JP6441114B2 - Copper-containing composite polyanion composite oxide, method for producing the same, and secondary battery using the same - Google Patents

Description

  The present invention relates to a copper-based positive electrode material that can be used in a secondary battery such as a lithium ion battery, and more particularly to a copper-containing composite polyanion composite oxide, a method for producing the same, and a secondary battery using the same.

  A non-aqueous electrolyte secondary battery using an alkaline metal such as lithium, an alkaline earth metal such as magnesium, an alloy thereof, or a compound thereof as a negative electrode active material is used for desorption of negative electrode metal ions from the positive electrode active material ( The large discharge capacity and charge reversibility are ensured by the deintercalation reaction or the insertion (intercalation) reaction of the negative electrode metal ions into the positive electrode active material.

Lithium ion batteries have a high operating potential and a high energy density can be achieved. Layered transition metal composite oxides are mainly used as positive electrode materials for such lithium ion batteries. For example, LiCoO ₂ that is widely used for consumer use is known as a typical lithium ion positive electrode material. Rare and is _{Co LiNi 1-x-y Co} x Al y O 2 with a reduced amount of (NCA), or _{LiNi 1/3 Co 1/3 Mn 1/3 O 2} (NCM) and the like are also developed, Some have been put to practical use. However, these all have a layered crystal structure called an α-NaFeO ₂ type structure and use a redox reaction between trivalent and tetravalent transition metal ions, so when the temperature rises in the charged state There was a problem in terms of thermal stability that transition metal ions were easily reduced and released oxygen.

In order to solve this problem, heat stability is achieved by using a divalent / trivalent redox reaction instead of a trivalent / 4 tetravalent redox reaction, and strongly covalently bonding oxygen to phosphorus (P). As systems having improved properties, phosphate compounds such as olivine-type LiCoPO ₄ or LiFePO ₄ have been proposed as positive electrode active materials (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1 below). Iron olivine (LiFePO ₄ ), which is a polyanionic compound having excellent chemical stability, has been put into practical use as a positive electrode material for secondary batteries.

Japanese Patent No. 3484003 Japanese Patent No. 3523397

Okada, Arai, Yamaki, Electrochemistry and Industrial Physical Chemistry, 65, No.10, p.802-808 (1997).

However, LiFePO ₄ has a low operating voltage of 3.3 V and a capacity of 170 mAh / g, which is insufficient for increasing the energy density of the secondary battery.

Therefore, a polyanion system capable of multi-electron reaction, excellent in chemical thermal stability, and having a higher capacity than LiFePO ₄ when used as a positive electrode material of a secondary battery is expected. Yes. In the automobile industry and the electric appliance industry, etc., it is necessary to increase the size of the battery. Therefore, there is a high expectation for a high energy density material having thermal stability, and a large market is expected in the future.

Accordingly, the present invention is a copper-based material which can multi-electron reaction, the copper-containing composite polyanionic is a novel material exhibiting a high capacity characteristics than conventional when used as an electrode active material for a secondary battery It is an object to provide a composite oxide, a method for producing the same, and a secondary battery using the same.

The copper-containing composite polyanion composite oxide according to the first aspect of the present invention is represented by the general formula Li _2-x CuVO ₄ (0 ≦ x <1 or 1 <x <2).

Preferably, the copper-containing composite polyanionic composite oxide is a VO ₄ tetrahedron, which is a tetrahedron obtained by substituting a sulfur atom with an oxygen atom and a zinc atom with a vanadium atom in ZnS having a wurtzite structure, and wurtzite. In the ZnS of the ore structure, LiO ₄ tetrahedron, which is a tetrahedron obtained by replacing sulfur atoms with oxygen atoms and zinc atoms with lithium atoms, and in the ZnS of wurtzite structure, the sulfur atoms are replaced with oxygen atoms. And a CuO ₄ tetrahedron that is a tetrahedron obtained by substituting a zinc atom with a copper atom, and the VO ₄ tetrahedron, the LiO ₄ tetrahedron, and the CuO ₄ tetrahedron share an oxygen atom located at the apex.

The copper-containing composite polyanion composite oxide according to the second aspect of the present invention is represented by the general formula LiCuVO ₄ , and in the ZnS having a wurtzite structure, a sulfur atom is replaced with an oxygen atom and a zinc atom is replaced with a vanadium atom. A tetrahedral VO ₄ tetrahedron, a wurtzite structure ZnS, and a LiO ₄ tetrahedron that is a tetrahedron obtained by replacing sulfur atoms with oxygen atoms and zinc atoms with lithium atoms, and wurtzite. In an ore-type ZnS, CuO ₄ tetrahedron, which is a tetrahedron obtained by substituting sulfur atoms with oxygen atoms and zinc atoms with copper atoms, includes VO ₄ tetrahedron, LiO ₄ tetrahedron, and CuO _4. The tetrahedron shares an oxygen atom located at the apex.

The method for producing a copper-containing composite polyanion composite oxide according to the third aspect of the present invention is a method for producing any one of the above copper-containing composite polyanion composite oxides. In this manufacturing method, the Li source material, the Cu source material, and the VO ₄ source material are mixed so that the molar ratio of Li, Cu, and VO ₄ is 2-x: 1: 1 (0 ≦ x <2). The first step of generating a mixture, the second step of causing the mixture to chemically react by heating the mixture to a predetermined temperature at which the mixture does not dissolve, and the second step followed by cooling the mixture with a low-temperature liquefied gas Including a third step.

  Preferably, the second step is performed in an atmosphere that is more reducing than the atmosphere.

  More preferably, the second step is performed in a stream of nitrogen or argon, or in an atmosphere where a reducing agent is disposed.

  More preferably, the predetermined temperature is a temperature of 510 ° C. or higher and 800 ° C. or lower.

Preferably, the Li source material is Li ₂ O, the Cu source material is CuO, and the VO ₄ source material is VO ₂ .

More preferably, the Li source material is Li ₂ CO ₃ , the Cu source material is Cu ₂ O, and the VO ₄ source material is V ₂ O ₅ .

  The secondary battery which concerns on the 4th aspect of this invention contains said copper containing composite polyanion type complex oxide as a positive electrode active material.

  Preferably, the secondary battery includes lithium or sodium as a negative electrode active material.

According to the present invention, by using a copper-containing composite polyanion-based composite oxide represented by the general formula Li _2-x CuVO ₄ (0 ≦ x <2) as a positive electrode active material of a secondary battery, LiFePO _{4 and the} like A secondary battery having a larger capacity than the conventional positive electrode using the olivine-type phosphate polyanion can be realized.

  Moreover, when using this copper containing composite polyanion type complex oxide as a positive electrode material, not only Li but Na can be used for a negative electrode. Therefore, it is possible to realize a lithium battery and a sodium battery with higher capacity than before.

  In addition, the present copper-containing composite polyanion composite oxide does not contain Co which is a rare element, is a resource-rich copper-based material, and has a low environmental load.

It is a perspective view which shows the crystal structure of a well-known wurtzite (ZnS) type structure. Is a perspective view showing the crystal structure of _Li 2-x CuVO ₄ according to the embodiment of the present invention (0 ≦ x <2). Is a graph showing the results of differential thermal analysis of the Li ₂ CuVO _4. Is a perspective view showing the crystal structure of LiCuVO _4, which may be produced as an impurity during the synthesis of Li ₂ CuVO _4. 6 is a graph showing a Rietveld analysis result of X-ray (copper Kα ray) diffraction of Li ₂ CuVO ₄ powder obtained in Example 6. FIG. It is a graph which shows the Le Bail analysis result of the X-ray (copper K alpha ray) diffraction of the powder of the sample obtained in Example 2. It is sectional drawing which shows schematic structure of the produced coin-type secondary battery. 10 is a graph showing a charge / discharge curve of a coin-type lithium battery produced in Example 8. 10 is a graph showing a charge / discharge curve of a coin-type lithium battery produced in Example 9.

  In the following embodiments, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

(Electrode active material for non-aqueous electrolyte secondary battery)
The electrode active material for a secondary battery according to the embodiment of the present invention is a copper-containing composite polyanion composite oxide represented by a general formula Li _2-x CuVO ₄ . Here, x is an arbitrary value within the range of 0 ≦ x <2.

The crystal structure of the copper-containing composite polyanion composite oxide is based on a known wurtzite (ZnS) structure. Referring to FIG. 1, the wurtzite structure has a ZnS ₄ tetrahedron in which four sulfur (S) coordinates around zinc (Zn) share S located at the apex of the tetrahedron, and a Zn layer. The crystal structure has a zigzag S layer sandwiched between them. In other words, the wurtzite structure has a hexagonal close-packed structure in which sulfide ions are present at each corner and center of the top surface and bottom surface of the regular hexagonal column, and further at three height positions within the hexagonal column. In this structure, zinc ions are present in tetrahedral voids formed by four adjacent sulfide ions.

The copper-containing composite polyanion-based composite oxide includes a VO ₄ tetrahedron having a structure in which W is substituted with oxygen (O) and Zn is replaced with vanadium (V) in ZnS having a wurtzite structure, and S is oxygen (O ) And a LiO ₄ tetrahedron having a structure in which Zn is replaced by lithium (Li) and a CuO ₄ tetrahedron having a structure in which S is replaced by oxygen (O) and Zn is replaced by copper (Cu). . With this structure, Li can be desorbed up to twice the number of moles of V. Therefore, the general formula of the present copper-containing composite polyanion-based composite oxide is represented by Li _2-x CuVO ₄ (0 ≦ x <2) as described above. In addition, said crystal structure was confirmed by performing well-known Rietveld analysis regarding the sample produced by the experiment mentioned later.

(Method for producing copper-containing composite polyanion composite oxide)
The above-described copper-containing composite polyanion-based composite oxide (general formula Li _2-x CuVO ₄ (0 ≦ x <2)) includes Li source material, Cu source material, and VO ₄ source material, Li, Cu, and VO _4. To form a mixture by causing a molar ratio of 2-x: 1: 1 (0 ≦ x <2), and a chemical reaction is caused to occur in the resulting mixture.

  The chemical reaction of the mixture is preferably performed in a reducing atmosphere rather than air. The chemical reaction of the mixture is more preferably performed, for example, in a nitrogen or argon stream or in an atmosphere where a reducing agent is disposed. Further, it is more preferable to cause a chemical reaction by heating the mixture to a predetermined temperature at which the mixture does not dissolve.

In the results of differential thermal analysis (DTA) of Li ₂ CuVO ₄ shown in FIG. 3, a peak that is thought to be derived from partial decomposition is observed at 502.6 ° C. Even at 800 ° C. or higher, a peak derived from another phase transition and a peak that seems to correspond to melting are observed (each peak is shown with an arrow and a temperature).

  Therefore, it is desirable that the synthesis of the copper-containing composite polyanionic composite oxide is performed at a temperature of 510 ° C. or higher and 800 ° C. or lower. More preferably, it is carried out at a temperature of 560 ° C. or higher and 720 ° C. or lower, more preferably 580 ° C. or higher and 650 ° C. or lower.

When a chemical reaction is caused in the mixture by heating, it is preferable to quench the mixture after heating. For example, as will be described later in Examples, when about 1 g of pellets is used, a rapid reaction to room temperature in argon gas causes a decomposition reaction, making it difficult to obtain single-phase Li ₂ CuVO ₄ . On the other hand, as will be described later in Examples, single-phase Li ₂ CuVO ₄ could be obtained by dropping the sample into liquid nitrogen (liquid refrigerant at −196 ° C.). Therefore, it is preferable to quench the mixture after heating the mixture to cause a chemical reaction.

  Since the rapid cooling rate is determined by the amount of the sample and the characteristics of the refrigerant, an appropriate cooling method may be used from the relationship between the amount of the sample and the temperature and heat capacity of the solvent. The method is not limited to the rapid cooling method using liquid nitrogen, and cooling may be performed using elemental liquid (low temperature liquefied gas: cryogenic liquid) such as liquid oxygen, liquid helium, liquid hydrogen, etc. at normal temperature and normal pressure.

(Electrode using copper-containing complex polyanion complex oxide)
The copper-containing composite polyanion composite oxide described above can be used for a secondary battery electrode. Specifically, the above-described copper-containing composite polyanion composite oxide powder is used as the electrode active material. What is necessary is just to set suitably content of this active material (copper containing composite polyanion type complex oxide) in an electrode according to the kind of active material to be used, a binder (binder), the usage-amount of a electrically conductive material, etc. In addition, in the electrode, as long as predetermined electrode characteristics can be obtained as an electrode active material, the above copper-containing composite polyanion composite oxide may be used alone or as a mixture with a known electrode active material. Good.

(Method for producing electrode using copper-containing composite polyanion composite oxide)
The manufacturing method of the above-mentioned electrode for secondary batteries is the same as the manufacturing method of a well-known electrode except using a copper containing composite polyanion type complex oxide. For example, the copper-containing composite polyanion composite oxide powder is mixed with a known binder as necessary. Furthermore, it is preferable to mix with a well-known electrically conductive material, and considering the electrical conductivity of a copper containing composite polyanion type complex oxide, it is more preferable to mix sufficiently with the electrically conductive material.

  An electrode for a secondary battery can be produced by pressure-molding the obtained mixed powder on a support made of stainless steel or the like, or filling a metal container. For example, the electrode for secondary batteries can be manufactured also by the method of apply | coating the slurry obtained by mixing this mixed powder with the organic solvent on metal substrates, such as aluminum or stainless steel.

  Here, known binders include, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine rubber, polyvinyl acetate, Polymethyl methacrylate, polyethylene, nitrocellulose, or the like. Known conductive materials are, for example, acetylene black, carbon, graphite, natural graphite, artificial graphite, or needle coke. Examples of the organic solvent include N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

  The thickness of the secondary battery electrode is usually about 1 to 10,000 μm, preferably about 3 to 200 μm, and more preferably about 5 to 100 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease. The electrode obtained by coating and drying may be consolidated by a roller press or the like in order to increase the packing density of the active material.

(Nonaqueous electrolyte secondary battery using copper-containing composite polyanion composite oxide)
The non-aqueous electrolyte secondary battery according to the embodiment of the present invention can employ constituent elements in known non-aqueous electrolyte secondary batteries except that the above-described copper-containing composite polyanion-based composite oxide is used as an electrode. . An electrode using the above-described copper-containing composite polyanion-based composite oxide can usually be used as a positive electrode. In this case, a known negative electrode active material can be used for the negative electrode as the electrode active material. For the negative electrode, it is preferable to use one substance selected from the group consisting of lithium, sodium, and a mixture thereof, or a content thereof.

The negative electrode active material in the non-aqueous electrolyte secondary battery can occlude and release alkali metal ions in addition to alkali metals such as lithium and sodium, alkali metal compounds, or alkali metal alloys. Materials (for example, graphite, hard carbon, soft carbon, Li _2.5 CO _0.5 N, Li ₄ Ti ₅ O _{12 and the} like) are also included.

  The manufacturing method of the negative electrode is the same as a known method. For example, it can be produced in the same manner as described above. That is, the negative electrode active material powder is mixed with a known binder, if necessary, with a known conductive material, if necessary, and then the mixed powder is formed into a sheet, which is made of stainless steel, copper, or the like. What is necessary is just to crimp | bond to a conductor net | network (current collector). For example, a negative electrode can be manufactured by apply | coating the slurry obtained by mixing said mixed powder with a well-known organic solvent on metal substrates, such as copper.

  As another component, what is used for a well-known nonaqueous electrolyte secondary battery can be used as a component. Examples are given below.

  The electrolytic solution usually includes an electrolyte and a solvent. The solvent of the electrolytic solution is not particularly limited as long as it is non-aqueous. As the solvent of the electrolytic solution, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, amines, esters, amides, or phosphate ester compounds are used. can do. These representatives are listed as follows: 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene carbonate, vinylene carbonate, methyl formate, dimethyl sulfoxide, propylene carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, dimethyl carbonate, diethyl carbonate, sulfolane, ethyl methyl carbonate, 1,4-dioxane, 4-methyl-2-pentanone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl Ether, sulfolane, methylsulfolane, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, trimethyl phosphate, triethyl phosphate, etc. It can be used. In addition, these can be used 1 type or in mixture of 2 or more types.

As the electrolytic solution, an alkali metal ion or an alkaline earth metal ion in the negative electrode active material electrochemically reacts with the positive electrode active material or the positive electrode active material and the negative electrode active material in the solvent. Electrolyte materials that can be transferred to can be used. Examples of the electrolyte include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, and LiN ( SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , or LiN (SO ₃ CF ₃ ) ₂ can be used. If it is soluble in the electrolyte, lithium chloride, lithium bromide, or the like can be used. Further, NaClO ₄ in Na _{salt, NaPF 6, NaBF 4, CF} 3 SO 3 Na, NaAsF 6, NaB (C 6 H 5) 4, CH 3 SO 3 Na, CF 3 SO 3 Na, NaN (SO 2 CF 3 ) ₂ , NaN (SO ₂ C ₂ F ₅ ) ₂ , NaC (SO ₂ CF ₃ ) ₃ , NaN (SO ₃ CF ₃ ) _{2, and} other various salts can be used. If it is soluble in the electrolytic solution, sodium chloride, sodium bromide, or the like can also be used. A known solid electrolyte such as LiTi ₂ (PO ₄ ) ₃ having a NASICON structure can also be used.

  Various known materials can also be used for elements such as separators, battery cases, and other structural materials, and there is no particular limitation. For example, when a separator is used between the positive electrode and the negative electrode, a microporous polymer film can be used. For example, those made of polyolefin polymers such as nylon (registered trademark), cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene can be used. From the viewpoint of the chemical and electrochemical stability of the separator, polyolefin polymers are preferred. From the viewpoint of self-occluding temperature, which is one of the purposes of the battery separator, it is desirable that the separator is made of polyethylene.

  In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of high temperature shape maintenance, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and even more preferably 1,500,000. The upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and even more preferably 3 million. This is because if the molecular weight is too large, the fluidity is too low and the pores of the separator may not close when heated.

  The nonaqueous electrolyte secondary battery according to the embodiment of the present invention can be assembled by a known method using the battery element described above. The outer shape of the battery is not particularly limited. For example, various shapes and sizes such as a cylindrical shape, a square shape, and a coin shape can be appropriately employed.

  The experimental results are shown below to show the effectiveness of the present invention. A copper-containing composite polyanion composite oxide that can be used as a positive electrode active material for a secondary battery was prepared.

Li ₂ O, Cu ₂ O, and V ₂ O ₅ were weighed at a molar ratio of 2: 1: 1 and mixed well in an agate mortar to produce pellets of about 1 g with a diameter of 10 mm. A platinum sheet was laid on an alumina boat, and the prepared pellets were placed on the platinum sheet and fired at 700 ° C. for 12 hours in an argon atmosphere. After firing, the sample was gradually cooled (natural cooling) in an electric furnace.

The obtained sample was pulverized in an agate mortar and identified by powder X-ray diffraction. As a result, it was confirmed that the obtained sample was a mixed phase in which Li ₂ CuVO ₄ contained LiCuVO ₄ and CuO as impurities.

LiCuVO ₄ corresponds to the case of x = 1 in the general formula Li _2-x CuVO ₄ (0 ≦ x <2). As shown in FIG. 4, the crystal structure includes a VO ₄ tetrahedron in which vanadium ions are located at the center, but both Li and Cu are located at the center of the tetrahedron formed by O. Not. That is, the crystal structure of LiCuVO ₄ does not include both the LiO ₄ tetrahedron and the CuO ₄ tetrahedron, and is different from the crystal structure shown in FIG.

Li ₂ O, CuO, V ₂ O ₅ and V ₂ O ₃ were weighed at a molar ratio of 4: 4: 1: 1 and mixed in a ball mill for 48 hours to produce pellets having a diameter of 10 mm and about 1 g. The produced pellet was put into a platinum crucible and vacuum-sealed with a quartz glass tube. The sealed tube was baked at 700 ° C. for 8 hours and then gradually cooled in an electric furnace.

The sample taken out from the enclosed tube was pulverized with an agate mortar and identified by powder X-ray diffraction. As a result, it was confirmed that the obtained sample was a mixed phase in which Li ₂ CuVO ₄ contained LiCuVO ₄ as an impurity.

Li ₂ CO ₃ , Cu ₂ O, and V ₂ O ₅ were weighed at a molar ratio of 2: 1: 1 and mixed well in an agate mortar to prepare pellets of about 1 g with a diameter of 10 mm. A platinum sheet was laid on an alumina boat, and the prepared pellets were placed on the platinum sheet, fired at a temperature of 460 ° C. for 6 hours, and further fired at a temperature of 700 ° C. for 6 hours in an argon atmosphere. . After firing, the sample was gradually cooled in an electric furnace.

The obtained sample was pulverized in an agate mortar and identified by powder X-ray diffraction. As a result, it was confirmed that the obtained sample was a mixed phase in which Cu ₂ O was contained as an impurity in Li ₂ CuVO ₄ .

Li ₂ CO ₃ , Cu ₂ O, and V ₂ O ₅ were weighed at a molar ratio of 2: 1: 1 and mixed well in an agate mortar to prepare pellets having a diameter of 10 mm and about 0.2 g. A platinum sheet was laid on an alumina boat, and the produced pellets were placed on the platinum sheet and fired at 600 ° C. for 1 hour in an argon atmosphere. After firing, the sample was gradually cooled (natural cooling) in an electric furnace.

The obtained sample was pulverized in an agate mortar and identified by powder X-ray diffraction. As a result, it was confirmed that the obtained sample was a mixed phase in which Li ₂ CuVO ₄ contained LiCuVO ₄ as an impurity.

Li ₂ CO ₃ , Cu ₂ O, and V ₂ O ₅ were weighed at a molar ratio of 2: 1: 1 and mixed well in an agate mortar to prepare pellets of about 1 g with a diameter of 10 mm. A platinum sheet was laid on an alumina boat, and the prepared pellets were placed on the platinum sheet and fired at 600 ° C. for 12 hours in an argon atmosphere. After firing, the sample was taken out from an electric furnace at 600 ° C. and rapidly cooled in a room temperature environment.

The obtained sample was pulverized in an agate mortar and identified by powder X-ray diffraction. As a result, it was confirmed that the obtained sample was a mixed phase in which Cu ₂ O was contained as an impurity in Li ₂ CuVO ₄ .

Li ₂ CO ₃ , Cu ₂ O, and V ₂ O ₅ were weighed at a molar ratio of 2: 1: 1 and mixed well in an agate mortar to prepare pellets of about 1 g with a diameter of 10 mm. A platinum sheet was laid on an alumina boat, and the produced pellets were placed on the platinum sheet and fired at 600 ° C. for 1 hour in an argon atmosphere. After firing, the sample was removed from the electric furnace at 600 ° C. and immediately cooled with liquid nitrogen.

The obtained sample was pulverized in an agate mortar and identified by powder X-ray diffraction. As a result, it was confirmed that the obtained sample was a Li ₂ CuVO ₄ single phase containing no impurities.

  The Rietveld analysis result of the X-ray (copper Kα ray) diffraction of the obtained sample powder is shown in FIG. In FIG. 5, the graph of the relative intensity at the uppermost stage is a calculated value calculated based on the crystal structure shown in FIG. The Miller index hkl of each peak at 2θ ≦ 50 (degrees) is added. The horizontal axis represents an observation angle (scattering angle) 2θ with respect to incident X-rays (copper Kα rays). The X marker superimposed on the calculated value graph indicates an actual measurement value. The vertical marker of interruption in FIG. 5 indicates the position of each peak, and the lowermost graph (residual) indicates the difference between the measured value and the calculated value. From the residual in FIG. 5, it can be confirmed that the crystal structure shown in FIG. 2 is correct.

For reference, FIG. 6 shows the results of Le Bail analysis of X-ray (copper Kα-ray) diffraction of the sample obtained in Example 2 above. In FIG. 6, the upper graph, the interruption marker, and the lower graph have the same meaning as in FIG. 5. In FIG. 6, a peak due to the impurity LiCuVO ₄ is observed.

  Using each of the samples obtained in Examples 3 and 5 above, pellets having a diameter of 10 mm and about 1 g were prepared. A platinum sheet was laid on an alumina boat, and the prepared pellets were placed on the platinum sheet and fired at 600 ° C. for 12 hours in an argon atmosphere. After firing, the sample was removed from the electric furnace at 600 ° C. and immediately cooled with liquid nitrogen.

The obtained sample was pulverized in an agate mortar and identified by powder X-ray diffraction. As a result, in any of the samples, the impurity Cu ₂ O disappeared and it was confirmed that the sample was Li ₂ CuVO ₄ single phase.

Weight ratio of Li ₂ CuVO ₄ obtained in Example 6 or 7 above, acetylene black (hereinafter also referred to as AB) as a conductive material, and polytetrafluoroethylene (hereinafter also referred to as PTFE) as a binder. The mixture was mixed at 62: 30: 8, placed on an Al film, and crushed using a roller (pulverization by hand). The crushed mixture was punched into a circular shape having a diameter of 14 mm and dried in a vacuum at 130 ° C. for 12 hours to obtain a positive electrode. A lithium metal sheet punched into a circular shape with a diameter of 16 mm was used as a negative electrode, and an electrolyte solution for lithium battery in which 1 mol · dm ⁻³ of LiPF ₆ was dissolved in an organic carbonate solvent was used as an electrolyte. A CR2032-type secondary battery was fabricated in an argon gas atmosphere with a dew point controlled to -60 ° C. or lower (see FIG. 7). The produced coin-type secondary battery includes a positive electrode case 1, a negative electrode case 2, a gasket 3, a positive electrode plate 4, a negative electrode plate 5, and a separator 6. FIG. 8 shows the evaluation results of the manufactured coin-type secondary battery and battery characteristics. In FIG. 8, the vertical axis represents voltage (V) and the horizontal axis represents capacity (mAh / g).

  As shown in FIG. 8, even in the 50 hour rate measurement, the initial charge / discharge capacity was 100 mAh / g or less, and the target characteristics could not be obtained.

The Li ₂ CuVO ₄ and AB obtained in Example 6 or 7 above were mixed for about 1 hour and 30 minutes using a ball mill, and the binder PTFE was added. Was made. The weight ratio of Li ₂ CuVO ₄ , AB, and PTFE is 62: 30: 8. The results of evaluating the battery characteristics of the manufactured coin cell are shown in FIG. The vertical axis represents voltage (V), and the horizontal axis represents capacity (mAh / g).

  As shown in FIG. 9, an excellent initial capacity of 257 mAh / g at a 50 hour rate could be realized, and the usefulness of the copper-containing composite polyanionic composite oxide as a positive electrode material was shown.

From the comparison of Examples 8 and 9, since the copper-containing composite polyanion composite oxide (Li ₂ CuVO ₄ ), which is a polyanion material, is poor in electrical conductivity, the crystal grain size is reduced and the conductive material is suitable. It became clear that mixing is important for the development of electrode properties.

  The present invention has been described above by describing the embodiment. However, the above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment, and is implemented with various modifications. be able to.

DESCRIPTION OF SYMBOLS 1 Positive electrode case 2 Negative electrode case 3 Gasket 4 Positive electrode plate 5 Negative electrode plate 6 Separator

Claims (11)

It is represented by the general formula Li ₂ C uVO ₄
VO ₄ tetrahedron, which is a tetrahedron obtained by substituting a sulfur atom with an oxygen atom and a zinc atom with a vanadium atom in ZnS having a wurtzite structure ,
LiO ₄ tetrahedron which is a tetrahedron obtained by substituting sulfur atoms with oxygen atoms and zinc atoms with lithium atoms in ZnS having a wurtzite structure ,
In the ZnS of the wurtzite structure , including a CuO ₄ tetrahedron that is a tetrahedron obtained by substituting sulfur atoms with oxygen atoms and zinc atoms with copper atoms ,
The VO ₄ tetrahedron, the LiO ₄ tetrahedron, and the CuO ₄ tetrahedron are copper-containing complex polyanionic complex oxides that share an oxygen atom located at the apex . Represented by the general formula Li _2-x CuVO ₄ (0 <x <2),
VO ₄ tetrahedron, which is a tetrahedron obtained by substituting a sulfur atom with an oxygen atom and a zinc atom with a vanadium atom in ZnS having a wurtzite structure,
LiO ₄ tetrahedron which is a tetrahedron obtained by substituting sulfur atoms with oxygen atoms and zinc atoms with lithium atoms in ZnS having a wurtzite structure,
In the ZnS of the wurtzite structure, including a CuO ₄ tetrahedron that is a tetrahedron obtained by substituting sulfur atoms with oxygen atoms and zinc atoms with copper atoms,
The VO ₄ tetrahedron, the LiO ₄ tetrahedron, and the CuO ₄ tetrahedron are copper- containing complex polyanionic complex oxides that share an oxygen atom located at the apex. A method for producing a copper-containing composite polyanionic composite oxide according to claim 1 ,
A first step of mixing a Li source material, a Cu source material, and a VO ₄ source material to form a mixture such that a molar ratio of Li, Cu, and VO ₄ is 2: 1: 1 ;
A second step of causing a chemical reaction in the mixture by heating the mixture to a predetermined temperature at which the mixture does not dissolve;
A method for producing a copper-containing composite polyanionic composite oxide, comprising a third step of cooling the mixture with a low-temperature liquefied gas following the second step. The method for producing a copper-containing composite polyanion-based composite oxide according to claim 3 , wherein the second step is performed in an atmosphere that is more reducing than air. 4. The method for producing a copper-containing composite polyanion composite oxide according to claim 3 , wherein the second step is performed in an air stream of nitrogen or argon or in an atmosphere in which a reducing agent is disposed. The method for producing a copper-containing composite polyanion-based composite oxide according to any one of claims 3 to 5 , wherein the predetermined temperature is a temperature of 510 ° C or higher and 800 ° C or lower. The Li source material is Li ₂ O,
The Cu source material is CuO, and
The method for producing a copper-containing composite polyanionic composite oxide according to any one of claims 3 to 6 , wherein the VO ₄ source material is VO ₂ . The Li source material is Li ₂ CO ₃ ,
The Cu source material is Cu ₂ O, and
The method for producing a copper-containing composite polyanion-based composite oxide according to any one of claims 3 to 6 , wherein the VO ₄ source material is V ₂ O ₅ . A secondary battery including a positive electrode active material,
The positive active material, the the discharge state of the secondary battery, including a copper-containing complex polyanion-based composite oxide according to claim 1, the secondary battery. The secondary battery according to claim 9 , comprising lithium or sodium as a negative electrode active material.   The copper-containing composite polyanionic composite oxide according to claim 2 is included as a positive electrode active material,
  A secondary battery containing lithium as a negative electrode active material.

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