Electrode material and method for producing the same

Abstract

To provide an electrode material with excellent output characteristics while suppressing changes in crystal structure due to moisture, and a simple method for manufacturing the electrode material.SOLUTION: An electrode material includes lithium vanadium phosphate bonded to a conductive carbon material, the lithium vanadium phosphate is a mixture with titanium or a titanium compound such as titanium (IV) oxide. The lithium vanadium phosphate forms a mixture in which particles of a titanium compound such as titanium or titanium (IV) oxide are mixed inside and on the surface of a crystal whose base material is lithium vanadium phosphate. This electrode material is manufactured through a crystallization step that combines a conductive carbon material and the lithium vanadium phosphate. The crystallization step includes an addition step of adding titanium (IV) oxide, a mixing step of mixing water as a solvent, and a drying step of spray drying.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode material used in electricity storage devices such as secondary batteries and electrochemical capacitors, and a method for producing the electrode material. [Background technology]

[0002] As electrodes for power storage devices such as secondary batteries and electrochemical capacitors, positive electrodes in which a positive electrode material containing lithium ions is fixed to the surface of a metal foil, and negative electrodes in which a negative electrode material capable of inserting and removing lithium ions is fixed to the surface of a metal foil are used. In recent years, lithium vanadium phosphate (Li3V2(PO4)3) with a NaSiCon structure (Na Super Ionic Conductor) has been attracting attention as an electrode material.

[0003] Lithium vanadium phosphate operates at 3.8V to 4.8V versus the Li / Li+ standard. It can exhibit a high capacity of up to 197mAh / g depending on the potential plateau. Furthermore, lithium vanadium phosphate has a crystalline structure that allows lithium to diffuse three-dimensionally, enabling high-speed charging and discharging. Lithium vanadium phosphate with P-O bonds has high thermal stability and excellent safety. For these reasons, lithium vanadium phosphate is being increasingly used as an electrode material.

[0004] As a result of the research conducted by the inventors of the present invention on lithium vanadium phosphate, it was pointed out that the crystal structure of lithium vanadium phosphate may change due to moisture in the atmosphere, and it was considered that this change in lithium vanadium phosphate due to moisture may cause deterioration in the performance characteristics of electrodes manufactured using lithium vanadium phosphate.

[0005] When lithium vanadium phosphate is left in a high-humidity environment, for example, with a humidity of 80% or higher, the XRD spectrum of the lithium vanadium phosphate changes before and after the storage, and it was speculated that the moisture in the atmosphere causes a change in the crystal structure of the lithium vanadium phosphate. Therefore, the inventors conducted extensive research to improve the durability of lithium vanadium phosphate against moisture, and discovered that mixing a specific metal salt in the manufacturing process of lithium vanadium phosphate can suppress changes in the crystal structure of lithium vanadium phosphate. In other words, lithium vanadium phosphate mixed with a metal oxide suppresses changes in its crystal structure due to moisture. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-52970 [Patent Document 2] Japanese Patent Application Publication No. 2020-163357 [Patent Document 3] Patent Publication No. 2021-163591 Summary of the Invention [Problem to be solved by the invention]

[0007] Lithium vanadium phosphate mixed with metal oxides is prone to deteriorating power output characteristics, and a complex and sophisticated manufacturing process is required to increase yield while maintaining good power output characteristics. In other words, mixing metal oxides using a simple manufacturing process such as that described in Patent Document 3 tends to diminish the high-speed charge / discharge characteristics that are an advantage of lithium vanadium phosphate.

[0008] The output characteristics of an electrode material using lithium vanadium phosphate mixed with a metal oxide can be improved simply by increasing the amount of conductive carbon material added. However, an excessive increase in the amount of conductive carbon material reduces the energy density of the electrode material. Therefore, it is desirable to improve the output characteristics of an electrode material using lithium vanadium phosphate mixed with a metal oxide even using a simple manufacturing process.

[0009] The present invention has been proposed to solve the above-mentioned problems, and its object is to provide an electrode material that exhibits excellent output characteristics while suppressing changes in crystal structure due to moisture, and a simple method for producing the electrode material. [Means for solving the problem]

[0010] To achieve the above object, an electrode material according to an embodiment of the present invention comprises lithium vanadium phosphate bound to a conductive carbon material, the lithium vanadium phosphate being in a mixture with titanium or a titanium compound.

[0011] The lithium vanadium phosphate may be a mixture in which particles of titanium or a titanium compound are present inside and on the surface of a crystal having the lithium vanadium phosphate as a base material.

[0012] The lithium vanadium phosphate may have a difference between the median diameter and the mode diameter of 3 μm or less.

[0013] The lithium vanadium phosphate may have a maximum particle size of 140 μm or less.

[0014] The lithium vanadium phosphate may have a mode diameter of 30 μm or less.

[0015] The titanium compound may be titanium (IV) oxide.

[0016] Furthermore, a manufacturing method of an electrode material according to an embodiment of the present invention includes a crystallization step of bonding a conductive carbon material with lithium vanadium phosphate, and the crystallization step includes an addition step of adding titanium(IV) oxide, a mixing step of mixing water as a solvent after the addition step, and a drying step of spray-drying after the mixing step.

[0017] In the mixing step, alcohol may not be added to the solvent. [Effects of the Invention]

[0018] According to the present invention, an electrode material that can easily obtain high output characteristics while suppressing changes in crystal structure due to moisture can be produced. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a flowchart showing a manufacturing procedure of an electrode material. [Figure 2] 1 is an SEM image of Example 1 observed at a magnification of 10,000 times. [Figure 3] 1 is an SEM image of Example 2 observed at a magnification of 10,000 times. [Figure 4] 1 is an SEM image of Example 3 observed at a magnification of 10,000 times. [Figure 5] 1 is an SEM image of Comparative Example 1 observed at a magnification of 10,000 times. [Figure 6] 1 is an SEM image of Comparative Example 2 observed at a magnification of 10,000 times. [Figure 7] 1 is a graph showing particle distributions in Examples 1 to 3. [Figure 8] 1 is a graph showing particle distribution in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] [composition] The electrode material of this embodiment includes lithium vanadium phosphate and a conductive carbon material. Lithium vanadium phosphate is represented by the general formula Li xIt has a Nasicon structure represented by V2(PO4)3. When lithium vanadium phosphate is used as an electrode material for an energy storage device, the valence of the vanadium ion can be 0≦x≦3, or 3 to 5, due to the deintercalation and insertion of lithium ions during charging and discharging.

[0021] The lithium vanadium phosphate and the conductive carbon material are bonded. The bonded state includes a state in which the lithium vanadium phosphate is in physical contact with the surface of the conductive carbon material and is electrically connected to the conductive carbon material, resulting in high conductivity. For example, the bonded state includes a state in which the lithium vanadium phosphate is bonded to the surface of the conductive carbon material at the atomic level, resulting in a shared structure.

[0022] Lithium vanadium phosphate forms a mixture with a metal oxide and is bonded to a conductive carbon material as a mixture. The lithium vanadium phosphate mixed with the metal oxide is less susceptible to structural changes caused by moisture. "Mixed" means that the two coexist in a doped state, with other crystals incorporated into the interior and surface of the lithium vanadium phosphate crystals that serve as the base material.

[0023] Lithium vanadium phosphate forms a mixture with titanium(IV) oxide, a metal oxide with the chemical formula TiO2. By forming this mixture with titanium(IV) oxide, lithium vanadium phosphate can be formed into a specific particle shape. The specific particle shape is one in which the particle size is uniform and close to spherical, and the absolute value |Δ| of the difference between the median diameter D50 and the mode diameter Md in the particle distribution is 3 μm or less. Hereinafter, this specific particle shape will be referred to as the "specific particle shape."

[0024] By adopting this specific particle shape, lithium vanadium phosphate can obtain a particularly large discharge capacity (mAh / g) at a wide range of discharge rates, for example, from 1 C to 300 C. This eliminates the need to include an excessive amount of conductive carbon material in the electrode material.

[0025] It is more preferable that the lithium vanadium phosphate has a small particle size, such that the maximum particle size D100 of the lithium vanadium phosphate is 140 μm or less, or the mode diameter Md of the lithium vanadium phosphate is 30 μm or less. When the lithium vanadium phosphate has a small particle size, even if the amount of the conductive carbon material is small, the contact area between the conductive carbon material and the lithium vanadium phosphate increases, resulting in better output characteristics.

[0026] The electrode material described above can be formed by first forming a precursor of lithium vanadium phosphate in a liquid-phase reaction such as a complexation reaction, oxidation reaction, polymerization reaction, or condensation reaction, followed by heating and calcination. For example, the electrode material can be obtained by mixing a phosphate source, a conductive carbon material, a lithium source, a vanadium source, and titanium(IV) oxide, followed by calcination. Note that titanium(IV) oxide may be reduced during the production process and doped as titanium into lithium vanadium phosphate.

[0027] Water is used as the solvent during mixing, and each material source is mixed in the aqueous phase. If an alcohol such as ethanol is used in addition to water as a solvent, the high affinity between water and ethanol will cause the vanadium source to recrystallize. Here, titanium compounds other than titanium(IV) oxide, such as titanium butoxide represented by the chemical formula Ti(OCH2CH2CH3)4, require alcohol such as ethanol and water to be highly dispersed in alcohol and hydrolyzed. Therefore, using titanium butoxide makes it easier for the vanadium source dissolved in water during the mixing process to recrystallize. On the other hand, using titanium(IV) oxide as the titanium compound allows water to be used as the solvent for mixing.

[0028] As the conductive carbon material, carbon nanotubes and conductive carbon black having a hollow shell structure (for example, Ketjenblack (registered trademark)) are suitable, but carbon black such as carbon nanofibers, acetylene black, amorphous carbon, carbon fibers, natural graphite, artificial graphite, activated carbon, mesoporous carbon, nanoporous carbon, graphene, fullerene, or a mixture of two or more of these can also be used.

[0029] The vanadium source and phosphate source may include metal acetates, sulfates, nitrates, halides, and chelating agents, whether the lithium vanadium phosphate is produced by hydrolysis or complexation. Specifically, the vanadium source may be NH4VO3. However, sources such as V2O5, V2O3, metallic vanadium, V2O4, vanadium(III) acetylacetonate, and vanadium(IV) oxyacetylacetonate may also be used.

[0030] The phosphate source can be H3PO4, although PO4-containing compounds such as NH4H2PO4, (NH4)2HPO4, P2O5, and Li3PO4 can also be used.

[0031] Lithium sources include CH3COOLi, but may also be LiNO3, Li2CO3, LiOH, LiOH·H2O, LiCl, Li2SO4, and LIC3H5O3.

[0032] The mixing ratio of titanium (IV) oxide, which suppresses changes in the crystal structure of lithium vanadium phosphate due to moisture, is preferably 1 to 25 mol %, more preferably 1 to 10 mol %, relative to vanadium, because if it exceeds 25 mol %, not only will the electrode capacity decrease but the resistance will also increase.

[0033] [Manufacturing method] The method for producing an electrode material of this embodiment includes the following steps. (1) A crystallization process in which a mixture of lithium vanadium phosphate and metal oxide is bonded to a conductive carbon material.

[0034] (1) Crystallization process The crystallization step is a step of bonding a mixture of metal oxide and lithium vanadium phosphate to the surface of a conductive carbon material. An example of the crystallization step is described below using FIG. 1. However, the crystallization step is not limited to the specific method described below, as long as the mixture of the conductive carbon material, titanium (IV) oxide, and lithium vanadium phosphate is bonded to each other. In other words, the order in which the material sources are mixed, and the number and timing of firings can be changed as appropriate.

[0035] In the crystallization process, an addition step is performed in which a phosphate source, a vanadium source, a lithium source, a conductive carbon material, and titanium (IV) oxide are added to water as a solvent while stirring. It is preferable to first add the phosphate source, the vanadium source, and the lithium source to water to prepare a homogeneous solution, and then add the conductive carbon material and titanium oxide, which are solid components. The additives are then mixed in a mixing step. A homogenizer, for example, is used in this mixing step. Instead of mixing using a homogenizer, mechanochemical treatment may be performed.

[0036] When mixing with a homogenizer, the mixture is guided to the rotating inner blade by convection currents generated in the container, crushed at the tip of the rotating inner blade, further crushed between the rotating inner blade and the fixed outer blade, and further crushed and homogenized by the Willem effect of ultrasonic waves and high frequency waves generated between the rotating inner blade and the fixed outer blade. For example, mixing can be carried out for about an hour at a speed of 7,000 to 15,000 rpm.

[0037] Mechanochemical processing is a process that applies mechanical energy such as shear stress and centrifugal force using a rotating reaction vessel, etc. Mechanochemical processing is also used in ultra-centrifugal force processing (hereinafter referred to as UC processing), which applies shear stress, centrifugal force, and other mechanical energy.

[0038] In mechanochemical treatment, shear stress and centrifugal force are applied to a solution in a rotating reactor. A suitable reactor is one consisting of an outer and inner concentric cylinder, with through-holes on the side of the inner cylinder that can rotate, and a sheathing board at the opening of the outer cylinder. This mechanical energy is thought to be converted into the chemical energy required for the reaction, the so-called activation energy. This allows the reaction to proceed in a short time. To provide sufficient mechanical energy, a force of 1500 N (kgms -2 It is desirable to generate a centrifugal force of 60,000 N (kgms) or more. -2 )That's all.

[0039] In this mixing step, a phosphate source or a vanadium source is attached to the conductive carbon material, and base points of lithium vanadium phosphate are generated on the surface of the conductive carbon material. Next, a precursor of a mixture of titanium(IV) oxide and lithium vanadium phosphate is generated at the base points generated on the surface of the conductive carbon material. Furthermore, the process promotes the generation of the lithium vanadium phosphate precursor through a complex formation reaction, a polymerization reaction, a condensation reaction, etc., promotes the mixing of lithium vanadium phosphate and titanium(IV) oxide, promotes bonding between the precursor of the mixture of titanium(IV) oxide and lithium vanadium phosphate and the conductive carbon material, and nanoparticles of the precursor of the mixture of titanium(IV) oxide and lithium vanadium phosphate.

[0040] After the mixing step, the process moves to a drying step. Here, when a titanium compound such as titanium butoxide is used, the vanadium source is likely to recrystallize during the mixing step. Therefore, the treatment solution obtained during the mixing step contains a mixture of vanadium in a solid state due to recrystallization and titanium butoxide, also in a solid state. If a spray dryer is used during the drying step in this state, it becomes difficult to accurately pump the lithium vanadium phosphate material in accordance with the stoichiometric ratio using a pump. Therefore, when a simple production method is employed and titanium butoxide or the like is used, an evaporator is preferred over a spray dryer during the drying step, so as to prevent deviations in the composition ratio of the lithium vanadium phosphate, resulting in poor quality, even with a simple production method.

[0041] In contrast, when titanium(IV) oxide is mixed with lithium vanadium phosphate, there is no need to use an alcohol such as ethanol as a solvent. In other words, water can be used as the solvent in the mixing process, and recrystallization of the vanadium source is easily suppressed. Therefore, the treated solution obtained in the mixing process is easily homogenized, and even if a spray dryer is used in the drying process, the lithium vanadium phosphate material can be pumped up in accordance with the stoichiometric ratio. Furthermore, when spray drying is used for drying, the lithium vanadium phosphate mixed with titanium(IV) oxide can efficiently obtain the specific particle shape, thanks to the suppression of recrystallization of the vanadium source by using water as a solvent.

[0042] The lithium vanadium phosphate having this specific particle shape can improve the output capacity of the electrode material over a wide range of C rates without excessively increasing the amount of conductive carbon material. Therefore, in this drying process, spray drying, also known as atomization drying, is performed.

[0043] In spray drying, the slurry is sprayed into hot air to evaporate the solvent in a short time and obtain a dry powder. A disk nozzle, a two-fluid nozzle, or a twin-jet nozzle can be used in spray drying. A disk nozzle supplies the slurry to a rapidly rotating disk, and centrifugal force causes the liquid raw material to fly. A two-fluid nozzle sprays the slurry by adding gas. This two-fluid nozzle sprays with high-pressure gas, producing smaller particles than a disk nozzle. A twin-jet nozzle further atomizes the fine droplets generated by the two-fluid nozzle by causing them to collide with each other.

[0044] After spray drying, the mixture is calcined in a nitrogen atmosphere at 700 to 900°C for 5 to 120 minutes. This calcination process allows the lithium vanadium phosphate and metal oxide to crystallize simultaneously without agglomeration. This results in an electrode material in the form of a composite powder in which metal oxide crystals are mixed within lithium vanadium phosphate crystals and bonded to the surface of the conductive carbon material.

[0045] A vacuum drying step and a pre-baking step may be included between the spray drying and the baking. In the vacuum drying step, the material is dried in a vacuum at 80 to 130°C. In the pre-baking step, the material is exposed to an air atmosphere at 50 to 300°C for 3 to 5 hours. The heat treatment in the pre-baking step can remove carbon other than that of the conductive carbon material.

[0046] [Action and effect] As described above, the electrode material of this embodiment contains lithium vanadium phosphate bound to a conductive carbon material, and the lithium vanadium phosphate is a mixture with titanium(IV) oxide. Because the lithium vanadium phosphate is a mixture with titanium(IV) oxide, it is possible to suppress structural changes due to moisture. Furthermore, because the lithium vanadium phosphate is a mixture with titanium(IV) oxide, it is possible to improve the output capacity of the electrode material over a wide range of C rates without excessively increasing the amount of conductive carbon material.

[0047] After the addition step, mixing step, spray drying step, and calcination step, the calcination temperature and the like may be adjusted so that titanium(IV) oxide is reduced to titanium and doped into the surface or interior of lithium vanadium phosphate. Such an electrode material also provides water resistance and can improve output capacity over a wide range of C rates.

[0048] Furthermore, the titanium compound may be a titanium phosphate compound which is mixed with lithium vanadium phosphate, or titanium (IV) oxide may be present in an amorphous state.

[0049] Lithium vanadium phosphate mixed with titanium (IV) oxide and a titanium compound such as titanium (IV) oxide can adopt this specific particle shape, which allows the electrode material to be water-resistant by being mixed with titanium (IV) oxide or titanium, while increasing the output capacity (mAh / g) during discharge over a wide range of C-rates.

[0050] This electrode material can be produced by a production method including the steps of adding titanium(IV) oxide to the crystallization step of bonding the conductive carbon material and lithium vanadium phosphate, mixing the titanium(IV) oxide in an aqueous phase after the addition step, and spray-drying the mixture after the mixing step. Thus, the output characteristics of the electrode material using lithium vanadium phosphate can be improved using a simple production process. [Example]

[0051] The present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.

[0052] Example 1 The electrode material of Example 1 was produced using the manufacturing method of Example 1. This electrode material consists of a composite of a mixture of titanium or titanium (IV) oxide and lithium vanadium phosphate, and carbon black. The sources of the lithium vanadium phosphate are ammonium metavanadate (NH4VO3), lithium acetate (CH3COOLi), and phosphoric acid (H3PO4). The weight ratio of each source of lithium vanadium phosphate to carbon black is 70:30.

[0053] First, ammonium metavanadate (NH4VO3), lithium acetate (CH3COOLi), and phosphoric acid (H3PO4) were added to the distilled water while stirring to prepare a treatment solution with the additives uniformly dispersed. Titanium dioxide (IV) and carbon black, which were solid components, were then added to this treatment solution. Next, the mixture was mixed using a homogenizer at 13,000 rpm for 1 hour.

[0054] Then, in the drying process, the mixture was concentrated and dried by spray drying. A spray dryer (manufactured by Okawara Kakoki) equipped with a twin-jet nozzle was used, and the hot air inlet temperature was set to 200°C. After the drying process, the mixture was pre-baked at 300°C for 5 hours. Then, it was baked at 850°C for 60 minutes in a nitrogen atmosphere.

[0055] Through the above crystallization process, an electrode material was obtained in which a mixture of titanium (IV) oxide and lithium vanadium phosphate was bound to the surface of the carbon black.

[0056] Example 2 The electrode material of Example 2 was produced by the production method of Example 2. The production method of Example 2 differs in the type of nozzle used in the spray drying. A two-fluid nozzle was used in the spray drying of Example 2. Except for the type of nozzle, the production method of Example 2, including the production conditions, was the same as that of Example 1. That is, the electrode material of Example 2 also comprises a composite of a mixture of titanium or titanium (IV) oxide and lithium vanadium phosphate, and carbon black.

[0057] Example 3 The electrode material of Example 3 was produced by the manufacturing method of Example 3. The manufacturing method of Example 3 differs in the type of nozzle used in the spray drying. A disk nozzle was used in the spray drying of Example 3. Except for the type of nozzle, the manufacturing method of Example 3, including the manufacturing conditions, was the same as that of Example 1. That is, the electrode material of Example 3 also comprises a composite of a mixture of titanium or titanium (IV) oxide and lithium vanadium phosphate, and carbon black.

[0058] (Comparative Example 1) An electrode material of Comparative Example 1 was produced using the manufacturing method of Comparative Example 1. The electrode material of Comparative Example 1 also consists of a composite of a mixture of Ti and lithium vanadium phosphate and carbon black. The source materials for the lithium vanadium phosphate are ammonium metavanadate (NH4VO3), lithium acetate (CH3COOLi), and phosphoric acid (H3PO4). The weight ratio of each source material for the lithium vanadium phosphate to the carbon black is 70:30. Unlike Examples 1 to 3, the source material for the titanium or titanium compound that forms the mixture with lithium vanadium phosphate is titanium butoxide, represented by the chemical formula Ti(OCH2CH2CH3)4.

[0059] In the addition step, ammonium metavanadate (NH4VO3), lithium acetate (CH3COOLi), phosphoric acid (H3PO4), and an aqueous solution of ethylene glycol and citric acid monohydrate were added to the distilled water while stirring, to prepare a treatment solution with a uniform dispersion of the additives. Titanium dioxide (IV) and carbon black, which are solid components, were then added to this treatment solution. Next, in the mixing step, the treatment solution was mixed using a homogenizer at 13,000 rpm for 1 hour.

[0060] Then, in the drying process, instead of spray drying, the mixed solution was concentrated and dried using an evaporator, vacuum dried at 80°C, and then pre-baked at 300°C for 5 hours. After that, it was baked at 800°C for 60 minutes in a nitrogen atmosphere. Through these crystallization processes, an electrode material was obtained in which a mixture of titanium or titanium butoxide and lithium vanadium phosphate was bonded to the surface of the carbon nanotubes.

[0061] (Comparative Example 2) An electrode material of Comparative Example 2 was produced by the manufacturing method of Comparative Example 2. The manufacturing method of Comparative Example 2 is the same as Comparative Example 1 in that titanium butoxide was used, but instead of an evaporator, spray drying was performed using a spray dryer equipped with the same two-fluid nozzle as in Example 2. The spray drying conditions of Comparative Example 2 were the same as in Example 1. The electrode material of Comparative Example 2 is also a composite of a mixture of titanium or titanium butoxide and lithium vanadium phosphate, and carbon black.

[0062] (particle image) The lithium vanadium phosphate of Examples 1 to 3 and Comparative Examples 1 and 2 was observed with a scanning electron microscope. FIG. 2 is a SEM image at a magnification of 10,000 times of Example 1, FIG. 3 is a SEM image at a magnification of 10,000 times of Example 2, FIG. 4 is a SEM image at a magnification of 10,000 times of Example 3, FIG. 5 is a SEM image at a magnification of 10,000 times of Comparative Example 1, and FIG. 6 is a SEM image at a magnification of 10,000 times of Comparative Example 2. In the SEM images of FIGS. 2 to 5, one scale division is 0.5 μm, and 10 scale divisions are 5.00 μm. In the SEM image of FIG. 6, one scale division is 10 μm, and 10 scale divisions are 100 μm.

[0063] As shown in FIGS. 2 to 4, the particles of lithium vanadium phosphate of Examples 1 to 3 are close to spherical. The lithium vanadium phosphate of Examples 1 to 3 is produced using titanium(IV) oxide as a metal oxide, water as a solvent in the mixing step, and spray drying in the drying step.

[0064] On the other hand, as shown in FIG. 5, the lithium vanadium phosphate of Comparative Example 1 is a coarse, angular, distorted polyhedron. The lithium vanadium phosphate of Comparative Example 1 is produced using titanium butoxide, ethanol is added to the solvent, and an evaporator is used in the drying step. As shown in FIG. 6, the lithium vanadium phosphate of Comparative Example 2 has an increased circularity of individual particles compared to Comparative Example 1, but there are distorted agglomerated particles where the primary particles are connected without an interface, or the particle diameter is non-uniform. The lithium vanadium phosphate of Comparative Example 2 uses spray drying in the drying step as in Examples 1 to 3, but uses titanium butoxide and ethanol is added to the solvent in the mixing step.

[0065] (Particle size distribution) The particle size distributions of the lithium vanadium phosphate of Examples 1 to 3 and Comparative Examples 1 and 2 were measured. FIG. 7 is a graph showing the particle size distributions of Examples 1 to 3, the broken line indicates Example 1, the solid line indicates Example 2, and the dotted line indicates Example 3. FIG. 8 is a graph showing the particle size distribution of Comparative Example 1.

[0066] 7 and 8, the indexes showing the particle size distribution characteristics of Examples 1 to 3 and Comparative Examples 1 and 2 were calculated. The results are shown in Table 1 below. (Table 1) TIFF0007811494000001.tif78161

[0067] As shown in Figures 7 and 8 and Table 1, Examples 1 to 3 showed a clear normal distribution, had a clear spherical shape, and had uniform particle size. Comparative Examples 1 and 2 showed a distorted particle size distribution in which particles with particle sizes below the peak were broadly distributed, and coarse, distorted particles had non-uniform particle size. The absolute value |Δ| obtained by subtracting the mode diameter from the median diameter was 1 μm or less in Examples 1 to 3, which falls within the specific particle shape. In addition, Examples 1 to 3 had a minimum of about 3% and a maximum of about 0.7% of Comparative Examples 1 and 2.

[0068] As described above, the electrode materials of Examples 1 to 3 contain lithium vanadium phosphate bound to a conductive carbon material, and this lithium vanadium phosphate is a mixture with titanium(IV) oxide, and it was confirmed that this falls within the range of the specific particle shape. The maximum value D100 is within the range of 140 μm, and the mode diameter Md is within the range of 30 μm.

[0069] (output characteristics) The output characteristics of the electrode materials of Examples 1 to 3, which contain lithium vanadium phosphate mixed with titanate (IV) and having the specific particle shape, and the electrode materials of Comparative Examples 1 and 2, which contain lithium vanadium phosphate mixed with titanium butoxide and deviating from the specific particle shape, were measured.

[0070] To measure the output characteristics, the electrode materials of Examples 1 to 3 and Comparative Examples 1 and 2 were made into electrodes using PVDF, and half cells were prepared using a metal lithium cell as the counter electrode and an electrolyte containing 1 M LiPF. The solvent for the electrolyte was prepared by mixing ethylene carbonate and diethyl carbonate in a 1:1 volume ratio. The discharge capacity (mAh / g) was measured when the C rates were 1 C, 180 C, and 300 C.

[0071] The results of the discharge capacity measurements are shown in Table 2 below. (Table 2) TIFF0007811494000002.tif78161

[0072] As shown in Table 2, it was confirmed that when the electrode materials of Examples 1 to 3 are used in an electricity storage device, a larger discharge capacity (mAh / g) can be obtained at each C rate in a wide range of discharge rates, such as from 1 C to 300 C, than that of Comparative Examples 1 and 2. The electrode materials of Examples 1 to 3 also exceed those of Comparative Examples 1 and 2 in terms of the retention rate of discharge capacity at high output C rates, such as 180 C and 300 C relative to 1 C.

[0073] The lithium vanadium phosphates of Examples 1 to 3 were prepared using titanium (IV) oxide, water as the solvent in the mixing step, and spray drying in the drying step. The lithium vanadium phosphate of Comparative Example 1 was prepared using titanium butoxide, ethanol as the solvent in the mixing step, and an evaporator in the drying step. The lithium vanadium phosphate of Comparative Example 2 was prepared using spray drying in the drying step as in Examples 1 to 3, but titanium butoxide was used and ethanol was used as the solvent in the mixing step.

[0074] The lithium vanadium phosphates of Examples 1 to 3 fall within the range of the specific particle shape. That is, it was confirmed that the lithium vanadium phosphates of Examples 1 to 3 have the specific particle shape due to the fact that they contain lithium vanadium phosphate bound to a conductive carbon material, the lithium vanadium phosphate is mixed with titanium(IV) oxide, and are mixtures of titanium or a titanium compound such as titanium(IV) oxide and lithium vanadium phosphate.

[0075] This confirmed that good discharge capacity (mAh / g) can be obtained over a wide range of C-rates without increasing the amount of conductive carbon material, while suppressing changes in the crystal structure due to moisture. It was also confirmed that the discharge capacity retention rate at high-power C-rates relative to 1C is good.

Claims

1. comprising lithium vanadium phosphate bound to a conductive carbon material; The lithium vanadium phosphate is a mixture with titanium or a titanium compound, The lithium vanadium phosphate has a difference between a median diameter and a mode diameter of 3 μm or less. An electrode material characterized by:

2. the lithium vanadium phosphate forms a mixture in which particles of titanium or a titanium compound are present inside and on the surface of a crystal having the lithium vanadium phosphate as a base material; The electrode material according to claim 1 ,

3. comprising lithium vanadium phosphate bound to a conductive carbon material; The lithium vanadium phosphate is a mixture with titanium (IV) oxide; An electrode material characterized by:

4. The lithium vanadium phosphate has a maximum particle size of 140 μm or less; The electrode material according to claim 1,

5. The lithium vanadium phosphate has a mode diameter of 30 μm or less; The electrode material according to claim 1 or 4, characterized in that

6. the titanium compound is titanium(IV) oxide; 6. The electrode material according to claim 1, 2, 4 or 5, characterized in that:

7. A crystallization step of bonding a conductive carbon material and lithium vanadium phosphate, The crystallization step includes: an adding step of adding titanium (IV) oxide; a mixing step of mixing water as a solvent after the adding step; a drying step of spray-drying the mixture after the mixing step; containing, A method for producing an electrode material, characterized by:

8. In the mixing step, no alcohol is added to the solvent; The method for producing an electrode material according to claim 7, characterized by:

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