferable because the low temperature characteristics are further improved while maintaining the characteristics of the combination of ethylene carbonate and dialkyl carbonate.

  Among the combinations of ethylene carbonate and dialkyl carbonate, those containing asymmetric chain alkyl carbonate as dialkyl carbonate are more preferable, in particular, ethylene carbonate and dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, Cycle characteristics include ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, which contain one or more of ethylene carbonate and symmetric chain alkyl carbonate and one or more of asymmetric chain alkyl carbonate. And a large current discharge characteristic are preferable. Among them, the asymmetric chain alkyl carbonate is preferably ethyl methyl carbonate, and the alkyl group of the alkyl carbonate preferably has 1 to 2 carbon atoms.

  When diethyl carbonate is contained as a dialkyl carbonate in the non-aqueous solvent, the lower limit of the proportion of diethyl carbonate in the total non-aqueous solvent is usually 10% by volume or more, preferably 20% by volume or more, more preferably 25%. A range in which the upper limit is usually 90% by volume or less, preferably 80% by volume or less, more preferably 75% by volume or less, and further preferably 70% by volume or less. It is preferable to contain it because it suppresses gas generation during high-temperature storage.

  When dimethyl carbonate is contained as a dialkyl carbonate in the non-aqueous solvent, the lower limit of the proportion of dimethyl carbonate in the total non-aqueous solvent is usually 10% by volume or more, preferably 20% by volume or more, more preferably 25%. More than 30% by volume, more preferably 30% by volume or more, and the upper limit is usually 90% by volume or less, preferably 80% by volume or less, more preferably 75% by volume or less, more preferably 70% by volume or less. The inclusion is preferable because the load characteristics of the battery are improved.

Among them, the non-aqueous solvent according to the present invention contains, as dialkyl carbonate, dimethyl carbonate and ethyl methyl carbonate, and by increasing the content ratio of dimethyl carbonate to the content ratio of ethyl methyl carbonate, the electric conductivity of the electrolyte solution It is preferable because the battery characteristics after high-temperature storage can be improved while ensuring the above.
In this case, the lower limit of the capacity ratio of dimethyl carbonate to ethyl methyl carbonate (dimethyl carbonate / ethyl methyl carbonate) in all non-aqueous solvents is to improve the electric conductivity of the electrolyte and the battery characteristics after storage. .1 or more is preferable, 1.5 or more is more preferable, 2.5 or more is further preferable, 3 or more is particularly preferable, and 4 or more is most preferable. The upper limit of the volume ratio (dimethyl carbonate / ethyl methyl carbonate) is preferably 40 or less, more preferably 20 or less, still more preferably 10 or less, and particularly preferably 8 or less, in order to improve low temperature characteristics.

  In the combination mainly composed of ethylene carbonate and dialkyl carbonate, the non-aqueous solvent may further contain another solvent.

  Other examples of preferred non-aqueous solvents include one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone, or two or more organic solvents selected from the group The mixed solvent becomes 60% by volume or more of the whole. The non-aqueous electrolyte using this mixed solvent is less likely to evaporate or leak when used at high temperatures. Among them, the total of ethylene carbonate and γ-butyrolactone in the nonaqueous solvent is 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more, and ethylene carbonate and γ-butyrolactone. The volume ratio is 5:95 to 45:55, or the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more. In addition, if a volume ratio of ethylene carbonate to propylene carbonate of 30:70 to 60:40 is used, the balance between cycle characteristics and high temperature storage characteristics is generally improved.

  In the present specification, the capacity of the non-aqueous solvent is a measured value at 25 ° C., but a measured value at the melting point is used for a solid at 25 ° C. such as ethylene carbonate.

<Essential compounds>
The nonaqueous electrolytic solution of the present invention includes an electrolyte and a nonaqueous solvent, and further includes (a) diphenyl carbonate, (b) vinylene carbonate, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate. May be referred to as at least one compound selected from the group consisting of (hereinafter referred to as “compound (b))”. And (a) the proportion of diphenyl carbonate in the non-aqueous electrolyte is 0.001 wt% or more and less than 5 wt%, and the total proportion of the compound (b) is 0.001 to 20 wt% It is characterized by being.

  The proportion of diphenyl carbonate in the non-aqueous electrolyte is 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and particularly preferably 0.1% by weight or more. If the ratio of diphenyl carbonate in the non-aqueous electrolyte is lower than this, the effects of the present invention may not be easily achieved. On the other hand, if the concentration of diphenyl carbonate is too high, the high-temperature storage characteristics of the battery may deteriorate, so the upper limit is less than 5% by weight, preferably 4% by weight or less, more preferably 3% by weight, particularly preferably 2% by weight. % Or less, and most preferably 1.5% by weight or less.

  Examples of the cyclic carbonate compound having a fluorine atom include fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, 4,4,5,5. -Tetrafluoroethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4,4,5-trifluoro-5-methyl Examples include ethylene carbonate and trifluoromethyl ethylene carbonate. Of these, fluoroethylene carbonate, 4,5-difluoroethylene carbonate, and 4-fluoro-5-methylethylene carbonate are preferable from the viewpoints of the effect of improving cycle characteristics and the effect of improving high-temperature storage characteristics.

  The counter cation of monofluorophosphate and difluorophosphate is not particularly limited, and examples thereof include lithium, sodium, potassium, magnesium, calcium, and lithium is preferable.

  Specific examples of monofluorophosphate and difluorophosphate include lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, lithium difluorophosphate, sodium difluorophosphate, and potassium difluorophosphate. And lithium monofluorophosphate and lithium difluorophosphate are preferable, and lithium difluorophosphate is more preferable.

  These may be used alone or in combination of two or more.

As the compound (b), only one of vinylene carbonate, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate may be used, or two or more may be used in combination.
For example, a cyclic carbonate compound having a fluorine atom may be used in combination with vinylene carbonate, monofluorophosphate and / or difluorophosphate, and these are used in combination in terms of improving cycle characteristics and improving high-temperature storage characteristics. Is preferred.
In addition, monofluorophosphate and / or difluorophosphate may be used in combination with vinylene carbonate or a cyclic carbonate compound having a fluorine atom. From the viewpoint of improving cycle characteristics and characteristics after storage at high temperature, The fluorophosphate and / or difluorophosphate is preferably used in combination with vinylene carbonate or fluoroethylene carbonate, and more preferably used in combination with vinylene carbonate.

  The total proportion of the compound (b) in the non-aqueous electrolyte solution of the present invention is 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and particularly preferably 0.8%. 1% by weight or more. If the content of the compound (b) in the non-aqueous electrolyte is lower than this, the effect of improving the cycle characteristics and high-temperature storage characteristics of the battery may not be sufficiently exhibited. On the other hand, if the concentration of the compound (b) is too high, the amount of gas generated may increase during storage at high temperatures, or the discharge characteristics at low temperatures may decrease, so the upper limit is 20% by weight or less, preferably 10% by weight or less. More preferably, it is 5% by weight, particularly preferably 4% by weight or less, and most preferably 3% by weight or less.

  When the non-aqueous electrolyte contains vinylene carbonate as the compound (b), the lower limit of the proportion in the non-aqueous electrolyte is preferably 0.001% by weight or more, more preferably 0.01% by weight or more, Particularly preferably, it is 0.1% by weight or more, most preferably 0.3% by weight or more, and the upper limit thereof is preferably 8% by weight or less, more preferably 4% by weight or less, and particularly preferably 3% by weight or less. .

  When the non-aqueous electrolyte contains a cyclic carbonate compound having a fluorine atom as the compound (b), the lower limit of the proportion in the non-aqueous electrolyte is preferably 0.001% by weight or more, more preferably 0.00. 1% by weight or more, particularly preferably 0.3% by weight or more, most preferably 0.5% by weight or more, and the upper limit thereof is preferably 20% by weight or less, more preferably 10% by weight or less, and still more preferably 5% by weight. % By weight or less, particularly preferably 3% by weight or less.

  When the non-aqueous electrolyte contains a monofluorophosphate and / or difluorophosphate as the compound (b), the ratio of the non-aqueous electrolyte in the non-aqueous electrolyte is preferably at least 0.001% by weight, More preferably 0.01% by weight or more, particularly preferably 0.1% by weight or more, most preferably 0.2% by weight or more, and the upper limit thereof is preferably 5% by weight or less, more preferably 3% by weight or less. Particularly preferably, it is 2% by weight or less.

  The details of the reason why the nonaqueous electrolytic solution of the present invention containing diphenyl carbonate and compound (b) in a predetermined ratio is excellent in safety during overcharge and excellent in high temperature storage characteristics are not clear, The operational principle of the invention is not limited to the following description, but is presumed as follows.

  Diphenyl carbonate has a lower oxidation potential than that of the solvent component, and can react on the positive electrode at an earlier stage during overcharge, thereby enhancing safety during overcharge. However, it is more likely to be reduced than the solvent component, causing side reactions on the negative electrode during high temperature storage and degrading battery characteristics after high temperature storage. However, by using diphenyl carbonate in combination with the compound (b) that forms a stable protective film on the surface of the negative electrode, these compounds form a stable protective film on the surface of the negative electrode. It is thought that the side reaction of can be suppressed. Moreover, when it contains a monofluorophosphate and a difluorophosphate, it is thought that a protective film is formed also on the positive electrode side and a side reaction on the positive electrode side during high temperature storage can be suppressed.

  Furthermore, when vinylene carbonate is contained, since the oxidation potential of vinylene carbonate is lower than that of the solvent component and the oxidation potential is close to that of diphenyl carbonate, it is considered that the safety during overcharge can be improved together with diphenyl carbonate during overcharge. It is done.

In order to effectively exhibit the above-described effects, the content weight ratio of diphenyl carbonate and compound (b) in the non-aqueous electrolyte solution should be diphenyl carbonate: compound (b) = 1: 0.1-10. preferable.
In the case where vinylene carbonate and monofluorophosphate and / or difluorophosphate are used in combination as compound (b), the content weight ratio of vinylene carbonate to monofluorophosphate and / or difluorophosphate is , Vinylene carbonate: monofluorophosphate and / or difluorophosphate = 1: 0.1 to 5 is preferable.

<Other compounds>
The non-aqueous electrolyte solution according to the present invention may contain various other compounds such as a conventionally known overcharge inhibitor as an auxiliary agent as long as the effects of the present invention are not impaired.
Conventionally known overcharge inhibitors include alkylbiphenyls such as biphenyl and 2-methylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene (phenylcyclohexane), cis-1-propyl-4- Phenylcyclohexane, trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, etc. Aromatic compounds such as 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, etc. Portion fluoride of the serial aromatics; 2,4-difluoro anisole, 2,5-difluoro anisole, 2,6-difluoro anisole, 3,5-difluoro anisole, etc. fluorinated anisole compound of the like.

  Among these, biphenyl, alkylbiphenyl such as 2-methylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane, trans-1-propyl-4 -Aromatic compounds such as phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, Partially fluorinated products of the aromatic compounds such as 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene are preferred. Partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane, trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1 -Butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene are more preferable, and a partially hydrogenated terphenyl and cyclohexylbenzene are particularly preferable.

  These overcharge inhibitors may be used alone or in combination of two or more.

  When two or more overcharge inhibitors are used in combination, in particular, a partially hydrogenated terphenyl, a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, biphenyl, alkylbiphenyl, terphenyl, Those selected from oxygen-free aromatic compounds such as partially hydrogenated phenyl, cyclohexylbenzene, t-butylbenzene, and t-amylbenzene; and those selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran. Use in combination is preferable in terms of the balance between overcharge prevention characteristics and high-temperature storage characteristics.

  The proportion of these overcharge inhibitors in the non-aqueous electrolyte is usually 0.1% by weight or more, preferably 0.2% by weight or more, particularly preferably 0.3% by weight or more, most preferably 0.5% by weight. The upper limit is usually 5% by weight or less, preferably 3% by weight or less, particularly preferably 2% by weight or less. If the concentration is lower than this lower limit, the desired effect of the overcharge inhibitor may hardly be exhibited. Conversely, when the concentration of the overcharge inhibitor is too high, battery characteristics such as high-temperature storage characteristics tend to deteriorate.

  Other auxiliaries include carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, methoxyethyl-methyl carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, itaconic anhydride, citraconic anhydride, anhydrous Carboxylic anhydrides such as glutaconic acid, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride; dimethyl succinate, diethyl succinate, diallyl succinate, dimethyl maleate , Diethyl maleate, diallyl maleate, dipropyl maleate, dibutyl maleate, bis (trifluoromethyl) maleate, bis (pentafluoroethyl) maleate, bis (2,2,2-trifluoroethyl) maleate, etc. Dicarbo Acid diester compounds; spiro compounds such as 2,4,8,10-tetraoxaspiro [5.5] undecane and 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; Ethylene sulfite, propylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, methyl methane sulfonate, ethyl methane sulfonate, methyl-methoxy methane sulfonate, methyl- 2-methoxyethanesulfonate, busulfan, diethylene glycol dimethanesulfonate, 1,2-ethanediol bis (2,2,2-trifluoroethanesulfonate), 1,4-butanediol bis (2,2,2-trifluoroethane) Sulfonate), sulfolane, sulphone Sulfur-containing compounds such as lene, dimethylsulfone, diphenylsulfone, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl Nitrogen-containing compounds such as 2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone and N-methylsuccinimide; heptane, octane, nonane, decane, cycloheptane, methylcyclohexane, ethylcyclohexane, propylcyclohexane, n -Hydrocarbon compounds such as butylcyclohexane, t-butylcyclohexane, dicyclohexyl; fluorinated benzene and fluorided toluene such as fluorobenzene, difluorobenzene, hexafluorobenzene, benzotrifluoride; acetonitrile, propylene Examples thereof include nitrile compounds such as nitrile, butyronitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile and the like.

  These other auxiliaries may be used alone or in combination of two or more.

  Among these, ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, busulfan, 1,4 in terms of improving battery characteristics after high-temperature storage -Sulfur-containing compounds such as butanediol bis (2,2,2-trifluoroethanesulfonate); nitrile compounds such as acetonitrile, propionitrile, butyronitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile and the like are more preferable.

  The ratio of these auxiliaries in the non-aqueous electrolyte solution is not particularly limited in order to exhibit the effects of the present invention, but is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably. Is 0.2% by weight or more, and the upper limit is usually 10% by weight or less, preferably 5% by weight or less, more preferably 3% by weight or less, and particularly preferably 1% by weight or less. By adding these auxiliaries, capacity maintenance characteristics and cycle characteristics after high-temperature storage can be improved, but if the concentration is lower than this lower limit, the effect of the auxiliaries may be hardly expressed. On the other hand, if the concentration is too high, battery characteristics such as high load discharge characteristics may deteriorate.

<Preparation of electrolyte>
The non-aqueous electrolyte solution of the present invention comprises, in a non-aqueous solvent, an electrolyte, diphenyl carbonate, and compound (b) (vinylene carbonate, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate. It can be prepared by dissolving at least one compound selected) and other compounds and auxiliaries blended as necessary. In preparing the non-aqueous electrolyte solution of the present invention, each raw material is preferably dehydrated in advance in order to reduce the water content when the electrolyte solution is used, and the water content is usually 50 ppm or less, preferably 30 ppm or less, particularly It is preferable to use after dehydrating to 10 ppm or less. Moreover, you may implement dehydration, a deoxidation process, etc. after electrolyte solution preparation.

  The non-aqueous electrolyte of the present invention is suitable for use as a secondary battery among non-aqueous electrolyte batteries, that is, as an electrolyte for a non-aqueous electrolyte secondary battery, for example, a lithium secondary battery.

  Hereinafter, a non-aqueous electrolyte secondary battery using the electrolyte of the present invention will be described.

[Non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte battery including a negative electrode and a positive electrode capable of occluding and releasing lithium ions, and a non-aqueous electrolyte solution, and the non-aqueous electrolyte solution of the present invention described above. It is a non-aqueous electrolyte solution.

<Battery configuration>
A non-aqueous electrolyte secondary battery according to the present invention is similar to a conventionally known non-aqueous electrolyte secondary battery except that it is prepared using the above-described electrolyte of the present invention. A non-aqueous electrolyte battery including a positive electrode and a non-aqueous electrolyte solution, usually obtained by housing the positive electrode and the negative electrode in a case through a porous membrane impregnated with the non-aqueous electrolyte solution according to the present invention. . The shape of the secondary battery according to the present invention is not particularly limited, and may be any of a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, and the like.

<Electrode>
(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. Specific examples thereof include carbonaceous materials, alloy-based materials, lithium-containing metal composite oxide materials, and the like. Of these, preferred are carbonaceous materials and alloy materials.
These negative electrode active materials may be used alone or in combination of two or more.

<Carbonaceous material>
Among the carbonaceous materials, graphite and graphite whose surface is coated with amorphous carbon as compared with graphite are particularly preferable.

  Graphite preferably has a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.338 nm, particularly 0.335 to 0.337 nm, as determined by X-ray diffraction using the Gakushin method. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is usually 10 nm or more, preferably 50 nm or more, and particularly preferably 100 nm or more. The ash content is usually 1% by weight or less, preferably 0.5% by weight or less, particularly preferably 0.1% by weight or less.

  The graphite surface coated with amorphous carbon is preferably graphite having a d-value of 0.335 to 0.338 nm on the lattice plane (002 plane) in X-ray diffraction as a core material. A carbonaceous material having a larger d-value on the lattice plane (002 plane) in X-ray diffraction than the core material is attached, and the d-value on the lattice plane (002 plane) in X-ray diffraction is greater than that of the core material and the core material The ratio with respect to the carbonaceous material having a large is 99/1 to 80/20 by weight. When this is used, a negative electrode having a high capacity and hardly reacting with the electrolytic solution can be produced.

  The particle size of the carbonaceous material is a median diameter measured by a laser diffraction / scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, most preferably 7 μm or more, and usually 100 μm or less, preferably 50 μm or less. More preferably, it is 40 micrometers or less, Most preferably, it is 30 micrometers or less.

BET specific surface area of the carbonaceous material is usually 0.3 m ² / g or more, preferably 0.5 m ² / g or more, more preferably 0.7 m ² / g or more, most preferably 0.8 m ² / g or more, usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more preferably 15.0 m ² / g or less, and most preferably 10.0 m ² / g or less.

Further, the carbonaceous material is analyzed by Raman spectrum using argon ion laser light, the peak is the peak intensity of the peak _{P A} in the range of 1570~1620cm ^-1 _I A, in the range of 1300~1400cm ^-1 P If the peak intensity of the _B was _{I B,} R value represented by the ratio of _{I B} and _{I a (= I B / I} a) is what is preferably in the range of 0.01 to 0.7. Further, the half width of the peak in the range of 1570～1620Cm ^-1 is, 26cm ^-1 or less, are preferred in particular 25 cm ^-1 or less.

<Alloy material>
The alloy material is not particularly limited as long as it can occlude and release lithium, and single metals and alloys forming lithium alloys, or oxides, carbides, nitrides, silicides, sulfides, Any of compounds such as phosphides may be used. It is preferably a material containing a single metal and an alloy forming a lithium alloy, more preferably a material containing a metal or a metalloid element (that is, excluding carbon) of Groups 13 and 14 of the periodic table, further aluminum, It is preferably a single metal of silicon and tin (hereinafter sometimes referred to as “specific metal element”) and an alloy or compound containing these specific metal elements.

  Examples of the negative electrode active material having at least one element selected from the specific metal elements include a single metal element of any one specific metal element, an alloy composed of two or more specific metal elements, one type, or two or more types An alloy composed of the specific metal element and one or more other metal elements, a compound containing one or more specific metal elements, and oxides, carbides, nitrides of the compounds, Examples include composite compounds such as silicides, sulfides, and phosphides. By using one or more selected from these simple metals, alloys and metal compounds as the negative electrode active material, the capacity of the battery can be increased.

  In addition, compounds in which these complex compounds are complexly bonded to several elements such as a simple metal, an alloy, or a non-metallic element can be given as examples. More specifically, for example, for silicon and tin, an alloy of these elements and a metal that does not operate as a negative electrode can be used. In addition, for example, in the case of tin, a complex compound containing 5 to 6 kinds of elements in combination with a metal that acts as a negative electrode other than tin and silicon, a metal that does not operate as a negative electrode, and a nonmetallic element can also be used. .

  Among these negative electrode active materials, since the capacity per unit weight is large when a battery is made, any single element of a specific metal element, an alloy of two or more specific metal elements, an oxide of a specific metal element In particular, silicon and / or tin metal alone, alloys, oxides, carbides, nitrides, and the like are preferable because of their large capacity per unit weight.

  In addition, although the capacity per unit weight is inferior to that of using a single metal or an alloy, the following compounds containing silicon and / or tin are also preferable because of excellent cycle characteristics.

The elemental ratio of silicon and / or tin to oxygen is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin oxide of 3 or less, more preferably 1.1 or less.
The elemental ratio of silicon and / or tin to nitrogen is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin nitride of 3 or less, more preferably 1.1 or less.
The element ratio of silicon and / or tin to carbon is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin carbide of 3 or less, more preferably 1.1 or less.

  These alloy materials may be in the form of powder or thin film, and may be crystalline or amorphous.

  The average particle size of the alloy-based material is not particularly limited in order to exhibit the effects of the present invention, but is usually 50 μm or less, preferably 20 μm or less, particularly preferably 10 μm or less, usually 0.1 μm or more, preferably 1 μm. As described above, it is particularly preferably 2 μm or more. When the average particle size exceeds this upper limit, the expansion of the electrode is increased, and the cycle characteristics may be deteriorated. Moreover, when an average particle diameter is less than this lower limit, current collection becomes difficult, and there is a possibility that the capacity is not sufficiently developed.

<Lithium-containing metal composite oxide material>
The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it can occlude and release lithium, but lithium-containing composite metal oxide materials containing titanium are preferable. The composite oxide (hereinafter abbreviated as “lithium titanium composite oxide”) is more preferable.

  Further, lithium or titanium of the lithium titanium composite oxide is at least selected from the group consisting of other metal elements such as Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb. Those substituted with one element are also preferred.

Furthermore, it is a lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ , and 0.7 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.3, and 0 ≦ z ≦ 1.6. It is preferable that the structure at the time of occlusion / release of lithium ions is stable (where M is Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb). Represents at least one element selected from the group consisting of:

Above all, in Li _x Ti _y M _z O ₄
(A) 1.2 ≦ x ≦ 1.4, 1.5 ≦ y ≦ 1.7, z = 0
(B) 0.9 ≦ x ≦ 1.1, 1.9 ≦ y ≦ 2.1, z = 0
(C) 0.7 ≦ x ≦ 0.9, 2.1 ≦ y ≦ 2.3, z = 0
This structure is particularly preferable because of a good balance of battery performance, and a particularly preferable representative composition is Li _4/3 Ti _5/3 O ₄ in (a), Li ₁ Ti ₂ O ₄ in (b), ( In c), it is Li _4/5 Ti _11/5 O ₄ .

_Further, in the _{Li x Ti y M z O 4} , the structure of the z = O, for _example, be mentioned as Li _4/3 Ti _{4/3 Al} 1/3 _{O 4} are preferred.

(Positive electrode active material)
The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. The positive electrode active material is preferably a substance containing lithium and at least one transition metal, and examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound.

The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples include lithium / cobalt composite oxide such as LiCoO ₂ or LiNiO ₂ . Lithium / nickel composite oxide, LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO _{3 and} other lithium / manganese composite oxides, Al, Ti , V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and those substituted with other metals such as Si. Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O _4, etc. Is mentioned.

As the transition metal of the lithium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable, and specific examples include, for example, LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ). ₃ , iron phosphates such as LiFeP ₂ O ₇ , cobalt phosphates such as LiCoPO ₄ , and some of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds are Al, Ti, V, Cr, Mn , Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si and the like substituted with other metals.

These positive electrode active materials may be used alone or in combination.

  In addition, a material in which a substance having a composition different from that of the substance constituting the main cathode active material is attached to the surface of the cathode active material can be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate and carbonates such as lithium carbonate, calcium carbonate and magnesium carbonate.

  The amount of the surface-adhering substance is not particularly limited in order to exhibit the effects of the present invention, but is preferably 0.1 ppm or more, more preferably 1 ppm or more as a lower limit by mass with respect to the positive electrode active material. The upper limit is preferably 10 ppm or more, preferably 20% or less, more preferably 10% or less, and still more preferably 5% or less. The surface adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material, and can improve the battery life. If the amount is too large, the resistance may increase in order to inhibit the entry and exit of lithium ions.

(Binders, thickeners, etc.)
As the binder for binding the active material, any material can be used as long as it is a material that is stable with respect to the solvent and the electrolytic solution used during electrode production. For example, fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, polyolefins such as polyethylene and polypropylene, polymers having unsaturated bonds such as styrene / butadiene rubber, isoprene rubber and butadiene rubber, and copolymers thereof, ethylene-acrylic Examples thereof include acrylic acid polymers such as acid copolymers and ethylene-methacrylic acid copolymers, and copolymers thereof. These may be used alone or in combination.

  The electrode may contain a thickener, a conductive material, a filler and the like in order to increase mechanical strength and electrical conductivity.

  Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These may be used alone or in combination.

  Examples of the conductive material include metal materials such as copper and nickel, and carbon materials such as graphite and carbon black. These may be used alone or in combination.

(Manufacture of electrodes)
The electrode may be manufactured by a conventional method. For example, it can be formed by adding a binder, a thickener, a conductive material, a solvent or the like to a negative electrode or a positive electrode active material to form a slurry, applying the slurry to a current collector, drying it, and then pressing it.

  In addition, a material obtained by adding a binder or a conductive material to an active material is roll-formed as it is to form a sheet electrode, a pellet electrode is formed by compression molding, and an electrode is formed on the current collector by a technique such as vapor deposition, sputtering, or plating. A thin film of material can also be formed.

When graphite is used as the negative electrode active material, the density of the negative electrode active material layer after drying and pressing is usually 1.45 g / cm ³ or more, preferably 1.55 g / cm ³ or more, more preferably 1.60 g. / Cm ³ or more, particularly preferably 1.65 g / cm ³ or more.

The density of the positive electrode active material layer after drying and pressing is usually 2.0 g / cm ³ or more, preferably 2.5 g / cm ³ or more, more preferably 3.0 g / cm ³ or more.

(Current collector)
Various types of current collectors can be used, but metals and alloys are usually used. Examples of the current collector for the negative electrode include copper, nickel, and stainless steel, and copper is preferred. Examples of the current collector for the positive electrode include metals such as aluminum, titanium, and tantalum, and alloys thereof, and aluminum or an alloy thereof is preferable.

<Separator, exterior body>
A porous film (separator) is interposed between the positive electrode and the negative electrode to prevent a short circuit. In this case, the electrolytic solution is used by impregnating the porous membrane. The material and shape of the porous film are not particularly limited as long as it is stable to the electrolytic solution and excellent in liquid retention, and a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene is preferable.

  The material of the battery case used in the battery according to the present invention is also arbitrary, and nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a laminate film, or the like is used.

  The operating voltage of the above-described non-aqueous electrolyte secondary battery of the present invention is usually in the range of 2V to 4.9V.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples unless it exceeds the gist.

  In addition, each evaluation method of the battery obtained by the following Example and the comparative example is shown below.

[Capacity evaluation]
The non-aqueous electrolyte secondary battery is charged to 4.2 V at a constant current corresponding to 0.2 C at 25 ° C. in a state of being sandwiched between glass plates in order to improve the adhesion between the electrodes, and then 0.2 C The battery was discharged to 3 V at a constant current of. This is done for 3 cycles to stabilize the battery. In the 4th cycle, after charging to 4.2V with a constant current of 0.5C, charging is performed until the current value reaches 0.05C with a constant voltage of 4.2V. The initial discharge capacity was determined by discharging to 3 V at a constant current of 0.2C.

  Here, 1C represents a current value for discharging the reference capacity of the battery in one hour, and 0.2C represents a current value of 1/5 thereof.

[Overcharge characteristics evaluation]
After the capacity evaluation test was completed, the volume was measured by immersing the battery in an ethanol bath. Then, at 25 ° C., the battery was charged at a constant current of 0.2 C to 5 V, and the current was cut when 5 V was reached. Then, the open circuit voltage (OCV) of the battery after the overcharge test was measured.
Next, the volume was measured by immersion in an ethanol bath, and the amount of gas generated from the volume change before and after overcharging was determined.

The lower the OCV of the battery after the overcharge test, the lower the overcharge depth and the higher the safety during overcharge.
In addition, the larger the amount of gas generated after overcharging, the more preferable the battery that senses this when the internal pressure rises abnormally due to an abnormality such as overcharging and activates the safety valve because the safety valve can be activated earlier. .
In addition, the greater the difference between the amount of gas generated after overcharging and the amount of gas generated during high-temperature storage, etc., prevents the safety valve from malfunctioning during high-temperature storage, etc., while reliably operating the safety valve during overcharging. Is preferable.

[Evaluation of high-temperature storage characteristics (continuous charging characteristics)]
After the capacity evaluation test was completed, the volume was measured by immersing the battery in an ethanol bath. Then, constant current charging was performed at a constant current of 0.5 C at 60 ° C., and after reaching 4.25 V, constant voltage charging was performed. Switching was performed continuously for one week.
After the battery was cooled, it was immersed in an ethanol bath to measure the volume, and the amount of gas generated from the volume change before and after continuous charging was determined.

  After measuring the amount of gas generated, discharge to 3 V at a constant current of 0.2 C at 25 ° C., measure the remaining capacity after the continuous charge test, and determine the ratio of the discharge capacity after the continuous charge test to the initial discharge capacity. Was the remaining capacity (%) after the continuous charge test.

  Next, after charging to 4.2V at a constant current of 0.5C at 25 ° C, charging is carried out until the current value reaches 0.05C at a constant voltage of 4.2V, and discharged to 3V at a constant current of 1C. Then, the 1C discharge capacity after the continuous charge test was measured, the ratio of the 1C discharge capacity after the continuous charge test to the initial discharge capacity was determined, and this was defined as the 1C capacity (%) after the continuous charge test.

[Example 1]
<Manufacture of negative electrode>
The d-value of the lattice plane (002 plane) in X-ray diffraction is 0.336 nm, the crystallite size (Lc) is 652 nm, the ash content is 0.07 wt%, the median diameter by laser diffraction / scattering method is 12 μm, and the ratio by BET method The half-value width of a peak whose surface area is 7.5 m ² / g and the R value (= I _B / I _A ) determined from Raman spectrum analysis using an argon ion laser beam is in the range of 0.12, 1570 to 1620 cm ^−1. Was mixed with 94 parts by weight of natural graphite powder having a weight of 19.9 cm ⁻¹ and 6 parts by weight of polyvinylidene fluoride, and N-methyl-2-pyrrolidone was added to form a slurry. This slurry was uniformly applied to one side of a 12 μm thick copper foil and dried, and then pressed to obtain a negative electrode active material layer having a density of 1.67 g / cm ³ to form a negative electrode.

<Production of positive electrode>
90 parts by weight of LiCoO ₂ , 4 parts by weight of carbon black and 6 parts by weight of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name “KF-1000”) are mixed, and N-methyl-2-pyrrolidone is added to form a slurry. Was uniformly coated on both sides of an aluminum foil having a thickness of 15 μm, dried, and then pressed so that the density of the positive electrode active material layer was 3.2 g / cm ³ to obtain a positive electrode.

<Manufacture of electrolyte>
Under a dry argon atmosphere, 2% by weight of vinylene carbonate and 1% by weight of diphenyl carbonate are mixed with a mixture of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (volume ratio 2: 3: 3) as the content in the non-aqueous electrolyte. Then, sufficiently dried LiPF ₆ was dissolved at a rate of 1.0 mol / liter to obtain an electrolytic solution.

<Manufacture of lithium secondary batteries>
The positive electrode, the negative electrode, and the polyethylene separator were laminated in the order of the negative electrode, the separator, the positive electrode, the separator, and the negative electrode to produce a battery element. The battery element was inserted into a bag made of a laminate film in which both surfaces of aluminum (thickness: 40 μm) were coated with a resin layer while projecting positive and negative terminals, and then the electrolyte was poured into the bag and vacuum sealed. Then, a sheet-like lithium secondary battery was produced, and overcharge characteristics and continuous charge characteristics were evaluated. The evaluation results are shown in Table 1.

[Example 2]
In the electrolyte solution of Example 1, a sheet-like lithium secondary battery was prepared in the same manner as in Example 1 except that fluoroethylene carbonate was used instead of vinylene carbonate, and the overcharge characteristics and the continuous charge characteristics were evaluated. It was. The evaluation results are shown in Table 1.

[Example 3]
In a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 2: 3: 3), the content in the non-aqueous electrolyte is 2% by weight of vinylene carbonate, 0.5% by weight of lithium difluorophosphate, and diphenyl carbonate 1 The weight percent was mixed. Next, a sheet-like lithium secondary battery was prepared in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Charging characteristics and continuous charging characteristics were evaluated. The evaluation results are shown in Table 1.

[Example 4]
2% by weight of vinylene carbonate and 1% by weight of diphenyl carbonate as a content in the non-aqueous electrolyte were mixed with a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 2: 1: 5). Next, a sheet-like lithium secondary battery was prepared in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Charging characteristics and continuous charging characteristics were evaluated. The evaluation results are shown in Table 1.

[Comparative Example 1]
As a content in the non-aqueous electrolyte, 2% by weight of vinylene carbonate was mixed with a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 2: 3: 3). Next, a sheet-like lithium secondary battery was prepared in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Charging characteristics and continuous charging characteristics were evaluated. The evaluation results are shown in Table 1.

[Comparative Example 2]
In the electrolytic solution of Example 1, a sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that phenylcyclohexane was used instead of diphenyl carbonate, and the overcharge characteristics and the continuous charge characteristics were evaluated. went. The evaluation results are shown in Table 1.

[Comparative Example 3]
A sheet-like lithium secondary battery was prepared in the same manner as in Example 1 except that vinylethylene carbonate was used instead of vinylene carbonate in the electrolytic solution of Example 1, and the overcharge characteristics and continuous charge characteristics were evaluated. It was. The evaluation results are shown in Table 1.

[Comparative Example 4]
As a content in the non-aqueous electrolyte solution, 1% by weight of diphenyl carbonate was mixed with a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 2: 3: 3). Next, a sheet-like lithium secondary battery was prepared in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Charging characteristics and continuous charging characteristics were evaluated. The evaluation results are shown in Table 1.

[Comparative Example 5]
Uses an electrolyte prepared by dissolving LiPF ₆ in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 2: 3: 3) to a ratio of 1.0 mol / liter. Except for the above, a sheet-like lithium secondary battery was produced in the same manner as in Example 1, and the overcharge characteristics and the continuous charge characteristics were evaluated. The evaluation results are shown in Table 1.

[Comparative Example 6]
A mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 6: 1: 3) is mixed with 2% by weight of vinylene carbonate and 1% by weight of diphenyl carbonate as the content in the non-aqueous electrolyte, and then thoroughly dried. A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that an electrolytic solution prepared by dissolving LiPF ₆ at a ratio of 1.0 mol / liter was used. The charging characteristics were evaluated. The evaluation results are shown in Table 1.

From Table 1, the following is clear.
The battery of Comparative Example 2 using an electrolytic solution containing phenylcyclohexane instead of diphenyl carbonate has high safety during overcharge, but generates a lot of gas due to high-temperature storage, and the battery characteristics are greatly deteriorated.
In the batteries of Comparative Examples 3 and 4 in which the electrolytic solution does not contain the compound (b), gas generation due to high-temperature storage is small, but battery characteristics are greatly deteriorated.
The batteries of Comparative Examples 1 and 5 in which the electrolytic solution does not contain diphenyl carbonate are excellent in battery characteristics after high-temperature storage, but can be said to have low safety during overcharge.
In Comparative Example 6 in which the ratio of ethylene carbonate with respect to the total of ethylene carbonate and dialkyl carbonate (ethyl methyl carbonate and dimethyl carbonate) in the non-aqueous solvent exceeds 50% by volume, gas generation due to high-temperature storage is large, and battery characteristic deterioration is large. .
On the other hand, the electrolytic solution of the present invention in which diphenyl carbonate and compound (b) are used in combination, and the ratio of ethylene carbonate to the total of ethylene carbonate and dialkyl carbonate in the nonaqueous solvent is in the range of 5 to 50% by volume. It can be seen that a battery using is highly safe during overcharge and has excellent high-temperature storage characteristics.

Claims (2)

In a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent,
A non-aqueous electrolyte containing (a) diphenyl carbonate, (b) vinylene carbonate, at least one compound selected from the group consisting of a cyclic carbonate compound having a fluorine atom, a monofluorophosphate and a difluorophosphate (A) The proportion of diphenyl carbonate in (a) is 0.001 wt% or more and less than 5 wt%, and (b) a group consisting of vinylene carbonate, a cyclic carbonate compound having a fluorine atom, monofluorophosphate and difluorophosphate The total proportion of at least one compound selected from 0.001 to 20% by weight,
The non-aqueous solvent contains ethylene carbonate and dialkyl carbonate,
A nonaqueous electrolytic solution, wherein the ratio of ethylene carbonate to the total of ethylene carbonate and dialkyl carbonate in the nonaqueous solvent is 5% by volume or more and 50% by volume or less.   A non-aqueous electrolyte battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is the non-aqueous electrolyte solution according to claim 1. Non-aqueous electrolyte battery.