JP7208147B2 - Lithium vanadium oxide crystal, electrode material, and storage device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a lithium vanadium oxide crystal, an electrode material containing this lithium vanadium oxide crystal, and an electric storage device using this electrode material for a positive electrode or a negative electrode.

Crystals of lithium vanadium oxide represented by lithium vanadate of the chemical formula Li ₃ VO ₄ have a charge-discharge potential (vs Li/Li+) of lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and B-type titanium oxide (TiO ₂ (B)). Therefore, when lithium vanadium oxide crystals are used as a negative electrode material for an electric storage device, the electric storage device achieves high energy density. On the other hand, this lithium vanadium oxide crystal has a higher charge/discharge potential (vs Li/Li+) than graphite. Therefore, when lithium vanadium oxide crystals are used as a negative electrode material for an electric storage device, the electric storage device can be expected to have high safety.

Furthermore, there is a report that the theoretical capacity of a capacitor using lithium vanadium oxide crystals as a negative electrode material is at least twice that of lithium titanate. In terms of cycle characteristics as well, a capacitor using lithium vanadium oxide crystals as a negative electrode material maintains a high capacity retention ratio and a high charge/discharge efficiency.

Therefore, this lithium vanadium oxide crystal is used in a lithium ion secondary battery using metal compound particles for the positive electrode and the negative electrode, or using activated carbon for the positive electrode and a material capable of reversibly adsorbing/desorbing lithium ions for the negative electrode. It is expected to be used for electric storage devices such as hybrid capacitors, and research continues.

FIG. 1 shows the conventionally known crystal structure of lithium vanadate among lithium vanadium oxide crystals. FIG. 1 is a simulated graph showing the results of powder X-ray diffraction analysis of a conventional lithium vanadate crystal. As shown in FIG. 1, when the conventional lithium vanadate crystal is analyzed by X-ray diffraction, a Bragg peak appears near an incident angle 2θ of 32.2 degrees (±0.7 degrees). This Bragg peak indicates that the crystal structure of lithium vanadate has an alignment rule of LiO ₄ -coordination structure and VO ₄ -coordination structure with an interplanar distance of 2.72 Å on the 020 plane.

Five Bragg peaks also appear in a lower angle range than the Bragg peak near 32.2 degrees. Five Bragg peaks appear, one in the range from 25 degrees to 30 degrees, three in the range from 20 degrees to 25 degrees, and one in the range from 15 degrees to 20 degrees. In order from the larger angle, the 111 plane, 011 plane, 101 plane, 110 plane and 010 plane have interplanar distances of 3.17 Å, 3.66 Å, 3.90 Å, 4.13 Å and 5.45 Å. It indicates the existence of ordering rules of LiO ₄ -coordination structure and VO ₄ -coordination structure.

The repeating pattern of the arrangement in the long-range by the LiO ₄ -coordination structure and the VO ₄ -coordination structure indicated by these five Bragg peaks is called long-range order. It has five types of long-range order in the range of angles lower than 2θ of 32.2 degrees. Also, the coordination structure of V ⁵⁺ is tetrahedral coordination.

JP 2008-77847 A

FIG. 2 is a graph showing the charge/discharge characteristics of a capacitor in which the lithium vanadate crystal is compounded with carbon and the compound is used as the active material for the negative electrode material. The horizontal axis indicates capacity, and the vertical axis indicates charge/discharge potential (vs Li/Li+). As shown in FIG. 2, the capacitor using this lithium vanadate crystal has a large charging/discharging hysteresis of about 0.4 to 0.5 V, and has a problem of large energy loss due to charging/discharging.

FIG. 3 is a graph showing the lithium ion diffusion coefficient of a capacitor in which this lithium vanadate crystal is compounded with carbon and the compound is used as a negative electrode material. As shown in FIG. 3, there is a problem that there is a range in which the diffusion coefficient drops sharply as the capacity increases. As described above, lithium vanadium oxide has many points to be improved in terms of electrochemical properties.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lithium vanadium oxide crystal that can achieve better electrochemical properties and uses thereof.

In order to achieve the above object, a lithium vanadium oxide crystal according to the present invention is characterized by having a crystal structure in which cations are disordered.

This lithium vanadium oxide crystal may be lithium vanadate represented by the chemical formula Li ₃ VO ₄ .

Regarding this lithium vanadium oxide crystal, the crystal structure represented by the result of X-ray diffraction has a peak at an incident angle 2θ of around 32.2 degrees, and a lower angle than the peak around 32.2 degrees. There is no peak in the range, or even if there is a peak, the diffraction intensity of all peaks existing in the range of angles lower than the peak near 32.2 degrees is less than the diffraction intensity of the peak near 32.2 degrees. is also small.

The diffraction intensity of a peak appearing in a range of angles lower than the peak near 32.2 degrees may be 50 or less when the diffraction intensity of the peak near 32.2 degrees is 100.

The LiO ₆ -coordination structure and the VO ₆ -coordination structure are arranged side by side, and all or part of the long-range order in the lower angle range than the peak near 32.2 degrees is broken and random. good too.

In addition, the LiO ₆ -coordination structure and the VO ₆ -coordination structure are arranged side by side, and at least a part of the VO ₆ -coordination structure maintains octahedral coordination regardless of the insertion and withdrawal of lithium ions. good too.

Also, the LiO ₆ -coordination structure and the VO ₆ -coordination structure are arranged side by side, and at least a part of the VO ₆ -coordination structure adopts octahedral coordination and hexahedral coordination according to lithium ion insertion and extraction. may

An electrode material containing this lithium vanadium oxide crystal is also one embodiment of the present invention.

This electrode material has composite particles obtained by combining the lithium vanadium oxide crystal and carbon, and the crystal structure represented by the result of X-ray diffraction of the composite particles has an incident angle 2θ of A peak appears around 32.2 degrees, and there is no peak in the range of angles lower than the peak around 32.2 degrees, or even if there is a peak, it is lower than the peak around 32.2 degrees. The diffraction intensity of all the peaks present in the angle range is smaller than the diffraction intensity of the peak near 32.2 degrees, and a broad halo pattern appears in the range of angles lower than the peak near 32.2 degrees. You can let it be.

A power storage device using this electrode material for a positive electrode or a negative electrode is also one embodiment of the present invention.

In addition to high energy density, high safety, high capacity retention rate, and high charge/discharge efficiency, the lithium vanadium oxide crystal of the present invention has a dramatically improved lithium ion diffusion coefficient and excellent charge/discharge hysteresis and rate characteristics. Good electrochemical properties can be achieved even at points.

FIG. 10 is a simulation graph showing the result of powder X-ray diffraction analysis of a conventional lithium vanadium oxide crystal; FIG. 1 is a graph showing charge/discharge characteristics of a capacitor using a conventional composite of lithium vanadium oxide crystals and carbon. 1 is a graph showing lithium ion diffusion coefficients of capacitors using conventional composites of lithium vanadium oxide crystals and carbon. 1 is a simulated graph showing the results of powder X-ray diffraction analysis of the present lithium vanadium oxide crystal. FIG. 2 is a schematic diagram showing a first estimation of the VO ₆ coordination structure during lithium ion insertion/extraction, relating to the present lithium vanadium oxide crystal. FIG. 2 is a schematic diagram showing a second estimation of the VO ₆ coordination structure during lithium ion insertion and extraction, relating to the present lithium vanadium oxide crystal. 4 is a graph showing the results of powder X-ray diffraction analysis of a mixture of carbon and the present lithium vanadium oxide crystals. FIG. 2 is a schematic diagram showing a first presumption of the mechanism of change to the present lithium vanadium oxide crystal. FIG. 4 is a schematic diagram showing a second estimation of the mechanism of change to the present lithium vanadium oxide crystals. 1 is a flow chart showing a manufacturing process of an intermediate of an example. It is an example of a reactor for producing the intermediates of the examples. It is an HRTEM image (x 30k) of the intermediate of the example. 2 is an HRTEM image showing the results of measuring the size and number of particles in region 1. FIG. 3 is an HRTEM image showing the results of measuring the particle size and the number of particles in region 2. FIG. 3 is an HRTEM image showing the results of measuring the size and number of particles in region 3. FIG. 2 is a graph showing the CC-CV processing profile for the intermediates of the Examples. 4 is a graph showing the results of powder X-ray diffraction analysis of the intermediate before CC-CV treatment. 1 is a graph showing the results of powder X-ray diffraction analysis of the final product after CC-CV treatment. FIG. 4 is a schematic diagram showing the transition of results analyzed by powder X-ray diffraction during CC-CV processing. 4 is a graph showing lithium diffusion coefficients of a composite of carbon and a cation-order intermediate and a composite of carbon and the present lithium vanadium oxide crystal of cation-disorder. 4 is a graph showing charge-discharge hysteresis of a half-cell using a composite of carbon and a cationic-order intermediate. 4 is a graph showing the charge-discharge hysteresis of a half-cell using a composite of carbon and the lithium vanadium oxide crystal of cation disorder. 4 is a graph showing the rate characteristics during charging of each half-cell using a composite of carbon and a cation-order intermediate and a composite of carbon and the present lithium vanadium oxide crystal of cation-disorder. 4 is a graph showing the rate characteristics during discharge of each half-cell using a composite of carbon and a cation-order intermediate and a composite of carbon and the present lithium vanadium oxide crystal of cation-disorder.

Embodiments for carrying out the present invention will be described below. In addition, this invention is not limited to embodiment described below.

(Industrial applicability)
First, the lithium vanadium oxide crystal of the present invention (hereinafter referred to as the present lithium vanadium oxide crystal) is a material into which lithium ions can be reversibly intercalated and deintercalated. This lithium vanadium oxide crystal is suitable for use as, for example, an electrode material for an electric storage device. Electricity storage devices include lithium ion secondary batteries and hybrid capacitors.

In the lithium ion secondary battery, the positive electrode has an active material layer containing a lithium metal compound, the negative electrode has an active material layer containing the present lithium vanadium oxide crystals, and lithium ions are reversibly inserted into the positive electrode and the negative electrode. and desorbed Faraday reaction electrode. In the hybrid capacitor, the positive electrode is, for example, a polarizable electrode having activated carbon, and the electric double layer formed at the interface between the activated carbon and the electrolyte is used to store electricity, and the negative electrode is an active material containing the present lithium vanadium oxide crystals. It is a faradaic reaction electrode with a layer into which lithium ions are reversibly intercalated and deintercalated.

(this lithium vanadium oxide crystal structure)
The present lithium vanadium oxide crystals have a crystal structure that yields the X-ray diffraction results shown in FIG. FIG. 4 is a graph showing the result of powder X-ray diffraction analysis based on simulation of the present lithium vanadium oxide crystal. As shown in FIG. 4, it is the same as the conventional case (see FIG. 1) in that a sharp peak appears near the incident angle 2θ of 32.2 degrees. Incidentally, the vicinity of 32.2 degrees means 32.2±0.7 degrees.

However, all the peaks present in the lower angle range than the peak near 32.2 degrees have diffraction intensities smaller than the peak near 32.2 degrees. Preferably, as shown in FIG. 4, the peak disappears in a lower angle range than the peak near 32.2 degrees. In other words, no peak with a higher diffraction intensity than the peak near 32.2 degrees exists in the range of angles lower than near 32.2 degrees. On the other hand, the peak at an incident angle 2θ of around 32.2 degrees or more still exists.

This lithium vanadium oxide crystal, which is inferred from the results of this X-ray diffraction, has a cation disordered structure in which cations are disordered. That is, the present lithium vanadium oxide crystal has the following two structures. The present lithium vanadium oxide crystal may have only one of these two structures, or both of them may be mixed.

First, as a first structure, as shown in FIG. 5A, when lithium ions are inserted, the coordination structure of vanadic acid has an octahedral structure of VO ₆ with vanadium ions having an oxidation number of 3+ as lattice centers. In addition, even when lithium ions are desorbed, the coordination structure of vanadic acid maintains the octahedral structure of VO ₆ with an oxidation number of 5+. In the octahedral structure of VO ₆ with an oxidation number of 5+, the vanadium ions are positioned off the center of the crystal lattice. A portion of the VO ₄ -coordination structure that reverts to the tetrahedral structure when lithium ions are desorbed may remain. Furthermore, the LiO ₆ coordination structure centered on the lithium ion also has an octahedral structure.

Next, as a second structure, as shown in FIG. 5B, when lithium ions are inserted, the coordination structure of vanadic acid has an octahedral structure of VO ₆ with vanadium ions having an oxidation number of 3+ as lattice centers. . The structure at the time of lithium insertion is the same as the first structure. On the other hand, when lithium ions are desorbed, the coordination structure of vanadic acid may become a hexahedral structure due to VO ₆ with an oxidation number of 5+. In the hexahedral structure of VO ₆ with oxidation number 5+, vanadium ions are centered in the crystal lattice. A portion of the VO ₄ -coordination structure that reverts to the tetrahedral structure when lithium ions are desorbed may remain. Furthermore, the LiO ₆ coordination structure centered on lithium ions also has a hexahedral structure.

And, both of the two structures are mixed, that is, the coordination structure of vanadic acid at the time of lithium ion insertion has an octahedral structure of VO ₆ with vanadium ions having an oxidation number of 3+ as the lattice center, During the desorption of lithium ions, the coordination structure of some vanadates maintains an octahedral structure with VO ₆ of oxidation state 5+, with vanadium ions positioned off-center in the crystal lattice, while others The coordination structure of vanadic acid in part changes to a hexahedral structure by VO ₆ with an oxidation number of 5+, vanadium ions are placed at the center of the crystal lattice, and LiO ₆ coordination structure centering on lithium ions has a hexahedral structure.

In both structures, the arrangement of the VO ₆ -coordinated structure and the LiO ₆ -coordinated structure is random because all or part of the various long-range orders appearing in the lower angle range than the peak near 32.2 degrees are broken. It's becoming In other words, the regularity of the arrangement of the VO ₆ -coordination structure and the LiO ₆ -coordination structure at the distance appearing in the lower angle range than the peak near 32.2 degrees is lost, or the proportion following the regularity is reduced. ing.

More specifically, the present lithium vanadium oxide crystal has an arrangement rule of LiO ₄ -coordination structure and VO ₄ -coordination structure with an interplanar distance of 2.72 Å on the 020 plane (hereinafter referred to as standard order) There is On the other hand, the LiO ₄ coordination structure with interplanar distances of 3.17 Å, 3.66 Å, 3.90 Å, 4.13 Å and 5.45 Å on the 111, 011, 101, 110 and 010 planes. The proportion of the VO ₄ -coordination structure that maintains the arrangement rule (hereinafter referred to as long-range order) is smaller than the standard order, or the long-range order is lost.

Such lithium vanadium oxide crystals include lithium vanadate crystals represented by the chemical formula Li ₃ VO ₄ . When lithium ions are inserted, the composition formula becomes Li _3+x VO ₄ . x is the lithium ion inserted. The present lithium vanadium oxide crystals are preferably nanoparticles with a size of 10 nm or more and 50 nm or less, more preferably 10 nm or more and 30 nm or less. is the body.

Moreover, it is preferable that this lithium vanadate crystal is a composite compounded with carbon. Carbon can be used without particular limitation as long as it has conductivity. For example, carbon black such as ketjen black, acetylene black, channel black, fullerene, carbon nanotube, carbon nanofiber, amorphous carbon, carbon fiber, natural graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, vapor phase method Carbon fiber etc. can be mentioned. Carbon nanotubes may be either single-wall carbon nanotubes (SWCNT) or multi-wall carbon nanotubes (MWCNT).

A composite of carbon and the present lithium vanadium oxide crystal yields the X-ray diffraction results shown in FIG. FIG. 6 is a graph showing the results of powder X-ray diffraction analysis based on simulation of a composite of carbon and the present lithium vanadium oxide crystal. As shown in FIG. 6, the point that the peak appears near the incident angle 2.theta.

Moreover, all the peaks present in a range of angles lower than the peak near 32.2 degrees have diffraction intensities smaller than that of the peak near 32.2 degrees. Preferably, as shown in FIG. 6, the peak disappears in a lower angle range than the peak near 32.2 degrees. However, in the lower angle range than the peak near 32.2 degrees, a broad halo pattern appears when the carbon is a multi-walled carbon nanotube, for example. That is, a gentle mountain spreads over a wide range of low angles.

In such a present lithium vanadium oxide crystal, since the long-range arrangement regularity of the LiO ₆ -coordination structure and the VO ₆ -coordination structure has already been disturbed, LiO ₆ The long-range alignment of the coordination and VO ₆ coordination structures is not altered, so less energy is required for lithium ion insertion and extraction. In fact, the present lithium vanadium oxide crystal has an improved diffusion coefficient of lithium ions. Therefore, charge/discharge hysteresis and rate characteristics are improved. In addition, the combination with carbon improves the electrical conductivity, and together with the improvement of the diffusion coefficient of lithium ions, the rate characteristics are further improved.

(Manufacturing method of the present lithium vanadium oxide crystal)
CC-CV (Constant Current Constant Voltage) treatment is applied to conventional lithium vanadate crystals (hereinafter referred to as intermediates) having long-range order and _VO4 having a tetrahedral coordination structure when lithium ions are desorbed. By performing, the present lithium vanadium oxide crystal is obtained. The intermediate is obtained through a step of mixing a lithium source and a vanadium source and a heat treatment step. In the case of producing a composite with carbon, the carbon source may be further added in the mixing step in the process of producing the intermediate.

The manufacturing method will be described in detail below, taking the present lithium vanadium oxide crystal compounded with carbon as an example. In addition, when compounding with carbon is unnecessary, the carbon source may not be included in the production process.

(Preparation of intermediates)
First, the method for producing the intermediate will be described. The intermediate undergoes a mixing step, a dispersion step, a polymer chain forming step, a removal step and a crystallization step. In the mixing step, a mixed solvent is prepared by mixing a metal particle source containing a vanadium source and a lithium source, a conductive carbon material, a complex ligand, and a polymerization agent. In the dispersing step, a metal particle source is attached to the surface of the carbon material to produce a lithium vanadate precursor. In the polymer chain forming step, a polymer chain is formed on the lithium vanadate precursor deposited on the carbon material. In the removing step, the carbon material to which the lithium vanadate precursor forming the polymer chain is attached is heated to remove the polymer chain. In the crystallization step, the carbon material to which the lithium vanadate precursor is attached is fired to obtain a composite material of lithium vanadate and the carbon material.

Specifically, in the mixing step, a vanadium source, a lithium source, a carbon source, a complex ligand, and a polymerization agent are added to a solvent to prepare a mixed solution. Vanadium sources include metallic vanadium and vanadium-containing compounds. The composition ratio of the materials added to the solvent can be, for example, 10 to 20 mol % of the metal particle source, which is a combination of the vanadium source and the lithium source, 10 to 20 mol % of the complex ligand, and 40 to 80 mol % of the polymerization agent. Also, the weight ratio of the metal particle source and the carbon source is preferably 80:20 to 60:40. The vanadium source and the lithium source may be in accordance with the stoichiometric ratio of the present vanadic acid crystals. For example, in the case of Li ₃ VO ₄ , they may be mixed in a molar ratio of Li:V=3:1. The weight ratio of the metal particle source and the carbon source, which is the sum of the vanadium source and the lithium source, is preferably 80:20 to 60:40, although not limited thereto.

Vanadium-containing compounds include metavanadates ( _NH4VO3 , _NaVO3 , _{KVO3 ,} etc.), vanadium oxides _{( V2O5 , V2O4} , _V2O3 , _V3O4 ), vanadium _{( III} ) acetylacetonate, vanadium (IV) oxyacetylacetonate, vanadium oxytrichloride, vanadium tetrachloride, vanadium trichloride, polyvanadate and the like can be used. Lithium-containing compounds such as lithium hydroxide, lithium hydroxide hydrate, lithium acetate, lithium nitrate, lithium carbonate, lithium chloride, and lithium lactate can be used as the lithium source.

A carbon source means carbon (powder) itself or a material that can be converted to carbon by heat treatment. As the carbon (powder), any conductive carbon material can be used without particular limitation. Materials that can be converted to carbon by heat treatment include those that are converted to carbon in the subsequent heat treatment process, such as polyhydric alcohols (ethylene glycol, etc.), polymers (polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, etc.), sugars (glucose, etc.), Organic substances such as amino acids (such as glutamic acid).

An organic compound having a plurality of carboxyl groups is used as the complex ligand. For example, it is preferable to use the tricarboxylic acid citric acid. Alternatively, dicarboxylic acids such as oxalic acid, malonic acid and succinic acid may be used. An alcohol having a plurality of hydroxyl groups is used as the polymerizing agent. For example, it is preferred to use ethylene glycol. Alternatively, other dihydric alcohols such as propylene glycol or trihydric alcohols such as glycerin may be used. Any solvent can be used without any particular limitation as long as it does not adversely affect the reaction, and water, methanol, ethanol, isopropyl alcohol and the like can be preferably used. A mixture of two or more solvents may be used.

A metal complex is formed by the metal particle source and the complex ligand by mixing the aqueous solution to which each material is added by a stirring means. Also, during mixing, an esterification reaction occurs between the carboxyl groups of some of the metal ligands and the hydroxyl groups of some of the polymerizing agents to form polymer chains. In the mixing step, after preparing a plurality of aqueous solutions, the solutions may be mixed to obtain an aqueous solution to which the above materials are added. For example, by adding only the metal particle source and the complex ligand to water and mixing them, the formation of the metal complex can be promoted. The carbon source can also be added after mixing this aqueous solution with, for example, an aqueous ethylene glycol solution. As the stirring means, a magnetic stirrer, an electric motor stirrer, an air motor stirrer, or the like is used.

In the dispersing step, a metal particle source is attached to the surface of the carbon source. A mechanochemical treatment is mentioned as a method of adhering the metal particle source to the surface of the carbon source. Mechanochemical treatment is treatment that applies mechanical energy such as shear stress and centrifugal force using a rotating reaction vessel or the like. The mechanochemical treatment may be an ultra-centrifugal force processing method (hereinafter referred to as UC treatment) or the like, as long as shear stress, centrifugal force, or other mechanical energy can be applied. In short, the mechanical energy should be able to attach the metal particle source to the carbon source and produce a lithium vanadium oxide precursor on the surface of the carbon source. The mechanochemical treatment can also serve as a finer and highly dispersed treatment for the metal particle source and the carbon source.

The UC process applies shear stress and centrifugal force to the solution in the swirling reactor. The reactor is composed of concentric cylinders of an outer cylinder and an inner cylinder, as described in FIG. 1 of JP-A-2007-160151. A reactor in which a weir is arranged at one end is preferably used. A reactant is charged into the inner cylinder of the reactor, and the inner cylinder is swirled, whereby the centrifugal force causes the reactant inside the inner cylinder to move to the inner wall of the outer cylinder through the through-hole of the inner cylinder. At this time, the reactant collides with the inner wall of the outer cylinder due to the centrifugal force of the inner cylinder, forms a thin film, and slides up to the upper part of the inner wall.

In this state, both the shear stress with the inner wall and the centrifugal force from the inner cylinder are simultaneously applied to the reactant, and large mechanical energy is applied to the thin film-like reactant. It is believed that this mechanical energy is converted into the chemical energy required for the reaction, the so-called activation energy. Thereby, the reaction proceeds in a short time. For satisfactory application of mechanical energy, it is desirable to generate a centrifugal force of 1500 N (kgms ^-2 ) or more. It is preferably 60000 N (kgms ^-2 ) or more.

The mechanochemical treatment can be divided into at least two treatments. For example, in the first treatment, shear stress and centrifugal force are applied to the vanadium source and the carbon source to cause the vanadium source to adhere to the carbon source. Then, in the second treatment, a shear stress and a centrifugal force are applied to the lithium source and the vanadium source attached to the surface of the carbon source, and the vanadium base formed on the surface of the carbon source is used as a starting point for lithium. Precursors of vanadium oxide can be produced. In the UC treatment as described above, the bundle of the fibrous carbon source is loosened and the carbon source is dispersed in the solution. Also, the metal complex in the mixed solution is finely divided into fine particles, which are uniformly dispersed and adsorbed on the surface of the carbon source.

As a dispersing method, mixer, jet mixing (jet impingement), ultrasonic treatment, etc. can be used in addition to UC treatment. In the dispersion method using a mixer, physical force is applied to the mixed solution by a bead mill, rod mill, roller mill, stirring mill, planetary mill, vibration mill, ball mill, homogenizer, homomixer, or the like to stir the mixed solution. By applying an external force to the carbon source, the aggregated carbon source can be subdivided and homogenized, and the bundle can be loosened. Among them, a planetary mill, a vibration mill, and a ball mill are preferable because they can obtain a crushing force.

In the dispersion method by jet mixing, a mixed solution is pressurized by a high-pressure pump and jetted from the pair of nozzles to collide head-on in the chamber. This allows the carbon source bundles to be pulverized, dispersed and homogenized. The conditions for jet mixing are preferably a pressure of 100 MPa or more and a concentration of less than 5 g/l.

In the polymer chain forming step, the UC-treated mixed solution is heated to form a polymer chain on the precursor of lithium vanadate adhering to the carbon source. For example, the mixed solution from which impurities have been removed by filtration is dried at 80 to 150° C. in vacuum. The drying time is 12-24 hours. By this polymer chain forming treatment, an esterification reaction between the carboxylic acid of the complex ligand coordinated to the lithium vanadate precursor and the hydroxyl group of the polymerizing agent proceeds. Moreover, polymerization (dehydration condensation) proceeds between the hydroxyl groups of the polymerizing agent. These reactions form many polymer chains.

The polymer chain includes an aspect in which it is formed on a lithium vanadate precursor alone and an aspect in which it is formed between lithium vanadate precursors. By the polymer chain forming step as described above, a polymer chain is formed between the precursors of lithium vanadate, and the precursors of lithium vanadate are prevented from being bonded to each other to form aggregates. That is, fine precursors of lithium vanadate are uniformly dispersed on the surface of the carbon source.

In the removing step, the carbon source to which the lithium vanadium oxide precursor forming polymer chains is attached is heated to remove the polymer chains. For example, the carbon source is heated at 300 to 320° C. in an air atmosphere. The heating time is 3 to 5 hours. This heating step thermally decomposes and removes the polymer chains formed by the metal ligands and the polymerizing agent. Therefore, only fine particles of the lithium vanadium oxide precursor are left on the carbon source.

In the crystallization step, the carbon source to which the precursor of lithium vanadate is adhered is fired to obtain a composite material of lithium vanadate and carbon. During the firing process, the precursor of lithium vanadate is crystallized, and metal particles of lithium vanadate are supported on the carbon. As for the heating conditions, for example, firing is performed at 500 to 900° C. in a nitrogen atmosphere. The baking time is 0 to 5 minutes. In the sintering process, it is preferable to rapidly heat from room temperature to the sintering temperature. The firing time of 0 minutes means that the temperature is raised to 800° C. over 3 minutes, and when the temperature reaches 800° C., the heating is terminated and the material is naturally cooled. Such rapid heating promotes crystallization of the lithium vanadium oxide and prevents particle growth. That is, nanoparticles of small particle size are maintained.

Moreover, the rapid heating is preferably performed in an atmosphere with a low oxygen concentration of about 1000 ppm. Rapid heating under these conditions prevents oxidation of carbon. Lithium vanadate is crystallized by the firing process as described above, and a composite material in which lithium vanadium oxide as nanoparticles is supported on carbon is obtained.

Here, in order to obtain the present lithium vanadium oxide crystals, that is, to efficiently change the structure to a cationic disordered structure, lithium vanadate is desirably nanoparticles. The size of the nanoparticles has an average size of 30 nm or less and a maximum of less than 50 nm. According to the method for producing the intermediate as described above, it is possible to easily satisfy the size requirements of the nanoparticles.

(CC-CV processing)
By subjecting the obtained intermediate to a CC-CV treatment, a composite of the present lithium vanadium oxide crystal and carbon can be obtained. The CC-CV treatment is a treatment in which a half cell is produced using an intermediate as a negative electrode, and a constant current and a constant voltage are applied to this half cell.

Half-cell working electrode W. E. is formed by mixing and kneading a composite with a binder, forming it into a sheet, and bonding it to a current collector. An electrode may be formed by coating a mixed solution of the composite and the binder on a current collector by a doctor blade method or the like and drying it. Alternatively, the electrode can be formed by molding the electrode material into a predetermined shape and pressing it onto the current collector.

Conductive materials such as aluminum, copper, iron, nickel, titanium, steel, and carbon can be used as current collectors. In particular, it is preferable to use aluminum and copper. This is because it has high thermal conductivity and high electronic conductivity. The shape of the current collector may be any shape such as film, foil, plate, net, expanded metal, and cylindrical.

Examples of binders include rubbers such as fluorine-based rubbers, diene-based rubbers, and styrene-based rubbers, fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride, celluloses such as carboxymethyl cellulose and nitrocellulose, and other polyolefin resins and polyimides. Examples include resins, acrylic resins, nitrile resins, polyester resins, phenol resins, polyvinyl acetate resins, polyvinyl alcohol resins, epoxy resins, and the like. These binders may be used alone or in combination of two or more.

Half-cell counter electrode C.I. E. The active material may be lithium metal or non-lithium metal as long as it is a lithium-containing compound capable of releasing lithium. Lithium metal is preferred. This active material is used as a working electrode W.A. E. After mixing and kneading with a binder that is the same as or different from W.W. E. It is formed by bonding to a current collector that is the same as or different from the current collector. The electrolytic solution is not particularly limited, but may be, for example, a mixed solution of 1.0 M lithium hexafluorophosphate (LiPF ₆ )/ethylene carbonate (EC) and dimethyl carbonate (DEC). The volume ratio is, for example, EC:DEC=1:1.

In the CC-CV process, a constant current continues to flow through the half-cell in the first stage, a constant voltage current continues to flow through the half-cell in the second stage, and a constant current continues to flow through the half-cell again in the third stage. The constant current in the first stage is desirably 20 to 400 mAg ⁻¹ (g is per Li ₃ VO ₄ ), and the starting voltage in the first stage is desirably 2.0 to 3.5V. The transition to the second stage is desirably at the timing when the voltage drops to the range of 0.05 to 0.5V. When aluminum is used as the current collector, the voltage is preferably 0.4 V or more and 0.5 V or less. It is preferable that the second stage is continued for a certain period of time and the constant voltage is maintained for a period of 4 hours or more and 10 hours or less. At this time, it is more desirable that the value of the current flowing during the constant voltage is 1/10 or less of that in the first stage. The transition to the third stage is at the end of the fixed period of time in the second stage. The constant current in the third stage is desirably 20 or more and 400 mAg ⁻¹ (g is per Li ₃ VO ₄ ). The end timing of the third stage is desirably when the voltage returns to the starting voltage of the first stage.

In this first stage, the voltage is varied to the point where cation disordering due to lithium insertion proceeds. A current value exceeding 400 mAg ⁻¹ leads to deterioration of the present lithium vanadium oxide crystal. Although it is speculation, it is thought that the voltage drop becomes large, the insertion reaction of lithium ions does not proceed, and a large current flows at the time of transition to the second stage. On the other hand, if it is less than 20 mAg ⁻¹ , CC-CV processing takes a long time. The starting point of the voltage value is the voltage when the half-cell is assembled, but it does not necessarily have to be that voltage. 2.0 to 3.5 V is a margin when the voltage deviates due to the half-cell quality.

Then, it is presumed that cation disordering progresses in the second stage. It is considered that the lower the voltage value, the higher the certainty that cation disordering progresses. However, when the voltage value is less than 0.05 V, lithium metal is deposited. On the other hand, it was found that cation disordering does not occur when the voltage exceeds 0.5V. The range of 0.05 V or more is for the case of using copper as the current collector of the half cell. When aluminum is used as the current collector of the half cell, the voltage is preferably 0.4 V or more and 0.5 V or less before the alloying reaction of aluminum and lithium occurs.

In the third stage, lithium ions are desorbed from the present lithium vanadium oxide crystal having the cation disordered structure while maintaining the cation disordered structure. A current value exceeding 400 mAg ⁻¹ leads to deterioration of the present lithium vanadium oxide crystal. Although it is speculation, it is thought that the voltage drop becomes large, the insertion reaction of lithium ions does not proceed, and a large current flows at the time of transition to the second stage. On the other hand, if it is less than 20 mAg ⁻¹ , CC-CV processing takes a long time. The starting point of the voltage value is the voltage when the half-cell is assembled, but it does not necessarily have to be that voltage. 2.0 to 3.5 V is a margin when the voltage deviates due to the half-cell quality.

Although it is a guess, it is effective to apply a low constant voltage of 0.05 V or more and 0.5 V or less in the second stage in this CC-CV treatment continuously for a long time of 4 hours or more and 10 hours or less. It is considered to be a thing. That is, as shown in FIGS. 7A and 7B, in the conventional lithium vanadium oxide crystal, a tetrahedral VO ₄ -coordination structure centered on vanadium ions with an oxidation number of 5+ is formed in accordance with the intercalation and deintercalation of lithium ions. and reversibly take a hexahedral VO ₅ -coordination structure centered on vanadium ions with an oxidation number of 4+.

However, when a low constant voltage is applied for a long period of time, as shown in FIGS. 7A and 7B, the hexahedral VO ₅ -coordination structure centered on vanadium ions with an oxidation state of 4+ changes to an octahedral structure centered on V ³⁺ . It irreversibly transforms into a faceted VO ₆ -coordinated structure. The fraction of octahedral VO ₆ -coordination structures with V ³⁺ as the lattice center increases with the application of a low constant voltage for a long time.

Finally, according to the insertion and extraction of lithium ions, as shown in FIG. 7A, the octahedral VO ₆ coordination structure with V ³⁺ as the lattice center and V ⁵⁺ were placed at positions shifted from the lattice center. It is believed that a reversible change with the octahedral VO ₆ coordination structure occurs, resulting in the present lithium vanadium oxide crystal in which the long-term order is partially or wholly disrupted.

Alternatively, depending on the insertion and extraction of lithium ions, an octahedral VO ₆ -coordination structure with V ³⁺ as the lattice center and a hexahedral VO ₆ -coordination structure with V ⁵⁺ at the lattice center, as shown in FIG. 7B It is thought that the present lithium vanadium oxide crystals in which a part or all of the long-term order is destroyed.

Alternatively, depending on the insertion of lithium ions, V ⁵⁺ was shifted from the lattice centered octahedral VO ₆ coordination structure with V ³⁺ as shown in FIGS. 7A and 7B. The present lithium vanadium oxide crystals undergo both a reversible change to an octahedral VO ₆ -coordination structure and a reversible change to a hexahedral VO ₆ -coordination structure with V ⁵⁺ placed at the lattice center. It is considered to be a thing.

As a method for obtaining the present lithium vanadium oxide crystal having a cationic disorder structure, the intermediate may be processed by a mechanical milling method instead of the CC-CV processing. In the mechanical milling method, for example, a planetary ball mill, ball mill, bead mill, rotary mill, vibration mill, or the like is used to impart mechanical energy to the intermediate. The treatment environment is preferably an inert gas atmosphere such as argon gas, and the treatment time is preferably about 6 hours to about 100 hours.

(Example)
Examples of the present invention are shown below, but the present invention is not limited to the examples. First, a composite material (Li ₃ VO ₄ /CNT) of lithium vanadate and carbon nanotubes (CNT) was produced as an intermediate by the following production method.

A metal particle source for lithium vanadate is obtained by using ammonium metavanadate (NH ₄ VO ₃ ) as a vanadium source and a lithium hydroxide (LiOH) solution as a lithium source, and mixing such that the molar ratio of Li:V is 3:1. bottom. Multi-walled carbon nanotubes were used as CNTs. The average fiber diameter of CNT was 11 nm. The weight ratio of the lithium vanadate metal particle source and CNT used was 60:40. Citric acid was used as a metal ligand, and ethylene glycol was used as a polymerization agent. One equivalent of citric acid and 4 equivalents of ethylene glycol were added to the vanadium source.

Specifically, as shown in FIG. 8, as a first solution, ammonium metavanadate and citric acid were added to distilled water (H ₂ O) and stirred using a magnetic stirrer. In the first solution, a metal complex of ammonium metavanadate is formed. Also, as a second solution, ethylene glycol was added to distilled water and stirred using a magnetic stirrer. The first solution and the second solution were mixed and stirred using a magnetic stirrer. A lithium hydroxide solution, carbon nanotubes, and distilled water were added to a mixed solution of the first solution and the second solution to obtain a third solution.

This third solution was subjected to UC treatment in an environment of 80°C. In the UC treatment, a reactor as shown in FIG. 9 was used, the rotation speed was 50 m/s, and a centrifugal force of 66000 N (kgms ⁻² ) was applied to the third solution for 5 minutes. It is believed that this UC treatment unravels the CNT bundles and promotes the formation of fine particles of the precursor of lithium vanadate having a metal complex, which is uniformly dispersed and adheres to the surface of the CNTs.

Next, impurities were filtered from the third solution, and vacuum drying was performed at 130° C. overnight. In this vacuum drying, an esterification reaction proceeds between the carboxyl group of citric acid and the hydroxyl group of ethylene glycol with the precursor of lithium vanadate attached to the surface of the CNT as a nucleus to form a polymer chain. It is believed that the formation of polymer chains results in the formation of polymer chains between precursors of lithium vanadate and prevents the precursors of lithium vanadate from binding to each other to form aggregates. Therefore, the fine precursor of lithium vanadate is uniformly dispersed on the surface of the CNT.

The vacuum-dried CNTs were heated at 300° C. for 3 hours in an air atmosphere. This heat treatment at 300° C. thermally decomposes the polymer chains formed by the esterification of citric acid and ethylene glycol. Therefore, only fine precursors of lithium vanadate remain on the surface of the CNT.

After that, sintering was performed at 800° C. for 0 minute in a nitrogen atmosphere. In this firing, the temperature was raised to 800° C. over 3 minutes, and when the temperature reached 800° C., the heating was terminated and natural cooling was performed. By this baking, the precursor of lithium vanadate is crystallized, and the surface of the CNT is in a state in which nanoparticles of lithium vanadate are bonded. As described above, a composite material (Li ₃ VO ₄ /CNT) in which nanoparticle lithium vanadate was supported on CNT was obtained as an intermediate.

An HRTEM image of this intermediate was taken to analyze the crystal structure. FIG. 10 is an HRTEM image showing the intermediate. 11 to 13 show the results of visually measuring the size of particles containing aggregates and the number of particles per area for lithium vanadate in regions 1 to 3 shown in FIG. As is clear from FIGS. 11 to 13, the largest particle size of lithium vanadate confirmed in each region was about 50 nm. Also, the proportion of fine nanoparticles of 30 nm or less in each region was calculated. As a result, about 90% of region 1, about 79% of region 2, and about 89% of region 3 contained metal particles of 30 nm or less. Over the entire area, approximately 87% were metal particles of 30 nm or less.

Next, a half cell was produced using the obtained intermediate. A 2032 type coin cell was used as the half cell. Specifically, polyvinylidene fluoride PVDF was selected as the binder, and the intermediate and the binder were stirred together to form a slurry, which was applied onto a copper foil, and the working electrode W.D. E. and The charging ratio was Li ₃ VO ₄ :CNT:PVDF=56:38:6 in weight ratio. Lithium metal was used as the counter electrode, and was attached to the lower lid of the 2032 type coin cell. Counter electrode C.I. A glass fiber separator, a gasket, a working electrode W.E. E, a spacer, a spring, and an upper lid were placed in this order and crimped to prepare a cell. The electrolytic solution was prepared by using ethylene carbonate (EC) and dimethyl carbonate (DEC) as solvents and adding 1.0 M lithium hexafluorophosphate (LiPF ₆ ) as a solute. The volume ratio was EC:DEC=1:1. This electrolytic solution was permeated to form a cell.

Then, the intermediate was subjected to CC-CV treatment according to the profile shown in FIG. As shown in FIG. 14, as a first step, from a starting voltage of 2.5 V until the voltage reaches 0.4 V, 0.02 Ag ⁻¹ (g per lithium vanadate) with a C rate of 0.05 C of constant current was applied to insert lithium ions into the intermediate. Then, as the second step, a constant voltage of 0.4 V was maintained for 10 hours. Finally, as the third step, a constant current of 0.02 Ag ⁻¹ (g is per lithium vanadate) with a C rate of 0.05 C is applied from the starting voltage of 0.4 V until the voltage returns to 2.5 V, Lithium ions were eliminated from the intermediate.

(Powder X-ray diffraction analysis)
The product before and after this CC-CV treatment was analyzed by powder X-ray diffraction. The results are shown in FIGS. 15 and 16. FIG. FIG. 15 is the result of analysis of the intermediate before CC-CV treatment, and FIG. 16 is the result of analysis of the final product after CC-CV treatment.

The powder X-ray diffraction analysis results shown in FIG. 15 were obtained by measuring the range of 15°-40° at 1.5°min ⁻¹ with the beamline BL5S2 of the Aichi Synchrotron. In addition, the analysis results shown in FIG. 16 were obtained by using the SmartLab of the equipment manufacturer Rigaku while the final product was in the half cell after the CC-CV treatment, and the range of 15 ° -40 ° was 1.5 ° min ^-1 obtained by measuring In creating the graph, processing was performed to remove the broad halo pattern derived from the electrolyte in the half-cell.

As shown in FIG. 15, the result of analysis of the intermediate before CC-CV treatment shows a sharp peak near an incident angle 2θ of 32.2 degrees. This peak indicates that the canonical order of LiO ₄ -coordination structure and VO ₄ -coordination structure with interplanar distance period of 2.72 Å on the 020 plane exists in the intermediate.

Also, it can be seen that there are five types of peaks in the lower angle range than the peak near the incident angle 2θ of 32.2 degrees. The five peaks are LiO4 with interplanar distances of 3.17 Å, 3.66 Å, 3.90 Å, _4.13 Å and 5.45 Å on the 111, 011, 101, 110 and 010 planes. indicating that long-range order of coordination and _VO4 -coordination structures is present in the intermediates.

In addition, a broad halo pattern appears in a range of angles lower than the peak near the incident angle 2θ of 32.2 degrees. This halo pattern is multi-walled carbon nanotubes combined with lithium vanadate.

In the intermediate before the CC-CV treatment, the diffraction intensity of the peak appearing in the range of 25 to 30 degrees was 52, assuming that the diffraction intensity of the peak near the incident angle 2θ of 32.2 degrees was 100. The diffraction intensities of the three peaks appearing in the range of 20 to 25 degrees were 76, 106 and 111 from the highest angle. The diffraction intensity of the peak appearing in the range of 15 degrees to 20 degrees was 38. That is, the diffraction intensity for the 110 plane and the 010 plane is a higher value than the diffraction intensity for the 020 plane appearing near 32.2 degrees. This indicates that the long-range order of LiO ₄ -coordination structure and VO ₄ -coordination structure with interplanar distances of 4.13 Å and 5.45 Å is abundant.

On the other hand, as shown in FIG. 16, the result of analysis of the final product after CC-CV treatment maintains a sharp peak around an incident angle 2θ of 32.2 degrees. However, in the range where the incident angle 2θ is lower than the peak near 32.2 degrees, all the peaks that existed before the CC-CV treatment are smaller than the peak appearing near 32.2 degrees. Also, the peak at which the diffraction intensity is high does not exist in the lower angle range than the vicinity of 32.2 degrees.

That is, assuming that the diffraction intensity of the peak near the incident angle 2θ of 32.2 degrees is 100, the diffraction intensity of the peak related to the 111 plane that appears in the range of 25 to 30 degrees decreases from 52 to 20. The diffraction intensity of the peak related to the 011 plane, which appears at the largest angle in the range of 20 degrees to 30 degrees, is reduced from 76 to 33. The diffraction intensity of the peak related to the 101 plane, which appears at the second largest angle in the range of 20 to 30 degrees, decreases from 106 to 43. The diffraction intensity of the peak related to the 110 plane, which appears at the largest angle in the range of 20 degrees to 30 degrees, is reduced from 111 to 47. The diffraction intensity of the peak related to the 010 plane that appears in the range of 15 degrees to 20 degrees is reduced from 38 to 10 degrees.

Thus, all the peaks that appear in the range of angles lower than the incident angle 2θ of 32.2 degrees are half or less of the peak near 32.2 degrees. Therefore, the present lithium vanadium oxide crystal after CC-CV treatment has a cation-disordered crystal structure.

Here, X-ray diffraction analysis (in situ XRD) was performed in the half-cell state during CC-CV processing. The results are shown in FIG. As shown in FIG. 17, the diffraction intensity of the five types of peaks in the lower angle range than the peak near 32.2 degrees decreases over time during the constant voltage application process, which is the second stage of the CC-CV treatment. I know you are. That is, by extending the time of the second stage or lowering the constant voltage value, the five types of peaks in the lower angle range than the peak near 32.2 degrees are zero or close to zero as simulated. I understand.

In FIG. 17, there is a relatively tall broad in the range lower than the peak near 32.2 degrees, and the existence of this broad makes it 5 degrees lower than the peak near 32.2 degrees. The species peak is higher than the peak around 32.2 degrees. However, this broadness is derived from the half-cell electrolytic solution, which was obtained by performing the X-ray diffraction analysis in the half-cell state. Therefore, when graph processing was performed to subtract the broad derived from the electrolytic solution of this half-cell, for example, after performing the second stage of CC-CV for 10 hours, the results were the same as those shown in FIG.

(Evaluation of lithium ion diffusion coefficient)
The lithium ion diffusion coefficient of the intermediate before the CC-CV treatment, that is, the conventional lithium vanadium oxide crystal and carbon composite, and the present lithium vanadium oxide crystal obtained by CC-CV treatment of the intermediate. evaluated.

For the evaluation of the lithium ion diffusion coefficient, the same half-cell as the half-cell produced during the CC-CV treatment was produced for the intermediate under the same conditions. Both half-cells were previously subjected to charge/discharge stabilization treatment. The charge-discharge stabilization treatment for the intermediate was 5 cycles of charge-discharge at 0.76 V-2.5 V and 0.1 Ag ⁻¹ , and the charge-discharge stabilization treatment for the present lithium vanadium oxide crystal was 0.76V-2.5V. 5 cycles of 4V CC-CV charging and discharging. Then, the diffusion coefficient of lithium ions was measured by GITT (Galvanostatic Intermittent Titration Technique). The voltage range is 0.76-2.5 V (vs. Li/Li ⁺ ), the current value is 0.01 Ag ⁻¹ (g is per lithium vanadate), the constant current charging time is 30 minutes, A rest period of 2 hours was given. The results are shown in FIG.

As shown in FIG. 18, at each capacity (mAhg ⁻¹ ), the lithium ion diffusion coefficient of the present lithium vanadium oxide crystal and carbon composite is higher than that of the conventional lithium vanadium oxide crystal and carbon composite. It can be seen that the coefficient of diffusion is higher than that of the ion diffusion coefficient and is smooth with no abrupt drops. According to FIG. 18, the lithium-ion diffusion coefficient of the composite of lithium vanadium oxide crystal and carbon is 10 to 100 times the lithium-ion diffusion coefficient of the conventional composite of lithium vanadium oxide crystal and carbon. improving.

(Evaluation of charge/discharge hysteresis)
Next, charge and discharge of the intermediate before the CC-CV treatment, that is, the conventional lithium vanadium oxide crystal and carbon composite, and the present lithium vanadium oxide crystal obtained by CC-CV treatment of the intermediate. Hysteresis was evaluated. When evaluating the charge-discharge hysteresis, the voltage range was 0.1-2.5 V (vs. Li/Li ⁺ ) and the current value was 0.01 Ag ⁻¹ (g is per lithium vanadate) for both half-cells. and The results are shown in FIGS. 19 and 20. FIG.

First, as shown in FIG. 19, the potential hysteresis was 0.4 to 0.5 V when the conventional composite of lithium vanadium oxide crystal and carbon was used. On the other hand, as shown in FIG. 20, when the present lithium vanadium oxide crystal and carbon composite was used, the potential hysteresis was reduced to 90 mV, which is 0.1 V or less.

When converted to energy efficiency, it is 85% when the conventional lithium vanadium oxide crystal and carbon composite is used, whereas when the present lithium vanadium oxide crystal and carbon composite is used, the energy efficiency is 85%. is found to reach 95%. The energy was obtained from integration of the potential and volume of the charge/discharge curves shown in FIGS. 19 and 20. FIG. That is, the present lithium vanadium oxide crystal can achieve good electrochemical properties in terms of charge-discharge hysteresis.

(Evaluation of rate characteristics)
Next, the intermediate before the CC-CV treatment, that is, the conventional lithium vanadium oxide crystal and carbon composite, and the present lithium vanadium oxide crystal obtained by CC-CV treatment of the intermediate and carbon was evaluated for the rate characteristics of the composite.

For the rate evaluation, the same half-cell as the half-cell produced during the CC-CV treatment was produced for the intermediate under the same conditions. For both half-cells the working electrode W. E. The potential range of (vs Li/Li+) was 2.5V-0.76V. During the charge test, the lithium ion desorption is fixed at 0.1Ag ^-1 (g is per lithium vanadate complex), and the lithium ion insertion current is varied from 0.02 to 5Ag ^-1 . . In addition, during the discharge test, the desorption of lithium ions was fixed at 0.1Ag ^-1 (g is per lithium vanadate complex), and the current for insertion of lithium ions was varied from 0.02 to 12Ag ^-1 . ing. The results are shown in FIGS. 21 and 22. FIG.

FIG. 21 is a graph showing the relationship between current density and charge capacity during charging. The horizontal axis represents current density (Ag ⁻¹ ), and the vertical axis represents charge capacity (mAhg ⁻¹ ). As shown in FIG. 21, the present composite of lithium vanadium oxide crystal and carbon could be charged with a large capacity at each current density compared to the conventional composite of lithium vanadium oxide crystal and carbon. I understand.

FIG. 22 is a graph showing the relationship between current density and discharge capacity during discharge. The horizontal axis represents current density (Ag ⁻¹ ), and the vertical axis represents charge capacity (mAhg ⁻¹ ). As shown in FIG. 22, with regard to the composite of the present lithium vanadium oxide crystal and carbon, it was possible to discharge a large capacity at each current density compared to the conventional composite of lithium vanadium oxide crystal and carbon. I understand. Moreover, with respect to the conventional lithium vanadium oxide crystal and carbon composite, the discharge capacity drops sharply when the current density is increased in the range of 1 Ag ⁻¹ or less, whereas the present lithium vanadium oxide In the composite of crystal and carbon, the drop in discharge capacity was very smooth even when the current density was increased.

That is, according to the present lithium vanadium oxide crystal, it was confirmed that high output and high capacity and high input and high capacity can be realized and the rate characteristics are improved by improving the lithium ion diffusion coefficient. Moreover, by combining with carbon, the composite containing lithium vanadium oxide crystals synergistically acquires high electrical conductivity together with the improvement of the lithium ion diffusion coefficient, resulting in a dramatic improvement in rate characteristics. are doing.

Claims (8)

having a crystal structure in which cations are disordered,
The crystal structure represented by the result of X-ray diffraction is
A peak appears near the incident angle 2θ of 32.2 degrees,
Furthermore, whether there is a peak in the lower angle range than the peak near 32.2 degrees,
Alternatively, even if there is a peak, the diffraction intensity of all peaks present in a range of angles lower than the peak near 32.2 degrees is 50 or less when the diffraction intensity of the peak near 32.2 degrees is 100. thing,
A lithium vanadium oxide crystal characterized by: Represented by the chemical formula Li ₃ VO ₄ ,
The lithium vanadium oxide crystal according to claim 1, characterized by: consists of a LiO ₆ -coordination structure and a VO ₆ -coordination structure side by side,
All or part of the long-range order in the range of angles lower than the peak near 32.2 degrees is broken and random;
3. The lithium vanadium oxide crystal according to claim 1 or 2 . consists of a LiO ₆ -coordination structure and a VO ₆ -coordination structure side by side,
at least a portion of the VO ₆ -coordinated structure maintains octahedral coordination despite insertion and withdrawal of lithium ions;
4. The lithium vanadium oxide crystal according to any one of claims 1 to 3 . consists of a LiO ₆ -coordination structure and a VO ₆ -coordination structure side by side,
at least a portion of the VO ₆ -coordination structure adopts octahedral and hexahedral coordination upon lithium ion insertion and extraction;
5. The lithium vanadium oxide crystal according to any one of claims 1 to 4 . An electrode material comprising the lithium vanadium oxide crystal according to any one of claims 1 to 5 . Composite particles obtained by combining the lithium vanadium oxide crystal and carbon,
The crystal structure represented by the result of X-ray diffraction of the composite particles is
A peak appears near the incident angle 2θ of 32.2 degrees,
Furthermore, whether there is a peak in the lower angle range than the peak near 32.2 degrees,
Alternatively, even if there is a peak, the diffraction intensity of all peaks present in a range of angles lower than the peak near 32.2 degrees is 50 or less when the diffraction intensity of the peak near 32.2 degrees is 100. ,
Furthermore, a broad halo pattern appears in a range of angles lower than the peak near 32.2 degrees,
The electrode material according to claim 6 , characterized by: Using the electrode material according to claim 6 or 7 for a positive electrode or a negative electrode,
An electricity storage device characterized by:

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