JP2007194209A - Lithium secondary cell, and battery pack formed by connecting the plurality of it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a safe lithium secondary cell which ensures the high capacity, good product cycle and high output and maintains gas generation at low level even when its size is increased. <P>SOLUTION: The lithium secondary cell has a set of electrodes constituting a positive electrode and a negative electrode via a porous membrane separator and employs a nonaqueous electrolyte including a compound of general formula (1) [in this formula, R<SP>1</SP>and R<SP>2</SP>represent organic groups each of which includes 1 to 12 carbons and n is an integer from 3 to 10], a compound of general formula (2) [in this formula, R<SP>3</SP>to R<SP>5</SP>represent organic groups each of which includes 1 to 12 carbons, x is an integer from 1 to 3 and p, q and r are integers from 0 to 3 which meet the requirement of 1≤p+q+r≤3], a compound of general formula (3) [in this formula, R<SP>6</SP>to R<SP>8</SP>represent organic groups each of which includes 1 to 12 carbons and A is a group consisting of H, C, N, O, F, S, Si and/or P], a compound having an S-F bonding, a nitrate, a nitrite salt, a monofluorophosphate, a difluorophosphate, an acetate, and/or a propionate. A battery pack is formed by connecting the lithium secondary cells, in which a cooling mechanism is prepared for keeping the temperature of the battery pack below a specific temperature. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery, and more specifically, by using a non-aqueous electrolyte solution for a lithium secondary battery containing a specific component, a long life, high output, high safety, and large size. The present invention relates to a lithium secondary battery.

  Lithium secondary batteries are high-capacity secondary batteries and are used in various applications. However, they are mainly used for relatively small batteries such as mobile phones. The use of is expected to expand.

  Large batteries are particularly required to have a long life, high output and high safety, and simply increasing the size of a conventional small battery is not sufficient as performance. Various improvements of battery materials for improving output and life have been proposed (for example, Patent Document 1), but the structure and usage of large batteries are greatly different from those of small batteries. It has become clear whether batteries are effective.

Furthermore, a large battery for automobiles and the like is required to be lighter. However, when a lightweight laminate film is used as an exterior material, there is a problem because the large battery is easily affected by gas generation.
JP 2005-306619 A

  The present invention has been made in view of the background art, and the problem is that even when it is made larger, it has a large capacity, good life and high output, generates less gas, and is overcharged. In particular, it is to provide a lithium secondary battery with improved safety.

  As a result of diligent research to solve the above problems, the inventors have a long life and high output by using a non-aqueous electrolyte containing a compound selected from a specific group in a battery having a specific structure. In addition, the present inventors have found that a lithium secondary battery with low gas generation and high safety can be obtained, and the present invention has been completed.

［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 includes at least an electrode group in which a positive electrode and a negative electrode are interposed via a microporous membrane separator, and a non-aqueous electrolyte solution containing a lithium salt in a non-aqueous solvent, and these are provided on the battery exterior. A lithium secondary battery that is housed, wherein the positive electrode and the negative electrode are each formed by forming an active material layer containing an active material capable of inserting and extracting lithium ions on a current collector, The non-aqueous electrolyte 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 an SF bond in the molecule. And at least one compound selected from the group consisting of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate in an amount of 10 ppm or more in the entire non-aqueous electrolyte The exterior material that forms the battery exterior is a non-aqueous electrolytic solution having a sheet formed by using at least a part of the inner surface of the battery using a thermoplastic resin, accommodates the electrode group, and The present invention provides a lithium secondary battery that is an exterior material capable of sealing the electrode group by heat-sealing the plastic resin layers.

[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 an assembled battery comprising five or more lithium secondary batteries connected in series.

  The present invention also provides an assembled battery comprising a plurality of lithium secondary batteries connected to each other, the battery having a cooling mechanism for maintaining the battery at a constant temperature or lower. It is.

  According to the present invention, a lithium secondary battery with high capacity, long life, high output, less gas generation, and high safety even in overcharging can be obtained. A particularly suitable lithium secondary battery can be provided.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the gist of the present invention. The specific content of is not limited.

<Non-aqueous electrolyte for lithium 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. The electrolyte is not particularly limited as long as it is known to be a lithium salt that can be used as an electrolyte for a non-aqueous electrolyte solution for a lithium secondary battery, and examples thereof include the following.

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

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

A preferable example in the case of using two or more types together is a combination use of LiPF ₆ and LiBF _{4. In} this case, the ratio of LiBF _{4 in} the total of both is 0.01% by mass or more and 20% by mass or less. It is preferable that it is 0.1 mass% or more and 5 mass% or less especially. Another 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, more preferably 80% by mass or more and 98% by mass or less. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

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

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

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

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

  In this mixed solvent, a lithium salt and a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), and S in the molecule A non-aqueous electrolyte solution containing at least one compound selected from the group consisting of a compound having a -F bond, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate is This 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) and suppression of gas generation of a battery manufactured using this 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. When propylene carbonate is contained, the volume ratio of ethylene carbonate to propylene carbonate is usually 99: 1 to 40:60, preferably 95: 5 to 50:50.

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

  Other examples of preferred non-aqueous solvents are those containing chain esters. As the chain ester, methyl acetate, ethyl acetate and the like are particularly preferable. The capacity of the chain ester in the non-aqueous solvent is usually 5% or more, preferably 8% or more, more preferably 15% or more, usually 50% or less, preferably 35% or less, more preferably 30% or less, More preferably, it is 25% or less. 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 other preferable non-aqueous solvents include one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone, or two or more organic solvents selected from the group. The mixed solvent becomes 60% by volume or more of the whole. Such a mixed solvent preferably has a flash point of 50 ° C. or higher, and particularly preferably has a flash point of 70 ° C. or higher. A non-aqueous electrolyte using this solvent reduces evaporation of the solvent and leakage even when used at high temperatures. Among them, the amount of γ-butyrolactone in the nonaqueous solvent is 60% by volume or more, and the total of ethylene carbonate and γ-butyrolactone in the nonaqueous solvent is 80% by volume or more, preferably 90% by volume or more. And the volume ratio of ethylene carbonate to γ-butyrolactone is 5:95 to 45:55, or the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 80% by volume or more, preferably 90% When the ratio of ethylene carbonate to propylene carbonate is 30:70 to 60:40, the balance between cycle characteristics and large current discharge characteristics is generally improved.

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

  By adsorbing these specific compounds to the surface of the positive electrode active material or the surface of the metal material, side reactions with the electrolytic solution or the like can be suppressed. By suppressing side reactions on the surface of the positive electrode active material, gas generation is small, and even when a sheet-like exterior material is used, it is preferable that the battery is not deformed or the internal pressure is not increased. Further, it is preferable for use in a large battery that the side life on the surface of the positive electrode active material is suppressed to improve the battery life, output, and safety during overcharge. In addition, the suppression of side reactions on the surface of the metal material suppresses an increase in the DC resistance component during long-term use even when a simple welding method with low resistance is used to connect the current collecting tab and the terminal. Therefore, it is preferable for use in a large battery. Further, lowering the reaction resistance of the positive electrode is effective and preferable in order to further improve the output in a battery designed for high output such as the battery shape and the positive electrode area.

[[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. Alkenyl groups act on non-aqueous electrolytes and coatings on electrode surfaces to improve input / output characteristics, and aryl groups have the effect of capturing radicals generated in the battery during charge and discharge to improve overall battery performance. Therefore, it is preferable. Accordingly, R ¹ and R ² are particularly preferably a methyl group, a vinyl group, or a phenyl group.

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

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

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

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

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

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

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

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

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

  Examples of the compound represented by the general formula (3) include siloxane compounds such as hexamethyldisiloxane, 1,3-diethyltetramethyldisiloxane, hexaethyldisiloxane, and octamethyltrisiloxane; methoxytrimethylsilane, ethoxy Alkoxysilanes such as trimethylsilane; peroxides such as bis (trimethylsilyl) peroxide; carboxylic acid esters such as trimethylsilyl acetate, triethylsilyl acetate, trimethylsilyl propionate, trimethylsilyl methacrylate, 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 preferred. For example, methanesulfonyl fluoride, ethanesulfonyl fluoride, methanebis (sulfonyl fluoride), ethane-1,2-bis (sulfonyl fluoride), propane-1,3-bis (sulfonyl fluoride), 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 preferred from the standpoint of improving output characteristics and cycle characteristics, and lithium difluorophosphate is particularly preferred. These compounds synthesized in a non-aqueous solvent may be used as they are, or those synthesized separately and substantially isolated are added in a non-aqueous solvent or a non-aqueous electrolyte. May be.

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

  The ratio of these specific compounds in the non-aqueous electrolyte solution is essential to be 10 ppm or more (0.001 mass% or more) in total with respect to the total non-aqueous electrolyte solution, but is preferably 0.01 mass% or more. Preferably it is 0.05 mass% or more, More preferably, it is 0.1 mass% or more. The upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less.

If the concentration of the specific compound is too low, the following problems may occur. That is, since gas may be generated during long-term use and the battery internal pressure may increase or the battery exterior may be deformed, the weight of the battery and the battery shape can be reduced by using a specific exterior material described later in the present invention. The effect of high degree of freedom may not be exhibited. In addition, if the battery capacity of the lithium secondary battery exceeds 3 ampere hours (Ah), the decomposition reaction of the electrolyte solution on the electrode plate may not be suppressed during overcharging, and the battery may burst or ignite. However, even if it is 20 milliohms (mΩ) or less, a high output may not be obtained due to a large reaction resistance. In addition, even when a lithium secondary battery having a value of (2 × S ₁ / T), which will be described later, is set to 100 or more, the reaction resistance of the electrode plate is large, and heat is generated during an abnormality such as overcharge. ”Or“ fire ”. Even when a lithium secondary battery is formed with a value of (L / (2 × S ₂ )) of 1 or less, a high output may not be obtained due to the large reaction resistance of the electrode plate. Furthermore, when a current collector and a conductor that draws current to the outside are joined by either spot welding, high-frequency welding or ultrasonic welding, the welded portion will deteriorate over a long period of use, and the DC resistance component will increase. However, the output may decrease. Moreover, it may be difficult to obtain the effect of improving the battery output or the effect of improving the battery life. On the other hand, if the concentration of the specific compound is too high, the charge / discharge efficiency may be reduced.

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

  The nonaqueous electrolytic solution in the present invention can be prepared by dissolving an electrolyte lithium salt, a specific compound, and other compounds as required in a nonaqueous solvent. In preparing the non-aqueous electrolyte, each raw material is preferably dehydrated in advance, and the water content is usually 50 ppm or less, preferably 30 ppm or less, particularly preferably 10 ppm or less.

[Other compounds]
The non-aqueous electrolyte solution in the present invention contains a lithium salt that is an electrolyte and a specific compound as essential components in a non-aqueous solvent, but other compounds are optionally added within the range that does not impair the effects of the present invention. Can be contained in an amount of. Specific examples of such other compounds include:
(1) Aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluoro Partially fluorinated products of the above-mentioned aromatic compounds such as benzene and p-cyclohexylfluorobenzene; fluorinated anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole Overcharge inhibitors such as compounds;
(2) vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, etc. Negative electrode film-forming agent;
(3) Ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetra Positive electrode protecting agents such as methylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide;
Etc.

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

  As the negative electrode film forming agent, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, succinic anhydride, and maleic anhydride are preferable. Two or more of these may be used in combination. When using 2 or more types together, vinylene carbonate and vinyl ethylene carbonate, fluoroethylene carbonate, succinic anhydride, or maleic anhydride are preferable. As the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate, and busulfan are preferable. Two or more of these may be used in combination. Moreover, the combined use of a negative electrode film forming agent and a positive electrode protective agent, or the combined use of an overcharge inhibitor, a negative electrode film forming agent, and a positive electrode protective agent is particularly preferable.

  The content ratio of these other compounds in the non-aqueous electrolyte solution is not particularly limited, but is usually 0.01% by mass or more, preferably 0.1% by mass or more, and more preferably 0% with respect to the whole non-aqueous electrolyte solution. The upper limit is usually 5% by mass or less, preferably 3% by mass or less, and more 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 solution in the present invention is not particularly limited, and can be prepared by dissolving a lithium salt, a specific compound, and, if necessary, other compounds in a non-aqueous solvent according to a conventional method.

<Lithium secondary battery>
The lithium secondary battery of the present invention will be described in detail below.

[Battery configuration]
The rechargeable lithium secondary battery of the present invention includes a positive electrode and a negative electrode capable of occluding and releasing lithium ions, the above-described non-aqueous electrolyte, a microporous membrane separator disposed between the positive electrode and the negative electrode, a current collecting terminal, And an exterior case or the like. If necessary, a protective element may be mounted inside the battery and / or outside the battery.

[Battery exterior]
In the present invention, the exterior material forming the battery exterior is made of a sheet in which at least a part of the inner surface side of the battery is formed using a thermoplastic resin, houses the electrode group, and the thermoplastic resin layers The electrode group can be sealed by heat sealing.

  The battery exterior material is lightweight for battery weight reduction and is stable with respect to the non-aqueous electrolyte used, and it is necessary to seal the electrode group easily and reliably. It is essential to consist of a sheet formed using a thermoplastic resin.

  In the present invention, the electrode group is hermetically sealed by heat-sealing the thermoplastic resin layers. Here, the “heat seal” means that the thermoplastic resin layers are brought into close contact with each other. The temperature is equal to or higher than the melting point, and the thermoplastic resin layers are bonded together. It is preferable to use a sealer that has a belt-like heat generating portion and can be heated while being pressurized. Further, a thermoplastic resin is used for at least a part of the inner surface side of the battery. Here, "at least a part" means a region including a part that can seal the electrode group at the outer peripheral part of the sheet, A thermoplastic resin may be used only in a portion to be heat sealed. It is preferable from the efficiency of a sheet | seat preparation process that the sheet | seat whole surface of the inner surface side of a battery is covered with the thermoplastic resin layer.

  Further, when the microporous membrane separator described later has a property that the pores are clogged by heating, at least a part of the inner surface side of the battery has a melting point higher than the clogging start temperature of the pores of the microporous membrane separator. It is preferable from the point of safety at the time of abnormality, such as an overcharge, to consist of a sheet | seat formed using the thermoplastic resin which has. That is, when abnormal heat generation occurs due to overcharge or the like, the battery temperature rises and exceeds the melting point of the thermoplastic resin of the exterior material, the battery exterior may rupture or electrolyte leakage may result in ignition, If the microporous membrane separator has the property that the pores are closed by heating, the pores of the microporous membrane separator are closed before leakage of the electrolyte from the exterior material occurs, so that further heat generation can be suppressed. It may not lead to ignition, which is preferable. Here, melting | fusing point means melting temperature as measured by JISK7121.

  Although there is no limitation in particular as a thermoplastic resin, Preferably, polyolefins, such as polyethylene, a polypropylene, a modified polyolefin, and a polyolefin copolymer; Polyesters, such as a polyethylene terephthalate; Polyamides, such as nylon, etc. are mentioned. One type of thermoplastic resin may be used, or two or more types may be used.

  As such “at least part of the exterior material”, only a thermoplastic resin can be used, but a composite material of a thermoplastic resin and a thermosetting resin, an elastomer, a metal material, glass fiber, carbon fiber, or the like. It is also preferable to use. Moreover, fillers, such as a filler, may contain. As the composite material, a laminated sheet of a thermoplastic resin layer and a single metal such as aluminum, iron, copper, nickel, titanium, molybdenum, and gold, or an alloy such as stainless steel or hastelloy is particularly preferable, and an aluminum metal excellent in workability. And a laminated sheet is more preferable. That is, it is more preferable that the exterior material is composed of a laminated sheet that is laminated including at least an aluminum layer and a thermoplastic resin layer. These metals or alloys may be used as a metal foil or a metal vapor deposition film.

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

  The thickness of the exterior material is not particularly limited, but is preferably 0.03 mm or more, particularly preferably 0.04 mm or more, and further preferably 0.05 mm or more. The upper limit is preferably 0.5 mm or less, particularly preferably 0.3 mm or less, and further preferably 0.2 mm or less. If the exterior material is thinner than this range, the strength may be reduced, and deformation, breakage, and the like may occur. On the other hand, if the exterior material is thicker than this range, the mass of the exterior case increases, so the purpose of reducing the battery weight may not be achieved.

  A battery using the above-described exterior material has an advantage that it is lightweight and has a high degree of freedom in shape. On the other hand, when gas is generated inside the battery, the internal pressure increases and the exterior material may be easily deformed. In the lithium secondary battery according to the present invention, the specific compound in the non-aqueous electrolyte is adsorbed on the surface of the positive electrode active material, thereby suppressing the side reaction of the positive electrode and suppressing the generation of gas components. Even when an exterior material is used, the above disadvantages are not manifested, and only the above advantages of the exterior material are manifested.

[Microporous membrane separator]
The microporous membrane separator used in the present invention has a predetermined mechanical strength that electrically insulates both electrodes, has a high ion permeability, and is resistant to oxidation on the side in contact with the positive electrode and reducibility on the negative electrode side. There is no particular limitation as long as it has both. As a material of the microporous membrane separator having such characteristics, a resin, an inorganic material, glass fiber, or the like is used.

  Although it does not specifically limit as said resin, For example, an olefin polymer, a fluorine-type polymer, a cellulose polymer, a polyimide, nylon etc. are mentioned. Specifically, it is preferable to select from materials that are stable with respect to non-aqueous electrolytes and have excellent liquid retention properties, and porous sheets or nonwoven fabrics made from polyolefins such as polyethylene and polypropylene are used. Is preferred. The inorganic material is not particularly limited, and for example, oxides such as alumina and silicon dioxide; nitrides such as aluminum nitride and silicon nitride; sulfates such as barium sulfate and calcium sulfate are used. As the shape, a particle shape or a fiber shape is used.

  As a form, thin-film-shaped things, such as a nonwoven fabric, a woven fabric, and a microporous film, are preferable. 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 composite porous layer containing inorganic particles using a resin binder can be used on the surface layer of the positive electrode and / or the negative electrode. . Examples of such a form include a porous layer in which alumina particles having a 90% particle diameter of 1 μm or less are formed on both surfaces of a positive electrode using a fluororesin as a binder.

  The microporous membrane separator used in the present invention preferably has a property that the pores are closed by heating. A combination of such a microporous membrane separator and an exterior material formed by using at least a part of the inner surface side of the battery using a thermoplastic resin having a melting point higher than the pore closing start temperature of the microporous membrane separator In this case, when abnormal heat generation such as overcharge occurs, the heat generation can be stopped before the battery exterior ruptures or the electrolyte leaks. In addition, here, “the property that the pores are blocked by heating” means that the porous layer formed so that the electrolyte can move between the positive and negative electrodes is made of a thermoplastic resin and is heated to near the melting point of the thermoplastic resin. In this case, the porous layer is blocked, and the electrolyte solution can move between the positive and negative electrodes.

[Discharge capacity]
When the non-aqueous electrolyte for secondary battery in the present invention is used, the electric capacity of the battery element housed in one battery exterior of the secondary battery (electric capacity when the battery is discharged from the fully charged state to the discharged state) ) Is 3 ampere hours (Ah) or more, since the effect of improving output characteristics is increased. Therefore, the positive electrode plate is preferably designed such that the discharge capacity is fully charged and is 3 ampere hours (Ah) or more and 20 ampere hours (Ah) or less, and more preferably 4 Ah or more and 10 Ah or less. If it is less than 3 Ah, the voltage drop due to the electrode reaction resistance becomes large when taking out a large current, and the power efficiency may deteriorate. Above 20 Ah, the electrode reaction resistance decreases and the power efficiency improves, but the temperature distribution due to the internal heat generation of the battery during pulse charge / discharge is large, the durability of repeated charge / discharge is inferior, and abnormalities such as overcharge and internal short circuit The heat dissipation efficiency also deteriorates due to sudden heat generation, and the battery contents erupt violently without stopping the phenomenon that the internal pressure rises and the gas release valve operates (hereinafter abbreviated as “valve operation”). The probability of reaching a phenomenon (burst) may increase.

  Since the battery having the above-described battery capacity has a large volume, the battery shape may be restricted depending on the usage environment of the battery. The sheet-shaped exterior of the present invention is preferable because it has a high degree of freedom in battery shape and can easily cope with the restrictions on the battery shape as compared with exterior materials such as metal cans. In addition, when it is necessary to combine two or more types of batteries in the assembled battery described later, it is necessary to prepare a plurality of cans for exterior materials such as metal cans, and the cost of creating them is high. However, in the sheet-like exterior of the present invention, it may be sufficient to change the size to be cut out, which is preferable because it can be prepared at a lower cost.

[Current collection structure]
The current collecting structure is not particularly limited, but in order to more effectively realize the output characteristics improvement by the non-aqueous electrolyte solution of the present invention, it is necessary to make the structure to reduce the resistance of the wiring part and the joint part. is there. When such an internal resistance is small, the effect of using the nonaqueous electrolytic solution of the present invention is exhibited particularly well.

  When the electrode group has a laminated structure described later, a structure formed by bundling current collecting tabs of each electrode layer and connecting them to terminals is preferably used. When the area of one electrode increases, the internal resistance increases. Therefore, it is also preferable to reduce the resistance by providing a plurality of current collecting tabs in the electrode. When the electrode group has a wound structure described later, the internal resistance can be lowered by providing a plurality of current collecting tabs on the positive electrode and the negative electrode, respectively, and bundling the terminals.

  By optimizing the current collecting structure described above, the internal resistance can be made as small as possible. In a battery used at a high current, the impedance measured by the 10 kHz AC method (hereinafter abbreviated as “DC resistance component”) is preferably 20 milliohms (mΩ) or less, and preferably 10 milliohms (mΩ) or less. Is more preferable, and it is still more preferable to set it as 5 milliohm (mohm) or less. On the other hand, regarding the lower limit, when the direct current resistance component is less than 0.1 milliohm, the high output characteristics are improved, but the ratio of the current collecting structure used increases and the battery capacity may decrease. The battery using the sheet-shaped outer casing of the present invention is preferable because the degree of freedom of the battery shape is high and there are few restrictions on the shape of the current collecting structure material.

  The impedance is measured by using a solartron battery measuring device 1470 and a solartron frequency response analyzer 1255B as measuring devices, and measuring the resistance when a 10 kHz alternating current is applied with a bias of 5 mV to obtain a direct current resistance component. .

  The non-aqueous electrolyte in the present invention is effective in reducing reaction resistance related to lithium insertion / extraction with respect to the electrode active material, which is considered to be a factor that can realize good output characteristics. However, it was found that a battery having a large direct current resistance is inhibited by the direct current resistance, and the effect of reducing the reaction resistance cannot be reflected 100% on the output characteristics. This can be improved by using a battery having a small direct current resistance component, and the effects 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 having high output characteristics, this requirement and the above-described electric capacity of the battery element housed in one battery exterior of the secondary battery are described. It is particularly preferable to satisfy the requirement that (electric capacity when the battery is discharged from a fully charged state to a discharged state) (battery capacity) is 3 ampere hours (Ah) or more at the same time.

  The connection between the current collecting tab and the terminal is preferably performed by spot welding, high frequency welding or ultrasonic welding. Conventionally, these welding methods are simple welding methods with low resistance, but if the welded part reacts with impurities or by-products in the non-aqueous electrolyte and deteriorates due to long-term use, the DC resistance increases. It had been. However, when using the non-aqueous electrolyte containing the specific compound, a stable coating can be formed on the welded portion, and side reactions at the positive electrode of the non-aqueous electrolyte are suppressed. Deterioration of the welded portion is unlikely to progress even during long-term use.

[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 area S _{1 of the} largest surface (the product of the width and height of the outer dimensions excluding the terminal portion, unit cm ² ) is twice the thickness T (unit cm) of the battery outer shape. The ratio (2 × S ₁ / T) is preferably 100 or more, and more preferably 200 or more. By increasing the maximum surface, it is possible to improve characteristics such as cycle performance and high-temperature storage, even for high-power and large-capacity batteries, and increase the heat dissipation efficiency during abnormal heat generation. Can be prevented from becoming a dangerous state. The area may be simply abbreviated as “S ₁ ” and the thickness as “T”.

[Electrode group]
The electrode group is formed by laminating a positive electrode plate and a negative electrode plate, which will be described later, with a microporous membrane separator, which will be described later, or a spiral shape, with a positive electrode plate and a negative electrode plate, which will be described later, being interposed with a microporous membrane separator, which will be described later. Any of those wound in a wound structure may be used.

In the case where the electrode group has a laminated structure, the positive electrode and the negative electrode have a ratio (L / (2 × S ₂ ) between the total electrode peripheral length L (unit cm) and twice the electrode area S ₂ (unit cm ² ). )) Is preferably 1 or less, more preferably 0.5 or less, and even more preferably 0.3 or less. The lower limit is preferably 0.02 or more, more preferably 0.03 or more, and still more preferably 0.05 or more. In the case of a laminated structure, the electrode film adhesion may be inferior due to residual stress or impact due to cutting in a portion close to the periphery of the electrode. Therefore, when L / (2 × S ₂ ) is larger than the above range, the output characteristics are May decrease. On the other hand, if L / (2 × S ₂ ) is smaller than the above range, the battery area may be too large to be practical. The sum of the lengths may be simply abbreviated as “L” and the area as “S ₂ ”.

  In the case where the electrode group has a wound structure, it is preferable that the ratio of the length in the long direction to the length in the short direction of the positive electrode is 15 or more and 200 or less. If this ratio is smaller than the above range, the bottomed cylindrical shape of the battery exterior is too high with respect to the bottom area, and the balance becomes poor and impractical, or the positive electrode active material layer becomes thick and high output cannot be obtained. There is a case. Also, if this ratio is less than the above range, the bottomed cylindrical shape of the battery exterior is too small relative to the bottom area, the balance becomes worse and impractical, or the proportion of the current collector increases, Battery capacity may be reduced.

[Positive electrode area]
In the present invention, when the above non-aqueous electrolyte is used, the area of the positive electrode active material layer is preferably larger than the outer surface area of the battery outer case from the viewpoint of increasing the stability at high output and high temperature. Specifically, the sum of the electrode areas of the positive electrode with respect to the surface area of the exterior of the secondary battery should be 15 times or more in terms of area ratio, which improves output and generates heat generated by charging and discharging via the current collector. It is preferable in terms of efficient heat dissipation, and more preferably 20 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. In the battery using the sheet-shaped exterior of the present invention, the thickness of the exterior material can be reduced, and a power generation element of the same size is preferable because the battery surface area can be made smaller than a battery using a metal can or the like.

[Positive electrode]
The positive electrode used for the lithium 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, it is preferable to use a material in which a material having a composition different from the material constituting the main body of the positive electrode active material is attached to the surface of the positive electrode active material. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate, and carbon.

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

  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 non-aqueous electrolyte solution on the surface of the positive electrode active material, and can improve the battery life. However, when the amount of the adhering quantity is too small, the effect is not sufficiently exhibited. If the amount is too large, the resistance may increase in order to inhibit the entry and exit of lithium ions.

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

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

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

[[[Median diameter d ₅₀ ]]]
The median diameter d ₅₀ of the positive electrode active material particles (secondary particle diameter when primary particles aggregate to form secondary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably Is 1 μm or more, most preferably 3 μm or more, and the upper limit is usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. If the lower limit is not reached, a high tap density product may not be obtained, and if the upper limit is exceeded, it takes time to diffuse lithium in the particles. When a conductive material, a binder, or the like is slurried with a solvent and applied as a thin film, problems such as streaking may occur. Here, by mixing two or more types of positive electrode active materials having different median diameters d ₅₀ , the filling property at the time of forming the positive electrode can be further improved.

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

[[[Average primary particle size]]]
When primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, Most preferably, it is 0.1 μm or more, 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 lithium secondary battery of the present invention is usually 0.2 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.4 m ² / g or more, The upper limit is usually 4.0 m ² / g or less, preferably 2.5 m ² / g or less, more preferably 1.5 m ² / g or less. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered, and if the BET specific surface area is larger, the tap density is difficult to increase, and there may be a problem in applicability when forming the positive electrode active material.

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

[[[Production method]]]
As a manufacturing method of the positive electrode active material, a general method is used as a manufacturing method of the inorganic compound. In particular, various methods are conceivable for producing a spherical or elliptical spherical active material. For example, transition metal raw materials such as transition metal nitrates and transition metal sulfates and, if necessary, raw materials of other elements are mixed with water. It is dissolved or pulverized and dispersed in a solvent such as, and the pH is adjusted while stirring to produce and recover a spherical precursor, which is dried as necessary, and then LiOH, Li ₂ CO ₃ , LiNO _3, etc. A method of obtaining an active material by adding a Li source of the above, a transition metal source material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, and other elements as required The raw material is dissolved or pulverized and dispersed in a solvent such as water, and is then dried and molded with a spray dryer or the like to obtain a spherical or elliptical precursor, and LiOH, Li ₂ CO ₃ , LiNO _{3 and} other Li Add the source at high temperature A method of obtaining an active material by firing, a transition metal source material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, and LiOH such as LiOH, Li ₂ CO ₃ , and LiNO ₃ Dissolve or pulverize the source and other elemental raw materials as necessary in a solvent such as water, and dry-mold them with a spray drier or the like to obtain a spherical or elliptical precursor, which is heated at a high temperature. Examples thereof include a method for obtaining an active material by firing.

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

  In the present invention, 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 powder in the positive electrode active material layer is low, the electric capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient. In addition, a positive electrode active material may be used individually by 1 type, and may use together 2 or more types of a different composition or different powder physical properties by arbitrary combinations and ratios.

[[[Consolidation]]]
The positive electrode active material layer obtained by coating and drying is preferably consolidated by a hand press, a roller press or the like in order to increase the packing density of the positive electrode active material. The density of the positive electrode active material layer is preferably 1 g / cm ³ or more as a lower limit, more preferably 1.5 g / cm ³ or more, still more preferably 2 g / cm ³ or more, and preferably 4 g / cm ³ or less as an upper limit. More preferably, it is in the range of 3.5 g / cm ³ or less, still more preferably 3 g / cm ³ or less. If this range is exceeded, the permeability of the non-aqueous electrolyte solution to the vicinity of the current collector / active material interface may decrease, and the charge / discharge characteristics at a high current density may decrease. On the other hand, if it is lower, the conductivity between the active materials may be reduced, and the battery resistance may be increased.

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

  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% by mass. % Or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

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

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

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

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

  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 to the positive electrode active material layer may decrease, the battery capacity may decrease, and the resistance between the positive electrode active materials may increase.

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

  Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal in the case of a metal material. Examples include thin films and carbon cylinders. 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 ratio of the thickness of the current collector to the positive electrode active material layer is not particularly limited, but the (active material layer thickness on one side immediately before the nonaqueous electrolyte solution injection) / (current collector thickness) is 150 or less. Preferably, it is 20 or less, most preferably 10 or less, and the lower limit is preferably 0.1 or more, more preferably 0.4 or more, and most preferably 1 or more. Above this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. Below this range, the volume ratio of the current collector to the positive electrode active material increases and the battery capacity may decrease.

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

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

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

As a carbonaceous material,
(1) natural graphite,
(2) Artificial carbonaceous material and artificial graphite material; carbonaceous material [for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or those obtained by oxidizing these pitches, needle coke, pitch Coke and carbon materials partially graphitized, furnace black, acetylene black, pyrolysis products of organic substances such as pitch-based carbon fibers, carbonized organic substances (for example, coal tar pitch from soft pitch to hard pitch, or dry distillation Coal heavy oil such as liquefied oil, normal pressure residual oil, direct current heavy oil of reduced pressure residual oil, cracked petroleum heavy oil such as ethylene tar produced during thermal decomposition of crude oil, naphtha, etc., acenaphthylene, Aromatic hydrocarbons such as decacyclene, anthracene, phenanthrene, N-ring compounds such as phenazine and acridine, thiophene, bithiophene S-ring compound, polyphenylene such as biphenyl and terphenyl, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized product of these, organic polymer such as nitrogen-containing polyacrylonitrile, polypyrrole, sulfur-containing polythiophene, Organic polymers such as polystyrene, natural polymers such as polysaccharides 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 Carbides] The one or more times in the range of 400 to 3200 ° C. heat treated carbon material,
(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 secondary battery, any one or more of the following (1) to (19) It is desirable to satisfy them at the same time.

(1) X-ray parameters For carbonaceous materials, the d value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method is preferably 0.335 nm or more, and the upper limit is usually It is 0.36 nm or less, preferably 0.35 nm or less, more preferably 0.345 nm or less. The crystallite size (Lc) of the carbonaceous material determined by X-ray diffraction by the Gakushin method is preferably 1 nm or more, and more preferably 1.5 nm or more.

(2) Ash content The ash content contained in the carbonaceous material is usually 1% by mass or less, particularly 0.5% by mass or less, especially 0.1% by mass or less, and the lower limit relative to the total mass of the carbonaceous material. Usually, it is preferably 1 ppm or more. If the above range is exceeded, deterioration of battery performance due to reaction with the non-aqueous electrolyte during charge / discharge 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 3 μm or more. Is 5 μm or more, more preferably 7 μm or more. Moreover, an upper limit is 100 micrometers or less normally, Preferably it is 50 micrometers or less, More preferably, it is 40 micrometers or less, More preferably, it is 30 micrometers or less, Most preferably, it is 25 micrometers or less. If it falls below the above range, the irreversible capacity may increase, leading to loss of the initial battery capacity. On the other hand, when the above range is exceeded, when an electrode is produced by coating, a non-uniform coating surface tends to be formed, which may be undesirable in the battery production process.

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

(4) Raman R value, Raman half-value width The Raman R value of the carbonaceous material measured using the argon ion laser Raman spectrum method is usually 0.01 or more, preferably 0.03 or more, more preferably 0.1 or more. The upper limit is usually 1.5 or less, preferably 1.2 or less, more preferably 1.0 or less, and still more preferably 0.5 or less. When the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge / discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics. On the other hand, if it exceeds this range, the crystallinity of the particle surface will decrease, the reactivity with the non-aqueous electrolyte will increase, and the efficiency and gas generation may increase.

Further, the Raman half-width in the vicinity of 1580 cm ^{−1 of the} carbonaceous material used in the present invention is not particularly limited, but is usually 10 cm ⁻¹ or more, preferably 15 cm ⁻¹ or more, and the upper limit is usually 100 cm ⁻¹ or less. Preferably it is 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 non-aqueous electrolyte will increase, and the efficiency and gas generation 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, Raman half width analysis: Background processing ・ Smoothing processing: Simple average, 5 points of convolution

(5) BET specific surface area The specific surface area of the carbonaceous material in the present invention measured by using the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ^2. / G or more, more preferably 1.5 m ² / g or more. The upper limit is usually 100 m ² / g or less, preferably 25 m ² / g or less, more preferably 15 m ² / g or less, and still more preferably 10 m ² / g or less. When the value of the specific surface area is less than this range, the acceptability of lithium is likely to deteriorate during charging when used as a negative electrode material, and lithium may easily precipitate on the electrode surface. On the other hand, if it exceeds this range, when used as a negative electrode material, the reactivity with the non-aqueous 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 accurately adjusted so that the pressure value becomes 0.3.

(6) Pore size distribution The pore size distribution of the carbonaceous material used in the present invention is determined by mercury porosimetry (mercury intrusion method), and the pore diameter is within a particle corresponding to 0.01 μm or more and 1 μm or less. The amount of voids, irregularities due to particle surface steps, contact surfaces between particles, etc. is usually 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, Usually, it is 0.6 mL / g or less, preferably 0.4 mL / g or less, more preferably 0.3 mL / g or less. If it exceeds this range, a large amount of binder may be required when forming an electrode plate. If it is less than the range, the high current density charge / discharge characteristics may be deteriorated, and the effect of 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, As an upper limit, it is 10 mL / g or less normally, Preferably it is 5 mL / g or less, More preferably, it is the range of 2 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 that, it may not be possible to obtain the effect of dispersing the thickener or the binder during the electrode plate formation.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, and the upper limit is usually 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. It is. Beyond this range, a large amount of binder may be required. If it is less, the high current density charge / discharge characteristics may deteriorate.

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

(7) Circularity Circularity is used as the degree of sphericity of the carbonaceous material, and the circularity of particles having a particle size in the range of 3 to 40 μm is usually 0.1 or more, preferably 0.5 or more, more preferably 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 the particles 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. It is cm ³ or more, and the upper limit is usually 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 1.0 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 by a method similar to the method described in the section of the positive electrode and is defined thereby.

(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, light receiving slit = 0.15 mm, scattering slit = 0.5 degree. Measurement range and step angle / measurement time:
(110) plane: 75 degrees ≦ 2θ ≦ 80 degrees 1 degree / 60 seconds (004) plane: 52 degrees ≦ 2θ ≦ 57 degrees 1 degree / 60 seconds

(11) Aspect ratio (powder)
The aspect ratio is theoretically 1 or more, and the upper limit is usually 10 or less, preferably 8 or less, more preferably 5 or less. If the upper limit is exceeded, streaking or a uniform coated surface may not be obtained during electrode plate formation, and the high current density charge / discharge characteristics may deteriorate. The aspect ratio is expressed as A / B when the longest diameter A of the carbonaceous material particles when observed three-dimensionally and the shortest diameter B orthogonal to the carbonaceous material particles. The carbon particles are observed with a scanning electron microscope capable of magnifying observation. Arbitrary 50 graphite particles fixed on the end face of a metal plate having a thickness of 50 μm or less are selected, and the stage on which the sample is fixed is rotated and tilted, and A and B are measured. Find the average value.

(12) Sub-material mixing “Sub-material mixing” means that two or more carbonaceous materials having different properties are contained in the negative electrode and / or the negative electrode active material. The properties described here include one or more of X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, circularity, and ash content. Show 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 material such as natural graphite, graphite such as artificial graphite, carbon black such as acetylene black, amorphous carbon such as needle coke, etc. is contained as a conductive material, so that electric resistance is increased. It can be reduced. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When added as a conductive material, it is usually 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 usually 45% by mass or less, preferably It is in the range of 40% by mass. 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 in the stage immediately before the non-aqueous electrolyte injection step of the battery is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is usually 150 μm or less, preferably Is 120 μm or less, more preferably 100 μm or less. If it exceeds this range, the non-aqueous electrolyte solution hardly penetrates to the vicinity of the current collector interface, and thus the high current density charge / discharge characteristics may deteriorate. On the other hand, below this range, the volume ratio of the current collector to the negative electrode active material increases, and the battery capacity may decrease. Further, the negative electrode active material may be roll-formed to form a sheet electrode, or may be formed into a pellet electrode by compression molding.

(14) Current collector Any known current collector can be used. The negative electrode current collector is preferably a metal material such as copper, nickel, stainless steel, or nickel-plated steel, and copper is particularly preferred from the standpoint 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, and 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. Electrolytic copper foil, for example, immerses a metal drum in a non-aqueous electrolyte solution in which copper ions are dissolved, and causes the copper to precipitate on the surface of the drum by flowing current while rotating it. Is obtained. Copper may be deposited on the surface of the rolled copper foil by an electrolytic method. One side or both sides of the copper foil may be subjected to a roughening treatment or a surface treatment (for example, a chromate treatment having a thickness of about several nm to 1 μm, a base treatment such as Ti).

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

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

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

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

(15) Ratio of thickness of current collector and active material layer The ratio of the thickness of current collector and active material layer is not particularly limited, but (thickness of active material layer on one side immediately before non-aqueous electrolyte injection) ) / (Current collector thickness) is usually 150 or less, preferably 20 or less, more preferably 10 or less, and the lower limit is usually 0.1 or more, preferably 0.4 or more, more preferably 1 It is the above range. 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 or more, more preferably 1.3 g / cm ³ or more, and the upper limit is usually 2.0 g / cm ³ or less, preferably 1.9 g / cm ³ or less, more preferably 1. The range is 8 g / cm ³ or less, more preferably 1.7 g / cm ³ or less. Exceeding this range may destroy active material particles, leading to an increase in initial irreversible capacity and deterioration of high current density charge / discharge characteristics due to reduced permeability of the non-aqueous electrolyte 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 non-aqueous electrolyte solution and the solvent used during electrode production. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluorine rubber, Rubber polymers such as NBR (acrylonitrile-butadiene rubber) and ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof; EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, Soft resinous polymers such as tylene / vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer, etc. Fluorine-based polymers; polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions), and the like. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

  The solvent for forming the slurry is not particularly limited as long as it is a solvent that can dissolve or disperse the active material, the binder, and the thickener and conductive material used as necessary. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, a mixed solvent of alcohol and water, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, acrylic acid. Methyl, diethyltriamine, N, N-dimethylaminopropylamine, propylene oxide, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine , Methyl naphthalene, hexane and the like. 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 usually 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 usually 20% by mass or less, preferably 15%. It is in the range of not more than mass%, more preferably not more than 10 mass%, still more preferably not more than 8 mass%. When it exceeds this range, the binder ratio in which the binder amount does not contribute to the battery capacity increases, and the battery capacity may be reduced. 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 usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0%. The upper limit is usually 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 usually 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more. The upper limit is usually 15% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less.

  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. Further, when a thickener is blended, 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. When it exceeds, the ratio of the active material to a negative electrode active material layer may fall, the capacity | capacitance of a battery may fall, or the resistance between negative electrode active materials may increase.

(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 Sample preparation: Fix the electrode to the glass plate with double-sided tape with a thickness of 0.1 mm

(19) Impedance The resistance of the negative electrode when charged from the discharged state to 60% of the nominal capacity is usually 100Ω or less, preferably 50Ω or less, more preferably 20Ω or less, and / or the double layer capacity is usually 1 × 10. ^{It is −6} F or more, preferably 1 × 10 ⁻⁵ F, more preferably 1 × 10 ⁻⁴ F. 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 secondary battery to be measured was charged at a current value at which the nominal capacity could be charged in 5 hours, then maintained in a state where no charge / discharge was performed for 20 minutes, and then discharged at a current value at which the nominal capacity could be discharged in 1 hour. Use the one whose capacity is 80% or more of the nominal capacity. The lithium secondary battery in the above-described discharge state is charged to 60% of the nominal capacity at a current value that can be charged in 5 hours, and the lithium secondary battery is immediately transferred into a glove box under an argon gas atmosphere. Here, the lithium secondary battery is quickly disassembled and taken out in a state where the negative electrode does not discharge or short-circuit, and if it is a double-sided coated electrode, the electrode active material on one side is peeled off without damaging the electrode active material on the other side, and the negative electrode Are punched out to 12.5 mmφ, and face each other through a microporous membrane separator so that the active material surface does not shift. 60 μL of the non-aqueous electrolyte used in the battery was dropped and adhered between the microporous membrane separator and both negative electrodes, kept in contact with the outside air, and the current collectors of both negative electrodes were made conductive, and AC impedance Implement the law. The measurement is performed at a temperature of 25 ° C., and a complex impedance measurement is performed in a frequency band of 10 ⁻² to 10 ⁵ Hz. The surface resistance (impedance Rct) is obtained by approximating the arc of the negative resistance component of the obtained Cole-Cole plot with a semicircle. ) And double layer capacity (Cdl).

  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. However, the thickness of the composite layer obtained by subtracting the thickness of the metal foil of the core is usually 15 μm. Above, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is usually 150 μm or less, preferably 120 μm or less, more preferably 100 μm or less.

[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 can be used. 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.

[Battery]
When the lithium secondary battery of the present invention is put into practical use as a power source, the voltage required for the power source is often higher than the unit cell voltage, and there are measures such as connecting unit cells in series or using a booster. is necessary. For this reason, it is preferable to use the lithium secondary battery of this invention as an assembled battery which connected the plurality in series. By forming the assembled battery, it is possible to reduce the resistance of the connection portion and suppress the decrease in output as the assembled battery. From the viewpoint of power supply voltage, it is preferable to connect five or more batteries in series.

  In addition, when an assembled battery is formed by connecting a plurality, it is preferable to have a cooling mechanism for maintaining the battery at a certain temperature or lower because the influence of heat generation associated with charging / discharging increases. As battery temperature, 10 to 40 degreeC is preferable and it is preferable to cool using external air by water cooling or air cooling.

[Usage]
The lithium secondary battery of the present invention and the assembled battery formed by connecting a plurality of lithium secondary batteries of the present invention have high output, long life, high safety, etc. It is preferably used for at least an application supplied to a drive system of a vehicle.

  In the battery structure described above, by using the non-aqueous electrolyte described above, gas generation is suppressed, and the mechanism for improving the life, output, safety, etc. is not clear, but the surface of the positive electrode active material is not in the non-aqueous electrolyte. It is considered that an undesirable reaction between the positive electrode active material and the non-aqueous electrolyte solution can be suppressed by adsorbing the additive. It can be considered that gas generation can be suppressed and the battery life can be improved by suppressing side reactions during storage and repeated charge / discharge. In addition, since the direct current resistance component in the battery described above is small, the proportion of the resistance on the positive electrode surface is large with respect to the total resistance of the battery, so reducing the resistance on the positive electrode surface is effective for improving the output of the battery. It is considered to be greatly preferable. In addition, even when the reactivity of the positive electrode increases during overcharge or high temperature, it is possible to suppress a rapid reaction with the non-aqueous electrolyte and improve safety. The effect is difficult to be manifested because the heat radiation is large, and it is considered that the effect became clear by using a large battery. Moreover, since there is little gas generation | occurrence | production, a sheet-like exterior material can be used and it is thought that a power density can further be improved by weight reduction of a battery. In addition, the sheet-shaped exterior material increases the degree of freedom of the battery shape and facilitates battery design.

  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.

Example 1
<< Preparation of non-aqueous electrolyte >>
Under a dry argon atmosphere, it was sufficiently dried at a concentration of 1 mol / L in a mixed solvent of purified ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4. Lithium hexafluorophosphate (LiPF6) was dissolved. Furthermore, hexamethylcyclotrisiloxane was contained so that it might become 0.3 mass%.

<< Preparation of positive electrode >>
The positive electrode active material is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula LiMn _0.33 Ni _0.33 Co _0.33 O ₂ . Mn ₃ O ₄ as a manganese raw material, NiO as a nickel raw material, and Co (OH) ₂ as a cobalt raw material are weighed so as to have a molar ratio of Mn: Ni: Co = 1: 1: 1, and pure water is added thereto. In addition, the slurry was agitated, and the solid content in the slurry was wet pulverized to a median diameter of 0.2 μm using a circulating medium agitation type wet bead mill while stirring.

The slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a particle size of about 5 μm, which consisted only of manganese raw material, nickel raw material and cobalt raw material. LiOH powder with a median diameter of 3 μm is added to the resulting granulated particles so that the ratio of the number of moles of Li to the total number of moles of Mn, Ni and Co is 1.05 and mixed with a high speed mixer. Thus, a mixed powder of granulated particles of nickel raw material, cobalt raw material and manganese raw material and lithium raw material was obtained. This mixed powder was fired at 950 ° C. for 12 hours under air flow (climbing temperature rate 5 ° C./min) and then crushed and passed through a sieve having an opening of 45 μm to obtain a positive electrode active material. The positive electrode active material had a BET specific surface area of 1.2 m ² / g, an average primary particle diameter of 0.8 μm, a median diameter d ₅₀ of 4.4 μm, and a tap density of 1.6 g / cm ³ .

90% by mass of the positive electrode active material described above, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in an N-methylpyrrolidone solvent, Slurried. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 81 μm with a press, and the positive electrode active material layer had a width of 100 mm, a length of 100 mm, and a width of 30 mm. A positive electrode was cut out into a shape having a coating part. The density of the positive electrode active material layer is 2.35 g / cm ³ , (the thickness of the positive electrode active material layer on one side) / (the thickness of the current collector) is 2.2, and L / (2 × S ₂ ) Was 0.2.

<Production of negative electrode>
In order to prevent mixing of coarse particles of commercially available natural graphite powder as a particulate carbonaceous material, a sieve of ASTM 400 mesh was repeated 5 times. The negative electrode material obtained here was a carbonaceous material (A).

  The carbonaceous material (A) is mixed with petroleum heavy oil obtained at the time of naphtha pyrolysis, subjected to carbonization treatment at 1300 ° C. in an inert gas, and then the sintered product is classified, whereby the carbonaceous material (A ) A composite carbonaceous material in which carbonaceous materials having different crystallinity were deposited on the particle surface was obtained as a negative electrode active material. During classification, ASTM 400 mesh sieving was repeated 5 times in order to prevent the inclusion of coarse particles. From the residual carbon ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite. The physical properties of the negative electrode active material are shown in Table 1.

98 parts by weight of the above negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of 1% by weight of carboxymethylcellulose sodium) as a thickener and a binder, respectively, and an aqueous dispersion of styrene-butadiene rubber 2 parts by weight (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 rolled copper foil having a thickness of 10 μm, dried, and rolled to a thickness of 75 μm with a press machine. The active material layer had a width of 104 mm, a length of 104 mm, and a width of 30 mm. It cut out in the shape which has a coating part, and was set as the negative electrode. At this time, the density of the active material of the negative electrode was 1.35 g / cm ³ , and L / (2 × S ₂ ) was 0.19.

<Production of battery>
32 positive electrodes and 33 negative electrodes were alternately arranged and laminated so that a microporous membrane separator (thickness 25 μm) of a porous polyethylene sheet 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. The uncoated portions of each of the positive electrode and the negative electrode were bundled together and connected together with a metal piece serving as a current collecting terminal by spot welding to produce a current collecting tab to obtain an electrode group. The porous polyethylene sheet had pores blocked at 135 ° C. or higher.

As a battery exterior material, a sheet (a total thickness of 0.1 mm) in which a polypropylene film, an aluminum foil having a thickness of 0.04 mm, and a nylon film are laminated in this order (total thickness: 0.1 mm) is rectangular so that the polypropylene film comes on the inner surface side. Molded into a cup to form an outer case. The melting point of this polypropylene film was 165 ° C. The electrode group described above was sealed in an outer case so that the current collecting terminal came out from the unsealed portion at the upper end of the cup, and 20 mL of non-aqueous electrolyte was injected to sufficiently infiltrate the electrode. The upper end of the cup was heat-sealed under reduced pressure and sealed to prepare a battery. The battery is approximately square, and the ratio of the total electrode area of the positive electrode to the sum of the outer surface area of the battery (exterior material surface area not including the heat seal portion) is 22.6, and (2 × S ₁ / T) Was 411.

<Battery evaluation>
(Battery capacity measurement method)
For a new battery that has not undergone a charge / discharge cycle, a voltage range of 4.1 V to 3.0 V at 25 ° C., a current value of 0.2 C (the current value that discharges the rated capacity with a discharge capacity of 1 hour rate in 1 hour) The initial charge / discharge was performed for 5 cycles at 1C. The 5th cycle 0.2C discharge capacity at this time was defined as “battery capacity” (Ah). Table 3 shows the results of battery evaluation.

(Measurement method of DC resistance component)
In a 25 ° C. environment, the battery was charged with a constant current of 0.2 C for 150 minutes, and an impedance of 10 kHz was measured by applying an alternating current of 10 kHz to obtain a “DC resistance component” (mΩ). Table 3 shows the results of battery evaluation.

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

(Cycle test)
(Measurement method of battery capacity after endurance, DC resistance component after endurance, output after endurance)
The cycle test was performed in a high temperature environment of 60 ° C., which is regarded as the actual maximum use temperature of the lithium secondary battery. A charge / discharge cycle in which charging was performed at a constant current of 2 C to a discharge end voltage of 3.0 V after charging with a constant current constant voltage method of 2 C to a charging upper limit voltage of 4.1 V was defined as one cycle, and this cycle was repeated up to 500 cycles. The battery after the cycle test was charged and discharged for 3 cycles at a current value of 0.2 C in a 25 ° C. environment, and the 0.2 C discharge capacity of the third cycle was defined as “battery capacity after endurance”. In addition, the direct current resistance component was measured for the battery after the cycle test, and the output was measured as “post-endurance direct current resistance component”, and “output after endurance” was obtained. Table 3 shows the results of battery evaluation.

(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 a gas discharge valve is activated and a non-aqueous electrolyte component is released, and “rupture” is a case where the battery container is violently broken and the contents are forcibly released. Represents a phenomenon. Table 3 shows the results of battery evaluation.

(Measurement method of volume change rate)
The battery volume in a discharged state (3 V) was measured under a 25 ° C. environment. The volume was measured by putting ethanol in a graduated container and immersing the battery in ethanol. The ratio of the volume after the cycle test to the volume before the cycle test was defined as “volume change rate”. The evaluation results are shown in Table 3.

Example 2
In Example 1, a battery was prepared in the same manner as in Example 1 except that 0.3% by mass of trimethylsilyl methanesulfonate was contained in the nonaqueous electrolytic solution instead of hexamethylcyclotrisiloxane. Went. The results are also shown in Table 3.

Example 3
In Example 1, a battery was prepared in the same manner as in Example 1 except that 0.3% by mass of phenyldimethylfluorosilane was contained in the nonaqueous electrolytic solution instead of hexamethylcyclotrisiloxane. Went. The results are also shown in Table 3.

Example 4
In Example 1, a battery was prepared in the same manner as in Example 1 except that 0.3% by mass of lithium difluorophosphate was contained in the nonaqueous electrolytic solution instead of hexamethylcyclotrisiloxane, and the battery was evaluated in the same manner. Went. The results are also shown in Table 3.

Comparative Example 1
In Example 1, a battery was produced in the same manner as in Example 1 except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution, and the battery was evaluated in the same manner. The results are also shown in Table 3.

  From the results in Table 3, the inclusion of the specific compound in the non-aqueous electrolyte improves the initial output, capacity retention rate, and safety, and the battery capacity and output are sufficiently maintained even after the cycle test. I found it small.

  The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorbikes, bicycles, lighting equipment, toys, game equipment, watches, electric tools, strobes, cameras, etc. Can do. The lithium secondary battery of the present invention has a large capacity, a good life and a high output, generates less gas, and is highly safe even when overcharged. Can be used widely and suitably.

Claims (14)

At least an electrode group comprising a positive electrode and a negative electrode via a microporous membrane separator, and a non-aqueous electrolyte solution containing a lithium salt in a non-aqueous solvent, and containing these in a battery exterior In the secondary battery, the positive electrode and the negative electrode are each formed by forming an active material layer containing an active material capable of occluding and releasing lithium ions on a current collector, and the non-aqueous electrolyte solution comprises: A cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an SF bond in the molecule, a nitrate, Nonaqueous electrolytic solution containing at least 10 ppm of at least one compound selected from the group consisting of nitrite, monofluorophosphate, difluorophosphate, acetate and propionate in the entire nonaqueous electrolytic solution And the exterior material that forms the battery exterior is made of a sheet in which at least a part of the inner surface side of the battery is formed using a thermoplastic resin, houses the electrode group, and heats the thermoplastic resin layers together. A lithium secondary battery, characterized by being an exterior material capable of sealing the electrode group by sealing.

[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 non-aqueous electrolyte 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 an SF bond in the molecule. At least one compound selected from the group consisting of a compound having a salt, nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate and propionate, 0.01% by mass or more and 5% by mass 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is contained in an amount of 1% or less.   The microporous membrane separator has a property that the pores are closed by heating, and the exterior material forming the battery exterior has at least part of the inner surface side of the battery compared to the pore closure start temperature of the microporous membrane separator. The lithium secondary battery according to claim 1 or 2, wherein the lithium secondary battery is an exterior material made of a sheet formed using a thermoplastic resin having a high melting point.   The lithium secondary battery according to any one of claims 1 to 3, wherein the exterior material comprises a laminated sheet in which at least an aluminum layer and a thermoplastic resin layer are laminated.   The lithium secondary battery according to any one of claims 1 to 4, wherein a battery capacity of the lithium secondary battery is 3 ampere hours (Ah) or more.   The lithium secondary battery according to any one of claims 1 to 5, wherein a DC resistance component of the lithium secondary battery is 20 milliohms (mΩ) or less. The lithium secondary battery has a battery casing having a bottomed square shape, and the area S ₁ of the largest surface of the battery casing (the product of the width and height of the outer dimensions excluding the terminal portion, unit cm) ^2. The ratio (2 × S ₁ / T) between twice the thickness of the battery ² ) and the thickness T (unit: cm) of the outer shape of the battery is 100 or more, The lithium according to any one of claims 1 to 6 Secondary battery. The lithium secondary battery is a secondary battery including a group of stacked electrodes, and the positive electrode and the negative electrode are 2 of the total electrode peripheral length L (unit cm) and electrode area S ₂ (unit cm ² ). 8. The lithium secondary battery according to claim 1, wherein a ratio (L / (2 × S ₂ )) to 1 times is 1 or less.   The current collectors of the positive electrode and the negative electrode of the lithium secondary battery are each made of a metal material, and the metal material of the current collector and the conductor for taking out current to the outside are spot welding or high frequency welding or The lithium secondary battery according to any one of claims 1 to 8, which is joined by any one of ultrasonic welding.   10. The lithium secondary battery according to claim 1, wherein a sum of the electrode areas of the positive electrode with respect to a surface area of the exterior of the lithium secondary battery is 15 times or more in terms of an area ratio.   An assembled battery comprising five or more lithium secondary batteries according to any one of claims 1 to 10 connected in series.   An assembled battery formed by connecting a plurality of lithium secondary batteries according to any one of claims 1 to 10 has a cooling mechanism for maintaining the battery at a constant temperature or lower. Assembled battery.   The lithium secondary battery according to any one of claims 1 to 10, wherein the lithium secondary battery is mounted on a vehicle and used for an application in which electric power is supplied to at least a drive system of the vehicle.   The assembled battery according to claim 11 or 12, wherein the assembled battery is used in an application in which the assembled battery is mounted on a vehicle and the electric power is supplied to at least a drive system of the vehicle.