JP2010218829A - ACTIVE MATERIAL PARTICLE MAINLY COMPOSED OF LIVOPO4 HAVING alpha TYPE CRYSTAL STRUCTURE, ELECTRODE CONTAINING THE ACTIVE MATERIAL PARTICLE, LITHIUM SECONDARY BATTERY INCLUDING THE ELECTRODE, AND METHOD FOR MANUFACTURING THE ACTIVE MATERIAL PARTICLE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide active material particles mainly composed of LiVOPO<SB>4</SB>having an α type crystal structure, while having a large discharge capacity, an electrode containing the active material particles, a lithium secondary battery including the electrode, and a method for manufacturing the active material particles. <P>SOLUTION: The active material particles 1 are mainly composed of LiVOPO<SB>4</SB>having an α type crystal structure and respectively have a porous structure in which a total pore volume is ≥0.55 cm<SP>3</SP>/g. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an active material particle mainly composed of LiVOPO ₄ having an α-type crystal structure, an electrode including the same, a lithium secondary battery including the electrode, and a method for producing the active material particle.

LiVOPO ₄ has been studied as a positive electrode material capable of inserting and extracting lithium (for example, Patent Document 1 and Non-Patent Document 1). LiVOPO ₄ has different crystal structures such as α-type and β-type, and α-type is said to be a thermodynamically stable structure compared to β-type. It has been reported that LiVOPO ₄ having an α-type crystal structure has a smaller discharge capacity than LiVOPO ₄ having a type crystal structure. In Non-Patent Document 1, a change in capacity due to a difference in rate is examined for LiVOPO _{4 having} α _II , γ, and δ type crystal structures.

JP 2004-303527 A

N. Dupre et al. , Solid State Ionics, 140, p. 532-534 (2001)

However, sufficient studies have not been made on increasing the capacity of LiVOPO ₄ having an α-type crystal structure.

Accordingly, the present invention provides an active material particle mainly composed of LiVOPO ₄ having an α-type crystal structure and a large discharge capacity, an electrode including the active material particle, a lithium secondary battery including the electrode, and production of the active material particle. It aims to provide a method.

The active material particles of the present invention have a porous structure mainly composed of LiVOPO ₄ having an α-type crystal structure and a total pore volume of 0.55 cm ³ / g or more.

According to the active material particles of the present invention, a large discharge capacity can be realized even if the active material particles are mainly composed of αVO crystal LiVOPO ₄ . Although the reason for this is not clear, for example, the porous structure having a total pore volume of 0.55 cm ³ / g or more makes it easy for the electrolyte to penetrate into the active material particles, and the α-type crystal structure It is conceivable that lithium ions are easily inserted into and extracted from the crystal lattice of LiVOPO ₄ .

Here, the active material particles of the present invention preferably have a specific surface area of 1 m ² / g or more. When the specific surface area is 1 m ² / g or more, the contact area between the electrolytic solution and the active material particles is further increased, and insertion and desorption of lithium ions into the crystal lattice of LiVOPO ₄ having an α-type crystal structure is further increased. It becomes easy to be done. Thereby, a larger discharge capacity can be obtained.

  The electrode of the present invention includes a current collector and an active material layer including the above-described active material particles and provided on the current collector. Thereby, an electrode having a large discharge capacity can be obtained.

  The lithium ion secondary battery of this invention is equipped with the electrode mentioned above. Thereby, a lithium ion secondary battery having a large discharge capacity can be obtained.

The method for producing active material particles mainly composed of LiVOPO ₄ having an α-type crystal structure according to the present invention comprises a precursor of LiVOPO ₄ having an α-type crystal structure by hydrothermal synthesis in the presence of an organic compound having a reducing action. this firing step to obtain a hydrothermal synthesis to obtain a precursor of the LiVOPO ₄ of α-type crystal structure obtained by hydrothermal synthesis was heated to 500 to 750 ° C. the LiVOPO ₄ of the porous structure cutlet α-type crystal structure And comprising.

By performing hydrothermal synthesis in the presence of an organic compound having a reducing action, a precursor of LiVOPO ₄ having an α-type crystal structure can be obtained. Then, by heating the precursor of LiVOPO ₄ having the α-type crystal structure thus obtained to 500 to 750 ° C., the above-described predetermined porous structure mainly composed of LiVOPO ₄ having the α-type crystal structure is provided. Active material particles can be obtained.

Here, in the method for producing active material particles mainly composed of LiVOPO ₄ having an α-type crystal structure according to the present invention, the heating temperature in the main firing step is preferably 600 to 750 ° C. When the main baking is performed in this temperature range, the total pore volume is further increased, and a larger discharge capacity can be obtained.

In the method for producing active material particles mainly composed of LiVOPO ₄ having an α-type crystal structure according to the present invention, a precursor of LiVOPO ₄ having an α-type crystal structure obtained by hydrothermal synthesis is added before the main firing step. It is preferable to provide a calcination step of heating at 300 to 500 ° C. for 1 to 48 hours. This also further increases the total pore volume, and a larger discharge capacity can be obtained.

According to the present invention, there are provided active material particles mainly composed of LiVOPO ₄ having an α-type crystal structure and a large discharge capacity, an electrode including the active material particles, a lithium secondary battery including the electrode, and a method for manufacturing the same. can do.

FIG. 1 is a schematic view of active material particles according to the present embodiment. FIG. 2 is an electron micrograph of the surface of the active material particles of Example 5 in which the heating temperature in the main baking step is 600 ° C. FIG. 3 is an electron micrograph of the surface of the active material particles of Example 7 in which the heating temperature in the main baking step is 750 ° C. FIG. 4 is a schematic cross-sectional view of the lithium ion secondary battery according to this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the dimension ratio of each drawing does not necessarily correspond with an actual dimension ratio.

<Active material particles>
The active material particles according to this embodiment will be described. FIG. 1 is a schematic view of an active material particle 1 according to the present embodiment. The active material particle 1 of the present embodiment is a particle mainly composed of LiVOPO ₄ having an α-type crystal structure, and has a porous structure having pores 2 extending from a large number of surfaces to the inside. Total pore volume of the active material particles 1 is 0.55 cm ³ / g or more, preferably 0.6 cm ³ / g or more, more preferably 0.8 cm ³ / g or more. The upper limit value of the total pore volume of the active material particles 1 is not particularly limited, but is usually about 3 cm ³ / g. Moreover, the specific surface area of the active material particles 1 is preferably 1.0 m ² / g or more, and more preferably 1.2 m ² / g or more. The average particle size of the primary particles of the active material particles 1 is preferably 0.05 to 1 μm, and preferably 0.1 to 0.5 μm. The pore volume can be measured by a mercury porosimeter, the specific surface area can be measured by nitrogen gas adsorption, and the average particle diameter can be measured by a laser diffraction / scattering method.

The phrase “having α-type crystal structure LiVOPO ₄ as a main component” means that the amount of α-type crystal structure LiVOPO ₄ in the particles is 90% or more, preferably 92% or more on a mass basis. As a component other than LiVOPO ₄ of α-type crystal structure, mainly, but LiVOPO ₄ of β-type crystal structure and the like, the raw material components such as also unreacted than LiVOPO ₄ may include trace amounts. Here, the amount of LiVOPO ₄ having an α-type crystal structure or LiVOPO _{4 having a} β-type crystal structure in the particles can be measured by, for example, an X-ray diffraction method. Usually, LiVOPO ₄ of α-type crystal structure peaks appear in 2 [Theta] = 27.2 degrees, LiVOPO ₄ of β-type crystal structure peaks appear in 2 [Theta] = 27.0 degrees. Incidentally, LiVOPO ₄ of β-type crystal structure, it is preferred for LiVOPO ₄ of α-type crystal structure is 10% by mass or less.

  Although the surface of the active material particle 1 is not illustrated, at least a part of the surface may be covered with a carbon film. The carbon film may be composed of carbon fine particles having an average particle diameter of 0.03 to 0.1 μm, for example. Thereby, when using the active material particle 1 for an electrode or a battery, it functions as a conductive material, and the conductivity between the active material particles 1 is improved. In addition, the electronic conductivity with a conductive material (described later) mixed with the active material particles 1 is improved as necessary. The active material particles 1 may be supported on carbon particles larger than the active material particles 1.

<Method for producing active material particles>
Then, the manufacturing method of the active material particle 1 is demonstrated. The method for producing active material particles 1 according to the present embodiment includes a hydrothermal synthesis step of obtaining a precursor of LiVOPO ₄ having an α-type crystal structure by hydrothermal synthesis in the presence of an organic compound having a reducing action, And a main firing step of heating the precursor of LiVOPO ₄ having an α-type crystal structure obtained by thermal synthesis to 500 to 750 ° C. to obtain LiVOPO ₄ having a porous structure and an α-type crystal structure.

[Hydrothermal synthesis process]
(Raw material of precursor)
The raw material of the precursor of LiVOPO _{4 having} an α-type crystal structure includes at least a lithium source, a phosphate source, and a vanadium source.

Examples of the lithium source include lithium compounds such as LiNO ₃ , Li ₂ CO ₃ , LiOH, LiCl, Li ₂ SO _4, and CH ₃ COOLi.

Examples of the phosphoric acid source include PO ₄ -containing compounds such as H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO _4, and Li ₃ PO ₄ .

Examples of the vanadium source include vanadium compounds such as V ₂ O ₅ and NH ₄ VO ₃ .

  Then, by mixing these three kinds of compounds and water into an aqueous solution, it can be used as a precursor raw material.

In order to obtain a precursor of LiVOPO _{4 having} an α-type crystal structure by hydrothermal synthesis, an organic compound having a reducing action is further mixed with the above raw materials. Specific examples of the organic compound having a reducing action include ascorbic acid, citric acid, maleic acid, fumaric acid, glucose, polyvinyl pyrrolidone, polysaccharides and oligosaccharides containing glucose as a structural unit. Of these, ascorbic acid is particularly preferred, although the reason is not clear. What is necessary is just to mix 1-8 mass% of content of the organic compound which has a reducing effect with respect to the mass of the aqueous solution which mixed the said 3 types of compound and water.

  The content of the organic compound having a reducing action in the mixture is such that the ratio C1 / M between the number of moles C1 of the organic compound having a reducing action and the number of moles M of the vanadium element contained in the vanadium compound is 0.02 ≦ It is preferable to adjust so as to satisfy C1 / M ≦ 2. When there is too little content (molar number C1) of the organic compound which has a reducing effect, there exists a tendency for the electronic conductivity of the active material particles 1 and active material particles 1 and the electrically conductive material mentioned later to fall. When there is too much content of the organic compound which has a reducing action, the weight of the active material particle 1 which occupies for the active material particle 1 and the electrode active material comprised by the electrically conductive material mentioned later reduces relatively, and the capacity density of an active material Tend to decrease. By setting the content of the organic compound having a reducing action within the above range, these tendencies can be suppressed.

  The pH value of the raw material mixture immediately before the hydrothermal synthesis is not particularly limited, but when ascorbic acid is used as the organic compound having a reducing action, the pH is preferably 7-9. The pH of the mixture used as the raw material for hydrothermal synthesis can be adjusted depending on the type of the lithium source compound, the phosphoric acid source compound, and the vanadium source vanadium compound. It can be adjusted even if it is used.

The mixing ratio of the lithium compound, vanadium compound and PO ₄ -containing compound in the mixture is such that the composition is represented by the composition formula: LiVOPO ₄ , that is, Li atom: V atom: P atom: O atom = 1: 1: What is necessary is just to adjust so that it may become 1: 5 (molar ratio).

  By the way, in the active material-containing layer of the electrode, a conductive material such as a carbon material is usually brought into contact with the surface of the active material particles in order to increase conductivity. As this method, active material particles and a conductive material may be mixed after the production of active material particles to form an active material-containing layer. For example, an organic compound having a reducing action added to a raw material for hydrothermal synthesis may be used. Carbon (film or particles) may be attached to the active material particles by pyrolysis in the main firing step or calcining step described later, or a conductive material that is a carbon material is added to the raw material for hydrothermal synthesis. Thus, carbon can be attached to the active material particles.

  Examples of the conductive material in the case where a conductive material that is a carbon material is added to the raw material for hydrothermal synthesis include activated carbon, carbon black, graphite, soft carbon, and hard carbon. Among these, it is preferable to use activated carbon or carbon black that can easily disperse carbon particles in the mixture (aqueous solution) as the raw material during hydrothermal synthesis. In particular, the use of acetylene black as carbon black makes it easier to obtain these effects. However, the conductive material does not necessarily have to be mixed in the mixture as a raw material at the time of hydrothermal synthesis, and it is preferable that at least a part of the conductive material is mixed into the mixture as a raw material at the time of hydrothermal synthesis. Thereby, the binder at the time of forming an active material content layer can be reduced, and a capacity density can be increased.

  The content of the conductive material such as carbon particles in the mixture serving as the raw material for hydrothermal synthesis is the ratio C2 / C2 of the number of moles C2 of carbon atoms constituting the carbon particles and the number of moles M of vanadium atoms contained in the vanadium compound, for example. It is preferable to prepare such that M satisfies 0.02 ≦ C2 / M ≦ 2. When the content of carbon atoms (number of moles C2) is too small, the electron conductivity and capacity density of the electrode active material tend to decrease. When there is too much content of a electrically conductive material, there exists a tendency for the weight of the active material particle which occupies for an electrode active material to reduce relatively, and the capacity density of an electrode active material to reduce. By setting the content of the conductive material within the above range, these tendencies can be suppressed.

(Hydrothermal synthesis)
In the hydrothermal synthesis process, first, the precursor raw materials (for example, lithium compound, vanadium compound, PO ₄ -containing compound, reducing action) in a reaction vessel (for example, an autoclave) having a function of heating and pressurizing the inside. And an aqueous solution (hereinafter referred to as “raw material mixture”) in which these are dispersed is prepared. In preparing the raw material mixture, for example, first, a mixture of a vanadium compound, a PO ₄ -containing compound, and water is refluxed, and then a lithium compound, an organic compound having a reducing action, and a conductive material are added thereto. May be. By this reflux, a complex of the vanadium compound and the PO ₄ -containing compound can be formed.

Next, the reaction vessel is sealed, and the hydrothermal reaction of the mixture is allowed to proceed by, for example, refluxing while the raw material mixture is pressurized and heated. Thereby, the substance containing the precursor of LiVOPO _{4 having} an α-type crystal structure is hydrothermally synthesized.

A substance containing a precursor of LiVOPO ₄ having an α-type crystal structure obtained by hydrothermal synthesis is usually a tar-like substance. The precursor of LiVOPO _{4 having} an α-type crystal structure contained in this substance is considered to be in a hydrate state.

In the hydrothermal synthesis step, the pressure applied to the raw material mixture is preferably 0.2 to 1.0 MPa. When the pressure applied to the mixture is too low, the crystallinity of the active material particles mainly composed of LiVOPO ₄ having the α-type crystal structure finally obtained tends to be lowered, and the capacity density of the active material tends to be reduced. If the pressure applied to the mixture is too high, the reaction vessel is required to have high pressure resistance, and the production cost of the active material tends to increase. By setting the pressure applied to the raw material mixture within the above range, these tendencies can be suppressed.

The temperature of the raw material mixture in the hydrothermal synthesis step is preferably 120 to 180 ° C. If the temperature of the mixture is too low, the crystallinity of the active material particles mainly composed of LiVOPO ₄ having an α-type crystal structure finally obtained tends to decrease, and the capacity density of the active material tends to decrease. When the temperature of the mixture is too high, the reaction vessel is required to have high heat resistance, and the production cost of the active material tends to increase. By setting the temperature of the mixture within the above range, these tendencies can be suppressed.

[Main firing process]
Then, the main baking process which heats the obtained precursor to 500-750 degreeC is performed. Thereby, crystallization and porosification occur and the above-mentioned active material particles 1 are obtained. In this process, a phenomenon occurs in which organic compounds and impurities having a reducing action remaining in the mixture after hydrothermal synthesis are removed, and the precursor of LiVOPO ₄ having an α-type crystal structure is dehydrated to be crystallized and porous. It is thought that qualification will occur.

Here, in this baking process, it is preferable to heat the above-mentioned precursor to 500-750 degreeC for 0.5 to 12 hours. When the heating time is too short, the crystallinity of the active material particles mainly composed of LiVOPO ₄ having an α-type crystal structure as a main component is lowered, and the capacity density of the active material tends to be reduced. On the other hand, if the heating time is too long, the particle growth of the active material particles proceeds and the particle size increases, so that the diffusion of lithium in the electrode active material becomes slow and the capacity density of the electrode active material tends to decrease. By setting the heating time within the above range, these tendencies can be suppressed.

  Moreover, it is more preferable that heating temperature is 600-750 degreeC. In this temperature range, the reason is unknown, but the total pore volume is particularly increased, and a larger discharge capacity can be obtained.

  The atmosphere of the main baking step is not particularly limited, but is preferably performed in an inert atmosphere such as argon gas in order to prevent conductive materials such as carbon and carbon particles derived from organic compounds having a reducing action from being oxidized. .

  Moreover, it is preferable to provide the calcination process which heats the substance containing the precursor obtained by the hydrothermal synthesis mentioned above at 300-500 degreeC for 1 to 48 hours before this baking process. By performing the calcination step, the total pore volume of the active material particles is further increased, and a larger discharge capacity can be obtained. Although the reason for this is unknown, for example, the calcination step sufficiently removes impurities such as organic compounds having a reducing action added from the inside of the precursor in the hydrothermal synthesis step, and the crystallization and porosity in the main firing step. It is conceivable that the quality improvement is performed more efficiently. Note that the firing atmosphere in the calcination step is not particularly limited.

<Lithium ion secondary battery>
Next, the electrode and the lithium ion secondary battery according to this embodiment will be briefly described with reference to FIG.

  The lithium ion secondary battery 100 mainly includes a laminate 30, a case 50 that accommodates the laminate 30 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 30.

  The laminated body 30 is configured such that a pair of electrodes 10 and 20 are arranged to face each other with the separator 18 interposed therebetween. The positive electrode 10 is a product in which a positive electrode active material layer 14 is provided on a positive electrode current collector 12. The negative electrode 20 is a product in which a negative electrode active material layer 24 is provided on a negative electrode current collector 22. The positive electrode active material layer 14 and the negative electrode active material layer 24 are in contact with both sides of the separator 18. Leads 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the case 50.

  As the positive electrode current collector 12 of the positive electrode 10, for example, an aluminum foil or the like can be used. The positive electrode active material layer 14 is a layer containing the above-described active material particles 1, a binder, and a conductive material added as necessary. Examples of the conductive material added as necessary include carbon blacks, carbon materials, and conductive oxides such as ITO.

  The binder is not particularly limited as long as it can bind the active material particles and the conductive material to the current collector, and a known binder can be used. Examples thereof include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and vinylidene fluoride-hexafluoropropylene copolymer.

  Such a positive electrode is a known method, for example, an electrode active material including the active material particles 1 described above, or an active material particle 1, a binder, and a conductive material, and a solvent according to their type, for example, PVDF. The slurry can be produced by applying a slurry added to a solvent such as N-methyl-2-pyrrolidone or N, N-dimethylformamide on the surface of the positive electrode current collector 12 and drying it.

  As the negative electrode current collector 22, a copper foil or the like can be used. Moreover, as the negative electrode active material layer 24, the thing containing a negative electrode active material, a electrically conductive material, and a binder can be used. It does not specifically limit as a electrically conductive material, A well-known electrically conductive material can be used. Examples thereof include carbon blacks, carbon materials, metal powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal powders, and conductive oxides such as ITO. As the binder used for the negative electrode, known binders can be used without any particular limitation. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer ( Fluorine resins such as ECTFE and polyvinyl fluoride (PVF). This binder not only binds constituent materials such as active material particles and conductive materials added as necessary, but also contributes to binding between the constituent materials and the current collector. . In addition to the above, as the binder, for example, polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber, and the like may be used. Also, thermoplastic elastomeric polymers such as styrene / butadiene / styrene block copolymers, hydrogenated products thereof, styrene / ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers, and hydrogenated products thereof. May be used. Further, syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (carbon number 2 to 12) copolymer and the like may be used. Further, a conductive polymer may be used.

Examples of the negative electrode active material include graphite, non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon that can occlude / release (intercalate / deintercalate or dope / dedope) lithium ions. Carbon materials, metals that can be combined with lithium such as Al, Si and Sn, amorphous compounds mainly composed of oxides such as SiO ₂ and SnO ₂ , lithium titanate (Li ₄ Ti ₅ O ₁₂ ), etc. The particle | grains containing are mentioned.

  The manufacturing method of the negative electrode 20 should just adjust slurry and apply | coat to a collector like the manufacturing method of the positive electrode 10. FIG.

The electrolyte solution is contained in the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. The electrolyte solution is not particularly limited. For example, in the present embodiment, an electrolyte solution containing a lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, the electrolyte aqueous solution is preferably an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent because the electrochemical decomposition voltage is low, and the withstand voltage during charging is limited to a low level. As the electrolyte solution, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ , CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , A salt such as LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , LiBOB or the like can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Moreover, as an organic solvent, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate etc. are mentioned preferably, for example. These may be used alone or in combination of two or more at any ratio.

  In the present embodiment, the electrolyte solution may be a gel electrolyte obtained by adding a gelling agent in addition to liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

  The separator 18 may also be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose. And a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polyester and polypropylene.

  The case 50 seals the laminated body 30 and the electrolytic solution therein. The case 50 is not particularly limited as long as it can suppress leakage of the electrolytic solution to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside. For example, as the case 50, as shown in FIG. 4, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52, and a film such as polypropylene can be used as the synthetic resin film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is preferably polyethylene or polypropylene.

  The leads 60 and 62 are made of a conductive material such as aluminum.

  The preferred embodiments of the active material particles, the electrode including the active material particles, the battery including the electrode, and the method for producing the active material particles have been described above in detail, but the invention is limited to the above embodiment. is not.

  For example, the active material particles can also be used as an electrode material for electrochemical elements other than lithium ion secondary batteries. As such an electrochemical element, a secondary battery other than a lithium ion secondary battery, such as a metallic lithium secondary battery (which uses an electrode containing the composite particles of the present invention as a cathode and metallic lithium as an anode). And electrochemical capacitors such as lithium capacitors. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

  Next, specific examples are shown to describe the present invention in more detail. In addition, this invention is not limited to a following example.

Example 1
<Hydrothermal synthesis process>
An H ₃ PO ₄ aqueous solution prepared by dissolving 23.1 g of H ₃ PO ₄ in 500 g of water is charged into a 1.5 L autoclave container, and then 18.4 g of V ₂ O ₅ is gradually added into the container. It was. After all the V ₂ O ₅ was added, the vessel was sealed and refluxed at 95 ° C./200 rpm for 16 hours. After the reflux, after the contents of the container had cooled to room temperature, the container was once opened, and 8.5 g of LiOH.H ₂ O and 7.1 g of ascorbic acid (C ₆ H ₈ O ₆ ) were added to the container. Further, 1.0 g of carbon black was added. At this time, the pH of the contents of the container was 7. Next, the container was sealed again, the pressure in the container was 0.5 MPa, and the contents were held for 8 hours while refluxing at 160 ° C./300 rpm. Thereby, a tar-like mixture was obtained. When the pH of the obtained tar-like mixture was measured, the pH was 4.

  Next, about 300 ml of water was added to the tar-like mixture obtained in the hydrothermal synthesis step. The obtained mixture was heat-treated at 90 ° C. for about 23 hours using an oven and then pulverized to obtain a gray powder.

(Calcination process)
The obtained powder is put in an alumina crucible, and the temperature is raised from room temperature to 450 ° C. over 45 minutes in an air atmosphere. After that, heat treatment is performed by holding at 450 ° C. for 3 hours, and then the temperature is reached in about 10 minutes. It was cooled rapidly. By this calcination step, a brown powder (active material particles of Example 1) was obtained. The resulting brown powder was classified with a sieve (30 μm mesh). As a result of X-ray diffraction measurement, the obtained brownish-brown powder mainly contained LiVOPO ₄ having an α-type crystal structure. Ratio of peak intensity (2θ = 27.2 °) of LiVOPO ₄ having an α-type crystal structure and peak intensity (2θ = 27.0 °) of LiVOPO ₄ having a β-type crystal structure, measured by X-ray diffraction measurement Was 12: 1.

(Main firing process)
The obtained powder was heated at 500 ° C. for 4 hours under an argon atmosphere to obtain active material particles having a large number of pores on the surface and inside. Table 1 shows the total pore volume and specific surface area of the obtained active material particles.

<Production of evaluation cell>
A mixture of the active material particles of Example 1, polyvinylidene fluoride (PVDF) as a binder, and acetylene black was dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a slurry. The slurry was prepared so that the weight ratio of the active material particles, acetylene black, and PVDF was 84: 8: 8 in the slurry. This slurry was applied onto an aluminum foil as a current collector, dried, and then rolled to obtain an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 1 was formed.

Next, the obtained electrode and the Li foil as the counter electrode were laminated with a separator made of a polyethylene microporous film interposed therebetween to obtain a laminate (element body). This laminate was put in an aluminum laminator pack, and 1M LiPF ₆ solution was injected as an electrolyte into the aluminum laminate pack, followed by vacuum sealing to produce an evaluation cell of Example 1. The charge / discharge capacity at 0.1 C of the evaluation cell is shown in Table 1.

(Example 2)
Active material particles of Example 2 were obtained in the same manner as in Example 1 except that heat treatment was performed at 550 ° C. in the main firing step. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 2 was formed and an evaluation cell were produced.

Example 3
Active material particles of Example 3 were obtained in the same manner as in Example 1 except that the calcination step was not performed and heat treatment was performed at 600 ° C. in the main baking step. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 3 was formed and an evaluation cell were produced.

Example 4
Active material particles of Example 4 were obtained in the same manner as in Example 1 except that heat treatment was performed at 300 ° C. in the calcination step and heat treatment was performed at 600 ° C. in the main firing step. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 4 was formed and an evaluation cell were produced.

(Example 5)
Active material particles of Example 5 were obtained in the same manner as in Example 1 except that heat treatment was performed at 450 ° C. in the calcination step and heat treatment was performed at 600 ° C. in the main firing step. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 5 was formed and an evaluation cell were produced.

(Example 6)
Active material particles of Example 6 were obtained in the same manner as in Example 1 except that heat treatment was performed at 500 ° C. in the calcination step and heat treatment was performed at 600 ° C. in the main firing step. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 6 was formed and an evaluation cell were produced.

(Example 7)
Active material particles of Example 7 were obtained in the same manner as in Example 1 except that heat treatment was performed at 450 ° C. in the calcination step and heat treatment was performed at 750 ° C. in the main firing. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 7 was formed and an evaluation cell were produced.

(Example 8)
By adding ammonia water, the pH of the aqueous raw material solution before hydrothermal synthesis was set to 9, heat treatment was performed at 450 ° C. in the calcination step, and heat treatment was performed at 750 ° C. in the main firing step, which was the same as in Example 1. Thus, active material particles of Example 8 were obtained. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Example 8 was formed and an evaluation cell were produced.

(Comparative Example 1)
Active material particles of Comparative Example 1 were obtained in the same manner as in Example 1 except that heat treatment was performed at 450 ° C. in the calcination step and heat treatment was performed at 450 ° C. in the main firing step. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Comparative Example 1 was formed and an evaluation cell were produced.

(Comparative Example 2)
Active material particles of Comparative Example 2 were obtained in the same manner as in Example 1 except that heat treatment was performed at 450 ° C. in the calcination step and heat treatment was performed at 800 ° C. in the main firing step. Further, in the same manner as in Example 1, an electrode (positive electrode) on which an active material-containing layer containing active material particles of Comparative Example 2 was formed and an evaluation cell were produced.

As in Example 1, Table 1 shows the firing conditions of the active material particles of Examples 2 to 8 and Comparative Examples 1 and 2, and the charge / discharge capacity at 0.1 C of the evaluation cell using the active material particles. Α / β is a mass ratio obtained by a ratio between the peak intensity of LiVOPO ₄ having an α-type crystal structure and the peak intensity of LiVOPO ₄ having a β-type crystal structure.

By conducting hydrothermal synthesis in the presence of ascorbic acid and carrying out main firing in the range of 500 to 750 ° C., porous structure active material particles mainly composed of α-type crystal structure LiVOPO ₄ can be obtained. These showed a high discharge capacity. In particular, when the main calcination was performed in the range of 600 to 750 ° C., the total pore volume was large, and the 0.1 C discharge capacity was particularly high. Moreover, when Example 3 and Example 4 are contrasted, the active material particles of Example 4 obtained by calcining the precursor at 300 to 500 ° C. before the main firing are the active material of Example 3. Compared to the particles, the total pore volume increased and the 0.1 C discharge capacity also increased.

As described above, according to the present invention, active material particles mainly composed of LiVOPO ₄ having an α-type crystal structure having a thermodynamically stable structure and a large discharge capacity, an electrode including the active material particles, and A lithium secondary battery including the electrode can be provided.

Active material particles 1 ... the LiVOPO ₄ of α-type crystal structure as the main component, 2 ... pore, 10, 20 ... electrode, 12 ... cathode current collector, 14 ... positive electrode active material layer, 18 ... separator, 22 ... negative electrode Current collector, 24 ... negative electrode active material layer, 30 ... laminate, 50 ... case, 52 ... metal foil, 54 ... polymer film, 60, 62 ... lead, 100 ... lithium ion secondary battery.

Claims (7)

Active material particles having a porous structure mainly composed of αVO crystal LiVOPO ₄ and having a total pore volume of 0.55 cm ³ / g or more. The active material particles according to claim 1, wherein the specific surface area is 1 m ² / g or more.   An electrode comprising: a current collector; and an active material layer comprising the active material particles according to claim 1 or 2 and provided on the current collector.   A lithium ion secondary battery comprising the electrode according to claim 3. A hydrothermal synthesis step of obtaining a precursor of LiVOPO ₄ having an α-type crystal structure by hydrothermal synthesis in the presence of an organic compound having a reducing action;
A main-firing step of heating the precursor of LiVOPO ₄ having an α-type crystal structure obtained by the hydrothermal synthesis to 500 to 750 ° C. to obtain LiVOPO ₄ having a porous structure and an α-type crystal structure. A method for producing active material particles having LiVOPO ₄ having a structure as a main component.   The manufacturing method of the active material particle of Claim 5 whose heating temperature of the said main baking process is 600-750 degreeC. Wherein before the calcination step, according to claim 5 or 6 active according comprising a calcination step of heating for 1 to 48 hours a precursor of LiVOPO ₄ to 300 to 500 ° C. of α-type crystal structure obtained by the hydrothermal synthesis Method for producing substance particles.