JP2012069346A - Active material, method for manufacturing active material, electrode, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active material realizing a lithium ion secondary battery having a large capacity.SOLUTION: The active material contains LiVOPOand satisfies the requirement that A(102)/{A(201)+A(020)} is in the range of 0.5 to 10 where A(102) is the peak area derived from the (102) face, A(201) is the peak area derived from the (201) face, and A(020) is the peak area derived from the (020) face, in the X-ray diffraction pattern of LiVOPO.

Description

  The present invention relates to an active material, a method for producing the active material, an electrode, and a lithium ion secondary battery.

LiCoO ₂ is widely used as a positive electrode active material for lithium ion secondary batteries. However, it has been pointed out that LiCoO ₂ has a high raw material cost and has a low thermal stability and a safety problem. As positive electrode active materials that overcome these problems, phosphoric acid-based positive electrode active materials such as LiFePO ₄ and LiVOPO ₄ have attracted attention. (See Patent Documents 1 and 2 and Non-Patent Document 1 below.) These phosphoric acid-based positive electrode active materials are attracting attention as candidates for active materials for lithium ion secondary batteries mounted on electric vehicles.

Japanese Patent No. 4314859 Special table 2009-534288

Journal of The Electrochemical Society, 151 (6) A796-A800 (2004)

  However, even if a lithium ion secondary battery using a conventional phosphoric acid-based positive electrode active material can have a relatively high charge / discharge capacity at a low rate, the charge / discharge is sufficiently high at a practical high rate. It was difficult to have a capacity.

  The present invention has been made in view of the above-described problems of the prior art, and includes an active material capable of improving the capacity of a lithium ion secondary battery, a method for producing the active material, an electrode, and a lithium ion secondary battery. The purpose is to provide.

In order to achieve the above object, the active material according to the present invention comprises LiVOPO _4, and in the X-ray diffraction pattern of LiVOPO ₄ , the peak area of the (102) plane is A (102), and the (201) plane When the peak area of A is A (201) and the peak area of the (020) plane is A (020), A (102) / {A (201) + A (020)} is 0.5-10. It is.

  The electrode according to the present invention includes a current collector and an active material layer, and the active material layer includes the active material according to the present invention. A lithium ion secondary battery according to the present invention includes a positive electrode having a positive electrode current collector and a positive electrode active material layer, a negative electrode having a negative electrode current collector and a negative electrode active material layer, a positive electrode active material layer, A separator positioned between the negative electrode active material layer, a negative electrode, a positive electrode, and a non-aqueous electrolyte in contact with the separator, and the positive electrode active material layer includes the active material according to the present invention.

  Since the lithium ion secondary battery of the present invention includes the active material of the present invention in the positive electrode active material layer, it can have a high capacity.

In the active material according to the present invention, when the peak area of the (002) plane is A (002) in the X-ray diffraction pattern of LiVOPO ₄ , A (002) / {A (201) + A (020)} Is preferably 0.35 to 5.0. This facilitates increasing the capacity of the battery.

In the lithium ion secondary battery according to the present invention, the positive electrode active material layer includes a conductive auxiliary agent, and the content of the conductive auxiliary agent in the positive electrode active material layer is based on the total mass of LiVOPO _{4 in} the positive electrode active material layer. It is preferable that it is 5-20 mass%. This facilitates increasing the capacity of the battery.

  A first method for producing an active material according to the present invention includes a first firing step of firing a raw material mixture containing lithium, vanadium, and phosphorus, and a second firing step of firing the raw material mixture after the first firing step. The temperature of the firing atmosphere of the second firing step is higher than the temperature of the firing atmosphere of the first firing step, the maximum temperature of the firing atmosphere of the first firing step is 325 to 575 ° C, The maximum temperature of the firing atmosphere is 425-675 ° C. According to the first method for producing an active material according to the present invention, the active material according to the present invention can be produced.

In said 1st manufacturing method, it is preferable that the baking atmosphere of a 1st baking process is an inert atmosphere, and the baking atmosphere of a 2nd baking process is an oxidizing atmosphere. Thus, generation of the above LiVOPO ₄ is promoted.

  The second method for producing an active material according to the present invention includes a firing step of firing a raw material mixture containing lithium, vanadium, and phosphorus, and an average temperature increase rate of a firing atmosphere in the firing step is 12.5 to 135 ° C./hour. The maximum temperature of the firing atmosphere is 425-675 ° C. According to the second method for producing an active material according to the present invention, the active material according to the present invention can be produced.

In the second manufacturing method, it is preferable that, in the firing step, the raw material mixture is fired in an inert atmosphere and then the raw material mixture is fired in an oxidizing atmosphere. Thus, generation of the above LiVOPO ₄ is promoted.

In the first production method or the second production method, the raw material mixture preferably contains VOPO ₄ or VOPO ₄ .2H ₂ O. Thereby, it becomes easy to obtain the active material according to the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the active material which can improve the capacity | capacitance of a lithium ion secondary battery, the manufacturing method of an active material, an electrode, and a lithium ion secondary battery can be provided.

FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery including a positive electrode active material layer containing an active material according to an embodiment of the present invention. FIG. 2 is an X-ray diffraction pattern of the positive electrode active material layer containing the active material of Example 1 of the present invention. FIG. 3 is an X-ray diffraction pattern of LiVOPO ₄ having no orientation.

  Hereinafter, an embodiment of the present invention will be described. In addition, this invention is not limited to the following embodiment.

(Active material)
The active material according to the present embodiment contains LiVOPO ₄ . In this X-ray diffraction (XRD) pattern of LiVOPO ₄ , A (102) / {A (201) + A (020)} is 0.5-10. Preferably, A (102) / {A (201) + A (020)} is 1.2 to 3.3.

Here, A (102) is the peak area of the diffracted X-ray from the (102) plane of the LiVOPO ₄ crystal. A (102), for example, measures the diffraction pattern of a sample (LiVOPO ₄ crystal) with an X-ray diffractometer using Cu-Kα rays, and appears at a position where the diffraction angle 2θ is approximately 27.59 ° in the diffraction pattern. It is obtained by subtracting the background integrated intensity from the peak integrated intensity. The background and integrated intensity can be calculated using software attached to the X-ray diffractometer. As software, for example, analysis software PDXL manufactured by Rigaku Corporation may be used. A (201) is the peak area of the diffracted X-ray from the (201) plane of the LiVOPO ₄ crystal. A (201) is obtained in the same manner as A (102) except that the diffraction angle 2θ at which the peak appears is approximately 27.0 °. A (020) is the peak area of the diffracted X-ray from the (020) plane of the LiVOPO ₄ crystal. A specific method for obtaining A (020) is the same as that for A (102) except that the diffraction angle 2θ at which the peak appears is approximately 28.3 °.

A (102) / {A (201) + A (020)} is an index indicating the orientation of LiVOPO ₄ toward the (102) plane. Hereinafter, the orientation toward the (102) plane is referred to as “(102) orientation”. LiVOPO ₄ in which A (102) / {A (201) + A (020)} is in the above numerical range has high (102) orientation. The present inventors consider that in the LiVOPO ₄ crystal having high (102) orientation, the diffusion of lithium ions in the (102) direction and the (002) direction is fast. Therefore, a lithium ion secondary battery including LiVOPO ₄ having high (102) axial orientation as a positive electrode active material can have a high charge / discharge capacity. When A (102) / {A (201) + A (020)} is smaller than the above numerical range, the (102) orientation of LiVOPO ₄ is small and the charge / discharge capacity is also small. On the other hand, when A (102) / {A (201) + A (020)} is larger than the above numerical range, the stability of the crystal is likely to deteriorate, and the charge / discharge capacity tends to decrease.

In the X-ray diffraction pattern of LiVOPO ₄ , A (002) / {A (201) + A (020)} is preferably 0.35 to 5.0. More preferably, A (002) / {A (201) + A (020)} is 0.74 to 1.60. Thereby, the charge / discharge capacity of the battery is easily improved. A (002) is the peak area of the diffracted X-ray from the (002) plane of the LiVOPO ₄ crystal. A specific method for obtaining A (002) is the same as A (102) except that the diffraction angle 2θ at which the peak appears is approximately 24.8 °.

A (002) / {A (201) + A (020)} is an index indicating the orientation of LiVOPO _{4 on} the (002) plane. Hereinafter, the orientation toward the (002) plane is referred to as “(002) orientation”. In the crystal of LiVOPO ₄ in which A (002) / {A (201) + A (020)} is within the above numerical range, the present inventors show that lithium ions diffuse in the (102) and (002) directions. Think fast. When A (002) / {A (201) + A (020)} is smaller than the above numerical range, the discharge capacity tends to be small. On the other hand, when A (002) / {A (201) + A (020)} is larger than the above numerical range, the stability of the crystal is likely to deteriorate, and the charge / discharge capacity tends to decrease. However, even when A (002) / {A (201) + A (020)} is outside the above numerical range, the capacity of the lithium ion secondary battery can be increased.

Incidentally, A (102) / {A (201) + A (020)} and A (002) / {A ( 201) + A (020)} may be determined from the XRD pattern of the LiVOPO ₄ itself, the LiVOPO ₄ You may obtain | require from the XRD pattern of the positive electrode active material layer to contain.

The present inventors consider that LiVOPO _{4 according} to this embodiment is an orthorhombic crystal (β-type crystal) having (102) orientation and (002) orientation. Since the β-type crystal of LiVOPO ₄ has a linear and short ion conduction path (lithium ion path) as compared with the triclinic crystal (α-type crystal), it has excellent characteristics for reversibly inserting and extracting lithium ions. Therefore, in a battery using a LiVOPO ₄ β-type crystal, the charge / discharge capacity is improved.

(Lithium ion secondary battery)
As shown in FIG. 1, a lithium ion secondary battery 100 according to the present embodiment is disposed adjacent to each other between a plate-like negative electrode 20 and a plate-like positive electrode 10 facing each other, and the negative electrode 20 and the positive electrode 10. A plate-like separator 18, a non-aqueous electrolyte solution containing lithium ions, a case 50 containing these in a sealed state, and one end of the negative electrode 20 is electrically connected. A negative electrode lead 60 whose other end protrudes outside the case, and a positive electrode lead 62 whose one end is electrically connected to the positive electrode 10 and whose other end protrudes outside the case. Is provided.

  The negative electrode 20 includes a negative electrode current collector 22 and a negative electrode active material layer 24 formed on the negative electrode current collector 22. The positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. The separator 18 is located between the negative electrode active material layer 24 and the positive electrode active material layer 14.

The positive electrode active material layer 14 contains the active material according to the present embodiment. That is, the positive electrode active material layer 14 contains LiVOPO _{4 in} which A (102) / {A (201) + A (020)} is 0.5 to 10.

The positive electrode active material layer 14 preferably contains a conductive additive. The content of the conductive additive in the positive electrode active material layer 14 is more preferably ₄ to 22.5% by mass, and more preferably 5 to 20% by mass with respect to the total mass of LiVOPO ₄ . Thereby, the capacity | capacitance of a battery increases notably.

It does not specifically limit as a conductive support agent, A well-known conductive support agent can be used. Specific examples thereof include carbon materials such as carbon blacks, metal powders such as copper, nickel, stainless steel, and iron, and conductive oxides such as ITO. For example, acetylene black is preferably used as the carbon material. Acetylene black is a kind of carbon black and is produced by thermal decomposition of acetylene. Examples of commercially available acetylene black include Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd. In a battery including LiVOPO ₄ and acetylene black according to the present embodiment in the positive electrode active material layer, the charge / discharge capacity is easily improved.

The positive electrode active material layer 14 may contain a binder (binder) in addition to the LiVOPO ₄ and the conductive additive.

  As the binder, known binders can be used without particular limitation. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF). -HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), and the like.

  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.

The negative electrode active material contained in the negative electrode active material layer 24 includes insertion and extraction of lithium ions, desorption and insertion (intercalation) of lithium ions, or counter ions of lithium ions and the lithium ions (for example, PF ₆ ⁻ If it is possible to reversibly proceed with doping and dedoping with a), a known negative electrode active material can be used. Examples of such active materials include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon, and metals that can be combined with lithium such as Al, Si, and Sn. , SiO _x (1 <x ≦ 2), SnO _x (1 <x ≦ 2) and other amorphous compounds mainly composed of oxide, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), TiO _{2 and the like.} It is done.

  As the binder used for the negative electrode 20, the same binder as that used for the positive electrode 10 can be used. Moreover, as a conductive support agent used for the negative electrode 20 as needed, the same conductive support agent used for the positive electrode 10 can be used.

  The negative electrode current collector 22 and the positive electrode current collector 12 are good conductors that can sufficiently transfer charges to the negative electrode active material layer 24 and the positive electrode active material layer 14, and in the case of the negative electrode current collector, lithium and In the case of an alloy not made or a positive electrode current collector, there is no particular limitation as long as it does not corrode. For example, examples of the negative electrode current collector 22 and the positive electrode current collector 12 include metal foils such as copper and aluminum.

  As the separator 18, a porous body having electronic insulation may be used. Examples of the separator 18 include a laminate of films made of polyethylene, polypropylene, or polyolefin, a stretched film of a mixture of the above polymers, or at least one constituent material selected from the group consisting of cellulose, polyester, and polypropylene. The fiber nonwoven fabric etc. which become.

An electrolyte solution (not shown) is filled in the internal space of the case 50, and a part thereof is contained in the negative electrode 20, the positive electrode 10, and the separator 18. As the electrolyte solution, an organic solvent in which a lithium salt is dissolved, that is, a non-aqueous electrolyte solution is 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 , LiN Salts such as (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 are used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together. Further, the electrolyte solution may be gelled by adding a polymer or the like.

  As the organic solvent for dissolving the lithium salt, for example, a single solvent or a mixed solvent such as cyclic carbonates, chain carbonates, lactones, and esters can be used. More specifically, for example, propylene carbonate, ethylene carbonate, diethyl carbonate and the like are preferable. These may be used alone or in combination of two or more at any ratio.

(Method for producing active material)
[First production method]
The first method for producing an active material according to the present embodiment includes a step of preparing a raw material mixture containing lithium, vanadium and phosphorus, a first baking step of baking the raw material mixture, and baking the raw material mixture after the first baking step. A second firing step. According to this first manufacturing method, LiVOPO ₄ having A (102) / {A (201) + A (020)} of 0.5 to 10 in the X-ray diffraction pattern can be manufactured. Below, each process of a 1st manufacturing method is demonstrated.

<Preparation process of raw material mixture>
In the raw material mixture preparation step, first, a phosphoric acid source, a vanadium source, and distilled water are stirred to prepare a mixed solution, and the mixed solution is heated. Thereby, an intermediate body produces | generates in a liquid mixture. The intermediate is a precursor of LiVOPO ₄ and is a compound that does not contain Li. The present inventors consider that VOPO ₄ .2H ₂ O, which is a hydrate of an intermediate, is generated in the mixed solution by heating the mixed solution.

  In the preparation step, the mixed solution is preferably heated to 50 to 120 ° C. That is, it is preferable to adjust the temperature of the reaction for forming the intermediate from the phosphoric acid source, vanadium source and distilled water within the above range. When the temperature of the mixed liquid is too low, it tends to be difficult to generate an intermediate as compared with the case where the temperature of the mixed liquid is within the above range. When the temperature of the liquid mixture is too high, the particle size of the intermediate is increased compared to the case where the temperature of the liquid mixture is within the above range, and the reactivity in the first baking step and the second baking step is reduced. Tend. However, it is possible to synthesize the active material according to the present embodiment even when the heating temperature of the mixed liquid is outside the above range. Although the heating time of a liquid mixture is not specifically limited, It is about 1 to 12 hours.

  In addition, in a preparation process, you may adjust a liquid mixture by adding a phosphoric acid source and a vanadium source to distilled water, heating distilled water to said temperature range. Again, an intermediate is formed.

As the phosphoric acid source, for example, at least one selected from the group consisting of H ₃ PO ₄ , NH ₄ H ₂ PO ₄ and (NH ₄ ) ₂ HPO ₄ can be used. Two or more phosphate sources may be used in combination. As the vanadium source, for example, either V ₂ O ₅ or NH ₄ VO ₃ can be used. Two or more vanadium sources may be used in combination.

The mixing ratio of the phosphoric acid source and the vanadium source is such that the ratio of the number of moles of phosphorus element contained in the phosphoric acid source to the number of moles of vanadium element contained in the vanadium source is the stoichiometric ratio of LiVOPO ₄ (1: 1). It may be adjusted so that Note that the blending ratio of the phosphate source and the vanadium source does not necessarily satisfy the above stoichiometric ratio.

  You may make a liquid mixture contain a carbon source. The carbon source is, for example, an organic compound or a carbon material. Examples of the organic compound include water-soluble polymers such as sucrose, glucose, polyvinyl alcohol, fructooligosaccharide, sorbitol, and lactose or saccharides, ascorbic acid, polyvinylidene fluoride, and the like. Examples of the carbon material include graphite and acetylene black. The organic compound may be carbonized by firing described later and function as a reducing agent. Moreover, it may remain as an impurity in the finally obtained active material and function as a conductive additive. The carbon material may also function as a conductive additive in the active material.

  In the preparation step, it is preferable to heat the mixed solution to form an intermediate in the mixed solution, and then dry the mixed solution using a spray dryer or the like. By drying, the production of the intermediate further proceeds in the mixed solution, and moisture is removed from the mixed solution, whereby a residue containing the intermediate is obtained. Moreover, when a liquid mixture contains an organic compound, an intermediate body is coat | covered with an organic compound during drying. Therefore, excessive grain growth of the intermediate is suppressed. In particular, when a water-soluble organic compound is used, the intermediate is easily covered with the organic compound during drying. In addition, you may perform filtration drying, freeze drying, etc. as a drying method of a liquid mixture.

In the present embodiment, it is preferable to heat the above-described mixed liquid or the intermediate recovered from the mixed liquid in an atmosphere of 150 to 500 ° C. This heating makes the intermediate anhydrous. That is, the present inventors consider that VOPO ₄ .2H ₂ O is heated to become VOPO ₄ . The atmosphere for heating the mixed liquid or the intermediate is preferably an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere. In addition, heating of a liquid mixture or an intermediate body is not an essential process for obtaining an intermediate body. That is, a raw material mixture obtained by mixing hydrated VOPO ₄ · 2H ₂ O and a lithium salt may be fired in a first firing step and a second firing step described later.

By mixing the intermediate obtained by the above method and the lithium salt, a raw material mixture of LiVOPO ₄ is obtained. In addition, you may prepare a raw material mixture solution by stirring the distilled water which added the intermediate body and lithium salt. What is necessary is just to adjust the temperature of distilled water to about 30-80 degreeC when preparing a raw material mixture solution. This promotes dissolution and diffusion of the lithium salt into the raw material mixture solution. What is necessary is just to adjust suitably the density | concentration of the lithium salt in a raw material mixture solution to such an extent that lithium salt melt | dissolves in a liquid. Instead of mixing the lithium salt with the intermediate formed from the vanadium source and the phosphoric acid source as described above, a raw material mixture was prepared by simultaneously mixing the vanadium source, the phosphoric acid source and the lithium salt. Also good.

Examples of the lithium salt include one or more selected from the group consisting of Li ₂ CO ₃ , LiF, LiNO ₃ , LiOH, LiCl, LiBr, LiI, Li ₂ SO ₄ , Li ₃ PO _4, and CH ₃ COOLi. Can be used. In particular, when a water-soluble lithium salt is used, the discharge capacity of the lithium ion secondary battery tends to be improved. Examples of the water-soluble lithium salt include LiNO ₃ , LiOH, LiCl, LiI, Li ₂ SO ₄ and CH ₃ COOLi.

The compounding ratio of the lithium salt and the intermediate is such that the ratio of the number of moles of lithium element contained in the lithium salt, the number of moles of vanadium element contained in the intermediate, and the number of moles of phosphorus element contained in the intermediate is LiVOPO ₄ The stoichiometric ratio (1: 1: 1) may be adjusted. Note that the mixing ratio of the lithium salt and the intermediate does not necessarily satisfy the above stoichiometric ratio. For example, in order to prevent the loss of Li in the finally obtained LiVOPO ₄ , a large amount of lithium salt may be added.

It is preferable to dry the raw material mixture solution with a spray dryer or the like. Thereby, the raw material mixture in which the fine lithium salt is uniformly dispersed can be obtained. Therefore, the present inventors consider that the deviation of the composition of LiVOPO ₄ can be suppressed and the charge / discharge capacity of the battery is easily improved. In addition, you may bake in a 1st baking process and a 2nd baking process, without drying a raw material mixture solution.

<First firing step and second firing step>
In the first firing step, the raw material mixture prepared by the above method is fired. The maximum value of the firing atmosphere temperature (first firing temperature) in the first firing step is 325 to 575 ° C. Preferably, the maximum value of the first firing temperature is 350 to 550 ° C. When the maximum value of the first firing temperature is too low, the orientation of the LiVOPO ₄ crystal is lowered, and as a result, the charge / discharge capacity of the battery is lowered. When the maximum value of the first firing temperature is too high, the orientation of the LiVOPO ₄ crystal is lowered, and as a result, the charge / discharge capacity of the battery is lowered. In the first firing step, the first firing temperature may be maintained at a constant temperature within the range of 325 to 575 ° C. The firing time in the first firing step (the time for maintaining the first firing temperature at a constant temperature) may be 1 to 48 hours.

In the second firing step, the raw material mixture after firing in the first firing step is fired. The temperature of the firing atmosphere in the second firing step (second firing temperature) is higher than the first firing temperature. When the second firing temperature is equal to or lower than the first firing temperature, the orientation of the LiVOPO ₄ crystal is lowered, and as a result, the charge / discharge capacity of the battery is lowered. The maximum value of the second firing temperature is 425 to 675 ° C. Preferably, the maximum value of the second firing temperature is 450 to 650 ° C. When the maximum value of the second firing temperature is too low, the orientation of the LiVOPO ₄ crystal is lowered, and as a result, the charge / discharge capacity of the battery is lowered. When the maximum value of the second baking temperature is too high, the orientation of the LiVOPO ₄ crystal is lowered, and as a result, the charge / discharge capacity of the battery is lowered. In the second firing step, the first firing temperature may be maintained at a constant temperature within the range of 425 to 675 ° C.

The present inventors have found that in the first firing step, LiVOPO ₄ generates proceeds mutual diffusion of lithium and VOPO _4, in the second firing step, has progressed grain growth of LiVOPO ₄ to some extent, considered. Note that the second firing step may be continued from the first firing step. That is, after maintaining the temperature of the firing atmosphere of the raw material mixture in the range of 325 to 575 ° C, the temperature of the firing atmosphere is raised and the temperature of the firing atmosphere is maintained in the range of 425 to 675 ° C. In addition, you may perform a 1st baking process and a 2nd baking process intermittently.

  The average rate of temperature rise from the start of the temperature increase in the firing atmosphere in the first firing step until the firing atmosphere reaches the maximum value of the second firing temperature may be about 12.5 to 135 ° C./hour.

The firing atmosphere (first firing atmosphere) in the first firing step is preferably an inert atmosphere, and the firing atmosphere (second firing atmosphere) in the second firing step is preferably an oxidizing atmosphere. When the first firing atmosphere is an inert atmosphere, pentavalent vanadium (V ⁵⁺ ) constituting VOPO ₄ in the raw material mixture is reduced and tetravalent vanadium (V ⁴⁺ ) is generated in the first firing step. The present inventors consider that the production of LiVOPO ₄ having tetravalent vanadium as a constituent element is promoted. In particular, when the organic compound used for preparing the raw material mixture remains in the raw material mixture in the first firing step, pentavalent vanadium constituting VOPO ₄ is reduced without burning the organic compound in an inert atmosphere. The inventors consider. In the second firing step, generation of LiVOPO ₄ and crystal growth are promoted in an oxidizing atmosphere.

  The first firing atmosphere is not particularly limited as long as it is an inert atmosphere. For example, it may be at least one gas selected from the group consisting of nitrogen, helium and argon. The second firing atmosphere may be an oxidizing atmosphere as compared with the first firing atmosphere, and may be air or an oxidizing gas having an oxygen concentration of 1% by volume or more.

By passing through the above first baking step and second baking step, LiVOPO ₄ having A (102) / {A (201) + A (020)} of 0.5 to 10 is obtained.

[Second production method]
In the second manufacturing method, LiVOPO ₄ having A (102) / {A (201) + A (020)} of 0.5 to 10 in the X-ray diffraction pattern is manufactured as in the case of the first manufacturing method. It becomes possible to do. In the first manufacturing method, the raw material mixture is fired twice by the first firing step and the second firing step. In the second manufacturing method, LiVOPO ₄ is formed by firing the raw material mixture only once. To do. The second production method is the same as the first production method except that the number of firings is one. Below, the baking process in a 2nd manufacturing method is demonstrated.

  The average temperature increase rate of the firing atmosphere in the firing step of the second production method is 12.5 to 135 ° C./hour. Preferably, the average heating rate of the second production method is 20 to 120 ° C./hour. When the average rate of temperature increase is low, the charge / discharge capacity of the battery decreases. Even when the average temperature rising rate is too high, the charge / discharge capacity of the battery decreases.

The maximum value of the temperature (firing temperature) of the firing atmosphere in the firing step of the second production method is 425 to 675 ° C. Preferably, the maximum temperature of the firing atmosphere is 450 to 650 ° C. When the maximum value of the firing temperature is too low, the orientation of the LiVOPO ₄ crystal is lowered, and as a result, the charge / discharge capacity of the battery is lowered. When the maximum firing temperature is too high, the orientation of the LiVOPO ₄ crystal is lowered, and as a result, the charge / discharge capacity of the battery is lowered. In addition, what is necessary is just to hold | maintain a calcination temperature in the range of 425-675 degreeC at the constant temperature in the baking process of a 2nd manufacturing method. The firing time in the firing step of the second production method may be 1 to 48 hours.

In the second production method, it is preferable that after firing the raw material mixture in an inert atmosphere in the firing step, the raw material mixture is fired in an oxidizing atmosphere. The influence of the inert atmosphere and the oxidizing atmosphere on the production of LiVOPO ₄ is the same as in the case of the first production method. The composition of the inert atmosphere and the oxidizing atmosphere used in the second manufacturing method is the same as in the first manufacturing method.

(Method for producing lithium ion secondary battery)
A positive electrode active material layer 14 containing an active material (LiVOPO ₄ ) and a conductive additive obtained by the manufacturing method according to the present embodiment is formed on the positive electrode current collector 12. In this way, the positive electrode 10 including the positive electrode current collector 12 and the positive electrode active material 14 formed on the positive electrode current collector 12 is produced. Further, the negative electrode material layer 24 containing the negative electrode active material is formed on the negative electrode current collector 22. In this way, the negative electrode 20 including the negative electrode current collector 22 and the negative electrode active material 24 formed on the negative electrode current collector 22 is produced.

  Next, the negative electrode lead 60 and the positive electrode lead 62 are electrically connected to the negative electrode 20 and the positive electrode 10, respectively. Thereafter, the separator 18 is arranged in contact with the negative electrode 20 and the positive electrode 10 to form the power generation element 30. At this time, the surface of the negative electrode 20 on the negative electrode active material layer 24 side and the surface of the positive electrode 10 on the positive electrode active material layer 14 side are arranged so as to be in contact with the separator 18.

  Next, a power generation element is inserted into the battery case 50, and a nonaqueous electrolyte solution is injected. Subsequently, the lithium ion secondary battery 100 is completed by sealing the opening of the battery case 60 with the leading ends of the negative electrode lead 60 and the positive electrode lead 62 disposed outside the battery case.

  The preferred embodiments of the active material, the method for producing the active material, the electrode, and the lithium ion secondary battery according to the present invention have been described in detail above, but the present invention is not limited to the above embodiments.

  For example, the active material of the present invention can also be used as an electrode material for electrochemical devices other than lithium ion secondary batteries. As such an electrochemical element, a lithium ion such as a metal lithium secondary battery (using the electrode containing the active material of the present invention for the positive electrode and using a lithium alloy such as metal lithium or lithium aluminum for the negative electrode) Examples include secondary batteries other than secondary batteries, 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.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
The active material of Example 1 was produced by the first production method shown below.

<Process of raw material mixture>
In 500 ml of ion-exchanged water, 18.01 g of V ₂ O ₅ and 118.0 g of ₂ H ₃ PO ₄ (concentration: 85% by mass) are added, and these are stirred to obtain a mixture (slurry). It was adjusted. The mixture was heated at 90 ° C. for 16 hours. After cooling the mixed solution after heating, filtration of the mixed solution and washing of the filtrate were repeated three times. The obtained filtrate was dried. The dried filtrate was heated in an argon atmosphere at 450 ° C. for 1 hour, and crystal water was removed from the filtrate to obtain an intermediate (VOPO ₄ ). The raw material mixture of Example 1 was prepared by mixing the intermediate and Li ₂ CO _{3 at} a mass ratio of 3.24: 0.74.

<First firing step>
In the first firing step, the raw material mixture of Example 1 was fired in a firing furnace. In the first firing step, the temperature of the firing atmosphere (first firing temperature) was maintained at 510 ° C. for 20 hours. Argon gas was used for the firing atmosphere (first firing atmosphere) in the first firing step. Hereinafter, the time for maintaining the first firing temperature constant is referred to as “first firing time”.

<Second firing step>
In the second firing step, the argon gas at 510 ° C. in the firing furnace in which the raw material mixture was installed was replaced with the air at 510 ° C., and the atmosphere was heated to 550 ° C. That is, the firing atmosphere was switched from argon gas to air. Next, in the second firing step, the raw material mixture after the first firing step was further fired by maintaining the temperature (second firing temperature) in the atmosphere (second firing atmosphere) at 550 ° C. for 4 hours. Hereinafter, the temperature of the firing atmosphere when the firing atmosphere is switched from the argon gas to the air is referred to as “switching temperature”. In addition, the time during which the second firing temperature is kept constant is referred to as “second firing time”.

  In Example 1, the average rate of temperature increase from the start of the temperature increase of the argon gas in the first baking step until the atmosphere reaches the second baking temperature (550 ° C.) was adjusted to 23 ° C./hour.

The active material of Example 1 was formed from the raw material mixture by the above first baking step and second baking step. From the result of powder X-ray diffraction (XRD), it was confirmed that the active material of Example 1 was a β-type crystal (orthorhombic) of LiVOPO ₄ . Further, in the XRD pattern of LiVOPO ₄ of Example 1, it was confirmed that the area of each peak on the (102) plane and the (002) plane was larger than the areas of other peaks.

[Production of evaluation cell]
A mixture of the active material of Example 1 (LiVOPO ₄ ), polyvinylidene fluoride (PVDF) as a binder, and acetylene black was dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent to obtain a slurry. Prepared. The slurry was prepared so that the mass ratio of the active material, acetylene black, and PVDF in the slurry was 84: 8: 8. The slurry was applied on an aluminum foil as a current collector and dried, and then rolled. By such a method, the positive electrode in which the positive electrode active material layer containing the active material of Example 1 was formed was obtained. As acetylene black, Denka Black (grade: DAB 50%) manufactured by Denki Kagaku Kogyo Co., Ltd. was used. The content of acetylene black in the positive electrode active material layer was adjusted to 12.5% by mass with respect to the total mass of LiVOPO ₄ in the positive electrode active material layer.

  XRD measurement of the positive electrode active material layer included in the positive electrode of Example 1 was performed. The XRD pattern of the positive electrode active material layer of Example 1 is shown in FIG. In the obtained XRD pattern, it was confirmed that each peak area of (102) plane and (002) plane was larger than other peak areas. From the XRD pattern of the positive electrode active material layer of Example 1, A (102) / {A (201) + A (020)} and A (002) / {A (201) + A (020)} were obtained. A (102) / {A (201) + A (020)} of Example 1 was 3.1. A (002) / {A (201) + A (020)} in Example 1 was 1.6. Hereinafter, A (102) / {A (201) + A (020)} is referred to as “Rate (102)”. In addition, A (002) / {A (201) + A (020)} is referred to as “Rate (002)”.

FIG. 3 shows an X-ray diffraction pattern of LiVOPO ₄ having a structure having no orientation at all. Rate (102) obtained from the X-ray diffraction pattern of FIG. 3 was 0.17, and Rate (002) was 0.095.

Next, the positive electrode of Example 1 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.

[Measurement of discharge capacity]
Using the evaluation cell of Example 1, the discharge capacity (unit: mAh / g) when the discharge rate is 1 C (current value at which discharge is completed in 1 hour when constant current discharge is performed at 25 ° C.) Was measured. The discharge capacity of the evaluation cell of Example 1 was 113 mAh / g.

(Examples 2-10, 21-24, 31-36, Comparative Examples 1-4, 31-34)
In the same manner as in Example 1, except that the first baking temperature, the first baking time, the average heating rate, the switching temperature, the second baking temperature, and the second baking time were set to the values shown in Table 1. Each active material of 2-9 and Comparative Examples 1-4 was produced. The active materials of Examples 21 to 24 were produced by the same method as Example 1. In the production of the active material of Example 10, the first firing temperature, the first firing time, the average heating rate, the second firing temperature, and the second firing time were set to values shown in Table 1. In the production of the active material of Example 10, argon gas was used as the first firing atmosphere and the second firing atmosphere. That is, in the production of the active material of Example 10, the firing atmosphere was not switched.

  Each active material of Examples 31-36 and Comparative Examples 31-34 was produced by the 2nd manufacturing method. That is, the active materials of Examples 31 to 36 and Comparative Examples 31 to 34 were produced by firing the same raw material mixture as that of Example 1 only once. In each baking process of Examples 31-36 and Comparative Examples 31-34, the average temperature increase rate, switching temperature, baking temperature, and baking time of the baking atmosphere were adjusted to the values shown in Table 3.

  An evaluation cell for each example and comparative example was prepared in the same manner as in Example 1 except that the active materials of Examples 2 to 10, 31 to 36 and Comparative Examples 1 to 4, 31 to 34 were used. did.

The content of the acetylene black relative to the total weight of the LiVOPO ₄ in the positive electrode active material layer, except that it has adjusted to the values shown in Table 2, in the same manner as in Example 1, the evaluation of Examples 21 to 24 A cell was prepared.

  The rate (102) and rate (002) of each of Examples 2 to 10, 21 to 24, 31 to 36 and Comparative Examples 1 to 4, 31 to 34 were determined in the same manner as in Example 1. Tables 1 to 3 show Rate (102) and Rate (002) of each Example and Comparative Example.

  In the same manner as in Example 1, the discharge capacities of the evaluation cells of each Example and Comparative Example were measured. Each discharge capacity is shown in Tables 1-3.

The evaluations AA, A, B, C, and D shown in Tables 1 to 3 are based on the following criteria. The discharge capacity is preferably 50 mAh / g or more.
Evaluation AA discharge capacity: 110 mAh / g or more Evaluation A discharge capacity: 100 mAh / g or more and less than 110 mAh / g Evaluation B discharge capacity: 70 mAh / g or more and less than 100 mAh / g Evaluation C discharge capacity: 50 mAh / g or more and 70 mAh / g Discharge capacity of less than g evaluation D: less than 50 mAh / g

  Only the method for producing the active material of each example shown in Tables 1 and 2 satisfied the condition that the first firing temperature was 325 to 575 ° C and the second firing temperature was 425 to 675 ° C. .

  The average temperature increase rate of the firing atmosphere in the firing step is 12.5 to 135 ° C./hour, and the condition that the firing temperature is 425 to 675 ° C. satisfies the conditions of the active materials of the respective examples shown in Table 3. Only the manufacturing method.

A (102) / {A (201) + A (020)} of LiVOPO ₄ of all Examples shown in Tables 1 to 3 was 0.5 to 10. The discharge capacity of all the examples was 50 mAh / g or more.

A (102) / {A (201) + A (020)} of LiVOPO ₄ of all comparative examples shown in Tables 1 to 3 was out of the range of 0.5 to 10. The discharge capacity of all comparative examples was less than 50 mAh / g.

  DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 20 ... Negative electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 22 ... Negative electrode collector, 24 ... Negative electrode Active material layer, 30 ... power generation element, 50 ... case, 60, 62 ... lead, 100 ... lithium ion secondary battery.

Claims (10)

With LiVOPO ₄
In the LiVOPO ₄ X-ray diffraction pattern, the peak area of the (102) plane is A (102), the peak area of the (201) plane is A (201), and the peak area of the (020) plane is Is A (020),
A (102) / {A (201) + A (020)} is 0.5-10.
Active material. In the X-ray diffraction pattern, when the area of the (002) plane peak is A (002),
A (002) / {A (201) + A (020)} is 0.35 to 5.0.
Active material. A current collector and an active material layer;
The active material layer contains the active material according to claim 1 or 2,
electrode. A positive electrode having a positive electrode current collector and a positive electrode active material layer;
A negative electrode having a negative electrode current collector and a negative electrode active material layer;
A separator positioned between the positive electrode active material layer and the negative electrode active material layer;
A non-aqueous electrolyte in contact with the negative electrode, the positive electrode, and the separator,
The positive electrode active material layer contains the active material according to claim 1 or 2.
Lithium ion secondary battery. The positive electrode active material layer includes a conductive additive,
The content of the conductive additive of the positive electrode active material layer is 5 to 20% by weight, based on the total weight of the LiVOPO ₄ of the positive electrode active material layer,
The lithium ion secondary battery according to claim 4. A first firing step of firing a raw material mixture containing lithium, vanadium and phosphorus;
A second firing step of firing the raw material mixture after the first firing step,
The temperature of the firing atmosphere of the second firing step is higher than the temperature of the firing atmosphere of the first firing step,
The maximum value of the firing atmosphere in the first firing step is 325 to 575 ° C,
The maximum value of the firing atmosphere in the second firing step is 425 to 675 ° C.
A method for producing an active material. The firing atmosphere of the first firing step is an inert atmosphere;
The firing atmosphere of the second firing step is an oxidizing atmosphere;
The manufacturing method of the active material of Claim 6. Comprising a firing step of firing a raw material mixture containing lithium, vanadium and phosphorus;
The average heating rate of the firing atmosphere in the firing step is 12.5 to 135 ° C./hour;
The maximum temperature of the firing atmosphere is 425-675 ° C.
A method for producing an active material. In the firing step, after firing the raw material mixture in an inert atmosphere, the raw material mixture is fired in an oxidizing atmosphere.
The manufacturing method of the active material of Claim 8. The raw material mixture contains VOPO ₄ or VOPO ₄ · 2H ₂ O,
The manufacturing method of the active material as described in any one of Claims 6-9.

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