JP6208584B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have a high voltage and high energy density, and therefore there is an increasing demand for driving power sources for portable devices and the like. Currently, lithium cobalt oxide having a large capacity and good reversibility is mainly used as a positive electrode active material of the non-aqueous electrolyte secondary battery.

  Currently, non-aqueous electrolyte secondary batteries are required to have higher capacities as the applied equipment is improved. However, the battery capacity using lithium cobalt oxide is almost close to the limit.

  For this reason, for example, studies are being made to meet the demand for higher battery capacity by increasing the upper limit voltage during battery charging than before. However, if the upper limit voltage is set high and the battery is repeatedly charged and discharged, there may be a problem that the capacity rapidly decreases.

  In view of this, technical development has been made to ensure good charge / discharge cycle characteristics while increasing the upper limit voltage during charging. For example, in Patent Document 1, as a positive electrode active material, a lithium cobaltate compound having a specific composition and a lithium nickel cobaltate compound having a specific composition are used at a specific composition ratio, and the density is set to a specific value or more. By using a positive electrode having a positive electrode mixture layer, a lithium ion secondary battery has been proposed that can exhibit good charge / discharge cycle characteristics even when the upper limit voltage during charging is 4.3 V or higher.

JP 2006-294482 A

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery that can exhibit excellent charge / discharge cycle characteristics even when the upper limit voltage during charging is increased by means different from the technique disclosed in Patent Document 1. To do.

The non-aqueous electrolyte secondary battery of the present invention that has achieved the above object is a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode is a positive electrode active material, a conductive additive. And a positive electrode mixture layer containing a binder,
The positive electrode mixture layer has the following general formula (1) as the positive electrode active material.
Li _a Co _1-bc M ¹ _b M ² _c O ₂ (1)
[In the general formula (1), M ¹ is at least one element selected from the group consisting of Al and Mg, and M ² is Zr, Ti, Ni, Mn, Na, Bi, Ca, F, It is at least one element selected from the group consisting of P, Sr, W, Ba, Si, Fe, Mo, V, Sn, Sb, Ta, Nb, Ge, Cr, K, S, Cu, and Zn 0.9 ≦ a ≦ 1.10, 0.015 ≦ b ≦ 0.1, 0 ≦ c, b + c ≦ 0.12], and the positive electrode The conductive auxiliary agent content in the mixture layer is more than 0.5% by mass and 2.0% by mass or less, and the negative electrode has a negative electrode mixture layer containing a negative electrode active material and a binder, The negative electrode mixture layer is a graphite having an average particle diameter of more than 15 μm and 25 μm or less as the negative electrode active material. When the average particle diameter is not less 8μm than 15μm or less, and the graphite B the surface of the graphite particles are coated with amorphous carbon, and is characterized in that it contains at least.

  ADVANTAGE OF THE INVENTION According to this invention, even if it raises the upper limit voltage at the time of charge, the nonaqueous electrolyte secondary battery which can exhibit the outstanding charging / discharging cycling characteristics can be provided.

It is a fragmentary longitudinal cross-sectional view which represents typically an example of the nonaqueous electrolyte secondary battery of this invention. FIG. 2 is a perspective view of FIG. 1.

  In non-aqueous electrolyte secondary batteries, a lithium-containing composite oxide such as lithium cobaltate is generally used as the positive electrode active material, and a carbon material such as graphite is used as the negative electrode active material. In the case of a combination of negative electrode active materials, the lithium ion desorption speed from the positive electrode is faster than the lithium ion acceptance speed at the negative electrode during charging.

  If lithium ions released from the positive electrode during charging are not sufficiently received by the negative electrode and stagnate in the vicinity of the negative electrode surface, for example, lithium dendrite may precipitate on the negative electrode surface, which may impair the battery characteristics. Repeating the discharge is one of the causes of the battery capacity decreasing at an early stage, that is, the cause of the deterioration of the charge / discharge cycle characteristics of the battery.

  Many current non-aqueous electrolyte secondary batteries exhibit good charge / discharge cycle characteristics when charging / discharging is repeated with the normally used voltage of about 4.2 V being the upper limit voltage for charging. In the combination of the positive electrode and the negative electrode that are currently employed, the balance between the lithium ion desorption speed from the positive electrode and the lithium ion acceptance speed at the negative electrode is well maintained. This is probably because the precipitation of dendrites is relatively difficult to occur.

  However, if the upper limit voltage for charging the nonaqueous electrolyte secondary battery is increased, the lithium ion desorption speed from the positive electrode increases, and the balance with the lithium ion acceptance speed at the negative electrode is lost. It is presumed that the characteristics deteriorate.

  Therefore, in the nonaqueous electrolyte secondary battery of the present invention, the lithium ion desorption speed from the positive electrode is reduced and the lithium ion acceptance speed at the negative electrode is improved. For example, the upper limit voltage during charging is 4.4 V. Even if the desorption speed of lithium ions from the positive electrode is increased as described above, the lithium ions are smoothly accepted by the negative electrode. As a result, in the nonaqueous electrolyte secondary battery of the present invention, it is possible to suppress the precipitation of lithium dendrite at the negative electrode even if the upper limit voltage during charging is increased, and thus exhibit excellent charge / discharge cycle characteristics. Can do. In the nonaqueous electrolyte secondary battery of the present invention, even when the upper limit voltage during charging is increased, the balance between the lithium ion desorption speed from the positive electrode during charging and the lithium ion acceptance speed during the negative electrode is good. Since it is maintained, continuous charge characteristics and thermal stability are also improved.

  The positive electrode according to the nonaqueous electrolyte secondary battery of the present invention has a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive auxiliary agent, and the like. For example, the positive electrode mixture layer is disposed on one side of a current collector. Or it has the structure which has on both surfaces.

  As the positive electrode active material, the lithium-containing metal oxide represented by the general formula (1) is used.

In the lithium-containing metal oxide represented by the general formula (1), the element M ¹ is a component that contributes to the suppression of the lithium ion desorption speed of the lithium-containing metal oxide during battery charging. Elemental M ¹ also contributes to improvement of stability and thermal stability at high voltages of the lithium-containing metal oxide represented by the general formula (1). Lithium-containing metal oxide represented by the general formula (1) is, as the element M ^1, may contain only one of Al and Mg, may contain two or more kinds.

In Formula (1), b representing the amount of the element M ¹ is the suppression of desorption speed of the lithium ions by the lithium-containing metal oxide represented by the general formula (1) contains an element M ¹ From the viewpoint of satisfactorily securing the effect, the effect of improving the stability under high voltage, and the effect of improving the thermal stability, it is 0.015 or more and preferably 0.023 or more.

Moreover, the said General formula (1) is Zr, Ti, Ni, Mn, Na, Bi, Ca, F, P, Sr, W, Ba, Si, Fe, Mo, V, Sn, Sb, Ta, Nb, At least one element M ² selected from the group consisting of Ge, Cr, K, S, Cu, and Zn may or may not be contained. That is, in the general formula (1), c representing the amount of the element M ² is 0 or more.

However, in the lithium-containing metal oxide represented by the general formula (1), if the amount of the element M ¹ and the element M ² is too large, for example, Co that is a component that contributes to the capacity improvement of the lithium-containing metal oxide There is a risk that the amount of the battery will decrease and the capacity will decrease. Therefore, in the general formula (1), b representing the amount of the element M ¹ is 0.1 or less, and preferably 0.04 or less, and the amount b of the element M ^{1 and} the amount of the element M ² The total b + c with the amount c is 0.12 or less, and preferably 0.04 or less.

  The lithium-containing metal oxide represented by the general formula (1) has a higher true density and a higher energy volume density, particularly when the composition is close to the stoichiometric ratio. In the general formula (1), 0.9 ≦ a ≦ 1.10, and by adjusting the value of the Li amount a in this way, the true density and reversibility at the time of charge / discharge can be improved. Can do.

Lithium-containing metal oxide represented by the general formula (1) may, Li-containing compound (lithium hydroxide, etc.), Co-containing compound (such as cobalt sulfate), compound containing an element M ¹ (oxides, hydroxides , Sulfate, etc.) and, if necessary, a compound containing the element M ² (oxide, hydroxide, sulfate, etc.) can be mixed, and this raw material mixture can be fired. In addition, in order to synthesize the lithium-containing metal oxide represented by the general formula (1) with higher purity, a composite compound (hydroxylation) containing Co and the element M ¹ and, if necessary, the element M ² is used. It is preferable to mix a material, an oxide, etc.) and a Li-containing compound, and to fire the raw material mixture.

  The firing condition of the raw material mixture for synthesizing the lithium-containing metal oxide represented by the general formula (1) can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once the firing temperature is exceeded. It is preferable to heat up to a low temperature (for example, 250 to 850 ° C.), hold it at that temperature, perform preheating, and then raise the temperature to the firing temperature to advance the reaction. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just to be about 0.5 to 30 hours. The atmosphere during firing can be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, or an oxygen gas atmosphere. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

  As the positive electrode active material, only the lithium-containing metal oxide represented by the general formula (1) can be used, but the lithium-containing metal oxide represented by the general formula (1) and other positive electrode active materials can be used. A substance can be used in combination.

Other positive electrode active materials that can be used in combination with the lithium-containing metal oxide represented by the general formula (1) include, for example, lithium cobalt oxides such as LiCoO ₂ [other than those represented by the general formula (1) Lithium cobalt oxide]; lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium nickel oxides such as LiNiO ₂ ; spinel structures such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ Examples include lithium-containing composite oxides; lithium-containing metal oxides having an olivine structure such as LiFePO ₄ ; oxides having the above-described oxide as a basic composition and substituted with various elements;

  However, from the viewpoint of better securing the above-described effect due to the use of the lithium-containing metal oxide represented by the general formula (1), the general formula in the total amount of the positive electrode active material contained in the positive electrode mixture layer It is preferable that the content of the lithium-containing metal oxide represented by (1) is 70% by mass or more [that is, in the total amount of the positive electrode active material contained in the positive electrode mixture layer, according to the general formula (1). It is preferable that the content of the positive electrode active material other than the lithium-containing metal oxide is 30% by mass or less. In addition, since only the lithium containing metal oxide represented by the said General formula (1) may be used for a positive electrode active material, the said General formula (1) in the positive electrode active material whole quantity which a positive mix layer contains. The preferred upper limit of the content of the lithium-containing metal oxide represented by) is 100% by mass.

  The content of the positive electrode active material in the positive electrode mixture layer is preferably 94 to 99% by mass.

  Examples of the conductive auxiliary agent related to the positive electrode mixture layer include graphites such as natural graphite (flaky graphite, etc.) and artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. It is preferable to use carbon materials such as carbon blacks; carbon fibers; and conductive fibers such as metal fibers; carbon fluorides; metal powders such as aluminum; zinc oxide; Conductive whiskers; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used. As the conductive assistant, those exemplified above may be used singly or in combination of two or more. Among these conductive auxiliaries, acetylene black is particularly preferable because good conductivity can be secured with a relatively small amount.

  In the case of using acetylene black as a conductive additive, the content of acetylene black in the total amount of conductive additive is preferably 60% by mass or more, thereby improving the conductivity by using acetylene black. It can be secured well. In addition, since only acetylene black may be used for a conductive support agent, the suitable upper limit of content of acetylene black in the total amount of conductive support agents is 100 mass%.

  The content of the conductive additive in the positive electrode mixture layer is 2.0% by mass or less and 1.5% by mass or less from the viewpoint of suppressing the speed of lithium ion desorption at the positive electrode during charging. Is preferred. However, if the amount of the conductive auxiliary agent in the positive electrode mixture layer is too small, the electric conductivity in the positive electrode mixture layer is insufficient, and there is a possibility that the capacity is reduced. The content of is more than 0.5% by mass, and is preferably 1.0% by mass or more.

  Examples of the binder related to the positive electrode mixture layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyvinylpyrrolidone (PVP).

  The binder content in the positive electrode mixture layer is preferably 0.4 to 3.5% by mass.

  For example, the positive electrode mixture containing a positive electrode active material, a conductive additive, a binder, and the like is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water to form a paste-like or slurry-like positive electrode mixture. Prepare an agent-containing composition (however, the binder may be dissolved in a solvent), apply it to one or both sides of the current collector, dry it, and then apply a press treatment such as calendering if necessary. It can manufacture through the process to give. However, the positive electrode is not limited to those manufactured by the above method, and may be manufactured by other methods.

  As the positive electrode current collector, an aluminum foil, a punching metal, a net, an expanded metal, or the like can be used, but an aluminum foil is usually used. The thickness of the positive electrode current collector is preferably 10 to 30 μm.

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

  The thickness of the positive electrode mixture layer is preferably 40 to 90 μm per one side of the current collector.

  The negative electrode according to the nonaqueous electrolyte secondary battery of the present invention has a negative electrode active material, a binder, and a negative electrode mixture layer containing a conductive auxiliary agent as necessary. For example, the negative electrode mixture layer Of the current collector on one or both sides.

  The negative electrode active material includes at least graphite A having an average particle diameter of more than 15 μm and 25 μm or less, and graphite B having an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles coated with amorphous carbon. And use.

  Graphite A is graphite other than graphite B, and examples thereof include highly crystalline natural graphite and artificial graphite. Moreover, when using the said natural graphite, you may heat-process at high temperature, coat | cover the fine particle (granular shape, flat shape, etc.) of artificial graphite, or coat organic substances, such as resin, and use it. Furthermore, as long as the average particle diameter is in the above range, two or more kinds of graphite may be used for the graphite A.

Graphite B is composed of graphite particles serving as mother particles and amorphous carbon covering the surface. Specifically, 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 is graphite as a 0.1 to 0.6. Such graphite B uses, for example, natural graphite having d ₀₀₂ of 0.338 nm or less or graphite obtained by spherically shaping artificial graphite as a base material (base particle), and the surface thereof is coated with an organic compound. It can be obtained by calcining at 0 ° C., pulverizing, and sizing through a sieve. The organic compound covering the base material includes aromatic hydrocarbons; tars or pitches obtained by polycondensation of aromatic hydrocarbons under heat and pressure; tars mainly composed of a mixture of aromatic hydrocarbons. , Pitch or asphalt; In order to coat the base material with the organic compound, a method of impregnating and kneading the base material into the organic compound can be employed. Alternatively, graphite B can be produced by a vapor phase method in which a hydrocarbon gas such as propane or acetylene is carbonized by pyrolysis and deposited on the surface of graphite having d ₀₀₂ of 0.338 nm or less.

  Graphite A has an average particle size of 25 μm or less, and Graphite B has an average particle size of 15 μm or less. By using the graphite A and the graphite B of such a size together, it is possible to increase the receiving speed of lithium ions at the negative electrode during charging.

  In addition, when the particle diameter of graphite A is too small, the specific surface area is excessively increased (the irreversible capacity is increased), so that the particle diameter is preferably not too small. Therefore, in the present invention, graphite A having an average particle diameter of more than 15 μm is used. In addition, if the particle size of graphite B is too small, the coating amount of amorphous carbon covering the surface varies, and there are reasons that the features of graphite B cannot be fully exhibited. It is preferable not to be too small. Therefore, in the present invention, graphite B having an average particle diameter of 8 μm or more is used.

  The average particle size of graphite (graphite A, graphite B, and graphite other than these) referred to in the present specification is, for example, a laser scattering particle size distribution meter (for example, Nikkiso Co., Ltd. Microtrac particle size distribution measuring device “HRA9320”). A 50% diameter median value (D50%) median in the volume-based integrated fraction when the integrated volume is determined from particles having a small particle size distribution measured by dispersing graphite in a medium that does not dissolve or swell graphite Is the diameter.

The specific surface area of the graphite A and graphite B (according to the BET method. Device example like manufactured by Nippon Bell "Bell soap mini".) Is preferably 1.0 m ² / g or more,, 5.0 m ² / g or less is preferable.

  In addition, the negative electrode active material includes a negative electrode active material other than graphite A and graphite B (for example, graphite A, which is the same type as graphite A and has an average particle diameter of less than 15 μm or more than 25 μm. And graphite not corresponding to graphite B) can also be used together with graphite A and graphite B.

  From the viewpoint of improving the lithium ion acceptance speed at the negative electrode during charging, the content of graphite B in the total negative electrode active material contained in the negative electrode is preferably 20% by mass or more, and 30% by mass. More preferably. Moreover, since the surface of the graphite B coated with amorphous carbon is relatively hard, there is a possibility that problems such as destruction of the particles of the graphite A may occur if excessively added and pressed. is there. Therefore, the content of graphite B in all negative electrode active materials contained in the negative electrode is preferably 60% by mass or less, and more preferably 50% by mass or less.

  Further, when a negative electrode active material other than graphite A and graphite B is used as the negative electrode active material, from the viewpoint of favorably securing the above-described effect by using graphite A and graphite B, all of the negative electrode contains The total content of graphite A and graphite B in the negative electrode active material is preferably 80% by mass or more (that is, the content of negative electrode active materials other than graphite A and graphite B in all negative electrode active materials contained in the negative electrode) The amount is preferably 20% by mass or less).

  The content of the negative electrode active material in the negative electrode mixture layer is preferably 90 to 99% by mass, for example.

The binder related to the negative electrode mixture layer may be either a thermoplastic resin or a thermosetting resin. Specifically, for example, the same materials as those exemplified above as the binder relating to the positive electrode mixture layer, styrene butadiene rubber (SBR), ethylene-acrylic acid copolymer, or Na ⁺ ion crosslinked body of the copolymer , Ethylene-methacrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-methyl acrylate copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-methyl methacrylate copolymer or the copolymer Copolymer Na ⁺ ion cross-linked bodies can be used, and these materials may be used alone or in combination of two or more.

Among these binders, PVDF, SBR, ethylene-acrylic acid copolymer or Na ⁺ ion cross-linked product of the copolymer, ethylene-methacrylic acid copolymer or Na ⁺ ion cross-linked product of the copolymer, ethylene- A methyl acrylate copolymer or a Na ⁺ ion crosslinked product of the copolymer, an ethylene-methyl methacrylate copolymer or a Na ⁺ ion crosslinked product of the copolymer is particularly preferable. The binder content in the negative electrode mixture layer is preferably, for example, 1 to 10% by mass.

  When the conductive additive is contained in the negative electrode mixture layer, as the conductive assistant, the same materials as those exemplified above as the conductive auxiliary agent related to the positive electrode mixture layer can be used. However, when a conductive additive is used for the negative electrode, the content of the conductive additive in the negative electrode mixture layer is preferably 10% by mass or less in order to increase the capacity.

  The negative electrode includes, for example, a negative electrode active material, a binder, and a negative electrode mixture containing a conductive auxiliary agent, if necessary, in a solvent such as NMP or water, and a paste-like or slurry-like negative electrode mixture-containing composition (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 calendaring process as necessary. Can do. However, the negative electrode is not limited to those manufactured by the above method, and may be manufactured by other methods.

  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.

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

  The thickness of the negative electrode mixture layer is preferably 50 to 150 μm per one side of the current collector.

  The positive electrode and the negative electrode are used in the non-aqueous electrolyte secondary battery of the present invention in the form of a laminated electrode body with a separator interposed therebetween or a wound electrode body obtained by winding the separator in a spiral shape. be able to.

  The separator according to the non-aqueous electrolyte secondary battery of the present invention has a property that the pores are blocked at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower) (ie, shutdown function). It is preferable to have a separator used in a nonaqueous electrolyte secondary battery such as a normal lithium ion 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.

  Moreover, you may use the laminated separator which formed the heat resistant porous layer containing a heat resistant inorganic filler on the surface of the said microporous film. When such a stacked separator is used, the shrinkage of the separator is suppressed even when the temperature in the battery rises, and a short circuit due to contact between the positive electrode and the negative electrode can be suppressed. A high nonaqueous electrolyte secondary battery can be obtained.

  As the inorganic filler to be contained in the heat-resistant porous layer, boehmite, alumina, silica and the like are preferable, and one or more of them can be used.

  The heat-resistant porous layer preferably contains a binder for binding the inorganic fillers or bonding the heat-resistant porous layer and the microporous film. The binder includes an ethylene-vinyl acetate copolymer (EVA, having a structural unit derived from vinyl acetate of 20 to 35 mol%), an ethylene-acrylic acid copolymer such as an ethylene-ethyl acrylate copolymer, and a fluorine-based rubber. Styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy resin, etc. Are preferred, and one or more of these can be used.

  The thickness of the separator (a separator made of a microporous membrane made of polyolefin, or the laminated separator) is preferably 10 to 30 μm, for example. In the case of the laminated separator, the heat-resistant porous layer preferably has a thickness of 3 to 8 μm, for example.

  For the non-aqueous electrolyte according to the non-aqueous electrolyte secondary battery of the present invention, for example, a solution (non-aqueous electrolyte) prepared by dissolving a lithium salt in the following non-aqueous solvent can be used.

Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone (γ-
BL), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane, acetonitrile, nitromethane , Aprotic such as methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone The organic solvent can be used alone or as a mixed solvent in which two or more are mixed.

The lithium salt according to the non-aqueous electrolyte solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, At least 1 selected from 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] Species are mentioned. The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

  Non-aqueous electrolytes used in non-aqueous electrolyte secondary batteries include vinylene carbonate, vinyl ethylene carbonate, anhydrous water 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 acid, sulfonic acid ester, dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, fluorobenzene, and t-butyl benzene may be added as appropriate.

  Further, as the non-aqueous electrolyte of the non-aqueous electrolyte 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.

  Examples of the form of the non-aqueous electrolyte secondary battery of the present invention include a tubular shape (such as a square tubular shape or a cylindrical shape) using a steel can or an aluminum can as an exterior body. 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 non-aqueous electrolyte secondary battery of the present invention can be used with the upper limit voltage of charging being about 4.2 V as in the case of the conventional non-aqueous electrolyte secondary battery, but the upper limit voltage of charging is higher than this. It is also possible to use it by setting it to 4 V or higher. With this, it is possible to stably exhibit excellent characteristics even when repeatedly used over a long period of time while increasing the capacity. In addition, it is preferable that the upper limit voltage of charge of a nonaqueous electrolyte secondary battery is 4.7V or less.

  The non-aqueous electrolyte secondary battery of the present invention can be applied to the same applications as conventionally known non-aqueous electrolyte secondary batteries.

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

Example 1
<Synthesis of lithium-containing metal oxide>
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.651: 0.022: 0.022 : 0.002: 0.002 was mixed, and the mixture was heat-treated at 950 ° C. for 12 hours in the atmosphere (oxygen concentration: about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, the lithium-containing metal oxide was represented by Li _1.0 Co _0.976 Al _0.011 Mg _0.011 Ti _0.001 Zr _0.001 O _2. The composition was found to be

<Preparation of positive electrode>
Lithium-containing metal oxide (positive electrode active material): 96.5 parts by mass; N-methyl-2-pyrrolidone (NMP) solution containing PVDF as a binder at a concentration of 10% by mass: 20 parts by mass; A positive electrode mixture-containing paste was prepared by kneading 1.5 parts by mass of acetylene black, which is a conductive additive, using a biaxial kneader and further adding NMP to adjust the viscosity.

  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>
The average particle diameter D50% is 22 _.mu.m, with _{d 002} is 0.338 nm, the graphite BET specific surface area is 3.8m ² / g A (graphite no surface coating with amorphous carbon), the average particle diameter D50% is 10 [mu] _m, with _{d 002} is 0.336 nm, the graphite BET specific surface area is 3.9m ² / g B (graphite covering the surface of the mother particle made of graphite with amorphous carbon) A mixture of 98:50 parts by mass, CMC: 1.0 parts by mass, and SBR: 1.0 parts by mass with ion-exchanged water was mixed with a water-based negative electrode mixture-containing paste. Prepared.

The negative electrode mixture-containing paste is intermittently applied to both sides of a 6 μm-thick current collector made of copper foil, dried, and calendered to give a coating layer density of 1.58 g / cm. ^The negative electrode mixture layer was adjusted to have a thickness of ³ to obtain a negative electrode. The negative electrode was cut to a width of 53 mm, and a tab was welded to the exposed portion of the copper foil to form a lead portion.

<Preparation of non-aqueous electrolyte>
A nonaqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which 3% by mass of vinylene carbonate was dissolved in a volume ratio of 3: 7 between ethylene carbonate (EC) and diethyl carbonate (DEC). .

<Preparation of separator>
PE microporous separator for non-aqueous electrolyte secondary battery [porous layer (I): thickness 8 μm, porosity 40%, average pore diameter 0.02 μm, PE melting point 135 ° C.] the amount 40W · min / m ²⁾ and subjected, porous layer (II) forming slurry a was coated by a micro gravure coater to the treated surface, to obtain a separator to form a porous layer (II) and dried . The thickness of the porous layer (II) was adjusted to 4 μm. The boehmite content in the total volume of the constituent components of the porous layer (II) was 88% by volume.

<Battery assembly>
The belt-like positive electrode is overlapped with the belt-like negative electrode via the separator, wound in a spiral shape, and then pressed so as to be flattened to form an electrode winding body having a flat winding structure. The wound 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 nonaqueous electrolyte is injected from the inlet provided on the cover plate, and left for 1 hour, and then the inlet is sealed. The nonaqueous electrolyte secondary having the structure shown in FIG. A battery was obtained.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1 is a partial cross-sectional view. As shown in FIG. 1, the positive electrode 1 and the negative electrode 2 are spirally wound via a separator 3. Thereafter, the flat wound electrode body 6 is pressurized so as to be flat, and is accommodated in a rectangular (square tube) battery case 4 together with a non-aqueous electrolyte. However, in FIG. 1, in order to avoid complication, the metal foil, the separator layers, the non-aqueous electrolyte, and the like used as the current collector used in the production of 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. As a result, the battery is sealed by welding. 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 Example 1, the battery case 4 and the cover plate 9 function as positive terminals by directly welding the positive electrode lead body 7 to the cover 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.

Example 2
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.642: 0.048: 0.022 : 0.002: 0.002 was mixed, and the mixture was heat-treated at 950 ° C. for 12 hours in the atmosphere (oxygen concentration: about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. The lithium-containing metal oxide was represented by Li _1.0 Co _0.963 Al _0.024 Mg _0.011 Ti _0.001 Zr _0.001 O _2. The composition was found to be

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Example 3
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.645: 0.022: 0.040 : 0.002: 0.002 was mixed, and the mixture was heat-treated at 950 ° C. for 12 hours in the atmosphere (oxygen concentration: about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, the lithium-containing metal oxide was represented by Li _1.0 Co _0.967 Al _0.011 Mg _0.020 Ti _0.001 Zr _0.001 O _2. The composition was found to be

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Example 4
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.649: 0.022: 0.022 : 0.008: 0.002 was mixed, and this mixture was heat-treated at 950 ° C. for 12 hours in the atmosphere (oxygen concentration: about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, the lithium-containing metal oxide was represented by Li _1.0 Co _0.973 Al _0.011 Mg _0.011 Ti _0.004 Zr _0.001 O _2. The composition was found to be

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Example 5
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.649: 0.022: 0.022 : 0.002: 0.006, and the mixture was heat-treated at 950 ° C. for 12 hours in the air (oxygen concentration: about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, the lithium-containing metal oxide was represented by Li _1.0 Co _0.974 Al _0.011 Mg _0.011 Ti _0.001 Zr _0.003 O _2. The composition was found to be

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Example 6
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, ZrO ₂ , and Na ₂ CO ₃ .H ₂ O in a molar ratio of 1: 0.650 : 0.022: 0.022: 0.002: 0.002: 0.001 and the mixture was heat-treated at 950 ° C. for 12 hours in the atmosphere (oxygen concentration is about 20 vol%). The powder was pulverized in a mortar. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. Li _1.0 Co _0.975 Al _0.011 Mg _0.011 Ti _0.001 Zr _0.001 Na _0.001 O It was found that the composition represented by ₂ .

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Example 7
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, ZrO ₂ , and Ni (OH) ₂ in a molar ratio of 1: 0.650: 0. 022: 0.022: 0.002: 0.002: 0.002 was mixed, and this mixture was heat-treated at 950 ° C. for 12 hours in the atmosphere (oxygen concentration is about 20 vol%), and then pulverized in a mortar To obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, Li _1.0 Co _0.975 Al _0.011 Mg _0.011 Ti _0.001 Zr _0.001 Ni _0.001 O It was found that the composition represented by ₂ .

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Example 8
The same lithium-containing metal oxide (positive electrode active material) used in Example 1: 96.0 parts by mass, NMP solution containing PVDF as a binder at a concentration of 10% by mass: 20 parts by mass, and conductivity Acetylene black as an auxiliary agent: 2.0 parts by mass was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

  Then, a positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture paste was used, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 9
The same lithium-containing metal oxide (positive electrode active material) as used in Example 1: 97 parts by mass, NMP solution containing PVDF as a binder at a concentration of 10% by mass: 20 parts by mass, and conductive additive Acetylene black: 1.0 part by mass was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

  Then, a positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture paste was used, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 1
LI ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.657: 0.002: 0.022: 0.002: 0.002 was mixed, and this mixture was heat-treated at 950 ° C. for 12 hours in the air (oxygen concentration of about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, Li _1.0 Co _0.986 Al _0.001 Mg _0.011 Ti _0.001 Zr _0.001 O ₂ was expressed. The composition was found to be

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Comparative Example 2
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.657: 0.022: 0.002: 0.002: 0.002 was mixed, and this mixture was heat-treated at 950 ° C. for 12 hours in the air (oxygen concentration of about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, Li _1.0 Co _0.986 Al _0.011 Mg _0.001 Ti _0.001 Zr _0.001 O ₂ was expressed. The composition was found to be

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Comparative Example 3
Li ₂ CO ₃ , Co ₃ O ₄ , Al (OH) ₃ , Mg (OH) ₂ , TiOSO ₄ .H ₂ O, and ZrO ₂ in a molar ratio of 1: 0.664: 0.002: 0.002: 0.002: 0.002 was mixed, and this mixture was heat-treated at 950 ° C. for 12 hours in the air (oxygen concentration of about 20 vol%), and then pulverized in a mortar to obtain a powder. The lithium-containing metal oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing metal oxide was performed using an ICP method. As a result, Li _1.0 Co _0.996 Al _0.001 Mg _0.001 Ti _0.001 Zr _0.001 O ₂ was expressed. The composition was found to be

  A positive electrode was produced in the same manner as in Example 1 except that this lithium-containing metal oxide was used as the positive electrode active material, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used. .

Comparative Example 4
The same lithium-containing metal oxide (positive electrode active material) used in Example 1: 95.5 parts by mass, NMP solution containing PVDF as a binder at a concentration of 10% by mass: 20 parts by mass, and conductive The auxiliary agent acetylene black: 2.5 parts by mass was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

  Then, a positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture paste was used, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 5
The same lithium-containing metal oxide (positive electrode active material) as used in Example 1: 97.5 parts by mass, NMP solution containing PVDF as a binder at a concentration of 10% by mass: 20 parts by mass, and conductivity The auxiliary agent acetylene black: 0.5 parts by mass was kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

  Then, a positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture paste was used, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 6
A water-based negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that only graphite A was used instead of the mixture of graphite A and graphite B. Then, a negative electrode was produced in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Comparative Example 7
A water-based negative electrode mixture-containing paste was prepared in the same manner as in Example 1 except that only graphite B was used instead of the mixture of graphite A and graphite B. Then, a negative electrode was produced in the same manner as in Example 1 except that this negative electrode mixture-containing paste was used, and a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

  For the same electrodes (positive electrode and negative electrode) used for the non-aqueous electrolyte secondary batteries of the examples and comparative examples, the following load characteristic evaluation is performed, and for the non-aqueous electrolyte secondary batteries of the examples and comparative examples The following battery characteristics were evaluated.

<Evaluation of electrode load characteristics>
About each electrode used for the nonaqueous electrolyte secondary battery of an Example and a comparative example, a model cell was produced by making a counter electrode into lithium foil, and it was 4.5V with respect to the electric potential of lithium with the electric current value of 0.1 C at 23 degreeC. Then, the battery was charged at a constant voltage of 4.5 V with respect to the lithium potential until the current value reached 0.01 C, and the charge capacity (0.1 C charge capacity) was measured. Thereafter, each battery after charging was discharged at a constant current until the voltage became 3.1 V with respect to the potential of lithium at a current value of 0.1 C, and the 0.1 C discharge capacity was measured.

  Further, constant current-constant voltage charging and constant current charging under the same conditions as the 0.1 C charging / discharging capacity measurement, except that each model cell was used and the current value during constant current charging and constant current charging was changed to 0.5 C. Constant current discharge was performed, and 0.5C charge capacity and 0.5C discharge capacity were measured.

  And about each electrode, the value which remove | divided 0.5C discharge capacity by 0.1C discharge capacity was represented by the percentage, and the capacity | capacitance maintenance factor was calculated | required. The load characteristic of the positive electrode serves as an index of the lithium ion desorption speed from the positive electrode, and the higher the capacity retention rate of the positive electrode (that is, the better the load characteristic), the lithium ion desorption speed from the positive electrode. Means fast. The load characteristics of the negative electrode serve as an index of the lithium ion acceptance speed at the negative electrode. The higher the capacity retention rate of the negative electrode (that is, the better the load characteristics), the faster the lithium ion acceptance speed at the negative electrode. It means that.

<Charge / discharge cycle characteristics evaluation at 45 ° C.>
The nonaqueous electrolyte secondary batteries of Examples and Comparative Examples were left in a constant temperature bath at 45 ° C. for 5 hours, and then each battery was charged with a constant current of 1.0 C up to 4.4 V. Then, constant voltage charging was performed at 4.4 V until the current reached 0.05C. Each of the batteries thereafter was discharged at a constant current of 1.0 C until the voltage reached 3.0V. A series of these charging and discharging operations was taken as one cycle, and 500 cycles of charging and discharging were repeated. And about each battery, the value which remove | divided the discharge capacity of the 500th cycle by the discharge capacity of the 1st cycle was represented by percentage, and the capacity | capacitance maintenance factor was calculated | required.

<Heating test>
Five nonaqueous electrolyte secondary batteries of Examples and Comparative Examples were each placed in a thermostat, the thermostat was heated to 150 ° C. at 2 ° C./min, and held at 150 ° C. for 60 minutes. The surface temperature of each battery during heating and holding was measured with a thermocouple, and the number of batteries whose surface temperature was maintained at 180 ° C. or lower was examined.

  Tables 1 and 2 show the configurations and characteristics of the positive electrode and the negative electrode used in the nonaqueous electrolyte secondary battery of the example, and Tables 3 and 2 show the configurations and characteristics of the positive electrode and the negative electrode used in the nonaqueous electrolyte secondary battery of the comparative example. Table 4 shows the battery characteristics of these nonaqueous electrolyte secondary batteries, respectively.

  As shown in Table 1 to Table 5, a positive electrode using a lithium-containing metal oxide having an appropriate composition as a positive electrode active material and an appropriate value for the content of acetylene black in the positive electrode mixture layer, and graphite as a negative electrode active material The nonaqueous electrolyte secondary batteries of Examples 1 to 9 having a negative electrode using both A and graphite B have a high capacity retention rate at the time of charge / discharge cycle characteristics evaluation at 45 ° C., and a high upper limit voltage during charging. Even so, excellent charge / discharge cycle characteristics could be exhibited.

Incidentally, the positive electrode used for the nonaqueous electrolyte secondary batteries of Examples 1 to 9, for example, as compared to the positive electrode of the battery of Comparative Example 1-3 using the amount of the element M ¹ is small lithium-containing metal oxide The capacity retention rate at the time of load characteristic evaluation was low, and the lithium ion desorption speed was reduced. And the negative electrode used for the nonaqueous electrolyte secondary battery of Examples 1-9 is compared with the negative electrode which concerns on the battery of the comparative examples 6 and 7 which used only the graphite A or only the graphite B for the negative electrode active material. The capacity maintenance rate at the time was high, and the receiving speed of lithium ions was increasing. Therefore, in the nonaqueous electrolyte secondary batteries of Examples 1 to 9, the balance between the lithium ion desorption speed from the positive electrode and the lithium ion acceptance speed at the negative electrode when the end voltage during charging is increased is good. Therefore, it can be said that the excellent charge / discharge cycle characteristics as described above could be secured.

  In addition, in the nonaqueous electrolyte secondary batteries of Examples 1 to 9, no thermal runaway and high surface temperature were observed during the heating test, and the thermal stability was excellent.

On the other hand, the battery of Comparative Example 1-3 where the amount of the element M ¹ is using less lithium-containing metal oxide has a low charge-discharge cycle characteristics at the time of evaluation capacity retention rate at 45 ° C., high maximum voltage during charging In this case, the charge / discharge cycle characteristics were inferior, and in the heating test, thermal runaway was observed and the surface temperature was increased, and the thermal stability was also inferior. Furthermore, the battery of Comparative Example 4 using a positive electrode with too much content of acetylene black in the positive electrode mixture layer, the battery of Comparative Example 5 using a positive electrode with too little content of acetylene black in the positive electrode mixture layer, The battery of Comparative Example 6 that uses only graphite A as the negative electrode active material and the battery of Comparative Example 7 that uses only graphite B as the negative electrode active material have a low capacity retention rate when evaluating charge / discharge cycle characteristics at 45 ° C. The charge / discharge cycle characteristics when the upper limit voltage during charging was increased were inferior.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (3)

A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The positive electrode has a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder,
The positive electrode mixture layer has the following general formula (1) as the positive electrode active material.
Li _a Co _1-bc M ¹ _b M ² _c O ₂ (1)
[In the general formula (1), M ¹ is at least one element selected from the group consisting of Al and Mg, and M ² is Zr, Ti, Ni, Mn, Na, Bi, Ca, F, It is at least one element selected from the group consisting of P, Sr, W, Ba, Si, Fe, Mo, V, Sn, Sb, Ta, Nb, Ge, Cr, K, S, Cu, and Zn 0.9 ≦ a ≦ 1.10, 0.015 ≦ b ≦ 0.1, 0 ≦ c, b + c ≦ 0.12, and a lithium-containing metal oxide represented by
The content of the conductive auxiliary in the positive electrode mixture layer is more than 0.5% by mass and 2.0% by mass or less,
The negative electrode has a negative electrode mixture layer containing a negative electrode active material and a binder,
The negative electrode mixture layer has, as the negative electrode active material, an average particle diameter of more than 15 μm and 25 μm or less , and graphite A whose surface is not coated with amorphous carbon, and an average particle diameter of 8 μm or more and 15 μm or less. A non-aqueous electrolyte secondary battery comprising at least graphite B having a graphite particle surface coated with amorphous carbon.   The nonaqueous electrolyte secondary battery according to claim 1, wherein acetylene black is contained as the conductive additive, and the content of acetylene black in the total amount of the conductive additive is 60% by mass or more.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein an upper limit voltage for charging is set to 4.4 V or more.