JP2010135305A - Positive electrode material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical active material consisting of lithium manganese phosphate with a high electron conductivity, and a nonaqueous electrolyte secondary battery having a high capacity upon discharging. <P>SOLUTION: The electrochemical active material consisting of lithium manganese phosphate with a surface on which a nickel compound or an iron compound is arranged has carbon arranged on the nickel compound or the iron compound. Thereby, Ni or Fe shows a catalytic action to the decomposition carbonization reaction of an organic material which becomes a carbon source. Thus, carbon coating on the lithium manganese phosphate is carried out suitably. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a positive electrode material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery including the same.

  In recent years, non-aqueous electrolyte secondary batteries having high energy density and excellent cycle characteristics have attracted attention as power sources for portable devices such as mobile phones and notebook computers and electric vehicles. Among such non-aqueous electrolyte secondary batteries, the most widely on the market at present is for small-sized consumer use mainly for mobile phones of 2 Ah or less.

At present, there are many positive electrode active materials for non-aqueous electrolyte secondary batteries, but the most commonly known positive electrode active materials are lithium cobaltate (LiCoO ₂ ) and nickel acid having an operating voltage of around 4V. It is a lithium-containing transition metal oxide based on lithium (LiNiO ₂ ), lithium manganate having a spinel structure (LiMn ₂ O ₄ ), or the like. Among them, lithium cobaltate is widely adopted as a positive electrode active material because of its excellent charge / discharge characteristics and energy density in a small capacity lithium secondary battery up to a battery capacity of 2 Ah.

  However, considering the future development of medium-sized and large-sized products, especially industrial applications where large demand is expected, the safety of batteries is very important. I can't be satisfied. One of the causes is that the thermal stability of these positive electrode active materials is low.

  Therefore, recently, lithium iron phosphate having an olivine structure with high thermal stability has attracted attention as a positive electrode active material. In this lithium iron phosphate, phosphorus and oxygen are covalently bonded, so that oxygen is not released even at high temperatures, and the safety of the battery can be drastically improved by using it as a positive electrode active material.

  In order to improve the electronic conductivity of the lithium iron phosphate material, Patent Documents 1 to 7 disclose techniques for supporting carbon on the particle surface.

In Patent Document 1, orchid steel (Fe ₃ (PO ₄ ) ₂ · 8H ₂ O) and lithium orthophosphate (Li ₃ PO ₄ ) are mixed, and the mixture atmosphere is 350 to 700 ° C. in a mixture atmosphere of 1% propene in nitrogen. A technique for heating to obtain lithium iron phosphate (LiFePO ₄ ) coated with a carbonaceous deposit is disclosed (see example 2 in paragraph 0043).

In Patent Document 2, Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ · 8H ₂ O are mixed, acetylene black powder is added to form a mixture, milled using a planetary ball mill, and then fired at 600 ° C. Thus, a method for obtaining a LiFePO ₄ / carbon composite is disclosed.

In Patent Document 3, a lithium compound, an iron compound, a phosphorus-containing ammonium salt, and carbon black as a carbon material fine particle are mixed to form a mixture, and this mixture is fired at a temperature of 600 to 750 ° C. A method for producing a carbon-containing lithium iron composite oxide for a positive electrode material for a lithium secondary battery in which carbon material fine particles are combined with particles of a composite oxide (LiFePO ₄ ) is disclosed.

In Patent Document 4, ferrous phosphate hydrate (Fe ₃ (PO ₄ ) ₂ · 8H ₂ O), lithium phosphate (Li ₃ PO ₄ ), and ketjen black as a conductive carbon material are mixed, and this mixture the specific volume was pulverized with a dry is obtained the following reaction precursor 1.5 ml / g, coated with crushed particles the surface of LiFePO ₄ by firing the reaction precursor with a conductive carbon material, LiFePO ₄ Discloses a method for producing a lithium iron-phosphorus-based composite oxide carbon composite obtained by coating the particle surface with a conductive carbon material.

In Patent Document 5 and Patent Document 6, LiMPO is prepared by mixing an element M source, a lithium compound, and a compound serving as a P source, and thermally decomposing the carbon source in the presence of a conductive carbon source composed of a furfuryl alcohol polymer. _A method for synthesizing a positive electrode material in which a core consisting of ₄ is coated with carbon is disclosed.

Patent Document 7 discloses a method for supporting carbon in LiFePO ₄ powder by introducing a nitrogen stream containing vaporized methanol into a 600 ° C. firing furnace. Further, Example 2 of Patent Document 7 discloses a method of obtaining LiFePO ₄ powder by synthesizing a LiFePO ₄ precursor from a raw material aqueous solution containing ascorbic acid by a hydrothermal method and then heat-treating the LiFePO ₄ precursor. .
JP 2001-015111 A JP 2002-117833 A JP 2003-034534 A JP 2003-292308 A Japanese translation of PCT publication No. 2004-509058 JP-T-2004-509447 However, since the lithium insertion potential of lithium iron phosphate is as low as 3.4 V (vs. Li / Li +), the energy density of the non-aqueous electrolyte secondary battery equipped with it is increased. Can not do it.

On the other hand, lithium manganese phosphate is known as a material having the same olivine structure as lithium iron phosphate. Lithium manganese phosphate has a theoretical capacity of 170 mAh / g and a lithium insertion potential of about 4 V (vs. Li / Li ⁺ ), which is noble compared to lithium iron phosphate. There is a possibility that the energy density of the secondary battery can be increased.

  However, the positive electrode material containing lithium manganese phosphate has a problem that its electronic conductivity is much lower than that of lithium iron phosphate, and only a small discharge capacity can be obtained.

  Therefore, it is conceivable to apply a carbon coat to the particle surface by applying the methods disclosed in Patent Documents 1 to 7 to lithium manganese phosphate. However, there is a problem that even if the methods disclosed in Patent Documents 1 to 7 are applied to lithium manganese phosphate, the expected effect cannot be obtained. This problem is much lower than the expected problem because the electronic conductivity of lithium manganese phosphate itself is lower than that of lithium iron phosphate itself. It was recognized as a problem that was perceived as if carbon was not coated. In other words, the problem that the present invention intends to solve is that the surface of the particles cannot be coated with carbon is peculiar to lithium manganese phosphate, and in lithium iron phosphate, the problem to be solved by the present invention is not exist.

  Nevertheless, in the hydrothermal synthesis method as described in Example 2 of Patent Document 7, ascorbic acid in the solution can be carbonized at the time of subsequent firing, so that lithium manganese phosphate is synthesized by the hydrothermal synthesis method. In this case, it can be said that there is no possibility that carbon derived from ascorbic acid is arranged on the particle surface. However, in the case of synthesizing lithium manganese phosphate by the solid phase method without adopting the hydrothermal method, the above problem cannot be avoided at least.

  The present invention has been made in view of the above problems, and has positive electrode for a non-aqueous electrolyte secondary battery in which carbon is supported on base particles made of lithium manganese phosphate, electron conductivity is increased, and discharge capacity is large. It is an object of the present invention to provide a material, a positive electrode for a nonaqueous electrolyte secondary battery including the material, and a nonaqueous electrolyte secondary battery including the material.

  The present invention is a positive electrode material for a non-aqueous electrolyte secondary battery comprising carbon on the surface of base particles made of lithium manganese phosphate, wherein the base particles are made of nickel element or the surface of the base particles. A positive electrode material for a non-aqueous electrolyte secondary battery, characterized in that an iron element is present.

  Moreover, this invention is a positive electrode for nonaqueous electrolyte secondary batteries provided with the said positive electrode material for nonaqueous electrolyte secondary batteries.

  The present invention also provides a nonaqueous electrolyte secondary battery comprising the positive electrode material for a nonaqueous electrolyte secondary battery.

  Moreover, it is preferable that the transition metal contained in the base particle has an element ratio of nickel of 3% or less.

The lithium manganese phosphate referred to in the present specification includes LiMnPO ₄ , specifically, the basic composition is LiMn _1-x MPO ₄ (M is a transition metal element other than Mn, 0 ≦ x ≦ 0.1). The present invention can be applied to the present invention without any limitation. Further, the polyanion portion is not limited to only PO ₄ but may be partially combined with SiO _4, and such a component is also included in the scope of the present invention.

  If the positive electrode material of the present invention is used, a battery having a large capacity during discharging can be provided.

  The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention includes a nickel compound or an iron compound on the surface of the base particles made of lithium manganese phosphate, and further includes carbon on the nickel compound or the iron compound. It is a feature.

  Although the manufacturing method of the positive electrode material of this invention is illustrated below, this invention is not limited to the form.

  The positive electrode material for a non-aqueous electrolyte secondary battery of the present invention is a mixture obtained by immersing base particles made of lithium manganese phosphate in an aqueous solution containing nickel ions or iron ions, and then drying the solution. It can be produced by supporting carbon.

  Examples of aqueous solutions containing nickel ions or iron ions that can be applied to the present invention include, but are not limited to, nickel acetate aqueous solutions, iron oxalate aqueous solutions, nickel sulfate aqueous solutions, and iron sulfate aqueous solutions.

  The solution concentration is preferably in the range of 0.01 to 50%. When the concentration is less than 0.01%, the time for supporting the nickel compound or iron compound on the surface of the base particles made of lithium manganese phosphate becomes very long, which is not industrial. Further, if the concentration is higher than 50%, the supported nickel compound or iron compound may be non-uniform.

  In addition to the above-described method of supporting nickel or iron only on the surface of the base material particle, or in place of the above-described method of supporting nickel or iron only on the surface of the base material particle, the base of lithium manganese phosphate A method of mixing nickel element or iron element as a raw material when synthesizing the material particles itself may be adopted, and if this method is adopted, it is preferable in that it is not necessary to provide the supporting step independently. .

  The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention has secondary particles formed by agglomeration of primary particles of lithium manganese phosphate. The primary particle of lithium manganese oxide.

  The method of supporting carbon that can be applied to the present invention is not limited, but is obtained by heat-treating polymer organic material and base particles made of lithium manganese phosphate supporting nickel compound or iron compound. Can do. The heat treatment temperature needs to be equal to or higher than the temperature at which the polymer organic substance is thermally decomposed, and is preferably equal to or lower than the temperature at which particle growth of the base particles made of lithium manganese phosphate occurs. Examples of the organic polymer include sucrose and polyvinyl alcohol.

  In the positive electrode material for a non-aqueous electrolyte secondary battery of the present invention in which carbon is supported, the ratio of the mass of carbon to the mass of the base particles made of lithium manganese phosphate is preferably 0.01 to 30%. If this proportion is less than 0.01%, the amount of carbon is too small and the effect of increasing the electron conductivity is not seen. Moreover, when larger than 30%, the ratio of the base material particle | grains which consist of lithium manganese phosphate becomes relatively small, and when using it for a battery, an energy density becomes small.

  Furthermore, the form of the nonaqueous electrolyte secondary battery by this invention is shown. The non-aqueous electrolyte secondary battery of the present invention is composed of a positive electrode including a positive electrode material manufactured by the above manufacturing method, a negative electrode including a negative electrode material, and a non-aqueous electrolyte containing an electrolyte salt in a non-aqueous solvent. In general, a separator is sandwiched between a positive electrode and a negative electrode, and stacked or wound to form an electrode group, and an outer package for packaging the electrode group is provided.

  As the nonaqueous electrolyte, those generally proposed for use in nonaqueous electrolyte secondary batteries and the like can be used. Non-aqueous solvents include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and chloroethylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like. Chain carbonates; chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxy Ethers such as ethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof alone or a mixture of two or more of them However, the present invention is not limited to these.

Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF _3). ) (SO ₂ C ₄ F ₉ ), LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN, etc. These ionic compounds can be used alone or in admixture of two or more. Among these ionic compounds, LiN (SO ₂ C ₂ F ₅ ) ₂ is desirable because it is excellent in high-temperature stability and can suppress corrosion of the aluminum current collector and terminals during charging.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.5 mol / l to 5 mol / l, and more preferably 1 mol / l to 2.mol in order to reliably obtain a non-aqueous electrolyte battery having excellent battery characteristics. 5 mol / l.

Negative electrode materials include lithium metal, lithium alloys (lithium metal-containing alloys such as lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), and lithium Examples include releasable alloys, carbon materials (eg, graphite, hard carbon, low-temperature calcined carbon, amorphous carbon, etc.), metal oxides, lithium metal oxides (eg, Li ₄ Ti ₅ O ₁₂ ), and polyphosphate compounds. .

  Among these, graphite is preferable as a negative electrode material because it has an operating potential very close to that of metallic lithium and can realize charge and discharge at a high operating voltage. For example, artificial graphite and natural graphite are preferable.

In particular, graphite in which the surface of the negative electrode active material particles is modified with amorphous carbon or the like is desirable because it generates less gas during charging. Li ₄ Ti ₅ O ₁₂ is preferable as a negative electrode material because it can reduce self-discharge and reduce irreversible capacity in charge and discharge when a lithium salt is employed as an electrolyte salt.

  It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 50 μm or less from the viewpoint of electron conductivity. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used.

  For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as ethanol can also be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler Etc. may be contained as other constituents.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite (such as scale-like graphite, scale-like graphite, earth-like graphite), artificial graphite, carbon black, acetylene black, A conductive material such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one type or a mixture thereof. . Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability.

  The addition amount of the conductive agent is preferably 0.1% by mass to 50% by mass, and particularly preferably 0.5% by mass to 30% by mass with respect to the total mass of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced.

  These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by mass, particularly preferably 2 to 30% by mass with respect to the total mass of the positive electrode or the negative electrode.

  As said thickener, polysaccharides, such as carboxymethylcellulose and methylcellulose, can be normally used as a 1 type, or 2 or more types of mixture. Moreover, it is desirable that the thickener having a functional group that reacts with lithium, such as a polysaccharide, be deactivated by, for example, methylation. The addition amount of the thickener is preferably 0.5 to 10% by mass, particularly preferably 1 to 2% by mass with respect to the total mass of the positive electrode or the negative electrode.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by mass or less with respect to the total mass of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the active material, the conductive agent and the binder in an organic solvent such as N-methylpyrrolidone and toluene, and then applying the obtained mixed solution onto the current collector described in detail below. Then, it is preferably produced by drying.

  As for the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc., but it is not limited to these. It is not something.

  The current collector may be anything as long as it is an electronic conductor that does not adversely affect the constructed battery, and the following materials can be used. The surface of these materials can be oxidized.

  In addition to aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., the positive electrode current collector includes aluminum and copper for the purpose of improving adhesiveness, conductivity and oxidation resistance. A material obtained by treating the surface such as carbon, nickel, titanium, silver, or the like can be used.

  In addition to copper, nickel, iron, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., the negative electrode current collector is adhesive, conductive, anti-reduction For the purpose of the property, the thing which processed the surface of copper etc. with carbon, nickel, titanium, silver, etc. can be used.

  Regarding the shape of the current collector, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foamed body, a formed body of fiber groups, and the like are used in addition to the foil shape. Although there is no particular limitation on the thickness, a thickness of 1 to 500 μm is used.

  Among these current collectors, an aluminum foil having excellent oxidation resistance is used as the positive electrode, and a copper foil, nickel foil, iron foil, and the like that are excellent in reduction resistance and conductivity as the negative electrode. It is preferable to use an alloy foil containing a part of the above.

  Furthermore, a foil having a rough surface surface roughness of 0.2 μmRa or more is preferable, whereby the adhesion between the positive electrode active material or the negative electrode material and the current collector is excellent. Therefore, it is preferable to use an electrolytic foil because it has such a rough surface. In particular, an electrolytic foil that has been subjected to a cracking treatment is most preferable. Furthermore, when the double-sided coating is applied to the foil, it is desirable that the surface roughness of the foil is the same or nearly equal.

  As the separator for a nonaqueous electrolyte battery, it is preferable to use a porous film or a nonwoven fabric exhibiting excellent rate characteristics alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the non-aqueous electrolyte battery separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics. The separator for a nonaqueous electrolyte battery may use a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte.

  Further, when the separator for a non-aqueous electrolyte battery is used in combination with the above-described porous film, nonwoven fabric or the like and a polymer gel, it is desirable because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an active ray such as an electron beam (EB).

  For the purpose of controlling strength and physical properties, the solvophilic polymer can be used by blending a physical property modifier in a range that does not interfere with the formation of a crosslinked product. Examples of the physical property modifier include inorganic fillers (metal oxides such as silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide and iron oxide, and metal carbonates such as calcium carbonate and magnesium carbonate). And polymers (polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc.) and the like. The amount of the physical property modifier added is usually 50% by mass or less, preferably 20% by mass or less, based on the crosslinkable monomer.

  The nonaqueous electrolyte battery according to the present invention is prepared by injecting an electrolyte before or after laminating a separator for a nonaqueous electrolyte battery, a positive electrode, and a negative electrode, and finally sealing with an exterior material. Produced suitably. Further, in a non-aqueous electrolyte battery in which a power generation element in which a positive electrode and a negative electrode are laminated via a separator for a non-aqueous electrolyte battery is wound, the electrolyte is injected into the power generation element before and after the winding. Is preferred. As the injection method, it is possible to inject at normal pressure, but a vacuum impregnation method and a pressure impregnation method can also be used.

  Examples of the material of the outer package of the lithium secondary battery include nickel-plated iron, stainless steel, aluminum, and a metal resin composite film. The configuration of the lithium secondary battery is not particularly limited, and a coin battery or button battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery having a positive electrode, a negative electrode, and a roll separator. Examples include square batteries, flat batteries, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
(Production of LiMn _0.99 Ni _0.01 PO ₄ / C)
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), nickel acetate tetrahydrate (Ni (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate ( NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) were measured so that the molar ratio was 0.99: 0.01: 1.00: 0.51, and then these were converted to nitrogen. Under an atmosphere, alcohol was used as a solvent, and pulverization and mixing were performed for 2 hours with a ball mill to obtain a LiMn _0.99 Ni _0.01 PO ₄ precursor. Next, after drying the LiMn _0.99 Ni _0.01 PO ₄ precursor, the mixture was put into a rotary kiln, and a mixed gas of vaporized methanol and nitrogen was supplied, and conditions were 750 ° C. and 6 hours. Then, nickel manganese lithium phosphate A (LiMn _0.99 Ni _0.01 PO ₄ / C) substituted with 1% of Ni according to the present invention was produced. The rotational speed of the kiln is 1 r. p. m. It was. Moreover, the mixed gas of vaporized methanol and nitrogen was produced by enclosing a methanol solution maintained at 45 ° C. in a sealed container and bubbling with nitrogen as a carrier gas.

[Example 2]
(Production of LiMn _0.98 Ni _0.02 PO ₄ / C)
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), nickel acetate tetrahydrate (Ni (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate ( NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) were measured so that the molar ratio was 0.98: 0.02: 1.00: 0.51, and then these were converted to nitrogen. Under an atmosphere, alcohol was used as a solvent, and pulverization and mixing were performed for 2 hours by a ball mill to obtain a LiMn _0.98 Ni _0.02 PO ₄ precursor. Next, after drying the LiMn _0.98 Ni _0.02 PO ₄ precursor, the mixture was put into a rotary kiln, and a mixed gas of vaporized methanol and nitrogen was supplied, and the conditions were 750 ° C. and 6 hours. Then, nickel manganese lithium phosphate B (LiMn _0.98 Ni _0.02 PO ₄ / C) substituted with 2% of Ni according to the present invention was produced. The rotational speed of the kiln is 1 r. p. m. It was. Moreover, the mixed gas of vaporized methanol and nitrogen was produced by enclosing a methanol solution maintained at 45 ° C. in a sealed container and bubbling with nitrogen as a carrier gas.

[Example 3]
(Production of LiMn _0.96 Ni _0.04 PO ₄ / C)
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), nickel acetate tetrahydrate (Ni (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate ( NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) were measured so that the molar ratio was 0.96: 0.04: 1.00: 0.51, and then these were converted to nitrogen. Under an atmosphere, alcohol was used as a solvent, and pulverization and mixing were performed for 2 hours by a ball mill to obtain a LiMn _0.98 Ni _0.02 PO ₄ precursor. Next, after the LiMn _0.96 Ni _0.04 PO ₄ precursor was dried, it was put into a rotary kiln, and a mixed gas of vaporized methanol and nitrogen was supplied, and conditions were 750 ° C. and 6 hours. Then, nickel manganese lithium phosphate B (LiMn _0.96 Ni _0.04 PO ₄ / C) substituted with 2% of Ni according to the present invention was produced. The rotational speed of the kiln is 1 r. p. m. It was. Moreover, the mixed gas of vaporized methanol and nitrogen was produced by enclosing a methanol solution maintained at 45 ° C. in a sealed container and bubbling with nitrogen as a carrier gas.

[Comparative Example 1]
(Production of LiMnPO ₄ / C)
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) in molar ratio Was measured to be 1.00: 1.00: 0.51, and these were pulverized and mixed in a ball mill for 2 hours using an alcohol as a solvent under a nitrogen atmosphere to obtain LiMnPO ₄ precursors. Obtained. Next, after drying the LiMnPO ₄ precursor, it was put into a rotary kiln and baked at 750 ° C. for 6 hours while supplying vaporized mixed gas of methanol and nitrogen, and manganese phosphate. Lithium C (LiMnPO ₄ / C) was produced. The rotational speed of the kiln is 1 r. p. m. It was. Moreover, the mixed gas of vaporized methanol and nitrogen was produced by enclosing a methanol solution maintained at 45 ° C. in a sealed container and bubbling with nitrogen as a carrier gas.

[Comparative Example 2]
(Production of LiMn _0.95 Ni _0.05 PO ₄ / C)
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), nickel acetate tetrahydrate (Ni (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate ( NH ₄ H ₂ PO ₄ ) and lithium carbonate (Li ₂ CO ₃ ) were measured so that the molar ratio was 0.95: 0.05: 1.00: 0.51, and then these were converted to nitrogen. Under an atmosphere, alcohol was used as a solvent, and pulverization and mixing were performed for 2 hours by a ball mill to obtain a LiMn _0.95 Ni _0.05 PO ₄ precursor. Next, after drying the LiMn _0.95 Ni _0.05 PO ₄ precursor, the mixture was put into a rotary kiln, and a mixed gas of vaporized methanol and nitrogen was supplied, and the conditions were 750 ° C. and 6 hours. The nickel manganese lithium phosphate D (LiMn _0.95 Ni _0.05 PO ₄ / C) in which 5% of Ni was substituted was produced. The rotational speed of the kiln is 1 r. p. m. It was. Moreover, the mixed gas of vaporized methanol and nitrogen was produced by enclosing a methanol solution maintained at 45 ° C. in a sealed container and bubbling with nitrogen as a carrier gas.

Each of the positive electrode materials obtained in Examples 1 to 3 and Comparative Examples 1 and 2 was used as a positive electrode active material, N-methylpyrrolidone was used as a solvent, and after the mixer mixing step, the positive electrode active material, acetylene black, and polyvinylidene fluoride A positive electrode paste containing (PVdF) at a mass ratio of 80: 8: 12 was obtained. The positive electrode paste was applied to an aluminum mesh as a base material, and then vacuum dried at 150 ° C. to prepare a positive electrode plate. Using a positive electrode plate obtained as a positive electrode active material, using a Li plate as a counter electrode and a reference electrode, LiPF ₆ in a 1: 1 solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) as an electrolyte is 1 mol / l. A tripolar glass cell was produced in a glove box under an argon atmosphere using the one dissolved at a concentration, and used as a nonaqueous electrolyte secondary battery for evaluation.

The four types of nonaqueous electrolyte secondary batteries for evaluation corresponding to each of Examples 1 to 3 and Comparative Examples 1 and 2 were charged at a current of 0.01 ItmA and then discharged at a current of 0.01 ItmA. Here, charging is all constant current and constant voltage charging, with a charging potential of 4.5 V (vs. Li ^/ Li ⁺ ) and a charging time of 150 hours. Moreover, all discharges are constant current discharges, and the discharge end potential is 2.0 V (vs. Li ^/ Li ⁺ ). All these tests were carried out at 25 ° C. In order to clarify the Ni-containing effect, the ratio of the capacity of each nonaqueous electrolyte battery to the discharge capacity of the battery of Comparative Example 1 not containing Ni was calculated. The result is shown in FIG. This ratio was calculated by the following formula.

(Ratio of discharge capacity to battery of Comparative Example 1 = discharge capacity obtained during 0.01 ItmA discharge of each battery / discharge capacity obtained during 0.01 ItmA discharge of the battery of Comparative Example × 100)
In addition, the horizontal axis indicates the content ratio of Ni element in the transition metal contained in the positive electrode material. From the left of the data point, Comparative Example 1 (0%), Example 1 (1%), and Example 2 (2%), corresponding to Example 3 (4%) and Comparative Example 2 (5%).

  As can be seen from FIG. 1, in the nonaqueous electrolyte batteries of Examples 1 to 3, the discharge capacity increased compared to the nonaqueous electrolyte battery of Comparative Example 1. Since nickel in lithium manganese phosphate does not change in valence, the theoretical discharge capacity of lithium manganese phosphate should surely decrease when lithium manganese phosphate contains nickel. On the contrary, the reason why the discharge capacity of the non-aqueous electrolyte batteries of Examples 1 to 3 containing nickel was increased compared to the non-aqueous electrolyte battery of Comparative Example 1 containing no nickel is that of lithium manganese phosphate particles. It is presumed that the nickel element present on the surface serves as a catalyst and the thermal decomposition carbonization reaction of methanol is remarkably accelerated, and as a result, carbon is effectively supported on lithium manganese phosphate.

  In Comparative Example 2 with a high nickel content, the discharge capacity was reduced as compared with Comparative Example 1. In Examples 1 to 3 and Comparative Example 2, this was found in the raw material during the synthesis of lithium manganese phosphate. In addition, nickel was mixed at the same time to synthesize lithium manganese phosphate, so that nickel elements that do not act electrochemically exist not only on the surface of the lithium manganese phosphate base particles but also inside the base particles. For this reason, it is considered that the theoretical capacity of lithium manganese phosphate has been reduced. Therefore, when adopting an embodiment in which nickel is present even inside the base particles of lithium manganese phosphate as in the above example, the elemental ratio of nickel in the whole base particles is 3%. It can be seen that the following is preferable. Conversely, when adopting a method in which nickel or iron is disposed only on the surface of the lithium manganese phosphate base material particles, the nickel on the surface of the base material particles is considered in view of the action mechanism of catalytic action for the pyrolytic carbonization reaction. Or even if the amount of iron exceeds 3%, it is not considered a problem.

[Example 4]
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) in a molar ratio of 2 After weighing to 2: 1, these were pulverized and mixed in an inert atmosphere with a ball mill for 2 hours to obtain a LiMnPO ₄ precursor. Furthermore, LiMnPO ₄ powder was obtained by firing the LiMnPO ₄ precursor under a nitrogen flow (2.0 l / min) at 700 ° C. for 12 hours.

Next, LiMnPO ₄ powder was added to a beaker containing a 5 mol / l nickel acetate aqueous solution and stirred at 45 ° C. for 2 hours. Subsequently, the beaker was allowed to stand at 60 ° C. for 24 hours to volatilize the solvent to obtain a powder having a nickel compound on the surface of LiMnPO ₄ particles.

Furthermore, the powder provided with the nickel compound on the surface of the LiMnPO ₄ particles and polyvinyl alcohol were mixed so that the carbon mass generated by the heat treatment of polyvinyl alcohol was 5% by mass of the powder. This mixture was heat-treated at 700 ° C. for 2 hours under a nitrogen flow (1.5 l / min), and the carbon was supported on LiMnPO ₄ having a nickel compound on the particle surface for the non-aqueous electrolyte secondary battery according to the present invention. A positive electrode material A was produced.

[Example 5]
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) in a molar ratio of 2 After weighing to 2: 1, these were pulverized and mixed in an inert atmosphere with a ball mill for 2 hours to obtain a LiMnPO ₄ precursor. Furthermore, LiMnPO ₄ powder was obtained by firing the LiMnPO ₄ precursor under a nitrogen flow (2.0 l / min) at 700 ° C. for 12 hours.

Next, LiMnPO ₄ powder was added to a beaker containing 5 mol / l of an iron oxalate aqueous solution and stirred at 45 ° C. for 2 hours. Subsequently, the beaker was allowed to stand at 60 ° C. for 24 hours to volatilize the solvent to obtain a powder having an iron compound on the surface of LiMnPO ₄ particles.

Furthermore, the powder provided with the iron compound on the surface of LiMnPO ₄ particles and polyvinyl alcohol were mixed so that the carbon mass generated by the heat treatment of polyvinyl alcohol was 5% by mass of the powder. This mixture was heat-treated at 700 ° C. for 2 hours under a nitrogen flow (1.5 l / min), and the carbon was supported on LiMnPO ₄ having an iron compound on the particle surface, for the non-aqueous electrolyte secondary battery according to the present invention. A positive electrode material B was produced.

[Comparative Example 3]
First, manganese acetate tetrahydrate (Mn (CH ₃ COO) ₂ .4H ₂ O), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) in a molar ratio of 2 After weighing to 2: 1, these were pulverized and mixed in an inert atmosphere with a ball mill for 2 hours to obtain a LiMnPO ₄ precursor. Furthermore, LiMnPO ₄ powder was obtained by firing the LiMnPO ₄ precursor under a nitrogen flow (2.0 l / min) at 700 ° C. for 12 hours.

Next, LiMnPO ₄ powder and polyvinyl alcohol were mixed so that the mass of carbon produced by heat treatment of polyvinyl alcohol was 5% by mass of the powder. This mixture was heat-treated under a nitrogen flow (1.5 l / min) at 700 ° C. for 2 hours to prepare a positive electrode material C for a non-aqueous electrolyte secondary battery in which carbon was supported on LiMnPO ₄ .

Each of the positive electrode materials obtained in Examples 4 and 5 and Comparative Example 3 was used as a positive electrode active material, N-methylpyrrolidone was used as a solvent, and after the mixer mixing step, the positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) ) Was obtained at a mass ratio of 80: 8: 12. The positive electrode paste was applied to an aluminum mesh as a base material, and then vacuum dried at 150 ° C. to prepare a positive electrode plate. Using a positive electrode plate obtained as a positive electrode active material, using a Li plate as a counter electrode and a reference electrode, LiPF ₆ in a 1: 1 solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) as an electrolyte is 1 mol / l. A tripolar glass cell was produced in a glove box under an argon atmosphere by using a solution dissolved at a concentration, and designated as non-aqueous electrolyte secondary batteries A, B, and C for evaluation.

For the two types of evaluation non-aqueous electrolyte secondary batteries A, B, and C corresponding to each of Examples 4 and 5 and Comparative Example 3, after charging at a current of 0.01 ItmA, discharging was performed at a current of 0.01 ItmA. went. Here, charging is all constant current and constant voltage charging, with a charging potential of 4.5 V (vs. Li ^/ Li ⁺ ) and a charging time of 150 hours. Moreover, all discharges are constant current discharges, and the discharge end potential is 2.0 V (vs. Li ^/ Li ⁺ ). All these tests were carried out at 25 ° C. Table 1 shows the results of the discharge capacity obtained during the 0.01 ItmA discharge.

  From the table, it can be seen that the discharge capacity of the nonaqueous electrolyte secondary batteries A and B according to the present invention is larger than that of the nonaqueous electrolyte secondary battery C.

  This is because the thermal decomposition carbonization reaction of polyvinyl alcohol is remarkably accelerated because the nickel compound or iron compound supported on the surface of lithium manganese phosphate particles serves as a catalyst. It is presumed to be caused by being supported on lithium manganese oxide.

  In the above embodiment, an example using a liquid or solid organic material as a carbon source has been described. However, as shown in Patent Document 7, an organic material such as a lower alcohol is used in a gaseous state as lithium manganese phosphate. Needless to say, the effects of the present invention can be achieved even when applied to the above.

  In the above examples, the case where the compound provided on the particle surface is a nickel compound and the case where it is an iron compound has been shown to have the same effect in terms of discharge capacity. From the viewpoint of life performance, it is preferable to select a nickel compound. The reason for this is that in the process of carbon growth using Ni or Fe as a catalyst, when the catalyst contains Fe, the catalytic element Fe is located at the carbon growth end, that is, Fe is phosphoric acid. While carbon growth proceeds so as to separate from the manganese lithium particles, when the catalyst contains Ni, the carbon growth proceeds while Ni as the catalytic element remains at the carbon growth root. Therefore, when a nickel compound is used as the catalyst, elution of the metal element that has become the catalyst in the battery is suppressed as compared with the case where an iron compound is used as the catalyst. Therefore, by selecting a nickel compound as the catalyst element, it is possible to reduce the possibility that the eluted metal element reaches the negative electrode and causes a decrease in battery performance.

It is a graph which shows the discharge capacity of this invention battery and a comparison battery.

Claims (3)

A cathode material for a non-aqueous electrolyte secondary battery comprising carbon on the surface of base particles made of lithium manganese phosphate, wherein the base particles have nickel element or iron element on the surface of the base particles A positive electrode material for a non-aqueous electrolyte secondary battery. A positive electrode for a nonaqueous electrolyte secondary battery comprising the positive electrode material for a nonaqueous electrolyte secondary battery according to claim 1. A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to claim 2.