JP5671774B2 - Lithium ion secondary battery - Google Patents

Lithium ion secondary battery Download PDF

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JP5671774B2
JP5671774B2 JP2007005190A JP2007005190A JP5671774B2 JP 5671774 B2 JP5671774 B2 JP 5671774B2 JP 2007005190 A JP2007005190 A JP 2007005190A JP 2007005190 A JP2007005190 A JP 2007005190A JP 5671774 B2 JP5671774 B2 JP 5671774B2
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lithium
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JP2007214120A (en
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正和 横溝
正和 横溝
竜一 加藤
竜一 加藤
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三菱化学株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage
    • Y02E60/12Battery technologies with an indirect contribution to GHG emissions mitigation
    • Y02E60/122Lithium-ion batteries

Description

  The present invention relates to a lithium ion secondary battery, and more particularly, to a lithium ion secondary battery using a specific non-aqueous electrolyte and a specific negative electrode active material.

  In the field of information-related equipment and communication equipment, along with the downsizing of personal computers, video cameras, mobile phones, etc., lithium-ion secondary batteries have been put to practical use because of their high energy density as the power source used for these equipment. It has become widespread.

  In recent years, in addition to the above fields, in the field of automobiles, lithium ion secondary batteries have been developed mainly for use as power sources for electric vehicles, which are urgently developed against the background of environmental and resource problems. Is being considered.

  Among lithium secondary batteries, secondary batteries using metal lithium as a negative electrode have been actively studied since long ago as batteries capable of achieving high capacity. However, these batteries have a problem that metallic lithium grows in a dendrite shape by repeated charging and discharging, eventually reaches the positive electrode, and a short circuit occurs inside the battery, and this problem is a metallic lithium secondary battery. Has become the biggest technical challenge when putting to practical use.

  Therefore, a nonaqueous electrolyte secondary battery using a carbonaceous material capable of occluding and releasing lithium ions such as coke, artificial graphite, and natural graphite has been proposed for the negative electrode. In such a non-aqueous electrolyte secondary battery, since lithium does not exist in a metal state, formation of dendrites is suppressed, and battery life and safety can be improved. In particular, graphite-based carbonaceous materials such as artificial graphite and natural graphite are expected as materials capable of improving the energy density per unit volume.

  However, lithium primary batteries are generally preferred as non-aqueous electrolyte secondary batteries using various graphite-based electrode materials alone or mixed with other negative electrode materials capable of occluding and releasing lithium as negative electrodes. When a non-aqueous electrolyte containing propylene carbonate used as a main solvent is used, the decomposition reaction of the solvent proceeds vigorously on the surface of the graphite electrode, making it impossible to smoothly occlude and release lithium into the graphite electrode. On the other hand, ethylene carbonate is often used as the main solvent of the electrolyte of non-aqueous electrolyte secondary batteries because of such a small amount of decomposition. However, even when ethylene carbonate is used as the main solvent, the surface of the electrode is charged and discharged. There is a problem in that charge / discharge efficiency and cycle characteristics are degraded due to decomposition of the electrolytic solution.

  Furthermore, in order to use a lithium ion secondary battery as a power source for an electric vehicle, it is an important performance to operate energy more efficiently at the time of input by regeneration during deceleration or at the time of output during acceleration. . Based on the above, a material having a higher resistance at the time of input / output consumes energy wastefully as Joule heat, resulting in lower environmental performance. With respect to such output resistance, it has not been said that sufficient performance has been obtained yet.

  Thus, as a means for improving the input / output characteristics of a lithium ion secondary battery, many techniques have been studied for various battery components including positive and negative active materials.

  As a technique related to the negative electrode active material, in Patent Document 1, lithium titanate obtained by mixing a lithium compound and titanium oxide and heat-treating the lithium compound, or a mixed crystal body in which lithium titanate and rutile titanium oxide coexist is lithium. There is a description that by using as a negative electrode material to be doped / dedoped with ions, an effect excellent in improving the charge / discharge cycle life of the battery can be exhibited. However, even with this method, the output resistance cannot be reduced sufficiently.

  As a technique related to the non-aqueous electrolyte solution, Patent Document 2 discloses that in a non-aqueous electrolyte secondary battery, when lithium monofluorophosphate or lithium difluorophosphate is added to the non-aqueous electrolyte solution, a good film is formed at the electrode interface. As a result, it is described that the decomposition of the electrolytic solution is suppressed and a battery having improved storage characteristics can be obtained.

However, even with this method, the output resistance cannot be reduced sufficiently.
JP-A-6-275263 Japanese Patent Application Laid-Open No. 11-067270

  This invention is made | formed in view of this background art, The subject is that output resistance is small and provides the lithium ion secondary battery which can use energy effectively.

  As a result of diligent research in view of the above problems, the present inventor has found that the output resistance is a metal oxide containing titanium that can occlude and release lithium rather than a carbon-based negative electrode active material that has been conventionally used. We found that it is important to use the negative electrode active material contained, and at the same time, by containing a specific compound in the non-aqueous electrolyte solution, the output resistance is drastically reduced, enabling effective use of energy. As a result, the present invention was completed.

That is, the present invention relates to a non-aqueous electrolyte solution containing a non-aqueous solvent and a lithium salt, and a lithium ion secondary battery having a positive electrode active material and a negative electrode active material, wherein the non-aqueous electrolyte solution has 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, nitrate, nitrite, mono The negative electrode contains at least one compound selected from the group consisting of fluorophosphate, difluorophosphate, acetate, and propionate in a total amount of 10 ppm or more in the non-aqueous electrolyte solution, and the negative electrode The present invention provides a lithium ion secondary battery, wherein the active material is a negative electrode active material containing a metal oxide containing titanium capable of inserting and extracting lithium.
[In General Formula (1), R 1 and R 2 represent the same or different organic group having 1 to 12 carbon atoms, and n represents an integer of 3 to 10. ]
[In General Formula (2), R 3 to R 5 represent an organic group having 1 to 12 carbon atoms which may be the same or different from each other, x represents an integer of 1 to 3, p, q and Each r represents an integer of 0 to 3, and 1 ≦ p + q + r ≦ 3. ]
[In General Formula (3), R 6 to R 8 represent an organic group having 1 to 12 carbon atoms which may be the same as or different from each other, and A represents H, C, N, O, F, S, Represents a group composed of Si and / or P; ]

  According to the present invention, it is possible to provide a lithium ion secondary battery having a small output resistance and capable of effectively using energy.

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

<Non-aqueous electrolyte>
The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention contains a lithium salt and a non-aqueous solvent that dissolves the lithium salt.
[Lithium salt]
The lithium salt is not particularly limited as long as it is known to be used as an electrolyte of a non-aqueous electrolyte solution for a lithium ion secondary battery, and 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. Perfluoroalkanesulfonylimide salt; Perfluoroalkanesulfonylmethide salt such as LiC (CF 3 SO 2 ) 3 ; Li [PF 5 (CF 2 CF 2 CF 3 )], Li [PF 4 (CF 2 CF 2 CF 3) 2 ], Li [PF 3 (CF 2 CF 2 CF 3 ) 3 ], Li [PF 5 (CF 2 CF 2 CF 2 CF 3 )], Li [PF 4 (CF 2 CF 2 CF 2 CF 3 ) 2 ], Fluoroalkyl fluorophosphates such as Li [PF 3 (CF 2 CF 2 CF 2 CF 3 ) 3 ].
Oxalatoborate salt:
Lithium difluorooxalatoborate, lithium bis (oxalato) borate and the like.

These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and ratios. Among these, LiPF 6 , LiBF 4 and the like are preferable, and LiPF 6 is particularly preferable when comprehensively judging the solubility in the non-aqueous solvent, the charge / discharge characteristics in the case of the secondary battery, the output characteristics, the cycle characteristics, and the like. .

  The concentration of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is usually 0.3 mol / L or more, preferably 0.6 mol / L or more, more preferably 0.7 mol / L or more. Moreover, the upper limit is 2 mol / L or less normally, Preferably it is 1.8 mol / L or less, More preferably, it is 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity. Performance may be degraded.

  The non-aqueous electrolyte preferably contains a fluorine-containing lithium salt as the lithium salt, and the concentration of the fluorine-containing lithium salt in the non-aqueous electrolyte is not particularly limited, but is 0.5 mol / L or more. The amount is particularly preferably 0.7 mol / L or more. Moreover, the upper limit is preferably 2 mol / L or less, particularly preferably 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the non-aqueous electrolyte solution may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity decreases due to an increase in viscosity, and the performance of the lithium ion secondary battery May decrease.

Lithium salts may be used singly or in combination of two or more in any combination and ratio. Preferred examples when two or more lithium salts are used are LiPF 6 and LiBF 4. In this case, the proportion of LiBF 4 in the total of both is particularly preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 5% by mass. More preferably, it is as follows. Another preferred example is the combined use of an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt. In this case, the proportion of the inorganic fluoride salt in the total of both is 70% by mass or more and 99% by mass. % Or less, particularly preferably 80% by mass or more and 98% by mass or less. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

[Nonaqueous solvent]
As the non-aqueous solvent, it can be appropriately selected from those conventionally proposed as solvents for non-aqueous electrolyte solutions. For example, the following are mentioned.
1) Cyclic carbonate:
As for carbon number of the alkylene group which comprises a cyclic carbonate, 2-6 are preferable, Most preferably, it is 2-4. Specific examples include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Of these, ethylene carbonate and propylene carbonate are preferable.
2) Chain carbonate:
As the chain carbonate, dialkyl carbonate is preferable, and the number of carbon atoms of the alkyl group is preferably 1 to 5, and particularly preferably 1 to 4, respectively. Specifically, for example, symmetric chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; asymmetric chain carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate And dialkyl carbonates. Of these, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like 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 diethylsulfone.

  These may be used alone or in combination of two or more, but it is preferable to use in combination of two or more. For example, it is preferable to use a high dielectric constant solvent such as cyclic carbonates and cyclic esters in combination with a low viscosity solvent such as chain carbonates and chain esters.

  One preferred combination of non-aqueous solvents is a combination mainly composed of cyclic carbonates and chain carbonates. Among them, the total of the cyclic carbonates and the chain carbonates in the nonaqueous solvent is 85% by volume or more, preferably 90% by volume or more, and more preferably 95% by volume or more. Further, the capacity of the cyclic carbonate with respect to the total of the cyclic carbonate and the chain carbonate is 5% or more, preferably 10% or more, more preferably 15% or more, usually 50% or less, preferably 35% or less, More preferably, it is 30% or less. It is particularly preferred that the above preferred volume range of the total amount of carbonates occupying the entire non-aqueous solvent is combined with the preferred above volume range of cyclic carbonates relative to cyclic and chain carbonates.

  Specific examples of preferred combinations of cyclic carbonates and chain carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate And ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. A combination in which propylene carbonate is further added to the combination of these ethylene carbonates and chain carbonates is also a preferable combination. In the case of containing propylene carbonate, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99: 1 to 40:60, particularly preferably 95: 5 to 50:50.

  Among these, those containing asymmetric chain carbonates are more preferable, 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 such as methyl carbonate, symmetric chain carbonates, and asymmetric chain carbonates are preferred because of a good balance between cycle characteristics and large current discharge characteristics. Among these, those in which the asymmetric chain carbonate is ethyl methyl carbonate are preferable, and the alkyl group constituting the dialkyl carbonate preferably has 1 to 2 carbon atoms.

  Other examples of preferred non-aqueous solvents are those containing chain esters. In particular, those containing a chain ester in the mixed solvent of cyclic carbonates and chain carbonates are preferable from the viewpoint of improving the low-temperature characteristics of the battery. Examples of the chain esters include methyl acetate and ethyl acetate. preferable. The capacity 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, More preferably, it is 25% or less.

  Examples of other preferable non-aqueous solvents include one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone, or two or more organic solvents selected from the group. The mixed solvent becomes 60% by volume or more of the whole. Such a mixed solvent preferably has a flash point of 50 ° C. or higher, and particularly preferably has a flash point of 70 ° C. or higher. A non-aqueous electrolyte using this solvent reduces evaporation of the solvent and leakage even when used at high temperatures. Among them, the amount of γ-butyrolactone in the nonaqueous solvent is 60% by volume or more, and the total of ethylene carbonate and γ-butyrolactone in the nonaqueous solvent is 80% by volume or more, preferably 90% by volume or more. And the volume ratio of ethylene carbonate to γ-butyrolactone is 5:95 to 45:55, or the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 80% by volume or more, preferably 90% When the ratio of ethylene carbonate to propylene carbonate is 30:70 to 60:40, the balance between cycle characteristics and large current discharge characteristics is generally improved.

[Specific compounds]
The non-aqueous electrolyte used for the lithium ion secondary battery of the present invention is represented by the cyclic siloxane compound represented by the general formula (1), the fluorosilane compound represented by the general formula (2), and the general formula (3). A compound having an SF bond in the molecule, at least one compound selected from the group consisting of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, and propionate (Hereinafter, these may be abbreviated as “specific compounds”) 10 ppm or more is essential.

  Provided is a lithium ion secondary battery that has low output resistance and enables effective use of energy by combining a non-aqueous electrolyte solution containing such a specific compound and a specific negative electrode active material described later as a negative electrode active material. can do.

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

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

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

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

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

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

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

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

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

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

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

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

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

[[Compound with SF bond in molecule]]
The compound having an S—F bond in the molecule is not particularly limited, but sulfonyl fluorides and fluorosulfonic acid esters are preferable. For example, methanesulfonyl fluoride, ethanesulfonyl fluoride, methanebis (sulfonylfluoride), ethane-1,2-bis (sulfonylfluoride), propane-1,3-bis (sulfonylfluoride), butane-1,4 -Bis (sulfonyl fluoride), difluoromethane bis (sulfonyl fluoride), 1,1,2,2-tetrafluoroethane-1,2-bis (sulfonyl fluoride), 1,1,2,2,3 Examples include 3-hexafluoropropane-1,3-bis (sulfonyl fluoride), methyl fluorosulfonate, ethyl fluorosulfonate, and the like. Of these, methanesulfonyl fluoride, methanebis (sulfonyl fluoride) or methyl fluorosulfonate is preferable.

[[Nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate]]
The counter cation of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate is not particularly limited, but metal elements such as Li, Na, K, Mg, Ca, Fe, Cu, etc. In addition, ammonium or quaternary ammonium represented by NR 9 R 10 R 11 R 12 (wherein R 9 to R 12 each independently represents a hydrogen atom or an organic group having 1 to 12 carbon atoms). Is mentioned. Here, the organic group having 1 to 12 carbon atoms of R 9 to R 12 is an alkyl group which may be substituted with a halogen atom, a cycloalkyl group which may be substituted with a halogen atom, or a halogen atom. An aryl group which may be present, a nitrogen atom-containing heterocyclic group, and the like. R 9 to R 12 are each preferably a hydrogen atom, an alkyl group, a cycloalkyl group, a nitrogen atom-containing heterocyclic group, or the like. Among these counter cations, lithium, sodium, potassium, magnesium, calcium, or NR 9 R 10 R 11 R 12 is preferable, and lithium is particularly preferable from the viewpoint of battery characteristics when used in a lithium ion secondary battery. Of these, nitrate or difluorophosphate is preferable in terms of the effect of improving output, battery cycle and high-temperature storage characteristics, and lithium difluorophosphate is particularly preferable. These compounds synthesized in a non-aqueous solvent may be used as they are, or those synthesized separately and substantially isolated are added in a non-aqueous solvent or a non-aqueous electrolyte. May be.

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

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

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

[Other compounds]
The non-aqueous electrolyte solution in the lithium ion secondary battery of the present invention contains a lithium salt that is an electrolyte and a specific compound as essential components. It can be contained in any amount. As such other compounds, specifically, for example,
(1) Aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluoro Partially fluorinated products of the above-mentioned aromatic compounds such as benzene and p-cyclohexylfluorobenzene; fluorinated anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole Overcharge inhibitors such as compounds;
(2) vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, etc. Negative electrode film-forming agent;
(3) Ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethylsulfur Cathodic protective agents such as foxoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide;
Etc.

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

  As the negative electrode film forming agent, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, succinic anhydride, and maleic anhydride are preferable. Two or more of these may be used in combination. As the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate, and busulfan are preferable. Two or more of these may be used in combination. Moreover, the combined use of a negative electrode film forming agent and a positive electrode protective agent, or the combined use of an overcharge inhibitor, a negative electrode film forming agent, and a positive electrode protective agent is particularly preferable.

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

<Negative electrode>
The negative electrode used for the lithium ion secondary battery of this invention is demonstrated below.
[Negative electrode active material]
The negative electrode active material used for the negative electrode is described below.

[[Configuration of negative electrode active material]]
The negative electrode active material used in the lithium ion secondary battery of the present invention contains a metal oxide containing titanium that can occlude and release lithium. Among metal oxides, lithium-titanium composite oxide (hereinafter abbreviated as “lithium-titanium composite oxide”) is preferable, and the metal oxide is a titanium-containing metal oxide having a spinel structure. Is preferred. Further, it is particularly preferable to use a metal oxide satisfying these simultaneously, that is, a lithium-titanium composite oxide having a spinel structure in a negative electrode active material for a lithium ion secondary battery, because the output resistance is greatly reduced.

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

The metal oxide is a lithium titanium composite oxide represented by the general formula (4). In the general formula (4), 0.7 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.3, It is preferable that 0 ≦ z ≦ 1.6 because the structure upon doping and dedoping of lithium ions is stable.
Li x Ti y M z O 4 (4)
[In General Formula (4), M represents at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb. ]

Among the compositions represented by the general formula (4), the structure shown below is particularly preferable because the battery performance balance is good.
In the general formula (4) Li x Ti y M z O 4 ,
(A) 1.2 ≦ x ≦ 1.4, 1.5 ≦ y ≦ 1.7, z = 0
(B) 0.9 ≦ x ≦ 1.1, 1.9 ≦ y ≦ 2.1, z = 0
(C) 0.7 ≦ x ≦ 0.9, 2.1 ≦ y ≦ 2.3, z = 0

Particularly preferred representative compositions of the above compounds are Li 4/3 Ti 5/3 O 4 in (a), Li 1 Ti 2 O 4 in (b), and Li 4/5 Ti 11/5 O in (c). 4 .

As for the structure of Z ≠ 0, for example, Li 4/3 Ti 4/3 Al 1/3 O 4 is preferable.

[[Physical properties, shape, etc. of negative electrode active material]]
In addition to the above requirements, the negative electrode active material of the present invention preferably further satisfies at least one of the following physical properties. In addition to the above requirements, it is particularly preferable to satisfy two or more of the following physical properties at the same time.

[[[BET specific surface area]]]
The specific surface area of the metal oxide containing titanium used as the negative electrode active material of the lithium ion secondary battery of the present invention is preferably 0.5 m 2 / g or more, particularly preferably 0.7 m, measured using the BET method. 2 / g or more, more preferably 1.0 m 2 / g or more, still more preferably 1.5 m 2 / g or more. The upper limit is preferably 200 m 2 / g or less, particularly preferably 100 m 2 / g or less, more preferably 50 m 2 / g or less, and still more preferably 25 m 2 / g or less. If the value of the BET specific surface area is less than this range, the reaction area in contact with the non-aqueous electrolyte when used as the negative electrode material may decrease, and the output resistance may increase. On the other hand, if it exceeds this range, the surface of the metal oxide crystal containing titanium and the portion of the end face increase, and due to this, crystal distortion also occurs, irreversible capacity cannot be ignored, which is preferable. It may be difficult to obtain a battery.

  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), preliminarily drying the sample for 15 minutes at 350 ° C. under a nitrogen flow, and then measuring the relative pressure of nitrogen with respect to atmospheric pressure. This is defined by a value measured by a nitrogen adsorption BET one-point method using a gas flow method, using a nitrogen-helium mixed gas that is accurately adjusted to have a value of 0.3.

[[[Volume average particle size]]]
The volume average particle diameter of the metal oxide containing titanium used as the negative electrode active material of the lithium ion secondary battery of the present invention is (the secondary particle diameter when the primary particles are aggregated to form secondary particles. ) Is defined by a volume-based average particle diameter (median diameter) obtained by a laser diffraction / scattering method, preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 0.7 μm or more. Moreover, an upper limit is 50 micrometers or less normally, Preferably it is 40 micrometers or less, More preferably, it is 30 micrometers or less, More preferably, it is 25 micrometers or less. Below the above range, a large amount of binder is required at the time of electrode preparation, and as a result, the battery capacity may decrease. On the other hand, if the ratio exceeds the above range, a non-uniform coating surface tends to be formed at the time of forming an electrode plate, which may be undesirable in the battery manufacturing process.

[[[Average primary particle size]]]
When primary particles are aggregated to form secondary particles, the average primary particle size of the metal oxide containing titanium used as the negative electrode active material of the lithium ion secondary battery of the present invention is preferably 0.01 μm or more, more preferably 0.05 μm or more, further preferably 0.1 μm or more, most preferably 0.2 μm or more, and the upper limit is preferably 2 μm or less, more preferably 1.6 μm or less, and still more preferably 1.3 μm or less, most preferably 1 μm or less. If the above upper limit is exceeded, it is difficult to form spherical secondary particles, which adversely affects the powder filling property, or the specific surface area is greatly reduced, so that there is a high possibility that battery performance such as output characteristics will deteriorate. is there. On the other hand, when the value falls below the lower limit, there is a case where problems such as inferior reversibility of charge / discharge are usually caused because crystals are not developed.

  The primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification at which particles can be confirmed, for example, a magnification of 10,000 to 100,000 times, the longest value of the intercept by the left and right boundary lines of the primary particles with respect to the horizontal straight line is determined for any 50 primary particles. Obtained and obtained by taking an average value.

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

[[[Tap density]]]
The tap density of the metal oxide containing titanium used as the negative electrode active material of a lithium ion secondary battery of the present invention is preferably 0.05 g / cm 3 or more, more preferably 0.1 g / cm 3 or more, more preferably Is 0.2 g / cm 3 or more, particularly preferably 0.4 g / cm 3 or more. The upper limit is preferably 2.8 g / cm 3 or less, more preferably 2.4 g / cm 3 or less, and particularly preferably 2 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 the contact area between the particles decreases, so that the resistance between the particles increases and the output resistance may increase. On the other hand, if this range is exceeded, the voids between the particles in the electrode may become too small, and the output resistance may increase due to a decrease in the flow path of the non-aqueous electrolyte solution.

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

[[[Circularity]]]
The circularity of the titanium-containing metal oxide used as the negative electrode active material of the lithium ion secondary battery of the present invention is usually 0.10 or more, preferably 0.80 or more, particularly preferably 0.85 or more, more preferably 0.90 or more. The upper limit is a theoretical sphere when the circularity is 1. Below this range, the fillability of the negative electrode active material is lowered, the resistance between the particles is increased, and the high current density charge / discharge characteristics for a short time may be lowered.

The circularity referred to in the present invention is defined by the following equation.
Circularity = (perimeter of equivalent circle having the same area as the particle projection shape) / (actual circumference of particle projection shape)

  As the circularity value, a flow type particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.) was used, and about 0.2 g of a sample was added to a polyoxyethylene (20) sorbitan monolaurate, which is a surfactant, in an amount of 0. Dispersed in a 2% by weight aqueous solution (about 50 mL), irradiated with 28 kHz ultrasonic waves at 60 W output for 1 minute, specified a detection range of 0.6 to 400 μm, and measured particles with a particle size in the range of 3 to 40 μm Use the value obtained.

[[[aspect ratio]]]
The aspect ratio of the metal oxide containing titanium used as the negative electrode active material of the lithium ion secondary battery of the present invention is theoretically 1 or more, and the upper limit is 5 or less, preferably 4 or less, more preferably 3 or less. More preferably, it is 2 or less. If the upper limit is exceeded, streaking or a uniform coated surface cannot be obtained when forming an electrode plate, and the high current density charge / discharge characteristics may be deteriorated for a short time.

  The aspect ratio is expressed as A / B when the diameter is the longest diameter A when observed three-dimensionally and the shortest diameter B is perpendicular to the diameter. The particles are observed with a scanning electron microscope capable of magnifying observation. Select 50 arbitrary particles fixed to the end face of a metal with a thickness of 50 μm or less, rotate and tilt the stage on which the sample is fixed, measure A and B, and average A / B Ask for.

[[Production method of negative electrode active material]]
The production method of the negative electrode active material containing titanium in the present invention is not particularly limited as long as it does not exceed the gist of the present invention, but there are several methods, which are general methods for producing inorganic compounds. Is used. For example, a method of obtaining an active material by uniformly mixing a titanium source material such as titanium oxide and a source material of another element and a Li source such as LiOH, Li 2 CO 3 , or LiNO 3 as necessary, and firing at a high temperature. Is mentioned. Various methods are conceivable in particular for producing a spherical or elliptical active material. For example, a titanium raw material such as titanium oxide and, if necessary, a raw material of another element may be dissolved in a solvent such as water. After pulverizing and dispersing, adjusting the pH while stirring to create and recover a spherical precursor, drying it if necessary, adding a Li source such as LiOH, Li 2 CO 3 , LiNO 3, etc. A method of obtaining an active material by firing with, a titanium raw material such as titanium oxide, and a raw material of another element as required, dissolved or pulverized and dispersed in a solvent such as water, and then dried by a spray dryer or the like A method of obtaining an active material by adding a Li source such as LiOH, Li 2 CO 3 , LiNO 3 and the like to obtain an active material, and a titanium raw material such as titanium oxide; , LiOH, Li 2 CO 3, and LiNO Li source such as 3, a raw material of the other elements necessary to dissolve or pulverized and dispersed in a solvent such as water, which was dried molded with a spray dryer or the like spherical or ellipsoidal And a method of obtaining an active material by baking the precursor at a high temperature.

  Also, during these steps, elements other than Ti, such as Al, Mn, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, C, Si, Sn , Ag may be present in the metal oxide structure containing titanium and / or in contact with the oxide containing titanium. By containing these elements, the operating voltage and capacity of the battery can be controlled.

[Electrode production]
The negative 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 a negative electrode active material to form a slurry, which is applied to a current collector, dried and then pressed. Can do. The thickness of the negative electrode active material layer per side in the stage immediately before the non-aqueous electrolyte injection process 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 150 μm or less, preferably 120 μm. Hereinafter, it is more preferably 100 μm or less. If it exceeds this range, the non-aqueous electrolyte solution hardly penetrates to the vicinity of the current collector interface, and thus the high current density charge / discharge characteristics may deteriorate. On the other hand, below this range, the volume ratio of the current collector to the negative electrode active material increases, and the battery capacity may decrease. Further, the negative electrode active material may be roll-formed to form a sheet electrode, or may be formed into a pellet electrode by compression molding.

[[Current collector]]
As the current collector for holding the negative electrode active material, a known material can be arbitrarily used. Examples of the current collector for the negative electrode include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Of these, copper is particularly preferable from the viewpoint of ease of processing and cost. When the current collector is a metal material, examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among them, a metal foil film containing copper (Cu) and / or aluminum (Al) is preferable, copper foil and aluminum foil are more preferable, rolled copper foil by a rolling method, and electrolytic copper by an electrolytic method are more preferable. There are foils, both of which can be used as current collectors. When the thickness of the copper foil is less than 25 μm, a copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) having higher strength than pure copper can be used. Moreover, since the specific gravity of aluminum foil is light, when it is used as a current collector, the weight of the battery can be reduced and can be preferably used.

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

Further, the following physical properties are desired for the current collector substrate.
(1) Average surface roughness (Ra)
The average surface roughness (Ra) of the active material thin film forming surface of the current collector substrate defined by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.01 μm or more, preferably 0.03 μm or more, usually It is 1.5 μm or less, preferably 1.3 μm or less, particularly preferably 1.0 μm or less. By setting the average surface roughness (Ra) of the current collector substrate within the range between the lower limit and the upper limit described above, good charge / discharge cycle characteristics can be expected. By setting it to the above lower limit or more, the area of the interface with the active material thin film is increased, and the adhesion with the active material thin film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, but those having an average surface roughness (Ra) exceeding 1.5 μm are generally difficult to obtain as foils having a practical thickness as a battery. 1.5 μm or less is preferable.

(2) Tensile Tensile strength strength collector substrate is not particularly limited, normally 50 N / mm 2 or more, preferably 100 N / mm 2 or more, more preferably 150 N / mm 2 or more. The tensile strength is obtained by dividing the maximum tensile force required until the test piece breaks by the cross-sectional area of the test piece. The tensile strength in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high tensile strength, cracking of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained.

(3) 0.2% proof stress of 0.2% proof stress current collector substrate is not particularly limited, normally 30 N / mm 2 or more, preferably 100 N / mm 2 or more, particularly preferably 150 N / mm 2 or more . The 0.2% proof stress is the magnitude of the load necessary to give a plastic (permanent) strain of 0.2%. It means that The 0.2% proof stress in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high 0.2% proof stress, plastic deformation of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained. it can. Although the thickness of a metal thin film is arbitrary, it is 1 micrometer or more normally, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more. Moreover, an upper limit is 1 mm or less normally, Preferably it is 100 micrometers or less, More preferably, it is 30 micrometers or less. If the thickness is less than 1 μm, the strength may be reduced, and application may be difficult. If it is thicker than 100 μm, it may be difficult to transform it into a desired electrode shape by winding or the like. The metal thin film may be mesh.

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

[[Electrode density]]
The electrode structure when the negative electrode active material is converted into an electrode is not particularly limited, but the density of the active material present on the current collector is preferably 1 g / cm 3 or more, more preferably 1.2 g / cm 3. Or more, more preferably 1.3 g / cm 3 or more, particularly preferably 1.5 g / cm 3 or more, and the upper limit is 3 g / cm 3 or less, preferably 2.5 g / cm 3 or less, more preferably 2.2 g. / Cm 3 or less, more preferably in the range of 2 g / cm 3 or less. The binding between the current collector and the active material exceeding this range is weakened, and the electrode and the active material may be separated. On the other hand, if it is lower, the conductivity between the active materials may be reduced, and the battery resistance may be increased.

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

  The solvent for forming the slurry is not particularly limited as long as it is a solvent that can dissolve or disperse the active material, binder, thickener and conductive material used as necessary. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, a mixed solvent of alcohol and water, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, acrylic acid. Methyl, diethyltriamine, N, N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamerylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, Hexane etc. are mentioned. In particular, when an aqueous solvent is used, a dispersant or the like is added to the above-described thickener, and a slurry such as SBR is formed. In addition, these may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

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

  A thickener is usually used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When a thickener is further added, the ratio of the thickener to the active material is 0.1% by mass or more, preferably 0.5% or more, more preferably 0.6% or more. It is 5 mass% or less, Preferably it is 3 mass% or less, More preferably, it is the range of 2 mass% or less. Below this range, applicability may be significantly reduced. If it exceeds the upper limit, the ratio of the active material in the negative electrode active material layer may be reduced, resulting in a problem that the capacity of the battery is reduced and a problem that the resistance between the negative electrode active materials is increased.

[[Impedance]]
The resistance of the negative electrode when charged to 60% of the nominal capacity from the discharged state is preferably 500Ω or less, particularly preferably 100Ω or less, more preferably 50Ω or less, and / or the double layer capacity is preferably 1 × 10 −6 F or more. Particularly preferably, it is 1 × 10 −5 F or more, more preferably 3 × 10 −5 F or more. Within this range, the output characteristics are good and preferable.

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

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

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

The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples include lithium / cobalt composite oxide such as LiCoO 2 or LiNiO 2 . Lithium / nickel composite oxide, LiMnO 2 , LiMn 2 O 4 , Li 2 MnO 3 and other lithium / manganese composite oxides, Al, Ti , V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and those substituted with other metals such as Si. Specific examples of the substituted ones include, for example, LiNi 0.5 Mn 0.5 O 2 , LiNi 0.85 Co 0.10 Al 0.05 O 2 , LiNi 0.33 Co 0.33 Mn 0.33 O 2 , LiMn 1.8 Al 0.2 O 4 , LiMn 1.5 Ni 0.5 O 4, etc. Is mentioned.

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

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

  These surface adhering substances are, for example, a method of dissolving or suspending in a solvent and impregnating and drying the positive electrode active material, and a method of dissolving or suspending a surface adhering substance precursor in a solvent and impregnating and adding to the positive electrode active material, followed by heating. It can be made to adhere to the positive electrode active material surface by the method of making it react by the method etc., the method of adding to a positive electrode active material precursor, and baking simultaneously. In addition, when attaching carbon, the method of attaching carbonaceous material mechanically later, for example in the form of activated carbon etc. can also be used.

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

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

[[[Tap density]]]
The tap density of the positive electrode active material is usually 1.3 g / cm 3 or more, preferably 1.5 g / cm 3 or more, more preferably 1.6 g / cm 3 or more, and most preferably 1.7 g / cm 3 or more. . If the tap density of the positive electrode active material is lower than the lower limit, the amount of the required dispersion medium increases when the positive electrode active material layer is formed, and the necessary amount of the conductive material and the binder increases. In some cases, the filling rate of the substance is limited, and the battery capacity is limited. By using a metal composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. In general, the tap density is preferably as large as possible, but there is no particular upper limit. However, if the tap density is too large, diffusion of lithium ions using the non-aqueous electrolyte solution as a medium in the positive electrode active material layer becomes rate-determining, and load characteristics may be likely to deteriorate. Usually, it is 2.5 g / cm 3 or less, preferably 2.4 g / cm 3 or less. The tap density of the positive electrode active material is also measured and defined by the same method as that described in the section of the negative electrode active material.

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

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

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

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

[[[BET specific surface area]]]
The BET specific surface area of the positive electrode active material used for the secondary battery of the present invention is 0.2 m 2 / g or more, preferably 0.3 m 2 / g or more, more preferably 0.4 m 2 / g or more, and the upper limit is 4 .0m 2 / g or less, preferably 2.5 m 2 / g or less, still more preferably not more than 1.5 m 2 / g. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered, and if the BET specific surface area is larger, the tap density is difficult to increase, and there may be a problem in applicability when forming the positive electrode active material.

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

[[[Production method of positive electrode active material]]]
As a manufacturing method of the positive electrode active material, a general method is used as a manufacturing method of the inorganic compound. In particular, various methods are conceivable for producing a spherical or elliptical spherical active material. For example, transition metal raw materials such as transition metal nitrates and transition metal sulfates and, if necessary, raw materials of other elements are mixed with water. It is dissolved or pulverized and dispersed in a solvent such as, and the pH is adjusted while stirring to produce and recover a spherical precursor, which is dried as necessary, and then LiOH, Li 2 CO 3 , LiNO 3, etc. A method of obtaining an active material by adding a Li source of the above, a transition metal source material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, and other elements as required The raw material is dissolved or pulverized and dispersed in a solvent such as water, and is then dried and molded with a spray dryer or the like to obtain a spherical or elliptical precursor, and LiOH, Li 2 CO 3 , LiNO 3 and other Li Add the source at high temperature A method of obtaining an active material by firing, a transition metal source material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, and LiOH such as LiOH, Li 2 CO 3 , and LiNO 3 Dissolve or pulverize the source and other elemental raw materials as necessary in a solvent such as water, and dry-mold them with a spray drier or the like to obtain a spherical or elliptical precursor, which is heated at a high temperature. Examples thereof include a method for obtaining an active material by firing.

[[Composition of positive electrode]]
Below, the structure of the positive electrode used for this invention is described.

[[[Electrode structure and fabrication method]]]
The positive electrode for a lithium ion secondary battery of the present invention is produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. Manufacture of the positive electrode using a positive electrode active material can be performed by a conventional method. That is, a positive electrode active material and a binder, and if necessary, a conductive material and a thickener mixed in a dry form are pressure-bonded to a positive electrode current collector, or these materials are liquid media A positive electrode can be obtained by forming a positive electrode active material layer on the current collector by applying it to a positive electrode current collector and drying it as a slurry by dissolving or dispersing in a slurry. Two or more types of positive electrode active materials may be mixed in advance and used, or may be mixed by adding them simultaneously when forming the positive electrode.

  The content of the positive electrode active material used in the positive electrode of the lithium ion secondary battery of the present invention in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. It is. Moreover, an upper limit becomes like this. Preferably it is 95 mass% or less, More preferably, it is 93 mass% or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

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

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

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

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

[[[Liquid medium]]]
The liquid medium for forming the slurry may be any type of solvent that can dissolve or disperse the positive electrode active material, the conductive material, the binder, and the thickener used as necessary. 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 hexamethylphosphalamide and dimethylsulfoxide.

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

[[[Consolidation]]]
The positive electrode active material layer obtained by coating and drying is preferably consolidated by a hand press, a roller press or the like in order to increase the packing density of the positive electrode active material. Density of the positive electrode active material layer, preferably as a lower limit 1.5 g / cm 3 or more, more preferably 2 g / cm 3 or more, still more preferably 2.2 g / cm 3 or more, the upper limit is preferably 3. The range is 5 g / cm 3 or less, more preferably 3 g / cm 3 or less, and still more preferably 2.8 g / cm 3 or less. If this range is exceeded, the permeability of the non-aqueous electrolyte solution to the vicinity of the current collector / active material interface may decrease, and the charge / discharge characteristics at a high current density may decrease. On the other hand, if it is lower, the conductivity between the active materials may be reduced, and the battery resistance may be increased.

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

  Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal in the case of a metal material. A thin film, a carbon cylinder, etc. are mentioned. Of these, metal thin films are preferred. In addition, you may form a thin film suitably in mesh shape. 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 for the current collector may be insufficient. Conversely, if the thin film is thicker than this range, the handleability may be impaired.

  The ratio of the thickness of the current collector to the positive electrode active material layer is not particularly limited, but the value of (thickness of active material layer on one side immediately before non-aqueous electrolyte injection) / (thickness of current collector) is It is preferably 20 or less, more preferably 15 or less, most preferably 10 or less, and the lower limit is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. Above this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. On the other hand, 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]]]
In the case of the present invention, it is preferable that the area of the positive electrode active material layer is larger than the outer surface area of the battery outer case from the viewpoint of increasing the stability at high output and high temperature. Specifically, the total electrode area of the positive electrode with respect to the surface area of the exterior of the secondary battery is preferably 20 times or more, and more preferably 40 times or more. The outer surface area of the outer case, in the case of a bottomed square shape, means the total area obtained by calculation from the vertical, horizontal, and thickness dimensions of the case part filled with the power generation element excluding the protruding part of the terminal. . In the case of a bottomed cylindrical shape, the geometric surface area approximates the case portion filled with the power generation element excluding the protruding portion of the terminal as a cylinder. The total electrode area of the positive electrode is the geometric surface area of the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in the structure in which the positive electrode mixture layer is formed on both sides via the current collector foil. , The sum of the areas where each surface is calculated separately.

[[[Discharge capacity]]]
When the non-aqueous electrolyte containing the specific compound of the present invention is used, the electric capacity of the battery element housed in one battery case of the secondary battery (the electric capacity when the battery is discharged from the fully charged state to the discharged state) When the (capacity) is 3 ampere hours (Ah) or more, the contact area with the peripheral member is increased, which is preferable from the viewpoint of improving thermal conductivity. Therefore, the positive electrode plate is preferably designed such that the discharge capacity is fully charged and is 3 ampere hours (Ah) or more and 20 Ah or less, and more preferably 4 Ah or more and 10 Ah or less. If it is less than 3 Ah, the voltage drop due to the electrode reaction resistance becomes large when taking out a large current, and the power efficiency may deteriorate. If it is larger than 20 Ah, the electrode reaction resistance is reduced and the power efficiency is improved, but the temperature distribution due to the internal heat generation of the battery during pulse charge / discharge is large, the durability of repeated charge / discharge is inferior, and overcharge, internal short circuit, etc. The heat radiation efficiency also deteriorates due to sudden heat generation at the time of abnormality, and the probability that the internal pressure rises and the gas release valve operates (valve operation) and the battery contents erupt violently (explosion) increases. There is a case.

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

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

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

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

<Battery configuration>
The rechargeable lithium ion 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 of the present invention, a separator disposed between the positive electrode and the negative electrode, and a current collecting terminal , And an exterior case. Further, if necessary, a protective element may be mounted inside the battery and / or outside the battery.

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

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

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

  The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter abbreviated as “electrode group occupation ratio”) is preferably 40% to 90%, and more preferably 50% to 80%. When the electrode group occupancy is less than 40%, the battery capacity is small, and when it is more than 90%, the void space is small, the member expands when the battery becomes high temperature, and the vapor pressure of the liquid component of the electrolyte increases. In some cases, the internal pressure rises due to an increase in the pressure, which deteriorates various characteristics such as charge / discharge repetition performance and high-temperature storage as a battery, and further, a gas release valve that releases the internal pressure to the outside may operate.

[Current collection structure]
The current collecting structure is not particularly limited, but in order to more effectively realize the output recovery by the temperature adaptation according to the present invention, it is necessary to have a structure that reduces the resistance of the wiring portion and the junction portion. When such an internal resistance is small, the effect of combining the non-aqueous electrolyte solution of the present invention and the negative electrode active material is exhibited particularly well.

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

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

  The non-aqueous electrolyte containing the specific compound used in the present invention is effective in reducing reaction resistance related to lithium desorption / insertion with respect to the electrode active material. However, in a battery having a large direct current resistance, it is inhibited by the direct current resistance. Thus, it was found that the effect of reducing the reaction resistance cannot be reflected 100% on the low temperature discharge characteristics. This can be improved by using a battery having a small DC resistance component, and the effect of the non-aqueous electrolyte solution of the present invention can be sufficiently exhibited.

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

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

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

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

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

<Action and principle>
By combining “a non-aqueous electrolyte solution containing a specific compound” and “a negative electrode active material containing a metal oxide containing titanium (preferably having a spinel structure) capable of inserting and extracting lithium”. The action / principle that can provide a lithium ion secondary battery with low output resistance is not clear, but the present invention is not limited by the following action / principle. It is presumed that de-doping occurs by a mechanism different from that in the case where a certain compound is present in the vicinity to promote some advantageous surface reaction and reduce the output resistance.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.
In addition, Examples 4-9 shall be read as Reference Examples 4-9.

(Preparation of negative electrode active material 1)
In order to prevent mixing of coarse particles, commercially available Li 1.33 Ti 1.66 O 4 having a volume average particle size of 23 μm was repeated five times with ASTM 400 mesh to obtain lithium titanium composite oxide (A).

(Preparation of negative electrode active material 2)
In order to prevent mixing of coarse particles, commercially available Li 1.33 Ti 1.66 O 4 having a volume average particle size of 1.0 μm was repeated five times with ASTM 400 mesh to obtain lithium titanium composite oxide (B). .

(Preparation of negative electrode active material 3)
In order to prevent mixing of coarse particles, commercially available Li 1.33 Ti 1.66 O 4 having a volume average particle size of 0.1 μm was repeated five times with ASTM 400 mesh to obtain lithium titanium composite oxide (C). .

(Preparation of negative electrode active material 4)
In order to prevent mixing of coarse particles, commercially available scaly natural graphite powder was repeated five times with an ASTM 400 mesh sieve. The negative electrode active material obtained here was graphitic carbonaceous (D).

  The composition, structure, shape, physical properties, etc. of the negative electrode active material are summarized in Table 1.

[Production of battery]
<< Preparation of positive electrode 1 >>
90% by mass of lithium cobaltate (LiCoO 2 ) as a positive electrode active material, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder, an N-methylpyrrolidone solvent Mixed in to a slurry. The obtained slurry was applied to one side of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 80 μm with a press. At this time, the density of the active material of the positive electrode was 2.35 g / cm 3 .

<< Preparation of negative electrode 1 >>
90 parts by weight of the negative 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 in an N-methylpyrrolidone solvent to form a slurry. The obtained slurry was applied to one side of a rolled copper foil having a thickness of 10 μm, dried, and rolled to a thickness of 90 μm with a press.

<< Preparation of non-aqueous electrolyte 1 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF 6 ) was dissolved. Furthermore, lithium difluorophosphate (LiPO 2 F 2 ) was contained so as to be 0.3% by mass.

<< Preparation of non-aqueous electrolyte 2 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF 6 ) was dissolved. Furthermore, trimethylsilyl methanesulfonate was contained so as to be 0.3% by mass.

<< Preparation of non-aqueous electrolyte 3 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF 6 ) was dissolved. Furthermore, hexamethylcyclotrisiloxane was contained so that it might become 0.3 mass%.

<< Preparation of non-aqueous electrolyte solution 4 >>
Under a dry argon atmosphere, a well-dried hexafluorophosphorus at a concentration of 1 mol / L in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4) Lithium acid (LiPF 6 ) was dissolved.

(Production of battery 1)
The negative electrode and the positive electrode were punched to 12.5 mmφ, vacuum-dried at 110 ° C., and then transferred to a glove box. In an argon atmosphere, the positive electrode and the negative electrode were opposed to each other via a polyethylene separator punched to 14 mmφ, and the nonaqueous electrolyte solution was A 2032 type coin battery (lithium ion secondary battery) was prepared by adding the non-aqueous electrolyte described in the preparation section.

Example 1
A negative electrode prepared as the lithium-titanium composite oxide (A) as the negative electrode active material in the section <Preparation of Negative Electrode 1>, a positive electrode prepared in the section <Preparation of Positive Electrode 1>, and a preparation in the section <Preparation of Nonaqueous Electrolytic Solution 1> Using the non-aqueous electrolyte solution, a battery was prepared by the method described in “Preparation of battery 1”. With respect to this battery, the battery evaluation described in the section << Battery evaluation >> was performed. The results are shown in Table 2.

Example 2
A battery was prepared in the same manner as in Example 1 except that the lithium-titanium composite oxide (B) was used as the negative electrode active material in the section <Preparation of negative electrode 1>, and the battery evaluation described in section <Battery evaluation> was performed. . The results are shown in Table 2.

Example 3
A battery was prepared in the same manner as in Example 1 except that the lithium-titanium composite oxide (C) was used as the negative electrode active material in the section <Preparation of negative electrode 1>, and the battery evaluation described in section << Battery evaluation >> was performed. . The results are shown in Table 2.

Examples 4-6
Batteries were prepared and evaluated in the same manner except that the non-aqueous electrolytes of Examples 1 to 3 were replaced with the non-aqueous electrolyte prepared in the section “Preparation of Non-Aqueous Electrolyte 2”. did. The results are shown in Table 2.

Examples 7-9
Batteries were prepared and evaluated in the same manner except that the non-aqueous electrolytes of Examples 1 to 3 were replaced with the non-aqueous electrolyte prepared in the section << Preparation of Non-Aqueous Electrolytic Solution 3 >>. did. The results are shown in Table 2.

Comparative Examples 1-3
Batteries were prepared and evaluated in the same manner except that the non-aqueous electrolytes of Examples 1 to 3 were replaced with the non-aqueous electrolyte prepared in the section << Preparation of Non-Aqueous Electrolyte 4 >>. did. The results are shown in Table 2.

Comparative Example 4
A battery was prepared in the same manner as in Example 1 except that graphite carbonaceous material (D) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed. The results are shown in Table 2.

Comparative Example 5
Batteries were prepared and evaluated in the same manner except that the non-aqueous electrolyte solution of Comparative Example 4 was replaced with the non-aqueous electrolyte solution prepared in the section “Preparation of Non-Aqueous Electrolyte Solution 2”. The results are shown in Table 2.

Comparative Example 6
Batteries were prepared and evaluated in the same manner except that the non-aqueous electrolyte solution of Comparative Example 4 was replaced with the non-aqueous electrolyte solution prepared in the section “Preparation of Non-Aqueous Electrolyte Solution 3”. The results are shown in Table 2.

Comparative Example 7
Batteries were prepared and evaluated in the same manner except that the non-aqueous electrolyte solution of Comparative Example 4 was replaced with the non-aqueous electrolyte solution prepared in the section “Preparation of non-aqueous electrolyte solution 4”. The results are shown in Table 2.

<Battery evaluation>
(Capacity measurement)
The battery capacity was calculated from the amount of active material present on the copper foil by converting the lithium-titanium composite oxide to 175 mAh / g and the graphitic carbonaceous material to 350 mAh / g for a new battery that has not been charged and discharged. . With respect to the lithium-titanium composite oxide at 0.2 C (the rated capacity due to the discharge capacity at 1 hour rate is assumed to be 1 C, the same applies hereinafter) with this battery capacity as a reference, the voltage range 2. Initial charge / discharge of 5 cycles was performed at 7V to 1.9V and 25 ° C. Similarly, initial charge / discharge of the graphitic carbon was performed in a voltage range of 4.1 V to 3.0 V and 25 ° C. The discharge capacity at the 5th cycle at this time was defined as the initial capacity.

(Measurement of output resistance)
Charging for 150 minutes at a constant current of 0.2C in an environment of 25 ° C and discharging for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C and 10.0C, respectively, in an environment of -30 ° C The voltage at the 10th second was measured. The slope of the current-voltage line is defined as output resistance (Ω), and the results are shown in Table 2.

In Table 2, “output resistance reduction rate” is a reduction rate (%) of the output resistance compared to the output resistance of the corresponding battery not containing the specific compound.

  As can be seen from the results in Table 2, it contains lithium difluorophosphate, trimethylsilyl methanesulfonate, hexamethylcyclotrisiloxane, and contains a metal oxide containing titanium that can occlude and release lithium. It was found that the output resistance was drastically reduced by using the negative electrode active material.

  The use of the lithium ion secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. , Electronic notebook, calculator, memory card, portable tape recorder, radio, backup power supply, motor, automobile, motorcycle, motorbike, bicycle, lighting equipment, toy, game equipment, clock, electric tool, strobe, camera, etc. Can do. In particular, the lithium ion secondary battery of the present invention has a low output resistance and a low environmental load, and can be widely and suitably used for various purposes.

Claims (11)

  1. A non-aqueous electrolyte solution containing a non-aqueous solvent and a lithium salt, and a lithium ion secondary battery having a positive electrode active material and a negative electrode active material,
    The non-aqueous electrolyte contains 10 ppm or more of lithium difluorophosphate in the whole non-aqueous electrolyte,
    In addition, the negative electrode active material is a negative electrode active material containing a lithium-titanium composite oxide containing titanium that can occlude and release lithium represented by the following general formula (4). Lithium ion secondary battery.
    Li x Ti y M z O 4 (4)
    [In General Formula (4), 1.2 ≦ x ≦ 1.4, 1.5 ≦ y ≦ 1.7, 0 ≦ z ≦ 1.6, and M is Na, K, Co, Al, Fe , Ti, Mg, Cr, Ga, Cu, Zn, and at least one element selected from the group consisting of Nb. ]
  2. The lithium ion secondary battery according to claim 1, wherein the metal oxide has a spinel structure.
  3. 3. The lithium ion secondary battery according to claim 1 , wherein, in the general formula (4), 1.2 ≦ x ≦ 1.4, 1.5 ≦ y ≦ 1.7, and z = 0.
  4. The lithium ion secondary battery according to any one of claims 1 to 3 , wherein the metal oxide has a BET specific surface area of 0.5 m 2 / g or more and 200 m 2 / g or less.
  5. The volume average particle diameter of the metal oxide, 0.1 [mu] m or more, the lithium ion secondary battery according to any one of claims 1 to claim 4 is 50μm or less.
  6. The average primary particle diameter of the metal oxide, 0.01 [mu] m or more, the lithium ion secondary battery according to any one of claims 1 to claim 5 is 2μm or less.
  7. The lithium ion secondary battery according to any one of claims 1 to 6 , wherein the current collector of the lithium ion secondary battery is a metal foil film containing Cu and / or Al.
  8. Nonaqueous electrolytic solution, the lithium difluorophosphate in the entire nonaqueous electrolyte 0.01 mass% or more, according to any one of claims 1 to claim 7 are those containing more than 5 wt% Lithium ion secondary battery.
  9. The lithium ion secondary battery according to any one of claims 1 to 8 , wherein the total area of the positive electrode area with respect to the surface area of the exterior of the secondary battery is 20 times or more in terms of area ratio.
  10. The lithium ion secondary battery according to any one of claims 1 to 9 , wherein a DC resistance component of the secondary battery is 10 milliohms (mΩ) or less.
  11. The lithium ion secondary according to any one of claims 1 to 10, wherein an electric capacity of a battery element housed in one battery case of the secondary battery is 3 ampere hours (Ah) or more. battery.
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