JP5636623B2 - Non-aqueous electrolyte for secondary battery and non-aqueous electrolyte secondary battery using the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte for a secondary battery and a secondary battery using the same, and more specifically, a non-aqueous electrolyte for a lithium secondary battery containing a specific component and the use thereof. The present invention relates to a lithium secondary battery.

  In recent years, with the miniaturization of electronic devices, the demand for higher capacity for secondary batteries has increased, and lithium secondary batteries with higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries have attracted attention. Yes.

  As a solvent used for the electrolyte solution of the lithium secondary battery, ethylene carbonate having a high dielectric constant is frequently used. However, ethylene carbonate has a high freezing point of 36.4 ° C., is solid at room temperature, and is difficult to handle due to its high viscosity even as a liquid. Therefore, an electrolyte solution using ethylene carbonate is usually mixed with about 70% of a low viscosity solvent such as ethyl methyl carbonate or diethyl carbonate as a secondary solvent. However, low-viscosity solvents generally have a low boiling point, and when added in large quantities, the salt tends to precipitate due to evaporation of the solvent, the flash point decreases, and the internal pressure tends to increase when the battery is stored at high temperatures. There are problems such as.

  Therefore, it is required to reduce the content of the low-viscosity solvent as much as possible. However, if only a small amount is added, the low-temperature characteristics and output characteristics of the battery are deteriorated.

  On the other hand, as the use of lithium secondary batteries expands, characteristics that can instantaneously extract large energy, that is, output characteristics, are increasingly required. While lithium secondary batteries are used in various electronic devices, as well as automobiles and power tools, there is a strong demand for electrolyte solutions that can contribute to improved output characteristics.

  Among these, Patent Document 1 includes an example in which a non-aqueous electrolytic solution containing a cyclic siloxane and / or a reaction product thereof is used as a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate. Although an example using a non-aqueous electrolyte solution containing a silicon compound having the structure of is described, a linear carbonate that is a low-boiling solvent is used in a large amount, so that the above-mentioned problems are solved It wasn't.

JP 2004-71458 A JP 2004-87459 A

  The present invention has been made in view of the background art, and the problem is that the salt is deposited by evaporation of the solvent, the flash point is lowered, or the internal pressure is increased when the battery is stored at a high temperature. Non-aqueous electrolyte solution and secondary battery for secondary battery that can maintain high low-temperature characteristics and output characteristics with less electrolyte problem composition when low viscosity solvent such as easy to contain It is to provide.

  As a result of intensive studies to solve the above problems, the present inventors have found that the non-aqueous solvent contains a solvent having a flash point of 70 ° C. or higher, 60% by volume or more of the whole non-aqueous solvent, and a certain amount of a specific compound. The present inventors have found that when a non-aqueous electrolyte solution added or contained in a non-aqueous electrolyte solution is used, high low-temperature characteristics and output characteristics can be kept good, and the present invention has been achieved.

［一般式（１）中、Ｒ^１及びＲ^２は互いに同一であっても異なっていてもよい炭素数１〜１２の有機基を表し、ｎは３〜１０の整数を表す。］

［一般式（２）中、Ｒ^３〜Ｒ^５は互いに同一であっても異なっていてもよい炭素数１〜１２の有機基を表し、ｘは１〜３の整数を表し、ｐ、ｑ及びｒはそれぞれ０〜３の整数を表し、１≦ｐ＋ｑ＋ｒ≦３である。］

［一般式（３）中、Ｒ^６〜Ｒ^８は互いに同一であっても異なっていてもよい炭素数１〜１２の有機基を表し、ＡはＨ、Ｃ、Ｎ、Ｏ、Ｆ、Ｓ、Ｓｉ及び／又はＰから構成される基を表す。］ That is, the present invention is a non-aqueous electrolyte solution for a secondary battery in which at least a lithium salt is dissolved in a non-aqueous solvent, and the non-aqueous solvent is a solvent having a flash point of 70 ° C. or higher. In addition, the cyclic siloxane compound represented by the general formula (1), the fluorosilane compound represented by the general formula (2), the compound represented by the general formula (3), and S- At least one compound selected from the group consisting of a compound having an F bond, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate is contained in the entire non-aqueous electrolyte. The present invention provides a nonaqueous electrolytic solution for a secondary battery characterized by containing 10 ppm or more.

[In General Formula (1), R ¹ and R ² represent the same or different organic group having 1 to 12 carbon atoms, and n represents an integer of 3 to 10. ]

[In General Formula (2), R ^{3 to} R ⁵ represent an organic group having 1 to 12 carbon atoms which may be the same or different from each other, x represents an integer of 1 to 3, p, q and Each r represents an integer of 0 to 3, and 1 ≦ p + q + r ≦ 3. ]

[In General Formula (3), R ^{6 to} R ⁸ represent an organic group having 1 to 12 carbon atoms which may be the same as or different from each other, and A represents H, C, N, O, F, S, Represents a group composed of Si and / or P; ]

  Further, the present invention is a non-aqueous electrolyte secondary battery including at least a non-aqueous electrolyte, a negative electrode capable of inserting and extracting lithium ions, and a positive electrode, wherein the non-aqueous electrolyte is claim 1 to claim A non-aqueous electrolyte secondary battery characterized by being a non-aqueous electrolyte solution for a secondary battery according to any one of claims 5.

  According to the present invention, electrolysis with less problems caused when a large amount of a low-viscosity solvent such as salt is precipitated by evaporation of the solvent, the flash point is lowered, or the internal pressure is likely to increase at high temperatures is included. In spite of the liquid composition, it is possible to provide a non-aqueous electrolyte solution for a secondary battery and a secondary battery that can maintain high low-temperature characteristics and output characteristics.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these specific contents. Various modifications can be made within the scope of the gist.

<Nonaqueous electrolyte for secondary battery>
The non-aqueous electrolyte solution for secondary batteries of the present invention contains a solvent having a non-aqueous solvent with a flash point of 70 ° C. or higher, 60% by volume or more of the whole non-aqueous solvent, and is further represented by the general formula (1). Compound, fluorosilane compound represented by general formula (2), compound represented by general formula (3), compound having SF bond in molecule, nitrate, nitrite, monofluorophosphate, difluorophosphorus It is characterized in that at least one compound selected from the group consisting of acid salts, acetates and propionates is contained in the whole non-aqueous electrolyte solution in an amount of 10 ppm or more. As with the electrolytic solution, a conventionally known lithium salt or non-aqueous solvent can be used.

[Lithium salt]
The electrolyte is not particularly limited as long as it is a lithium salt that is known to be usable as an electrolyte of a non-aqueous electrolyte for a lithium secondary battery, and examples thereof include the following.

Inorganic lithium salts: inorganic fluoride salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; perhalogenates such as LiClO ₄ , LiBrO ₄ , LiIO ₄ ; inorganic chloride salts such as LiAlCl ₄ .
Fluorine-containing organic lithium salt: perfluoroalkane sulfonate such as LiCF ₃ SO ₃ ; LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F Perfluoroalkanesulfonylimide salts such as ₉ SO ₂ ); perfluoroalkanesulfonylmethide salts such as LiC (CF ₃ SO ₂ ) ₃ ; Li [PF ₅ (CF ₂ CF ₂ CF ₃ )], Li [PF ₄ ( CF ₂ CF ₂ CF ₃ ) ₂ ], Li [PF ₃ (CF ₂ CF ₂ CF ₃ ) ₃ ], Li [PF ₅ (CF ₂ CF ₂ CF ₂ CF ₃ )], Li [PF ₄ (CF ₂ CF ₂₎ CF ₂ CF ₃ ) ₂ ], Li [PF ₃ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₃ ] and other fluoroalkyl fluorophosphates.
Oxalatoborate salt: lithium bis (oxalato) borate, lithium difluorooxalatoborate and the like.

These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and ratios. Among these, LiPF ₆ is preferable when comprehensively judging solubility in a non-aqueous solvent, charge / discharge characteristics in the case of a secondary battery, output characteristics, cycle characteristics, and the like.

  The concentration of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is usually 0.5 mol / L or more, preferably 0.6 mol / L or more, more preferably 0.7 mol / L or more. Moreover, the upper limit is 2 mol / L or less normally, Preferably it is 1.8 mol / L or less, More preferably, it is 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity. May decrease.

A preferable example when two or more lithium salts are used in combination is a combination of LiPF ₆ and LiBF _{4. In} this case, the proportion of LiBF _{4 in} the total of both is 0.01% by mass or more and 20% by mass. % Or less is particularly preferable, and it is more preferably 0.1% by mass or more and 5% by mass or less. Another preferred example is the combined use of an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt. In this case, the proportion of the inorganic fluoride salt in the total of both is 70% by mass or more and 99% by mass. % Or less, particularly preferably 80% by mass or more and 98% by mass or less. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

When the non-aqueous solvent contains 50% by volume or more of γ-butyrolactone or γ-valerolactone, the lithium salt is preferably LiBF ₄ or LiBF ₄ in combination with another. In this case, LiBF ₄ preferably accounts for 40 mol% or more of the entire lithium salt. In particular, the proportion of LiBF _{4 in} the lithium salt is 40 to 95 mol%, and the remainder is composed of LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) _2. A combination that is at least one lithium salt selected from the group is preferred.

[Nonaqueous solvent]
In the present invention, it is essential that the non-aqueous solvent contains 60% by volume or more of the total non-aqueous solvent with a flash point of 70 ° C. or higher. Furthermore, it is preferable that the total of the solvents having a flash point of 80 ° C. or higher is 60% by volume or more of the total amount of the non-aqueous solvent, and it is particularly preferable that the total of solvents having a flash point of 90 ° C. or higher is 60% by volume or more.

  The solvent having a flash point of 70 ° C. or higher is not particularly limited, and examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, and the like. Among them, ethylene carbonate, propylene carbonate, or γ- Butyrolactone is particularly preferred. These solvents may be used alone or in combination of two or more, and the combination is not particularly limited.

  A composition containing 10% by volume or more of ethylene carbonate or propylene carbonate with respect to the whole non-aqueous solvent is preferable in terms of improving cycle characteristics. On the other hand, when a large amount of ethylene carbonate is contained, the low temperature characteristics are deteriorated. Therefore, the content of ethylene carbonate is preferably 70% by volume or less, and particularly preferably 60% by volume or less of the entire non-aqueous solvent.

A preferred example of the non-aqueous solvent containing a total of 60% by volume of the solvent having a flash point of 70 ° C. or higher is
(1) The amount of γ-butyrolactone in the whole non-aqueous solvent is 60% by volume or more,
(2) The total of ethylene carbonate and γ-butyrolactone in the entire nonaqueous solvent is 80% by volume or more, preferably 85% by volume or more, and the volume ratio of ethylene carbonate and γ-butyrolactone is 5:95 to What is 45:55,
(3) The total of ethylene carbonate and propylene carbonate in the entire non-aqueous solvent is 80% by volume or more, preferably 85% by volume or more, and the volume ratio of ethylene carbonate to propylene carbonate is 30:70 to 60:40. It is what is.

  When these nonaqueous solvents are used, the balance between the cycle characteristics and the large current discharge characteristics is improved.

  The non-aqueous electrolyte is preferably one having a flash point of 40 ° C. or higher, particularly preferably 50 ° C. or higher, more preferably 60 ° C. or higher, and further preferably 70 ° C. or higher. If the flash point of the non-aqueous electrolyte is too low, the electrolyte may be ignited when the battery is exposed to high temperatures.

  The non-aqueous solvent used for the non-aqueous electrolyte for secondary batteries of the present invention is a solvent having a flash point of 70 ° C. or higher, and a non-aqueous solvent component having a flash point of less than 70 ° C. (hereinafter “other non-aqueous solvent components”). Abbreviated as “)”. Such other non-aqueous solvent components can be appropriately selected and used from those conventionally proposed as solvents for non-aqueous electrolytes. Examples thereof include the following.

(1) Chain carbonate As a chain carbonate, dialkyl carbonate is preferable, and, as for carbon number of the alkyl group to comprise, 1-5 are respectively preferable, Most preferably, it is 1-4. Specific examples include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.
(2) Chain ester Specific examples include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.
(3) Cyclic ether Specific examples include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like.
(4) Chain ether Specific examples include dimethoxyethane and dimethoxymethane.

  Other non-aqueous solvent components may be used alone or in combination with a “solvent having a flash point of 70 ° C. or higher” or in combination of two or more. In this case, it is particularly preferable to use a chain carbonate and / or a chain ester in combination with a “solvent having a flash point of 70 ° C. or higher” in terms of cycle characteristics and large current discharge characteristics.

  The content of the solvent having a flash point of 70 ° C. or higher in all nonaqueous solvents is essential to be 60% by volume or higher, preferably 70% by volume or higher, particularly preferably 75% by volume or higher, more preferably 80% by volume. As mentioned above, More preferably, it is 85 volume% or more. Moreover, an upper limit is 100 volume% or less, and 90 volume% or less is especially preferable. If the content of the solvent having a flash point of 70 ° C. or higher is too small, a desired effect such as an increase in internal pressure may not be obtained when the battery is stored at a high temperature. The electrical conductivity may decrease due to the increase, and the performance of the lithium secondary battery may decrease.

[Specific compounds]
The non-aqueous electrolyte of the present invention includes a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and S in the molecule. A compound having —F bond, at least one compound selected from the group consisting of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate (these are referred to as “specific compound”) 10 ppm or more in the whole non-aqueous electrolyte solution.

[[Cyclic Siloxane Compound Represented by General Formula (1)]]
R ¹ and although R ² are identical there may be different even if an organic group having 1 to 12 carbon atoms with each other, as R ¹ and R ² in the general formula (1) cyclic siloxane compound represented by, Chain alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group and t-butyl group; cyclic alkyl groups such as cyclohexyl group and norbornanyl group; vinyl group, Alkenyl groups such as 1-propenyl group, allyl group, butenyl group, 1,3-butadienyl group; alkynyl groups such as ethynyl group, propynyl group, butynyl group; halogenated alkyl groups such as trifluoromethyl group; 3-pyrrolidino An alkyl group having a saturated heterocyclic group such as a propyl group; an aryl group such as a phenyl group optionally having an alkyl substituent; a phenylmethyl group; Examples thereof include aralkyl groups such as an phenylethyl group; trialkylsilyl groups such as a trimethylsilyl group; trialkylsiloxy groups such as a trimethylsiloxy group.

Among them, those having a smaller number of carbon atoms are more likely to exhibit characteristics, and organic groups having 1 to 6 carbon atoms are preferable. Alkenyl groups act on non-aqueous electrolytes and coatings on electrode surfaces to improve input / output characteristics, and aryl groups have the effect of capturing radicals generated in the battery during charge and discharge to improve overall battery performance. Therefore, it is preferable. Accordingly, R ¹ and R ² are particularly preferably a methyl group, a vinyl group, or a phenyl group.

  In general formula (1), n represents an integer of 3 to 10, but an integer of 3 to 6 is preferable, and 3 or 4 is particularly preferable.

  Examples of the cyclic siloxane compound represented by the general formula (1) include, for example, hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane, hexaphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5. -Cyclotrisiloxane such as trivinylcyclotrisiloxane, cyclotetrasiloxane such as octamethylcyclotetrasiloxane, cyclopentasiloxane such as decamethylcyclopentasiloxane, and the like. Of these, cyclotrisiloxane is particularly preferred.

[[Fluorosilane compound represented by general formula (2)]]
R ^{3 to} R ⁵ in the fluorosilane compound represented by the general formula (2) are organic groups having 1 to 12 carbon atoms which may be the same as or different from each other, but R in the general formula (1) Examples of the chain alkyl group, cyclic alkyl group, alkenyl group, alkynyl group, halogenated alkyl group, alkyl group having a saturated heterocyclic group, phenyl group optionally having an alkyl group, etc. mentioned as examples of ¹ and R ² In addition to aryl groups, aralkyl groups, trialkylsilyl groups, trialkylsiloxy groups, carbonyl groups such as ethoxycarbonylethyl groups; carboxyl groups such as acetoxy groups, acetoxymethyl groups, trifluoroacetoxy groups; methoxy groups, ethoxy groups, Oxy group such as propoxy group, butoxy group, phenoxy group, allyloxy group; amino group such as allylamino group; Mention may be made of the group, and the like.

  In general formula (2), x represents an integer of 1 to 3, p, q, and r each represents an integer of 0 to 3, and 1 ≦ p + q + r ≦ 3. Inevitably, x + p + q + r = 4.

  Examples of the fluorosilane compound represented by the general formula (2) include trimethylfluorosilane, triethylfluorosilane, tripropylfluorosilane, phenyldimethylfluorosilane, triphenylfluorosilane, vinyldimethylfluorosilane, vinyldiethylfluorosilane, In addition to monofluorosilanes such as vinyldiphenylfluorosilane, trimethoxyfluorosilane, and triethoxyfluorosilane, difluorosilanes such as dimethyldifluorosilane, diethyldifluorosilane, divinyldifluorosilane, and ethylvinyldifluorosilane; methyltrifluorosilane, Also included are trifluorosilanes such as ethyltrifluorosilane.

  If the boiling point of the fluorosilane compound represented by the general formula (2) is low, it will volatilize, and therefore it may be difficult to contain a predetermined amount in the non-aqueous electrolyte. Moreover, even if it is made to contain in a non-aqueous electrolyte solution, there exists a possibility that it may volatilize on the conditions that the heat_generation | fever of a battery by charging / discharging or external environment becomes high temperature. Accordingly, those having a boiling point of 50 ° C. or higher at 1 atm are preferable, and those having a boiling point of 60 ° C. or higher are particularly preferable.

  Further, like the compound of the general formula (1), the organic group having a smaller number of carbon atoms is more effective, and the alkenyl group having 1 to 6 carbon atoms acts on the non-aqueous electrolyte solution or the electrode surface coating. Thus, the input / output characteristics are improved, and the aryl group has the effect of capturing radicals generated in the battery during charge / discharge and improving the overall battery performance. Therefore, from this viewpoint, the organic group is preferably a methyl group, a vinyl group, or a phenyl group, and examples of the compound include trimethylfluorosilane, vinyldimethylfluorosilane, phenyldimethylfluorosilane, and vinyldiphenylfluorosilane. .

[[Compound represented by formula (3)]]
R ^{6 to} R ⁸ in the compound represented by the general formula (3) are organic groups having 1 to 12 carbon atoms which may be the same as or different from each other. A chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, a halogenated alkyl group, an alkyl group having a saturated heterocyclic group, or an alkyl group, which are mentioned as examples of R ^{3 to} R ⁵ Aryl groups such as phenyl groups, aralkyl groups, trialkylsilyl groups, trialkylsiloxy groups, carbonyl groups, carboxyl groups, oxy groups, amino groups, benzyl groups, and the like can be similarly exemplified.

  A in the compound represented by the general formula (3) is not particularly limited as long as A is a group composed of H, C, N, O, F, S, Si and / or P, but the general formula (3) C, S, Si or P is preferable as the element directly bonded to the oxygen atom therein. Examples of the existence form of these atoms include a chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, a halogenated alkyl group, a carbonyl group, a sulfonyl group, a trialkylsilyl group, a phosphoryl group, and a phosphinyl group. Those are preferred. The molecular weight of the compound represented by the general formula (3) is preferably 1000 or less, particularly preferably 800 or less, and more preferably 500 or less.

  Examples of the compound represented by the general formula (3) include siloxane compounds such as hexamethyldisiloxane, 1,3-diethyltetramethyldisiloxane, hexaethyldisiloxane, and octamethyltrisiloxane; methoxytrimethylsilane, ethoxy Alkoxysilanes such as trimethylsilane; peroxides such as bis (trimethylsilyl) peroxide; carboxylic acid esters such as trimethylsilyl acetate, triethylsilyl acetate, trimethylsilyl propionate, trimethylsilyl methacrylate, and trimethylsilyl trifluoroacetate; methanesulfonic acid Sulfonic acid esters such as trimethylsilyl, trimethylsilyl ethanesulfonate, triethylsilyl methanesulfonate, trimethylsilyl fluoromethanesulfonate; bis (trimethylsilyl) Sulfuric esters such as sulfates; tris (trimethylsiloxy) borate esters such as boron; tris (trimethylsilyl) phosphate, tris (trimethylsilyl) phosphite phosphoric acid or phosphorous acid esters such as phosphite and the like.

  Of these, siloxane compounds, sulfonic acid esters, and sulfuric acid esters are preferable, and sulfonic acid esters are particularly preferable. The siloxane compound is preferably hexamethyldisiloxane, the sulfonic acid ester is preferably trimethylsilyl methanesulfonate, and the sulfuric acid ester is preferably bis (trimethylsilyl) sulfate.

[[Compound with SF bond in molecule]]
The compound having an S—F bond in the molecule is not particularly limited, but sulfonyl fluorides and fluorosulfonic acid esters are preferable.

  For example, methanesulfonyl fluoride, ethanesulfonyl fluoride, methanebis (sulfonylfluoride), ethane-1,2-bis (sulfonylfluoride), propane-1,3-bis (sulfonylfluoride), butane-1,4 -Bis (sulfonyl fluoride), difluoromethane bis (sulfonyl fluoride), 1,1,2,2-tetrafluoroethane-1,2-bis (sulfonyl fluoride), 1,1,2,2,3 Examples include 3-hexafluoropropane-1,3-bis (sulfonyl fluoride), methyl fluorosulfonate, ethyl fluorosulfonate, and the like. Of these, methanesulfonyl fluoride, methanebis (sulfonyl fluoride) or methyl fluorosulfonate is preferable.

[[Nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate]]
The counter cation of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate is not particularly limited, but metal elements such as Li, Na, K, Mg, Ca, Fe, Cu, etc. In addition, ammonium or quaternary ammonium represented by NR ⁹ R ¹⁰ R ¹¹ R ¹² (wherein R ^{9 to} R ¹² each independently represents a hydrogen atom or an organic group having 1 to 12 carbon atoms). Is mentioned. Here, the organic group having 1 to 12 carbon atoms of R ^{9 to} R ¹² is an alkyl group which may be substituted with a halogen atom, a cycloalkyl group which may be substituted with a halogen atom, or a halogen atom. An aryl group which may be present, a nitrogen atom-containing heterocyclic group, and the like. R ^{9 to} R ¹² are each preferably a hydrogen atom, an alkyl group, a cycloalkyl group, a nitrogen atom-containing heterocyclic group, or the like. Among these counter cations, lithium, sodium, potassium, magnesium, calcium or NR ⁹ R ¹⁰ R ¹¹ R ¹² is preferable, and lithium is particularly preferable from the viewpoint of battery characteristics when used in a lithium secondary battery.

  Among them, nitrate or difluorophosphate is preferable in terms of the effect of improving output, battery cycle characteristics and high-temperature storage characteristics, and lithium difluorophosphate is particularly preferable. Those compounds synthesized in a non-aqueous solvent may be used substantially as they are, or synthesized separately and added to a non-aqueous solvent or a non-aqueous electrolyte after being substantially isolated. May be.

  A specific compound, that is, a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and an SF bond in the molecule. Compound, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate or propionate may be used alone, or two or more compounds may be used in any combination and ratio May be. Moreover, even if it is a compound classified into said each with a specific compound, 1 type may be used independently and 2 or more types of compounds may be used together by arbitrary combinations and ratios.

  The ratio of these specific compounds in the non-aqueous electrolyte solution is essential to be 10 ppm or more (0.001 mass% or more) in total with respect to the total non-aqueous electrolyte solution, but is preferably 0.01 mass% or more. Preferably it is 0.05 mass% or more, More preferably, it is 0.1 mass% or more. The upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less. If the concentration of the specific compound is too low, it may be difficult to obtain the effect of improving the output characteristics. On the other hand, if the concentration is too high, the charge / discharge efficiency may be lowered.

  In addition, when these specific compounds are actually used in the production of secondary batteries as non-aqueous electrolytes, the content of the specific compounds is significantly reduced even if the battery is disassembled and the non-aqueous electrolyte is taken out again. There are many. Therefore, what can detect the said specific compound at least from the non-aqueous electrolyte solution extracted from the battery is considered to be included in this invention.

  The reason why the non-aqueous electrolyte secondary battery using the non-aqueous electrolyte of the present invention is superior in low temperature characteristics and output characteristics after using a certain amount of a solvent having a high flash point is not clear. The invention is not limited to the following reasons, but is considered as follows. That is, it is considered that the specific compound acts on the electrode to reduce the reaction resistance related to lithium ion desorption and improve the output characteristics. Also, solvents with a high flash point such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, etc. have a higher dielectric constant than chain carbonates, and a solvent with a higher dielectric constant exists to some extent. In addition, the effect is considered to be remarkable. Further, when the electric capacity of the battery element housed in one battery case of the secondary battery is 3 ampere hours (Ah) or more and / or the DC resistance component of the secondary battery is 10 milliohms (Ω) or less. In some cases, the contribution of the direct current resistance component is reduced, and the original effect of the non-aqueous electrolyte solution is likely to appear compared to a battery in which the contribution of the direct current resistance component is large.

[Other compounds]
The non-aqueous electrolyte solution of the present invention contains a lithium salt that is an electrolyte and a specific compound as essential components in a non-aqueous solvent containing a chain carboxylic acid ester. It can be contained in any amount as long as the effect is not impaired.
Examples of such other compounds include:
(1) aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran;
(2) Partially fluorinated products of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole And overcharge inhibitors such as fluorine-containing anisole compounds such as 3,5-difluoroanisole;
(3) vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, etc. Negative electrode film-forming agent: ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide , Tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide, etc. Agent;
Etc.

  As the overcharge inhibitor, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran are preferable. Two or more of these may be used in combination. When using 2 or more types together, it is particularly preferable to use cyclohexylbenzene or terphenyl (or a partially hydrogenated product thereof) together with t-butylbenzene or t-amylbenzene.

  As the negative electrode film forming agent, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, succinic anhydride, and maleic anhydride are preferable. Two or more of these may be used in combination. When using 2 or more types together, vinylene carbonate and vinyl ethylene carbonate, fluoroethylene carbonate, succinic anhydride, or maleic anhydride are preferable.

  As the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate, and busulfan are preferable. Two or more of these may be used in combination.

  Moreover, the combined use of a negative electrode film forming agent and a positive electrode protective agent, or the combined use of an overcharge inhibitor, a negative electrode film forming agent, and a positive electrode protective agent is particularly preferable.

  The content ratio of these other compounds in the non-aqueous electrolyte solution is not particularly limited, but is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, respectively, based on the whole non-aqueous electrolyte solution. The upper limit is preferably 5% by mass or less, particularly preferably 3% by mass or less, and further preferably 2% by mass or less. By containing these compounds, it is possible to suppress rupture / ignition of the battery at the time of abnormality due to overcharge, or to improve capacity maintenance characteristics and cycle characteristics after high temperature storage.

  There is no particular limitation on the method for preparing the non-aqueous electrolyte solution for the secondary battery of the present invention, and it is prepared by dissolving a lithium salt, a specific compound, and, if necessary, other compounds in a non-aqueous solvent according to a conventional method. Can do. In preparing the non-aqueous electrolyte, each raw material is preferably dehydrated in advance, and the water content is usually 50 ppm or less, preferably 30 ppm or less, particularly preferably 10 ppm or less.

<Non-aqueous electrolyte secondary battery>
Hereinafter, the non-aqueous electrolyte secondary battery of the present invention will be described in detail.

[Battery shape]
The battery shape is not particularly limited, and examples thereof include a bottomed cylindrical shape, a bottomed square shape, a thin shape, a sheet shape, and a paper shape. When incorporating into a system or device, in order to increase the volumetric efficiency and increase the storage capacity, it may be of a different shape such as a horseshoe shape, a comb shape, etc. considering the fit to the peripheral system arranged around the battery . From the viewpoint of efficiently releasing the heat inside the battery to the outside, a rectangular shape having at least one surface that is relatively flat and has a large area is preferable.

  In a battery having a bottomed cylindrical shape, since the outer surface area with respect to the power generating element to be filled becomes small, it is preferable to design so that Joule heat generated by the internal resistance at the time of charging and discharging efficiently escapes to the outside. Moreover, it is preferable to design so that the filling ratio of the substance having high thermal conductivity is increased and the temperature distribution inside is reduced.

In the bottomed square shape, the ratio between the area S of the largest surface (the product of the width and height of the outer dimensions excluding the terminal portion, unit cm ² ) and the thickness T (unit cm) of the battery outer shape The 2S / T value is preferably 100 or more, and more preferably 200 or more. By increasing the maximum surface, it is possible to improve characteristics such as cycle performance and high-temperature storage even for high-power and large-capacity batteries, and increase the heat dissipation efficiency during abnormal heat generation. Can be prevented from becoming a dangerous state.

[Battery configuration]
The chargeable / dischargeable secondary battery of the present invention includes a positive electrode and a negative electrode capable of occluding and releasing lithium ions, the non-aqueous electrolyte solution of the present invention, a separator disposed between the positive electrode and the negative electrode, a current collecting terminal, and an exterior It is configured at least by a case or the like. If necessary, a protective element may be mounted inside the battery and / or outside the battery.

[Positive electrode]
The positive electrode used for the non-aqueous electrolyte secondary battery of the present invention will be described below.
[[Positive electrode active material]]
The positive electrode active material used for the positive electrode is described below.

[[[composition]]]
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. A substance containing lithium and at least one transition metal is preferable, and examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound.

V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are preferable as the transition metal of the lithium transition metal composite oxide. Specific examples include lithium-cobalt composite oxides such as LiCoO ₂ and LiNiO ₂ . Lithium / nickel composite oxide, lithium / manganese composite oxide such as LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO _3, etc., and some of the transition metal atoms that are the main components of these lithium transition metal composite oxides are Al, Ti , V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and those substituted with other metals such as Si. As specific examples of the substituted ones, 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 and the} like.

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.

[[[Surface coating]]]
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.

  These surface adhering substances are, for example, a method of dissolving or suspending in a solvent and impregnating and drying the positive electrode active material, and a method of dissolving or suspending a surface adhering substance precursor in a solvent and impregnating and adding to the positive electrode active material, followed by heating. It can be made to adhere to the positive electrode active material surface by the method of making it react by the method etc., the method of adding to a positive electrode active material precursor, and baking simultaneously.

  The amount of the surface adhering substance is by mass with respect to the positive electrode active material, preferably 0.1 ppm or more, more preferably 1 ppm or more, still more preferably 10 ppm or more, and the upper limit is preferably 20% or less, more preferably 10%. % Or less, more preferably 5% or less. The surface adhering substance can suppress the oxidation reaction of the electrolyte solution on the surface of the positive electrode active material and can improve the battery life. However, when the amount of the adhering quantity is too small, the effect is not sufficiently manifested. If it is too high, the resistance may increase in order to inhibit the entry and exit of lithium ions.

[[[shape]]]
As the shape of the positive electrode active material particles in the present invention, a lump shape, a polyhedron shape, a sphere shape, an oval sphere shape, a plate shape, a needle shape, a column shape, etc., which are conventionally used, are used. It is preferably formed by forming particles, and the shape of the secondary particles is spherical or elliptical. In general, an electrochemical element expands and contracts as the active material in the electrode expands and contracts as it is charged and discharged. Therefore, the active material is easily damaged due to the stress or the conductive path is broken. Therefore, it is preferable that the primary particles are aggregated to form secondary particles, rather than a single particle active material having only primary particles, in order to relieve expansion and contraction stress and prevent deterioration. In addition, spherical or oval spherical particles are less oriented during molding of the electrode than plate-like equiaxed particles, so that the expansion and contraction of the electrode during charging and discharging is small, and the electrode is produced. The mixing with the conductive material is also preferable because it is easy to mix uniformly.

[[[Tap density]]]
The tap density of the positive electrode active material is usually 1.3 g / cm ³ or more, preferably 1.5 g / cm ³ or more, more preferably 1.6 g / cm ³ or more, and most preferably 1.7 g / cm ³ or more. . If the tap density of the positive electrode active material is lower than the lower limit, the amount of the required dispersion medium increases when the positive electrode active material layer is formed, and the necessary amount of the conductive material and the binder increases. In some cases, the filling rate of the substance is limited, and the battery capacity is limited. By using a complex oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. In general, the tap density is preferably as large as possible, but there is no upper limit. However, if the tap density is too large, diffusion of lithium ions using the electrolyte solution as a medium in the positive electrode active material layer becomes rate-determining, and load characteristics are likely to deteriorate. It is 2.9 g / cm ³ or less, preferably 2.7 g / cm ³ or less.

In the present invention, the tap density is measured by passing a sieve having a mesh size of 300 μm, dropping a sample onto a 20 cm ³ tapping cell to fill the cell volume, and then measuring a powder density measuring device (for example, a tap denser manufactured by Seishin Enterprise Co., Ltd.). , Tapping with a stroke length of 10 mm is performed 1000 times, and the density obtained from the volume and the weight of the sample is defined as the tap density.

[[[Median diameter d ₅₀ ]]]
The median diameter d _{50 of the} particles (when the primary particles are aggregated to form secondary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, most The upper limit is usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. If the lower limit is not reached, a high tap density product may not be obtained, and if the upper limit is exceeded, it takes time to diffuse lithium in the particles. When a conductive material, a binder, or the like is slurried with a solvent and applied as a thin film, problems such as streaking may occur. Here, by mixing two or more types of positive electrode active materials having different median diameters d ₅₀ , the filling property at the time of forming the positive electrode can be further improved.

The median diameter d ₅₀ in the present invention is measured by a known laser diffraction / scattering particle size distribution measuring device. When LA-920 manufactured by HORIBA is used as a particle size distribution meter, a 0.1% by mass sodium hexametaphosphate aqueous solution is used as a dispersion medium for measurement, and a measurement refractive index of 1.24 is set after ultrasonic dispersion for 5 minutes. Measured.

[[[Average primary particle size]]]
When primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, Most preferably, it is 0.1 μm or more, and the upper limit is usually 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. If the above upper limit is exceeded, it is difficult to form spherical secondary particles, which adversely affects the powder filling property, or the specific surface area is greatly reduced, so that there is a high possibility that battery performance such as output characteristics will deteriorate. is there. On the other hand, when the value falls below the lower limit, there is a case where problems such as inferior reversibility of charge / discharge are usually caused because crystals are not developed.

  The primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10000 times, the longest value of the intercept by the left and right boundary lines of the primary particles with respect to the horizontal straight line is obtained for any 50 primary particles and obtained by taking the average value. It is done.

[[[BET specific surface area]]]
The BET specific surface area of the positive electrode active material used for the non-aqueous electrolyte secondary battery of the present invention is 0.2 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.4 m ² / g or more. And the upper limit is 4.0 m ² / g or less, preferably 2.5 m ² / g or less, more preferably 1.5 m ² / g or less. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered, and if the BET specific surface area is larger, the tap density is difficult to increase, and there may be a problem in applicability when forming the positive electrode active material.

  The BET specific surface area is determined by using a surface area meter (for example, a fully automated surface area measuring device manufactured by Okura Riken), preliminarily drying the sample for 30 minutes at 150 ° C. under nitrogen flow, and then measuring the relative pressure of nitrogen relative to atmospheric pressure. It is defined by a value measured by a nitrogen adsorption BET one-point method using a gas flow method using a nitrogen-helium mixed gas that is accurately adjusted to have a value of 0.3.

[[[Production method]]]
As a manufacturing method of the positive electrode active material, a general method is used as a manufacturing method of the inorganic compound. In particular, various methods are conceivable for producing a spherical or elliptical spherical active material. For example, transition metal raw materials such as transition metal nitrates and sulfates and, if necessary, raw materials of other elements such as water. Dissolve or pulverize and disperse in a solvent, adjust the pH while stirring, create and recover a spherical precursor, and dry it as necessary. Then, LiOH, Li ₂ CO ₃ , LiNO _{3 and} other Li A method of obtaining an active material by adding a source and baking at a high temperature, transition metal raw materials such as transition metal nitrates, sulfates, hydroxides and oxides, and if necessary, raw materials of other elements in a solvent such as water Dissolve or pulverize and disperse in the powder and dry mold it with a spray drier to make a spherical or oval spherical precursor. To this, add a Li source such as LiOH, Li ₂ CO ₃ , or LiNO ₃ and calcinate at a high temperature. How to get active material Transition metal source materials such as transition metal nitrates, sulfates, hydroxides and oxides, Li sources such as LiOH, Li ₂ CO ₃ and LiNO ₃ , and source materials of other elements as necessary, such as water Examples thereof include a method of dissolving or pulverizing and dispersing in a solvent and drying and molding it with a spray dryer or the like to obtain a spherical or elliptical precursor, which is fired at a high temperature to obtain an active material.

[[Composition of positive electrode]]
Below, the structure of the positive electrode used for this invention is described.
[[[Electrode structure and fabrication method]]]
The positive electrode for a non-aqueous electrolyte secondary battery of the present invention is produced by forming a positive electrode active material layer containing positive electrode active material particles and a binder on a current collector. Manufacture of the positive electrode using a positive electrode active material can be performed by a conventional method. That is, a positive electrode active material and a binder, and if necessary, a conductive material and a thickener mixed in a dry form are pressure-bonded to a positive electrode current collector, or these materials are liquid media A positive electrode can be obtained by forming a positive electrode active material layer on the current collector by applying it to a positive electrode current collector and drying it as a slurry by dissolving or dispersing in a slurry.

  Content in the positive electrode active material layer of the positive electrode active material used for this invention is 10 mass% or more normally, Preferably it is 30 mass% or more, Most preferably, it is 50 mass% or more. Moreover, an upper limit is 99.9 mass% or less normally, Preferably it is 99 mass% or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient. In addition, the positive electrode active material in this invention may be used individually by 1 type, and may use together 2 or more types of a different composition or different powder physical properties by arbitrary combinations and ratios.

  The positive electrode active material layer obtained by coating and drying is preferably consolidated by a hand press, a roller press or the like in order to increase the packing density of the positive electrode active material.

The electrode structure when the positive electrode active material layer is converted into an electrode is not particularly limited, but the density of the positive electrode active material layer present on the current collector is preferably 1 g / cm ³ or more, more preferably 1 as the lower limit. .5g / cm ^3, and even more preferably at 2 g / cm ³ or more, upper limit is preferably 4g / cm ³ or less, more preferably 3.5 g / cm ³ or less, and more preferably at 3 g / cm ³ or less in the range . If it exceeds this range, the permeability of the electrolyte solution to the vicinity of the current collector / active material interface may decrease, and the charge / discharge characteristics at a high current density may decrease. On the other hand, if it is lower, the conductivity between the active materials may be reduced, and the battery resistance may be increased.

[[[Conductive material]]]
A known conductive material can be arbitrarily used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite (graphite); carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  The conductive material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the positive electrode active material layer, and the upper limit is usually 50% by mass or less, preferably It is used so as to contain 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[[[Binder]]]
The binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in electrode production may be used. Resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine rubber, isoprene rubber , Rubber polymers such as butadiene rubber and ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / butadiene / Ethylene copolymer, styrene Thermoplastic elastomeric polymer such as isoprene / styrene block copolymer or hydrogenated product thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer Soft resinous polymers such as polymers; Fluoropolymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers; alkali metal ions (especially lithium ions) And a polymer composition having ion conductivity. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  The ratio of the binder in the positive electrode active material layer is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and the upper limit is usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and most preferably 10% by mass or less. When the ratio of the binder is too low, the positive electrode active material cannot be sufficiently retained and the positive electrode has insufficient mechanical strength, which may deteriorate battery performance such as cycle characteristics. On the other hand, if it is too high, battery capacity and conductivity may be reduced.

[[[Liquid medium]]]
The liquid medium for forming the slurry may be any solvent that can dissolve or disperse the positive electrode active material powder, the conductive material, the binder, and the thickener used as necessary. There is no particular limitation on the type, and either an aqueous solvent or an organic solvent may be used.

  Examples of the aqueous medium include water, a mixed medium of alcohol and water, and the like. Examples of the organic medium include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone. Esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N, N-dimethylaminopropylamine; ethers such as diethyl ether and tetrahydrofuran (THF); N-methylpyrrolidone (NMP) and dimethylformamide Amides such as dimethylacetamide; aprotic polar solvents such as hexamethylphosphalamide and dimethylsulfoxide.

  In particular, when an aqueous medium is used, it is preferable to make a slurry using a thickener and a latex such as styrene-butadiene rubber (SBR). A thickener is usually used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When a thickener is further added, the ratio of the thickener to the active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, As an upper limit, it is 5 mass% or less normally, Preferably it is 3 mass% or less, More preferably, it is the range of 2 mass% or less. Below this range, applicability may be significantly reduced. If it exceeds, the ratio of the active material in the positive electrode active material layer may decrease, and there may be a problem that the capacity of the battery decreases and a problem that the resistance between the positive electrode active materials increases.

[[[Current collector]]]
There is no restriction | limiting in particular as a material of a positive electrode electrical power collector, A well-known thing can be used arbitrarily. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, are preferred.

  Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, foam metal, etc. A carbon thin film, a carbon cylinder, etc. are mentioned. Of these, metal thin films are preferred. In addition, you may form a thin film suitably in mesh shape. The thickness of the thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, the strength required for the current collector may be insufficient. Conversely, if the thin film is thicker than this range, the handleability may be impaired.

  The thickness ratio between the current collector and the positive electrode active material layer is not particularly limited, but (active material layer thickness on one side immediately before electrolyte injection) / (thickness of current collector) is 150 or less. Is preferably 20 or less, more preferably 10 or less, and the lower limit is preferably 0.1 or more, particularly preferably 0.4 or more, more preferably 1 or more. Above this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. Below this range, the volume ratio of the current collector to the positive electrode active material increases and the battery capacity may decrease.

[[[Electrode area]]]
From the viewpoint of increasing the stability at high output and high temperature, the area of the positive electrode active material layer is preferably larger than the outer surface area of the battery outer case. Specifically, the total electrode area of the positive electrode with respect to the surface area of the exterior of the secondary battery is preferably 20 times or more, and more preferably 40 times or more. The outer surface area of the outer case, in the case of a bottomed square shape, means the total area obtained by calculation from the vertical, horizontal, and thickness dimensions of the case part filled with the power generation element excluding the protruding part of the terminal. . In the case of a bottomed cylindrical shape, the geometric surface area approximates the case portion filled with the power generation element excluding the protruding portion of the terminal as a cylinder. The total electrode area of the positive electrode is the geometric surface area of the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in the structure in which the positive electrode mixture layer is formed on both sides via the current collector foil. , The sum of the areas where each surface is calculated separately.

[[[Discharge capacity]]]
When the non-aqueous electrolyte of the present invention is used, the electric capacity (electric capacity when the battery is discharged from the fully charged state to the discharged state) of the battery element housed in one battery exterior of the secondary battery is 3 The ampere hour (Ah) or more is particularly preferable because the effect of improving the low temperature discharge characteristics is increased. Therefore, the positive electrode plate is preferably designed so that the discharge capacity is fully charged and is 3 ampere hours (Ah) or more and 20 Ah or less, and more preferably 4 Ah or more and 10 Ah or less. If it is less than 3 Ah, the voltage drop due to the electrode reaction resistance becomes large when taking out a large current, and the power efficiency may deteriorate. In this case, the low-temperature discharge characteristics are also deteriorated, and the improvement of the low-temperature discharge characteristics and output characteristics obtained when using the non-aqueous electrolyte solution of the present invention containing a specific compound in a specific non-aqueous solvent is insufficient. There is.

  On the other hand, if it is greater than 20 Ah, the electrode reaction resistance is reduced and the power efficiency is improved, but the temperature distribution due to the internal heat generation of the battery during pulse charge / discharge is large, the durability of repeated charge / discharge is inferior, and overcharge and Due to sudden heat generation during abnormalities such as an internal short circuit, the heat dissipation efficiency also deteriorates, causing the internal pressure to rise and the gas release valve to operate (valve operation), and the battery contents to blow out to the outside (rupture) May increase the probability.

[[[Positive electrode plate thickness]]]
The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer obtained by subtracting the metal foil thickness of the core material is relative to one side of the current collector. The lower limit is preferably 10 μm or more, more preferably 20 μm or more, and the upper limit is preferably 200 μm or less, more preferably 100 μm or less.

[Negative electrode]
The negative electrode used for the non-aqueous electrolyte secondary battery of the present invention will be described below.
[[Negative electrode active material]]
The negative electrode active material used for the negative electrode is described below.

[[[composition]]]
The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. Carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium simple substance And lithium alloys such as lithium aluminum alloy and metals that can form alloys with lithium such as Sn and Si. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. Of these, carbonaceous materials or lithium composite oxides are preferably used from the viewpoint of safety. The metal composite oxide is not particularly limited as long as it can occlude and release lithium, but preferably contains titanium and / or lithium as a constituent component from the viewpoint of high current density charge / discharge characteristics.

As a carbonaceous material,
(1) natural graphite,
(2) Artificial carbonaceous material and artificial graphite material; carbonaceous material [for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or those obtained by oxidizing these pitches, needle coke, pitch Coke and carbon materials partially graphitized, furnace black, acetylene black, pyrolysis products of organic substances such as pitch-based carbon fibers, carbonized organic substances (for example, coal tar pitch from soft pitch to hard pitch, or dry distillation Coal heavy oil such as liquefied oil, normal pressure residual oil, direct current heavy oil of reduced pressure residual oil, cracked petroleum heavy oil such as ethylene tar produced during thermal decomposition of crude oil, naphtha, etc., acenaphthylene, Aromatic hydrocarbons such as decacyclene, anthracene, phenanthrene, N-ring compounds such as phenazine and acridine, thiophene, bithiophene S-ring compound, polyphenylene such as biphenyl and terphenyl, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized product of these, organic polymer such as nitrogen-containing polyacrylonitrile, polypyrrole, sulfur-containing polythiophene, Organic polymers such as polystyrene, natural polymers such as polysaccharides represented by cellulose, lignin, mannan, polygalacturonic acid, chitosan, saccharose, thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, furfuryl alcohol resin, phenol -Thermosetting resins such as formaldehyde resin and imide resin) and their carbides or carbonizable organic substances in low molecular organic solvents such as benzene, toluene, xylene, quinoline, n-hexane, and the like Heat-treated carbon material one or more times in the range of carbide] from 400 3200 ° C.,
(3) a carbon material in which the negative electrode active material layer is composed of at least two kinds of carbonaceous materials having different crystallinity and / or has an interface in contact with the different crystalline carbonaceous materials,
(4) a carbon material in which the negative electrode active material layer is composed of at least two kinds of carbonaceous materials having different orientations and / or has an interface in contact with the carbonaceous materials having different orientations;
Is preferably a good balance between initial irreversible capacity and high current density charge / discharge characteristics.

[[Negative electrode configuration, physical properties, preparation method]]
Regarding the properties of the carbonaceous material, the negative electrode containing the carbonaceous material, the electrodeification method, the current collector, and the lithium ion secondary battery, any one or more of (1) to (19) shown below It is desirable to satisfy

(1) X-ray parameters For carbonaceous materials, the d value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method is preferably 0.335 nm or more, and the upper limit is usually It is desired that the thickness is 0.360 nm or less, preferably 0.350 nm or less, and more preferably 0.345 nm or less. Further, the crystallite size (Lc) of the carbonaceous material obtained by X-ray diffraction by the Gakushin method is preferably 1.0 nm or more, and more preferably 1.5 nm or more.

(2) Ash content The ash content in the carbonaceous material is 1% by mass or less, particularly 0.5% by mass or less, especially 0.1% by mass or less, and the lower limit is 1 ppm or more with respect to the total mass of the carbonaceous material. It is preferable that When the above range is exceeded, deterioration of the battery performance due to the reaction with the electrolyte during charging / discharging may not be negligible. Below this range, the manufacturing process requires a lot of time, energy and equipment for preventing contamination, which may increase costs.

(3) Volume-based average particle diameter The volume-based average particle diameter of the carbonaceous material is usually 1 μm or more, preferably 3 μm or more, more preferably a volume-based average particle diameter (median diameter) determined by a laser diffraction / scattering method. Is 5 μm or more, more preferably 7 μm or more. Moreover, an upper limit is 100 micrometers or less normally, Preferably it is 50 micrometers or less, More preferably, it is 40 micrometers or less, More preferably, it is 30 micrometers or less, Most preferably, it is 25 micrometers or less. If it falls below the above range, the irreversible capacity may increase, leading to loss of the initial battery capacity. On the other hand, when the above range is exceeded, when an electrode is produced by coating, a non-uniform coating surface tends to be formed, which may be undesirable in the battery production process.

  In the present invention, the volume-based average particle size is determined by dispersing carbon powder in a 0.2% by mass aqueous solution (about 10 mL) of polyoxyethylene (20) sorbitan monolaurate, which is a surfactant, and laser diffraction / scattering type particle size. It is defined by the median diameter measured using a distribution meter (for example, LA-700 manufactured by Horiba, Ltd.).

(4) Raman R value, Raman half-value width The Raman R value of the carbonaceous material measured using the argon ion laser Raman spectrum method is usually 0.01 or more, preferably 0.03 or more, more preferably 0.1 or more. The upper limit is 1.5 or less, preferably 1.2 or less, more preferably 1 or less, and still more preferably 0.5 or less. When the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge / discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

Further, the Raman half-value width around 1580 cm ^{−1 of the} carbonaceous material used in the present invention is not particularly limited, but is usually 10 cm ⁻¹ or more, preferably 15 cm ⁻¹ or more, and the upper limit is usually 100 cm ⁻¹ or less, preferably The range is 80 cm ⁻¹ or less, more preferably 60 cm ⁻¹ or less, and still more preferably 40 cm ⁻¹ or less. When the Raman half width is less than this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge and discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

The Raman spectrum is measured using a Raman spectrometer (for example, a Raman spectrometer manufactured by JASCO Corporation), the sample is naturally dropped into the measurement cell and filled, and the sample surface in the cell is irradiated with an argon ion laser beam. The cell is rotated in a plane perpendicular to the laser beam. The obtained Raman spectrum, the intensity I _A of the peak P _A in the vicinity of 1580 cm ^-1, and measuring the intensity I _B of a peak P _B in the vicinity of 1360 cm ^-1, the intensity ratio R (R = I _B / I _A ) Is calculated and defined as the Raman R value of the carbonaceous material. Further, the half width of the peak P _A near 1580 cm ^{−1 of} the obtained Raman spectrum is measured, and this is defined as the Raman half width of the carbonaceous material.

Here, the Raman spectrum measurement conditions are as follows.
Argon ion laser wavelength: 514.5nm
・ Laser power on the sample: 15-25mW
・ Resolution: 10-20cm ^-1
Measurement range: 1100 cm ^{−1 to} 1730 cm ⁻¹
・ Raman R value, Raman half width analysis: Background processing ・ Smoothing processing: Simple average, 5 points of convolution

(5) BET specific surface area The specific surface area of the carbonaceous material used in the present invention measured by using the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1 m ^2. / G or more, more preferably 1.5 m ² / g or more. The upper limit is usually 100 m ² / g or less, preferably 25 m ² / g or less, more preferably 15 m ² / g or less, and still more preferably 10 m ² / g or less. When the value of the specific surface area is less than this range, the acceptability of lithium is likely to deteriorate during charging when used as a negative electrode material, and lithium may easily precipitate on the electrode surface. On the other hand, when it exceeds this range, when used as a negative electrode material, the reactivity with the electrolyte increases, gas generation tends to increase, and a preferable battery may not be obtained.

  The specific surface area according to the BET method is determined by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Riken Okura), preliminarily drying the sample at 350 ° C. for 15 minutes under a nitrogen flow, and then comparing the nitrogen relative to the atmospheric pressure. A value measured by a nitrogen adsorption BET one-point method using a gas flow method is used, using a nitrogen helium mixed gas that is accurately adjusted so that the pressure value becomes 0.3.

(6) Pore size distribution The pore size distribution of the carbonaceous material used in the present invention is determined by mercury porosimetry (mercury intrusion method), and the pore diameter is within a particle corresponding to 0.01 μm or more and 1 μm or less. The amount of voids, irregularities due to particle surface steps, contact surfaces between particles, etc. is 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and the upper limit is 0.6 mL. / G or less, preferably 0.4 mL / g or less, more preferably 0.3 mL / g or less. If it exceeds this range, a large amount of binder may be required when forming an electrode plate. If it is less than the range, the high current density charge / discharge characteristics may be deteriorated, and the effect of relaxing the expansion / contraction of the electrode during charge / discharge may not be obtained.

  Further, the total pore volume corresponding to the pore diameter in the range of 0.01 μm to 100 μm is preferably 0.1 mL / g or more, more preferably 0.25 mL / g or more, still more preferably 0.4 mL / g or more, The upper limit is 10 mL / g or less, preferably 5 mL / g or less, more preferably 2 mL / g or less. If it exceeds this range, a large amount of binder may be required when forming an electrode plate. If it is less than that, it may not be possible to obtain the effect of dispersing the thickener or the binder during the electrode plate formation.

  The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, and the upper limit is usually 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. It is. Beyond this range, a large amount of binder may be required. If it is less, the high current density charge / discharge characteristics may deteriorate.

  As an apparatus for mercury porosimetry, a mercury porosimeter (Autopore 9520: manufactured by Micromeritex Corporation) was used. About 0.2 g of a sample was sealed in a powder cell and pretreated by degassing for 10 minutes at room temperature under vacuum (50 μmHg or less). Subsequently, the pressure was reduced to 4 psia (about 28 kPa), mercury was introduced, the pressure was increased stepwise from 4 psia (about 28 kPa) to 40000 psia (about 280 MPa), and then the pressure was reduced to 25 psia (about 170 kPa). The number of steps at the time of pressure increase was 80 points or more, and the mercury intrusion amount was measured after an equilibration time of 10 seconds in each step. The pore size distribution was calculated from the mercury intrusion curve thus obtained using the Washburn equation. The surface tension (γ) of mercury was 485 dyne / cm, and the contact angle (ψ) was 140 °. As the average pore diameter, the pore diameter when the cumulative pore volume was 50% was used.

(7) Circularity Using circularity as the degree of sphericity of the carbonaceous material, the circularity of particles having a particle size in the range of 3 to 40 μm is preferably 0.1 or more, particularly preferably 0.5 or more. Preferably it is 0.8 or more, more preferably 0.85 or more, and most preferably 0.9 or more. High circularity is preferable because high current density charge / discharge characteristics are improved. The circularity is defined by the following formula. When the circularity is 1, a theoretical sphere is obtained.
Circularity = (perimeter of equivalent circle having the same area as the particle projection shape) / (actual circumference of particle projection shape)

  As the value of the circularity, for example, a flow type particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.) is used, and about 0.2 g of a sample is mixed with polyoxyethylene (20) sorbitan monolaurate as a surfactant. Particles having a detection range of 0.6 to 400 μm and a particle size in the range of 3 to 40 μm after being dispersed in a 0.2 mass% aqueous solution (about 50 mL) and irradiated with an ultrasonic wave of 28 kHz for 1 minute at an output of 60 W Use the value measured for.

  The method for improving the degree of circularity is not particularly limited, but a spheroidized sphere is preferable because the shape of the interparticle void when the electrode body is formed is preferable. Examples of spheroidizing treatment include a method of mechanically approximating a sphere by applying a shearing force and a compressive force, a mechanical / physical processing method of granulating a plurality of fine particles by an adhesive force possessed by a binder or particles, etc. Is mentioned.

(8) True density The true density of the carbonaceous material is usually 1.4 g / cm ³ or more, preferably 1.6 g / cm ³ or more, more preferably 1.8 g / cm ³ or more, and further preferably 2 g / cm ^3. The upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase. In the present invention, the true density is defined by a value measured by a liquid phase substitution method (pycnometer method) using butanol.

(9) Tap density The tap density of the carbonaceous material is usually 0.1 g / cm ³ or more, preferably 0.5 g / cm ³ or more, more preferably 0.7 g / cm ³ or more, and particularly preferably 1 g / cm ^3. It is desirable that it is the above. The upper limit is preferably 2 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and particularly preferably 1.6 g / cm ³ or less. When the tap density is below this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if it exceeds this range, there are too few voids between the particles in the electrode, it becomes difficult to ensure conductivity between the particles, and it may be difficult to obtain preferable battery characteristics. The tap density is measured and defined by the same method as that described in the section of the positive electrode active material.

(10) Orientation ratio The orientation ratio of the carbonaceous material is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. Below this range, the high-density charge / discharge characteristics may deteriorate.

The orientation ratio is measured by X-ray diffraction after pressure-molding the sample. X-ray diffraction is performed by setting a molded body obtained by filling 0.47 g of a sample into a molding machine having a diameter of 17 mm and compressing it at 600 kgf / cm ^{2 so} that it is flush with the surface of the sample holder for measurement. Measure. A ratio represented by (110) diffraction peak intensity / (004) diffraction peak intensity is calculated from the (110) diffraction and (004) diffraction peak intensities of the obtained carbon, and defined as the orientation ratio of the active material.

The X-ray diffraction measurement conditions here are as follows. “2θ” indicates a diffraction angle.
・ Target: Cu (Kα ray) graphite monochromator ・ Slit:
Divergence slit = 0.5 degree, light receiving slit = 0.15 mm, scattering slit = 0.5 degree. Measurement range and step angle / measurement time:
(110) plane: 75 degrees ≦ 2θ ≦ 80 degrees 1 degree / 60 seconds (004) plane: 52 degrees ≦ 2θ ≦ 57 degrees 1 degree / 60 seconds

(11) Aspect ratio (powder)
The aspect ratio is theoretically 1 or more, and the upper limit is 10 or less, preferably 8 or less, more preferably 5 or less. If the upper limit is exceeded, streaking may occur when forming an electrode plate, a uniform coated surface may not be obtained, and high current density charge / discharge characteristics may deteriorate.

  The aspect ratio is expressed as A / B when the longest diameter A of the carbonaceous material particles when observed three-dimensionally and the shortest diameter B orthogonal to the carbonaceous material particles. The carbon particles are observed with a scanning electron microscope capable of magnifying observation. Arbitrary 50 graphite particles fixed on the end face of a metal plate having a thickness of 50 μm or less are selected, and the stage on which the sample is fixed is rotated and tilted, and A and B are measured. Find the average value.

(12) Sub-material mixing “Sub-material mixing” means that two or more carbonaceous materials having different properties are contained in the negative electrode and / or the negative electrode active material. The properties described here include one or more of X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, circularity, and ash content. Show the characteristics. Particularly preferred embodiments include that the volume-based particle size distribution is not symmetrical when the median diameter is centered, that two or more carbonaceous materials having different Raman R values are contained, and the X-ray parameters are It is different.

  As an example of the effect, carbonaceous material such as natural graphite, graphite such as artificial graphite, carbon black such as acetylene black, amorphous carbon such as needle coke, etc. is contained as a conductive material, so that electric resistance is increased. It can be reduced. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When added as a conductive material, it is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 45% by mass or less, preferably 40% by mass. It is a range. Below this range, the effect of improving conductivity may be difficult to obtain. If it exceeds, the initial irreversible capacity may increase.

(13) Electrode production The electrode may be produced by a conventional method. For example, it is formed by adding a binder, a solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to a negative electrode active material to form a slurry, which is applied to a current collector, dried and then pressed. Can do. The thickness of the negative electrode active material layer per side at the stage immediately before the step of injecting the electrolyte into the battery is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is usually 150 μm or less, preferably 120 μm. Hereinafter, it is more preferably 100 μm or less. If it exceeds this range, the electrolyte solution hardly penetrates to the vicinity of the current collector interface, and thus the high current density charge / discharge characteristics may be deteriorated. On the other hand, below this range, the volume ratio of the current collector to the negative electrode active material increases, and the battery capacity may decrease. Further, the negative electrode active material may be roll-formed to form a sheet electrode, or may be formed into a pellet electrode by compression molding.

(14) Current collector Any known current collector can be used. Examples of the current collector for the negative electrode include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Of these, copper is particularly preferable from the viewpoint of ease of processing and cost. When the current collector is a metal material, examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among them, a metal thin film is preferable, a copper foil is more preferable, and a rolled copper foil by a rolling method and an electrolytic copper foil by an electrolytic method are more preferable, and both can be used as a current collector. When the thickness of the copper foil is less than 25 μm, a copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) having higher strength than pure copper can be used.

  A current collector made of a copper foil produced by a rolling method is suitable for use in a small cylindrical battery because the copper crystals are arranged in the rolling direction so that the negative electrode is hard to crack even if it is rounded sharply or rounded at an acute angle. be able to. For example, an electrolytic copper foil is prepared by immersing a metal drum in an electrolytic solution in which copper ions are dissolved, and flowing current while rotating the copper drum, thereby depositing copper on the surface of the drum and peeling it off. It is obtained. Copper may be deposited on the surface of the rolled copper foil by an electrolytic method. One side or both sides of the copper foil may be subjected to a roughening treatment or a surface treatment (for example, a chromate treatment having a thickness of about several nm to 1 μm, a base treatment such as Ti).

The following physical properties are desired for the current collector substrate.
(1) Average surface roughness (Ra)
The average surface roughness (Ra) of the active material thin film forming surface of the current collector substrate defined by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.05 μm or more, preferably 0.1 μm or more, particularly The upper limit is usually 1.5 μm or less, preferably 1.3 μm or less, particularly preferably 1.0 μm or less. By setting the average surface roughness (Ra) of the current collector substrate within the range between the lower limit and the upper limit described above, good charge / discharge cycle characteristics can be expected. By setting it to the above lower limit or more, the area of the interface with the active material thin film is increased, and the adhesion with the active material thin film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, but those having an average surface roughness (Ra) exceeding 1.5 μm are generally difficult to obtain as foils having a practical thickness as a battery. 1.5 μm or less is preferable.

(2) Tensile strength The tensile strength of the current collector substrate is not particularly limited, but is usually 100 N / mm ² or more, preferably 250 N / mm ² or more, more preferably 400 N / mm ² or more, and particularly preferably 500 N / mm ^2. That's it. The tensile strength is obtained by dividing the maximum tensile force required until the test piece breaks by the cross-sectional area of the test piece. The tensile strength in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high tensile strength, cracking of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained.

(3) 0.2% proof stress of 0.2% proof stress current collector substrate is not particularly limited, normally 30 N / mm ² or more, preferably 150 N / mm ² or more, particularly preferably 300N / mm ² or more . The 0.2% proof stress is the magnitude of the load necessary to give a plastic (permanent) strain of 0.2%. It means that The 0.2% proof stress is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high 0.2% proof stress, plastic deformation of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained. it can.

  Although the thickness of a metal thin film is arbitrary, it is 1 micrometer or more normally, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more. Moreover, an upper limit is 1 mm or less normally, Preferably it is 100 micrometers or less, More preferably, it is 30 micrometers or less. If the thickness is less than 1 μm, the strength may be reduced, and application may be difficult. On the other hand, when the thickness exceeds 100 μm, the shape of the electrode such as winding may be deformed. The metal thin film may be mesh.

(15) Ratio of current collector and active material layer thickness The ratio of current collector and active material layer thickness is not particularly limited, but (active material layer thickness on one side immediately before electrolyte injection) / The (current collector thickness) is preferably 150 or less, particularly preferably 20 or less, more preferably 10 or less, and the lower limit is preferably 0.1 or more, particularly preferably 0.4 or more, more preferably. Is a range of 1 or more. Above this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. Below this range, the volume ratio of the current collector to the negative electrode active material increases and the battery capacity may decrease.

(16) Electrode density The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the active material present on the current collector is preferably 1 g / cm ³ or more, more preferably 1 .2g / cm ^3, and even more preferably at 1.3 g / cm ³ or more, 2 g / cm ^3, preferably up 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, more preferably Is in the range of 1.7 g / cm ³ or less. If it exceeds this range, the active material particles are destroyed, which may lead to an increase in initial irreversible capacity and deterioration of high current density charge / discharge characteristics due to a decrease in the permeability of the electrolyte solution near the current collector / active material interface. On the other hand, if it is lower, the conductivity between the active materials is lowered, the battery resistance is increased, and the capacity per unit volume may be lowered.

(17) Binder The binder for binding the active material is not particularly limited as long as it is a material that is stable with respect to the electrolyte and the solvent used during electrode production. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluorine rubber, NBR ( Acrylonitrile-butadiene rubber), rubber-like polymers such as ethylene-propylene rubber; styrene / butadiene / styrene block copolymers or hydrogenated products thereof; EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / Thermoplastic elastomeric polymer such as butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer or hydrogenated product thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinegar Soft resinous polymers such as vinyl copolymers and propylene / α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene / ethylene copolymers Molecule: a polymer composition having ion conductivity of alkali metal ions (particularly lithium ions), and the like. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

  The solvent for forming the slurry is not particularly limited as long as it is a solvent that can dissolve or disperse the active material, the binder, and the thickener and conductive material used as necessary. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, alcohol and the like, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N , N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. .

  In particular, when an aqueous solvent is used, a dispersant or the like is added to the thickener, and a slurry such as SBR is used to make a slurry. In addition, these may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

  The ratio of the binder to the active material is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is usually 20% by mass or less, preferably Is 15% by mass or less, more preferably 10% by mass or less, and still more preferably 8% by mass or less. If it exceeds this range, the binder ratio that does not contribute to the battery capacity may increase, leading to a decrease in battery capacity. On the other hand, if it is lower, the strength of the negative electrode may be reduced. In particular, when the main component contains a rubbery polymer typified by SBR, the ratio of the binder to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.8%. The upper limit is 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. Further, when the main component contains a fluorine-based polymer typified by polyvinylidene fluoride, the ratio to the active material is 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more. As an upper limit, it is 15 mass% or less normally, Preferably it is 10 mass% or less, More preferably, it is the range of 8 mass% or less.

  A thickener is usually used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

  When a thickener is further added, the ratio of the thickener to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more. Is 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. Below this range, applicability may be significantly reduced. If it exceeds the upper limit, the ratio of the active material in the negative electrode active material layer may be reduced, resulting in a problem that the capacity of the battery is reduced and a problem that the resistance between the negative electrode active materials is increased.

(18) Electrode orientation ratio The electrode orientation ratio is preferably 0.001 or more, particularly preferably 0.005 or more, more preferably 0.01 or more, and the upper limit is 0.67 or less, which is a theoretical value. Below this range, the high-density charge / discharge characteristics may deteriorate.

  The measurement of the electrode plate orientation ratio is as follows. About the negative electrode after pressing to the target density, the active material orientation ratio of the electrode is measured by X-ray diffraction. The specific method is not particularly limited, but as a standard method, peak separation is performed by fitting the peaks of (110) and (004) diffraction of carbon by X-ray diffraction using asymmetric Pearson VII as a profile function. The integrated intensities of the peaks of (110) diffraction and (004) diffraction are calculated. From the obtained integrated intensity, a ratio represented by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated. The electrode active material orientation ratio calculated by this measurement is defined as the electrode plate orientation ratio.

The X-ray diffraction measurement conditions here are as follows. “2θ” indicates a diffraction angle.
-Target: Cu (Kα ray) graphite monochromator-Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree-Measurement range and step angle / measurement time:
(110) plane: 76.5 degrees ≦ 2θ ≦ 78.5 degrees 0.01 degrees / 3 seconds (004) plane: 53.5 degrees ≦ 2θ ≦ 56.0 degrees 0.01 degrees / 3 seconds Sample preparation: Fix the electrode to the glass plate with double-sided tape with a thickness of 0.1 mm

(19) Impedance The resistance of the negative electrode when charged to 60% of the nominal capacity from the discharged state is preferably 100Ω or less, particularly preferably 50Ω or less, more preferably 20Ω or less, and / or the double layer capacity is 1 × 10 ^−6. F or more is preferable, particularly preferably 1 × 10 ⁻⁵ F or more, and more preferably 1 × 10 ⁻⁴ F or more. Within this range, the output characteristics are good and preferable.

The resistance and double layer capacity of the negative electrode are measured by the following procedure. The lithium-ion secondary battery to be measured is charged at a current value that can be charged for 5 hours in a nominal capacity, then maintained in a state where it is not charged / discharged for 20 minutes, and then discharged at a current value that can be discharged in 1 hour for a nominal capacity. The capacity when the capacity is 80% or more of the nominal capacity is used. About the lithium ion secondary battery of the above-mentioned discharge state, it charges to 60% of a nominal capacity with the electric current value which can charge a nominal capacity in 5 hours, Immediately transfers a lithium ion secondary battery in the glove box under argon gas atmosphere. Here, the lithium ion secondary battery is quickly disassembled and taken out in a state where the negative electrode does not discharge or short-circuit, and if it is a double-sided coated electrode, the electrode active material on one side is peeled off without damaging the electrode active material on the other side, Two electrodes are punched to 12.5 mmφ, and are opposed to each other so that the active material surface does not shift through a separator. 60 μL of the electrolytic solution used in the battery is dropped and adhered between the separator and both negative electrodes, and kept in a state where it is not in contact with the outside air, the current collectors of both negative electrodes are made conductive, and the AC impedance method is performed. The measurement is performed at a temperature of 25 ° C., and the complex impedance is measured in a frequency band of 10 ⁻² to 10 ⁵ Hz. The surface resistance (R) is obtained by approximating the arc of the negative resistance component of the obtained Cole-Cole plot with a semicircle. And double layer capacity | capacitance (Cdl) is calculated | required.

  The area of the negative electrode plate is not particularly limited, but is designed to be slightly larger than the opposing positive electrode plate so that the positive electrode plate does not protrude from the negative electrode plate. From the viewpoint of suppressing the life of a cycle in which charge and discharge are repeated and deterioration due to high temperature storage, it is preferable that the area be as close to the positive electrode as possible, since the ratio of electrodes that work more uniformly and effectively is increased and the characteristics are improved. In particular, when the electrode is used at a large current, the design of the electrode area is important.

  The thickness of the negative electrode plate is designed according to the positive electrode plate to be used, and is not particularly limited. Preferably it is 20 micrometers or more, More preferably, it is 30 micrometers or more, and an upper limit is 150 micrometers or less, Preferably it is 120 micrometers or less, More preferably, it is 100 micrometers or less.

[Separator]
The separator used in the present invention has a predetermined mechanical strength that electrically insulates both electrodes, has a high ion permeability, and has resistance to oxidation on the side in contact with the positive electrode and reduction on the negative electrode side. There is no particular limitation as long as it has both. As a material for the separator having such required characteristics, a resin, an inorganic material, glass fiber, or the like is used. As the resin, olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon and the like are used. Specifically, it is preferable to select from materials that are stable with respect to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene.

  As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used, and those having a particle shape or fiber shape are used. As the form, a thin film shape such as a non-woven fabric, a woven fabric, or a microporous film is used. In the thin film shape, those having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the independent thin film shape, a separator formed by forming a composite porous layer containing the inorganic particles on the surface layer of the positive electrode and / or the negative electrode using a resin binder can be used. For example, a porous layer may be formed on both surfaces of the positive electrode using alumina particles having a 90% particle size of less than 1 μm as a binder.

[Electrode group]
The electrode group has a laminated structure in which the positive electrode plate and the negative electrode plate are interposed via the separator, and a structure in which the positive electrode plate and the negative electrode plate are wound in a spiral shape via the separator. Either may be used.

  The ratio of the volume of the electrode group to the battery internal volume (hereinafter referred to as electrode group occupancy) is preferably 40% to 90%, and more preferably 50% to 80%. If the electrode group occupancy is less than 40%, the battery capacity is small, and if it is 90% or more, the void space is small, the member expands when the battery becomes high temperature, and the vapor pressure of the liquid component of the electrolyte is high. As a result, the internal pressure rises, and various characteristics such as charge / discharge repetition performance and high-temperature storage as a battery are deteriorated. Further, a gas release valve that releases the internal pressure to the outside may operate.

[Current collection structure]
The current collecting structure is not particularly limited, but in order to more effectively realize the low temperature discharge characteristics by the nonaqueous electrolyte secondary battery of the present invention, a structure that reduces the resistance of the wiring part and the joint part. It is necessary to. When such internal resistance is small, the effect of using the non-aqueous electrolyte solution for secondary batteries of the present invention is exhibited particularly well.

  In the case where the electrode group has the laminated structure described above, a structure formed by bundling the metal core portions of the electrode layers and welding them to the terminals is preferably used. When the area of one electrode increases, the internal resistance increases. Therefore, it is also preferable to provide a plurality of terminals in the electrode to reduce the resistance. When the electrode group has the winding structure described above, the internal resistance can be lowered by providing a plurality of lead structures for the positive electrode and the negative electrode, respectively, and bundling the terminals.

  By optimizing the above structure, the internal resistance can be made as small as possible. In a battery used at a large current, the impedance measured by the 10 kHz AC method (hereinafter abbreviated as “DC resistance component”) is preferably 10 milliohms (mΩ) or less, and the DC resistance component is 5 milliohms (mΩ). It is more preferable to make it below. When the direct current resistance component is less than 0.1 milliohm, the high output characteristics are improved, but the ratio of the current collecting structure used increases and the battery capacity may decrease.

  The non-aqueous electrolyte of the present invention is effective in reducing reaction resistance related to lithium insertion / extraction with respect to the electrode active material, which is considered to be a factor that can realize good low-temperature discharge characteristics. However, it has been found that in a battery having a DC resistance larger than 10 milliohms (mΩ), the effect of reducing the reaction resistance cannot be reflected in the low-temperature discharge characteristics by being inhibited by the DC resistance. This can be improved by using a battery having a small DC resistance component, and the effect of the non-aqueous electrolyte solution of the present invention can be sufficiently exhibited.

  Further, from the viewpoint of drawing out the effect of the non-aqueous electrolyte and producing a battery having high low-temperature discharge characteristics, this requirement and the electric capacity of the battery element housed in one battery exterior of the secondary battery described above. It is particularly preferable to satisfy the requirement that (the electric capacity when the battery is discharged from the fully charged state to the discharged state) is 3 ampere hours (Ah) or more at the same time.

[Exterior case]
The material of the outer case is not particularly limited as long as it is a substance that is stable with respect to the non-aqueous electrolyte used. Specifically, a nickel-plated steel plate, stainless steel, aluminum, an aluminum alloy, a metal such as a magnesium alloy, or a laminated film (laminate film) of a resin and an aluminum foil is used. From the viewpoint of weight reduction, an aluminum or aluminum alloy metal or a laminate film is preferably used.

  In the exterior case using the above metals, a laser-sealed, resistance-welded, ultrasonic welding is used to weld the metals together to form a sealed sealed structure, or a caulking structure using the above-mentioned metals via a resin gasket To do.

  Examples of the outer case using the laminate film include those having a sealed and sealed structure by heat-sealing resin layers. In order to improve the sealing performance, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when a resin layer is heat-sealed through a current collecting terminal to form a sealed structure, a metal and a resin are joined, so that a resin having a polar group or a modified group having a polar group introduced as an intervening resin is used. Resins are preferably used.

[Protective element]
As the above-mentioned protective element, PTC (Positive Temperature Coefficient), thermal fuse, thermistor, whose resistance increases when abnormal heat generation or excessive current flows, current that flows in the circuit due to sudden rise in battery internal pressure or internal temperature during abnormal heat generation For example, a valve (current cutoff valve) that shuts off the current is mentioned. It is preferable to select a protective element that does not operate under normal use at a high current. From the viewpoint of high output, it is more preferable that the protective element is designed so as not to cause abnormal heat generation or thermal runaway without a protective element.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.

<Production of Secondary Battery-1 (Production of Square Battery)>
[Production of positive electrode]
90% by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder, an N-methylpyrrolidone solvent Mixed in to a slurry. The obtained slurry was applied on both sides of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 80 μm with a press machine, and the active material layer was uncoated with a width of 100 mm, a length of 100 mm and a width of 30 mm. It cut out into the shape which has a process part, and was set as the positive electrode.

[Production of negative electrode]
2 kg of artificial graphite powder KS-44 (trade name, manufactured by Timcal Co., Ltd.) and 1 kg of petroleum-based pitch were mixed, and the resulting slurry mixture was heated to 1100 ° C. for 2 hours in an inert atmosphere in a batch heating furnace. And the temperature was maintained for 2 hours.

  This was pulverized, adjusted to a particle size of 18-22 μm with a vibrating sieve, and finally an “amorphous-coated graphite-based carbon material” in which the graphite surface was coated with 7% by mass of amorphous carbon was obtained. This “amorphous-coated graphite-based carbon material” is used as a negative electrode active material, 98 parts by weight of “amorphous-coated graphite-based carbon material”, an aqueous dispersion of carboxymethylcellulose sodium (carboxymethylcellulose as a thickener and a binder, respectively) 100 parts by weight of sodium (concentration 1% by mass) and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by mass) were added and mixed to form a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, and rolled to a thickness of 75 μm with a press, and the size of the active material layer was 104 mm in width, 104 mm in length, and 30 mm in width. It cut out in the shape which has a process part, and was set as the negative electrode.

[Battery assembly]
The 32 positive electrodes and 33 negative electrodes were alternately arranged, and the porous polyethylene sheet separator (thickness 25 μm) was laminated between each electrode. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. A current collecting tab was prepared by welding uncoated portions of each of the positive electrode and the negative electrode, and an electrode group was sealed in a battery can (outside dimension: 120 × 110 × 10 mm) with a gas discharge valve. . Thereafter, 20 mL of a non-aqueous electrolyte solution described later was injected into a battery can loaded with the electrode group, sufficiently infiltrated into the electrode, and sealed to produce a square battery. The electric capacity of the battery element housed in one battery exterior of the secondary battery, that is, the rated discharge capacity of this battery is about 6 Ah, and the DC resistance component measured by the 10 kHz AC method is about 5 milliohms. It was.

<Battery evaluation>
(Capacity measurement)
For a new battery that has not undergone a charge / discharge cycle, a voltage range of 4.2 V to 3.0 V and a current value of 0.2 C at 25 ° C. The initial charge / discharge was performed for 5 cycles at 1C. The discharge capacity at the 5th cycle at this time was defined as the initial capacity.

(Output measurement)
In a 25 ° C. environment, the battery is charged with a constant current of 0.2 C for 150 minutes, discharged at 0.1 C, 0.3 C, 1.0 C, 3.0 C, and 10.0 C, respectively, for 10 seconds. The voltage was measured. The area of the triangle surrounded by the current-voltage line and the lower limit voltage (3 V) was defined as output (W).

Example 1
In a dry argon atmosphere, a mixture (volume ratio 2: 7: 1) of ethylene carbonate (EC: flash point 143 ° C.), γ-butyrolactone (GBL: flash point 101 ° C.) and diethyl carbonate (DEC: flash point 25 ° C.) , LiPF ₆ was added at 0.3 mol / L and LiBF ₄ was added at 0.7 mol / L and dissolved. In this mixed solution, 1% by mass of vinylene carbonate and 0.3% by mass of hexamethylcyclotrisiloxane were added. A non-aqueous electrolyte solution was prepared. The flash point of this non-aqueous electrolyte was 61 ° C. Using this non-aqueous electrolyte, a square battery was produced by the method described above, and the output was measured. The results are shown in Table 1.

Example 2
A square battery was prepared in the same manner as in Example 1 except that phenyldimethylfluorosilane was used instead of hexamethylcyclotrisiloxane as the non-aqueous electrolyte, and the output was measured. The results are shown in Table 1.

Example 3
A square battery was prepared in the same manner as in Example 1 except that methyl fluorosulfonate was used in place of hexamethylcyclotrisiloxane as the non-aqueous electrolyte, and the output was measured. The results are shown in Table 1.

Example 4
As the non-aqueous electrolyte, lithium difluorophosphate produced according to the method described on pages 581 to 582 of Inorganic Nuclear Chemistry Letters (1969), 5 (7) was used instead of hexamethylcyclotrisiloxane. Produced a rectangular battery in the same manner as in Example 1, and measured the output. The results are shown in Table 1.

Comparative Example 1
A square battery was prepared in the same manner as in Example 1 except that hexamethylcyclotrisiloxane was not included as the non-aqueous electrolyte solution, and the output was measured. The results are shown in Table 1.

<Production of secondary battery-2 (Production of cylindrical battery)>
[Production of positive electrode]
90% by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder, an N-methylpyrrolidone solvent Mixed in to a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, and rolled to a thickness of 80 μm with a press machine, cut into a width of 52 mm and a length of 830 mm, and used as a positive electrode. However, both the front and back sides are provided with a 50 mm uncoated portion in the length direction, and the length of the active material layer is 780 mm.

[Production of negative electrode]
2 kg of artificial graphite powder KS-44 (trade name, manufactured by Timcal Co., Ltd.) and 1 kg of petroleum-based pitch were mixed, and the resulting slurry mixture was heated to 1100 ° C. for 2 hours in an inert atmosphere in a batch heating furnace. And the temperature was maintained for 2 hours.

  This was pulverized, adjusted to a particle size of 18-22 μm with a vibrating sieve, and finally an “amorphous-coated graphite-based carbon material” in which the graphite surface was coated with 7% by mass of amorphous carbon was obtained. This “amorphous-coated graphite-based carbon material” is used as a negative electrode active material, 98 parts by weight of “amorphous-coated graphite-based carbon material”, an aqueous dispersion of carboxymethylcellulose sodium (carboxymethylcellulose as a thickener and a binder, respectively) 100 parts by weight of sodium (concentration 1% by mass) and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by mass) were added and mixed to form a slurry. The obtained slurry was uniformly applied on both sides of a negative electrode current collector 18 μm thick copper foil, dried, and further rolled to a thickness of 85 μm with a press machine, cut to a width of 56 mm and a length of 850 mm, A negative electrode was obtained. However, both the front and back sides are provided with a 30 mm uncoated portion in the length direction.

[Battery assembly]
The positive electrode and the negative electrode were wound together with a polyethylene separator so that the positive electrode and the negative electrode were not in direct contact with each other to obtain an electrode body. The positive electrode and negative electrode terminals were placed outside and accommodated in a battery can. Next, after injecting 5 mL of a non-aqueous electrolyte described later, caulking was performed to produce a 18650 type cylindrical battery. The electric capacity of the battery element housed in one battery case of the secondary battery, that is, the rated discharge capacity of this battery is about 0.7 ampere hour (Ah), and the DC resistance measured by the 10 kHz AC method. The component was about 35 milliohms (mΩ).

Example 5
A cylindrical battery was produced using the non-aqueous electrolyte solution used in Example 1 as the non-aqueous electrolyte solution, and the output was measured. The results are shown in Table 1.

Comparative Example 2
A cylindrical battery was prepared and the output was measured in the same manner as in Example 5 except that the non-aqueous electrolyte used in Comparative Example 1 was used as the non-aqueous electrolyte. The results are shown in Table 1.

  As is clear from Table 1, when compared with each of the square batteries (Examples 1 to 4, Comparative Example 1) and the cylindrical batteries (Example 5 and Comparative Example 2), the output of the lithium secondary battery of this Example Was found to be improved.

  As described above, the rated discharge capacities of the prismatic batteries of this example and this comparative example are 3 ampere hours (Ah) or more, and the DC resistance component is 10 milliohms (mΩ) or less. On the other hand, the rated discharge capacity of the cylindrical batteries of this example and this comparative example is less than 3 ampere hours (Ah), and the DC resistance component is greater than 10 milliohms (mΩ). That is, the prismatic batteries of this example and this comparative example have lower resistance and larger electric capacity than the cylindrical battery. And the output improvement degree of Example 1 with respect to the comparative example 1 is larger than the output improvement degree of Example 5 with respect to the comparative example 2, and the effect of this invention in the secondary battery with a large electrical capacity or a small direct current resistance. Was found to be larger.

  The use of the non-aqueous electrolyte for secondary batteries and the secondary battery for non-aqueous electrolyte of the present invention is not particularly limited, and can be used for various known applications. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. , Electronic notebook, calculator, memory card, portable tape recorder, radio, backup power supply, motor, automobile, motorcycle, motorbike, bicycle, lighting equipment, toy, game equipment, clock, electric tool, strobe, camera, etc. Can do. In particular, the secondary battery of the present invention is particularly suitable for applications that require a large current because a large current discharge characteristic can be obtained.

Claims (8)

A non-aqueous electrolyte solution for a secondary battery obtained by dissolving at least a lithium salt in a non-aqueous solvent, wherein the non-aqueous solvent contains a flash point of 70 ° C. or higher, 60% by volume or more of the whole non-aqueous solvent, Furthermore, the di-fluoro lithium phosphate, for a secondary battery characterized by containing 10ppm or more on the whole nonaqueous electrolyte nonaqueous electrolyte.   The secondary battery according to claim 1, wherein the solvent having a flash point of 70 ° C or higher is at least one solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, and γ-valerolactone. Non-aqueous electrolyte for use. Lithium salt, a non-aqueous electrolyte solution for a secondary battery according to claim 1 or claim 2 are those containing LiPF _6.   The non-aqueous electrolyte solution for a secondary battery according to any one of claims 1 to 3, wherein the non-aqueous electrolyte solution has a flash point of 40 ° C or higher.   The total content of compounds belonging to the group consisting of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate is 0.01% by mass or more and 5% by mass based on the total amount of the non-aqueous electrolyte. The nonaqueous electrolytic solution for a secondary battery according to any one of claims 1 to 4, which is as follows.   A non-aqueous electrolyte secondary battery comprising at least a non-aqueous electrolyte, a negative electrode capable of inserting and extracting lithium ions, and a positive electrode, wherein the non-aqueous electrolyte is any one of claims 1 to 5. A non-aqueous electrolyte secondary battery, characterized in that it is a non-aqueous electrolyte solution for a secondary battery as described in the item.   The non-aqueous electrolyte secondary battery according to claim 6, wherein the electric capacity of a battery element housed in one battery exterior of the secondary battery is 3 ampere hours (Ah) or more.   The non-aqueous electrolyte secondary battery according to claim 6 or 7, wherein a DC resistance component of the secondary battery is 10 milliohms (mΩ) or less.