JP2014007010A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery which has good load characteristic, good charge and discharge cycle characteristics and good storage suitability even after the battery is charged so that its battery voltage exceeds 4.25 V.SOLUTION: The lithium secondary battery has a positive electrode, a negative electrode, a nonaqueous electrolyte and a separator. The lithium secondary battery is subjected to a constant current-constant voltage charging with a final voltage of over 4.25 V before being put in use. The nonaqueous electrolyte includes: 0.1-5 mass% of a compound having, in its molecule, a carbon-carbon double bond or carbon-carbon triple bond, and P or S; and 0.1-5 mass% of 1,3-dioxane.

Description

  The present invention relates to a lithium secondary battery having good load characteristics, charge / discharge cycle characteristics and storage characteristics even when charged in a high voltage region where the battery voltage exceeds 4.25V.

  In recent years, along with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, small and light lithium secondary batteries with high capacity have been required.

  In addition, lithium secondary batteries are required to improve various battery characteristics as well as to increase the capacity in accordance with the spread of applied devices.

  As one means for achieving the improvement of the battery characteristics of such a lithium secondary battery, it is known to apply various additives to the non-aqueous electrolyte of the lithium secondary battery. For example, Patent Document 1 describes that the charge / discharge cycle characteristics and storage characteristics of a lithium secondary battery can be improved by using a nonaqueous electrolytic solution to which a phosphonoacetate compound having a specific structure is added.

  Patent Document 2 describes that the charge / discharge cycle characteristics of a lithium secondary battery can be improved by using a non-aqueous electrolytic solution to which 1,3-dioxane and a sulfonic acid ester compound are added. .

JP 2008-262908 A JP 2009-140919 A

  By the way, in order to increase the capacity of the lithium secondary battery, a method of increasing the charging voltage can be considered. For example, in current lithium secondary batteries, the upper limit value of the charging voltage is generally set so that the battery voltage is about 4.25V. By increasing it, the capacity is further increased.

  However, when a conventional lithium secondary battery is charged so that the battery voltage exceeds 4.25 V, the load characteristics and the charge / discharge cycle characteristics tend to deteriorate.

  For example, as described above, the non-aqueous electrolyte containing the additive described in Patent Document 1 is effective as a battery that can improve the charge / discharge cycle characteristics and storage characteristics of the battery. However, even when such an additive is charged so that the battery voltage exceeds 4.25 V, it is not easy to suppress a decrease in load characteristics and charge / discharge cycle characteristics of the lithium secondary battery.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium secondary having good load characteristics, charge / discharge cycle characteristics, and storage characteristics even when the battery voltage is charged to exceed 4.25V. To provide a battery.

  The lithium secondary battery of the present invention that has achieved the above object has a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and is capable of constant current-constant voltage charging at a final voltage exceeding 4.25 V before use. In the lithium secondary battery, a compound containing a carbon-carbon double bond or a carbon-carbon triple bond and P or S in the molecule in the non-aqueous electrolyte [hereinafter referred to as “compound (A)” It is characterized by using what contains 0.1-5 mass% and 0.13-5 mass% of 1, 3- dioxane.

  According to the present invention, it is possible to provide a lithium secondary battery having good load characteristics, charge / discharge cycle characteristics, and storage characteristics even when the battery voltage is charged to exceed 4.25V.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically an example of the lithium secondary battery of this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. It is a perspective view of the lithium secondary battery shown in FIG.

  The compound (A) containing a carbon-carbon double bond or carbon-carbon triple bond and P or S in the molecule is added to the non-aqueous electrolyte of a lithium secondary battery, for example, the battery voltage is reduced. Even when the battery is charged to exceed 4.25 V, it is possible to suppress the occurrence of swelling of the lithium secondary battery and to enhance its storage characteristics, but on the other hand, the load of the lithium secondary battery It also has an effect of impairing characteristics and charge / discharge cycle characteristics.

  The compound (A) has a function of forming a film on the surface of the negative electrode in the lithium secondary battery, but the film prevents decomposition of the non-aqueous electrolyte due to contact with the negative electrode, and gas associated therewith. By suppressing the generation, swelling of the lithium secondary battery can be suppressed.

  However, when the battery voltage exceeds 4.25 V, the compound (A) is decomposed by coming into contact with the positive electrode, which causes a decrease in load characteristics and charge / discharge cycle characteristics of the lithium secondary battery. It is speculated that

  Therefore, in the present invention, 1,3-dioxane is used together with the compound (A) as an additive for the non-aqueous electrolyte. 1,3-dioxane has a function of forming a film on the surface of the positive electrode by being added to the non-aqueous electrolyte of the lithium secondary battery. And the film derived from 1,3-dioxane formed on the surface of the positive electrode suppresses degradation of the compound (A) on the surface of the positive electrode, or suppresses a decrease in load characteristics of the lithium secondary battery due to the decomposition. It is done.

  In addition, when a lithium secondary battery is stored in a high temperature environment in a charged state, the subsequent discharge capacity is usually lower than the capacity before storage, but 1,3-dioxane is a lithium secondary battery. By adding to the non-aqueous electrolyte, the capacity before storage of the recovery capacity after high-temperature storage (discharge capacity when the charged lithium secondary battery is stored at high temperature and then discharged and then discharged) It also has an effect of suppressing a decrease from the above. Therefore, in the lithium secondary battery of the present invention, this action of 1,3-dioxane is combined with the action of suppressing the swelling of the battery at the time of high-temperature storage of the compound (A) to ensure good storage characteristics. be able to.

  Furthermore, 1,3-dioxane has an effect of enhancing the charge / discharge cycle characteristics by being added to the non-aqueous electrolyte of the lithium secondary battery, but the non-aqueous electrolyte is added together with the compound (A). It was also found that when added, the effect of improving the charge / discharge cycle characteristics of the lithium secondary battery is exhibited beyond the effect of improving the charge / discharge cycle characteristics of 1,3-dioxane alone. Although the reason is not certain, in the lithium secondary battery of the present invention, the combined use of the compound (A) and 1,3-dioxane, for example, the charge / discharge cycle characteristics by preventing the decomposition of the compound (A). In addition to the effect of suppressing the decrease, the charge / discharge cycle characteristics can also be improved satisfactorily.

  In addition, since a compound (A) superpose | polymerizes and forms a film | membrane by opening a carbon-carbon double bond or a carbon-carbon triple bond in the negative electrode surface as above-mentioned, the film | membrane formed is Since the constituent molecule (constituent polymer) has a flexible carbon-carbon bond as the main chain, the flexibility is high. When the lithium secondary battery is charged and discharged, the negative electrode active material expands and contracts accordingly, so that the entire negative electrode (negative electrode mixture layer) also changes in volume. When a film derived from the compound (A) is formed on the surface of the negative electrode (negative electrode mixture layer), the film is rich in flexibility as described above, and therefore follows the change in volume of the negative electrode accompanying charging / discharging of the battery. And since a crack, a crack, etc. do not arise easily, even if charging / discharging of a battery is repeated, the said effect by the membrane | film | coat derived from a compound (A) can be favorably maintained.

  The lithium secondary battery of the present invention has excellent load characteristics and charge / discharge cycle characteristics while achieving a high capacity by using constant current-constant voltage charging with a final voltage exceeding 4.25 V due to these actions. And storage characteristics can be secured.

  The non-aqueous electrolyte solution according to the lithium secondary battery of the present invention is a solution in which a lithium salt is dissolved in an organic solvent, and a carbon-carbon double bond or carbon-carbon triple bond and P or S are contained in the molecule. What contains the compound (A) to contain and 1, 3- dioxane is used.

  Specific examples of the compound (A) include, for example, 1-methyl-2-propynyl methanesulfonate, 1,1-dimethyl-2-propynyl methanesulfonate, 2-propynyl methanesulfonate, and 2-butynyl methanesulfonate. , 2-pentynyl methanesulfonate, 2-propynyl ethanesulfonate, 2-propynyl propanesulfonate, and allyldiethylphosphonoacetate.

  The content of the compound (A) in the non-aqueous electrolyte used for the lithium secondary battery favorably suppresses battery swelling when stored at a high temperature, particularly in a high-voltage charge state, and 1,3-dioxane and From the viewpoint of securing the effect of improving the charge / discharge cycle characteristics of the battery by the combination of the above, it is 0.1% by mass or more, and preferably 0.5% by mass or more. On the other hand, if the amount of the compound (A) in the non-aqueous electrolyte is too large, the load characteristics, charge / discharge cycle characteristics, and storage characteristics of the battery may be degraded. Therefore, the content of the compound (A) in the nonaqueous electrolytic solution used for the lithium secondary battery is 5% by mass or less, and preferably 2.5% by mass or less.

  The content of 1,3-dioxane in the non-aqueous electrolyte used for the lithium secondary battery increases the load characteristics of the battery when charged at a high voltage and the capacity recoverability after high-temperature storage, and the compound (A ) And 0.1% by mass or more, and preferably 0.5% by mass or more from the viewpoint of securing the effect of improving the charge / discharge cycle characteristics of the battery. On the other hand, if the amount of 1,3-dioxane in the nonaqueous electrolytic solution is too large, the load characteristics, charge / discharge cycle characteristics, and storage characteristics of the battery may be degraded. Therefore, the content of 1,3-dioxane in the nonaqueous electrolytic solution used for the lithium secondary battery is 5% by mass or less, and preferably 2.5% by mass or less.

  In addition, it is preferable to use a non-aqueous electrolyte containing a halogen-substituted cyclic carbonate. The halogen-substituted cyclic carbonate acts on the negative electrode and has an action of suppressing the reaction between the negative electrode and the non-aqueous electrolyte component. Therefore, by using a nonaqueous electrolytic solution that also contains a halogen-substituted cyclic carbonate, a lithium secondary battery with better charge / discharge cycle characteristics can be obtained.

  As the halogen-substituted cyclic carbonate, a compound represented by the following general formula (1) can be used.

In the general formula (1), R ¹ , R ² , R ³ and R ⁴ represent hydrogen, a halogen element, or an alkyl group having 1 to 10 carbon atoms, and a part or all of the hydrogen of the alkyl group is halogen. may be substituted with an ^element, at least one of R ^1, R 2, ^{R 3} and ^{R 4} are ^halogen, R ^1, R 2, ^{R 3} and ^{R 4} have different respective Two or more may be the same. When R ¹ , R ² , R ³ and R ⁴ are alkyl groups, the smaller the number of carbon atoms, the better. As the halogen element, fluorine is particularly preferable.

  Among the cyclic carbonates substituted with such a halogen element, 4-fluoro-1,3-dioxolan-2-one (FEC) is particularly preferable.

  The content of the halogen-substituted cyclic carbonate in the non-aqueous electrolytic solution used for the lithium secondary battery is preferably 0.1% by mass or more from the viewpoint of better ensuring the effect of the use. More preferably, it is 5 mass% or more. However, if the content of the halogen-substituted cyclic carbonate in the non-aqueous electrolyte is too large, the effect of improving storage characteristics may be reduced. Therefore, the content of the halogen-substituted cyclic carbonate in the nonaqueous electrolytic solution used for the lithium secondary battery is preferably 10% by mass or less, and more preferably 5% by mass or less.

  Further, it is preferable to use a non-aqueous electrolyte containing vinylene carbonate (VC). VC acts on a negative electrode (in particular, a negative electrode using a carbon material as a negative electrode active material) and has an action of suppressing a reaction between the negative electrode and a non-aqueous electrolyte component. Therefore, by using a non-aqueous electrolyte containing VC, a lithium secondary battery with better charge / discharge cycle characteristics can be obtained.

  The content of VC in the non-aqueous electrolyte used for the lithium secondary battery is preferably 0.1% by mass or more, and preferably 1.0% by mass or more from the viewpoint of ensuring better the effect of the use. More preferably. However, if the content of VC in the non-aqueous electrolyte is too large, the effect of improving storage characteristics may be reduced. Therefore, the content of VC in the nonaqueous electrolytic solution used for the lithium secondary battery is preferably 10% by mass or less, and more preferably 4.0% by mass or less.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it is dissociated in a solvent to form Li ⁺ ions and hardly causes a side reaction such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as 1,4-dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; acetonitrile, propionitrile, methoxypropionitrile and the like Nitriles; sulfites such as ethylene glycol sulfite; and the like. These may be used in combination of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

  In addition, non-aqueous electrolytes used for lithium secondary batteries include acid anhydrides, sulfonate esters, and the like for the purpose of further improving charge / discharge cycle characteristics and improving safety such as high-temperature storage and prevention of overcharge. Additives (including these derivatives) such as dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, and t-butylbenzene can be added as appropriate.

  Further, as the non-aqueous electrolyte of the lithium secondary battery, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer to the non-aqueous electrolyte can be used.

  The lithium secondary battery of the present invention has a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and the non-aqueous electrolyte may be used as the non-aqueous electrolyte. There is no particular limitation, and various configurations and structures employed in conventionally known lithium secondary batteries can be applied.

  As the positive electrode according to the lithium secondary battery, for example, one having a structure having a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive additive and the like on one side or both sides of a current collector can be used.

Examples of the positive electrode active material include lithium cobalt oxides such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium nickel oxides such as LiNiO ₂ ; lithium having a layered structure such as LiCo _1-x NiO _2. Containing complex oxide; lithium-containing complex oxide having a spinel structure such as LiMn ₂ O ₄ , Li _4/3 Ti _5/3 O ₄ ; lithium-containing complex oxide having an olivine structure such as LiFePO ₄ ; Oxides substituted with various elements as the composition can be used.

  Among these lithium-containing composite oxides, it is more preferable to use one represented by the following general composition formula (2) because of its larger capacity.

Li _{1 + a} Ni _1-bc-d Co _b Mn _c M ¹ _d O ₂ (2)

In the general composition formula (2), M ¹ is selected from the group consisting of Mg, Al, Ti, Fe, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Sn, W, B, P, and Bi. At least one element, −0.15 ≦ a ≦ 0.15, 0.05 ≦ b ≦ 0.4, 0.05 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.03, and b + c + d ≦ 0.7.

Further, the positive electrode active material includes a lithium-containing composite oxide (lithium nickel cobalt manganese oxide) represented by the general composition formula (2), LiCoO ₂ and an oxide represented by the following general composition formula (3). It is more preferable to use together with lithium cobalt oxide.

Li _{1 + o} Co _1-pq Mg _p M ² _q O ₂ (3)

In the general composition formula (3), M ² is at least one selected from the group consisting of Al, Ti, Fe, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Sn, W, B, P, and Bi. It is a seed element, with −0.3 ≦ o ≦ 0.3, 0.001 ≦ p ≦ 0.1, and 0 <q ≦ 0.1.

  When the lithium nickel cobalt manganese oxide and the lithium cobalt oxide are used in combination with the positive electrode active material, the content of the lithium cobalt oxide in a total of 100% by mass is 50 to 90% by mass. It is preferable to do.

  For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like is preferably used for the binder related to the positive electrode mixture layer. In addition, as the conductive auxiliary agent related to the positive electrode mixture layer, for example, graphite (graphite carbon material) such as natural graphite (flaky graphite), artificial graphite; acetylene black, ketjen black, channel black, furnace black, Carbon materials such as carbon black such as lamp black and thermal black; carbon fiber;

  For the positive electrode, for example, a paste-like or slurry-like positive electrode mixture-containing composition in which a positive electrode active material, a binder, a conductive auxiliary agent, and the like are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) is prepared ( However, the binder may be dissolved in a solvent), and this is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the positive electrode is not limited to those manufactured by the above manufacturing method, and may be manufactured by other methods.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium secondary battery according to a conventional method to a positive electrode as needed.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector. Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 60-95 mass%, for example, it is preferable that the quantity of a binder is 1-15 mass%, and the quantity of a conductive support agent. Is preferably 3 to 20% by mass.

  The positive electrode current collector can be the same as that used for the positive electrode of a conventionally known lithium secondary battery. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

  The negative electrode related to the lithium secondary battery has, for example, a negative electrode active material, a binder, and, if necessary, a negative electrode mixture layer including a negative electrode mixture containing a conductive auxiliary agent on one side or both sides of the current collector. A structure can be used.

  Examples of the negative electrode active material include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, and metals that can be alloyed with lithium (Si , Sn, etc.) or alloys thereof, oxides, etc., and one or more of these can be used.

Among the negative electrode active materials, in order to increase the capacity of the battery, in particular, a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5 Hereinafter, the material is preferably referred to as “SiO _x ”.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is sufficient that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5 in combination with Si. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

Then, SiO _x is preferably a complex complexed with carbon materials, for example, it is desirable that the surface of the SiO _x is coated with a carbon material. As described above, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of securing good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is used. It is necessary to form an excellent conductive network by mixing and dispersing the material and the conductive material well. If complexes complexed with carbon material SiO _x, for example, simply than with a material obtained by mixing a conductive material such as SiO _x and the carbon material, good conductive network in the negative electrode Formed.

The complex of the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, such as granules of SiO _x and the carbon material can be cited.

In addition, since the composite in which the surface of SiO _x is coated with a carbon material is further combined with a conductive material (carbon material or the like), a better conductive network can be formed in the negative electrode. Therefore, it is possible to realize a lithium secondary battery with higher capacity and more excellent battery characteristics (for example, charge / discharge cycle characteristics). The complex of the SiO _x and the carbon material coated with a carbon material, for example, like granules the mixture was further granulated with SiO _x and the carbon material coated with a carbon material.

Further, as SiO _x whose surface is coated with a carbon material, the surface of a composite (for example, a granulated body) of SiO _x and a carbon material having a smaller specific resistance value is further coated with a carbon material. Those can also be preferably used. In a state where SiO _x and the carbon material are dispersed inside the granulated body, a better conductive network can be formed. Therefore, in a lithium secondary battery having a negative electrode containing SiO _x as a negative electrode active material, a heavy load Battery characteristics such as discharge characteristics can be further improved.

Preferred examples of the carbon material that can be used to form a composite with SiO _x include carbon materials such as low crystalline carbon, carbon nanotubes, and vapor grown carbon fibers.

The details of the carbon material include at least one selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. A seed material is preferred. Fibrous or coil-like carbon materials are preferable in that they easily form a conductive network and have a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention, and even if SiO _x particles expand and contract. This is preferable in that it has a property of easily maintaining contact with the particles.

Further, as will be described in detail later, in the present invention, graphite is preferably used as a negative electrode active material together with SiO _x , but this graphite is used as a carbon material related to a composite of SiO _x and a carbon material. You can also. Graphite, like carbon black, has high electrical conductivity and high liquid retention, and also has the property of easily maintaining contact with the SiO _x particles even when they expand and contract. Therefore, it can be preferably used for forming a complex with SiO _x .

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable for use when the composite with SiO _x is a granulated body. Fibrous carbon material can follow the expansion and contraction of SiO _x with the charging and discharging of the battery due to the high shape is thin threadlike flexibility, also because bulk density is large, many and SiO _x particles It is because it can have a junction. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used.

The fibrous carbon material can also be formed on the surface of the SiO _x particles by, for example, a vapor phase method.

The specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, while the specific resistance value of the carbon material exemplified above is usually 10 ^{−5 to} 10 kΩcm.

The composite of SiO _x and the carbon material may further have a material layer (a material layer containing non-graphitizable carbon) that covers the carbon material coating layer on the particle surface.

When a composite of SiO _x and a carbon material is used for the negative electrode, the ratio of SiO _x and the carbon material is based on SiO _x : 100 parts by mass from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. The carbon material is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. Further, in the composite, if the ratio of the carbon material to be combined with SiO _x is too large, it may lead to a decrease in the amount of SiO _x in the negative electrode mixture layer, and the effect of increasing the capacity may be reduced. SiO _x: relative to 100 parts by weight, the carbon material, and more preferably preferably not more than 50 parts by weight, more than 40 parts by weight.

The composite of the SiO _x and the carbon material can be obtained, for example, by the following method.

First, a manufacturing method in the case of combining SiO _x will be described. A dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, and sprayed and dried to produce composite particles including a plurality of particles. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. In addition to the above method, similar composite particles can be produced also by a granulation method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

Incidentally, the SiO _x, in the case of manufacturing a granulated body with small carbon material resistivity value than SiO _x is adding the carbon material in the dispersion liquid of SiO _x are dispersed in a dispersion medium, the dispersion by using a liquid, by a similar method to the case of composite of SiO _x may be a composite particle (granule). Further, by granulation process according to the similar mechanical method, it is possible to produce a granular material of the SiO _x and the carbon material.

Next, when the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon-based material The gas is heated in the gas phase, and carbon generated by pyrolysis of the hydrocarbon-based gas is deposited on the surface of the particles. As described above, according to the vapor deposition (CVD) method, the hydrocarbon-based gas spreads to every corner of the composite particle, and the surface of the particle and the pores in the surface are thin and contain a conductive carbon material. Since a uniform film (carbon material coating layer) can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon material.

In the production of SiO _x coated with a carbon material, the processing temperature (atmosphere temperature) of the vapor deposition (CVD) method varies depending on the type of hydrocarbon gas, but usually 600 to 1200 ° C. is appropriate. Among these, the temperature is preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the treatment temperature, the less the remaining impurities, and the formation of a coating layer containing carbon having high conductivity.

  As the liquid source of the hydrocarbon-based gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

In addition, after the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is covered with a carbon material by a vapor deposition (CVD) method, a petroleum-based pitch or a coal-based pitch is used. At least one organic compound selected from the group consisting of a thermosetting resin and a condensate of naphthalene sulfonate and aldehydes is attached to a coating layer containing a carbon material, and then the organic compound is attached. The obtained particles may be fired.

Specifically, a dispersion liquid in which a SiO _x particle (SiO _x composite particle or a granulated body of SiO _x and a carbon material) coated with a carbon material and the organic compound are dispersed in a dispersion medium is prepared, The dispersion is sprayed and dried to form particles coated with the organic compound, and the particles coated with the organic compound are fired.

  An isotropic pitch can be used as the pitch, and a phenol resin, a furan resin, a furfural resin, or the like can be used as the thermosetting resin. As the condensate of naphthalene sulfonate and aldehydes, naphthalene sulfonic acid formaldehyde condensate can be used.

As a dispersion medium for dispersing the SiO _x particles coated with the carbon material and the organic compound, for example, water or alcohols (ethanol or the like) can be used. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. The firing temperature is usually 600 to 1200 ° C., preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the processing temperature, the less the remaining impurities, and the formation of a coating layer containing a high-quality carbon material with high conductivity. However, the processing temperature needs to be lower than the melting point of SiO _x .

When using SiO _x for the negative electrode active material according to the lithium secondary battery of the present invention, it is preferable to use graphite as the negative electrode active material. By reducing the ratio of SiO _x in the negative electrode active material using graphite, the negative electrode (negative electrode mixture) associated with charging / discharging of the battery is suppressed as much as possible while suppressing the decrease in the capacity-enhancing effect due to the reduction of SiO _x. It is possible to suppress a change in volume of the layer) and to suppress a decrease in battery characteristics that may be caused by the volume change.

Examples of graphite used as the negative electrode active material together with SiO _x include natural graphite such as flaky graphite; graphitizable carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB), and carbon fibers at 2800 ° C. or more. Artificial graphite subjected to chemical treatment; and the like.

In the negative electrode according to the present invention, from the viewpoint of satisfactorily ensuring the effect of the high capacity by using a SiO _x, the content of SiO _x in the anode active material is 0.01 wt% or more It is preferably 3% by mass or more. Further, from the viewpoint of better avoiding the problem due to the volume change of the negative electrode due to charge / discharge, the content of SiO _x in the negative electrode active material is preferably 30% by mass or less, and 20% by mass or less. Is more preferable.

  Moreover, the same thing as what was illustrated previously as what can be used for a positive electrode can be used for the binder and conductive support agent of a negative electrode.

  For the negative electrode, for example, a negative electrode active material, a binder, and a conductive auxiliary agent used as necessary are prepared in a paste-like or slurry-like negative electrode mixture-containing composition in which a solvent such as NMP or water is dispersed. (However, the binder may be dissolved in a solvent), which is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the negative electrode is not limited to those manufactured by the above manufacturing method, and may be manufactured by other methods.

  Moreover, you may form in the negative electrode the lead body for electrically connecting with the other member in a lithium secondary battery according to a conventional method as needed.

  The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per one surface of the current collector, for example. Moreover, as a composition of a negative mix layer, it is preferable that a negative electrode active material shall be 80.0-99.8 mass% and a binder shall be 0.1-10 mass%, for example. Furthermore, when making a negative mix layer contain a conductive support agent, it is preferable that the quantity of the conductive support agent in a negative mix layer shall be 0.1-10 mass%.

  As the current collector for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is 5 μm in order to ensure mechanical strength. Is desirable.

  The separator according to the lithium secondary battery has a property that the pores are closed at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower) (that is, a shutdown function). It is preferable that a separator used in a normal lithium secondary battery, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be.

  The thickness of the separator is preferably 10 to 30 μm, for example.

  The positive electrode, the negative electrode, and the separator are formed in the form of a laminated electrode body in which a separator is interposed between the positive electrode and the negative electrode, or a wound electrode body in which the separator is wound in a spiral shape. It can be used for the lithium battery of the invention.

  Examples of the form of the lithium secondary battery of the present invention include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The lithium secondary battery of the present invention can be used for the same applications as various applications to which conventionally known lithium secondary batteries are applied.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
100 parts by mass of a positive electrode active material obtained by mixing LiCoO ₂ and Li _1.0 Ni _0.5 Co _0.2 Mn _0.3 O _{2 at} a ratio (mass ratio) of 8: 2, and 10 parts by mass of PVDF as a binder. 20 parts by weight of NMP solution contained at a concentration of 1%, 1 part by weight of artificial graphite and 1 part by weight of ketjen black, which are conductive assistants, are kneaded using a biaxial kneader, and NMP is added to adjust the viscosity. Thus, a positive electrode mixture-containing paste was prepared.

  After coating the positive electrode mixture-containing paste on both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, vacuum drying is performed at 120 ° C. for 12 hours to form a positive electrode mixture layer on both surfaces of the aluminum foil. did. Thereafter, press treatment was performed to adjust the thickness and density of the positive electrode mixture layer, and a nickel lead body was welded to the exposed portion of the aluminum foil to produce a strip-like positive electrode having a length of 375 mm and a width of 43 mm. . The positive electrode mixture layer in the obtained positive electrode had a thickness of 55 μm per one side.

<Production of negative electrode>
A composite in which the surface of SiO having an average particle diameter D50% of 8 μm, which is a negative electrode active material, is coated with a carbon material (the amount of the carbon material in the composite is 10% by mass), and graphite having an average particle diameter D50% of 16 μm A mixture in which the amount of the composite having the SiO surface coated with a carbon material is 3.75% by mass: 97.5 parts by mass, SBR as a binder: 1.5 parts by mass, and a thickener CMC: 1 part by mass of water was added and mixed to prepare a negative electrode mixture-containing paste.

  After applying the negative electrode mixture-containing paste to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, vacuum drying is performed at 120 ° C. for 12 hours to form a negative electrode mixture layer on both sides of the copper foil. did. Thereafter, press treatment was performed to adjust the thickness and density of the negative electrode mixture layer, and a nickel lead body was welded to the exposed portion of the copper foil to produce a strip-shaped negative electrode having a length of 380 mm and a width of 44 mm. . The negative electrode mixture layer in the obtained negative electrode had a thickness of 65 μm per one surface.

<Preparation of non-aqueous electrolyte>
In a mixed solvent of ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) in a volume ratio of 2: 3: 1, LiPF ₆ was dissolved at a concentration of 1 mol / L, and methanesulfonic acid 2- Propinyl, 1,3-dioxane, VC and FEC were added in amounts of 1% by mass to prepare a non-aqueous electrolyte.

<Battery assembly>
The belt-like positive electrode is stacked on the belt-like negative electrode through a microporous polyethylene separator (porosity: 41%) having a thickness of 16 μm, wound in a spiral shape, and then pressed so as to be flat. An electrode winding body having a flat winding structure was formed, and the electrode winding body was fixed with an insulating tape made of polypropylene. Next, the electrode winding body is inserted into a rectangular battery case made of aluminum alloy having an outer dimension of 4.0 mm in thickness, 34 mm in width, and 50 mm in height to weld the lead body, and a lid made of aluminum alloy The plate was welded to the open end of the battery case. Thereafter, the non-aqueous electrolyte is injected from the inlet provided in the cover plate, and left for 1 hour, and then the inlet is sealed. The lithium secondary battery having the structure shown in FIG. Obtained.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 is spirally wound through a separator 3 and then pressed so as to be flattened and accommodated in a rectangular (square tube) battery case 4 together with a nonaqueous electrolyte as a flat wound electrode body 6. Has been. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, and the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 are not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes an outer package of the battery. The battery case 4 also serves as a positive electrode terminal. And the insulator 5 which consists of PE sheets is arrange | positioned at the bottom part of the battery case 4, and it connects to each one end of the positive electrode 1 and the negative electrode 2 from the flat wound electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the battery case 4 via a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is sealed by welding the joint part of both, and the inside of the battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. (See FIG. 1 and FIG. 2, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of this Example 1, the outer can 5 and the cover plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the battery case 4, the sign may be reversed. There is also.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Examples 2-5 and Comparative Examples 1-4
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the addition amounts of 2-propynyl methanesulfonate and 1,3-dioxane were changed as shown in Table 1, and this nonaqueous electrolytic solution was used. A lithium secondary battery was produced in the same manner as Example 1 except for the above.

  Table 1 shows each additive added to the non-aqueous electrolyte used in each of the lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 4 and their amounts. In Table 1, 2-propynyl methanesulfonate is described as “compound (A)” (the same applies to Table 3 described later). The “reference example” in Table 1 is the same as the battery of Comparative Example 2 (details of the reference example will be described later).

  Each lithium secondary battery of Examples 1 to 5 and Comparative Examples 1 to 4 was evaluated as follows. These results are shown in Table 2.

<Initial capacity measurement>
About each lithium secondary battery of an Example and a comparative example, constant current charge was performed to 4.35V with the electric current value of 1.0C, and then constant voltage charge was performed with the voltage of 4.35V. The total charging time for constant current charging and constant voltage charging was 2.5 hours. Thereafter, the battery was discharged to 3.0 V at a current value of 0.2 C, and the initial capacity was measured.

  As for the battery of Comparative Example 2, as a reference example, the initial capacity when charging / discharging was performed under the same conditions as described above except that the end voltage of constant current charge and the voltage at constant voltage charge were 4.2 V. Was also measured.

<Evaluation of load characteristics>
About each lithium secondary battery of an Example and a comparative example, constant current charge and constant voltage charge were performed on the same conditions as the time of initial stage capacity measurement, and it discharged to 3.0V with a current value of 1.5C, and was then discharged capacity (1.5 C discharge capacity) was determined. And the value which remove | divided the 1.5C discharge capacity of each battery by the initial stage capacity was represented by the percentage, and the capacity | capacitance maintenance factor was calculated | required. That is, the higher the capacity retention rate, the better the load characteristics of the battery.

  For the battery of Comparative Example 2, as a reference example, the 1.5 C discharge capacity was also obtained under the same conditions as above except that the constant voltage charging end voltage and the constant voltage charging voltage were 4.2 V. The capacity retention rate was determined using the initial capacity value of the reference example.

<Charge / discharge cycle characteristics evaluation>
About each lithium secondary battery of an Example and a comparative example (battery different from the thing which performed each said evaluation), constant current charge and constant voltage charge were performed on the same conditions as the time of initial stage capacity measurement, A series of operations for discharging to 3.0 V at a current value of 5 C was taken as one cycle, and 500 cycles of charge / discharge were repeated. For each subsequent battery, charge and discharge were performed under the same conditions as the initial capacity measurement, and the discharge capacity of each battery after 500 cycles was measured. The value obtained by dividing this by the initial capacity was expressed as a percentage. The maintenance rate was determined. It can be said that the higher the capacity retention rate, the better the charge / discharge cycle characteristics of the battery. The charge / discharge cycle characteristics were evaluated in an environment at room temperature (25 ° C.) and an environment at 45 ° C.

  For the battery of Comparative Example 2, as a reference example, under the same conditions as described above except that the end voltage of constant current charging and the voltage during constant voltage charging were set to 4.2 V, in a room temperature environment and a 45 ° C. environment. The discharge capacity after 500 cycles was also determined, and the capacity retention rate was determined using these values and the initial capacity value of the reference example.

<High temperature storage characteristics evaluation>
For each of the lithium secondary batteries of Examples and Comparative Examples (batteries different from those subjected to each of the above evaluations), after performing constant current charging and constant voltage charging under the same conditions as in the initial capacity measurement, 85 ° C. The battery was stored for 4 hours in an environment, and the change in thickness (swelling amount) of the battery before and after storage was determined.

  Moreover, after discharging to 3.0 V at a current value of 0.2 C for each battery after thickness measurement, constant current charging and constant voltage charging were performed under the same conditions as at the time of initial capacity measurement, followed by 0.2 C Discharge was performed at a current value of 3.0 V, and the discharge capacity after high temperature storage was determined. It can be said that the closer the discharge capacity after high-temperature storage is to the initial capacity, the better the capacity recovery after high-temperature storage and the better the high-temperature storage characteristics of the battery.

  As for the battery of Comparative Example 2, as a reference example, the change in thickness of the battery before and after storage under the same conditions as above except that the end voltage of constant current charge and the voltage at constant voltage charge were 4.2 V The discharge capacity after high temperature storage was also determined.

The lithium secondary batteries of Examples 1 to 5 are examples in which a composite of SiO _x and a carbon material and graphite were used in combination with a negative electrode active material. As shown in Tables 1 and 2, the compounds (A ) And 1,3-dioxane in appropriate amounts, both of capacity retention at the time of load characteristic evaluation and capacity retention after 500 cycles at room temperature and 45 ° C. The load characteristics and charge / discharge cycle characteristics at room temperature and high temperature are excellent. In addition, the lithium secondary batteries of Examples 1 to 5 are suppressed from swelling during high-temperature storage, and further, the discharge capacity after high-temperature storage is small from the initial capacity, and high-temperature storage characteristics are also excellent.

  On the other hand, the battery of Comparative Example 1 using the non-aqueous electrolyte not containing the phosphonoacetate compound represented by the general formula (1) and 1,3-dioxane was obtained at room temperature and 45 ° C. The capacity retention rate after 500 cycles is small, and the charge / discharge cycle characteristics are inferior.

  In addition, the battery of Comparative Example 2 using the non-aqueous electrolyte solution containing the compound (A) but not 1,3-dioxane had a capacity retention rate during load characteristic evaluation, room temperature, and 45 The capacity retention rate after 500 cycles at 0 ° C. is low, and the load characteristics and charge / discharge cycle characteristics at room temperature and high temperature are inferior. In the reference example in which the battery of Comparative Example 2 was evaluated with the upper limit voltage at the time of charging being 4.2 V, all of the load characteristics, the charge / discharge cycle characteristics at room temperature and high temperature, and the high temperature storage characteristics were Since the evaluation results of the respective batteries of the examples are not inferior, the problem solved in the present invention is that when the upper limit voltage during charging is increased, that is, under the condition that the battery voltage exceeds 4.25V. It can be seen that this occurs when charging.

  Further, the battery of Comparative Example 3 using the non-aqueous electrolyte containing 1,3-dioxane but not containing the compound (A) has a large amount of swelling during high-temperature storage, and further after high-temperature storage. The discharge capacity is greatly reduced from the initial capacity, and the high-temperature storage characteristics are inferior.

  The battery of Comparative Example 4 using a non-aqueous electrolyte in which the amount of the compound (A) and 1,3-dioxane is too large is a load characteristic, a charge / discharge cycle characteristic at room temperature and high temperature, and a high temperature storage characteristic. None of them are inferior.

  In addition, about the battery of the comparative example 3 using the non-aqueous electrolyte containing only 1, 3- dioxane which has the effect | action which improves the charging / discharging cycling characteristics of a battery, and the battery of Example 1, for example, charging / discharging cycling characteristics are shown. When compared, the battery of Example 1 is superior to the battery of Comparative Example 3 at both room temperature and high temperature. In addition to containing the compound (A) that is considered to have an effect of impairing the charge / discharge cycle characteristics of the battery, the nonaqueous electrolytic solution according to the battery of Example 1 -Although the content of dioxane is less than that of the nonaqueous electrolyte solution according to the battery of Comparative Example 3, the above evaluation results were obtained for the charge / discharge cycle characteristics. In the secondary battery, it can be seen that the compound (A) and 1,3-dioxane function synergistically to improve the charge / discharge cycle characteristics at room temperature and high temperature.

Example 6
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material was replaced with the same graphite as that used in Example 1 instead of the above mixture, and the same procedure as in Example 1 was conducted except that this negative electrode was used. Thus, a lithium secondary battery was produced.

Comparative Example 5
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material was replaced with the same graphite as that used in Example 1 instead of the above mixture, and the same procedure as in Comparative Example 1 was conducted except that this negative electrode was used. Thus, a lithium secondary battery was produced.

  Table 3 shows each additive added to the non-aqueous electrolyte used in the lithium secondary batteries of Example 6 and Comparative Example 5 and their amounts.

  The lithium secondary batteries of Example 6 and Comparative Example 5 were evaluated in the same manner as the battery of Example 1 and the like. These results are shown in Table 4.

Also in the lithium secondary battery of Example 6 using only graphite as the negative electrode active material, as shown in Tables 3 and 4, non-water containing the compound (A) and 1,3-dioxane in appropriate amounts Similar to the lithium secondary batteries of Examples 1 to 5 in which SiO _x and graphite are used in combination as the negative electrode active material by using the electrolytic solution, load characteristics, charge / discharge cycle characteristics at room temperature and high temperature, and high-temperature storage All of the characteristics are good as compared with the battery of Comparative Example 5 using the non-aqueous electrolyte not containing the compound (A) and 1,3-dioxane.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (7)

A lithium secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and performing constant current-constant voltage charging at a final voltage exceeding 4.25 V before use,
The non-aqueous electrolyte contains 0.1 to 5% by mass of a compound containing a carbon-carbon double bond or carbon-carbon triple bond and P or S in the molecule, and 1,3-dioxane is 0 A lithium secondary battery using 1 to 5% by mass of lithium secondary battery.   The negative electrode includes a negative electrode mixture layer containing, as a negative electrode active material, a material containing Si and O as constituent elements (however, the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5) The lithium secondary battery according to claim 1, which is provided on one side or both sides of the current collector.   The negative electrode mixture layer of the negative electrode contains a composite of a material containing Si and O as constituent elements and a carbon material, and the composite has a surface of the material containing Si and O as constituent atoms. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is coated with the carbon material.   The lithium secondary battery according to claim 3, wherein the surface of the composite of the material containing Si and O as constituent elements and the carbon material is further coated with the carbon material.   The lithium secondary battery according to claim 1, wherein the negative electrode mixture layer of the negative electrode further contains graphite as a negative electrode active material.   The lithium secondary battery according to any one of claims 1 to 5, wherein a non-aqueous electrolyte further containing a halogen-substituted cyclic carbonate is used.   The lithium secondary battery according to any one of claims 1 to 6, wherein a nonaqueous electrolyte further containing vinylene carbonate is used.

Images