JP5671773B2 - Lithium ion secondary battery - Google Patents

Description

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

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

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

  Among lithium ion secondary batteries, secondary batteries using metallic lithium as a negative electrode have been actively studied since long ago as batteries capable of achieving high capacity. However, these batteries have a problem that metallic lithium grows in a dendrite shape due to repeated charge and discharge, eventually reaches the positive electrode and causes a short circuit inside the battery. This is the biggest technical challenge when putting batteries into practical use.

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

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

  Further, when a lithium ion secondary battery is used as a power source for an electric vehicle, it is assumed that a lithium ion secondary battery mounted on the vehicle stored in a low temperature state also becomes low temperature when used outdoors. Currently, there is a problem that the battery output is lower than at normal temperature at the low temperature immediately after the start of the car, and sufficient performance cannot be demonstrated, and the time required to recover from this low output state to the high output state is also short. It becomes important performance.

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

  As a technique related to the negative electrode active material, Patent Document 1 discloses that, in order to improve the performance of the electrode, the graphite particles inside are highly crystalline and plate-shaped, and the thickness direction of the graphite particles is relatively thick. By using graphite particles with a high abundance ratio of the edge portion by making the basal surface rough, especially the basal surface is rough (because the basal surface has cracks and bends and the edge portion of the crystal is exposed) , Increase the amount of lithium ions that can enter and exit, and further use a carbon material with a more spherical graphite particle shape and a higher filling property to make particles more isotropic, that is, isotropic arrangement of edges There is a description that an electrode excellent in high-capacity rapid charge / discharge characteristics and cycle characteristics can be obtained by increasing the A However, even with this method, the recovery of the output from the low temperature state is not fast enough.

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

However, even with these methods, the recovery of the output from the low temperature state is not fast enough.
JP 2000-340232 A Japanese Patent Application Laid-Open No. 11-067270

  This invention is made | formed in view of this background art, The subject is providing the lithium ion secondary battery with which the recovery | restoration of the output from the low output state at the time of low temperature is quick.

  As a result of diligent research in view of the above problems, the present inventor considered that the thermal conductivity of the negative electrode active material is important for early output recovery from a low temperature, and the negative electrode active material filling property, that is, circularity as the factor. It was found that it is important that the degree of heat treatment is high, the crystallinity is high, and the Raman R value is high at the same time. Furthermore, by simultaneously containing a specific compound in the non-aqueous electrolyte solution and using graphitic carbon particles having specific physical properties, it has been found that output recovery from a low output state at low temperatures is accelerated, 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 is a lithium ion secondary battery having a nonaqueous electrolyte solution containing a nonaqueous solvent and a lithium salt, a positive electrode active material, and a negative electrode active material, and the nonaqueous electrolyte solution is represented by the general formula (1). Cyclic siloxane compound represented by formula (2), compound represented by formula (3), compound having SF bond in molecule, nitrate, nitrite, monofluorophosphoric acid And at least one compound selected from the group consisting of a salt, a difluorophosphate, an acetate and a propionate in an amount of 10 ppm or more in the whole non-aqueous electrolyte, and the negative electrode active material is The circularity is 0.85 or more, and the (002) plane spacing (d002) by the wide-angle X-ray diffraction method is less than 0.337 nm, which is 15 in the argon ion laser Raman spectrum method. Lithium ions Raman R value, defined as the ratio of the peak intensity of 1360 cm ^-1 to the peak intensity of the 0 cm ^-1 is characterized in that containing graphitic carbon particles is 0.12 to 0.8 A secondary battery is provided.

[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; ]

  ADVANTAGE OF THE INVENTION According to this invention, the recovery | restoration of the output from the low output state at the time of low temperature can be provided quickly.

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

<Non-aqueous electrolyte>
The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention contains a lithium salt and a non-aqueous solvent that dissolves the lithium salt.
[Lithium salt]
The lithium salt is not particularly limited as long as it is known to be used as an electrolyte of a non-aqueous electrolyte solution for a lithium ion secondary battery, and examples thereof include the following.

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

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

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

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

Lithium salts may be used singly or in combination of two or more in any combination and ratio. Preferred examples when two or more lithium salts are used are LiPF ₆ and LiBF _4. In this case, the proportion of LiBF _{4 in} the total of both is particularly preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 5% by mass. More preferably, it is as follows. Another preferred example is the combined use of an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt. In this case, the proportion of the inorganic fluoride salt in the total of both is 70% by mass or more and 99% by mass. % Or less, particularly preferably 80% by mass or more and 98% by mass or less. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

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

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

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

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

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

  Other examples of preferred non-aqueous solvents are those containing chain esters. In particular, those containing a chain ester in the mixed solvent of cyclic carbonates and chain carbonates are preferable from the viewpoint of improving the low-temperature characteristics of the battery. Examples of the chain esters include methyl acetate and ethyl acetate. preferable. The capacity of the chain ester in the non-aqueous solvent is usually 5% or more, preferably 8% or more, more preferably 15% or more, usually 50% or less, preferably 35% or less, more preferably 30% or less, More preferably, it is 25% or less.

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

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

  By combining a non-aqueous electrolyte containing such a specific compound with graphite-based carbon particles having specific physical properties, which will be described later, as a negative electrode active material, the recovery of the output from a low output state at low temperatures is quick. A secondary battery can be provided.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[Other compounds]
The non-aqueous electrolyte solution in the lithium ion secondary battery of the present invention contains a lithium salt that is an electrolyte and a specific compound as essential components. It can be contained in any amount. As such other compounds, specifically, for example,
(1) Aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluoro Partially fluorinated products of the above-mentioned aromatic compounds such as benzene and p-cyclohexylfluorobenzene; fluorinated anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole Overcharge inhibitors such as compounds;
(2) vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, etc. Negative electrode film-forming agent;
(3) Ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, 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, it is preferable that at least 1 type uses vinylene carbonate. As the positive electrode protective agent, ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate, and busulfan are preferable. Two or more of these may be used in combination. Moreover, the combined use of a negative electrode film forming agent and a positive electrode protective agent, or the combined use of an overcharge inhibitor, a negative electrode film forming agent, and a positive electrode protective agent is particularly preferable.

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

  The method for preparing the non-aqueous electrolyte solution for the secondary battery of the present invention is not particularly limited, and is prepared by dissolving a lithium salt, a specific compound, and, if necessary, other compounds in a non-aqueous solvent according to a conventional method. be able to.

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

As the negative electrode active material, a material capable of electrochemically inserting and extracting lithium ions is used. It is essential that the negative electrode active material used in the lithium ion secondary battery of the present invention contains at least graphitic carbon particles satisfying the following (a), (b) and (c).
(A) Circularity is 0.85 or more.
(B) The (002) plane spacing (d002) by the wide-angle X-ray diffraction method is less than 0.337 nm.
Raman R value, defined as the ratio of the peak intensity of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in (c) the argon ion laser Raman spectrum method (hereinafter, occasionally abbreviated simply as "Raman R value") is 0 .12 or more and 0.8 or less.

[[Circularity]]
The circularity of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention is essential to be 0.85 or more, preferably 0.87 or more, particularly preferably 0.89 or more. More preferably, it is 0.92 or more. The upper limit is a theoretical sphere when the circularity is 1. Below this range, the negative electrode active material fillability decreases and thermal conductivity decreases, which may impede early output recovery, and in particular, output recovery from a low output state at low temperatures. May be slow.

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

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

[[Surface spacing (d002)]]
Although the interplanar spacing (d002) of the (002) plane of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention by the wide angle X-ray diffraction method is essential to be less than 0.337 nm. Preferably, it is 0.336 nm or less. The lower limit is 0.335, which is the theoretical value of graphite. Above this range, the crystallinity will decrease, the thermal conductivity due to electrons will decrease, and the early output recovery characteristics may decrease, especially when the recovery of output from a low output state at low temperatures is delayed. There is.

  In the present invention, the (002) plane spacing (d002) by the wide angle X-ray diffraction method is the d value (interlayer distance) of the lattice plane (002 plane) obtained by the X-ray diffraction by the Gakushin method.

  The crystallite size (Lc) of the graphitic carbon particles determined by X-ray diffraction by the Gakushin method is not particularly limited, but is usually 10 nm or more, preferably 30 nm or more, more preferably 80 nm or more. Below this range, the crystallinity is lowered, the thermal conductivity due to electrons is lowered, and the early output recovery characteristics may be lowered.

[[Raman R value]]
The Raman R value of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention must be 0.12 or more, preferably 0.15 or more, particularly preferably 0.17 or more, More preferably, it is 0.2 or more. As an upper limit, Preferably it is 0.8 or less, Especially preferably, it is 0.6 or less, More preferably, it is 0.45 or less. If the Raman R value is below this range, the crystallinity of the particle surface becomes too high, and the output itself may decrease as the charge / discharge sites decrease. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, so that heat conduction by electrons is lowered and output recovery characteristics may be lowered.

The Raman spectrum is measured using a Raman spectrometer (for example, a Raman spectrometer manufactured by JASCO Corporation), and the sample is naturally dropped into the measurement cell, and the sample is filled with argon ion laser light on the sample surface in the cell. , While rotating the cell in a plane perpendicular to the laser beam. The obtained Raman spectrum, the intensity I _A of the peak P _A in the 1580 cm ^-1, and measuring the intensity I _B of a peak P _B of 1360 cm ^-1, the intensity ratio R of the (R = I _B / I _A) This is calculated and defined as the Raman R value of the graphitic carbon particles. Further, the half width of the peak P _{A at} 1580 cm ⁻¹ of the obtained Raman spectrum is measured, and this is defined as the Raman half width of the graphitic carbon particles.

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

Further, the 1580 cm ⁻¹ Raman half width of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of 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. As a range of usually 60 cm ⁻¹ or less, preferably 50 cm ⁻¹ or less, more preferably 45 cm ⁻¹ or less. When the Raman half width is less than this range, the crystallinity of the particle surface becomes too high, and the output itself may decrease as the charge / discharge sites decrease. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, so that heat conduction by electrons is lowered and output recovery characteristics may be lowered.

[[Tap density]]
The tap density of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention is preferably 0.55 g / cm ³ or more, more preferably 0.7 g / cm ³ or more, still more preferably 0.00. It is 8 g / cm ³ or more, particularly preferably 1 g / 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 less than this range, the packing density is difficult to increase when used as a negative electrode, and the contact area between the particles decreases, so that the thermal conductivity may be lowered. On the other hand, if this range is exceeded, the voids between the particles in the electrode may become too small, and the output itself may decrease due to a decrease in the flow path of the non-aqueous electrolyte.

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

[[BET specific surface area]]
The specific surface area of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention measured by the BET method is preferably 0.1 m ² / g or more, particularly preferably 0.7 m ² / g. As mentioned above, More preferably, it is 1 m < ² > / g or more, More preferably, it is 1.5 m < ² > / g or more. The upper limit is preferably 100 m ² / g or less, particularly preferably 50 m ² / g or less, more preferably 25 m ² / g or less, and further preferably 15 m ² / g or less. When the value of the BET specific surface area is less than this range, the acceptability of lithium tends 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 BET specific surface area was measured by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken), preliminarily drying the sample for 15 minutes at 350 ° C. under a nitrogen flow, and then measuring the relative pressure of nitrogen with respect to atmospheric pressure. This is defined by a value measured by a nitrogen adsorption BET one-point method using a gas flow method, using a nitrogen-helium mixed gas that is accurately adjusted to have a value of 0.3.

[[Volume average particle size]]
The volume average particle diameter of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention is defined by the volume-based average particle diameter (median diameter) obtained by the laser diffraction / scattering method, and is 1 μm or more. Is particularly preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more. Moreover, an upper limit is 50 micrometers or less normally, Preferably it is 40 micrometers or less, More preferably, it is 30 micrometers or less, More preferably, it is 25 micrometers or less. If it falls below the above range, the irreversible capacity may increase, leading to loss of the initial battery capacity. On the other hand, if the ratio exceeds the above range, a non-uniform coating surface tends to be formed at the time of forming an electrode plate, which may be undesirable in the battery manufacturing process.

[[Pore volume]]
The pore volume of graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention is determined by mercury porosimetry (mercury intrusion method), and the inside of the particles corresponding to a diameter of 0.01 μm or more and 1 μm or less. The amount of irregularities due to voids and particle surface steps is 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and the upper limit is 0.6 mL / g or less, preferably It is 0.4 mL / g or less, More preferably, it is the range of 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 is preferably 0.1 mL / g or more, more preferably 0.25 mL / g or more, and the upper limit is 10 mL / g or less, preferably 5 mL / g or less, more preferably 2 mL / g or less. It is. 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 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. 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. A sample (negative electrode material) was weighed so as to have a value of about 0.2 g, sealed in a powder cell, and pretreated by degassing at room temperature under vacuum (50 μmHg or less) for 10 minutes. 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 distribution was calculated from the mercury intrusion curve thus obtained using the Washburn equation. The mercury surface tension (γ) was calculated as 485 dyne / cm, and the contact angle (ψ) was calculated as 140 °. As the average pore diameter, the pore diameter when the cumulative pore volume was 50% was used.

[[ash]]
The ash content of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention is preferably 1% by mass or less, particularly preferably 0.5% by mass or less, based on the total mass of the graphitic carbon particles. More preferably, it is 0.1% by mass or less. Moreover, as a minimum, it is preferable that it is 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. On the other hand, if it falls below this range, a great amount of time, energy and equipment for preventing contamination may be required for production, which may increase costs.

[[True density]]
The true density of the graphitic carbon particles is usually 2.0 g / cm ³ or more, preferably 2.1 g / cm ³ or more, more preferably 2.2 g / cm ³ or more, and further preferably 2.22 g / cm ³ or more. Yes, and the upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase. In the present invention, the true density is defined by a value measured by a liquid phase substitution method (pycnometer method) using butanol.

[[Orientation ratio]]
The orientation ratio of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention 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. The peaks of (110) and (004) diffraction are integrated by fitting the peaks of (110) and (004) diffraction of carbon by X-ray diffraction using asymmetric Pearson VII as a profile function. Each intensity is calculated. From the obtained integrated intensity, a ratio represented by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated and defined as an active material 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

[[aspect ratio]]
The aspect ratio of the graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention is theoretically 1 or more, and the upper limit is 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 diameter is the longest diameter A when observed three-dimensionally and the shortest diameter B is perpendicular to the diameter. The particles are observed with a scanning electron microscope capable of magnifying observation. Select 50 arbitrary particles fixed to the end face of a metal with a thickness of 50 μm or less, rotate and tilt the stage on which the sample is fixed, measure A and B, and average A / B Ask for.

[[Graphitic carbon particles]]
The graphitic carbon particles used as the negative electrode active material of the lithium ion secondary battery of the present invention may be naturally produced or artificially produced. It is preferable that it contains natural graphite. Moreover, what added the specific process to what was produced naturally or manufactured artificially may be used. Further, the production method (including the sorting method) is not particularly limited, and for example, the graphitic carbon particles having the above characteristics can be sorted and obtained using a sorting means such as sieving or air classification.

  Of these, particularly preferred graphitic carbon particles are those produced by modifying mechanically produced carbonaceous particles or naturally produced carbonaceous particles by applying mechanical energy treatment. More preferably, the carbonaceous particles as the raw material for the mechanical energy treatment contain natural graphite.

[[Mechanical energy treatment]]
In the following, this mechanical energy treatment will be described. The raw material carbonaceous particles to which the mechanical energy treatment is applied are not particularly limited, and include natural or artificial graphite-based carbonaceous particles, carbonaceous particles that are graphite precursors, and the like. The characteristics of these raw materials are shown below.

[[[Graphitic carbonaceous particles as raw materials for mechanical energy treatment]]]
It is desirable that the properties of the raw material graphite-based carbonaceous particles satisfy one or more of the following (1) to (11). The physical property measurement methods and definitions are the same as in the case of the graphitic carbon particles described above.

(1) X-ray parameters The graphite-based carbonaceous particles of the raw material preferably have a d-value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method of 0.335 nm or more, The upper limit is usually 0.340 nm or less, preferably 0.337 nm or less. The crystallite size (Lc) of the graphite-based carbonaceous particles obtained by X-ray diffraction by the Gakushin method is usually in the range of 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more. Below this range, the crystallinity may decrease and the increase in initial irreversible capacity may increase.

(2) Ash content The ash content in the graphite carbonaceous particles of the raw material is 1% by mass or less, particularly 0.5% by mass or less, particularly 0.1% by mass or less, based on the total mass of the graphite carbonaceous material. The lower limit 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-average particle diameter of the graphite carbonaceous particles as a raw material is defined by a volume-based average particle diameter (median diameter) obtained by a laser diffraction / scattering method, but usually 1 μm or more, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more, More preferably, it is 7 micrometers or more. The upper limit is not particularly limited, but is usually 10 mm or less, preferably 1 mm or less, more preferably 500 μm or less, still more preferably 100 μm or less, and particularly preferably 50 μm or less. Below the above range, the addition of mechanical energy may make the particle size too small and increase the irreversible capacity. On the other hand, if the above range is exceeded, efficient operation by a device for applying mechanical energy becomes difficult, and time loss may occur.

(4) Raman R value, Raman half-value width The Raman R value of the raw material graphite-based carbonaceous particles measured by using an argon ion laser Raman spectrum method is usually 0.01 or more, preferably 0.03 or more, more preferably. 0.1 or more, and the upper limit is 0.6 or less, preferably 0.4 or less. If the Raman R value falls below this range, the crystallinity of the particle surface is too high, and even if the Raman value increases due to the addition of mechanical energy, the Li becomes less between the layers due to charge / discharge due to the low crystallinity. In some cases, the number of sites that enter the site decreases, that is, the charge acceptance may decrease. On the other hand, if it exceeds this range, by adding mechanical energy, the crystallinity of the particle surface is further reduced, the reactivity with the non-aqueous electrolyte is increased, and the efficiency and gas generation may be increased. .

Although the Raman half-value width of 1580 cm ^-1 is not particularly limited, usually 10 cm ^-1 or more, preferably 15cm ^-1 or higher, and the upper limit is usually 50 cm ^-1 or less, preferably 45cm ^-1 or less, more preferably 40 cm ^- The range is ¹ or less. When the Raman half-width is below this range, the crystallinity of the particle surface is too high, and Li increases between charge and discharge due to low crystallinity even when the Raman value increases due to the addition of mechanical energy. When the number of sites is reduced, that is, charge acceptance may be reduced. On the other hand, if it exceeds this range, by adding mechanical energy, the crystallinity of the particle surface is further reduced, the reactivity with the non-aqueous electrolyte is increased, and the efficiency and gas generation may be increased. .

(5) BET method specific surface area was measured using a graphite type carbonaceous particles having a BET specific surface area material is usually 0.05 m ² / g or more, preferably 0.2 m ² / g or more, more preferably 0.5m ² / g or more, more preferably 1 m ² / g or more. The upper limit is usually 50 m ² / g or less, preferably 25 m ² / g or less, more preferably 15 m ² / g or less, still more preferably 10 m ² / g or less. If the value of the BET specific surface area is below this range, even if the BET specific surface area is increased by adding mechanical energy, the lithium acceptability tends to deteriorate during charging, and lithium may easily precipitate on the electrode surface. is there. On the other hand, if it exceeds this range, the BET specific surface area is further increased by adding mechanical energy, and when used as a negative electrode active material, the reactivity with the non-aqueous electrolyte increases and gas generation tends to increase, which is preferable. It may be difficult to obtain a battery.

(7) Circularity As the degree of sphericity of the raw material graphite-based carbonaceous particles, the circularity of particles having a particle size in the range of 3 to 40 μm is preferably 0.1 or more, more preferably 0.2 or more. More preferably, it is 0.4 or more, more preferably 0.5 or more, and most preferably 0.6 or more. Below this range, even when mechanical energy is added, the spheroidization does not proceed sufficiently, and the high current density charge / discharge characteristics may be lowered.

(8) True Density The true density of the raw material graphite-based carbonaceous particles is usually 2 g / cm ³ or more, preferably 2.1 g / cm ³ or more, more preferably 2.2 g / cm ³ or more, and still more preferably 2. 22 g / cm ³ or more, the upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase.

The tap density of the graphite-based carbonaceous particles (9) Tap Density raw material is usually 0.05 g / cm ³ or more, preferably 0.1 g / cm ³ or more, more preferably 0.2 g / cm ³ or more, in particular Preferably it is 0.5 g / cm ³ or more. Further, it 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. If the tap density is below this range, even if mechanical energy is applied, the tap density is not sufficiently improved, and when used as a negative electrode active material, the packing density is difficult to increase and a high capacity battery may not be obtained. is there. On the other hand, when exceeding this range, when mechanical energy is applied, the tap density further increases, the gap between the particles in the electrode after electrode formation becomes too small, and the flow rate of the nonaqueous electrolyte solution is insufficient. Current density charge / discharge characteristics may be reduced. The tap density of the graphite-based carbonaceous particles is also measured and defined by the same method as described above.

(10) Orientation ratio (powder)
The orientation ratio of the graphite-based carbonaceous particles as a raw material is usually 0.001 or more, preferably 0.005 or more. The upper limit is theoretically 0.67 or less. Below this range, even if mechanical energy is applied, the orientation ratio is not sufficiently improved, and the high-density charge / discharge characteristics may deteriorate.

(11) Aspect ratio (powder)
The aspect ratio of the graphite-based carbonaceous particles is theoretically 1 or more, and the upper limit is 10 or less, preferably 8 or less, and more preferably 5 or less. When the upper limit is exceeded, the aspect ratio is not sufficiently lowered even when mechanical energy is applied, streaking or a uniform coated surface cannot be obtained when forming an electrode plate, and the high current density charge / discharge characteristics may be lowered.

  Among the above-mentioned raw material graphite-based carbonaceous particles, as a highly crystalline carbon material with a developed carbon hexagonal network structure, highly oriented graphite having a hexagonal network surface greatly grown in a plane orientation, and highly oriented graphite particles And isotropic high-density graphite in which the particles are gathered in the same direction. Suitable examples of highly oriented graphite include natural graphite from Sri Lanka or Madagascar, so-called quiche graphite precipitated as supersaturated carbon from molten iron, and artificial graphite with some highly graphitized degrees. it can.

  Natural graphite is classified into flake graphite (Flake Graphite), scale graphite (Crystalline (Vein) Graphite), and earthy graphite (Amorphous Graphite), depending on its properties ("Powder Process Technology Assembly" (Co., Ltd.). (Refer to "HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES" (published by Noyes Publications)). The degree of graphitization is the highest at 100% for scaly graphite, followed by 99.9% for scaly graphite, but as low as 28% for earthy graphite. Scaly graphite, which is natural graphite, is produced in Madagascar, China, Brazil, Ukraine, Canada, etc., and scaly graphite is produced mainly in Sri Lanka. Soil graphite is mainly produced in the Korean peninsula, China, Mexico, etc. Among these natural graphites, earthy graphite generally has a small particle size and low purity. In contrast, scaly graphite and scaly graphite have advantages such as a high degree of graphitization and a low amount of impurities, and therefore can be preferably used in the present invention.

  Artificial graphite can be produced by heating petroleum heavy oil, heavy coal oil, petroleum coke or coal coke at a temperature of 1500 to 3000 ° C. or higher in a non-oxidizing atmosphere. .

  In the present invention, any artificial graphite can be used as a raw material as long as it exhibits high orientation and high capacity after mechanical energy treatment and heat treatment. In addition, among the artificial graphite, a material that is not completely graphitized, for example, a graphite precursor, can be converted into the mechanical properties of the present invention as long as it can be converted into graphitic carbon particles satisfying the above physical properties by performing mechanical energy treatment. It can be used as a raw material for energy treatment.

[[[Contents of mechanical energy treatment]]]
Mechanical energy treatment of these raw materials with respect to graphite-based carbonaceous particles reduces the particle size so that the ratio of the volume average particle size before and after the treatment is 1 or less, increases the tap density by the treatment, and Raman R The value is 1.1 times or more due to processing.

  By performing such mechanical energy treatment, the carbonaceous particles such as graphite-based carbonaceous particles used as a raw material are roughened only in the vicinity of the surface of the particles while maintaining high crystallinity as a whole. It becomes exposed particles. This increases the number of surfaces through which lithium ions can enter and exit, resulting in a high capacity even at high current densities.

  Among the engineering unit operations that can be used for particle design such as grinding, classification, mixing, granulation, surface modification, reaction, etc., “mechanical energy treatment” in the present invention belongs to “grinding treatment”, but at the same time the surface structure In addition, surface treatment that causes fine structural defects by impact, friction, compression, or the like is also included.

  In general, pulverization refers to applying a force to a substance to reduce its size and adjusting the particle size, particle size distribution, and packing properties of the substance. The pulverization process is classified according to the type of force applied to the substance and the processing form. The force applied to a substance is roughly classified into four types: a crushing force (impact force), a crushing force (compression force), a crushing force (grinding force), and a scraping force (shearing force). On the other hand, the treatment mode is roughly divided into two types: volume pulverization in which cracks are generated and propagated inside the particles, and surface pulverization in which the particle surfaces are scraped off. Volume pulverization proceeds by impact force, compression force, and shear force, and surface pulverization proceeds by grinding force and shear force. The pulverization process is a process in which the types of forces applied to these substances and the processing forms are variously combined. The combination can be appropriately determined according to the processing purpose. The pulverization may be performed using chemical reaction such as blasting or volume expansion, but is generally performed using a mechanical device such as a pulverizer.

  The mechanical energy treatment preferably used for the production of the graphitic carbon particles of the present invention is such that the proportion of the pulverization (surface pulverization) of the particle surface portion including the surface treatment finally increases regardless of the presence or absence of volume pulverization. It is preferable that the process is simple. This is because the surface pulverization of the particles is important for taking the corners of carbonaceous particles such as graphitic carbon particles and introducing roundness into the particle shape. Specifically, mechanical energy treatment may be performed so that surface grinding is performed after volume grinding has progressed to some extent, or mechanical energy treatment is performed so that only surface grinding is performed with almost no volume grinding. You may go. Furthermore, you may perform a mechanical energy process so that volume grinding | pulverization and surface grinding | pulverization may be performed simultaneously. A mechanical energy treatment is preferred in which the surface pulverization finally proceeds and the angle is removed from the surface of the particles.

  In the mechanical energy treatment in the present invention, the particle diameter is reduced so that the ratio of the volume average particle diameter before and after the treatment is 1 or less, the tap density is increased by the treatment, and the Raman R value is 1.1 by the treatment. It will be more than double.

  The “ratio of volume average particle diameters before and after treatment” is a value obtained by dividing the volume average particle diameter after treatment by the volume average particle diameter before treatment. The value of (volume average particle diameter after treatment) / (volume average particle diameter before treatment) is 1 or less, preferably 0.95 or less. When it is substantially 1, the effect of improving the filling property due to the improvement in circularity may be small due to the mechanical energy treatment. The particle shape can also be controlled by reducing the particle size so that the average particle size ratio before and after the treatment is 1 or less.

  The mechanical energy treatment in the present invention is such that the tap density is increased by the treatment. An increase in tap density means an improvement in the degree of spheroidization typified by circularity as will be described in detail later, and therefore the mechanical energy treatment needs to be such. The value of (tap density after treatment) / (tap density before treatment) is 1 or more, preferably 1.1 or more. If it is less than 1, the effect of improving the filling property due to the improved circularity may be small.

  In the mechanical energy treatment in the present invention, the Raman R value is increased by 1.1 times or more by the treatment. An increase in the Raman R value means that the crystallinity in the vicinity of the particle surface is lowered as will be described later. Therefore, the mechanical energy treatment needs to be such. The value of (Raman R value after treatment) / (Raman R value before treatment) is 1.1 or more, preferably 1.4 or more. If it is less than 1.1, the effect of improving charge acceptance may be small due to a change in Raman R value.

  The mechanical energy treatment of the present invention introduces roundness into the particles and increases the tap density of these particles. In order to increase the tap density of the powder particles, it is known that smaller particles that can enter the voids formed between the particles are preferably filled. For this reason, it is considered that the tap density increases if the particle size is reduced by performing a treatment such as pulverization on the carbonaceous particles such as the graphite-based carbonaceous particles. In general, the tap density decreases instead. This is considered to be because the particle shape becomes more irregular by pulverization.

  On the other hand, the greater the number of particles (coordination number n) in contact with one particle (particle of interest) in the powder particle group, the lower the proportion of voids in the packed bed. That is, as a factor that affects the tap density, a ratio of particle sizes and a composition ratio, that is, a particle size distribution is important. However, this examination was performed with a model spherical particle group, carbonaceous particles such as graphite-based carbonaceous particles before the treatment handled in the present invention is scaly, scaly, plate-like, Even if it is attempted to increase the tap density by controlling the particle size distribution simply by general pulverization, classification, etc., such a high filling state cannot be produced.

  In general, the tap density of carbonaceous particles such as scaly, scaly, and plate-like graphite-based carbonaceous particles tends to decrease as the particle diameter decreases. This is because the particles become more irregular due to pulverization, and the generation of protrusions such as “crushing”, “peeling”, and “bending” is increased on the surface of the particles. This is considered to be because the resistance between adjacent particles is increased due to the adhesion of such irregular shaped particles with a certain degree of strength and the filling property is deteriorated.

  If these irregularities are reduced and the particle shape is close to a sphere, the decrease in filling property is reduced even if the particle size is reduced. Theoretically, the tap density is the same for both large and small particles. Should be shown.

  In the study by the present inventors, it has been confirmed that the carbon or graphite particles having the same true density and substantially the same average particle diameter have a higher tap density as the shape is spherical. That is, it is important to make the shape of the particles round and close to a spherical shape. If the particle shape is close to a spherical shape, the powder filling property is also greatly improved. In the present invention, for the reasons described above, the tap density of the powder is adopted as an index of the degree of applying mechanical energy. When the filling property of the granular material after the treatment is higher than that before the treatment, it can be considered as a result of the particles being spheroidized by the treatment method used. Further, the tap density of the carbon material obtained when the treatment is performed while greatly reducing the particle size in the method of the present invention is higher than the tap density of the carbon material having the same particle size obtained by general grinding. If so, it can be considered as a result of spheroidization.

  As an index of the crystallinity of the particle and the roughness of the particle surface, that is, the amount of the edge surface of the crystal, the (002) plane spacing (d002), crystallite size (Lc), and Raman R value by wide angle X-ray diffraction Can be used. In general, a carbon material has a smaller (002) plane spacing (d002) value, and the larger the crystallite size (Lc), the smaller the Raman R value. That is, the entire carbonaceous particles such as graphite-based carbonaceous particles are in a substantially similar crystal state. In contrast, the graphitic carbon particles of the present invention have a small (002) plane spacing (d002) value and a large crystallite size (Lc), but a large Raman R value. That is, although the bulk crystallinity of the graphitic carbon particles is high, the crystallinity in the vicinity of the surface (from the particle surface to about 100 °) is disturbed, indicating that the exposure of the edge surface is increased.

  In the mechanical energy treatment in the present invention, it is further preferable to increase the circularity by 1.02 times, particularly preferably 1.04 times, from the viewpoint of improving the filling property.

[[[Devices used for mechanical energy processing]]]
The apparatus for performing the mechanical energy treatment is selected from those capable of performing the above preferred treatment. As a result of studies by the present inventors, it can be achieved by using one or more of the above four, but preferably, compressive force including frictional force, friction force, shearing force, etc. mainly including impact force. It has become clear that a device that repeatedly applies mechanical action to particles is effective. Specifically, it has a rotor with a plurality of blades installed inside the casing, and when the rotor rotates at high speed, impact compression, friction, shearing force, etc. are applied to the carbonaceous particles introduced inside. An apparatus that imparts a mechanical action and performs surface grinding while advancing volume grinding is preferable. Moreover, it is more preferable to have a mechanism that repeatedly gives mechanical action by circulating or convection of carbonaceous particles. The number of blades inside the casing is preferably 3 or more, and particularly preferably 5 or more.

  As an example of a preferable apparatus satisfying such requirements, there can be mentioned a hybridization system manufactured by Nara Machinery Co., Ltd. When processing using this apparatus, the peripheral speed of the rotating rotor is preferably 30 to 100 m / sec, more preferably 40 to 100 m / sec, and further preferably 50 to 100 m / sec. preferable. Further, the treatment can be performed by simply passing the carbonaceous particles, but it is preferable to circulate or stay in the apparatus for 30 seconds or more, and to circulate or stay in the apparatus for 1 minute or more. Is more preferable.

  When the true density of the graphite-based carbon particles used as a raw material is less than 2.25 and the crystallinity is not so high, it is preferable to perform a heat treatment for further improving the crystallinity after performing the mechanical energy treatment. Such heat treatment is preferably performed at 2000 ° C. or more, more preferably at 2500 ° C. or more, and further preferably at 2800 ° C. or more.

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

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

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

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

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

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

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

[[Electrode density]]
The electrode structure when the negative electrode active material is converted into an electrode is not particularly limited, but the density of the active material present on the current collector is preferably 1 g / cm ³ or more, more preferably 1.2 g / cm ^3. More preferably, it is 1.3 g / cm ³ or more, and the upper limit is 2 g / cm ³ or less, preferably 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and still more preferably 1.7 g / cm ³ or less. It is a range of cm ³ or less. If this range is exceeded, the active material particles are destroyed, the initial irreversible capacity increases, the permeability of the non-aqueous electrolyte near the current collector / active material interface decreases, and the high current density charge / discharge characteristics decrease. There is. 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.

[[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 copolymers and hydrogenated products thereof; EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers and hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, Soft resinous polymers such as tylene / vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer, etc. Fluoropolymers; polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions). These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

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

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

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

[[Plate orientation ratio]]
The electrode plate orientation ratio is 0.001 or more, preferably 0.005 or more, more preferably 0.01 or more, and the upper limit is 0.67 or less, which is a theoretical value. Below this range, the high-density charge / discharge characteristics may deteriorate.

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

The X-ray diffraction measurement conditions here are as follows. “2θ” indicates a diffraction angle.
Target: Cu (Kα ray) graphite monochromator
(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

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

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

<Positive electrode>
The positive electrode used for the non-aqueous electrolyte secondary battery of the present invention will be described below.
[Positive electrode active material]
The positive electrode active material used for the positive electrode is described below.
[[Composition of positive electrode active material]]
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. A substance containing lithium and at least one transition metal is preferable, and examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound.

The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples include lithium / cobalt composite oxide such as LiCoO ₂ or LiNiO ₂ . Lithium / nickel composite oxide, LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO _{3 and} other lithium / manganese composite oxides, Al, Ti , V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and those substituted with other metals such as Si. Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O _4, etc. Is mentioned.

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

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

  These surface adhering substances are, for example, a method of dissolving or suspending in a solvent and impregnating and drying the positive electrode active material, and a method of dissolving or suspending a surface adhering substance precursor in a solvent and impregnating and adding to the positive electrode active material, followed by heating. It can be made to adhere to the positive electrode active material surface by the method of making it react by the method etc., the method of adding to a positive electrode active material precursor, and baking simultaneously. In addition, when 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% by mass or less, more preferably, as the lower limit. It is used at 10 mass% or less, more preferably 5 mass% or less. The surface adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material, and can improve the battery life. However, when the amount of the adhering quantity is too small, the effect is not sufficiently exhibited. If the amount is too large, the resistance may increase in order to inhibit the entry and exit of lithium ions.

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

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

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

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

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

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

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

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

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

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

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

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

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

[[[Binder]]]
The binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in electrode production may be used. , Polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, 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.

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

[[[Consolidation]]]
The positive electrode active material layer obtained by coating and drying is preferably consolidated by a hand press, a roller press or the like in order to increase the packing density of the positive electrode active material. Density of the positive electrode active material layer is preferably 1.5 g / cm ³ or more as a lower limit, more preferably 2 g / cm ^3, and even more preferably at 2.2 g / cm ³ or more, the upper limit, preferably 3.5g / Cm ³ or less, more preferably 3 g / cm ³ or less, and even more preferably 2.8 g / cm ³ or less. If this range is exceeded, the permeability of the non-aqueous electrolyte solution to the vicinity of the current collector / active material interface may decrease, and the charge / discharge characteristics at a high current density may decrease. On the other hand, if it is lower, the conductivity between the active materials may be reduced, and the battery resistance may be increased.

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

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

  The ratio of the thickness of the current collector to the positive electrode active material layer is not particularly limited, but the value of (thickness of active material layer on one side immediately before non-aqueous electrolyte injection) / (thickness of current collector) is It is preferably 20 or less, more preferably 15 or less, most preferably 10 or less, and the lower limit is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. Above this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. On the other hand, below this range, the volume ratio of the current collector to the positive electrode active material may increase, and the battery capacity may decrease.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  The non-aqueous electrolyte solution containing the specific compound used in the present invention is effective in reducing reaction resistance related to lithium desorption / insertion with respect to the electrode active material, which is a factor that can realize good low-temperature discharge characteristics. it is conceivable that. However, it has been 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 low temperature discharge characteristics. This can be improved by using a battery having a small DC resistance component, and the effect of the non-aqueous electrolyte solution of the present invention can be sufficiently exhibited.

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

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

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

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

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

<Action and principle>
“Non-aqueous electrolyte containing specific compound”, “circularity of 0.85 or more, (002) plane spacing (d002) by wide-angle X-ray diffraction method is less than 0.337 nm, Raman R value The action / principle that can provide a lithium-ion secondary battery capable of quickly recovering output from a low-temperature state by combining with a negative electrode active material containing graphitic carbon particles having a particle size of 0.12 or more and 0.8 or less is clear However, the present invention is not limited by its action and principle, but the SEI (Solid Electrolyte Interface solid electrolyte interface) coating produced in the presence of a specific substance during the first charge after the battery is fabricated is Spherical graphite with a high R value and a high degree of circularity forms a thin film with high thermal conductivity, so heat conduction from the outside to the electrode reaction site is fast when the ambient temperature rises. It is assumed that the output is improved with good responsiveness.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.
In addition, Examples 6-15 shall be read as Reference Examples 6-15.

(Preparation of negative electrode active material 1)
In order to prevent the mixing of coarse particles in the commercially available natural graphite powder (A), the ASTM 400 mesh sieve was repeated 5 times. The negative electrode active material obtained here was a carbonaceous material (B).

(Preparation of negative electrode active material 2)
Commercially available natural graphite powder (C) (d002: 0.336 nm, Lc: 100 nm or more, Raman R value: 0.11, tap density: 0.46 g / cm ³ , true density: 2.27 g / cm ³ , volume average In order to prevent mixing of coarse particles, a carbonaceous material (D) was prepared by repeating ASTM 400 mesh sieving five times to prevent coarse particles from being mixed.

(Preparation of negative electrode active material 3)
Natural graphite powder (C) is treated using a hybridization system (hybridization system NHS-1 type, manufactured by Nara Machinery Co., Ltd.) at a throughput of 90 g, a rotor peripheral speed of 60 m / s, and a treatment time of 3 minutes. In order to prevent spheroidization and mixing of coarse particles, ASTM 400 mesh sieve was repeated 5 times. The negative electrode active material obtained here was a carbonaceous material (E). By repeating this operation, an amount necessary for battery production was secured.

(Preparation of negative electrode active material 4)
Commercially available natural graphite powder (F) (d002: 0.336 nm, Lc: 100 nm or more, Raman R value: 0.09, tap density: 0.57 g / cm ³ , true density: 2.26 g / cm ³ , volume average Particle size: 85.4 μm) is spheroidized in a hybridization system with a throughput of 90 g, a rotor peripheral speed of 30 m / s, and a processing time of 1 minute, and in order to prevent mixing of coarse particles, ASTM400 mesh sieve is applied 5 times. Repeated. The negative electrode active material obtained here was a carbonaceous material (G). By repeating this operation, an amount necessary for battery production was secured.

(Preparation of negative electrode active material 5)
A coal tar pitch having a quinoline insoluble content of 0.05% by mass or less was heat-treated in a reaction furnace at 460 ° C. for 10 hours to obtain a meltable bulk carbonized precursor having a softening point of 385 ° C. The obtained bulk carbonized precursor was packed in a metal container and heat-treated at 1000 ° C. for 2 hours in a box-shaped electric furnace under nitrogen gas flow. The obtained amorphous lump was pulverized with a crusher (Roll jaw crusher manufactured by Yoshida Seisakusho), and further pulverized with a fine pulverizer (Turbo mill manufactured by Matsubo) to obtain an amorphous powder having a volume-based average diameter of 18 μm. Obtained. In order to prevent mixing of coarse particles in the obtained powder, ASTM 400 mesh sieving was repeated 5 times. The negative electrode active material obtained here was a carbonaceous material (H).

(Preparation of negative electrode active material 6)
The carbonaceous material (H) obtained in (Preparation of negative electrode active material 5) was further transferred to a graphite crucible and graphitized at 3000 ° C. for 5 hours in an inert atmosphere using a direct current furnace. In order to prevent the powder from being mixed with coarse particles, ASTM 400 mesh sieve was repeated 5 times. The negative electrode active material obtained here was a carbonaceous material (I).

(Preparation of negative electrode active material 7)
The carbonaceous material (I) obtained in (Preparation of negative electrode active material 6) was spheroidized with a hybridization system under the conditions of a processing amount of 90 g, a rotor peripheral speed of 30 m / s, and a processing time of 1 minute. In order to prevent contamination, ASTM 400 mesh sieve was repeated 5 times. The negative electrode active material obtained here was a carbonaceous material (J). By repeating this operation, an amount necessary for battery production was secured.

(Preparation of negative electrode active material 8)
Natural graphite powder (K) having a purity lower than that of natural graphite powder (A) (d002: 0.336 nm, Lc: 100 nm or more, Raman R value: 0.10, tap density: 0.49 g / cm ³ , true density: 2.27 g / cm ³ , volume average particle diameter: 27.3 μm, ash content of 0.5% by mass) were spheroidized and sieved under the same conditions as for (Preparation of negative electrode active material 3), and carbonaceous matter (L ) Was prepared. By repeating this operation, an amount necessary for battery production was secured.

(Preparation of negative electrode active material 9)
In order to prevent contamination of coarse particles of commercially available scaly natural graphite powder (M), ASTM 400 mesh sieve was repeated 5 times. The negative electrode active material obtained here was a carbonaceous material (N).

  The shape and physical properties of the carbonaceous materials (B), (D), (E), (G), (H), (I), (J), (L), and (N) were measured by the method described above. The results are shown in Table 1.

[Production of battery]
<< Preparation of positive electrode 1 >>
90% by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder, an N-methylpyrrolidone solvent Mixed in to a slurry. The obtained slurry was applied on both sides of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 80 μm with a press machine, and the active material layer was uncoated with a width of 100 mm, a length of 100 mm and a width of 30 mm. It cut out into the shape which has a process part, and was set as the positive electrode. At this time, the density of the active material of the positive electrode was 2.35 g / cm ³ .

<< Preparation of negative electrode 1 >>
98 parts by weight of the 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, and an aqueous dispersion of styrene-butadiene rubber (styrene) -Butadiene rubber concentration 50 mass%) 2 parts by weight 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, and 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 .

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

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

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

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

<< Production of Battery 1 >>
The 32 positive electrodes and 33 negative electrodes were alternately arranged, and the porous polyethylene sheet separator (thickness 25 μm) was laminated between each electrode. At this time, the positive electrode active material surface was faced so as not to deviate from the negative electrode active material surface. The uncoated portions of each of the positive electrode and the negative electrode were welded together to produce a current collecting tab, and an electrode group was enclosed in a battery can (outside dimension: 120 × 110 × 10 mm). Thereafter, 20 mL of a non-aqueous electrolyte solution was injected into a battery can loaded with the electrode group, sufficiently infiltrated into the electrode, and sealed to produce a prismatic battery. The rated discharge capacity of this battery is about 6 ampere hours (Ah), and the DC resistance component measured by the 10 kHz AC method is about 5 milliohms (mΩ). The ratio of the total electrode area of the positive electrode to the sum of the outer surface areas of the batteries was 20.6.

Example 1
The negative electrode produced as the carbonaceous material (D) as the negative electrode active material in the section << Preparation of Negative Electrode 1 >>, the positive electrode prepared in the section << Preparation 1 of Positive Electrode >>, and the non-aqueous system produced in the section << Preparation 1 of Nonaqueous Electrolytic Solution >> Using the electrolytic solution, a battery was prepared by the method described in “Preparation of battery 1”. This battery was measured by the method described in the section “Battery evaluation” below and the measurement method described above. The results are shown in Table 2.

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

Example 3
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (G) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed. The results are shown in Table 2.

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

Example 5
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (L) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed. The results are shown in Table 2.

Examples 6-10
Batteries were prepared and evaluated in the same manner except that the non-aqueous electrolytes of Examples 1 to 5 were replaced with the non-aqueous electrolyte prepared in the section “Preparation of Non-Aqueous Electrolyte 2”. did. The results are shown in Table 2.

Examples 11-15
Batteries were prepared and evaluated in the same manner, except that the non-aqueous electrolytes of Examples 1 to 5 were replaced with the non-aqueous electrolyte prepared in Section << Preparation of Non-Aqueous Electrolyte 3 >>. did. The results are shown in Table 2.

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

Comparative Example 2
A battery was prepared in the same manner except that the non-aqueous electrolyte prepared in Section << Preparation of Non-Aqueous Electrolyte 4 >> was used as the non-aqueous electrolyte of Comparative Example 1, and the battery evaluation described in << Battery Evaluation >> Carried out. The results are shown in Table 2.

Comparative Example 3
A battery was prepared in the same manner as in Example 2 except that the non-aqueous electrolyte prepared in Section << Preparation of Non-Aqueous Electrolyte 4 >> was used as the non-aqueous electrolyte of Example 2, and the battery evaluation described in << Battery Evaluation >> Carried out. The results are shown in Table 2.

Comparative Example 4
A battery was prepared in the same manner as in Example 1 except that the non-aqueous electrolyte prepared in Section << Preparation of Non-Aqueous Electrolyte 4 >> was used as the non-aqueous electrolyte of Example 1, and the battery evaluation described in << Battery Evaluation >> Carried out. The results are shown in Table 2.

Comparative Example 5
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (H) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed. The results are shown in Table 2.

Comparative Example 6
A battery was prepared in the same manner except that the non-aqueous electrolyte prepared in Section << Preparation of Non-Aqueous Electrolyte 4 >> was used as the non-aqueous electrolyte of Comparative Example 5, and the battery evaluation described in << Battery Evaluation >> Carried out. The results are shown in Table 2.

Comparative Example 7
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (N) was used as the negative electrode active material in the section <Preparation of negative electrode 1>, and the battery evaluation described in the section <Battery evaluation> was performed. The results are shown in Table 2.

Comparative Example 8
A battery was prepared in the same manner except that the non-aqueous electrolyte prepared in Section << Preparation of Non-Aqueous Electrolyte 4 >> was used as the non-aqueous electrolyte of Comparative Example 7, and the battery evaluation described in << Battery Evaluation >> Carried out. The results are shown in Table 2.

Comparative Example 9
A battery was prepared in the same manner as in Example 1 except that the carbonaceous material (I) was used as the negative electrode active material in the section “Preparation of negative electrode 1”, and battery evaluation described in the section “Battery evaluation” was performed. The results are shown in Table 2.

Comparative Example 10
A battery was prepared in the same manner except that the non-aqueous electrolyte prepared in Section << Preparation of Non-Aqueous Electrolyte 4 >> was used as the non-aqueous electrolyte of Comparative Example 9, and the battery evaluation described in section << Battery Evaluation >> Carried out. The results are shown in Table 2.

Comparative Examples 11-14
Batteries were prepared in the same manner except that the non-aqueous electrolytes of Comparative Examples 1, 5, 7, and 9 were replaced with the non-aqueous electrolyte prepared in the section “Preparation of Non-Aqueous Electrolyte 2”. The evaluation was carried out. The results are shown in Table 2.

Comparative Examples 15-18
Batteries were prepared in the same manner except that the non-aqueous electrolytes of Comparative Examples 1, 5, 7, and 9 were replaced with the non-aqueous electrolyte prepared in the section “Preparation of non-aqueous electrolyte 3”. The evaluation was carried out. The results are shown in Table 2.

<Battery evaluation>
(Capacity measurement)
An initial charge / discharge for 5 cycles was performed at 25 ° C. in a voltage range of 4.1 V to 3.0 V at 25 ° C. (voltage range of 4.1 V to 3.0 V) for a new battery that had not been charged or discharged. At this time, the discharge capacity was defined as the initial capacity 0.2C at the fifth cycle (the rated capacity due to the discharge capacity at the hour rate is 1 C, and the same applies hereinafter).

(Output measurement 1)
The battery was charged for 150 minutes at a constant current of 0.2C in an environment of 25 ° C., and allowed to stand for 3 hours in an environment of −30 ° C., then 0.1 C, 0.3 C, 1.0 C, 3.0 C, and 5. The battery was discharged at 0C for 10 seconds, and the voltage at the 10th second was measured. The area of the triangle surrounded by the current-voltage straight line and the lower limit voltage (3 V) was defined as the initial low temperature output (W).

(Output measurement 2)
After the output measurement 1, 4.1V low voltage charging was performed for 1 hour, and then the battery was moved to an environment of 25 ° C., and after 15 minutes, 0.1C, 0.3C, 1.0C, 3.0C The battery was discharged at 5.0 C for 10 seconds, and the voltage at the 10th second was measured. The area of the triangle surrounded by the current-voltage straight line and the lower limit voltage (3 V) was defined as the output (W) during temperature rise.

From the results of output measurement 1 and output measurement 2, the temperature adaptation output improvement rate (%) was calculated by the following formula.
Temperature adaptation output improvement rate (%)
= [(Temperature rise output (W) / initial low temperature output (W))-1] × 100

  The impedance Rct and double layer capacitance Cdl in Table 2 are one of the parameters that contribute to the output. The smaller the value of the impedance Rct and the larger the value of the double layer capacitance Cdl, the more the output tends to improve. is there. Note that “impedance Rct” and “double layer capacitance Cdl” were obtained by the method described in the section of impedance.

  As can be seen from the results in Table 2, it contains lithium difluorophosphate, trimethylsilyl methanesulfonate, hexamethylcyclotrisiloxane, and has a circularity of 0.85 or more and a wide angle X-ray diffraction method (002) By containing graphitic carbon particles having a face spacing (d002) of less than 0.337 nm and a Raman R value of 0.12 or more and 0.8 or less as a negative electrode active material, a low temperature state of −30 ° C. It was found that the recovery of the output due to the temperature rise has been dramatically accelerated.

  The use of the lithium ion secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. , Electronic notebook, calculator, memory card, portable tape recorder, radio, backup power supply, motor, automobile, motorcycle, motorbike, bicycle, lighting equipment, toy, game equipment, clock, electric tool, strobe, camera, etc. Can do. In particular, since the lithium ion secondary battery of the present invention can obtain good cycle characteristics and always high low temperature characteristics, it can be used widely and suitably for applications in environments where there is a great difference in temperature.

Claims (13)

A non-aqueous electrolyte solution containing a non-aqueous solvent and a lithium salt, a lithium ion secondary battery having a positive electrode active material and a negative electrode active material,
The non-aqueous electrolyte contains 10 ppm or more of lithium difluorophosphate in the whole non-aqueous electrolyte,
In addition, the negative electrode active material has a circularity of 0.85 or more, a (002) plane spacing (d002) of less than 0.337 nm by a wide angle X-ray diffraction method, and 1580 cm ⁻ in an argon ion laser Raman spectrum method. lithium ion secondary Raman R value, defined as the ratio of the peak intensity of 1360 cm ^-1 for ^one of the peak intensity is characterized in that containing graphitic carbon particles is 0.12 to 0.8 battery.   The lithium ion secondary battery according to claim 1, wherein the tap density of the graphitic carbon particles is 0.55 or more. 3. The lithium ion secondary battery according to claim 1, wherein the graphite carbon particles have a BET specific surface area of 0.1 m ² / g or more and 100 m ² / g or less.   The lithium ion secondary battery according to any one of claims 1 to 3, wherein the graphitic carbon particles have a volume average particle size of 1 µm or more and 50 µm or less.   The lithium ion secondary according to any one of claims 1 to 4, wherein the pore volume in the range of 0.01 µm to 1 µm in the mercury porosimetry of the graphite carbon particles is 0.01 mL / g or more. battery.   The lithium ion secondary battery according to any one of claims 1 to 5, wherein the ash content of the graphitic carbon particles is 1 ppm or more and 1 mass% or less.   The lithium ion secondary battery according to any one of claims 1 to 6, wherein the graphitic carbon particles contain natural graphite. The negative electrode active material is a graphitic carbon particle obtained by treating a carbonaceous particle with a mechanical energy treatment, and the mechanical energy treatment has a volume average particle size ratio of 1 or less before and after the treatment. subtracting the particle size such that, and increase the tap density by the processing, and the Raman R value is the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum by the processing 1. The lithium ion secondary battery according to any one of claims 1 to 7, wherein the mechanical energy treatment is one or more times.   The lithium ion secondary battery according to claim 8, wherein the carbonaceous particles contain natural graphite.   The lithium ion secondary battery according to claim 8 or 9, wherein the mechanical energy treatment is performed by using a device having a rotor having a plurality of blades installed in the casing and rotating the rotor at a high speed.   11. The lithium ion secondary battery according to claim 1, wherein the total area of the positive electrode area with respect to the surface area of the exterior of the secondary battery is 20 times or more in area ratio.   The lithium ion secondary battery according to any one of claims 1 to 11, wherein a DC resistance component of the secondary battery is 10 milliohms (mΩ) or less.   The lithium ion secondary according to any one of claims 1 to 12, wherein an electric capacity of a battery element housed in one battery exterior of the secondary battery is 3 ampere hours (Ah) or more. battery.