JP5503098B2 - Non-aqueous electrolyte for secondary battery and secondary battery using the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery using the same, and more particularly, a non-lithium secondary battery having high rate characteristics and excellent safety during overcharge. The present invention relates to an aqueous electrolyte and a lithium secondary battery using the same.

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

As an electrolyte for a lithium secondary battery, an electrolyte such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ (CF ₂ ) ₃ SO ₃ , Cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain esters such as methyl acetate and methyl propionate Cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and tetrahydropyran; chain ethers such as dimethoxyethane and dimethoxymethane; nonaqueous systems dissolved in nonaqueous solvents such as sulfur-containing organic solvents such as sulfolane and diethylsulfone Uses electrolyte It has been.

  In these lithium secondary batteries, excessive release of lithium occurs at the positive electrode during overcharge abnormality, while excessive storage of lithium occurs at the negative electrode, and in some cases, metallic lithium is deposited. Both the positive electrode and the negative electrode in such a state are placed in a thermally unstable state, causing decomposition of the electrolyte solution and rapid heat generation, thereby causing abnormal battery heat generation and impairing battery safety. Problem arises. Such a problem becomes particularly remarkable as the energy density of the non-aqueous electrolyte battery increases.

  In order to solve the above problems, a small amount of an aromatic compound (overcharge inhibitor) is added as an additive to the electrolyte of the non-aqueous electrolyte battery to ensure the safety of the battery in an overcharged state. Techniques to do so far have been proposed. For example, Patent Document 1 uses a small amount of biphenyl, 3-R-thiophene (R represents bromine, chlorine, or fluorine), furan, or 3-chlorothiophene as an additive to protect the battery in an overcharged state. And batteries incorporating these additives have been proposed. In this method, at a voltage higher than the maximum operating voltage of the battery, the additive is polymerized to increase the internal resistance of the battery, thereby ensuring the safety of the battery during overcharge.

  Furthermore, in Patent Document 2, terphenyl and alkyl group-substituted terphenyl are listed as additives, and in Patent Document 3, p-terphenyl is listed as an additive. This ensures battery safety during overcharge.

  Secondary batteries have been required to have high performance even in various usage environments due to the recent increase in market demand level. For example, as shown in the examples described later, Even when stored, the discharge capacity after storage can be kept large, the overvoltage at the time of large current discharge is small, and a large discharge capacity can be obtained, that is, the rate characteristics after high temperature storage are kept good. This is also an important characteristic.

  However, in the method described in Patent Document 1 to Patent Document 3, when the battery is stored at a high temperature in a charged state, a part of the additive reacts, and the polymer causes an increase in battery internal resistance. There was a problem that the battery characteristics deteriorated.

  In particular, in recent years, higher battery capacity has been required, but in general, a high-capacity battery, when it falls into an abnormal state such as overcharge, due to its inherent energy, If a phenomenon such as rupture occurs, it may cause serious damage. Therefore, in such a high capacity battery, the importance of the overcharge inhibitor is particularly increased. However, the high capacity battery is required to have a rate characteristic, that is, a discharge characteristic at a large current at the same time, for example, for automobiles. It is often done. However, as described above, when the overcharge inhibitor reacts after storage at a high temperature to increase the internal resistance of the battery, the rate characteristic is remarkably deteriorated.

Patent Document 4 uses a non-aqueous electrolyte containing a cyclic siloxane and / or a reaction product thereof, and Patent Document 5 uses a non-aqueous electrolyte containing a silicon compound having a specific structure. It is described that both the input / output characteristics and the cycle characteristics can be improved. Although these methods are certainly effective for that purpose, they are not supposed to be used during overcharging, and have not contributed to the safety during overcharging. In addition, there is no disclosure regarding special effects resulting from the combined use with an overcharge additive, and such effects have not been covered by the inventions described in these patent documents.
JP-A-9-106835 JP 2000-58116 A Japanese Patent Laid-Open No. 2001-15158 JP 2004-71458 A JP 2004-87459 A

  The present invention has been made in view of the background art, and the problem is that the non-aqueous electrolyte secondary battery can be compatible with both safety during overcharge and good rate characteristics after high-temperature storage. An object is to provide an aqueous electrolyte solution and a non-aqueous electrolyte secondary battery.

  As a result of intensive studies to solve the above problems, the present inventors have found that when a specific compound is added to or contained in a certain amount in addition to the overcharge inhibitor, a high temperature is maintained while maintaining overcharge safety. The inventors have found that the storage characteristics and the rate characteristics after storage can be kept good, and that the above object can be achieved, and the present invention has been achieved.

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

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

［一般式（３）中、Ｒ^６〜Ｒ^８は互いに同一であっても異なっていてもよい炭素数１〜１２の有機基を表し、ＡはＨ、Ｃ、Ｎ、Ｏ、Ｆ、Ｓ、Ｓｉ及び／又はＰから構成される基を表す。］ That is, the present invention is a non-aqueous electrolyte for a secondary battery in which a lithium salt is contained in a non-aqueous solvent, which contains an overcharge inhibitor, and is further a cyclic siloxane represented by the general formula (1) Compound, fluorosilane compound represented by general formula (2), compound represented by general formula (3), compound having SF bond in molecule, nitrate, nitrite, monofluorophosphate, difluorophosphorus A non-aqueous electrolyte for a secondary battery comprising at least one compound selected from the group consisting of acid salts, acetates, and propionates in an amount of 10 ppm or more in the whole non-aqueous electrolyte. .

[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; ]

  The present invention also provides a non-aqueous electrolyte secondary battery comprising at least a non-aqueous electrolyte, a negative electrode capable of inserting and extracting lithium ions, and a positive electrode, wherein the non-aqueous electrolyte is a non-aqueous electrolyte for a secondary battery as described above. It exists in the non-aqueous electrolyte secondary battery characterized by being an aqueous electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to supply the secondary battery which satisfy | fills simultaneously a high rate characteristic and the safety | security at the time of an overcharge.

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

<Nonaqueous electrolyte for secondary battery>
The non-aqueous electrolyte solution for secondary batteries of the present invention contains an electrolyte and a non-aqueous solvent that dissolves the electrolyte, in the same manner as a normal non-aqueous electrolyte solution.

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

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

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

A preferred example of using two or more lithium salts in combination is a combination of LiPF ₆ and LiBF _{4. In} this case, the proportion of LiBF _{4 in} the total of both is 0.01% by mass or more, 20 Those having a mass% or less are particularly preferred, and those having a mass% of 0.1% or more and 5% by mass or less are more preferred. 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 is particularly preferable, and 80% by mass or more and 98% by mass or less is more preferable. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

[Nonaqueous solvent]
Examples of the non-aqueous solvent include the following.
(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, particularly preferably 1 to 4, respectively. Specific examples include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.
(3) Cyclic ester Specific examples include γ-butyrolactone and γ-valerolactone.
(4) Cyclic ether Specific examples include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like.
(5) Chain ether Specific examples include dimethoxyethane and dimethoxymethane.
(6) Sulfur-containing organic solvent Specific examples include sulfolane and diethylsulfone.
(7) Chain ester Specific examples include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.

  These may be used alone or in combination of two or more, but it is preferable to use two or more compounds in combination. 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 80% by volume or more, preferably 85% by volume or more, more preferably 90% by volume or more, and the cyclic carbonates and the chain carbonates. The capacity of the cyclic carbonates with respect to the total with the carbonates is 5% or more, preferably 10% or more, more preferably 15% or more, and the upper limit is usually 50% or less, preferably 35% or less, more preferably 30%. It is as follows. Use of a combination of these non-aqueous solvents is preferable because the balance between cycle characteristics and high-temperature storage characteristics (particularly, remaining capacity and high-load discharge capacity after high-temperature storage) of a battery produced using the non-aqueous solvent is improved.

  In this mixed solvent, a lithium salt, a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and a molecule Non-aqueous electrolyte containing at least one compound selected from the group consisting of a compound having SF bond, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate Is preferable because the balance between the cycle characteristics and high-temperature storage characteristics (particularly, the remaining capacity and high-load discharge capacity after high-temperature storage) and gas generation suppression of a battery produced using the same is improved.

  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. Furthermore, the amount of propylene carbonate in the whole non-aqueous solvent is usually 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, usually 10% by volume or less, preferably 8% by volume or less, More preferably, it is preferably 5% by volume or less because the low-temperature characteristics are further excellent while maintaining the combination characteristics of ethylene carbonate and chain carbonates.

  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 number of carbon atoms of the alkyl group constituting the dialkyl carbonate is preferably 1 or 2.

  Another example of a preferable mixed solvent is one containing a chain ester. 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, and the upper limit is usually 50% or less, preferably 35% or less, more preferably 30 % Or less, more preferably 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 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.

The non-aqueous electrolyte for secondary batteries of the present invention is characterized by containing an overcharge inhibitor. Although there is no limitation in particular as an overcharge inhibiting agent, the compound etc. which are shown to following (1), (2) or (3) are preferable.
(1) Biphenyl, terphenyl, diphenyl ether or dibenzofuran optionally substituted with an alkyl group and / or a fluorine atom (2) Partially hydrogenated terphenyl (3) Tertiary alkyl group, cycloalkyl group, fluorine atom And / or benzene substituted with a methoxy group

  Although there is no limitation in particular as a compound of (1), For example, benzene ring connection compounds, such as biphenyl, alkylbiphenyl, and terphenyl; Fluorine-containing benzene ring connection compounds, such as 2-fluorobiphenyl; Aromatic ethers, such as diphenyl ether And heteroaromatic ring linking compounds such as dibenzofuran.

  The compound (3) is not particularly limited, but examples thereof include (cyclo) alkylbenzenes such as cyclohexylbenzene, t-butylbenzene, and t-amylbenzene; fluorine atoms such as o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene Substituted benzenes; fluorinated anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole and the like can be mentioned.

  Preferable specific examples include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran. These are particularly preferable because the effect of improving rate characteristics after high-temperature storage in the present invention is increased.

  Two or more overcharge inhibitors 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.

  Here, the partial hydride of terphenyl refers to a product in which hydrogen is partially added to the double bond of the benzene ring of terphenyl. The partial hydride of terphenyl may be a single compound or a mixture of a plurality of compounds. For example, it may be a mixture of two or more terphenyl partial hydrides having different partial hydrogenation rates, or a terphenyl partial hydride having the same partial hydrogenation rate. Moreover, even if it is a mixture of what is different in the position of the hydrogenated benzene ring, the mixture and the mixture containing a structural isomer from which the position of a double bond differs may be sufficient.

  The partial hydrogenation rate of terphenyl is 0% for the hydrogenation of the double bond of the benzene ring of terphenyl, but the partial hydrogenation rate is 0%. When hydrogen is added (when 1 mol of terphenyl adds 18 mol of hydrogen atoms), the partial hydrogenation rate is calculated as 100%, and in the case of a mixture, the value per mol average. For example, when 2 moles of hydrogen atoms are added to 1 mole of terphenyl, the partial hydrogenation rate is 11.1% (= 2/18).

  When the partial hydrogenation rate defined as described above is used, the partial hydrogenation rate of the terphenyl partial hydride used in the present invention can be greater than 0% and less than 100%. The terphenyl partial hydride may include terphenyl (partial hydrogenation rate 0%), m-terphenyl complete hydride (partial hydrogenation rate 100%), but the molar average partial hydrogenation rate of the mixture. Is preferably over 0% and less than 100%. From the viewpoint of storage characteristics of the battery and solubility in the electrolytic solution, the partial hydrogenation rate of terphenyl is preferably 30 to 70%, more preferably 35 to 60%. The terphenyl or terphenyl partial hydride is not particularly limited, but m-terphenyl or m-terphenyl partial hydride is particularly preferable.

  The ratio of these overcharge inhibitors in the non-aqueous electrolyte is usually 0.01% by mass or more, preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and the upper limit is Usually, it is 5 mass% or less, preferably 3 mass% or less, particularly preferably 2 mass% or less. If the lower limit is not reached, safety may not be sufficiently ensured during overcharge. If the upper limit is exceeded, a battery having good storage characteristics may not be obtained even when mixed with the following specific compound.

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

[[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 these, those having a small number of carbon atoms tend to exhibit characteristics, and organic groups having 1 to 6 carbon atoms are preferable. Also, the alkenyl group acts on the electrolyte solution and the electrode surface coating to improve input / output characteristics, and the aryl group is preferable because it captures radicals generated in the battery during charge / discharge and improves the overall battery performance. . 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. 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. Further, 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, so that it may be difficult to contain a predetermined amount in the electrolytic solution. Moreover, even if it is made to contain in 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.

  In addition, as with 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 electrolytic solution and the coating on the electrode surface. 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 point of view, the organic group is preferably a methyl group, a vinyl group or a phenyl group. Examples of the compound include monofluoro such as trimethylfluorosilane, vinyldimethylfluorosilane, phenyldimethylfluorosilane, vinyldiphenylfluorosilane. Silanes are particularly preferred.

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

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

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

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

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

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

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

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

  The ratio of these specific compounds in the non-aqueous electrolyte solution is essential to be 10 ppm or more (0.001 mass% or more) in total with respect to the total non-aqueous electrolyte solution, but is preferably 0.01 mass% or more. Preferably it is 0.05 mass% or more, More preferably, it is 0.1 mass% or more. The upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less. If the concentration of the specific compound is too low, it may be difficult to obtain the effect of improving the low temperature characteristics. On the other hand, if the concentration is too high, the charge / discharge efficiency may be lowered. When these specific compounds are actually used as non-aqueous electrolytes for the production of secondary batteries, even if the batteries are disassembled and the non-aqueous electrolytes are taken out again, the content of these specific compounds is often significantly reduced. . 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.

  In preparing the non-aqueous electrolyte, each raw material is preferably dehydrated in advance, and the water content is usually 50 ppm or less, preferably 30 ppm or less, and particularly preferably 10 ppm or less.

  The reason why the post-storage rate characteristics are hardly deteriorated by the overcharge additive when a specific compound is present is not clear, but is estimated as follows. Usually, the overcharge inhibitor forms a polymer film on the surface of the positive electrode during overcharge to greatly increase the internal resistance of the battery, or by operating a current interrupting device inside the battery can with the gas generated during this polymerization. , The safety of the secondary battery can be improved, etc., but this polymerized film is partially generated even when the charged battery is stored at a high temperature, which causes a decrease in the discharge capacity of the battery and a deterioration in the rate characteristics. It is thought that. When the specific compound specified in the present invention is present, the compound acts on the surface of the positive electrode to form a weak barrier, thereby suppressing the reaction between the overcharge inhibitor and the positive electrode active material in a normal charged state. However, if the battery is overcharged and the positive electrode becomes excessively active, this weak barrier breaks down, or the reaction between the positive electrode and the overcharge inhibitor is accelerated and polymerized by exceeding the barrier inhibition. It is considered that the reaction proceeds and safety can be secured during overcharge as intended.

[Other compounds]
The non-aqueous electrolyte solution of the present invention contains an electrolyte lithium salt, an overcharge inhibitor and a specific compound as essential components, but other compounds can be arbitrarily added as necessary as long as the effects of the present invention are not impaired. Can be contained in an amount of. Examples of such other compounds include vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride. , Negative electrode film forming agents such as cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, busulfan, toluene sulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, Diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide , The positive electrode protecting agent such as di-pyridinium disulfide and the like.

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

  As the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate, busulfan and the like 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 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.

  The method for preparing the non-aqueous electrolyte for secondary batteries of the present invention is not particularly limited, and a lithium salt, an overcharge inhibitor, a specific compound, and other compounds as required are dissolved in a non-aqueous solvent according to a conventional method. Can be prepared.

<Non-aqueous electrolyte secondary battery>
Hereinafter, the non-aqueous electrolyte secondary battery of the present invention will be described in detail.
[Battery shape]
The battery shape is not particularly limited, and examples thereof include a bottomed cylindrical shape, a bottomed square shape, a thin shape, a sheet shape, and a paper shape. When incorporating into a system or device, in order to increase the volumetric efficiency and improve the storage capacity, it may be of a different shape such as a horseshoe shape or a comb shape considering the fit in 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 cycleability and high-temperature storage even for high-power and large-capacity batteries, and increase the heat dissipation efficiency during abnormal heat generation. It is possible to suppress a dangerous state of “rupture”.

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

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

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

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

  These surface adhering materials are, for example, dissolved or suspended in a solvent and impregnated and added to the positive electrode active material, and dried. It can be made to adhere to the positive electrode active material surface by the method of making it react by the method etc., the method of adding to a positive electrode active material precursor, and baking simultaneously.

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

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

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

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

[[[Median diameter d ₅₀ ]]]
The median diameter d _{50 of the} particles (secondary particle diameter when primary particles are aggregated to form secondary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, most It is preferably 3 μm or more, 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. If the upper limit is exceeded, it takes time to diffuse lithium in the particles. When a conductive agent, 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 kinds of positive electrode active materials having different median diameters d ₅₀ , the filling property at the time of producing the positive electrode can be further improved.

The median diameter d ₅₀ in the present invention is measured by a known laser diffraction / scattering type particle size distribution measuring apparatus. 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, usually 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. If the above upper limit is exceeded, it is difficult to form spherical secondary particles, which adversely affects the powder filling property, or the specific surface area is greatly reduced, so that there is a high possibility that battery performance such as output characteristics will deteriorate. is there. On the other hand, when the value falls below the lower limit, there is a case where problems such as inferior reversibility of charge / discharge are usually caused because crystals are not developed.

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

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

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

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

[[Composition of positive electrode]]
Below, the structure of the positive electrode used for this invention is described.
[[[Electrode structure and fabrication method]]]
The positive electrode is produced by forming a positive electrode active material layer containing positive electrode active material particles and a binder on a current collector. Manufacture of the positive electrode using a positive electrode active material can be performed by a conventional method. That is, a positive electrode active material and a binder, and if necessary, a conductive material and a thickener mixed in a dry form into a sheet form are pressure-bonded to the 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.

  The content of the positive electrode active material in the positive electrode active material layer is usually 10% by mass or more, preferably 30% by mass or more, and particularly preferably 50% by mass or more. Moreover, an upper limit is 99.9 mass% or less normally, Preferably it is 99 mass% or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient. In the present invention, the positive electrode active material may be used alone, or two or more of different compositions or different powder properties may be used in any combination and ratio.

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

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

[[[Conductive material]]]
A known conductive material can be arbitrarily used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite (graphite); carbon black such as acetylene black; and carbonaceous 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.

  In the positive electrode active material layer, the conductive material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and the upper limit is usually 50% by mass or less, preferably 30%. It is used so as to contain not more than 15% by mass, more preferably not more than 15% by mass. 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), fluororubber, isoprene rubber , Rubber polymers such as butadiene rubber and ethylene / propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, EPDM (ethylene-propylene-diene terpolymer), styrene / ethylene / butadiene / Ethylene copolymer, styrene Thermoplastic elastomeric polymer such as isoprene / styrene block copolymer or hydrogenated product thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer Soft resinous polymers such as polymers; Fluoropolymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers; alkali metal ions (especially lithium ions) And a polymer composition having ion conductivity. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  The ratio of the binder in the positive electrode active material layer is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and usually 80% by mass or less, preferably 60% by mass or less. More preferably, it is 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 agent, 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.

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

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

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

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

[[[Electrode area]]]
In the non-aqueous electrolyte secondary battery of the present invention, the area of the positive electrode active material layer is preferably larger than the outer surface area of the battery outer case in order to improve the heat dissipation characteristics of the electrode in the event of an abnormality. . 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 is 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 square shape. . 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]]]
The non-aqueous electrolyte of the present invention is particularly effective when used for a secondary battery that requires high capacity, high rate characteristics, high output, long life, and high safety. As described above, it has been difficult to satisfy all of these conditions at the same time. However, this can be realized in the non-aqueous electrolyte secondary battery of the present invention using the non-aqueous electrolyte of the present invention for a high-capacity battery. Specifically, the electric capacity (electric capacity when the battery is discharged from the fully charged state to the discharged state) of the battery element housed in one battery exterior of the secondary battery is 3 ampere hours (Ah) or more. Is particularly preferred.

  Therefore, the positive electrode plate is preferably designed so that the discharge capacity is fully charged and is 3 ampere hours (Ah) or more and 20 Ah or less, and more preferably 4 Ah or more and 10 Ah or less. If it is less than 3 Ah, it is difficult to realize a high capacity and a high output, and the voltage drop due to the electrode reaction resistance becomes large when taking out a large current, and the power efficiency may be deteriorated. If it is larger than 20 Ah, the electrode reaction resistance is reduced and the power efficiency is improved, so that the capacity and the output are high, but the temperature distribution due to the internal heat generation of the battery during pulse charge and discharge is large, and the durability of repeated charge and discharge is inferior. In addition, the heat dissipation efficiency deteriorates due to sudden heat generation in the event of an abnormality such as an internal short circuit, and the probability that the internal pressure increases and the battery contents erupt violently (explosion) may increase.

[[[Positive electrode plate thickness]]]
The thickness of the positive electrode plate is not particularly limited. From the viewpoint of high capacity, high output, and high rate characteristics, the thickness of the composite material layer minus the metal foil thickness of the core material is The lower limit with respect to one side is preferably 10 μm or more, more preferably 20 μm or more, and the upper limit is preferably 200 μm or less, more preferably 100 μm or less.

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

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

  The metal composite oxide is not particularly limited as long as it can occlude and release lithium, but preferably contains titanium and / or lithium as a constituent component from the viewpoint of high current density charge / discharge characteristics.

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

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

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

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

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

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

(4) Raman R value, Raman half-value width The Raman R value of the carbonaceous material measured using the argon ion laser Raman spectrum method is usually 0.01 or more, preferably 0.03 or more, more preferably 0.10 or more. The upper limit is 1.50 or less, preferably 1.2 or less, more preferably 1.0 or less, and still more preferably 0.50 or less. When the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge / discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the electrolyte will increase, and the efficiency may decrease and the generation of gas may increase.

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

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

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

(5) BET specific surface area The specific surface area of the carbonaceous material measured using the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ² / g or more. More preferably, it is 1.5 m ² / g or more. The upper limit is usually 100 m ² / g or less, preferably 25 m ² / g or less, more preferably 15 m ² / g or less, and still more preferably 10 m ² / g or less. When the value of the specific surface area is less than this range, the acceptability of lithium is likely to deteriorate during charging when used as a negative electrode material, and lithium is liable to precipitate on the electrode surface, which may cause a safety problem. On the other hand, when it exceeds this range, when used as a negative electrode material, the reactivity with the electrolyte increases, gas generation tends to increase, and a preferable battery may be difficult to obtain.
The specific surface area according to the BET method is determined by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Riken Okura), preliminarily drying the sample at 350 ° C. for 15 minutes under a nitrogen flow, and then comparing the nitrogen relative to the atmospheric pressure. A value measured by a nitrogen adsorption BET one-point method using a gas flow method is used, using a nitrogen helium mixed gas that is accurately adjusted so that the pressure value becomes 0.3.

(6) Pore size distribution The pore size distribution of the carbonaceous material is determined by Hg porosimetry (mercury intrusion method). The pore diameter is 0.01 μm or more and 1 μm or less. The amount of unevenness due to steps, contact surfaces between particles, etc. is 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and the upper limit is 0.6 mL / g or less, preferably Is 0.4 mL / g or less, more preferably 0.3 mL / g or less. If this range is exceeded, a large amount of binder may be required during electrode plate formation. If it is less than the range, the high current density charge / discharge characteristics may be deteriorated, and the effect of mitigating the expansion / contraction of the electrode during charge / discharge may not be obtained.

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

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

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

(7) Circularity Using circularity as the degree of sphericity of the carbonaceous material, the circularity of particles having a particle size in the range of 3 to 40 μm is preferably 0.1 or more, particularly preferably 0.5 or more. Preferably it is 0.8 or more, more preferably 0.85 or more, and most preferably 0.9 or more. High circularity is preferable because high current density charge / discharge characteristics are improved.

The circularity is defined by the following formula. When the circularity is 1, a theoretical sphere is obtained.
Circularity = (perimeter of equivalent circle having the same area as the particle projection shape) / (actual circumference of particle projection shape)

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

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

(8) True density The true density of the carbonaceous material is usually 1.4 g / cm ³ or more, preferably 1.6 g / cm ³ or more, more preferably 1.8 g / cm ³ or more, and still more preferably 2.0 g / cm ^3. cm ³ and the upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase. In the present invention, the true density is defined by a value measured by a liquid phase substitution method (pycnometer method) using butanol.

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

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

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

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

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

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

(12) Sub-material mixing “Sub-material mixing” means that two or more carbonaceous materials having different properties are contained in the negative electrode and / or the negative electrode active material. The properties described here include one or more of X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, circularity, and ash content. Show properties.

  Particularly preferred embodiments include that the volume-based particle size distribution is not symmetrical when the median diameter is centered, that two or more carbonaceous materials having different Raman R values are contained, and the X-ray parameters are It is different.

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

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

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

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

The following physical properties are desired for the current collector substrate.
(1) Average surface roughness (Ra)
The average surface roughness (Ra) of the negative electrode active material thin film forming surface of the current collector substrate defined by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.05 μm or more, preferably 0.1 μm or more. The thickness is particularly preferably 0.15 μm or more, usually 1.5 μm or less, preferably 1.3 μm or less, particularly preferably 1.0 μm or less.

  By setting the average surface roughness (Ra) of the current collector substrate within the range between the lower limit and the upper limit described above, good charge / discharge cycle characteristics can be expected. By setting it to the above lower limit or more, the area of the interface with the negative electrode active material thin film is increased, and the adhesion with the negative electrode active material thin film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, but those having an average surface roughness (Ra) exceeding 1.5 μm are generally difficult to obtain as foils having a practical thickness as a battery. 1.5 μm or less is preferable.

(2) Tensile strength The tensile strength of the current collector substrate is not particularly limited, but is usually 100 N / mm ² or more, preferably 250 N / mm ² or more, more preferably 400 N / mm ² or more, and particularly preferably 500 N / mm ^2. That's it.

  The tensile strength is obtained by dividing the maximum tensile force required until the test piece breaks by the cross-sectional area of the test piece. The tensile strength in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high tensile strength, cracking of the current collector substrate due to expansion / contraction of the negative electrode active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained.

(3) 0.2% proof stress of 0.2% proof stress current collector substrate is not particularly limited, normally 30 N / mm ² or more, preferably 150 N / mm ² or more, particularly preferably 300N / mm ² or more .

  The 0.2% proof stress is the magnitude of the load necessary to give a plastic (permanent) strain of 0.2%. It means that The 0.2% proof stress 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 negative electrode active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained. Can do.

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

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

(16) Electrode density The electrode structure when the negative electrode active material is converted into an electrode is not particularly limited, but the density of the active material present on the current collector is preferably 1.0 g / cm ³ or more, more preferably Is 1.2 g / cm ³ , more preferably 1.3 g / cm ³ or more, and the upper limit is 2.0 g / cm ³ or less, preferably 1.9 g / cm ³ or less, more preferably 1.8 g / cm ^3. The range is ³ or less, more preferably 1.7 g / cm ³ or less. If it exceeds this range, the active material particles are destroyed, which may lead to an increase in initial irreversible capacity and deterioration of high current density charge / discharge characteristics due to a decrease in the permeability of the electrolyte solution near the current collector / active material interface. On the other hand, if it is lower, the conductivity between the active materials is lowered, the battery resistance is increased, and the capacity per unit volume may be lowered.

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

  The solvent for forming the slurry is not particularly limited as long as it is a solvent capable of dissolving or dispersing the negative electrode active material, the binder, and the thickener and conductive agent used as necessary. Alternatively, either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, alcohol and the like, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N , N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. . In particular, when an aqueous solvent is used, a dispersant or the like is added in addition to the above-described thickener, and a slurry is formed using a latex such as SBR. In addition, these may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

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

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

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

(18) Electrode orientation ratio The electrode orientation ratio is preferably 0.001 or more, particularly preferably 0.005 or more, more preferably 0.01 or more, and the upper limit is 0.67 or less, which is a theoretical value. Below this range, the high-density charge / discharge characteristics may deteriorate.
The measurement of the electrode plate orientation ratio is as follows. About the negative electrode after pressing to the target density, the active material orientation ratio of the electrode is measured by X-ray diffraction. The specific method is not particularly limited. As a standard method, peak separation is performed by fitting peaks of carbon (110) diffraction and (004) diffraction by X-ray diffraction using asymmetric Pearson VII as a profile function. The integrated intensities of the peaks of (110) diffraction and (004) diffraction are calculated. From the obtained integrated intensity, a ratio represented by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated. The electrode active material orientation ratio calculated by this measurement is defined as the electrode plate orientation ratio.

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

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

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

  The area of the negative electrode plate is not particularly limited, but is designed to be slightly larger than the opposing positive electrode plate so that the positive electrode plate does not protrude from the negative electrode plate. From the viewpoint of suppressing the life of a cycle in which charge and discharge are repeated and deterioration due to high temperature storage, it is preferable that the area be as close to the positive electrode as possible, since the ratio of electrodes that work more uniformly and effectively is increased and the characteristics are improved. In particular, when the electrode is used at a large current, the design of the electrode area is important. The thickness of the negative electrode plate is designed according to the positive electrode plate to be used and is not particularly limited, but the thickness of the composite layer obtained by subtracting the thickness of the metal foil of the core is usually 15 μm or more, Preferably it is 20 micrometers or more, More preferably, it is 30 micrometers or more, and an upper limit is 150 micrometers or less, Preferably it is 120 micrometers or less, More preferably, it is 100 micrometers or less.

[Separator]
The separator used in the non-aqueous electrolyte secondary battery of the present invention has a predetermined mechanical strength that electrically insulates both electrodes, has a high ion permeability, and has an oxidizing property and a negative electrode on the side in contact with the positive electrode. If it has the tolerance to the reducibility in the side, it will not specifically limit. As a material for the separator having such required characteristics, a resin, an inorganic material, glass fiber, or the like is used. As the resin, olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon and the like are used. Specifically, it is preferable to select from materials that are stable with respect to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene. As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used, and those having a particle shape or fiber shape are used. As the form, a thin film shape such as a non-woven fabric, a woven fabric, or a microporous film is used. In the thin film shape, those having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the independent thin film shape, a separator formed by forming a composite porous layer containing the inorganic particles on the surface layer of the positive electrode and / or the negative electrode using a resin binder can be used. For example, what formed the alumina particle whose 90% particle diameter is less than 1 micrometer on both surfaces of the positive electrode as a porous layer using the binder of a fluororesin is mentioned.

[Electrode group]
The electrode group has a laminated structure in which the positive electrode plate and the negative electrode plate are interposed via the separator, and a structure in which the positive electrode plate and the negative electrode plate are wound in a spiral shape via the separator. Either may be used. The ratio of the volume of the electrode group to the battery internal volume (hereinafter referred to as electrode group occupancy) is preferably 40% to 90%, and more preferably 50% to 80%. If the electrode group occupancy is less than 40%, the battery capacity is small, and if it is 90% or more, the void space is small, the member expands when the battery becomes high temperature, and the vapor pressure of the liquid component of the electrolyte is high. As a result, the internal pressure rises, and various characteristics such as charge / discharge repetition performance and high-temperature storage as a battery are deteriorated. Further, a gas release valve that releases the internal pressure to the outside may operate.

[Current collection structure]
The current collecting structure is not particularly limited, but in order to achieve high rate characteristics, which is the gist of the non-aqueous electrolyte secondary battery of the present invention, a structure that reduces the resistance of the wiring part and the joint part is adopted. There is a need. When such internal resistance is small, the effect of using the non-aqueous electrolyte solution for secondary batteries of the present invention is exhibited particularly well.

  In the case where the electrode group has the laminated structure described above, a structure formed by bundling the metal core portions of the electrode layers and welding them to the terminals is preferably used. When the area of one electrode increases, the internal resistance increases. Therefore, it is also preferable to provide a plurality of terminals in the electrode to reduce the resistance. When the electrode group has the winding structure described above, the internal resistance can be lowered by providing a plurality of lead structures on 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 0.1 milliohms or less, 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 for a secondary battery according to the present invention is effective in suppressing an increase in reaction resistance related to desorption / insertion of lithium with respect to an electrode active material due to a reaction of an overcharge inhibitor, and a factor that can realize good rate characteristics It is thought that. However, in a normal battery having a DC resistance of more than 10 Ωm, the effect of suppressing reaction resistance may not be reflected 100% on the rate characteristics due to inhibition by the DC resistance. This can be improved by producing a battery having a small DC resistance component, and the effect of the non-aqueous electrolyte solution for a secondary battery of the present invention can be sufficiently exhibited.

  Moreover, from the viewpoint of drawing out the effect of the non-aqueous electrolyte and producing a battery with high capacity, high output, high rate characteristics, long life, and high safety, this requirement and one battery of the secondary battery described above. It is particularly preferable that the battery element housed in the exterior satisfies the requirement that the electric capacity (electric capacity when the battery is discharged from a fully charged state to a discharged state) is 3 ampere hours (Ah) or more at the same time.

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

  In the exterior case using the above metals, a laser-sealed, resistance-welded, ultrasonic welding is used to weld the metals together to form a sealed sealed structure, or a caulking structure using the above-mentioned metals via a resin gasket To do. Examples of the outer case using the laminate film include those having a sealed and sealed structure by heat-sealing resin layers. In order to improve the sealing performance, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when a resin layer is heat-sealed through a current collecting terminal to form a sealed structure, a metal and a resin are joined, so that a resin having a polar group or a modified group having a polar group introduced as an intervening resin Resins are preferably used.

[Protective element]
PTC (Positive Temperature Coefficient), thermal fuse, thermistor, which increases resistance when abnormal heat is generated or excessive current flows, the current flowing through the circuit due to a 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 to design the protective element so as not to cause abnormal heat generation or thermal runaway even without the protective element.

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

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

[Production of negative electrode]
Artificial graphite powder KS-44 (manufactured by Timcal, trade name) 98 parts by mass, 100 parts by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration 1% by mass of carboxymethylcellulose sodium) as a thickener and binder, and 2 parts by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by mass) was added and mixed with a disperser to form a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, and rolled to a thickness of 75 μm with a press, and the size of the active material layer was 104 mm in width, 104 mm in length, and 30 mm in width. It cut out in the shape which has a process part, and was set as the negative electrode.

[Battery assembly]
The 32 positive electrodes and the 33 negative electrodes were alternately arranged, and the porous polyethylene sheet separator (thickness 25 μm) was sandwiched between the electrodes. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. A current collecting tab was prepared by welding uncoated portions of each of the positive electrode and the negative electrode, and an electrode group was sealed in a battery can (outside dimension: 120 × 110 × 10 mm) with a gas discharge valve. . Thereafter, 20 mL of a non-aqueous electrolyte solution was injected into a battery can loaded with the electrode group, sufficiently infiltrated into the electrode, and sealed to produce a prismatic battery.

[Electric capacitance and DC resistance component]
The rated discharge capacity of this battery (the electric capacity of the battery element housed in one battery case) was as high as about 6 Ah, and the DC resistance component measured by the 10 kHz AC method was about 5 milliohms. .

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

(5C discharge capacity after storage)
A storage test was conducted in a high temperature environment of 60 ° C. A battery charged in advance by a constant current constant voltage method up to a charging upper limit voltage of 4.2 V in an environment of 25 ° C. was stored at 60 ° C. for one month. A rate test was performed on the battery after storage in an environment of 25 ° C. That is, a battery charged in advance by a constant current constant voltage method up to a charging upper limit voltage of 4.2 V in an environment of 25 ° C. was discharged at a constant current value corresponding to 5 C, and a 5 C discharge capacity was obtained after storage.

(Overcharge test)
An overcharge test was conducted in a 25 ° C. environment. Charging was performed at a constant current of 3 C from the discharged state (3 V), and the behavior was observed. Here, “valve operation” represents a phenomenon in which the gas discharge valve is activated and the electrolyte component is released, and “rupture” is a phenomenon in which the battery container is torn at a violent momentum and the contents are forcibly released. Represents.

Example 1
In a dry argon atmosphere, lithium hexafluorophosphate (LiPF ₆ ) was added at 1 mol / L to a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio 3: 3: 4). A non-aqueous electrolyte solution is prepared by mixing cyclohexylbenzene (CHB) in an amount of 1% by mass and hexamethylcyclotrisiloxane in an amount of 0.3% by mass with respect to the mixed solution. Was prepared. A battery was prepared by the above-described method using this nonaqueous electrolytic solution, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 2
In Example 1, a battery was prepared using a non-aqueous electrolyte prepared by mixing phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 3
In Example 1, a battery was prepared using a non-aqueous electrolyte prepared by mixing trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 4
In Example 1, instead of hexamethylcyclotrisiloxane, lithium difluorophosphate produced in accordance with the method described in Inorganic Nuclear Chemistry Letters (1969), 5 (7), pages 581 to 582 was mixed. A battery was prepared using a non-aqueous electrolyte, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 5
In Example 1, a battery was prepared using a non-aqueous electrolyte prepared by mixing biphenyl instead of cyclohexylbenzene, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 6
In Example 5, a battery was prepared using a non-aqueous electrolyte prepared by mixing phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 7
In Example 5, a battery was prepared using a non-aqueous electrolyte prepared by mixing trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 8
In Example 5, instead of hexamethylcyclotrisiloxane, lithium difluorophosphate prepared according to the method described in Inorganic Nuclear Chemistry Letters (1969), 5 (7), pages 581 to 582 was mixed. A battery was prepared using a non-aqueous electrolyte, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 9
In Example 1, a battery was prepared using a non-aqueous electrolyte prepared by mixing t-amylbenzene in place of cyclohexylbenzene, and the 5C discharge capacity was measured after storage. The results are shown in Table 1.

Example 10
In Example 1, instead of cyclohexylbenzene, a non-aqueous system prepared by mixing “partially hydride of m-terphenyl” having a m-terphenyl content of 3.7% by mass and a partial hydrogenation rate of 42%. A battery was prepared using the electrolytic solution, and the 5C discharge capacity was measured after storage. The results are shown in Table 1. The m-terphenyl partial hydride used in the examples was prepared by reacting m-terphenyl as a raw material with hydrogen gas in the presence of platinum, palladium, or nickel-based catalyst under high temperature and pressure conditions. Using. Moreover, the partial hydrogenation rate was determined as an average value from the composition ratio of the components of the partial hydride of m-terphenyl obtained by gas chromatography analysis. The content of m-terphenyl was also determined from this gas chromatographic analysis value.

Comparative Example 1
In Example 1, a battery was prepared using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured. The results are shown in Table 1.

Comparative Example 2
In Example 5, a battery was prepared using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured. The results are shown in Table 1.

Comparative Example 3
In Example 9, a battery was prepared using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured. The results are shown in Table 1.

Comparative Example 4
In Example 10, a battery was prepared using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and the 5C discharge capacity was measured. The results are shown in Table 1.

Comparative Example 5
In Example 1, a battery was prepared using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane and CHB, and the 5C discharge capacity was measured. The results are shown in Table 1.

  As is clear from Table 1, the lithium secondary batteries of Examples 1 to 10 containing the overcharge inhibitor and the specific compound in the non-aqueous electrolyte solution avoid the battery from bursting during the overcharge test. Of course, in the large current (5C) discharge test after storage, the characteristics better than those of the lithium secondary batteries of Comparative Examples 1 to 4 were exhibited. Its characteristics are close to those of the lithium secondary battery of Comparative Example 5 that does not contain an overcharge inhibitor, and it has been found that its practical value is very high in combination with the improvement of overcharge safety. .

  As described above, in a non-aqueous electrolyte solution for a secondary battery obtained by mixing a lithium salt with a non-aqueous solvent, an overcharge inhibitor is contained, and further, a cyclic siloxane compound represented by the general formula (1), a general formula Fluorosilane compound represented by (2), compound represented by general formula (3), compound having SF bond in molecule, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetic acid By using at least one compound selected from the group consisting of a salt and a propionate in a total amount of 10 ppm or more in the whole non-aqueous electrolyte, by using a non-aqueous electrolyte for a secondary battery, It was possible to satisfy the high current discharge characteristics and overcharge safety at the same time. In particular, a battery element housed in one battery exterior has a capacity of 3 ampere hours (Ah) or more, which is higher than a battery that has conventionally been difficult to satisfy these two elements at the same time. It became possible to have practicality.

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

Claims (5)

A non-aqueous electrolyte solution for a secondary battery lithium salt is is contained in the nonaqueous solvent, overcharge prevention, which is a tertiary alkyl group, a cycloalkyl group, a benzene which is substituted by fluorine atom and / or a methoxy group agents, for the entire non-aqueous electrolyte solution, 0.01 wt% or more, contains more than 5 wt%, further characterized that you containing di-fluoro lithium phosphate, 10 ppm or more in the entire nonaqueous electrolyte A non-aqueous electrolyte for a secondary battery. Containing organic amount of di-fluoro lithium phosphate, relative to the entire non-aqueous electrolyte solution, 0.01 wt% or more, a non-aqueous electrolyte solution for a secondary battery in which claim 1 Symbol placement than 5 wt%. A nonaqueous electrolyte secondary battery comprising at least a nonaqueous electrolyte, a negative electrode capable of inserting and extracting lithium ions, and a positive electrode, wherein the nonaqueous electrolyte is for the secondary battery according to claim 1 or 2 . A non-aqueous electrolyte secondary battery, which is a non-aqueous electrolyte solution. Moreover, the electrical capacitance of the battery element housed in one battery case of the non-aqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery according to claim 3, wherein at 3 amps over hours (Ah) or higher. Furthermore, the DC resistance component of the nonaqueous electrolyte secondary battery, 10 milliohms (milliohms) or less is claim 3 or claim 4 nonaqueous electrolyte secondary battery according.