WO2022019313A1 - Lithium vanadium oxide granules and power storage device - Google Patents

Abstract

Provided are lithium vanadium oxide granules whereby increased input/output can be achieved in a power storage device, and a power storage device in which the granules are used. The granules include lithium vanadium oxide and carbon, and have a double structure including an inner layer 3 and an outer layer shell 2 that envelops the inner layer 3. The inner layer 3 is formed by a plurality of particles of lithium vanadium oxide being brought together while maintaining grain boundaries, and the outer layer shell 2 is formed by connection of at least some of the particles of lithium vanadium oxide without grain boundaries.

Description

Lithium vanadium oxide granules and power storage devices

The present invention relates to a granulated body of lithium vanadium oxide and a power storage device using the granulated body as an active material for an electrode as a positive electrode or a negative electrode.

Due to the rapid spread of digital cameras, smartphones and portable PCs, rising fuel prices and growing awareness of environmental loads, and expectations for application to automobile power or smart grid storage, secondary batteries and hybrid capacitors are used. The development of power storage devices is becoming active.

The secondary battery uses a positive electrode in which a positive electrode material containing lithium ions is fixed to the surface of the current collector, and a negative electrode in which a negative electrode material capable of inserting and removing lithium ions is fixed to the surface of the current collector. .. Further, as the hybrid capacitor, a positive electrode having an active material having an electric double layer action such as activated carbon formed on the surface of the current collector and a negative electrode having a negative electrode material containing lithium ions fixed to the surface of the current collector are used. .. These energy storage devices have advantages such as high working voltage, high energy density, light weight, and long service life, and are being actively developed as the best choice.

Electrode materials containing lithium ions generally do not reach the required level of conductivity. Therefore, as the electrode material containing lithium ions, a composite in which a metal compound capable of occluding and releasing lithium is supported on a carbon material as a conductive auxiliary agent is often used. Examples of the metal compound include lithium cobalt oxide, lithium iron phosphate, lithium titanate, lithium manganese phosphate, lithium vanadium and the like.

In recent years, the development of electric vehicles (EVs) and hybrid electric vehicles (HEVs) in which a part of the drive is assisted by an electric motor is rapidly advancing at each automobile manufacturer. The power storage devices used in these automobiles are required to have high input / output. One means of achieving high input / output is to make a composite of a metal compound and carbon capable of occluding and releasing lithium into nanoparticles. By making nanoparticles, the distance of the metal compound to the inside of the particles is shortened. That is, the diffusion coefficient of lithium ions is improved by making nanoparticles. Therefore, the insertion and removal of lithium ions is accelerated, and a secondary battery with high input / output can be realized.

Japanese Unexamined Patent Publication No. 2004-39538

However, if nanoparticles are used, the moldability and shape retention of the electrode active material layer deteriorate. Therefore, it is necessary to form a granulated body by a binder, sintering, or the like, and to improve the workability of electrode formation by using the granulated body.

When a granulated body is formed, many of the nanoparticles are in a dense state where they come into contact with each other, or the nanoparticles are aggregated to the extent that some of the nanoparticles are connected without grain boundaries. Then, even if the nanoparticles are formed, it becomes difficult for lithium ions to diffuse to the nanoparticles existing on the center side of the granulated body. That is, even if nanoparticles are used, the effect of increasing the input / output of the power storage device is diminished by granulation, and the capacity is also reduced.

An object of the present invention is to provide a lithium vanadium oxide granulation body capable of increasing input / output of a power storage device and a power storage device using the granulation body in order to solve the above problems.

In order to achieve the above object, the granulated body of lithium vanadium oxide according to the present invention contains lithium vanadium oxide and carbon, and has a double structure of an inner layer and an outer layer shell that encloses the inner layer, and the inner layer has a double structure. The outer layer shell is characterized in that a plurality of particles of the lithium vanadium oxide are gathered together while maintaining grain boundaries, and at least a part of the particles of the lithium vanadium oxide are connected without grain boundaries.

That is, the granulated body has a capsule structure in which the inner layer is wrapped with the outer layer shell. A plurality of particles of lithium vanadium oxide are present in the inner layer while retaining nanoparticles without agglomeration. Since the nanoparticles in the inner layer are not aggregated, they contribute to high input / output of the power storage device. On the other hand, the nanoparticles in the inner layer are wrapped in an outer shell in which a plurality of particles of lithium vanadium oxide are aggregated and do not fall apart, and the moldability and shape retention of the electrode active material layer are improved. The non-aggregated state in the inner layer means a state in which a plurality of particles of lithium vanadium oxide are present while maintaining grain boundaries, and the agglomerated state in the outer layer shell means that at least a part of the lithium vanadium oxide particles are present. A state in which they are connected without a grain boundary.

The outer layer shell may be opened at 50 nm or more and 150 nm or less, and may have a gap portion for communicating the inner layer and the outside of the granulated body. The gaps opened at 50 nm or more and 150 nm or less can allow the electrolytic solution to permeate into the inner layer. That is, even if the granulated body has a capsule structure due to the outer layer shell, lithium ions can reach the nanoparticles in the inner layer, resulting in higher input / output of the power storage device and formability and shape retention of the electrode active material layer. Is more highly compatible.

At least a part of the outer layer particles which are the particles of the lithium vanadium oxide in the outer layer shell may be hollow inside. Since the outer layer shell is also formed of the electrode active material, it contributes to the development of capacity. Unlike the particles in the inner layer, the outer layer particles in the outer layer shell have a surface that is connected to other particles and is difficult to touch the electrolytic solution. The surface area that comes into contact with the particles is large, and the distance to the inside of the outer layer particles is short, so that lithium ions can be easily inserted and removed.

A part of the carbon may be interposed between the inner layer particles which are the particles of the lithium vanadium oxide in the inner layer. By interposing carbon between the inner layer particles, the contact ratio between the inner layer particles is reduced to suppress aggregation, and further high input / output of the power storage device is achieved.

The carbon interposed between the inner layer particles is amorphous carbon, and the other part of the carbon may be attached to the surface of the inner layer particles as graphic carbon.

Amorphous carbon can create electron paths between the inner layer particles, and by using graphic carbon, that is, carbon with a high degree of graphitization and high electrical conductivity, the carbon adhering to the surface of the inner layer particles is used with respect to the inner layer particles. It becomes easier to transfer electrons. Moreover, since the graphic carbon formed on the surface of the inner layer particles does not reduce the contact ratio of the inner layer particles or create an electron path between the inner layer particles, the complex of the inner layer particles and the carbon becomes huge. However, a high ion diffusion coefficient can be realized.

The amorphous carbon may be contained in a proportion of 3.0 or more and 8.0 wt% or less with respect to the entire granulated body. Within this range, the granulated material develops a good capacity and has good output characteristics.

A further part of the carbon may be contained in the outer layer shell. Particles in the outer shell can also increase electrical conductivity.

The carbon may be carbonized sucrose or glucose. For carbonized sucrose or glucose, the granulated product exhibits a good volume and has good output characteristics.

The lithium vanadium oxide may include Li ₃ VO ₄ doped with a tetravalent metal species. Further, the tetravalent metal species may be Si.

A power storage device in which the granulated body of this lithium vanadium oxide is contained in the positive electrode or the negative electrode is also one of the embodiments of the present invention. The granulated body may be contained in which a part of the outer layer shell is collapsed and a part or the whole of the inner layer is exposed. As a result, the inner layer particles can be exposed more to the electrolytic solution without significantly impairing the shape retention and moldability of the electrode active material layer, the capacity of the power storage device can be improved, and further high input / output can be realized.

According to the present invention, it is possible to improve the formability and shape retention of the active material layer formed on the electrodes while achieving high input / output of the power storage device.

It is sectional drawing of the granulation body of lithium vanadium oxide. It is an enlarged view of the outer layer shell, and a cross section of a part of the outer layer particles is drawn. It is an enlarged view of the inner layer, and the inner layer particles are partially broken and the internal structure is drawn. It is a flochart which shows the manufacturing method of the granulation body of lithium vanadium oxide. It is a photograph which shows the surface SEM image of the granulation body of lithium vanadium oxide. It is a photograph which shows the cross-sectional SEM image of the granulation body of lithium vanadium oxide. It is a photograph which mapped the distribution of each element in a granule based on SEM-EDX, (a) is a carbon atom C, (b) is an oxygen atom O, (c) is a silicon atom Si, (d) is a vanadium atom. The distribution of V is shown. It is the photograph which observed the outer layer shell of the granulation body by STEM, (a) is a dark field photograph, (b) is a bright field photograph. It is a STEM image of the outer layer shell of the granulation body. It is a TEM image of the inner layer particles of a granulated body. It is a TEM image of the inner layer of the granulated body. It is a TEM image of the inner layer particles of a granulated body. FIG. 3 is a selected area diffraction diagram of the edge region of the inner layer particles of the granulated body. It is an SEM photograph which shows the cross section of the electrode active material layer. It is a graph which shows the output characteristic of Example 1 and Comparative Example 1. It is a graph which shows the amount of graffiti carbon and amorphous carbon in the granulation body of Examples 1 to 3 and Comparative Example 2. It is a graph which shows the relationship between the discharge current density and the discharge capacity of the half cell of Comparative Example 2 and Examples 1 to 3. It is a graph which shows the relationship between the discharge current density and the discharge capacity of the half cell of Examples 1 and 4 to 6.

Although the embodiment of the present invention will be described, the present invention is not limited to the following embodiments.

(Granulation of lithium vanadium oxide)
The granulation body of the present invention is an aggregate of particles of lithium vanadium oxide. Lithium vanadium oxide is composited with carbon. The lithium vanadium oxide is typically lithium vanadate represented by the _{chemical formula Li 3} VO _{4. Preferred is Li 3} VO ₄ doped with a tetravalent metal species M, represented by the chemical formula Li _{3 + x} V _1-x M _x O ₄ , which is a solid solution of _{Li 3} VO ₄ and Li ₄ MO _4. Examples of the tetravalent metal species M include Si, Ti, Ge and the like.

The lithium vanadium oxide doped with the tetravalent metal species M has Li ₃ VO ₄ as a matrix structure, and V ⁵⁺ is ^{partially replaced with M 4+} to introduce interstitial Li. In the chemical formula Li _{3 + x} V _1-x M _x O ₄ , the coefficient x of the metal species M is preferably 0.2 or more and 0.4 or less. When the coefficient x of the metal species M is 0.2 or more and 0.4 or less, the lithium vanadium oxide has a single crystal structure of only the γ phase in the temperature range of at least −40 to 60 ° C. including normal temperature.

The crystal structure of the γ phase in the lithium vanadium oxide is a so-called LISION (Lithium Super Ionic CONductor) type, and has a Pnma crystal structure. That is, the crystal of lithium vanadium oxide having a γ-phase crystal structure has a tetrahedral LiO _4- coordination structure and a tetrahedral VO _4- coordination structure as basic skeletons, and an octahedral LiO _{6-coordination structure.} Has a structure. Since the lithium vanadium oxide crystal has a γ-phase crystal structure, the mass diffusivity of lithium ions is improved. That is, in the log-log graph of the diffusion coefficient, there is no range in which the diffusion coefficient drops sharply as the capacity increases.

As shown in FIG. 1, this granulated body is a true sphere and has a double structure of an outer layer shell 2 and an inner layer 3. The inner layer 3 is a spherical nucleus containing the center of a true sphere. The outer layer shell 2 is a shell that encloses the inner layer 3. That is, this granulated body has a capsule structure in which the inner layer 3 is surrounded by the outer layer shell 2. Both the outer layer shell 2 and the inner layer 3 are composed of particles of lithium vanadium oxide.

The radius of the granulated body is from the center of the inner layer 3 to the outer surface of the outer layer shell 2, and the diameter of the granulated body is preferably 1 μm or more and 10 μm or less. When the diameter of the granulated body is 1 μm or more, the moldability and shape retention of the electrode active material layer containing the granulated body are good. The thickness of the outer layer shell 2 is preferably 100 nm or more and 200 nm or less. When the thickness exceeds 200 nm, it is possible to achieve both high input / output of the power storage device and formability and shape retention of the electrode active material layer, but the ratio of the outer layer shell 2 to the granulated body becomes large, and the ions of the granulated body become large. The diffusion coefficient drops below the peak, limiting the increase in input / output of the power storage device.

If the thickness of the outer layer shell 2 is 100 nm or more, it becomes robust enough to maintain the shape of at least a part of the outer layer shell 2 in the process of forming the electrode active material layer, and it becomes easy to form the electrode active material layer. When the thickness of the outer layer shell 2 is 200 nm or less, the shape of the other part can be maintained while the outer layer shell 2 is partially broken by applying pressure in the process of forming the electrode active material layer. Since the shape of a part of the outer layer shell 2 is maintained, the moldability and shape retention of the electrode active material layer can be maintained without being extremely deteriorated. On the other hand, the inner layer 3 can be exposed by collapsing a part of the outer layer shell 2. Due to the exposure of the inner layer 3, the particles of the lithium vanadium oxide of the inner layer 3 can be easily in contact with the electrolytic solution, and the ion diffusion coefficient is further improved.

As shown in FIG. 2, the outer layer shell 2 is composed of primary particles of lithium vanadium oxide aggregated. Further, the outer layer shell 2 contains carbon in the same amount as the inner layer 3. The primary particles of lithium vanadium oxide constituting the outer layer shell 2 are referred to as outer layer particles 21. Aggregation refers to a state in which part or all of the outer layer particles 21 are integrated at the crystal level and can be observed as if they are connected without grain boundaries, and the surface of the granulated body is confirmed with a scanning electron microscope at a magnification of 100,000 times. do it.

However, a gap 22 remains between some of the outer layer particles 21. The gap portion 22 is a pore penetrating the outer layer shell 2 and communicates the outer side of the granulated body with the inner layer 3. The gap portion 22 has a maximum opening width of 50 nm or more and 150 nm or less so that the electrolytic solution of the power storage device can pass through the outer layer shell 2.

The outer layer particles 21 have a hollow portion 23 inside. That is, the inside of the outer layer particles 21 is hollow. In the power storage device, the hollow portion 23 of the outer layer particles 21 is filled with the electrolytic solution, and the surface area of the outer layer particles 21 in contact with the electrolytic solution becomes large, so that the capacity developed in the outer layer shell 2 becomes large, and the outer layer particles 21 aggregate. Even if it is done, the ion diffusion coefficient can be improved. The diameter of the internal space is preferably 5 nm or more and 30 nm or less. When the diameter of the internal space is within this range, the outer layer particles 21 are less likely to collapse, and the formability and retention of the electrode active material layer are improved.

The particle size of the outer layer particles 21 is preferably distributed in the range of 50 nm or more and 100 nm or less. When the particle size of the outer layer particles 21 is 50 nm or more, gaps 22 having an opening width of 50 nm or more and 150 nm or less are likely to occur between the outer layer particles 21. The gap portion 22 having an opening width of 50 nm or more and 150 nm or less has little influence on the robustness of the granulated body, but easily allows the electrolytic solution to pass through. On the other hand, when the particle size of the outer layer particles 21 exceeds 100 nm, the gap portion 22 becomes larger, and when the opening width of the gap portion 22 exceeds 150 nm, the robustness of the granulated body drops from the peak.

Returning to FIG. 1, the inner layer 3 is composed of a large number of primary particles of lithium vanadium oxide. The primary particles of lithium vanadium oxide constituting the inner layer 3 are referred to as inner layer particles 31. The inner layer particles 31 are housed in the inner layer 3 while suppressing aggregation. The state in which aggregation is suppressed means a state in which the inner layer particles 31 are separated from each other, or even if the inner layer particles 31 are in contact with each other, the crystals are not bonded and the grain boundaries are maintained. In other words, the grain boundaries of the inner layer particles 31 can be observed with a scanning electron microscope or the like, unlike the outer layer shell 2.

The size of the inner layer particles 31 is not limited, but it is preferably smaller than the outer layer particles 21 and distributed in a range of 10 nm or more and 50 nm or less. As shown in FIG. 3, the graphic carbon 32 adheres to the surface of the inner layer particles 31. Further, amorphous carbon 33 exists between the inner layer particles 31. That is, the inner layer 3 is composed of particles in which inner layer particles 31 and carbon are composited, and carbon connecting the particles.

Amorphous carbon 33 is also called amorphous carbon and is an amorphous carbon material. Amorphous carbon 33 generally burns in a temperature range of 200 ° C. or higher. The graphic carbon 32 is a carbon having a high degree of graphitization, and carbon atoms are regularly arranged as compared with the amorphous carbon 33. The graphic carbon 32 generally burns in a temperature range of 600 ° C. or higher.

The graphic carbon 32 and the amorphous carbon 33 form an electron path between the inner layer particles 31 to improve electrical conductivity. Further, the amorphous carbon 33 is interposed between the inner layer particles 31 to maintain a state in which the aggregation of the inner layer particles 31 is suppressed.

The inner layer particles 31 may be electrically connected only by the graffiti carbon 32 by thickly adhering the graffiti carbon 32, but the particles in which the graffiti carbon 32 and the inner layer particles 31 are combined become enormous. , The distance between the surface of the particles and the inside of the inner layer particles 31 becomes long. On the other hand, if the inner layer particles 31 are connected by the amorphous carbon 33, the diameter of the inner layer particles 31 covered with the graphic carbon 32 does not need to be large, and a high ion diffusion coefficient can be realized.

Note that all of the carbon existing between the inner layer particles 31 does not have to be amorphous carbon 33, and a part of the carbon may be other graphitized carbon or glassy carbon. Further, the surface of the inner layer particles 31 may be at least partially covered with the graphic carbon 32, but it is more preferable that the entire surface is covered.

It is preferable to adjust the amorphous carbon 33 so that it is contained in the granulated body in the range of 3.0 wt% or more and 8.0 wt% or less with respect to the granulated body. When the content of the amorphous carbon 33 is 0.2 wt% or less with respect to the granulated body, the capacity is difficult to develop even if the current density is lowered. When the content of the amorphous carbon 33 is 16.2 wt% or more with respect to the granulated body, the proportion of the amorphous carbon 33 having a lower electric resistance than that of the graphic carbon 32 increases, and the output characteristics deteriorate.

That is, since the amorphous carbon 33 is contained in the granulated body in the range of 3.0 wt% or more and 8.0 wt% or less with respect to the granulated body, the amorphous carbon 33 is 16.2 wt% with respect to the granulated body. Compared with the case where the above is included, the capacity that can be output is high for the same current density, and the decrease in the capacity that can be output is suppressed even if the current density is high.

Further, a part of the surface of the inner layer particles 31 is transformed into the magnety phase 34. The magnety phase 34 is _{a vanadium oxide represented by the general formula V n} O _2n-1 (3 ≦ n ≦ 8). The magnety phase 34 is, for example, _{any simple substance selected from compounds represented by V 4} O ₇ or the general formula V _n O _2n-1 (3 ≦ n ≦ 8), or a mixed phase of two or more. The magnetic phase 34 has high electrical conductivity, and electrons that have passed through the amorphous carbon 33 and the graphic carbon 32 can be smoothly introduced and derived into the inner layer particles 31. For _example, V 4 _{O 7} has from about 10 to 100 times the electrical conductivity than the conductive carbon black.

As described above, between the inner layer particles 31, the amorphous carbon 33, which is amorphous and has a relatively high electric resistance, the graphic carbon 32, in which carbon electrons are regularly arranged and the electric conductivity is relatively high, and the electric conductivity are high. Like the high magnetic phase 34, they are connected so that the electrical conductivity increases as they approach the inner layer particles 31.

It should be noted that carbon is contained not only in the inner layer 3 but also in the outer layer shell 2. The outer layer shell 2 is also composed of a complex of outer layer particles 21 and carbon. Examples of carbon in the outer layer shell 2 and the inner layer 3 include carbonized polyhydric alcohols, polymers, sugars and amino acids. Examples of the polyhydric alcohol include ethylene glycol and the like, examples of the polymer include polyvinyl alcohol, polyalkylene oxide, polyvinylpyrrolidone and polyacrylic acid, and examples of the saccharide include monosaccharides such as galactose, mannose or fructose, lactose, sucrose or the like. Examples include small sugars such as maltose, polysaccharides such as glycogen, starch or cellulose, or derivatives thereof, and examples of amino acids include glutamate.

Preferably, the carbon in the outer layer shell 2 and the inner layer 3 is a carbonized saccharide, and sucrose, glucose or a mixture thereof is more preferable. Granulations containing carbon formed by carbonizing saccharides such as sucrose and glucose have good output characteristics. That is, the granulation body containing carbon obtained by carbonizing sucrose or glucose has a large capacity that can be output for a wide range of current densities, and can draw out a large capacity even if it is output at a high current density.

(Manufacturing method of granulated body of this lithium vanadium oxide)
The granulated body of this lithium vanadium oxide may be produced, for example, as follows. That is, as shown in FIG. 4, a lithium vanadium oxide is synthesized (step S01), and the obtained particles of the lithium vanadium oxide are pulverized as necessary to form nanoparticles (step S02), and the lithium vanadium oxide is formed. A carbon source is adhered to the surface of the nanoparticles of the above, and a composite of a lithium vanadium oxide and a carbon source is granulated (step S03), and the carbon source is carbonized by heating (step S04).

In the synthesis of the lithium vanadium oxide in step S01, first, a lithium source, a vanadium source, or in addition to this, a tetravalent metal species M source is mixed. In this mixing step, each material source is uniformly dispersed. As a mixing method of each material source, for example, a solid phase method can be used using a mixer. In the mixing method using a mixer, a physical force may be applied to the mixture of each material source by a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a ball mill, a homogenizer, a homomixer or the like.

In the mixing step, the mixing ratio of each material source may be according to the stoichiometric ratio of lithium vanadium oxide. For example, in the case of Li _3.2 V _0.8 M _0.2 O ₄ , each material source should be mixed so that the molar ratio is Li: V: M = 3.2: 0.8: 0.2. Just do it. As the lithium source, a lithium-containing compound such as lithium hydroxide, lithium hydroxide hydrate, lithium acetate, lithium nitrate, lithium carbonate, lithium chloride and lithium lactate can be used. Examples of vanadium sources include metavanadate (NH ₄ VO _{3 , NaVO 3,} KVO _3, etc.), vanadium oxide (V ₂ O ₅ , V ₂ O ₄ , V ₂ O ₃ , V ₃ O ₄ ), vanadium (III). Acetylacetonate, vanadium (IV) oxyacetylacetonate, vanadium oxytrichloride, vanadium tetrachloride, vanadium trichloride, polyvanazinate and the like can be used. As the metal type M source, when the metal type M is Si, a _{silicon oxide such as SiO 2} or Li ₂ SiO ₃ , powder Si, amorphous Si, or the like can be used.

In the synthesis of lithium vanadium oxide, a heat treatment process is performed after the mixing process. The heat treatment step is preferably divided into a preheating step and a firing step. A lithium vanadium oxide having a β-phase crystal structure can be synthesized by a preheating step, and the metal species M can be solid-dissolved by a firing step to undergo a phase transition to the present lithium vanadium oxide having a γ-phase crystal structure.

In the preheating step, the mixture of each material source is heated at a temperature lower than the temperature at which the structural phase transitions from the β phase to the γ phase. For example, in the preheating step, heating is performed for about 5 hours in an atmosphere of 600 or more and 800 ° C. or less and in the air. In the firing step, the mixture of the β-phase lithium vanadium oxide crystal synthesized by the preheating step and the material source of the tetravalent metal species M is heated at a temperature higher than the temperature at which the structural phase is transferred to the γ phase. .. In the firing step, heating is performed for about 8 hours in an atmosphere of 800 or more and 1000 ° C. or less and in the air. As a result, a crystal of lithium vanadium oxide having only a crystal structure of γ phase is synthesized, and the crystal of this lithium vanadium oxide maintains the crystal structure of γ phase even in the natural cooling process.

In the step of making nanoparticles in step S02, for example, a wet pulverization treatment may be performed using a mixer. In the mixing method using a mixer, for example, lithium vanadium oxide is added to an organic solvent such as ethanol, and physical force is applied by a bead mill, rod mill, roller mill, stirring mill, planetary mill, vibration mill, ball mill, homogenizer, homomixer, etc. Just add it. In addition to the wet pulverization treatment using these mixers, for example, lithium vanadium oxide may be added to water and stirred well with a mixer or the like to disperse the particles.

A spray-drying process can be used in the coating and granulation steps of step S03. In the spray-drying treatment, nanoparticles of lithium vanadium oxide are dispersed in a solution of a carbon source, and hot air is brought into contact with the dispersion to evaporate the solvent. By this spray-drying treatment, the surface of the nanoparticles of the lithium vanadium oxide is coated with a carbon source, and a granulated body of the nanoparticles of the lithium vanadium oxide whose surface is coated with the carbon source is produced.

The carbon source may be any material that can become carbon by heat treatment, and examples thereof include polyhydric alcohols, polymers, sugars and amino acids. Examples of the polyhydric alcohol include ethylene glycol and the like, examples of the polymer include polyvinyl alcohol, polyalkylene oxide, polyvinylpyrrolidone and polyacrylic acid, and examples of the saccharide include monosaccharides such as galactose, mannose or fructose, lactose, sucrose or the like. Examples thereof include small sugars such as maltose, polysaccharides such as glycogen, starch or cellulose, or derivatives thereof, and examples of amino acids include glutamate.

As the solvent, any liquid that does not adversely affect the reaction can be used without particular limitation. For example, water, methanol, ethanol, isopropyl alcohol and the like can be used, and it is particularly preferable to use water. Two or more kinds of solvents may be mixed and used. Examples of the method for dispersing the carbon source and the nanoparticles of the lithium vanadium oxide with respect to the solvent include ultracentrifugal treatment (treatment of applying shear stress and centrifugal force to the powder in a solution), a bead mill, a homogenizer, and the like. In the spray-drying treatment, the treatment may be performed at a pressure of about 0.1 MPa at a temperature at which the carbon source is not burnt down.

In the carbonization treatment of step S04, carbon is produced by carbonizing a carbon source coated with nanoparticles of lithium vanadium oxide. In the inner layer 3, graphic carbon 32 is generated on the surface of the inner layer particles 31 by carbonization of the carbon source, and amorphous carbon 33 is generated between the inner layer particles 31 by carbonization of the carbon source. Further, it is considered that some oxygen atoms are extracted from the lithium vanadium oxide during carbonization of the carbon source, and the surface of the inner layer particles 31 is altered to the magnety phase 34.

In the carbonization treatment, the granulated material is heated in an oxygen-free or hypoxic atmosphere so that the carbon source does not burn. The oxygen-free or low-oxygen atmosphere includes an inert atmosphere and a saturated steam atmosphere, typically in vacuum, nitrogen or argon atmosphere. In the carbonization treatment, the temperature in the atmosphere is preferably 650 or more and 750 ° C. or less, and is preferably maintained in this temperature range for 5 hours. Within this range, a granulated body having a double structure having a good outer layer shell 2 and an inner layer 3 can be obtained, and good input / output characteristics can be obtained. In a nitrogen atmosphere, the lithium vanadium oxide is doped with nitrogen to increase the conductivity, which is more preferable.

(Power storage device)
The above-mentioned granulated body of lithium vanadium oxide is a material in which lithium ions can be reversibly inserted and removed. Lithium vanadium oxide has a lower charge / discharge potential (vs Li / Li +) than lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and B-type titanium oxide (TIO ₂ (B)), and has a charge / discharge potential (vs Li /). Li +) is higher than graphite. Therefore, this lithium vanadium oxide granule is suitable for use as an electrode material for a power storage device.

A power storage device that uses lithium vanadium oxide as the negative electrode material achieves both high energy density and high safety. Further, the theoretical capacity of the capacitor using the lithium vanadium oxide crystal as the negative electrode material is higher than that of lithium titanate, and the capacitor using the lithium vanadium oxide as the negative electrode material maintains a high capacity in terms of cycle characteristics. Maintain rate and high charge / discharge efficiency.

Examples of power storage devices include lithium ion secondary batteries and hybrid capacitors. In the lithium ion secondary battery, the positive electrode has an electrode active material layer containing a lithium metal compound, and the negative electrode has an electrode active material layer containing a granule of the present lithium vanadium oxide. In the hybrid capacitor, the positive electrode has, for example, activated carbon, and the negative electrode has an electrode active material layer containing granulations of the present lithium vanadium oxide.

The granulated body of this lithium vanadium oxide is contained in the active material slurry by being kneaded together with the binder. After the active material slurry is molded into a predetermined shape and dried, it is pressure-bonded to a current collector and rolled to produce an electrode active material layer on the negative electrode. Alternatively, the active material slurry may be applied to the current collector by a doctor blade method or the like, dried, and then rolled. The granulated body has a capsule structure in which the inner layer 3 composed of nanoparticles is surrounded by the outer layer shell 2, and the particle size is 1 μm or more. Demonstrates excellent formability and retention. That is, the molded body does not easily collapse, and the applied active material slurry does not easily drip.

As the current collector, conductive materials such as aluminum, copper, iron, nickel, titanium, steel, and carbon are preferable for both the positive electrode and the negative electrode. In particular, aluminum or copper having high thermal conductivity and electron conductivity is preferable. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted. As the binder, known binders such as polytetrafluoroethylene, polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, carboxymethyl cellulose, and spirene butadiene rubber (SBR) are used. The content of the binder is preferably 1 or more and 30% by mass or less with respect to the total amount of the electrode material.

In the rolling process, for example, a press pressure of 10 to 500 MPa is applied to obtain a high-density electrode. At this time, a part of the outer layer shell 2 of the granulation body is broken while maintaining the shape of the other part of the outer layer shell 2 of the granulation body by the pressing pressure. Since a part of the shape of the outer layer shell 2 remains, the inner layer particles 31 can be exposed to the electrolytic solution while maintaining the shape retention of the electrode, and the ion diffusion coefficient becomes good.

Examples of active materials used for the positive electrode of a secondary battery include, first, layered rock salt type LiMO ₂ , layered Li ₂ MnO _3- LiMO ₂ solid solution, and spinel type LiM ₂ O ₄ (M in the formula is Mn, Fe). , Co, Ni or a combination thereof). Specific examples of these include LiCoO ₂ , LiNiO ₂ , LiNi _4/5 Co _1/5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _1/2 O. ₂ , _{LiFeO 2} , LiMnO ₂ , Li ₂ MnO _3- LiCoO ₂ , Li ₂ MnO _3- LiNiO ₂ , Li ₂ MnO _3- LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO _3- LiNi _1/2 Mn _1/2 O ₂ , Li ₂ MnO ₃ -LiNi _1/2 Mn _1/2 O _2- LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiMn _3/2 Ni _1/2 O ₄ can be mentioned. Also, sulfur and _{Li 2 S, TiS 2, MoS} 2, FeS 2, VS 2, sulfides such as _{Cr 1/2 V 1/2 S 2,} selenides such as _{NbSe 3, VSe 2, NbSe 3} , Cr 2 Oxides such as O ₅ , Cr ₃ O ₈ , VO ₂ , V ₃ O ₈ , V ₂ O ₅ , V ₆ O _{13 , LiNi 0.8} Co _0.15 Al _0.05 O ₂ , LiVOPO ₄ , LiV ₃ O ₅ , LiV ₃ O ₈ , MoV ₂ O ₈ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , LiFePO ₄ , LiFe _1/2 Mn _1/2 PO ₄ , LiMnPO ₄ , Li ₃ V ₂ (PO ₄ ) Examples thereof include composite oxides such as _3.

Carbon may be added to the active material layer of the positive electrode as a conductive auxiliary agent. The 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, etc. Examples thereof include natural graphite, artificial graphite, graphitized Ketjen black, mesoporous carbon, and vapor phase carbon fiber.

Activated carbon used for the active material layer of the positive electrode of the hybrid capacitor is made from natural plant tissues such as palm shavings, synthetic resins such as phenol, and fossil fuels such as coal, coke, and pitch. In addition to activated carbon, this active material layer includes carbon black such as ketjen black, acetylene black, and channel black, carbon nanohorns, amorphous carbon, natural graphite, artificial graphite, graphitized ketchen black, mesoporous carbon, and carbon nanotubes. , Carbon nanofibers and the like may be used. The specific surface area of these carbon materials may be improved by activation treatment such as steam activation, alkali activation, zinc chloride activation, electric field activation, and opening treatment.

The electrolyte arranged between the positive electrode and the negative electrode in the power storage device may be an electrolytic solution held in the separator, a solid electrolyte, or a gel-like electrolyte, and may be a conventional power storage device. The electrolyte used in the above can be used without particular limitation. _{For example, for a lithium ion secondary battery, lithium such as LiPF 6} , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) _{2 is used in} a solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, and dimethyl carbonate. The electrolytic solution in which the salt is dissolved is used in a state of being held by a separator such as a polyolefin fiber non-woven fabric or a glass fiber non-woven fabric. In addition, inorganic solid electrolytes such as _{Li 5} La ₃ Nb ₂ O ₁₂ , Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₇ P ₃ S _{11, etc.} An organic solid electrolyte composed of a composite of a lithium salt and a polymer compound such as polyethylene oxide, polymethacrylate, and polyacrylate, and a gel-like electrolyte in which an electrolytic solution is absorbed by polyvinylidene fluoride, polyacrylonitrile, or the like are also used. For the hybrid capacitor, an electrolytic solution in which a lithium salt is dissolved in propylene carbonate or the like or an electrolytic solution in which a quaternary ammonium salt is dissolved in propylene carbonate or the like is used.

The power storage device may be so-called separatorless as long as the solid electrolyte has a thickness sufficient to prevent contact between the positive and negative electrodes and has a hardness capable of maintaining its shape by itself. Further, a carbon coat layer containing a conductive agent such as graphite may be provided between the current collector and the active material layer. A carbon coat layer can be formed by applying a slurry containing a conductive agent such as graphite, a binder, or the like to the surface of the current collector and drying the slurry.

(Action effect)
The particle size of this granulated product can be increased to, for example, 1 μm or more, and the moldability and shape retention of the active material slurry containing the granulated product can be improved. On the other hand, since the inner layer 3 contains a large amount of nanoparticles, the capacity of the power storage device is improved and the input / output is high.

The inner layer particles 31 are gathered together while maintaining grain boundaries and are not aggregated. Therefore, each particle of the inner layer particles 31 can come into contact with the electrolytic solution on the entire surface or many surfaces, the capacity of the power storage device is further improved, and the input / output is further increased. On the other hand, at least a part of the outer layer particles 21 is connected without grain boundaries to create a robust outer layer shell 2. The robust outer layer shell 2 can maintain at least a part of the shape when forming the electrode active material layer, and maintains the moldability and shape retention of the electrode active material layer without breaking the nanoparticles of the inner layer 3 into pieces. can.

Since the outer layer shell 2 has a gap portion 22 that allows the inner layer 3 and the outside of the granulated body to communicate with each other even if the outer layer particles 21 are connected without grain boundaries and become dense, electrolysis is performed from the gap portion 22 to the inner layer 3. The liquid can be supplied more efficiently.

Moreover, since the outer layer shell 2 is also composed of composite particles of lithium vanadium oxide and carbon, it contributes as an electrode active material. In addition, since the outer layer particles 21 are hollow inside and the electrolytic solution can penetrate into the inside, the surface area of the outer layer particles 21 in contact with the electrolytic solution becomes large, and the distance to the inside of the outer layer particles 21 becomes short. The capacity of the outer layer shell 2 portion can also be greatly expressed, and the movement of lithium ions in the outer layer shell 2 portion also speeds up.

Carbon is interposed between the inner layer particles 31. This carbon prevents the agglomeration of the inner layer particles 31 and supports the high capacity and high input / output of the power storage device. Further, this carbon serves as an electron path between the inner layer particles 31 and improves the electrical conductivity of the electrode active material layer.

The carbon interposed between the inner layer particles 31 was amorphous carbon 33. If the inner layer particles 31 are connected by the amorphous carbon 33, the diameter of the inner layer particles 31 covered with the graphic carbon 32 does not need to be large, and a high ion diffusion coefficient can be realized. On the other hand, since the graphic carbon 32 is attached to the surface of the inner layer particles 31, it becomes easier to transfer electrons to the inner layer particles 31.

The amorphous carbon 33 is adjusted so as to be contained in the granulated body in a range of 3.8 wt% or more and 7.3 wt% or less with respect to the granulated body, and has a high output capacity with respect to the current density and a current density. Even if it becomes high, the decrease in the output capacity is suppressed.

Further, a part of the surface of the inner layer particles 31 is transformed into the magnety phase 34. Therefore, the electrons that have passed through the amorphous carbon 33 and the graphic carbon 32 can be introduced and derived more smoothly into the inner layer particles 31.

Hereinafter, examples of the present invention will be shown, but the present invention is not limited to the examples. As follows, a granulated body of lithium vanadium oxide represented by _{the chemical formula Li 3.2} V _0.8 Si _0.2 O ₄ having a Si coefficient x of 0.2 was prepared as Example 1. ..

Powder lithium carbonate as a lithium source _(Li 2 CO ₃₎ (trade name: 3N5, Kanto Chemical Co., Inc., 24121-08) using a powder of vanadium pentoxide as a vanadium source _(V 2 _{O 5) (trade} name: Oxidation Vanadium (V), Kanto Chemical Co., Ltd., 44017-00) was used, and silicon dioxide (SiO ₂ ) powder (trade name: silicon dioxide, 99.9%, Wako Pure Chemical Industries, Ltd., 192) was used as the metal type M source. -09071) was used. The lithium source, vanadium source and metal species M source were mixed according to stoichiometric ratios and the mixture was calcined.

Using a dry ball mill (Fritsch, Premium line P-7 (PL-7)), these lithium sources, vanadium sources, and metal species M sources were mixed. At the time of mixing, the mixer was operated at 300 rpm for 2 minutes, the mixer was stopped for 1 minute, and this was repeated 10 times. In the firing step, the mixture was exposed to an air environment of 600 ° C. for 5 hours. After this heating, the mixture was further exposed to an air environment of 900 ° C. for 8 hours. The powder obtained by firing was added to ethanol, pulverized with a ball mill (Fritsch, Premium line P-7 (PL-7)) for 2 minutes at a rotation speed of 800 rpm, and the mixer was stopped for 3 minutes, and these rotations and stops were performed. By repeating one cycle consisting of 5 times, nanoparticles were formed. After the nanoparticles were formed, they were vacuum dried at 80 ° C. overnight.

The dried collection was added to water together with sucrose and the solution was stirred. To the water, 33 wt% sucrose was added to the collection. Then, coating and granulation were performed using a spray dryer (BUCHI, mini spray dryer B-290 (spray dryer)). The inlet temperature was set to 160 ° C., the aspirator operating speed was set to 100% of the maximum value, the pump output was set to 25% of the maximum value, and the solution prepared using the compressed gas of nitrogen was sprayed. After coating and granulation by the spray-drying method, the obtained granulated product was exposed to a nitrogen environment at 700 ° C. for 5 hours to carbonize sucrose.

The surface of the obtained granulated lithium vanadium oxide was observed with a scanning electron microscope. 5 (a) and 5 (b) are photographs showing a surface SEM image, FIG. 5 (a) is a photograph magnified at a magnification of 2,000 times, and FIG. 5 (b) is a photograph at a magnification of 20,000 times. As shown in FIG. 5, it can be confirmed that a true spherical granule having a particle size distributed in the range of 0.51 μm or more and 15 μm or less is obtained.

In addition, a cross-sectional sample of the obtained granulated body was prepared, and the cross-section of the granulated body was observed with a scanning electron microscope. 6 (a) and 6 (b) are photographs showing a cross-sectional SEM image, (a) is a photograph showing the entire granulated body at a magnification of 70,000, and (b) is an outer layer shell 2 and an inner layer 3. It is a photograph with a magnification of 100,000 times that shows the vicinity of the boundary of. As shown in FIG. 6, the granulated body has an outer layer shell 2 in which at least a part of particles are connected without grain boundaries when observed in a cross-sectional SEM image, and an inner layer 3 in which the grain boundaries of the particles are visible. It can be confirmed that it has a double structure with. The outer layer shell 2 had a thickness of 100 nm or more and 300 nm or less when visually measured, and the inner layer particles 31 had a particle size of 30 nm or more and 50 nm or less when visually measured.

The cross-sectional sample shown in FIG. 6A was analyzed by energy dispersive X-ray spectroscopy (SEM-EDX) to obtain a photograph in which the distribution of each element was mapped. FIG. 7A is a color mapping image showing the distribution of carbon atom C, FIG. 7B is a color mapping image showing the distribution of oxygen atom O, and FIG. 7C is a color mapping image. It is a color mapping image which shows the distribution of a silicon atom Si, and (d) of FIG. 7 is a color mapping image which shows the distribution of vanadium atom V. As shown in FIGS. 7A to 7D, carbon atoms, oxygen atoms, silicon atoms and vanadium atoms are uniformly distributed over the entire area of the outer layer shell 2 and the inner layer 3 of the granulated body without distinction. Can be confirmed. That is, it can be confirmed that the outer layer shell 2 and the inner layer 3 are composed of carbon-composite lithium vanadium oxide particles.

The outer layer shell 2 of the granulated body is observed with a scanning transmission electron microscope (STEM), imaged with a DF (dark field) detector and a BF (bright field) detector, and photographs of the dark field image and the bright field image are taken. Obtained. FIG. 8A is a dark-field photograph having a magnification of 40,000 times, and FIG. 8B is a bright-field photograph having a magnification of 40,000 times. As shown in FIGS. 8A and 8B, a dark-field photograph shows a dark gap 22 and a light field 22 can be seen around a heavy element that is dark in the bright-field. When the size of the gap 22 was visually confirmed based on the photographs of FIGS. 8A and 8B, the diameter was 50 nm or more and 150 nm or less.

Further, the outer layer shell 2 of the granulated body was observed with a scanning transmission electron microscope (STEM) to obtain a STEM image at a magnification of 40,000 times shown in FIG. As shown in FIG. 9, it was confirmed that the outer layer particles 21 are hollow inside and the inner space has a width of 20 nm.

The inner layer 3 of the granulated body was observed with a transmission electron microscope (TEM). The TEM images obtained as a result are shown in FIGS. 10 and 11. FIG. 10 is a TEM image of the inner layer particles 31 of the granulated body at a magnification of 500,000 times. FIG. 11 is a TEM image of the inner layer 3 of the granulated body having a magnification of 400,000 times, and the edging of the inner layer particles 31 is added. As shown in FIG. 10, it can be confirmed that carbon crystals are attached to the surface of the inner layer particles 31. That is, it can be confirmed that the graphic carbon 32 is attached to the surface of the inner layer particles 31. On the other hand, as shown in FIG. 11, it can be confirmed that amorphous carbon is interposed between the inner layer particles 31 and the distance between the inner layer particles 31 is secured so that the inner layer particles 31 do not aggregate. .. That is, it can be confirmed that the amorphous carbon 33 is interposed between the inner layer particles 31.

Further, the inner layer particles 31 were observed with a transmission electron microscope (TEM). A TEM image with a magnification of 200,000 times obtained as a result is shown in FIG. As shown in FIG. 12, it can be confirmed that the edge 31a of the inner layer particles 31 appears dark. It is suggested that the darkened part is a crystal region composed of vanadium atoms and oxygen atoms by removing lithium atoms and silicon atoms from the lithium vanadium oxide.

Therefore, this crystal region was confirmed by selected area electron diffraction. FIG. 13 shows a selected area ED diagram. Obtains the actual measurement values based on the selected area ED view, results obtained by converting the measured value from the origin of the incident angle 2θ based on the distance to the diffraction point, to contain many V ₄ O ₇ in this crystal region I understand. That is, the magnetic phase 34 was confirmed on the surface of the inner layer particles 31. According to FIG. 13, the incident angle 2θ based on the distance from the origin to each diffraction point is 21.14 ° for the 103rd surface on the innermost circumference, and 26.76 ° for the 1-2-3 surface on the central side. Next, the 1-2-4 surface on the center side was 30.01 °, then the 104 surface on the center side was 32.29 °, and the 100 surface on the outermost circumference was 36.24 °. V ₄ O ₇ incident angle 2θ is 21.19 °, 26.75 °, 30.06 ° , 32.61 °, a peak appears in the 36.99 ° (ICDD card No. 01-0577).

From the above, the granulated body of Example 1 contains lithium vanadium oxide and carbon, has a double structure of an outer layer shell 2 and an inner layer 3, and the inner layer 3 is composed of a plurality of particles of lithium vanadium oxide. The outer layer shell 2 is formed by gathering together while maintaining the boundary, the outer layer shell 2 is formed by connecting at least a part of the particles of the lithium vanadium oxide without a grain boundary, and the outer layer shell 2 is opened at 50 nm or more and 150 nm or less and is formed with the inner layer 3. It has a gap 22 that communicates with the outside of the particles, at least a part of the outer layer particles 21 is hollow inside, the amorphous carbon 33 is interposed between the inner layer particles 31, and the graphic carbon 32 is the inner layer particles. It was confirmed that the particles were attached to the surface of 31 and that a part of the surface of the inner layer particles 31 was altered to the magnety phase 34.

The granulation body of Comparative Example 1 was produced in correspondence with the granulation body of Example 1. As the granulated product of Comparative Example 1, a lithium vanadium oxide having _{a Si coefficient x of 0.2 and represented by the chemical formula Li 3.2} V _0.8 Si _0.2 O _{4 was used as in Example 1.} However, it differs in that it is formed by granulating particles of a complex with multiwall carbon nanotubes (MWCNT). The structure of the granulated body is also different from that of Example 1.

The granulated body of Comparative Example 1 was prepared as follows. That is, the material source and the mixing ratio were the same as in Example 1, and mixing and firing were performed under the same method and conditions as in Example 1. After calcination, multiwall carbon nanotubes (MWCNT) were added to the collection vacuum dried at 80 ° C. overnight at a ratio of 20 wt% with respect to the collection. Then, the granulated product of Comparative Example 1 was obtained by mixing with a dry ball mill (Fritsch, Premium line P-7 (PL-7)) at a rotation speed of 300 rpm for 12 hours.

That is, in the granulation body of Comparative Example 1, the granulation body of Example 1 was subjected to the addition of sucrose, coating and granulation by the spray dry method, and carbonization of sucrose by heating, whereas the granulation body of Example 1 was added with MWCNT and dried. It differs from the method for producing a granulated product of Example 1 in that there is no coating and granulation by a ball mill and no final heat treatment.

The granulated body of Comparative Example 1 has a structure in which MWCNT is attached to the surface of a lithium vanadium oxide represented by _{Li 3.2} V _0.8 Si _0.2 O ₄ having a particle size of 50 or more and 500 nm or less. .. There is no magnety phase 34 on the surface. The lithium vanadium oxide particles of Comparative Example 1 aggregate at various places to form many secondary particles, and MWCNTs intervene between the secondary particles. In Example 1, most of the inner layer particles 31 which are primary particles do not aggregate, and the amorphous carbon 33 is interposed between the inner layer particles 31 which are primary particles. Further, the surface of the lithium vanadium oxide particles of Comparative Example 1 is not covered with the graphic carbon 32, and most of the surfaces of the lithium vanadium oxide particles of Comparative Example 1 are exposed. Further, the granulated body of Comparative Example 1 does not have an outer layer shell 2, and is formed only by a structure in which MWCNT is interposed between secondary particles.

The thermogravimetric analysis (TG) of the granulated bodies of Example 1 and Comparative Example 1 was performed. That is, the granulated product was allowed to stand in an atmosphere where the temperature changed up to 1000 ° C., and the weight was measured. As a result, the granulated body of Example 1 contained 10.2 wt% of carbon with respect to the total amount of the granulated body. The granulated body of Comparative Example 1 contained 20 wt% of carbon with respect to the total amount of the granulated body.

Half cells were prepared using the granulated bodies of Example 1 and Comparative Example 1. The half cell was a 2032 type coin cell. Specifically, polyvinylidene fluoride (PVDF) is selected as the binder, and the granulated body and the binder are stirred together to form a slurry, which is then applied to a copper foil current collector to form an electrode on the current collector. After forming the active material layer, a rolling process was performed. In the rolling process, a press pressure of 30 MPa was applied. This electrode is referred to as the working electrode W. E. And said.

The counter electrode was made of lithium metal and attached to the lower lid of the 2032 type coin cell. Opposite pole C. On E, a glass fiber separator, a gasket, and a working electrode W. E, spacer, spring, and top 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 infiltrated into a cell.

FIG. 14 is an SEM photograph showing a cross section of the electrode active material layer of Example 1. As shown in FIG. 14, it can be confirmed that a part of the outer layer shell 2 of some of the granulated bodies collapses due to the rolling process and the inner layer 3 is exposed. Therefore, the inner layer 3 of the granulated body in which a part of the outer layer shell 2 is collapsed is filled with the electrolytic solution without passing through the gap portion 22 of the outer layer shell 2.

The relationship between the discharge current density and the discharge capacity was measured for the half cells of Example 1 and Comparative Example 1. FIG. 15 is a graph showing the output characteristics of Example 1 and Comparative Example 1 obtained as a result of the measurement.

As shown in FIG. 15, it can be confirmed that the half cell of Example 1 has a larger capacity than the half cell of Comparative Example 1 in the entire range of the discharge current density from ^{0.05 to 15 Ag -1.} When the discharge current density is as close to zero as possible, the discharge capacity of the half cell of Comparative Example 1 is 134 mAhg ^-1, while that of the half cell of Example 1 is 154 mAhg ^-1 , and the capacity of Example 1 is higher than that of Comparative Example 1. Has improved by 15%. ^{Further, the ratio of the discharge capacity in the case of the discharge current density of 15 Ag -1 to} the discharge capacity in the case where the discharge current density is as close to zero as possible is 50% in the half cell of Comparative Example 1 and 68 in the half cell of Example 1. %, And the capacity of Example 1 is improved by 18% as compared with Comparative Example 1.

Moreover, the half cell of Example 1 has a carbon amount reduced by 49% as compared with the half cell of Comparative Example 1, and has higher input / output than that of Comparative Example 1. That is, it can be confirmed that the granulated body of Example 1 has a higher capacity and higher input / output than Comparative Example 1 even though the inner layer 3 is wrapped in the outer layer shell 2. rice field.

Further, the granulated bodies of Examples 2 and 3 and the granulated bodies of Comparative Example 2 were prepared. The granulated products of Examples 2 and 3 and the granulated products of Comparative Example 2 differ in the amount of sucrose added during the spray-drying treatment as compared with Example 1. In Example 1, 33 wt% sucrose was added to the lithium vanadium oxide, whereas in Example 2, 20 wt% sucrose was added to the lithium vanadium oxide, and in Example 3, lithium vanadium was added. 50 wt% sucrose was added to the oxide, and in Comparative Example 2, 11 wt% sucrose was added to the lithium vanadium oxide. The production method and conditions other than the amount of sucrose added are common to Examples 1 to 3 and Comparative Example 2.

FIG. 16 is a graph showing the amounts of graphic carbon 32 and amorphous carbon 33 in the granulated bodies of Examples 1 to 3 and Comparative Example 2. The amounts of graffiti carbon 32 and amorphous carbon 33 are based on thermogravimetric analysis (TG). That is, the weight of the amorphous carbon 33 is defined as the weight of the granulated bodies of Examples 1 to 3 and Comparative Example 2 reduced in the temperature range of 200 ° C. or higher and 400 ° C. or lower, and the atmospheric temperature is 600 ° C. or higher. The weight reduced in the temperature range of 800 ° C. or lower was defined as the weight of the graphic carbon 32. The amount of reduction was based on the result of thermogravimetric measurement of the granulated product produced by the same production method and the same conditions as in Example 1 except that carbon was not added.

As shown in FIG. 16, the amount of adhering graphic carbon 32 was almost constant regardless of the amount of sucrose added. On the other hand, the granulated body of Comparative Example 2 contained 0.2 wt% of amorphous carbon 33. As for the total amount of carbon, the granulated body of Comparative Example 2 contained 2.2 wt% in total with the graphic carbon 32. The granulated body of Example 2 contained 3.8 wt% of amorphous carbon 33. As for the total amount of carbon, the granulated body of Example 2 contained 7.0 wt% in total with the graphic carbon 32. The granulated body of Example 1 contained 7.3 wt% of amorphous carbon 33. As for the total amount of carbon, the granulated body of Example 1 contained 10.2 wt% in total with the graphic carbon 32. The granulated body of Example 3 contained 16.2 wt% of amorphous carbon 33. As for the total amount of carbon, the granulated body of Example 3 contained 18.3 wt% in total with the graphic carbon 32.

Half cells were prepared using the granulated bodies of Comparative Example 2 and Examples 1 to 3. The half cell was produced by the same manufacturing method and under the same conditions as in Example 1 and Comparative Example 1. The relationship between the discharge current density and the discharge capacity was measured for the half cells of Comparative Example 2 and Examples 1 to 3. The measurement results are shown in FIG. As shown in FIG. 17, the half cell of Comparative Example 2 in which the amorphous carbon 33 was 0.2 wt% with respect to the entire granulated body did not develop the capacity in the entire range of the discharge current density. On the other hand, in the half cells of Examples 1 to 3 in which the amorphous carbon 33 was 3.8 wt% or more with respect to the entire granulated body, the capacity was developed in the entire range of the discharge current density.

Therefore, if the amorphous carbon 33 is interposed between the inner layer particles 31 to suppress the aggregation of the inner layer particles 31, and if the electron path between the inner layer particles 31 is constructed, the inner layer 3 is wrapped by the outer layer shell 2. However, it was confirmed that the input / output characteristics of the power storage device using the granulated material were good.

In the half cell of Example 3, the amorphous carbon 33 having a higher electric resistance than the graphic carbon 32 was 16.2 wt% with respect to the entire granulated body, so that the capacity is proportionally drawn out when the discharge current density becomes high. Has decreased. On the other hand, the half cells of Examples 1 and 2 in which the amorphous carbon 33 is 3.8 wt% or more and 7.3 wt% or less with respect to the entire granulated body have a capacity to be drawn up to ^{a discharge current density of about 10 Ag -1.} The amount of decrease was suppressed. In the half cell of Example 1 in which the amorphous carbon 33 was 7.3 wt% with respect to the entire granulated body, the amount of decrease in the drawn capacity was particularly suppressed until the ^{discharge current density was about 10 Ag -1.}

As a result, when the amorphous carbon 33 is 3.8 wt% or more and 7.3 wt% or less with respect to the entire granulated body, the balance between the suppression of aggregation of the inner layer particles 31 and the electrical resistance between the inner layer particles 31 becomes good. It was confirmed that the input / output characteristics of the power storage device using the granulated material were further improved.

Further, the granulated bodies of Examples 4 to 6 were prepared. In the granulated product of Example 4, sucrose during the spray-drying treatment was added in Example 1, whereas glucose was added in the same weight as in Example 1. Polyvinyl alcohol (PVA) was added to the granulated product of Example 5 by the same weight as that of Example 1. Histidine was added to the granulated product of Example 6 by the same weight as that of Example 1. The production method and conditions other than the type of carbon source are common to Examples 1 and 4 to 6.

Then, a half cell was prepared using the granulated bodies of Examples 4 to 6. The half cell was produced by the same manufacturing method and under the same conditions as in Example 1. For these half cells of Examples 4 to 6, the relationship between the discharge current density and the discharge capacity was measured. The measurement results are shown in FIG. 18 together with the results of Example 1. As shown in FIG. 18, it can be confirmed that the capacity develops from a low current density to a high current density regardless of the type of carbon source, and in particular, Examples 1 and Implementation using the saccharides sucrose and glucose as carbon sources. The half cell of Example 4 develops a large capacity in the entire range of the discharge current density as compared with Examples 5 and 6, and the half cell of Example 1 using sucrose as a carbon source has a large capacity in the entire range of the discharge current density. It was confirmed that the capacity was maintained.

2 Outer layer shell 21 Outer layer particles 22 Gap 23 Hollow part 3 Inner layer 31 Inner layer particles 32 Graphic carbon 33 Amorphous carbon 34 Magneti phase

Claims (12)

1. Contains lithium vanadium oxide and carbon,
   It has a double structure of an inner layer and an outer layer shell that encloses the inner layer.
   The inner layer is formed by gathering a plurality of particles of the lithium vanadium oxide while maintaining grain boundaries.
   The outer layer shell is formed by connecting at least a part of the particles of the lithium vanadium oxide without grain boundaries.
   A granulated body of lithium vanadium oxide characterized by.
2. The outer layer shell has an opening at 50 nm or more and 150 nm or less, and has a gap portion for communicating the inner layer and the outside of the granulated body.
   The granulated body of the lithium vanadium oxide according to claim 1.
3. At least a part of the outer layer particles, which are the particles of the lithium vanadium oxide in the outer layer shell, is hollow inside.
   The granulated body of the lithium vanadium oxide according to claim 1 or 2.
4. A part of the carbon is interposed between the inner layer particles which are the particles of the lithium vanadium oxide in the inner layer.
   The granulated body of the lithium vanadium oxide according to any one of claims 1 to 3.
5. The carbon interposed between the inner layer particles is amorphous carbon, and is
   The other part of the carbon adheres to the surface of the inner layer particles as graphic carbon.
   4. The granulated body of lithium vanadium oxide according to claim 4.
6. The amorphous carbon should be contained in a proportion of 3.0 or more and 8.0 wt% or less with respect to the entire granulated body.
   5. The granulated body of lithium vanadium oxide according to claim 5.
7. A part of the carbon is contained in the outer layer shell,
   The granulated body of the lithium vanadium oxide according to any one of claims 1 to 6.
8. The carbon is carbonized sucrose or glucose.
   The granulated body of the lithium vanadium oxide according to any one of claims 1 to 7.
9. The lithium vanadium oxide comprises Li ₃ VO ₄ doped with a tetravalent metal species.
   The granulated body of the lithium vanadium oxide according to any one of claims 1 to 8.
10. The tetravalent metal species is Si.
    9. The granulated body of lithium vanadium oxide according to claim 9.
11. The positive electrode or the negative electrode contains the granulated body of the lithium vanadium oxide according to any one of claims 1 to 10.
    A power storage device featuring.
12. The granulation body in which a part of the outer layer shell is collapsed and a part or the whole of the inner layer is exposed is included.
    11. The power storage device according to claim 11.

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