JP2009064707A - Active material for nonaqueous electrolyte secondary battery, and battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active material for a nonaqueous electrolyte secondary battery with heat generation restrained accompanying oxidation reaction of a negative electrode active material and an nonaqueous solvent, even in case battery temperature rises at overcharging. <P>SOLUTION: For the active material for a nonaqueous electrolyte secondary battery, lithium transition metal oxyfluoride represented by general formula (1): Li<SB>x</SB>Fe<SB>1-y</SB>M<SB>y</SB>OF (provided, M is at least a kind selected from a group consisting of Mn, Co and Ni, and x and y satisfy 0≤x≤1 and 0≤y≤0.5, respectively), having a crystal structure belonging to a space group P42/mnm is used. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an active material used therefor. The active material according to the present invention improves the safety of the non-aqueous electrolyte secondary battery even when the battery temperature is significantly increased.

  Conventionally, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries with high energy density have been widely used as power sources used in the field of portable devices such as personal computers, mobile phones, digital cameras, and camcorders. In addition, non-aqueous liquid secondary batteries have been actively developed for use as power sources for electric vehicles that are expected to contribute to solving environmental and resource problems.

In general, a nonaqueous electrolyte solution containing a flammable nonaqueous solvent is used for a nonaqueous electrolyte secondary battery. Further, a lithium transition metal oxide such as lithium cobaltate is used for the positive electrode active material, and a carbon material such as graphite is used for the negative electrode active material.
In a non-aqueous electrolyte secondary battery, when the battery temperature rises during overcharge, the positive electrode active material is decomposed and oxygen is easily generated. And the negative electrode active material and the non-aqueous solvent are oxidized by the oxygen, and the battery temperature may be significantly increased by the oxidation reaction (exothermic reaction).

In order to suppress the above heat generation during overcharge, various overcharge prevention mechanisms have been studied for non-aqueous electrolyte secondary batteries, and in recent years, overcharge prevention mechanisms using electronic circuits have been mainly adopted. . However, it is difficult to completely eliminate the anxiety about the failure of the electronic circuit by the method relying only on the electronic circuit.
In addition, for the purpose of improving safety, it has been studied to replace the non-aqueous electrolyte, which is a flammable material, with a non-flammable inorganic solid electrolyte, but the battery characteristics required in the market cannot be sufficiently obtained, It has not been put into practical use yet.

By the way, conventionally, materials for positive electrode active materials have been studied mainly for the purpose of increasing the capacity of batteries.
For example, Patent Document 1 proposes using amorphous lithium transition metal oxide in which part of oxygen contained in lithium transition metal oxide is replaced with fluorine for the purpose of increasing the capacity of a lithium secondary battery. Yes. Specifically, the general _{formula: Li x M 2 O 4-a} F a ( wherein, M is Fe, Mn, Co, Ni, Ti, at least one element selected from the group consisting of V and Cu And x and a satisfy 2 <x ≦ 7 and 0.5 ≦ a ≦ 1.5, respectively.) It has been proposed to use an amorphous lithium transition metal oxide represented by:

In Patent Document 2, proposed to use for the purpose of high energy density at low cost of the lithium secondary batteries, a lithium transition metal oxyfluoride obtained by replacing part of the oxygen of LiMnO ₂ or LiFeO ₂ fluorine Has been. Specifically, the general _{formula: LiMO} in _{2-x F} x (wherein, M is at least one element selected from the group consisting of Mn and Fe, x satisfies 0.05 ≦ x ≦ 0.3 .) Is proposed. This crystal structure is a layered structure, and the space group is considered to be R-3m.

As a method for suppressing the heat generation of the battery at the time of overcharge, it is conceivable to improve the positive electrode active material in addition to the overcharge prevention mechanism by the electronic circuit and the use of a nonflammable inorganic solid electrolyte. However, studies on the positive electrode active material aiming at suppressing the heat generation of the overcharged battery have not been sufficiently performed.
JP 2006-190556 A Japanese Patent Laid-Open No. 08-171900

  Accordingly, an object of the present invention is to provide a high-capacity non-aqueous electrolyte secondary battery active material in which a significant increase in battery temperature is suppressed during overcharging in order to solve the above-described conventional problems. To do. It is another object of the present invention to provide a high capacity and high reliability non-aqueous electrolyte secondary battery by using the above active material.

In order to solve the above problem, for example, the following conditions (1) to (3) are required for the positive electrode active material.
(1) Increase the stability of the positive electrode active material and suppress the decomposition of the positive electrode active material.
(2) The amount of oxygen generated by the decomposition of the positive electrode active material is reduced.
(3) Even when the positive electrode active material is decomposed, a material having a small amount of heat of reaction with the negative electrode active material or the nonaqueous solvent is generated.

  In order to realize the improvement of the positive electrode active material that satisfies the above conditions (1) to (3), the inventor has intensively studied. As a result, it was found that a lithium transition metal oxide in which a part of oxygen is substituted with fluorine is excellent in stability. Compared with oxygen, fluorine has a large difference in electronegativity with transition metals, and thus the substance is considered to be stabilized and decomposition can be suppressed. Further, since a part of oxygen is substituted with fluorine, the amount of oxygen generated from the active material is naturally reduced. Moreover, even if it decomposes | disassembles and generate | occur | produces, it was thought that the calorie | heat amount of reaction with a negative electrode active material and a nonaqueous solvent will be less than oxygen.

A material having a composition in which all of oxygen contained in lithium transition metal oxide is substituted with fluorine is lithium transition metal fluoride. However, since fluorine has a larger difference in electronegativity with transition metal than oxygen, lithium transition metal fluoride is used. The bond between the transition metal and fluorine in the ionic bond increases. As a result, it was considered that the electron conductivity of the material was reduced and the discharge characteristics of the battery were impaired. Therefore, lithium transition metal oxyfluoride containing both fluorine and oxygen was considered preferable.
Examples of the lithium transition metal oxyfluoride include the materials of Patent Documents 1 and 2 described above, but it has not been sufficiently studied to suppress the heat generation of the battery during overcharge.

  Therefore, the composition and crystal structure of the lithium transition metal oxyfluoride were studied in detail for the purpose of reducing the amount of heat generated during overcharge while maintaining a high capacity. As a result, an active material having the following three compositions and crystal structures was found.

That is, the first non-aqueous electrolyte secondary battery active material of the present invention has the general formula (1): Li _x Fe _1-y M _y OF (wherein M is a group consisting of Mn, Co, and Ni) At least one selected from the group consisting of x and y satisfying 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5, respectively, and having a crystal structure belonging to the space group P42 / mnm It is a metal oxyfluoride.

The second non-aqueous electrolyte secondary battery active material of the present invention has the general formula (2): Li _x Ti _1-y M _y OF ₂ (wherein M is Mn, Fe, Co, and Ni). And at least one selected from the group wherein x and y satisfy 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5, respectively, and have a crystal structure belonging to the space group Pm3-m It is a transition metal oxyfluoride.

The third non-aqueous electrolyte secondary battery active material of the present invention has the general formula (3): Li _x Nb _1-y M _y OF ₃ (wherein M is Mn, Fe, Co, and Ni). At least one selected from the group, and x and y satisfy 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5, respectively, and have a crystal structure belonging to the space group R3c An active material for a non-aqueous electrolyte secondary battery, characterized by being oxyfluoride.

  The present invention also relates to a non-aqueous electrolyte secondary battery using any one of the first to third active materials.

  According to the present invention, even when the battery temperature rises during overcharge, the heat generated by the oxidation reaction of the negative electrode active material or the nonaqueous solvent is reduced, and the highly reliable nonaqueous electrolyte secondary battery is excellent in safety. Can be provided.

The first non-aqueous electrolyte secondary battery active material of the present invention (hereinafter referred to as the first active material) is represented by the general formula (1): Li _x Fe _1-y M _y OF (where M is And at least one selected from the group consisting of Mn, Co, and Ni, and x and y satisfy 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5, respectively, and the space group P42 / It is a lithium transition metal oxyfluoride having a crystal structure belonging to mnm.
The present inventor has found that Li _x FeOF having a crystal structure belonging to the space group P42 / mnm is suitable for battery materials. It is considered that the main factor that functions as a battery material is to contain Fe that can be oxidized / reduced and to have an atomic arrangement in which Li can diffuse in the crystal structure. Even in Li _x Fe _1-y M _y OF, in which part of Fe in Li _x FeOF is replaced with M, the constituent elements Fe, Mn, Co, and Ni can be oxidized and reduced, and atoms defined by the space group Since the arrangement is the same, Li is considered to be diffusible.

The second non-aqueous electrolyte secondary battery active material of the present invention (hereinafter referred to as the second active material) is represented by the general formula (2): Li _x Ti _1-y M _y OF ₂ (where M Is at least one selected from Mn, Fe, Co, and Ni, and x and y satisfy 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5, respectively, and the space group Pm3− It is a lithium transition metal oxyfluoride having a crystal structure belonging to m.
The present inventor has found that Li _x TiOF ₂ having a crystal structure belonging to the space group Pm3-m is suitable for battery materials. It is considered that the inclusion of Ti that can be oxidized / reduced and the atomic arrangement in which Li can diffuse in the crystal structure are the main factors that function as a battery material. Li _x a part of Ti in TiOF ₂ even _{Li x Ti 1-y M y} OF 2 substituted on M, a Ti as an element, Fe, Mn, Co, and Ni can redox, space group Since the defined atomic arrangement is the same, Li is considered to be diffusible.

The third non-aqueous electrolyte secondary battery active material of the present invention (hereinafter referred to as a third active material) is represented by the general formula (3): Li _x Nb _{1- y My} OF ₃ (where M Is at least one selected from the group consisting of Mn, Fe, Co, and Ni, and x and y satisfy 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5, respectively. Lithium transition metal oxyfluoride having a crystal structure belonging to Group R3c.
The present inventor has found that Li _x NbOF ₃ having a crystal structure belonging to the space group R3c is suitable as a battery material. It is considered that the inclusion of Ti that can be oxidized / reduced and the atomic arrangement in which Li can diffuse in the crystal structure are the main factors that function as a battery material. Li _x a part of Ti in NbOF ₃ even _{Li x Nb 1-y M y} OF 3 substituted on M, a Nb as a constituent element, Fe, Mn, Co, and Ni can redox, space group Since the defined atomic arrangement is the same, Li is considered to be diffusible.

In the above general formulas (1) to (3), x indicating the composition of lithium changes during charge and discharge. The value of x at the time of active material synthesis is 1. At the time of charging / discharging, x changes in the range of 0-1. When y in the general formulas (1) to (3) exceeds 0.5, a by-product is obtained at the time of preparing an active material described later, and it is difficult to obtain an active material having a target composition.
By using the first to third active materials, heat generation of the battery during overcharge is suppressed, and a high capacity and high reliability nonaqueous electrolyte secondary battery is obtained.

  In order to obtain a high positive electrode potential, M in the general formulas (1) to (3) is preferably Co or Ni, and y is preferably 0.3 to 0.5.

The active material is obtained, for example, by the following method.
As the first method, there is a method in which a lithium oxide or fluoride as a raw material containing lithium and a transition metal oxide or fluoride as a raw material containing a transition metal are mixed and then heated. As a second method, there is a method in which a raw material containing lithium not containing fluorine and a raw material containing a transition metal not containing fluorine are mixed, and then the mixture is heated in an atmosphere containing fluorine. As a third method, there is a method of mixing lithium fluoride as a raw material containing lithium and a transition metal fluoride as a raw material containing a transition metal, and then heating the mixture in an oxygen-containing atmosphere. .

  Examples of the raw material containing lithium include metal lithium, lithium oxide, lithium peroxide, lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Examples of the raw material containing a transition metal include, for example, a single metal, an alloy composed of a constituent metal element, a simple oxide, a composite oxide composed of a constituent metal element, a simple fluoride, a composite fluoride composed of a constituent metal element, Simple hydroxides, composite hydroxides composed of constituent metal elements, simple carbonates, and composite carbonates composed of constituent metal elements.

For the atmosphere during heating, for example, a pure gas such as oxygen, fluorine or hydrogen fluoride, a mixed gas thereof, a rare gas such as argon, or a mixed gas containing nitrogen is used. What is necessary is just to adjust the pressure in atmosphere suitably. When the raw material composition of elements including not only lithium and transition metals but also fluorine and oxygen is the same as the composition of lithium transition metal oxyfluoride to be obtained, the raw material mixture in an atmosphere containing fluorine and oxygen Therefore, the raw material mixture may be heated in a sealed container.
In the above method, the lithium transition metal oxyfluoride is usually obtained as a powder or a sintered body thereof. The active material is pulverized or classified as necessary to obtain a powder having an appropriate shape and particle size. Can be used as

The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.
The positive electrode includes, for example, a positive electrode current collector, and a positive electrode mixture layer including a positive electrode active material, a conductive material, and a binder formed on the positive electrode current collector.
The positive electrode is obtained, for example, as follows. A positive electrode active material, a conductive material, and a binder are mixed, and an appropriate solvent is added to the mixture to obtain a paste-like positive electrode mixture. The positive electrode mixture is applied to the surface of a current collector of a metal foil such as aluminum, dried, and then rolled. In this way, a positive electrode in which a positive electrode mixture layer containing an active material is formed on the positive electrode current collector is obtained.
For example, an organic solvent such as N-methyl-2-pyrrolidone or water is used as the solvent in which the active material, the conductive material, and the binder are dispersed. In order to improve the temporal stability and dispersibility of the paste-like positive electrode mixture, an additive such as a surfactant may be added to the positive electrode mixture.

  The conductive material is used to increase the electrical conductivity of the positive electrode mixture layer. Examples of the conductive material include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more.

The binder is used to maintain a good contact state between the active material particles and the conductive material particles, and to reliably bind the positive electrode mixture layer containing these particles to the current collector surface. Examples of the binder include polytetrafluoroethylene (PTFE), a modified PTFE, a polyvinylidene fluoride (PVDF), a modified PVDF, a fluorine-containing resin such as fluororubber, a thermoplastic resin such as polypropylene and polyethylene, or a modified material. Acrylonitrile rubber particles (such as “BM-500B (trade name)” manufactured by Nippon Zeon Co., Ltd.) are used. PTFE and BM-500B are preferably used in combination with a thickener. As the thickener, for example, carboxymethyl cellulose (CMC), polyethylene oxide (PEO), modified acrylonitrile rubber (“BM-720H (trade name)” manufactured by Nippon Zeon Co., Ltd.) and the like are used.
As the positive electrode current collector, a metal foil that is stable in the potential range of the positive electrode such as aluminum, a film in which a metal that is stable in the potential range of the positive electrode such as aluminum is disposed on the surface layer, or the like is used. In order to improve the current collecting property, the surface of the current collector may be provided with irregularities or may be perforated.

The negative electrode includes, for example, a negative electrode current collector, and a negative electrode active material layer that is formed on the negative electrode current collector and includes a negative electrode active material capable of inserting and extracting lithium ions and a binder.
A negative electrode is obtained as follows, for example. A binder is mixed with the negative electrode active material, and an appropriate solvent is added to obtain a paste-like negative electrode mixture. This negative electrode mixture is applied to the surface of a current collector of a metal foil such as copper, dried, and then rolled. In this way, a negative electrode in which a negative electrode mixture layer containing an active material is formed on a current collector is obtained.

  Examples of the negative electrode active material include natural graphite, artificial graphite, petroleum coke, carbon fiber, organic polymer fired product, carbon material such as carbon nanotube and carbon nanohorn, silicon such as oxide and silicide, tin-containing composite material, various metals or Known active materials such as alloy materials are used.

The binder is not particularly limited, but rubber particles are preferable from the viewpoint of exhibiting binding properties in a small amount, and those containing styrene units and butadiene units are particularly preferable. As the binder, for example, a styrene-butadiene copolymer (SBR), a modified SBR, or the like is used. When rubber particles are used as the negative electrode binder, it is desirable to use a thickener composed of a water-soluble polymer. As the water-soluble polymer, a cellulose resin is preferable, and CMC is particularly preferable. In addition, PVDF or a modified PVDF may be used as the binder.
As the negative electrode current collector, a metal foil that is stable in the potential range of the negative electrode such as copper, a film in which a metal that is stable in the potential range of the negative electrode such as copper is arranged on the surface layer, or the like can be used. In order to improve the current collecting property, the surface of the current collector may be provided with irregularities or may be perforated.

  The separator is made of a material that can withstand the use environment of the battery, and may be a microporous film or a non-woven fabric having a property of allowing ions of the electrolytic solution to permeate and insulating between the positive and negative electrodes. Generally, a microporous film made of a polyolefin resin is used for the separator. As the polyolefin resin, for example, polyethylene or polypropylene is used. The microporous film may be a single layer film made of one kind of resin or a multilayer film made of two or more kinds of resins. Further, it may be a multilayer film made of an inorganic material such as resin and alumina.

  An organic solvent in which the supporting salt is dissolved is used for the non-aqueous electrolyte. The organic solvent is not particularly limited as long as it can be used for a normal nonaqueous electrolyte secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, and oxolane compounds are used. Among these, a mixed solvent of a high dielectric constant solvent such as ethylene carbonate (EC) or propylene carbonate (PC) and a low viscosity solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). Is preferred. Further, dimethoxyethane (DME), tetrahydrofuran (THF) and γ-butyrolactone (GBL) may be used as a co-solvent. Various additives may be added for the purpose of improving battery characteristics such as storage characteristics, cycle characteristics, and safety. Additives include vinylene carbonate (VC), cyclohexylbenzene (CHB), and derivatives thereof.

As the supporting salt, an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ and derivatives thereof are used. Further, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ , LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ And organic derivatives selected from these and derivatives thereof. Although the density | concentration of the support salt in electrolyte solution is not specifically limited, Usually, it is 0.5-2.0 mol / l.
The shape of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited. For example, it can be used with known batteries such as a cylindrical type, a square type and a sheet type.

Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.
Example 1
(1) Preparation of positive electrode active material A reagent made by Rare Metallic Co., Ltd. was used as a raw material. Specifically, lithium oxide (Li ₂ O), iron fluoride (FeF ₃ ), iron oxide (Fe ₂ O ₃ ), manganese fluoride (MnF ₂ ), manganese oxide (MnO ₂ ), cobalt fluoride (CoF ₂ ), cobalt oxide (Co ₃ O ₄ ), nickel fluoride (NiF ₂ ), nickel oxide (NiO), titanium fluoride (TiF ₄ ), titanium oxide (TiO ₂ ), niobium fluoride (NbF ₅ ), oxidation Niobium (Nb ₂ O ₅ ) was used.

According to the chemical composition of the lithium transition metal oxyfluoride to be obtained from these, raw materials were appropriately selected from the above, weighed, and mixed in a mortar. The mixture was put in a gold sealed container and heated at a temperature of 500 to 1000 ° C. for 20 to 60 hours to synthesize lithium transition metal oxyfluoride. When heating, the heating temperature and the heating time were adjusted so that no by-product was contained in the lithium transition metal oxyfluoride. The obtained product was pulverized in a mortar, and powder that passed through a sieve having an opening of 45 μm was used as an active material.
About each powder material, the powder X-ray-diffraction measurement was performed using the X-ray-diffraction apparatus (RINT2500 by Rigaku Corporation), and the space group of the crystal structure was determined from the obtained diffraction profile.

The composition of the active material produced in this example is shown below.
As the active material represented by the general formula (1), active material 1-1: LiFeOF, active material 1-2: LiFe _0.9 Mn _0.1 OF, active material 1-3: LiFe _0.7 Mn _0.3 OF, active material 1-4 : LiFe _0.5 Mn _0.5 OF, active material 1-5: LiFe _0.9 Co _0.1 OF, active material 1-6: LiFe _0.7 Con _0.3 OF, active material 1-7: LiFe _0.5 Co _0.5 OF, active material 1-8: LiFe _0.9 Ni _0.1 OF, active material 1-9: LiFe _0.7 Ni _0.3 OF, active material 1-10: LiFe _0.5 Ni _0.5 OF, active material 1-11:
LiFe _0.7 Mn _0.1 Co _0.1 Ni _0.1 OF was prepared. From the results of analysis by powder X-ray diffraction, the space group of these powder materials was assigned to P42 / mnm. In addition, when the value of y exceeded 0.5 in General formula (1), the by-product existed and the target product could not be obtained.

As the active material represented by the general formula (2), active material 2-1: LiTiOF ₂ , active material 2-2: LiTi _0.9 Mn _0.1 OF ₂ , active material 2-3: LiTi _0.7 Mn _0.3 OF ₂ , active material 2-4: LiTi _0.5 Mn _0.5 OF ₂ , active material 2-5: LiTi _0.9 Fe _0.1 OF ₂ , active material 2-6: LiTi _0.7 Fe _0.3 OF ₂ , active material 2-7: LiTi _0.5 Fe _0.5 OF ₂ , Active material 2-8: LiTi _0.9 Co _0.1 OF ₂ , Active material 2-9: LiTi _0.7 Co _0.3 OF ₂ , Active material 2-10: LiTi _0.5 Co _0.5 OF ₂ , Active material 2-11: LiTi _0.9 Ni _0.1 OF ₂ , Active material 2-12: LiTi _0.7 Ni _0.3 OF ₂ , Active material 2-13: LiTi _0.5 Co _0.5 OF ₂ , Active material 2-14: LiTi _0.6 Mn _0.1 Fe _0.1 Co _0.1 Ni _0.1 OF ₂ were prepared. From the results of analysis by powder X-ray diffraction, the space group of these powder materials was assigned to Pm3-m. In general formula (2), when the value of y exceeded 0.5, by-products were present and the desired product could not be obtained.

As the active material represented by the general formula (3), active material 3-1: LiNbOF ₃ , active material 3-2: LiNb _0.9 Mn _0.1 OF ₃ , active material 3-3: LiNb _0.7 Mn _0.3 OF ₃ , active material 3-4: LiNb _0.5 Mn _0.5 OF ₃ , active material 3-5: LiNb _0.9 Fe _0.1 OF ₃ , active material 3-6: LiNb _0.7 Fe _0.3 OF ₃ , active material 3-7: LiNb _0.5 Fe _0.5 OF ₃ , Active material 3-8: LiNb _0.9 Co _0.1 OF ₃ , Active material 3-9: LiNb _0.7 Co _0.3 OF ₃ , Active material 3-10: LiNb _0.5 Co _0.5 OF ₃ , Active material 3-11: LiNb _0.9 Ni _0.1 OF ₃ , active material 3-12: LiNb _0.7 Ni _0.3 OF ₃ , active material 3-13: LiNb _0.5 Ni _0.5 OF ₃ , active material 3-14: LiNb _0.6 Mn _0.1 Fe _0.1 Co _0.1 Ni _0.1 OF ₃ were prepared. From the results of analysis by powder X-ray diffraction, the space group of these powder materials was assigned to R3c. In addition, when the value of y exceeded 0.5 in General formula (3), the by-product existed and the target product could not be obtained.

(2) Production of positive electrode 300 g of the above positive electrode active material powder (active material 1-1 to active material 3-14) and “# 1320 (trade name)” (PVDF) manufactured by Kureha Chemical Co., Ltd. as a positive electrode binder. NMP solution containing 12 wt%), 9 g of acetylene black as a conductive agent, and an appropriate amount of NMP were stirred with a double-arm kneader to obtain a paste-like positive electrode mixture. This positive electrode mixture was applied to both surfaces of a 15 μm-thick aluminum foil as a positive electrode current collector, excluding the connection portion of the positive electrode lead and the conductive polymer film, and the dried coating film was rolled with a roller. . A positive electrode mixture layer having an active material density (active material weight / mixture layer volume) of 3.3 g / cm ³ was formed on both surfaces of the aluminum foil. Under the present circumstances, the thickness of the electrode plate which consists of aluminum foil and a positive mix layer was controlled to 160 micrometers. Thereafter, the electrode plate was slit to a width that can be inserted into a battery can of a cylindrical battery (Part No. 18650) to obtain a hoop-shaped positive electrode.

(3) Production of negative electrode 300 g of artificial graphite as a negative electrode active material, and “BM-400B (trade name)” manufactured by Nippon Zeon Co., Ltd. as a negative electrode binder (40% by weight of a modified styrene-butadiene copolymer) An aqueous dispersion containing 7.5 g, 3 g of CMC as a thickener, and an appropriate amount of water were stirred with a double-arm kneader to obtain a paste-like negative electrode mixture. This negative electrode mixture was applied to both surfaces of a 10 μm thick copper foil as a negative electrode current collector, excluding the negative electrode lead connecting portion and the conductive polymer film joint, and the dried coating film was rolled with a roller. In this way, negative electrode mixture layers having an active material density (active material weight / mixture layer volume) of 1.4 g / cm ³ were formed on both surfaces of the copper foil. Under the present circumstances, the thickness of the electrode plate which consists of copper foil and a negative mix layer was controlled to 180 micrometers. Thereafter, the electrode plate was slit to a width that can be inserted into a battery can of a cylindrical battery (Part No. 18650) to obtain a hoop-shaped negative electrode.

(4) Preparation of Nonaqueous Electrolyte Solution A nonaqueous electrolyte solution was obtained by dissolving LiPF ₆ as a supporting salt at a concentration of 1 mol / L in a mixed solvent containing EC, DMC, and EMC at a volume ratio of 2: 3: 3. . Further, 3 parts by weight of VC per 100 parts by weight of the non-aqueous electrolyte was added to this non-aqueous electrolyte.

(5) Production of Cylindrical Battery Using the positive electrode, the negative electrode, and the nonaqueous electrolytic solution obtained above, a cylindrical battery having a product number 18650 shown in FIG. 1 was produced by the following procedure. FIG. 1 is a longitudinal sectional view of a cylindrical battery.
First, the hoop-shaped positive electrode and the negative electrode were each cut into predetermined lengths to obtain the positive electrode 5 and the negative electrode 6. One end of the positive electrode lead 5 a was connected to the positive electrode lead connection portion of the positive electrode 5, and one end of the negative electrode lead 6 a was connected to the negative electrode lead connection portion of the negative electrode 6 through the negative electrode lead connection portion. The positive electrode 5 and the negative electrode 6 were wound through a separator 7 made of a microporous film made of polyethylene resin having a thickness of 15 μm to constitute a cylindrical electrode body. The electrode body was sandwiched between a ring-shaped upper insulating plate 8a and a lower insulating plate 8b and accommodated in the battery can 1.

  Next, 5 g of the above non-aqueous electrolyte was weighed and injected into the battery can 1. And the non-aqueous electrolyte was included in the electrode body by decompressing the inside of the battery can 1 to 133 Pa. The other end of the positive electrode lead 5a was welded to the back surface of the battery lid, and the other end of the negative electrode lead 6a was welded to the inner bottom surface of the battery can 1. Finally, the opening of the battery can 1 was closed with a battery lid having an insulating packing 3 disposed on the periphery. The battery lid includes a sealing plate 2 that also serves as a positive electrode terminal. In this way, the cylindrical battery shown in FIG. 1 was produced. During the production of the battery, batteries 1-1 to 3-14 were obtained using the active materials 1-1 to 3-14, respectively.

<< Comparative Example 1 >>
A mixture of lithium oxide and cobalt oxide was placed in an alumina crucible and heated to 900 ° C. in air to obtain lithium cobaltate (LiCoO ₂ ). This was pulverized in a mortar, and the powder that passed through a sieve having an opening of 45 μm was used as the positive electrode active material. A cylindrical battery (comparative battery) was produced in the same manner as in Example 1 except that lithium cobaltate (LiCoO ₂ ) powder was used as the positive electrode active material. LiCoO ₂ is a typical active material conventionally used in non-aqueous electrolyte secondary batteries.

[Evaluation]
Each battery of Example 1 and Comparative Example 1 was charged 120% of the calculated capacity (theoretical capacity) in an environment of 20 ° C., and the battery was overcharged. The calculated capacity is a capacity (unit: Ah) calculated by the following equation, where W (g) is the weight of the active material contained in the positive electrode and M is the composition formula amount of the active material.
Calculation capacity = W / M × 96500/3600
That is, the calculated capacity of 100% is a calculated charge capacity that is considered that all lithium contained in the positive electrode active material is used for the charge reaction. However, in practice, the charging current is consumed not only for the lithium extraction reaction (charging reaction) at the positive electrode but also for side reactions such as decomposition of the electrolyte. For this reason, as described above, the battery was charged in excess of 20% with respect to the calculated capacity.
Each battery in an overcharged state was allowed to stand for 1 hour in a thermostat maintained at 160 ° C., 190 ° C., and 220 ° C., and the state of the battery at that time was observed. The results are shown in Tables 1-3.

In Tables 1 to 3, circles indicate that the battery heat generation during overcharge is suppressed and the battery temperature is equivalent to the temperature of the thermostatic bath, and x indicates that the battery heat generation during overcharge is large. The case where the battery temperature rises significantly and the battery temperature exceeds 300 ° C. is shown.
In a comparative battery using a conventional positive electrode active material, the battery temperature rose significantly when the ambient temperature was 160 ° C. or higher. On the other hand, in the batteries 1-1 to 1-11, the batteries 2-1 to 2-14, and the batteries 3-1 to 3-14 of the examples of the present invention, when the ambient temperature is 160 ° C., The battery heat generation was suppressed during overcharge, and the battery reliability was improved.

In the batteries 1-2 to 1-6, the batteries 1-8, and the batteries 1-11 in Table 1, even when the ambient temperature is 190 ° C., the heat generation of the batteries is suppressed during overcharge, and the reliability of the batteries is improved. .
In addition, in the batteries 2-1 to 2-14 and the batteries 3-1 to 3-14 in Tables 2 and 3, even when the ambient temperature is 190 ° C., heat generation of the battery during overcharge is suppressed, Reliability was improved.

  Since the active material of the present invention can reduce the exothermic reaction of the negative electrode active material and the nonaqueous solvent even when the battery temperature rises due to overcharging, it is suitably used for a nonaqueous electrolyte secondary battery.

It is a longitudinal cross-sectional view of the cylindrical battery which is an example of the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation gasket 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a Upper insulating plate 8b Lower insulating plate

Claims (4)

General formula (1): Li _x Fe _1-y M _y OF (wherein M is at least one selected from the group consisting of Mn, Co, and Ni, and x and y are each 0 ≦ x ≦ 1 And 0 ≦ y ≦ 0.5), and a lithium transition metal oxyfluoride having a crystal structure belonging to the space group P42 / mnm. material. General formula (2): Li _x Ti _1-y M _y OF ₂ (wherein M is at least one selected from the group consisting of Mn, Fe, Co, and Ni, and x and y are each 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5.) and a lithium transition metal oxyfluoride having a crystal structure belonging to the space group Pm3-m. Battery active material. General formula (3): Li _x Nb _1-y M _y OF ₃ (wherein M is at least one selected from the group consisting of Mn, Fe, Co, and Ni, and x and y are each 0 ≦ x ≦ 1 and 0 ≦ y ≦ 0.5.) and a lithium transition metal oxyfluoride having a crystal structure belonging to the space group R3c, for a non-aqueous electrolyte secondary battery Active material.   The nonaqueous electrolyte secondary battery provided with the electrode containing the active material in any one of Claims 1-3.