JP2020064873A - Nonaqueous electrolyte solution for secondary battery and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

To provide a nonaqueous electrolyte solution for a secondary battery and a nonaqueous electrolyte secondary battery which enable the large enhancement of low-temperature characteristics.SOLUTION: The above problem is solved by a nonaqueous electrolyte solution for a secondary battery, comprising: a nonaqueous solvent; and a lithium salt. The nonaqueous solvent is a mixed solvent containing at least ethylene carbonate and a chain carbonate. The proportion of the ethylene carbonate to a total amount of the nonaqueous solvent is 1 vol.% or more and 25 vol.% or less. Of the nonaqueous solvent, the total percentage of the ethylene carbonate and chain carbonate which account for is 80 vol.% or more. The electrolyte solution further comprises a compound having a S-F bond in its molecule, which is a sulfonyl fluoride or fluorosulfonate and which is included at a total amount of 10 ppm or more and 5 mass% or less in the whole nonaqueous electrolyte solution. The compound may be otherwise added to the electrolyte solution.SELECTED DRAWING: None

Description

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

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

As the electrolytic solution of the lithium secondary battery, electrolytes such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ and LiCF ₃ (CF ₂ ) ₃ SO ₃ are used. Cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, chain esters such as methyl acetate and methyl propionate , Cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and tetrahydropyran, chain ethers such as dimethoxyethane and dimethoxymethane, and non-aqueous solvents such as sulfur-containing organic solvents such as sulfolane and diethyl sulfone. The aqueous electrolyte It is needed.

  In a secondary battery using such a lithium non-aqueous electrolytic solution, the reactivity and the ionic conductivity are different depending on the composition of the non-aqueous electrolytic solution, so the battery characteristics are greatly changed depending on the non-aqueous electrolytic solution. Further, as a characteristic of the battery, there is a problem that the internal resistance is increased in a low temperature environment, and the discharge capacity is reduced when the battery is discharged at a constant discharge rate (hereinafter, abbreviated as “rate”).

  While lithium secondary batteries are used in various electronic devices, automobiles and power tools, there has been a demand for an electrolytic solution that does not significantly deteriorate the performance even in a low temperature environment. For example, in Patent Document 1, 2-methyltetrahydrofuran, 1,2-dimethoxyethane, 4-methyl-1,3-dioxolane, and the like are mixed in a mixed solvent of ethylene carbonate and diethyl carbonate to improve low-temperature characteristics. Proposed. However, with these methods, it was not possible to obtain sufficient characteristics when the battery was used in a severe cold region such as −20 ° C. or −30 ° C.

  Further, Patent Document 2 uses a non-aqueous electrolytic solution containing a cyclic siloxane and / or a reaction product thereof, and Patent Document 3 uses a non-aqueous electrolytic solution containing a silicon compound having a specific structure. Are described, and both can improve the input / output characteristics and the cycle characteristics. Although these methods are effective, they have not been sufficient.

JP-A-3-55770 JP, 2004-71458, A JP, 2004-87459, A

  The present invention has been made in view of the background art described above, and an object thereof is to provide a non-aqueous electrolytic solution for a secondary battery and a non-aqueous electrolytic solution secondary battery that greatly improve low-temperature characteristics.

  MEANS TO SOLVE THE PROBLEM As a result of earnest research in view of the said subject, this inventor uses the mixed solvent containing ethylene carbonate as a nonaqueous solvent of a nonaqueous electrolyte solution, and the ratio of ethylene carbonate in this mixed solvent is 1 volume% or more, 25 volume. The inventors have found that synergistically excellent low-temperature characteristics can be realized by making a specific chemical substance contained at the same time in an amount of not more than 0.1%, and have reached the present invention.

［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 for a secondary battery comprising a non-aqueous solvent and a lithium salt, the non-aqueous solvent is a mixed solvent containing at least ethylene carbonate, the ethylene to the total amount of non-aqueous solvent The proportion of carbonate is 1% by volume or more and 25% by volume or less, and further, the cyclic siloxane compound represented by the general formula (1), the fluorosilane compound represented by the general formula (2), and the general formula (3). At least one selected from the group consisting of a compound represented by the formula, a compound having an SF bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate and a propionate. The present invention also relates to a non-aqueous electrolyte solution for a secondary battery, characterized by containing or adding 10 ppm or more of the compound to the whole non-aqueous electrolyte solution.

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

[In the general formula (2), R ^{3 to} R ⁵ represent the same or different organic groups having 1 to 12 carbon atoms, x represents an integer of 1 to 3, p, q and r represents an integer of 0 to 3, and 1 ≦ p + q + r ≦ 3. ]

[In the general formula (3), R ^{6 to} R ⁸ represent the same or different organic groups having 1 to 12 carbon atoms, and A represents H, C, N, O, F, S, It represents a group composed of Si and / or P. ]

  Further, the present invention is a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, a negative electrode capable of inserting and extracting lithium ions, and a positive electrode, wherein the non-aqueous electrolyte is the non-aqueous electrolyte for the secondary battery. A non-aqueous electrolyte secondary battery characterized by being a liquid.

Further, the present invention is a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, a negative electrode capable of inserting and extracting lithium ions, and a positive electrode, wherein the non-aqueous electrolyte is the non-aqueous electrolyte for the secondary battery. A non-aqueous electrolyte secondary battery which is a liquid and has the following properties (1), (2) and / or (3).
(1) The sum of the electrode area of the positive electrode with respect to the surface area of the exterior of the secondary battery is 20 times or more in area ratio.
(2) The direct current resistance component of the secondary battery is 10 milliohms (mΩ) or less.
(3) The electric capacity of the battery element housed in one battery exterior of the secondary battery is 3 ampere hour (Ah) or more.

  According to the present invention, it is possible to greatly improve the low temperature characteristics of a non-aqueous electrolyte secondary battery, and more specifically, it is possible to improve the low temperature characteristics without deteriorating the cycle characteristics and the storage characteristics.

  Hereinafter, the embodiments of the present invention will be described in detail, but the description of the constituent elements described below is an example (representative example) of the embodiments of the present invention and is not specified by these contents. Various modifications can be implemented within the scope of the gist.

<Non-aqueous electrolyte for lithium secondary battery>
The non-aqueous electrolytic solution for a secondary battery of the present invention contains an electrolyte and a non-aqueous solvent that dissolves the same, as in a commonly used non-aqueous electrolytic solution.

[Lithium salt]
In the present invention, a lithium salt that is known to be usable as an electrolyte of a non-aqueous electrolyte solution for a lithium secondary battery is preferably used as the electrolyte and is not particularly limited, but examples thereof include the following.

Inorganic lithium salt:
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 sulfonates 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 ₉ SO ₂ ) etc. perfluoroalkanesulfonyl imide salt; LiC (CF ₃ SO ₂₎ perfluoroalkanesulfonyl methide salts of _{3 such; 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 ], A fluoroalkyl fluorophosphate such as Li [PF ₃ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₃ ] and the like.
Oxalatoborate salt:
Lithium bis (oxalato) borate, lithium difluorooxalatoborate, etc.

These may be used alone or in any combination of two or more at any ratio. Among these, LiPF ₆ is preferable when comprehensively judging the solubility in a non-aqueous solvent, the charge / discharge characteristics in the case of a secondary battery, the output characteristics, the cycle characteristics, and the like.

  The concentration of the lithium salt in the non-aqueous electrolyte 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. The upper limit is usually 2 mol / L or less, preferably 1.8 mol / L or less, and more preferably 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the electrolyte may be insufficient, while if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity, and the performance of the lithium secondary battery may decrease. There is a case.

A preferred example of using two or more kinds in combination is using LiPF ₆ and LiBF ₄ , and 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 preferable, and 0.1% by mass or more and 5% by mass or less is particularly preferable.

  Another example is the combined use of an inorganic fluoride salt and a perfluoroalkanesulfonic acid imide salt, and 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, and more preferably 80% by mass or more and 98% by mass or less. The combined use of both is effective in suppressing deterioration due to high temperature storage.

[Non-aqueous solvent]
The non-aqueous solvent of the present invention is a mixed solvent containing ethylene carbonate as an essential component, but as a non-aqueous solvent other than ethylene carbonate, from those conventionally proposed as a solvent for a non-aqueous electrolytic solution, it is appropriately selected. Can be used. Examples of such a thing include the following.
1) Cyclic Carbonates Other than Ethylene Carbonate Ethylene carbonates are cyclic carbonates, but in the present invention, other cyclic carbonates can be added. When another cyclic carbonate is used, the number of carbon atoms of the alkylene group constituting the other cyclic carbonate is preferably 3 to 6, and particularly preferably 3 to 4. Among them, propylene carbonate and butylene carbonate are preferable, and propylene carbonate is particularly preferable.
2) Chain carbonate As the chain carbonate, a dialkyl carbonate is preferable, and the number of carbon atoms of the constituting alkyl group is preferably 1 to 5, and particularly preferably 1 to 4. Specific examples thereof include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethylmethyl carbonate, methyl-n-propyl carbonate and ethyl-n-propyl carbonate. Among them, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are preferable.
3) Cyclic ester Specific examples include γ-butyrolactone and γ-valerolactone.
4) Chain ester Specific examples include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.
5) Cyclic ether Specific examples include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, and the like.
6) Chain ether Specific examples include dimethoxyethane and dimethoxymethane.
7) Sulfur-containing organic solvent Specific examples include sulfolane and diethyl sulfone.

  These non-aqueous solvents may be used alone or in combination of two or more kinds other than ethylene carbonate. For example, it is preferable to use a low-viscosity solvent such as a chain carbonate or a chain ester together from the viewpoint of charge / discharge characteristics at a high current value.

  One of the preferable combinations of the non-aqueous solvent is a combination mainly composed of ethylene carbonate and chain carbonates. Above all, the total of ethylene carbonates and chain carbonates in the non-aqueous solvent is preferably 80% by volume or more, preferably 85% by volume or more, and more preferably 90% by volume or more.

  In this mixed solvent, a lithium salt, 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. The non-aqueous electrolytic solution containing at least one selected from the group consisting of a compound having a —F bond, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate and a propionate is It is preferable because the battery produced by using it has good low-temperature characteristics, and also has good balance between cycle characteristics and high-temperature storage characteristics (particularly, remaining capacity after high-temperature storage and high-load discharge capacity) and suppression of gas generation.

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

  Combinations in which propylene carbonate is further added to these combinations of ethylene carbonate and chain carbonates are also mentioned as preferable combinations. When propylene carbonate is contained, the volume ratio of ethylene carbonate and propylene carbonate is preferably 99: 1 to 40:60, particularly preferably 95: 5 to 50:50. Further, the amount of propylene carbonate in the whole non-aqueous solvent is usually 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, usually 10% by volume or less, preferably 8% by volume or less, More preferably, it is 5% by volume or less because the low-temperature characteristics are further excellent while maintaining the characteristics of the combination of ethylene carbonate and chain carbonates.

  Among these, those containing asymmetric chain carbonates are more preferable, and particularly, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl. Those containing ethylene carbonate, symmetric chain carbonates and asymmetric chain carbonates such as methyl carbonate are preferable because both cycle characteristics and low temperature output characteristics are good. From the viewpoint of viscosity and electric conductivity as an electrolytic solution, the alkyl group constituting the dialkyl carbonate preferably has a small carbon number, and particularly preferably 1 or 2. Specifically, the asymmetric chain carbonate is preferably ethyl methyl carbonate because it has a low viscosity and the low-temperature output improving effect when a specific compound is used is large.

  Another example of the preferable mixed solvent is one containing a chain ester. In particular, in the mixed solvent of the cyclic carbonate and the chain carbonate, the one containing the chain ester is preferable from the viewpoint of improving the low temperature characteristics of the battery. As the chain ester, methyl acetate and ethyl acetate are particularly preferable. preferable. The volume of the chain ester in the non-aqueous solvent is usually 5% or more, preferably 8% or more, more preferably 15% or more, usually 50% or less, preferably 35% or less, more preferably 30% or less, It is more preferably 25% or less.

  In the present invention, the proportion of ethylene carbonate in the entire mixed solvent is 1% by volume or more, particularly preferably 3% by volume or more, further preferably 5% by volume or more, and further preferably 10% by volume or more. The upper limit is 25% by volume or less, preferably 20% by volume or less, and more preferably 15% by volume or less. If it is less than the lower limit, the repetitive charge / discharge (cycle) characteristics and the high temperature storage characteristics of the battery may be deteriorated, and further, the output characteristics may be deteriorated due to the decrease of electric conductivity. When the amount exceeds the upper limit, the effect of improving the low temperature characteristics obtained when mixed with the specific compound of the present invention may be reduced. In addition, the non-aqueous electrolyte solution of the present invention is a secondary battery having a low direct current resistance component of 10 milliohms (mΩ) or less, or a relatively large secondary battery having a rated discharge capacity of 3 ampere hours (Ah) or more and less than 20 Ah. It is particularly preferable to use it for a battery, and a large low temperature output can be exhibited.

[Specific compound]
The non-aqueous electrolyte solution 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. At least one compound selected from the group consisting of a compound having a —F bond, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate and a propionate (these are referred to as “specific compounds”). It may be abbreviated).

[[Cyclic Siloxane Compound Represented by General Formula (1)]]
R ¹ and R ² in the cyclic siloxane compound represented by the general formula (1) are organic groups having 1 to 12 carbon atoms which may be the same or different, and as R ¹ and R ² , Chain alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, 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 which may have an alkyl substituent; a phenylmethyl group; Examples thereof include an aralkyl group such as a phenylethyl group; a trialkylsilyl group such as a trimethylsilyl group; and a trialkylsiloxy group such as a trimethylsiloxy group.

Among them, those having a smaller number of carbon atoms are more likely to exhibit characteristics, and an organic group having a carbon number of 1 to 6 is preferable. In addition, the alkenyl group is preferable because it acts on the electrolytic solution and the film on the surface of the electrode to improve the input / output characteristics, and the aryl group has the effect of trapping radicals generated in the battery during charge / discharge and improving the overall battery performance. . Therefore, as R ¹ and R ² , a methyl group, a vinyl group or a phenyl group is particularly preferable.

  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. Examples thereof include cyclotrisiloxane such as trivinylcyclotrisiloxane, cyclotetrasiloxane such as octamethylcyclotetrasiloxane, cyclopentasiloxane such as decamethylcyclopentasiloxane. Of these, cyclotrisiloxane is particularly preferable.

[[Fluorosilane compound represented by the 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 or different from each other. ¹ and R ² as examples of chain alkyl group, cyclic alkyl group, alkenyl group, alkynyl group, halogenated alkyl group, alkyl group having saturated heterocyclic group, phenyl group which may have alkyl group, and the like. In addition to the aryl group, aralkyl group, trialkylsilyl group, trialkylsiloxy group, carbonyl group such as ethoxycarbonylethyl group; acetoxy group, acetoxymethyl group, carboxyl group such as trifluoroacetoxy group; methoxy group, ethoxy group, An oxy group such as a propoxy group, a butoxy group, a phenoxy group and an allyloxy group; an amino group such as an 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 represent an integer of 0 to 3, and 1 ≦ p + q + r ≦ 3.

  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 it may be difficult to include a predetermined amount in the electrolytic solution. Further, even after being contained in the electrolytic solution, there is a possibility that the battery may generate heat due to charge / discharge and may be volatilized under the condition that the external environment becomes high temperature. Therefore, 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), an organic group having a smaller number of carbon atoms is more likely to exhibit the effect, and the alkenyl group having a carbon number of 1 to 6 acts on the electrolytic solution or the coating film on the surface of the electrode. The input / output characteristics are improved, and the aryl group has a function of trapping radicals generated in the battery during charging / discharging and improving 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 are particularly preferably trimethylfluorosilane, vinyldimethylfluorosilane, phenyldimethylfluorosilane and vinyldiphenylfluorosilane. .

[[Compound Represented by General 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 or different, and examples thereof include the general formula (2 ) ^{May have} 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 given as examples of R ^{3 to} R ^5. An aryl group such as a phenyl group, an aralkyl group, a trialkylsilyl group, a trialkylsiloxy group, a carbonyl group, a carboxyl group, an oxy group, an amino group, a benzyl group and the like can be similarly mentioned.

  A in the compound represented by the general formula (3) is not particularly limited as long as it is a group composed of H, C, N, O, F, S, Si and / or P, but the general formula (3) The element directly bonded to the oxygen atom therein is preferably C, S, Si or P. The existence form of these atoms includes, for example, 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, a phosphinyl group, and the like. Those are preferable. The molecular weight of the compound represented by the general formula (3) is preferably 1,000 or less, particularly preferably 800 or less, and further preferably 500 or less.

  Examples of the compound represented by the general formula (3) include hexamethyldisiloxane, 1,3-diethyltetramethyldisiloxane, hexaethyldisiloxane, octamethyltrisiloxane, and other siloxane compounds; 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, trimethylsilyl trifluoroacetate; methanesulfonic acid Sulfonic acid esters such as trimethylsilyl, trimethylsilyl ethanesulfonate, triethylsilyl methanesulfonate, and 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. Hexamethyldisiloxane is preferable as the siloxane compound, trimethylsilyl methanesulfonate is preferable as the sulfonic acid ester, and bis (trimethylsilyl) sulfate is preferable as the sulfuric acid ester.

[[Compound having 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 thereof include 3-hexafluoropropane-1,3-bis (sulfonyl fluoride), methyl fluorosulfonate, ethyl fluorosulfonate and the like. Among them, 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, and propionate is not particularly limited, but metallic elements such as Li, Na, K, Mg, Ca, Fe, and Cu. In addition, ammonium and quaternary ammonium represented by NR ⁹ R ¹⁰ R ¹¹ R ¹² (in the formula, 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 optionally substituted with a halogen atom, a cycloalkyl group optionally substituted with a halogen atom, or a halogen atom. And an aryl group which may be present, a nitrogen atom-containing heterocyclic group, and the like. Each of R ^{9 to} R ¹² is 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.

  Further, among them, nitrates or difluorophosphates are preferable in terms of output characteristic improvement rate and cycle characteristics, and lithium difluorophosphate is particularly preferable. Further, as these compounds, those synthesized in a non-aqueous solvent may be used substantially as they are, and those synthesized separately and isolated in a non-aqueous solvent or a non-aqueous electrolyte solution. May be added to.

  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. The compounds, nitrates, nitrites, monofluorophosphates, difluorophosphates, acetates or propionates may be used alone or in combination of two or more compounds in any combination and ratio. You may. Further, among the compounds classified into the above respective specific compounds, one kind may be used alone, or two or more kinds of compounds may be used in optional combination and ratio.

  The proportion of these specific compounds in the non-aqueous electrolyte solution is essentially 10 ppm or more (0.001 mass% or more) in total with respect to the total non-aqueous electrolyte solution, but preferably 0.01 mass% or more, It is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. Further, the upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and further 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 low temperature characteristics, while if the concentration is too high, the charge / discharge efficiency may be reduced.

  Further, when these specific compounds are actually subjected to secondary battery production as a non-aqueous electrolytic solution, even if the battery is disassembled and the non-aqueous electrolytic solution is taken out again, if the content in them is significantly reduced. There are many. It is considered to be included in the present invention that the specific compound can be detected in at least 10 ppm from the non-aqueous electrolyte extracted from the battery.

  When preparing the non-aqueous electrolyte, it is preferable to dehydrate each raw material in advance, and the water content is usually 50 ppm or less, preferably 30 ppm or less, particularly preferably 10 ppm or less.

  It is not clear why the non-aqueous solvent containing a specific proportion of ethylene carbonate and the specific compound significantly improve the low temperature discharge characteristics, but the specific compound may have a certain low temperature discharge characteristic improving effect. is there. It is thought that it is because it exerts some action on the electrode and further interacts with lithium ions in the non-aqueous electrolyte solution.It is widely used as a solvent for the non-aqueous electrolyte solution for lithium secondary batteries. The existing ethylene carbonate seems to have the effect of inhibiting this action. Ethylene carbonate is easily coordinated (solvated) with lithium ions, which interferes with the interaction (and de-insertion) between lithium ions and a specific compound (and positive electrode), and reduces the effect of improving low temperature discharge characteristics. it is conceivable that.

  On the other hand, ethylene carbonate is useful for ensuring the solubility of the lithium salt that is the electrolyte and increasing the electrical conductivity of the non-aqueous electrolyte solution. The present invention is a result achieved by finding a means for suppressing the inhibition of the effect of improving the low temperature characteristics to the minimum while securing the conductivity as a result of diligent studies in consideration of these two characteristics, and particularly to use at low temperature. It is of great industrial value as a non-aqueous electrolyte used for batteries.

[Other compounds]
The non-aqueous electrolytic solution of the present invention, in a non-aqueous solvent containing ethylene carbonate, contains an electrolyte lithium salt and a specific compound as essential components, but other compounds as necessary, impairing the effects of the present invention. It can be contained in any amount within the range not present.

  Examples of such other compounds include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; 2 -Fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, and other such partially fluorinated aromatic compounds; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5 -Overcharge preventing agents such as fluorine-containing anisole compounds such as difluoroanisole; vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride , Maleic anhydride, citraconic acid anhydride, glutaconic acid anhydride, itaconic acid anhydride, cyclohexanedicarboxylic acid anhydride and other negative electrode film forming agents; ethylene sulfite, propylene sulfite, dimethyl sulfite, propanesultone, butanesultone, methyl methanesulfonate, busulfan, Positive electrodes such as methyl toluene sulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide Examples include protective agents.

  The overcharge inhibitor is preferably an aromatic compound such as biphenyl, alkylbiphenyl, terphenyl, a partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether or dibenzofuran. You may use these in combination of 2 or more types. In the case of using two or more kinds in combination, it is particularly preferable to use t-butylbenzene or t-amylbenzene in combination with cyclohexylbenzene or terphenyl (or a partially hydrogenated form thereof).

  As the negative electrode film forming agent, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, succinic anhydride, and maleic anhydride are preferable. You may use these in combination of 2 or more types. When two or more kinds are used in combination, it is particularly preferable to use vinylene carbonate in combination with vinylethylene carbonate, fluoroethylene carbonate, succinic anhydride, and maleic anhydride.

  As the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate and busulfan are preferable. You may use these in combination of 2 or more types.

  Further, it is particularly preferable to use a negative electrode film forming agent and a positive electrode protective agent together, or to use an overcharge inhibitor, a negative electrode film forming agent and a positive electrode protective agent together.

  The content ratio of these other compounds in the non-aqueous electrolytic solution is not particularly limited, but is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, based on the whole non-aqueous electrolytic solution. It is preferably 0.2% by mass or more, and 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 adding these compounds, it is possible to prevent the battery from bursting or igniting at the time of abnormality due to overcharging, and to improve the capacity retention characteristics after high temperature storage and the cycle characteristics.

  There is no particular limitation on the method for preparing the non-aqueous electrolyte solution for a secondary battery of the present invention, a non-aqueous solvent containing ethylene carbonate, according to a conventional method, a lithium salt, a specific compound, and optionally other compounds are dissolved. Can be prepared.

<Non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present invention will be described in detail below.
[Battery shape]
The shape of the battery is not particularly limited, and examples thereof include a bottomed cylindrical shape, a bottomed rectangular shape, a thin shape, a sheet shape, and a paper shape. In order to improve volumetric efficiency and storability when installed in a system or device, it may be a horseshoe-shaped, comb-shaped, or other irregular shape that takes into account the fit in the peripheral system arranged around the battery. . From the viewpoint of efficiently dissipating the heat inside the battery to the outside, a prismatic shape having at least one relatively flat and large-area surface is preferable.

  In a bottomed cylindrical battery, the outer surface area of the power generating element to be filled is small, so it is preferable to design the Joule heat generated by internal resistance during charging or discharging to efficiently escape to the outside. Further, it is preferable to increase the filling ratio of the substance having high thermal conductivity so as to reduce the temperature distribution inside.

In the bottomed square shape, the ratio of twice the area S of the largest surface (product of width and height of external dimensions excluding terminals, unit cm ² ) and the thickness T of battery outer shape (unit cm). The value of 2S / T is preferably 100 or more, and more preferably 200 or more. By increasing the maximum surface, it is possible to improve characteristics such as cycleability and high temperature storage even with a high-output and large-capacity battery, and improve heat dissipation efficiency during abnormal heat generation. It is possible to prevent a dangerous state of “burst”.

[Battery configuration]
The rechargeable secondary battery of the present invention includes a positive electrode and a negative electrode capable of inserting and extracting 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. At least it is composed of a case and the like. If necessary, a protective element may be mounted inside the battery and / or outside the battery.

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

[[[composition]]]
The positive electrode active material is not particularly limited as long as it can electrochemically store 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.

The transition metal of the lithium-transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples thereof include lithium-cobalt composite oxides such as LiCoO ₂ and LiNiO ₂ . Lithium-nickel composite oxides, lithium-manganese composite oxides such as LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ MnO ₃ , and some of the transition metal atoms that are the main constituents of these lithium-transition metal composite oxides are Al and Ti. , V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, and the like. Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O _4, etc. Is mentioned.

The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples thereof include 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 constituents 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.

[[[Surface coating]]]
It is also possible to use a material having a composition different from that of the material constituting the positive electrode active material, which is the main component, attached to the surface of these positive electrode active materials. Surface-adhering substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide and bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate. Examples thereof include sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate and magnesium carbonate.

  These surface-adhering substances are, for example, dissolved or suspended in a solvent and impregnated into a positive electrode active material, and then dried, or a surface-adhered substance precursor is dissolved or suspended in a solvent and impregnated into a positive electrode active material, and then heated. It can be attached to the surface of the positive electrode active material by, for example, a method of reacting with the above, a method of adding to the precursor of the positive electrode active material and simultaneously firing.

  The amount of the surface-adhering substance is preferably 0.1 ppm or more as a lower limit, more preferably 1 ppm or more as a lower limit, still more preferably 10 ppm or more as an upper limit, and preferably 20% or less as a upper limit, more preferably 10% by mass relative to the positive electrode active material. % Or less, more preferably 5% or less. The surface-adhered substance can suppress the oxidation reaction of the electrolytic solution on the surface of the positive electrode active material and can improve the battery life, but if the adhered amount is too small, the effect is not sufficiently expressed, and If it is too much, the resistance may increase because the lithium ion is prevented from entering and leaving.

[[[shape]]]
The shape of the positive electrode active material particles in the present invention, as conventionally used, such as lump, polyhedron, sphere, ellipsoid, plate, needle, column, etc. are used, but among them, primary particles are aggregated and secondary It is preferable that the secondary particles are formed by forming particles and the shape of the secondary particles is spherical or ellipsoidal. Usually, in an electrochemical device, the active material in the electrode expands and contracts as it is charged and discharged, and the stress is likely to cause the active material to be destroyed and the conductive path to be broken. Therefore, it is preferable that primary particles are aggregated to form secondary particles rather than a single particle active material containing only primary particles, because the stress of expansion and contraction is relieved and deterioration is prevented. In addition, spherical or elliptic spherical particles have less orientation during molding of the electrode than particles having plate-like equiaxed orientation, and therefore less expansion and contraction of the electrode during charge and discharge, and also create the electrode. Even in the case of mixing with a conductive agent, it is easy to mix uniformly, which is preferable.

[[[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. . When the tap density of the positive electrode active material is less than the above lower limit, the amount of the dispersion medium required increases at the time of forming the positive electrode active material layer, and the required amount of the conductive material and the binder increases, so that the positive electrode active material in the positive electrode active material layer increases. The filling rate of the substance is limited, and the battery capacity may be limited. By using the composite oxide powder having a high tap density, a high density positive electrode active material layer can be formed. The larger the tap density is, the more preferable it is, and there is no particular upper limit. However, if it is too large, the diffusion of lithium ions in the positive electrode active material layer using the electrolytic solution as a medium is rate-determining, and the load characteristics may be deteriorated. It is 2.5 g / cm ³ or less, preferably 2.4 g / cm ³ or less.

In the present invention, the tap density is measured by passing through a sieve with a mesh opening of 300 μm, dropping the sample into a tapping cell of 20 cm ³ to fill the cell volume, and then measuring the powder density (for example, Seiden Enterprise Tap Denser). Tapping with a stroke length of 10 mm is performed 1000 times using, and the density obtained from the volume at that time and the weight of the sample is defined as the tap density.

[[[Median diameter d50]]]
The median diameter d50 of particles (secondary particle diameter when 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 preferably It is preferably 3 μm or more, and the upper limit is usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, most preferably 15 μm or less. If it is less than the above lower limit, a high tap density product may not be obtained, and if it exceeds the upper limit, it takes time to diffuse lithium in the particles, resulting in deterioration of battery performance, or making a positive electrode of a battery, that is, an active material. When a conductive agent, a binder and the like are slurried with a solvent and applied as a thin film, problems such as streaking may occur. Here, by mixing two or more kinds of positive electrode active materials having different median diameters d50, the filling property at the time of producing the positive electrode can be further improved.

  The median diameter d50 in the present invention is measured by a known laser diffraction / scattering type 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 at the time of measurement, and a measurement refractive index of 1.24 is set after ultrasonic dispersion for 5 minutes. Then measured.

[[[Average primary particle size]]]
When the primary particles aggregate 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, It is most preferably 0.1 μm or more, 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 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, which may result in a high possibility that the battery performance such as output characteristics is deteriorated. is there. On the other hand, if it is less than the above lower limit, problems such as poor reversibility of charge and discharge may occur because crystals are usually undeveloped.

  The primary particle size is measured by observation with a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10000, 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 the average value is obtained. To be

[[[BET specific surface area]]]
The BET specific surface area of the positive electrode active material used for the 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 It 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 deteriorate, and if it is large, the tap density tends to be difficult to increase, and a problem may occur in the coating property at the time of forming the positive electrode active material.

  The BET specific surface area was measured by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and after predrying the sample at 150 ° C. for 30 minutes under nitrogen flow, the relative pressure of nitrogen to the atmospheric pressure was measured. It is defined as a value measured by a nitrogen adsorption BET one-point method by a gas flow method using a nitrogen-helium mixed gas that is precisely adjusted to a value of 0.3.

[[[Manufacturing]]]
As a method for producing the positive electrode active material, a general method for producing an inorganic compound is used. In particular, various methods can be considered for producing a spherical or elliptical active material. For example, transition metal raw materials such as transition metal nitrates and sulfates, and raw materials of other elements as necessary such as water It is dissolved or pulverized and dispersed in a solvent, and the pH is adjusted while stirring to prepare and recover a spherical precursor, which is then dried if necessary, and then LiOH, Li ₂ CO ₃ , LiNO ₃ or other Li Source to obtain an active material by firing at a high temperature, transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides, and raw materials of other elements as necessary in a solvent such as water. It is melted or pulverized and dispersed in it, and dried and molded by a spray dryer or the like to give a spherical or elliptic spherical precursor, and a Li source such as LiOH, Li ₂ CO ₃ or LiNO ₃ is added to this and baked at a high temperature. To obtain active material, Transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides; Li sources such as LiOH, Li ₂ CO ₃ and LiNO _3; and raw materials of other elements, if necessary, such as water. Examples thereof include a method of dissolving or pulverizing and dispersing in a solvent, drying and molding the same with a spray dryer or the like to give a spherical or elliptic spherical precursor, and firing this at a high temperature to obtain an active material.

[[Constitution of positive electrode]]
The constitution of the positive electrode used in the present invention will be described below.
[[[Electrode structure and fabrication method]]]
The positive electrode is manufactured by forming a positive electrode active material layer containing positive electrode active material particles and a binder on a current collector. The production of the positive electrode using the positive electrode active material can be performed by a conventional method. That is, a positive electrode active material, a binder, and optionally a conductive material, a thickener, etc. are dry-mixed and formed into a sheet, which is then pressed onto a positive electrode current collector, or these materials are used as a liquid medium. A positive electrode can be obtained by forming a positive electrode active material layer on the current collector by dissolving or dispersing it in a slurry to form a slurry, which is applied to the positive electrode current collector and dried.

  The content of the positive electrode active material in the positive electrode active material layer is usually 10% by mass or more, preferably 30% by mass or more, and particularly preferably 50% by mass or more. The upper limit is usually 99.9% by mass or less, preferably 99% by mass or less. When the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. On the other hand, if the content is too high, the strength of the positive electrode may be insufficient. In the present invention, one kind of positive electrode active material may be used alone, or two or more kinds having different compositions or different powder physical properties may be used in optional combination and ratio.

  The positive electrode active material layer obtained by coating and drying is preferably compacted 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 formed into an electrode is not particularly limited, but the density of the positive electrode active material layer present on the current collector is preferably 1.0 g / cm ³ or more, more preferably the lower limit. Is 1.5 g / cm ³ , more preferably 2.0 g / cm ³ or more, and the upper limit is preferably 4.0 g / cm ³ or less, more preferably 3.5 g / cm ³ or less, and further preferably 3.0 g. / Cm ³ or less. If it exceeds this range, the permeability of the electrolytic solution into the vicinity of the collector / active material interface may be lowered, and the charge / discharge characteristics may be lowered especially at a high current density. On the other hand, if it falls below the range, the conductivity between the active materials may decrease, and the battery resistance may increase.

[[[Conductive material]]]
Any known conductive material can be used as the conductive material. Specific examples thereof include metal materials such as copper and nickel; graphite such as natural graphite and artificial 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 be used together by 2 or more types in arbitrary combinations and ratios.

  In the positive electrode active material layer, 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, and the upper limit is usually 50% by mass or less, preferably Is 30 mass% or less, more preferably 15 mass% or less. If the content is lower than this range, the conductivity may be insufficient. On the contrary, 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 the coating method, it may be any material that is dissolved or dispersed in the liquid medium used in the production of the electrode. , Polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, and other resin-based polymers; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber , Rubber polymers such as butadiene rubber, ethylene / propylene rubber; styrene / butadiene / styrene block copolymers or hydrogenated products 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 Flexible resin-like polymer such as coalesce; Fluorine-based polymer such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer; alkali metal ion (particularly lithium ion) The polymer composition etc. which have ion conductivity of 2) are mentioned. These substances may be used alone or in any combination of two or more at any ratio.

  The proportion 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%. It is not more than 40% by mass, more preferably not more than 40% by mass, most preferably not more than 10% by mass. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained and the mechanical strength of the positive electrode becomes insufficient, which may deteriorate battery performance such as cycle characteristics. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

[[[Liquid medium]]]
As the liquid medium for forming the slurry, if the solvent can dissolve or disperse the positive electrode active material, the conductive agent, the binder, and the thickener used as necessary, it may be of any kind. There is no particular limitation, 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, propylene oxide and tetrahydrofuran (THF); N-methylpyrrolidone (NMP) Amides such as dimethylformamide and dimethylacetamide; aprotic polar solvents such as hexamethylphosphamide and dimethylsulfoxide;

  Particularly when an aqueous medium is used, it is preferable to make it into a slurry by using a thickener and a latex such as styrene-butadiene rubber (SBR). Thickeners are commonly used to adjust the viscosity of slurries. The thickener is not particularly limited, and specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and salts thereof. These may be used alone or in any combination of two or more at any 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, The upper limit is usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. If it is less than this range, the coating property may be significantly reduced. If it exceeds, the proportion of the active material in the positive electrode active material layer decreases, which may cause a problem of decreasing the battery capacity or a problem of increasing resistance between the positive electrode active materials.

[[[Current collector]]]
The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples thereof 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, metallic materials, particularly aluminum are preferable.

  Examples of the shape of the current collector include a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, and a foam metal in the case of a metal material, and a carbon plate in the case of a carbonaceous material, Examples thereof include carbon thin films and carbon cylinders. Of these, metal thin films are preferred. The thin film may be appropriately formed in a mesh shape. Although the thickness of the thin film is arbitrary, it 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 as a current collector may be insufficient. On the contrary, if the thin film is thicker than this range, the handling property may be impaired.

  The ratio between the thickness of the current collector and the thickness of the positive electrode active material layer is not particularly limited, but (the thickness of the active material layer on one surface immediately before the electrolyte injection) / (the thickness of the current collector) is 150 or less. Is particularly preferable, and it is 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, and more preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during high current density charging / discharging. Below this range, the volume ratio of the current collector to the positive electrode active material may increase, and the battery capacity may decrease.

[[[Electrode area]]]
When the non-aqueous electrolyte for a secondary battery of the present invention is used, the area of the positive electrode active material layer is preferably larger than the outer surface area of the battery outer case, from the viewpoint of exhibiting the effect of improving the low temperature output to a greater extent. . Specifically, the total area of the 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 is the total area obtained by calculation from the dimensions of the length, width and thickness of the case part filled with the power generation element excluding the protruding parts of the terminals in the case of the bottomed square shape. . In the case of a bottomed cylindrical shape, the geometric surface area approximates the case portion, excluding the protruding portion of the terminal, filled with the power generation element as a cylinder. The total of the 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 surfaces via the collector foil. , The sum of the areas calculated for each surface separately.

  It is not clear why the effect of improving the low temperature characteristics of the non-aqueous electrolyte solution is amplified by making the total area of the electrode area of the positive electrode with respect to the surface area of the exterior of the secondary battery 20 times or more, but (1) The decrease in the reaction resistance of lithium ion insertion / removal due to the large electrode area and the decrease in the reaction resistance due to the non-aqueous electrolytic solution may have some synergistic effect, and (2) the non-aqueous electrolytic solution of the present invention has The high content of ethylene carbonate is suppressed, so the permeability to the electrode mixture layer is good, and even when used for batteries with a large electrode surface area, the electrolyte solution diffuses and penetrates sufficiently to improve the output by a specific compound. It is possible that the effect is being drastically elicited. In order to utilize the effect of the above (2), it is preferable that the size of the electrode surface area and the requirements for a high-capacity battery and a low (DC) resistance battery described below are simultaneously satisfied. These requirements are to realize a large output improving effect by using in combination with the non-aqueous electrolyte solution of the present invention, a large electrode surface area is effective for expressing without inhibiting this effect. This is because it can be considered.

[[[Discharge capacity]]
When the non-aqueous electrolyte solution 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 An ampere hour (Ah) or more is particularly preferable because the effect of improving the low-temperature discharge characteristics becomes large. Therefore, it is preferable to design the positive electrode plate so that the discharge capacity is fully charged and is 3 ampere hours (Ah) or more and less than 20 Ah, and more preferably 4 Ah or more and less than 10 Ah. If it is less than 3 Ah, the voltage drop due to the electrode reaction resistance becomes large at the time of taking out a large current, and the power efficiency may deteriorate. In this case, the low-temperature discharge characteristics also deteriorate, and the low-temperature discharge characteristics obtained when the non-aqueous electrolyte solution of the present invention containing 1% by volume or more and 25% by volume or less of ethylene carbonate and the specific compound in the non-aqueous solvent are used. May be insufficiently improved. At 20 Ah or more, the electrode reaction resistance decreases and the power efficiency improves, but the temperature distribution due to the internal heat generation of the battery during pulse charging / discharging is large, the durability of repeated charging / discharging is poor, and abnormalities such as overcharging and internal short-circuiting occur. When the heat release efficiency deteriorates due to sudden heat generation, the internal pressure rises and the gas release valve operates (valve operation), and the probability that the battery contents are ejected violently (burst) increases. There is.

[[[Thickness of positive electrode plate]]]
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 material layer from which the metal foil thickness of the core material is subtracted is 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 in 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 will be described below.

[[[composition]]]
The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions electrochemically, and carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, and simple lithium And lithium alloys such as lithium aluminum alloys, metals capable of forming alloys with lithium such as Sn and Si, and the like. These may be used alone or in any combination of two or more at any ratio. Among them, 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 it is preferable to contain 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 an oxidation treatment of these pitches, needle coke, pitch Coke and partially graphitized carbon materials, pyrolysis products of organic substances such as furnace black, acetylene black, pitch-based carbon fibers, carbonizable organic substances (for example, coal tar pitch from soft pitch to hard pitch, or dry distillation liquefaction) Heavy oil such as coal-based heavy oil such as oil, atmospheric residual oil, direct-current heavy oil under reduced pressure residual oil, crude oil, heavy oil derived from petroleum decomposition oil such as ethylene tar produced by thermal decomposition of naphtha, acenaphthylene, decacyclene, Aromatic hydrocarbons such as anthracene and phenanthrene, N ring compounds such as phenazine and acridine, thiophene and bithiophene Ring compounds, polyphenylene such as biphenyl, terphenyl, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products of these, nitrogen-containing polyacnylonitrile, organic polymers such as polypyrrole, sulfur-containing polythiophene, Organic polymers such as polystyrene, cellulose, lignin, mannan, polygalacturonic acid, chitosan, natural polymers such as polysaccharides represented by saccharose, thermoplastic resins such as polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol -A thermosetting resin such as formaldehyde resin or imide resin) and a carbide or an organic substance thereof which can be carbonized, are dissolved in a low molecular organic solvent such as benzene, toluene, xylene, quinoline or n-hexane, and a solution thereof. Charcoal Carbon material is heat treated one or more times in a range things} from 400 3200 ° C.,

(3) A carbon material in which the negative electrode active material layer is made of at least two kinds of carbonaceous materials having different crystallinity and / or has an interface where the different carbonaceous materials having different crystallinity are in contact with each other,
(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 where the carbonaceous materials having different orientations are in contact with each other,
The one selected from the following is preferable because it has a good balance of initial irreversible capacity and high current density charge / discharge characteristics.

[[Constitution, Physical Properties, Preparation Method of Negative Electrode]]
Regarding the properties of the carbonaceous material, the negative electrode containing the carbonaceous material, the electrode forming method, the current collector, and the lithium ion secondary battery, any one or more of the following (1) to (19) It is desirable to satisfy both at the same time.

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

(2) Ash content The ash content contained in the carbonaceous material is 1 mass% or less, especially 0.5 mass% or less, particularly 0.1 mass% or less, and the lower limit is 1 ppm or more with respect to the total mass of the carbonaceous material. Is preferred. If it exceeds the above range, deterioration of battery performance due to reaction with the electrolytic solution during charge / discharge may not be negligible. Below this range, a large amount of time, energy, and equipment for preventing pollution are required for manufacturing, and the cost may increase.

(3) Volume-Based Average Particle Size The volume-based average particle size of the carbonaceous material is such that the volume-based average particle size (median size) determined by the laser diffraction / scattering method is usually 1 μm or more, preferably 3 μm or more. Is 5 μm or more, more preferably 7 μm or more. The upper limit is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, particularly preferably 25 μm or less. If it is less than the above range, the irreversible capacity may increase, which may lead to the loss of the initial battery capacity. On the other hand, if the amount exceeds the above range, an uneven coating surface is likely to be formed when an electrode is prepared by coating, which may be undesirable in the battery manufacturing 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 of polyoxyethylene (20) sorbitan monolaurate (about 10 mL), which is a surfactant, and using a laser diffraction / scattering 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 0.10 or more. The upper limit is 1.50 or less, preferably 1.2 or less, more preferably 1.0 or less, still more preferably 0.50 or less. If the R value is below this range, the crystallinity of the particle surface may become too high, and the number of sites where Li enters between layers may decrease with charge and discharge. That is, charge acceptability may decrease. In addition, when the negative electrode is densified by pressing after applying it to the current collector, crystals are likely to be oriented in the direction parallel to the electrode plate, which may cause deterioration of load characteristics. On the other hand, when it exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the electrolytic solution is increased, and the efficiency may be lowered and the gas generation may be increased.

The Raman half-value width near 1580 cm ^{-1 of the} carbonaceous material 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 80 cm ^-1 or less, The range is more preferably 60 cm ^-1 or less, and further preferably 40 cm ^-1 or less. If the Raman full width at half maximum is less than this range, the crystallinity of the particle surface may become too high, and the number of sites where Li enters between layers may decrease with charge and discharge. That is, charge acceptability may decrease. In addition, when the negative electrode is densified by pressing after applying it to the current collector, crystals are likely to be oriented in the direction parallel to the electrode plate, which may cause deterioration of load characteristics. On the other hand, when it exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the electrolytic solution is increased, and the efficiency may be lowered and the gas generation may be increased.

A Raman spectroscope (for example, a Raman spectroscope manufactured by JASCO Corporation) is used for the measurement of the Raman spectrum, and the sample is spontaneously dropped into the measurement cell and filled, while irradiating the sample surface in the cell 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 this is defined as the Raman R value of the carbonaceous material. Further, the full width at half maximum of the peak P _A around 1580 cm ⁻¹ in the obtained Raman spectrum was measured, and this was defined as the Raman full width at half maximum of the carbonaceous material.

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

(5) BET Specific Surface Area The specific surface area of the carbonaceous material measured by the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ² / g or more. And 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, still more preferably 10 m ² / g or less. If the value of the specific surface area is less than this range, the acceptability of lithium during charging when used as a negative electrode material tends to be poor, and lithium tends to deposit on the electrode surface, which may cause a safety problem. On the other hand, when it exceeds this range, the reactivity with the electrolytic solution increases when used as a negative electrode material, the amount of gas generation tends to increase, and it may be difficult to obtain a preferable battery.
The specific surface area according to the BET method was measured by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and pre-drying the sample at 350 ° C. for 15 minutes under nitrogen flow. A value measured by the nitrogen adsorption BET one-point method by a gas flow method is used by 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 is determined by Hg porosimetry (mercury porosimetry), and the pores in the particles and the surface of the particles have a diameter of 0.01 μm or more and 1 μm or less. The amount of unevenness due to steps, the contact surface 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 Is 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 falls below the range, the high current density charge / discharge characteristics may deteriorate, and the effect of alleviating 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 the above range, the effect of dispersing the thickener or the binder may not be obtained when the electrode plate is formed.

  The average pore size 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. Is. Above this range, a large amount of binder may be required. If it falls below the range, the high current density charge / discharge characteristics may deteriorate.

  A mercury porosimeter (Autopore 9520: manufactured by Micromeritex) was used as an apparatus for Hg porosimetry. About 0.2 g of the sample was enclosed in a powder cell and degassed at room temperature under vacuum (50 μmHg or less) for 10 minutes for pretreatment. Subsequently, the pressure was reduced to 4 psia (about 28 kPa), mercury was introduced, the pressure was stepwise increased 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 pressurization was 80 points or more, and in each step, the mercury intrusion amount was measured after the equilibration time of 10 seconds. 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 becomes 50% was used.

(7) Circularity The circularity is used as the degree of sphere of the carbonaceous material, and the circularity of the 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, It is preferably 0.8 or more, more preferably 0.85 or more, and most preferably 0.9 or more. A large circularity is preferable because the charge and discharge characteristics at high current density are improved.

The circularity is defined by the following formula, and when the circularity is 1, it becomes a theoretical true sphere.
Circularity = (perimeter of equivalent circle having the same area as the particle projection shape) / (actual perimeter 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 the sample is mixed with polyoxyethylene (20) sorbitan monolaurate which is a surfactant. After dispersing in a 0.2 mass% aqueous solution (about 50 mL) and irradiating with an ultrasonic wave of 28 kHz at an output of 60 W for 1 minute, the detection range is specified to 0.6 to 400 μm, and the particle size is in the range of 3 to 40 μm. The value measured for is used.

  The method of improving the circularity is not particularly limited, but a spherical shape obtained by subjecting to a spherical shape is preferable because the shape of the interparticle voids in the electrode body is adjusted. Examples of the spheroidizing treatment include a method of mechanically approximating a spherical shape by applying a shearing force or a compressing force, a mechanical / physical treatment method of granulating a plurality of fine particles by a binder or the adhesive force of the particles themselves, 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 2.0 g / cm ^3. cm ³ or more, and 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 carbon may be too low and the initial irreversible capacity may increase. In the present invention, the true density is defined as being 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. It is preferably 0 g / cm ³ or more. Further, it is preferably 2.0 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and particularly preferably 1.6 g / cm ³ or less. If the tap density is below this range, the packing density is difficult to increase when used as a negative electrode, and it may not be possible to obtain a high capacity battery. On the other hand, when it exceeds this range, voids between particles in the electrode become too small, it becomes difficult to secure conductivity between particles, and it may be difficult to obtain preferable battery characteristics. The tap density is measured and defined by a method similar to the method 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. is there. 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 was performed by setting 0.47 g of the sample into a molding machine with a diameter of 17 mm and compressing it at 600 kgf / cm ² so that the molded body was made flush with the surface of the sample holder for measurement. To measure. A ratio represented by (110) diffraction peak intensity / (004) diffraction peak intensity is calculated from the obtained (110) diffraction and (004) diffraction peak intensities of carbon, and is defined as the orientation ratio of the active material.
The X-ray diffraction measurement conditions here are as follows. In addition, "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, and more preferably 5 or less. If it exceeds the upper limit, streaks may occur when the electrode plate is formed, 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, where A is the longest diameter of the carbon material particles when observed three-dimensionally and B is the shortest diameter orthogonal to it. The carbon particles are observed with a scanning electron microscope capable of magnifying observation. Select 50 arbitrary graphite particles fixed to the end face of metal with a thickness of 50 μm or less, rotate and tilt the stage on which the sample is fixed for each, measure A, B, and average A / B Find the value.

(12) Mixing of Sub-Materials “Mixing of sub-materials” means that two or more kinds of 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. As a particularly preferred embodiment, the volume-based particle size distribution is not symmetrical about the median diameter, contains two or more carbonaceous materials having different Raman R values, and has X-ray parameters Different things can be mentioned.

  As an example of the effect, graphite (eg, graphite) such as natural graphite or artificial graphite, carbon black such as acetylene black, and carbonaceous material such as amorphous carbon such as needle coke are contained as a conductive agent, so that electric resistance is improved. It can be reduced. These may be used alone or in any combination of two or more at any ratio. When added as a conductive agent, 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, it may be difficult to obtain the effect of improving conductivity. If it exceeds, the initial irreversible capacity may increase.

(13) Preparation of Electrode The electrode may be manufactured 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 the negative electrode active material to form a slurry, which is applied to a current collector, dried and then pressed. You can The thickness of the negative electrode active material layer per one surface immediately before the electrolytic solution injection step of 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 It is 120 μm or less, more preferably 100 μm or less. If it exceeds this range, the electrolytic solution is less likely to permeate to the vicinity of the current collector interface, so that the high current density charge / discharge characteristics may be deteriorated. If it is less than this range, the volume ratio of the current collector to the negative electrode active material increases, and the capacity of the battery may decrease. Further, the negative electrode active material may be roll-formed into a sheet electrode or may be compression-formed into a pellet electrode.

(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. Among them, copper is particularly preferable from the viewpoint of workability and cost. When the current collector is a metal material, examples of the shape of the current collector include a metal foil, a metal column, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, and a 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 thinner 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.

  The current collector made of a copper foil produced by the rolling method has copper crystals arranged in the rolling direction, so that the negative electrode is hard to crack even if the negative electrode is tightly rolled or sharply rounded, and is suitably used for a small cylindrical battery. be able to. Electrolytic copper foil is, for example, by immersing a metal drum in an electrolytic solution in which copper ions are dissolved, and by passing an electric current while rotating this, copper is deposited on the surface of the drum and peeled off. Is what you get. Copper may be deposited on the surface of the rolled copper foil by an electrolytic method. One or both surfaces of the copper foil may be roughened or surface-treated (for example, a chromate treatment with a thickness of about several nm to 1 μm, a base treatment with Ti or the like).

The following physical properties are further 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 specified 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, and particularly preferably It is preferably 0.15 μm or more, and 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. When it is at least the above lower limit, the area of the interface with the negative electrode active material thin film is increased, and the adhesion with the negative electrode active material thin film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, but a material having an average surface roughness (Ra) of more than 1.5 μm is generally difficult to obtain as a foil 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 is all.

  The tensile strength is the maximum tensile force required until the test piece breaks, divided by the cross-sectional area of the test piece. The tensile strength in the present invention is measured by the same device and method as the elongation percentage. If the current collector substrate has high tensile strength, cracks in the current collector substrate due to expansion / contraction of the negative electrode active material thin film due to 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 required to give 0.2% plastic (permanent) strain, and even if the load of this magnitude is applied and then unloading, it will deform by 0.2%. It means that The 0.2% proof stress in the present invention is measured by the same device and method as the elongation percentage. If the current collector substrate has high 0.2% proof stress, it is possible to suppress plastic deformation of the current collector substrate due to expansion / contraction of the negative electrode active material thin film due to charge / discharge, and obtain good cycle characteristics. You can

  The thickness of the metal thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more. The upper limit is usually 1 mm or less, preferably 100 μm or less, more preferably 30 μm or less. If the thickness is less than 1 μm, the strength may be lowered and the application may be difficult. If it is thicker than 100 μm, the shape of the electrode such as winding may be deformed. Further, the metal thin film may have a mesh shape.

(15) Thickness Ratio of Current Collector and Active Material Layer The thickness ratio of the current collector and active material layer is not particularly limited, but ((thickness of active material layer 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, The range is preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during high current density charging / discharging. Below this range, the volume ratio of the current collector to the negative electrode active material increases, and the capacity of the battery 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 1.0 g / cm ³ or more, more preferably Is 1.2 g / cm ³ , more preferably 1.3 g / cm ³ or more, and the upper limit is 2.0 g / cm ³ or less, preferably 1.9 g / cm ³ or less, and more preferably 1.8 g / cm ^3. Hereafter, the range is more preferably 1.7 g / cm ³ or less. If it exceeds this range, the active material particles may be destroyed, and the initial irreversible capacity may increase, and the high current density charge / discharge characteristics may be deteriorated due to a decrease in the permeability of the electrolyte solution near the current collector / active material interface. On the other hand, if it falls below the range, the conductivity between the active materials may decrease, the battery resistance may increase, and the capacity per unit volume may decrease.

(17) Binder The binder that binds the active material is not particularly limited as long as it is a material that is stable with respect to the electrolytic solution and the solvent used during electrode production. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethylmethacrylate, aromatic polyamide, cellulose and nitrocellulose; SBR (styrene / butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, 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 polymers such as butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinegar Soft resinous polymers such as vinyl copolymers and propylene / α-olefin copolymers; Fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene / ethylene copolymers Molecules: polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions) and the like can be mentioned. These may be used alone or in any combination of two or more at any ratio.

The solvent for forming the slurry is not particularly limited in its type as long as it is a solvent capable of dissolving or dispersing the negative electrode active material, the binder, and the thickener and the conductive agent used as necessary. Alternatively, either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water and alcohol, 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, hexamethylphosphamide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane and the like. .
In particular, when an aqueous solvent is used, a dispersant or the like is added to the above-mentioned thickener and a latex such as SBR is used to form a slurry. In addition, these may be used individually by 1 type, and may be used together by 2 or more types in arbitrary combinations and ratios.

  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, still more preferably 8% by mass or less. If it exceeds this range, the proportion of the binder that is a component that does not contribute to the battery capacity in the negative electrode active material layer becomes excessive, which may lead to a decrease in the battery capacity. On the other hand, if it is below the range, the strength of the negative electrode may be lowered. In particular, when a rubber-like polymer represented by SBR is contained as a main component, the ratio of the binder to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0. It is 6 mass% or more, and the upper limit is 5 mass% or less, preferably 3 mass% or less, and more preferably 2 mass% or less. When the main component contains a fluoropolymer represented 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, The upper limit is usually 15% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less.

  Thickeners are commonly used to adjust the viscosity of slurries. The thickener is not particularly limited, and specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and salts thereof. These may be used alone or in any combination of two or more at any 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, and the upper limit. Is 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. If it is less than this range, the coating property may be significantly reduced. When it exceeds, the ratio of the active material in the negative electrode active material layer decreases, which may cause a problem that the capacity of the battery decreases and a problem that resistance between the negative electrode active materials increases.

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

The X-ray diffraction measurement conditions here are as follows. In addition, "2θ" indicates a diffraction angle.
-Target: Cu (Kα ray) graphite monochromator-Slit: divergence slit = 1 degree, light-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 degree / 3 seconds (004) plane: 53.5 degrees ≤ 2θ ≤ 56.0 degrees, 0.01 degree / 3 seconds ・ Sample Adjustment: Fix the electrodes on the glass plate with double-sided tape with a thickness of 0.1 mm

(19) Impedance The resistance of the negative electrode when charged from the discharged state to 60% of the nominal capacity is preferably 100Ω or less, particularly preferably 50Ω or less, and more preferably 20Ω or less, and / or the double layer capacity is 1 × 10 ^−6. F or more is preferable, 1 × 10 ⁻⁵ F or more is more preferable, and 1 × 10 ⁻⁴ F or more is more preferable. 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 capable of charging the nominal capacity in 5 hours, then maintained in a state of not being charged / discharged for 20 minutes, and then discharged at a current value capable of discharging the nominal capacity in 1 hour. The capacity at that time is 80% or more of the nominal capacity. The lithium ion secondary battery in the discharged state is charged to a nominal capacity of 60% of the nominal capacity at a current value capable of being charged in 5 hours, and immediately the lithium ion secondary battery is transferred into a glove box under an 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 surface is peeled off without damaging the electrode active material on the other surface, Two electrodes are punched out into 12.5 mmφ and faced each other with a separator interposed therebetween so that the active material surfaces do not shift. 60 μL of the electrolytic solution used in the battery was dropped between the separator and both negative electrodes and adhered closely to each other, keeping a state in which they did not come into contact with the outside air, and conducting electricity to the current collectors of both negative electrodes to carry out the AC impedance method. The measurement is performed at a temperature of 25 ° C. and a complex impedance is measured in a frequency band of 10 ⁻² to 10 ⁵ Hz, and the arc of the obtained negative resistance component of the Cole-Cole plot is approximated by a semicircle to measure the surface resistance (R). And the double layer capacity (Cdl) is obtained.

  The area of the negative electrode plate is not particularly limited, but is designed to be slightly larger than the facing 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 repeated charge / discharge cycles and deterioration due to high temperature storage, it is preferable to make the area as close as possible to the positive electrode, because the proportion of the electrodes that work more uniformly and effectively improves and the characteristics improve. Especially when used with a large current, the design of this electrode area is important.

  The thickness of the negative electrode plate is designed according to the positive electrode plate used, and is not particularly limited, but the thickness of the composite material layer after subtracting the metal foil thickness of the core material 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 or less, more preferably 100 μm or less.

[Separator]
The separator used in the non-aqueous electrolyte secondary battery of the present invention has a predetermined mechanical strength that electrically insulates between both electrodes, has a large ion permeability, and has an oxidizing property and a negative electrode on the side in contact with the positive electrode. It is not particularly limited as long as it has resistance to reducing property on the side. As a material of the separator having such required characteristics, resin, inorganic material, glass fiber or the like is used. As the resin, an olefin polymer, a fluorine polymer, a cellulosic polymer, polyimide, nylon, or the like is used. Specifically, it is preferable to select from materials that are stable to the electrolytic solution and have excellent liquid retaining properties, and it is preferable to use a porous sheet or nonwoven fabric made of polyolefin such as polyethylene or polypropylene as a raw material.

  As the inorganic material, 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 in particle shape or fiber shape are used. As the form, a non-woven fabric, a woven fabric, a thin film-shaped one such as a microporous film is used. In the form of a thin film, one having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above-mentioned independent thin film shape, a separator can be used in which a composite porous layer containing the particles of the inorganic material is formed on the surface layer of the positive electrode and / or the negative electrode using a resin binder. For example, alumina particles having a 90% particle size of less than 1 μm may be formed on both surfaces of the positive electrode as a porous layer using a binder of fluororesin.

[Electrode group]
The electrode group has a laminated structure including the positive electrode plate and the negative electrode plate with the separator interposed therebetween, and a structure having a structure in which the positive electrode plate and the negative electrode plate are spirally wound with the separator interposed therebetween. Either may be used. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is preferably 40% to 90%, more preferably 50% to 80%. When the electrode group occupancy rate is less than 40%, the battery capacity becomes small, and when it is 90% or more, the void space is small, and the member expands or the vapor pressure of the liquid component of the electrolyte becomes high due to the high temperature of the battery. In some cases, the internal pressure rises, the charging / discharging repetition performance of the battery and various characteristics such as high temperature storage are deteriorated, and further, the gas release valve that releases the internal pressure to the outside may operate.

[Current collecting structure]
The current collecting structure is not particularly limited, but in order to more effectively realize the improvement of the low temperature discharge characteristics by the non-aqueous electrolyte solution of the present invention, it is necessary to have a structure that reduces the resistance of the wiring part or the bonding part. There is. When the internal resistance is small, the effect of using the non-aqueous electrolyte solution of the present invention is particularly well exhibited. When the electrode group has the above-mentioned laminated structure, a structure formed by bundling the metal core portions of the electrode layers and welding the terminals is preferably used. Since the internal resistance increases when the area of one electrode increases, it is also preferable to provide a plurality of terminals in the electrode to reduce the resistance. When the electrode group has the above-mentioned wound structure, the internal resistance can be lowered by providing a plurality of lead structures for the positive electrode and the negative electrode, respectively, and bundling them into the terminals.

  By optimizing the above structure, the internal resistance can be minimized. 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). The following is more preferable. When the DC resistance component is 0.1 milliohm or less, high output characteristics are improved, but the proportion of the current collecting structure material used increases, and the battery capacity may decrease.

  It is considered that the non-aqueous electrolyte solution of the present invention is effective in reducing the reaction resistance associated with the insertion / removal of lithium from / into the electrode active material, which is a factor that can realize good low-temperature discharge characteristics. However, it has been found that in a normal battery having a DC resistance of more than 10 mΩ, the effect of reducing the reaction resistance cannot be reflected in the low temperature discharge characteristics by 100% due to the inhibition of the DC resistance. This can be improved by producing a battery having a small DC resistance component, and the effects of the non-aqueous electrolyte solution of the present invention can be sufficiently exhibited. In addition, from the viewpoint of drawing out the effect of the non-aqueous electrolyte solution and producing a high-output battery, this requirement and the electric capacity of the battery element housed in the battery exterior of one of the secondary batteries (the battery is It is particularly preferable to simultaneously satisfy the requirement that the electric capacity when discharged from the fully charged state to the discharged state) is 3 ampere hour (Ah) or more.

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

In the outer case using the metals, laser welding, resistance welding, ultrasonic welding to weld the metals to each other to form a hermetically sealed structure, or a caulking structure using the metals via a resin gasket. There are things to do.
Examples of the outer case using the laminate film include those having a sealed structure by heat-sealing resin layers. In order to improve the sealing property, 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 via a collector terminal to form a hermetically sealed structure, a metal and a resin are bonded, so a resin having a polar group or a modification having a polar group introduced as an intervening resin. Resin is preferably used.

[Protective element]
As the above-mentioned protection element, PTC (Positive Temperature Coefficient), temperature fuse, thermistor whose resistance increases when abnormal heat generation or excessive current flows, current flowing in the circuit due to sudden increase in internal battery pressure or internal temperature during abnormal heat generation A valve for shutting off (current cutoff valve) and the like can be mentioned. It is preferable to select the protection element under the condition that it does not operate at high current in normal use, and from the viewpoint of high output, it is more preferable to design it so as not to cause abnormal heat generation or thermal runaway without the protection element.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples as long as the gist thereof is not exceeded.
<Production of secondary battery>
[Production of positive electrode]
90% by mass of lithium cobalt oxide (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 were mixed with an N-methylpyrrolidone solvent. Mix in to make a slurry. The obtained slurry was applied to both sides of an aluminum foil with a thickness of 15 μm, dried, and rolled with a press to a thickness of 80 μm, and the uncoated layers having an active material layer size of 100 mm wide, 100 mm long and 30 mm wide It was cut out into a shape having a processed portion to obtain a positive electrode.

[Preparation of negative electrode]
98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by Timcal Co., Ltd.), 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (concentration of sodium carboxymethyl cellulose 1% by mass) as a thickener and a binder, respectively. Then, 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber of 50% by mass) was added and mixed with a disperser to form a slurry. The obtained slurry was applied on both sides of a copper foil having a thickness of 10 μm, dried, and rolled to a thickness of 75 μm with a press machine, and the uncoated material having a width of 104 mm, a length of 104 mm and a width of 30 mm was used as the size of the active material layer. It was cut out into a shape having a processed portion to obtain a negative electrode.

[Battery assembly]
The positive electrode 32 sheets and the negative electrode 33 sheet were arranged so as to alternate with each other, and laminated so that a separator (thickness 25 μm) of a porous polyethylene sheet was sandwiched between the respective electrodes. At this time, the positive electrode active material surface was faced so as not to come off from the negative electrode active material surface. The uncoated parts of each of the positive electrode and the negative electrode were welded to each other to produce a current collecting tab, and the current collector tab was sealed in a battery can (outer dimension: 120 × 110 × 10 mm). Then, 20 mL of the non-aqueous electrolytic solution was injected into the battery can loaded with the electrode group to sufficiently permeate the electrode and then sealed to manufacture a prismatic battery. The rated discharge capacity of this battery is about 6 Ah, and the direct current resistance measured by the 10 kHz AC method is about 5 milliohms.

[Battery evaluation]
(Measuring method of initial capacity)
A new battery that had not been charged and discharged was subjected to 5 cycles of initial charge and discharge at 25 ° C in a voltage range of 4.1V to 3.0V at 25 ° C (voltage range of 4.1V to 3.0V). At this time, the discharge capacity was taken as the initial capacity, which was 0.2 C in the fifth cycle (the rated capacity based on the discharge capacity of 1 hour rate was 1 C as the current value for discharging in 1 hour, and so on).

(Low-temperature output measurement method)
Charging is performed for 150 minutes at a constant current of 0.2C in a 25 ° C environment, and discharged for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C and 5.0C in a -30 ° C environment, respectively. The voltage at the 10th second was measured. The output (W) was the area of a triangle surrounded by the current-voltage line and the lower limit voltage (3V).

Example 1
Under a dry argon atmosphere, lithium hexafluorophosphate (LiPF ₆ ) was added and dissolved in a mixture (volume ratio 15:85) of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) at 1 mol / L, Hexamethylcyclotrisiloxane was mixed in an amount of 0.3% by mass with respect to this mixed solution to prepare a non-aqueous electrolyte solution. A battery was prepared by using the above non-aqueous electrolyte solution by the method described above, and the low temperature output was measured. The results are shown in Table 1.

Example 2
A battery was prepared using the non-aqueous electrolytic solution prepared in Example 1 with the volume ratio of EC to EMC being 20:80, and the low temperature output was measured. The results are shown in Table 1.

Example 3
In Example 1, a battery was prepared by using a non-aqueous electrolyte prepared by changing the mixture of EC, dimethyl carbonate (DMC) and EMC (volume ratio 15:40:45) as the non-aqueous solvent, and producing a low temperature output. It was measured. The results are shown in Table 1.

Example 4
In Example 1, a battery was prepared using a non-aqueous electrolyte solution in which phenyldimethylfluorosilane was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Example 5
In Example 1, a battery was prepared using the non-aqueous electrolyte solution in which hexamethyldisiloxane was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Example 6
In Example 1, a battery was prepared by using a non-aqueous electrolytic solution in which trimethylsilyl methanesulfonate was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Example 7
In Example 1, a battery was prepared by using a non-aqueous electrolytic solution in which methyl fluorosulfonate was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Example 8
In Example 1, lithium nitrate was mixed instead of hexamethylcyclotrisiloxane, and a battery was prepared using a non-aqueous electrolyte solution stored for 3 days, and the low temperature output was measured. The results are shown in Table 1.

Example 9
In Example 1, as the non-aqueous electrolyte, lithium difluorophosphate produced according to the method described in Inorganic Nuclear Chemistry Letters (1969), 5 (7), pages 581 to 582, instead of hexamethylcyclotrisiloxane. A battery was prepared by using a non-aqueous electrolyte solution mixed with and the low temperature output was measured. The results are shown in Table 1.

Example 10
In Example 9, a battery was prepared using a non-aqueous electrolyte solution in which the amount of lithium difluorophosphate mixed was changed to 0.08 mass% with respect to the mixed solution of the non-aqueous solvent and lithium hexafluorophosphate. Then, the low temperature output was measured. The results are shown in Table 1.

Example 11
In Example 1, lithium acetate was mixed in place of hexamethylcyclotrisiloxane, a non-aqueous electrolyte solution stored for 3 days was used to manufacture a battery, and the low-temperature output was measured. The results are shown in Table 1.

Example 12
<Preparation of secondary battery-2>
[Production of positive electrode]
90% by mass of lithium cobalt oxide (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 were mixed with an N-methylpyrrolidone solvent. Mix in to make a slurry. The obtained slurry was applied onto both sides of an aluminum foil having a thickness of 20 μm, dried, and rolled into a thickness of 80 μm with a press machine, and cut into a width of 52 mm and a length of 830 mm to obtain a positive electrode. However, both the front and back sides are provided with a 50 mm non-coated portion in the length direction, and the length of the active material layer is 780 mm.

[Preparation of negative electrode]
98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by Timcal Co., Ltd.), 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (concentration of sodium carboxymethyl cellulose 1% by mass) as a thickener and a binder, respectively. , 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber of 50% by mass) was added and mixed by a disperser to form a slurry. The obtained slurry was uniformly applied to both surfaces of a copper foil having a thickness of 18 μm, which is a negative electrode current collector, dried, and then rolled with a press to a thickness of 85 μm, and cut into a width of 56 mm and a length of 850 mm, It was used as the negative electrode. However, both the front and back sides are provided with a 30 mm uncoated portion in the length direction.

[Preparation of electrolyte]
A non-aqueous electrolyte solution similar to that in Example 1 was prepared.
[Battery assembly]
The positive electrode and the negative electrode were laminated and wound together with a polyethylene separator so that the positive electrode and the negative electrode did not come into direct contact with each other to obtain an electrode body. The positive electrode and the negative electrode were housed in a battery can so that the terminals were exposed to the outside. Next, after injecting 5 mL of an electrolytic solution described later into the solution, caulking was performed to produce a 18650 type cylindrical battery. The rated discharge capacity of this battery was about 0.7 ampere-hour (Ah), and the direct current resistance measured by the 10 kHz AC method was about 35 milliohm (mΩ). In addition, the sum of the electrode areas of the positive electrode with respect to the surface area of the exterior of the secondary battery is 19.4 times in area ratio. The low temperature output of the above battery was measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1
In Example 1, a battery was prepared using the non-aqueous electrolyte solution prepared without mixing hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative example 2
In Example 2, a battery was prepared using the non-aqueous electrolytic solution prepared without mixing hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 3
In Example 3, a battery was prepared using the non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 4
Under a dry argon atmosphere, lithium hexafluorophosphate (LiPF ₆ ) was added to a mixture of ethylene carbonate and ethylmethyl carbonate (volume ratio 4: 6) at a concentration of 1 mol / L and dissolved. Hexamethylcyclotrisiloxane was mixed in an amount of 0.3% by mass to prepare a non-aqueous electrolyte solution.
A battery was prepared using this non-aqueous electrolyte solution, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 5
In Comparative Example 4, a battery was prepared using a non-aqueous electrolytic solution in which phenyldimethylfluorosilane was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 6
In Comparative Example 4, a battery was prepared using a non-aqueous electrolyte solution in which hexamethyldisiloxane was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 7
In Comparative Example 4, a battery was prepared using a non-aqueous electrolyte solution in which trimethylsilyl methanesulfonate was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 8
In Comparative Example 4, a battery was prepared using a non-aqueous electrolyte solution in which methyl fluorosulfonate was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 9
In Comparative Example 4, lithium nitrate was mixed in place of hexamethylcyclotrisiloxane, a battery was prepared using a non-aqueous electrolyte solution stored for 3 days, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 10
In Comparative Example 4, a battery was prepared using a non-aqueous electrolyte solution in which lithium difluorophosphate was mixed instead of hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 11
In Comparative Example 4, lithium acetate was mixed in place of hexamethylcyclotrisiloxane, a battery was prepared using a non-aqueous electrolyte solution stored for 3 days, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 12
In Comparative Example 4, a battery was prepared using the non-aqueous electrolyte solution prepared without mixing hexamethylcyclotrisiloxane, and the low temperature output was measured. The results are shown in Table 1.

Comparative Example 13
In Example 12, a battery was prepared using the same non-aqueous electrolyte solution as in Comparative Example 1, and the low temperature output was measured. The results are shown in Table 1.

  As is clear from Table 1, the lithium secondary batteries of Examples 1 to 11 in which a specific amount of EC and a specific compound are contained in the non-aqueous electrolyte solution include an excessive amount of EC and do not contain the specific compound. Not only the lithium secondary battery of Example 12 but also Comparative Examples 1 to 3 in which the amount of EC falls within a specific range but does not contain a specific compound, and the lithium secondary batteries of Comparative Examples 4 to 11 in which a specific compound is contained but EC is excessive. It was found that the low-temperature output characteristics were improved even when compared with the next power station. Further, the lithium secondary battery of Example 12 containing a specific amount of EC and a specific compound in the non-aqueous electrolytic solution was the lithium secondary battery of Comparative Example 13 in which the EC amount was within the specific range but did not contain the specific compound. It was found that the low temperature output characteristics were improved compared to the ground.

  Moreover, this effect is not a simple addition of the two, but the effect is obviously amplified by satisfying both conditions. Table 1 shows the increase rate of the low-temperature output when using the non-aqueous electrolyte solution containing the specific compound (other than that having the same composition) as compared with the non-aqueous electrolyte solution containing no specific compound. In comparison with Comparative Examples 4 to 11 in which the EC amount is excessive, in Examples 1 to 12, this value is large and the effect of the present invention can be seen.

  Although the output increase rate of Example 12 is 20.8% with respect to Comparative Example 13, the output improvement rate of Comparative Example 1 of Example 1 using the same material but having a different battery structure is 26.4%. It can be seen that the structure of the battery influences the magnitude of the effect of the non-aqueous electrolyte solution of the present invention. That is, the effect of the present invention is particularly great in a battery having a high capacity and a battery having a small DC resistance.

  Further, although not shown in the table, in the case of using the electrolytic solution having an EC content of less than 1% by volume, the initial capacity is slightly lower than that in Example 1, and the output characteristics and the cycle characteristics at room temperature are low. Was inferior to

  As described above, the non-aqueous electrolytic solution of the present invention, that is, a mixed solvent containing at least ethylene carbonate, wherein the ratio of ethylene carbonate to the total amount of the non-aqueous solvent is 1% by volume or more and 25% by volume or less, and , 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), a compound having an SF bond in the molecule, a nitrate salt , At least one compound selected from the group consisting of nitrites, monofluorophosphates, difluorophosphates, acetates and propionates in an amount of 10 ppm or more in the entire non-aqueous electrolyte solution. By using the non-aqueous electrolyte solution for a secondary battery as described above, it has become possible to exhibit extremely low temperature output characteristics.

  Further, the effect can be more remarkably exhibited in the battery structure as in Example 1, that is, in the battery having a high capacity and the battery having a small DC resistance, as compared with the battery structure as in Example 12. It was

  The application of the non-aqueous electrolyte solution for a secondary battery or the non-aqueous electrolyte solution secondary battery of the present invention is not particularly limited, and it can be used for various known applications. Specific examples include laptop computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copiers, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidisks, transceivers. , Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting equipment, toys, game machines, clocks, power tools, strobes, cameras, etc. You can In particular, the non-aqueous electrolyte secondary battery of the present invention, since good cycle characteristics and always high low-temperature characteristics can be obtained, when used in an application under a severe temperature difference, a particularly large effect can be obtained. Therefore, it is widely used in this field.

Claims (5)

  In a non-aqueous electrolyte for a secondary battery containing a non-aqueous solvent and a lithium salt, the non-aqueous solvent is a mixed solvent containing at least ethylene carbonate and a chain carbonate, and ethylene carbonate based on the total amount of the non-aqueous solvent. Is 1% by volume or more and 25% by volume or less, and the total of ethylene carbonate and chain carbonates occupying the non-aqueous solvent is 80% by volume or more, and further the SF bond is contained in the molecule. A secondary compound characterized by containing or adding a compound which is a sulfonyl fluoride or a fluorosulfonic acid ester in a total amount of 10 ppm or more and 5% by mass or less in the whole non-aqueous electrolyte solution. Non-aqueous electrolyte for batteries.   The non-aqueous electrolyte solution for a secondary battery according to claim 1, wherein the ratio of ethylene carbonate to the total amount of the non-aqueous solvent is 20% by volume or less.   The non-aqueous electrolyte solution for a secondary battery according to claim 1 or 2, wherein the ratio of ethylene carbonate to the total amount of the non-aqueous solvent is 15% by volume or less.   A non-aqueous electrolyte secondary battery comprising 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 3. 2. A non-aqueous electrolyte secondary battery, which is a non-aqueous electrolyte for a secondary battery. A non-aqueous electrolyte secondary battery comprising 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 4. 2. A non-aqueous electrolyte secondary battery for a secondary battery, which has the following properties (1), (2) and / or (3).
(1) The sum of the electrode area of the positive electrode with respect to the surface area of the exterior of the secondary battery is 20 times or more in area ratio.
(2) The direct current resistance component of the secondary battery is 10 milliohms (mΩ) or less.
(3) The electric capacity of the battery element housed in one battery exterior of the secondary battery is 3 ampere hour (Ah) or more.