JP5235282B2 - Cathode active material and battery for non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a battery. More specifically, the present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a battery that can improve energy density by increasing the discharge voltage of the battery.

As secondary batteries for portable electronic devices, lithium secondary batteries have been put into practical use and are widely used. As the positive electrode active material, a layered transition metal oxide typified by LiCoO ₂ is mainly used. However, these layered transition metal oxides are prone to oxygen desorption at a relatively low temperature of about 150 ° C. in a fully charged state, which causes an oxidative exothermic reaction of the flammable electrolyte, thereby causing a thermal runaway reaction of the battery. It is a trigger.

On the other hand, by using a divalent / trivalent redox reaction instead of a trivalent / tetravalent redox reaction, the thermal stability is improved, and a hetero-element polyanion having a large electronegativity is formed around the central metal. As a system in which a high discharge voltage is ensured by arranging them, phosphates (olivine phosphate) such as olivine-type LiCoPO ₄ , LiMnPO ₄ , LiFePO ₄ have been proposed (for example, see Non-Patent Document 1). However, non-aqueous electrolyte secondary batteries that use LiCoPO ₄ as the positive electrode active material require the application of a voltage of 5 V or higher for full charge, and the oxidative decomposition of the electrolyte occurs simultaneously. There was a problem. Moreover, due to the large molecular weight of the phosphate polyanion, the theoretical capacity of a series of positive electrodes containing a series of LiMPO ₄ type olivine phosphate as the active material was only about 170 mAh / g.

Further, as a positive electrode active material similar to LiMPO ₄ type olivine phosphate, active materials such as Li ₂ FeSiO ₂ and Li ₂ MnSiO ₄ having _two lithium atoms in a unit cell have been proposed (for example, Patent Documents). 1, refer to Non-Patent Document 2).

Okada Shigeto, Arai Hajime, Yamaki Junichi, Electrochemistry and Industrial Physical Chemistry, 65, No. 10, 802-808 (1997) R. Dominko, et al., Electrochem. Commun., 8, 217 (2006). Japanese Patent Application No. 2001-266882

However, the battery proposed in the above publication has a problem that the operating potential is as low as 3.5V to 2.4V.
Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that has a theoretical capacity that is higher than that of a positive electrode containing olivine phosphate, a high operating potential, and battery characteristics that are excellent in reversible capacity density.

In order to achieve the above-described problems, the present inventors have made various improvements on olivine phosphate LiMPO ₄ . As a result, the present inventors have found that the theoretical capacity can be increased by substituting the hetero element of the phosphate polyanion PO ₄ with tetravalent silicon Si having a lower electronegativity than pentavalent phosphorus. Furthermore, the present inventors have also found that, when the charging voltage is lowered, not only the bivalent / trivalent but also the trivalent / tetravalent two-stage redox reaction can be used for charging / discharging.

Thus, according to the present invention, the general formula (Ia): Li _2-x Co _1-y M ′ _y SiO ₄ (wherein M ′ is Ni, V, Ti, x represents 0 ≦ x ≦ 2) , Y represents 0 ≦ y <1) , and a carbon component obtained by heat treatment at 300 to 500 ° C. in an inert atmosphere together with the solid solution compound. A positive electrode active material for a water electrolyte secondary battery is provided.
Furthermore, according to the present invention, the general formula (Ib): Li _2-x Mn _1-y M ″ _y SiO ₄ (where M ″ is Ni ³⁺ , Ni ⁴⁺ , Sc, Y, Zr, Nb, Mo, Ag, x represents 0 ≦ x ≦ 2, y represents 0 ≦ y <1 , and a solid solution compound at 300 to 500 ° C. in an inert atmosphere together with the solid solution compound. There is provided a positive electrode active material for a nonaqueous electrolyte secondary battery comprising a carbon component obtained by heat treatment .
According to the present invention, the general formula (II): Li _2-x Co _1-y Mn _y SiO ₄ (wherein x represents 0 ≦ x ≦ 2 and y represents 0 ≦ y <1) And a carbon component obtained by heat treatment at 300 to 500 ° C. in an inert atmosphere together with the solid solution compound. Is done.

Furthermore, according to the present invention, it is represented by the general formula (I): Li _2-X MSiO ₄ (wherein M represents a transition metal containing at least Co or Mn, and X represents 0 ≦ X ≦ 2). For a non-aqueous electrolyte secondary battery containing the solid solution compound and a carbon component derived from the carbon material by heat-treating a mixture containing the solid solution compound and the carbon material at 300 to 500 ° C. in an inert atmosphere. There is provided a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by producing a positive electrode active material.
Moreover, according to this invention, the nonaqueous electrolyte secondary battery provided with the positive electrode containing the said positive electrode active material is provided.

According to the present invention, it is possible to provide a highly safe non-aqueous electrolyte secondary battery with high capacity and high practicality. Moreover, the positive electrode active material and positive electrode for said secondary batteries can be provided.
Further, by partially substituting Co with a transition metal such as Ni, Mn, or Fe (particularly Mn), the discharge voltage can be continuously translated from a high voltage to a low voltage. Therefore, it is possible to freely design a secondary battery having a charge / discharge voltage optimum for the circuit used and the electrolyte used.
The secondary battery of the present invention can also be used for large batteries.

Hereinafter, the present invention will be described in more detail. Hereinafter, the positive electrode active material for a nonaqueous electrolyte secondary battery is referred to as a positive electrode active material, the positive electrode for a nonaqueous electrolyte secondary battery is referred to as a positive electrode, and the nonaqueous electrolyte secondary battery is referred to as a secondary battery. (1) Positive electrode active material The positive electrode active material includes general formula (I): Li _2-x MSiO ₄ (general formula (Ia): Li _2-x Co _1-y M ' _y SiO ₄ , general formula (Ib) : Li _2-x Mn _1-y M ″ _y SiO ₄ ) , which contains a solid solution compound called olivine silicate. M is a transition metal containing at least Co or Mn, and may be Co alone or Mn alone, but may be a mixture of Co and Mn, or a mixture of other transition metals other than Co and Mn. . Other transition metals include Fe, V, Ti, Ni and the like. In particular, when Co is contained in M, the operating potential can be increased, and as a result, the energy density can be improved. M ′ is Ni, V or Ti, and M ″ is Ni ³⁺ , Ni ⁴⁺ , Sc, Y, Zr, Nb, Mo or Ag.

  X is arbitrarily selected from the range of 0 ≦ X ≦ 2. Usually, a compound with X = 2 is synthesized to have an initial composition. Further, in the case of X = 2, immediately after the secondary battery is assembled, it can be started from discharging, so that there is an advantage that charging is unnecessary.

The basic skeleton of Li ₂ MSiO ₄ is shown in FIG. As shown in FIG. 1, Li ₂ MSiO ₄ has orthorhombic crystal symmetry and has a crystal structure similar to Li ₃ PO ₄ . In the figure, circles indicate lithium, and tetrahedrons indicate SiO ₄ and MO ₄ , respectively. Specifically, Li ₂ MSiO ₄ has an isolated structure in which the central metal M is surrounded by SiO ₄ (silicate group).
Further, the positive electrode active material is represented by the general formula (II): Li _2−X Co _1−y Mn _y SiO ₄ (wherein X represents 0 ≦ X ≦ 2 and Y represents 0 ≦ Y ≦ 1). It is preferable that it is a solid solution compound represented. By substituting a part of Co with inexpensive Mn, a low-cost positive electrode active material can be provided.

The Li ₂ MSiO ₄ can be synthesized by various synthesis methods, but a normal solid phase synthesis method as shown in the following examples (that is, firing a mixture of respective oxides of Li, M, and Si) (Method) can also be mass-produced.
The shape of the positive electrode active material is not particularly limited, but is preferably granular. Specifically, a granular material having an average particle diameter of 0.1 to 100 μm is preferable. This average particle diameter is a value measured by a laser diffraction / scattering method.

Next, the positive electrode active material preferably contains a carbon component. The carbon component has the general formula _{(I): Li 2-X} MSiO 4 or the general formula (II): heat treatment in an inert atmosphere with _{Li 2-X Co 1-y} Mn y solid solution compound represented by SiO ₄ This is a carbon component obtained. This carbon component is usually present so as to coat the surface of the solid solution compound. By providing the carbon component, the conductivity of the positive electrode active material can be improved.

  The weight ratio between the solid solution compound and the carbon component is preferably in the range of 1: 0.01 to 0.50. If it exceeds 0.25, the increase in the remaining amount of carbon after annealing is not preferable because the volume fraction of the solid solution compound in the positive electrode is lowered and the energy density of the battery is lowered. When it is less than 0.05, the reducing ability is lowered, and it is difficult to obtain the effect of improving the conductivity. A more preferred weight ratio is in the range of 1: 0.05 to 0.25.

  The method for forming the carbon component is not particularly limited, and any known method can be used. For example, the carbon component can be obtained from the attached carbon material by mechanically mixing the solid solution compound and the carbon material to attach the carbon material to the surface of the solid solution compound and then performing heat treatment in an inert atmosphere. . Here, examples of the mechanical mixing method include a method using a dry planetary mill. The heat treatment is preferably performed at 300 to 500 ° C. for 1 to 12 hours (for example, around 500 ° C. for about 1 hour). Furthermore, the inert atmosphere means an inert gas atmosphere that has little reactivity with the solid solution compound and the carbon material, and examples of such an inert gas include helium, argon, nitrogen, and the like.

(2) Positive electrode The positive electrode may consist of only the said positive electrode active material, and may contain the other additive as needed. Examples of other additives include a binder and a conductive agent.
The binder is not particularly limited, and any known agent can be used. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc. Can be mentioned.

The conductive agent is not particularly limited, and any known agent can be used. Specific examples include acetylene black, carbon, graphite, natural graphite, artificial graphite, and needle coke.
The positive electrode preferably has a thickness of 1 to 1000 μm, more preferably about 10 to 200 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease.
The positive electrode may be consolidated by a roller press or the like in order to increase the packing density of the active material.

The method for producing the positive electrode is not particularly limited, and any known method can be used. For example, after mixing the positive electrode active material with a binder and a conductive material as necessary, a method of pressure-bonding the obtained mixture on a stainless steel support, filling the mixture into a metal container It can obtain by the method of doing. As another method, for example, the above mixture is mixed with an organic solvent (for example, N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropyl). (Amine, ethylene oxide, tetrahydrofuran, etc.) to obtain a slurry, and the positive electrode can also be produced by a method of applying and drying this slurry on a metal substrate such as aluminum, nickel, stainless steel, copper or the like.
The positive electrode active material may be a known positive electrode active material (for example, LiCoO ₂ , LiCoPO ₄ , LiMnPO ₄ , LiFePO ₄ , Li ₂ FeSiO ₂ , Li ₂ MnSiO _4, etc.) as long as the object of the present invention is not impaired. Further, it may be included.

(3) Secondary battery The secondary battery can use the components in a known nonaqueous electrolyte secondary battery except that the positive electrode and the nonaqueous electrolyte are used. A secondary battery usually comprises a positive electrode, a negative electrode, and a nonaqueous electrolyte between both electrodes.
The negative electrode contains a negative electrode active material. As the negative electrode active material, a known negative electrode active material can be used. As a negative electrode active material, it is possible to occlude and release lithium metal ions in addition to carbon materials such as graphite and carbon black, lithium metal, or alloys of lithium and other metals (for example, aluminum-lithium alloys). The material (for example, Li _2.5 Co _0.5 N, Li ₄ Ti ₅ O ₁₂ or the like) is raised.

  The negative electrode may be produced by a known method, and for example, it can be produced in the same manner as the positive electrode. For example, after the negative electrode active material is mixed with the binder and the conductive material described in the column of the positive electrode as necessary, the obtained mixture is placed on a stainless steel or copper support (current collector). It can be obtained by a method of pressure forming. As another method, for example, the negative electrode can be produced by a method in which the mixture is mixed with an organic solvent described in the column of the positive electrode to obtain a slurry, and this slurry is applied to a metal substrate such as copper and dried.

  The non-aqueous electrolyte usually contains an electrolyte and a non-aqueous solvent. The non-aqueous solvent is not particularly limited. For example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides, phosphorus Examples include acid ester compounds. Typical examples of these include 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, Examples include sulfolane, methyl sulfolane, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, trimethyl phosphate, and triethyl phosphate. . These can be used alone or in combination of two or more.

The non-aqueous electrolyte may include an electrolyte capable of performing migration for causing the lithium metal ion in the negative electrode active material to electrochemically react with the positive electrode active material or the positive electrode active material and the negative electrode active material in the solvent. Good. 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, LiN ( _{SO 2 CF 3) 2, LiN} (SO 2 C 2 F 5) 2, LiC (SO 2 CF 3) 3, LiN (SO 3 CF 3) 2 and the like. A known solid electrolyte such as LiTi ₂ (PO ₄ ) ₃ having a NASICON structure can also be used.

  Other constituent members (for example, a separator, a battery case, etc.) may be included in the secondary battery of the present invention. As the other constituent members, any of those used in known nonaqueous electrolyte secondary batteries can be used.

  For example, a separator may be used between the positive electrode and the negative electrode. In this case, it is preferable to use a microporous polymer film. Specifically, a separator made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, or polybutene can be used. The separator is preferably made of polyolefin from the viewpoint of chemical and electrochemical stability, and is preferably made of polyethylene from the viewpoint of the self-closing temperature, which is one of the purposes of the battery separator.

When a separator consists of polyethylene, it is preferable that it is ultra high molecular weight polyethylene from the point of high temperature shape maintenance property. The lower limit of the molecular weight of this polyethylene is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. If the molecular weight is too large, the pores of the separator may not close when heated due to low fluidity. The molecular weight here means a number average molecular weight measured by a chromatography method.
What is necessary is just to assemble a battery according to a well-known method using the said structural member. The shape of the battery is not particularly limited, and various shapes and sizes such as a cylindrical shape, a square shape, and a coin shape can be appropriately employed.

(4) Battery Charging / Discharging Method In the present invention, the bivalent / trivalent oxidation-reduction reaction of the transition metal M in the positive electrode active material (Li _2-X MSiO ₄ ), and the trivalent / tetravalent oxidation-reduction. The secondary battery can be charged and discharged using the reaction. Conventional positive electrode active materials such as olivine phosphate (LiMPO ₄ etc.) can only use trivalent / divalent oxidation-reduction reactions. On the other hand, in the present invention, by introducing a silicate polyanion, not only a bivalent / trivalent but also a trivalent / tetravalent oxidation-reduction reaction can be used, and the charge / discharge capacity can be increased accordingly.

Furthermore, there is an advantage that the capacity can be designed freely by adjusting the amount of the transition metal that is stably present even if it is tetravalent. For example, the capacity between 3.5V and 2.5V can be freely designed by changing the blending ratio of the transition metal that is stably present even if M is tetravalent such as V or Ti.
In the present invention, a tetravalent / trivalent oxidation-reduction reaction and a trivalent / divalent oxidation-reduction reaction of a transition metal such as Co or Ni that is stably present even in a tetravalent state during charging / discharging of a non-aqueous secondary battery. Is preferably used.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, the battery was manufactured and measured in a dry box under an argon atmosphere.
FIG. 2 is a cross-sectional view of a coin-type battery, which is a specific example of the battery manufactured in Examples and Comparative Examples. In the figure, 1 is a sealing plate, 2 is a gasket, 3 is a positive electrode case, 4 is a negative electrode, and 5 is a negative electrode. A separator 6 represents a positive electrode material mixture pellet.

Example 1
The _{Li 2 Co 1-y Mn y} SiO 4 is synthesized by the following method as a solid solution compound for the cathode active material.
First, the starting material is Li ₂ CO ₃ as a lithium source, Co ₃ O ₄ as a cobalt source, MnC ₂ O ₄ · 2H ₂ O as a manganese source, and silicon dioxide SiO ₂ as a silicic acid source. : Co + Mn: Si = 2: 1: 1). The resulting mixture in the air, 12 hours later calcined at 650 ° C., by performing two times the firing for 24 hours at 1100 ° C., the single-phase _{Li 2 Co 1-y Mn y} SiO 4 powder (average particle A solid solution compound having a diameter of 50 μm) was synthesized.
In addition, five kinds of solid solution compounds of y = 0, y = 0.25, y = 0.5, y = 0.75, and y = 1.0 are synthesized, and are designated as solid solution compounds a1, a2, a3, a4, and a5, respectively.

FIG. 3 shows an X-ray diffraction pattern of the obtained solid solution compound a1, and FIG. 4 shows an X-ray diffraction pattern of the solid solution compound a5. 3 and 4, a slight impurity peak was mixed in the vicinity of 2θ = 36 ° after the first firing, but a complete single phase was obtained after the second firing. The powder X-ray diffraction pattern and the lattice constant (Table 1) shown in FIG. 3 agreed well with the literature values (IC D D No. 24-611), and were identified as orthorhombic crystals of the crystal group P mn b.

Example 2
Into a zirconia pot of an 80 ml planetary ball mill, 10 g of zirconia balls, a mixture of the solid solution compound a1 obtained in Example 1 and acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) in a weight ratio of 70:25 is added. And sealed. Thereafter, the sealed pot was set on a planetary ball mill manufactured by FRITSCH and operated at 200 rpm for 24 hours to perform dry mixing. In this way, a positive electrode active material in which the surface of the solid solution compound was coated with a carbon component was obtained. This positive electrode active material is designated as b1.

  Next, the positive electrode active material b1 was annealed at 300 ° C., 500 ° C., and 700 ° C. for 1 hour in an argon stream. Samples obtained in accordance with the annealing temperature are referred to as positive electrode active materials b1c, b1d, and b1e, respectively. The X-ray diffraction patterns of these samples are shown in FIG.

In the case of after annealing and before annealing, the original peak of Li ₂ CoSiO ₄ was hardly seen because carbon was coated around. In the positive electrode active material b1c after annealing at 300 ° C., peak recovery was observed. However, at 500 ° C, the peak of Co metal precipitated due to the reduction action of carbon begins to be observed, and in the positive electrode active material b1e annealed at 700 ° C, the peak of Li ₂ CoSiO ₄ disappears and the peak of only Co and Li ₂ SiO ₃ Was observed.

  Also for the solid solution compound a5, the surface was coated with a carbon component in the same procedure as above to obtain a positive electrode active material b5, and the obtained positive electrode active material b5 was heated at 300 ° C., 500 ° C., and 700 ° C. in an argon stream. Annealed for 1 hour. Samples obtained in accordance with the annealing temperature are referred to as positive electrode active materials b5c, b5d, and b5e, respectively. The X-ray diffraction results of these samples are shown in FIG.

In the case of after annealing and before annealing, the original peak of Li ₂ MnSiO ₄ was hardly seen because carbon was coated around. In the positive electrode active material b5c after annealing at 300 ° C., the peak recovery was insufficient, whereas the peak of Li ₂ MnSiO ₄ recovered as the annealing temperature increased to 500 ° C. and 700 ° C. Further, the peak of Co or Li ₂ SiO ₃ due to carbon reduction observed in the argon annealing treatment of the positive electrode active material b1c was not observed in the case of Li ₂ MnSiO ₄ .

Example 3
Next, the surface of each of the solid solution compounds a1, a2, a3, a4, and a5 was coated with a carbon component in the same procedure as in Example 2 to obtain positive electrode active materials b1, b2, b3, b4, and b5. Annealing treatment was performed in the same procedure as in Example 2, except that the positive electrode active materials b1 to b3 were set to 300 ° C., and b4 and b5 were set to 500 ° C. The positive electrode active materials after the annealing treatment are designated as c1, c2, c3, c4, and c5, respectively.
Each of the positive electrode active materials b1 to b5 and c1 to c5 was mixed with a binder (polytetrafluoroethylene) at a weight ratio of 95: 5. Ten kinds of positive electrode mixture pellets 6 (thickness 0.5 mm, diameter 15 mm) were obtained by roll-forming the obtained mixture.

Next, a metal lithium negative electrode 4 placed under pressure on a stainless steel sealing plate 1 was inserted into a recess of a polypropylene gasket 2. On the negative electrode 4, a polypropylene-made microporous separator (Celguard manufactured by Cellguard) 5 and a positive electrode mixture pellet 6 were arranged in this order. Next, as an electrolytic solution, an appropriate amount of 1N solution in which LiPF ₆ was dissolved in a 1: 1 mixed solvent of ethylene carbonate and dimethyl carbonate was injected and impregnated. Thereafter, a coin-type lithium battery having a thickness of 2 mm and a diameter of 23 mm shown in FIG. 2 was produced by covering with a positive electrode case 3 made of stainless steel.

Table 2 shows the discharge capacities of the coin-type lithium batteries using the positive electrode active materials b1 to b5 and c1 to c5. In addition, FIGS. 7, 8, 9, and 10 show charge and discharge curves at room temperature of the coin-type lithium battery using the positive electrode active materials b1, c1, b5, and c5. The current density was 0.2 mA / cm ² for both charging and discharging, switching from constant current charging to constant voltage charging mode at 4.5 V, and the cycle reversibility was measured with the discharge end voltage being 2 V.

From Table 2 and FIGS. 7 and 9, it can be seen that the number of batteries using the positive electrode active materials b1 to b5 that are only coated with a carbon component has a small discharge capacity.
Further, from Table 2, FIGS. 8 and 10, the battery using the positive electrode active materials c1 to c5 subjected to the argon annealing treatment has a discharge capacity of about 60 to 130 mAh / g. Therefore, it can be seen that the discharge capacity is greatly improved by the argon annealing treatment.

The crystal structure of Li ₂ MSiO ₄ is shown. 1 shows a schematic cross-sectional view of a coin-type battery. _{2 is} an X-ray diffraction pattern of Li ₂ CoSiO ₄ (a1) in Example 1. FIG. _{2 is} an X-ray diffraction pattern of Li ₂ MnSiO ₄ (a5) in Example 1. FIG. 3 is an X-ray diffraction pattern of positive electrode active materials b1, b1c, b1d, and b1e of Example 2. FIG. 3 is an X-ray diffraction pattern of positive electrode active materials b5, b5c, b5d, and b5e of Example 2. FIG. FIG. 4 is a charge / discharge curve diagram of a battery using the positive electrode active material b1 of Example 3. 4 is a charge / discharge curve diagram of a battery using the positive electrode active material c1 of Example 3. FIG. 6 is a charge / discharge curve diagram of a battery using the positive electrode active material b5 of Example 3. FIG. 4 is a charge / discharge curve diagram of a battery using a positive electrode active material c5 of Example 3. FIG.

Explanation of symbols

1 Sealing plate 2 Gasket 3 Positive electrode case 4 Negative electrode 5 Separator 6 Positive electrode mixture pellet

Claims (5)

General formula (Ia): Li _2-x Co _1-y M ′ _y SiO ₄ (wherein M ′ is Ni, V, Ti, x represents 0 ≦ x ≦ 2, y represents 0 ≦ y < and solid solution compounds represented 1 are expressed), for a non-aqueous electrolyte secondary battery you; and a carbon component obtained by the heat treatment at 300 to 500 ° C. in an inert atmosphere together with the solid solution compound Positive electrode active material. General formula (Ib): Li _2-x Mn _1-y M ″ _y SiO ₄ (where M ″ is Ni ³⁺ , Ni ⁴⁺ , Sc, Y, Zr, Nb, Mo, Ag, x represents 0 ≦ x ≦ 2 and y represents 0 ≦ y <1), and a carbon component obtained by heat treatment at 300 to 500 ° C. in an inert atmosphere together with the solid solution compound positive electrode active material for non-aqueous electrolyte secondary battery you comprising and. A solid solution compound represented by the general formula (II): Li _2-x Co _1-y Mn _y SiO ₄ (wherein x represents 0 ≦ x ≦ 2 and y represents 0 ≦ y <1); positive electrode active material for non-aqueous electrolyte secondary battery you; and a carbon component obtained by the heat treatment at 300 to 500 ° C. in an inert atmosphere together with the solid solution compound. A solid solution compound represented by the general formula (I): Li _2-x MSiO ₄ (wherein M represents a transition metal containing at least Co or Mn, and x represents 0 ≦ x ≦ 2), a carbon material, Producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing the solid solution compound and a carbon component derived from the carbon material by heat-treating the mixture containing the carbon material at 300 to 500 ° C. in an inert atmosphere. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. Non-aqueous electrolyte secondary battery, comprising a positive electrode containing a positive electrode active material according to any one of claims 1-3.