Lithium vanadium oxide, negative electrode active material, and battery

Abstract

A lithium vanadium oxide according to the present disclosure contains Li, V, M, and O, and M is at least one element that is selected from among tetravalent metal elements excluding V and tetravalent metalloid elements. The lithium vanadium oxide includes both a β phase and a γ phase as crystal phases.

Description

Lithium vanadium oxide, negative electrode active material, and battery

[0001] The present disclosure relates to lithium vanadium oxides, negative electrode active materials, and batteries.

[0002] Patent Document 1 discloses a non-aqueous secondary battery using Li3VO4 as the negative electrode active material.

[0003] Patent Document 2 discloses a co-fired all-solid-state battery using an anode active material obtained by doping LiVO with element A and / or element B. Element A is at least one element selected from the group consisting of Mg, Al, Ga, and Zn. Element B is at least one element selected from the group consisting of Zn, Al, Ga, Si, Ge, P, and Ti. The anode active material has either a β-phase or a γ-phase crystal phase.

[0004] JP 2008-77847 A International Publication No. 2019 / 044902

[0005] Doping lithium vanadium oxide with a metal element increases the expansion and contraction rate of the lithium vanadium oxide and reduces the theoretical capacity of the lithium vanadium oxide. The increased expansion and contraction rate reduces the durability of the battery using lithium vanadium oxide. The reduced theoretical capacity reduces the capacity of the battery using lithium vanadium oxide.

[0006] The present disclosure provides a technique for achieving both high capacity and durability in a battery that uses lithium vanadium oxide as an active material.

[0007] The present disclosure provides a lithium vanadium oxide containing Li, V, M, and O, wherein M is at least one selected from tetravalent metal elements other than V and tetravalent metalloid elements, and the lithium vanadium oxide contains both a β phase and a γ phase as crystalline phases.

[0008] According to the present disclosure, it is possible to achieve both high capacity and durability in a battery using lithium vanadium oxide as an active material.

[0009] Fig. 1 is a schematic cross-sectional view showing an electrode material according to a second embodiment. Fig. 2 is a schematic cross-sectional view showing an example of the configuration of a battery according to a third embodiment. Fig. 3 is a schematic cross-sectional view showing another example of the configuration of a battery according to the third embodiment. Fig. 4 is a graph showing X-ray diffraction patterns of Example 1, Comparative Example 1, and Comparative Example 2. Fig. 5 is a graph showing the change in discharge capacity retention rate during charge-discharge cycles for Examples 1 to 3 and Comparative Example 1.

[0010] (Findings that form the basis of the present disclosure) Lithium vanadium oxide may have a β-phase or a γ-phase. Batteries using lithium vanadium oxide with a β-phase as an active material have a large capacity. However, the active material has a large expansion and contraction rate due to the insertion and extraction of Li into the β-phase, which is disadvantageous in terms of battery durability. Active materials containing lithium vanadium oxide with a γ-phase have a low expansion and contraction rate, which is advantageous in terms of battery durability. However, doping lithium vanadium oxide with a metal element reduces the theoretical capacity. This reduction in theoretical capacity makes it difficult to obtain a high-capacity battery.

[0011] The present inventors have discovered that under certain conditions, both the β phase and the γ phase can exist, leading to the present disclosure.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0013] First Embodiment A lithium vanadium oxide according to a first embodiment contains Li, V, M, and O. Here, M is at least one selected from tetravalent metal elements and tetravalent metalloid elements excluding V. The lithium vanadium oxide contains both a β phase and a γ phase as crystalline phases.

[0014] The β phase is a crystalline phase having a crystalline structure belonging to the space group Pmn21. Specifically, the crystalline structure of the β phase has tetrahedra composed of LiO4 (hereinafter simply referred to as "LiO4 tetrahedra") and tetrahedra composed of VO4 (hereinafter simply referred to as "VO4 tetrahedra"). In the crystalline structure of the β phase, the LiO4 tetrahedra and the VO4 tetrahedra are oriented in the same direction (the c-axis direction, which is one side of the crystal lattice) with adjacent tetrahedra sharing vertices. The β phase has a high theoretical capacity as an active material. On the other hand, the β phase has a high expansion and contraction rate due to the insertion and desorption of Li into and from the crystalline phase.

[0015] The γ phase is a crystalline phase having a crystal structure belonging to the space group Pcmn. Specifically, the γ phase crystal structure has LiO4 tetrahedra and VO4 tetrahedra, similar to the β phase crystal structure. In the γ phase, the LiO4 tetrahedra and VO4 tetrahedra are tetrahedra generally oriented in one direction (the +c-axis direction, which is one side of the crystal lattice) and tetrahedra generally oriented in one direction opposite to the one direction (the −c-axis direction, which is one side of the crystal lattice), with approximately half of each tetrahedron present. In the γ phase crystal structure, LiO4 tetrahedra share vertices and one side with adjacent LiO4 tetrahedra, and VO4 tetrahedra share vertices with adjacent LiO4 tetrahedra or VO4 tetrahedra. The γ phase can be stably obtained by partially substituting the V (vanadium) sites in the crystal lattice with a tetravalent metal other than V. The γ phase has a low expansion / contraction rate due to insertion and desorption of Li into and from the crystalline phase, but on the other hand, the γ phase reduces the theoretical capacity of the lithium vanadium oxide as an active material.

[0016] In the lithium vanadium oxide according to the first embodiment, the ratio of the amount of substance of V to the sum of the amount of substance of V and the amount of substance of M (V / (M+V)) is, for example, more than 0% and less than 10%. With this configuration, a mixed phase of β phase and γ phase is likely to be generated. Furthermore, if the firing temperature during the production of the lithium vanadium oxide is high, the γ phase is likely to be generated. Furthermore, if a material with a low melting point is selected as a raw material for the lithium vanadium oxide, the γ phase is likely to be generated at a lower firing temperature. Therefore, the volume ratio of the β phase to the γ phase can be controlled by appropriately selecting the ratio of the amount of substance of V to the sum of the amount of substance of V and the amount of substance of M, the firing temperature during the production of the lithium vanadium oxide, and the type of raw material for the lithium vanadium oxide.

[0017] The lithium vanadium oxide according to the first embodiment includes a β phase and a γ phase, for example, Li 3+x V 1-x M x O4, and satisfies the relationship 0<x<1. According to this configuration, when the lithium vanadium oxide is used as an active material, insertion and desorption of Li into and from the active material is facilitated, thereby improving the capacity of a battery using the lithium vanadium oxide as an active material. The content x of M may satisfy the relationship 0<x≦0.2. According to this configuration, the capacity of a battery using the lithium vanadium oxide as an active material is further improved. The content x of M may satisfy the relationship 0<x<0.1. According to this configuration, the capacity of a battery using the lithium vanadium oxide as an active material is further improved. The content x of M may satisfy the relationship 0<x<0.08. According to this configuration, the capacity of a battery using the lithium vanadium oxide as an active material is further improved.

[0018] Note that Li may be contained in excess so as to deviate from the composition ratio of composition formula (1). Specifically, Li may be contained in excess of 30% or less based on the Li composition ratio of composition formula (1). The excess Li may be incorporated into the β-phase and / or γ-phase crystalline phase of the lithium vanadium oxide, or may exist as a crystalline phase other than the β-phase and / or γ-phase. This configuration further improves the capacity of a battery using the lithium vanadium oxide as an active material.

[0019] M can be selected from tetravalent metal elements and tetravalent metalloid elements excluding V. M is, for example, at least one selected from the group consisting of Ti, Zr, Si, Ge, and Sn. According to this configuration, when the lithium vanadium oxide is used as an active material, the active material is more likely to maintain a high theoretical capacity. M may include Ti. According to this configuration, when the lithium vanadium oxide is used as an active material, the active material is more likely to maintain a high theoretical capacity. Note that M may be Ti. According to this configuration, when the lithium vanadium oxide is used as an active material, the active material is more likely to maintain a high theoretical capacity.

[0020] The volume ratio of the β phase to the γ phase is not particularly limited. The volume ratio of the β phase to the γ phase correlates with the results of X-ray diffraction measurement of lithium vanadium oxide, and therefore the results of X-ray diffraction measurement can serve as a measure of the volume ratio of the β phase to the γ phase. However, the intensity of the diffraction peak represents the height of the diffraction peak, and does not indicate the area or volume of the β phase and the γ phase. For example, in an X-ray diffraction pattern using Cu-Kα radiation as a radiation source, the ratio of the intensity of the diffraction peak assigned to the (101) plane of the β phase to the intensity of the diffraction peak assigned to the (011) plane of the γ phase is 0.1 or more and 10.0 or less. The ratio of the diffraction peak intensities may be 0.1 or more and 7.0 or less. When the ratio of the diffraction peak intensities falls within this range, a battery having good charge / discharge characteristics can be realized when the lithium vanadium oxide is used as an active material in a battery.

[0021] The diffraction peak attributable to the (101) plane of the β phase appears at 22.7°±0.2°, taking into account the change in the lattice constant of the β phase due to doping with the element M. Similarly, the diffraction peak attributable to the (011) plane of the γ phase appears at 22.4°±0.2°, taking into account the change in the lattice constant of the γ phase due to doping with the element M. Therefore, instead of the condition regarding the ratio of the diffraction peak intensities, in an X-ray diffraction pattern using Cu-Kα radiation as a radiation source, the ratio of the intensity of the diffraction peak appearing at a diffraction angle 2θ of 22.7°±0.2° to the intensity of the diffraction peak appearing in a diffraction angle 2θ range of 22.4°±0.2° may be 0.1 or more and 10.0 or less. In addition, when two diffraction peaks are present at an overlapping angle "22.5° to 22.6°" between the diffraction angles 2θ of "22.4°±0.2°" and "22.7°±0.2°," the correspondence relationship between the diffraction peaks and the crystal planes is determined taking into consideration the magnitude relationship between the intensities of other comparable planes of the β phase and the γ phase. Furthermore, the diffraction peak attributable to the (011) plane of the γ phase is likely to appear at 22.4°±0.1°, and the diffraction peak attributable to the (101) plane of the β phase is likely to appear at 22.7°±0.1°. Therefore, in an X-ray diffraction pattern using Cu-Kα radiation as a radiation source, the ratio of the intensity of the diffraction peak appearing at a diffraction angle 2θ of 22.7°±0.1° to the intensity of the diffraction peak appearing in the range of a diffraction angle 2θ of 22.4°±0.1° may be 0.1 or more and 10.0 or less. The ratio of the intensities of the diffraction peaks may be 0.1 or more and 7.0 or less.

[0022] The shape of the lithium vanadium oxide according to the first embodiment is not limited. Examples of the shape include a needle shape, a sphere shape, or an oval sphere shape. The lithium vanadium oxide according to the first embodiment may be in the form of particles, pellets, or plates.

[0023] When the lithium vanadium oxide according to the first embodiment is in the form of particles (e.g., spherical), the lithium vanadium oxide may have a median diameter of 0.1 μm or more and 100 μm or less, or may have a median diameter of 0.5 μm or more and 10 μm or less. This allows the lithium vanadium oxide according to the first embodiment and other materials to be dispersed well. Here, the median particle diameter refers to the particle size (d50) corresponding to 50% cumulative volume in the volume-based particle size distribution. The volume-based particle size distribution can be measured using a laser diffraction measurement device or an image analysis device.

[0024] The lithium vanadium oxide according to the first embodiment may be included in the negative electrode active material.

[0025] <Method for Producing Lithium Vanadium Oxide> The lithium vanadium oxide according to the first embodiment can be produced by the following method. Raw material powder is prepared so as to have a target composition. Examples of raw material powder include oxides, hydroxides, carbonates, nitrates, or organic salts of Li, oxides, hydroxides, carbonates, nitrates, or organic salts of V, and oxides, hydroxides, carbonates, nitrates, or organic salts of M.

[0026] As an example, Li 3+x V 1-x M x In a lithium vanadium oxide having a composition represented by the composition formula (1) of LiCO4, M is assumed to be Ti, and x is assumed to be 0.05 when the raw materials are mixed. LiCO3, VO, and TiO2 are mixed in a molar ratio of LiCO3:VO:TiO2 = (3.05 / 2):(0.95 / 2):0.05. Lithium hydroxide or its hydrate may be used instead of LiCO3.

[0027] A reaction product is obtained by firing the mixture of raw material powders. The atmosphere during firing may be air or an inert gas atmosphere. Examples of the inert atmosphere include an argon atmosphere and a nitrogen atmosphere. The raw material mixture may be fired in a reducing atmosphere. Examples of the reducing atmosphere include an ammonia atmosphere, a methane atmosphere, and a hydrogen sulfide atmosphere.

[0028] The lithium vanadium oxide may be obtained by reacting a mixture of raw material powders mechanochemically (by mechanochemical milling) in a mixing device such as a planetary ball mill, which produces the lithium vanadium oxide according to the first embodiment.

[0029] Here, the molar ratio of the raw materials when mixed does not necessarily match the molar ratio of the reactants, because the raw materials may not be incorporated into the reactants due to evaporation or the like during the reaction.

[0030] Therefore, the composition x of the lithium vanadium oxide is determined by, for example, ICP emission spectroscopy, atomic absorption spectrometry, EPMA (Electron Probe Micro Analyzer) method, or the like.

[0031] Second Embodiment A second embodiment will be described below, and the matters described in the first embodiment will be omitted as appropriate.

[0032] FIG. 1 shows an electrode material 100 according to a second embodiment. The electrode material 100 includes an active material 111 and a solid electrolyte 112. The electrode material 100 may include a conductive additive 113 for the purpose of enhancing electronic conductivity. The active material 111, the solid electrolyte 112, and the conductive additive 113 are, for example, each in a particulate form. The active material 111 includes the lithium vanadium oxide according to the first embodiment. The lithium vanadium oxide according to the first embodiment is suitable for reducing the expansion and contraction rate of the electrode material 100 and for facilitating the insertion and desorption of Li in the electrode material 100.

[0033] The active material 111 may contain the lithium vanadium oxide according to the first embodiment as a main component. "Containing the lithium vanadium oxide according to the first embodiment as a main component" means that the component contained in the largest amount by mass is the lithium vanadium oxide according to the first embodiment. The active material 111 may be made of the lithium vanadium oxide according to the first embodiment.

[0034] The conductive additive 113 may be provided so as to cover at least a portion of the particles of the active material 111. This increases the contact area between the particles of the conductive additive 113 and the particles of the active material 111. As a result, when the electrode material 100 is used in a battery, the resistance of the battery decreases, thereby increasing the output of the battery.

[0035] The ratio of the volume of the particles of the conductive additive 113 to the total volume of the particles of the active material 111 and the conductive additive 113 may be 0.01 or more and 0.4 or less.

[0036] The electrode material 100 according to the second embodiment contains the lithium vanadium oxide according to the first embodiment, and therefore, by using the electrode material 100 according to the second embodiment, an electrode having a high theoretical capacity and durability can be realized.

[0037] The electrode material 100 according to the second embodiment can be included in a negative electrode.

[0038] Third Embodiment A third embodiment will be described below. The matters described in the first and second embodiments will be omitted as appropriate.

[0039] 3 shows a battery 1000 as an example of the third embodiment. The battery 1000 includes a positive electrode 101, an electrolyte layer 102, and a negative electrode 103. The electrolyte layer 102 is disposed between the positive electrode 101 and the negative electrode 103.

[0040] The positive electrode 101 includes an active material and a solid electrolyte.

[0041] The electrolyte layer 102 includes an electrolyte material, such as a solid electrolyte material.

[0042] The negative electrode 103 includes an active material 111 and a solid electrolyte 112 .

[0043] The negative electrode active material 111 is a particle containing the lithium vanadium oxide according to the first embodiment. The negative electrode active material 111 may be a particle containing the lithium vanadium oxide according to the first embodiment as a main component. "Particles containing the lithium vanadium oxide according to the first embodiment as a main component" means particles in which the lithium vanadium oxide according to the first embodiment is the component contained in the largest amount by mass. The negative electrode active material 111 may be a particle made of the lithium vanadium oxide according to the first embodiment.

[0044] The negative electrode active material 111 may have a median diameter of 0.1 μm or more and 100 μm or less. When the negative electrode active material 111 has a median diameter of 0.1 μm or more, the active material 111 and the solid electrolyte 112 can be well dispersed in the negative electrode 103. This improves the charge / discharge characteristics of the battery. When the negative electrode active material 111 has a median diameter of 100 μm or less, the lithium diffusion rate within the active material 111 improves. This allows the battery 1000 to operate at high power.

[0045] The negative electrode active material 111 may have a larger median diameter than the solid electrolyte 112. This allows the active material 111 and the solid electrolyte 112 to be dispersed well.

[0046] In order to improve the energy density and output of the battery 1000, in the negative electrode 103, the ratio of the volume of the active material 111 to the total volume of the active material 111 and the solid electrolyte 112 may be 0.30 or more and 0.95 or less.

[0047] In order to improve the energy density and output of the battery 1000, the negative electrode 103 may have a thickness of 10 μm or more and 500 μm or less.

[0048] The solid electrolyte 112 contained in the negative electrode 103 may be a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, or a polymer solid electrolyte.

[0049] In the present disclosure, a "sulfide solid electrolyte" refers to a solid electrolyte containing sulfur. An "oxide solid electrolyte" refers to a solid electrolyte containing oxygen. The oxide solid electrolyte may contain anions other than oxygen (excluding sulfur anions and halogen anions). A "halide solid electrolyte" refers to a solid electrolyte that contains a halogen element but does not contain sulfur. The halide solid electrolyte may contain not only a halogen element but also oxygen.

[0050] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4 or Li 10 GeP2S 12 is.

[0051] Examples of halide solid electrolytes include Li a Me b Y c X6, where a + mb + 3c = 6 and c > 0 are satisfied. Me is at least one element selected from the group consisting of metal elements other than Li and Y and metalloid elements. X is at least one element selected from the group consisting of F, Cl, Br, and I. The value of m represents the valence of Me.

[0052] The "metalloid elements" are B, Si, Ge, As, Sb, and Te. The "metal elements" are all elements included in Groups 1 to 12 of the periodic table (excluding H) and all elements included in Groups 13 to 16 of the periodic table (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0053] In order to increase the ionic conductivity of the halide solid electrolyte, Me may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0054] Another example of a halide solid electrolyte is Li α’ M β Oγ X δ Here, α, β, γ, and δ are all greater than 0. M is at least one element selected from the group consisting of metal elements and metalloid elements other than Li. X is at least one element selected from the group consisting of Cl, Br, and I. The composition of the compound satisfies 0.9≦α≦1.2, β=1.0, 1.0≦γ≦1.3, and 3.6≦δ≦4.0.

[0055] Examples of oxide solid electrolytes include: (i) NASICON-type solid electrolytes such as LiTi2(PO4)3 or its elemental substitution products; (ii) perovskite-type solid electrolytes such as (LaLi)TiO3; (iii) Li 14 ZnGeO 16 LISICON-type solid electrolytes such as LiSiO, LiGeO or elemental substitutions thereof; (iv) LiLaZrO 12 or an element-substituted product thereof, or (v) Li3PO4 or an N-substituted product thereof.

[0056] An example of a polymer solid electrolyte is a compound of a polymer compound and a lithium salt. The polymer compound may have an ethylene oxide structure. A polymer compound having an ethylene oxide structure can contain a large amount of lithium salt, and therefore has higher ionic conductivity. The polymer solid electrolyte may be, for example, a composite compound of polyethylene oxide and a lithium salt. An example of such a polymer solid electrolyte is lithium bis(trifluoromethanesulfonyl)imide.

[0057] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), or LiC(SOCF). One lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used.

[0058] The positive electrode 101 includes a material capable of absorbing and releasing metal ions such as lithium ions, and includes, for example, an active material (for example, particles of an active material).

[0059] Examples of the active material for the positive electrode include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Examples of lithium-containing transition metal oxides include Li(Ni,Co,Al)O, Li(Ni,Co,Mn)O, and LiCoO.

[0060] In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0061] From the viewpoint of cost and safety of the battery 1000, lithium phosphate may be used as the active material of the positive electrode.

[0062] The positive electrode active material may have a median diameter of 0.1 μm or more and 100 μm or less. When the positive electrode active material has a median diameter of 0.1 μm or more, the active material and the solid electrolyte can be well dispersed in the positive electrode 101. This improves the charge / discharge characteristics of the battery 1000. When the positive electrode active material has a median diameter of 100 μm or less, the lithium diffusion rate within the positive electrode active material improves. This allows the battery 1000 to operate at high power.

[0063] The positive electrode active material may have a larger median diameter than the solid electrolyte, which allows the positive electrode active material and the solid electrolyte to be dispersed well.

[0064] To improve the energy density and output of the battery 1000, the ratio of the volume of the active material to the total volume of the active material and the solid electrolyte in the positive electrode 101 may be 0.30 or more and 0.95 or less.

[0065] A coating layer may be formed on the surface of the electrode active material. This can suppress an increase in the reaction overvoltage of the battery. Examples of coating materials contained in the coating layer include a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a halide solid electrolyte.

[0066] The coating material may be a halide solid electrolyte material or an oxide solid electrolyte material. The halide solid electrolyte material may contain F. This improves the stability of the coating material at high potentials. As a result, the battery 1000 has high charge / discharge efficiency. The oxide solid electrolyte may be lithium niobate or a polyanion material that is stable even at high potentials. As a result, the battery 1000 has high charge / discharge efficiency.

[0067] In order to improve the energy density and output of the battery 1000, the positive electrode 101 may have a thickness of 10 μm or more and 500 μm or less.

[0068] The solid electrolyte contained in the positive electrode 101 may be a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or an organic polymer solid electrolyte.

[0069] The electrolyte layer 102 includes an electrolyte material. The electrolyte material is, for example, a solid electrolyte material. The electrolyte layer 102 may be a solid electrolyte layer. The solid electrolyte material included in the electrolyte layer 102 may be a sulfide solid electrolyte, a halide solid electrolyte, or a polymer solid electrolyte.

[0070] The electrolyte layer 102 may have a thickness of 1 μm or more and 100 μm or less. When the electrolyte layer 102 has a thickness of 1 μm or more, the positive electrode 101 and the negative electrode 103 are less likely to short-circuit. When the electrolyte layer 102 has a thickness of 100 μm or less, the battery 1000 can operate at high power.

[0071] FIG. 3 shows a battery 2000 that is another example of the third embodiment. In the example of FIG. 3, the battery 2000 includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. In this example, the electrolyte layer 202 includes an electrolyte layer 212 (hereinafter referred to as the "first electrolyte layer") configured similarly to the above-described electrolyte layer 102, and an electrolyte layer 222 (hereinafter referred to as the "second electrolyte layer") configured separately from the electrolyte layer 212. The second electrolyte layer 222 is provided between the first electrolyte layer 212 and the negative electrode 203. The positive electrode 201 and the negative electrode 203 are configured similarly to the positive electrode 101 and the negative electrode 103 shown in FIG. 2, respectively, for example.

[0072] When the electrolyte layer 202 is composed of the first electrolyte layer 212 and the second electrolyte layer 222, the second electrolyte layer 222 may be composed of a different solid electrolyte material that is electrochemically more stable than the first electrolyte layer 212. Specifically, the reduction potential of the solid electrolyte material that constitutes the second electrolyte layer 222 may be lower than the reduction potential of the solid electrolyte material that constitutes the first electrolyte layer 212. This allows the solid electrolyte material contained in the first electrolyte layer 212 to be used without being reduced. As a result, the charge / discharge efficiency of the battery can be improved.

[0073] At least one selected from the group consisting of positive electrode 101, electrolyte layer 102, and negative electrode 103 constituting battery 1000 shown in Fig. 2 may contain a nonaqueous electrolyte solution, a gel electrolyte, or an ionic liquid for the purpose of facilitating the transfer of lithium ions and improving the output characteristics of the battery. At least one selected from the group consisting of positive electrode 201, electrolyte layer 202, and negative electrode 203 constituting battery 2000 shown in Fig. 3 may also contain a nonaqueous electrolyte solution, a gel electrolyte, or an ionic liquid.

[0074] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent are cyclic carbonate ester solvents, chain carbonate ester solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, and fluorine solvents. Examples of the cyclic carbonate ester solvent are ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of the chain carbonate ester solvent are dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of the cyclic ether solvent are tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of the chain ether solvent are 1,2-dimethoxyethane and 1,2-diethoxyethane. An example of the cyclic ester solvent is γ-butyrolactone. An example of the chain ester solvent is methyl acetate.

[0075] Examples of fluorine-containing solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone. Alternatively, a mixture of two or more non-aqueous solvents selected from these may be used.

[0076] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF), LiN(SOCF)(SOCF), or LiC(SOCF). One lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L to 2 mol / L.

[0077] The gel electrolyte may be a polymer material impregnated with a non-aqueous electrolyte, such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0078] Examples of cations contained in the ionic liquid are: (i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium; (ii) aliphatic cyclic ammoniums such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, or piperidiniums; or (iii) nitrogen-containing heterocyclic aromatic cations such as pyridiniums or imidazoliums.

[0079] An example of an anion contained in an ionic liquid is PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) -, or C(SO2CF3)3 - is.

[0080] The ionic liquid may include a lithium salt.

[0081] At least one selected from the group consisting of the positive electrode 101, the electrolyte layer 102, and the negative electrode 103 constituting the battery 1000 shown in Fig. 2 may contain a binder for the purpose of improving adhesion between particles. At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 constituting the battery 2000 shown in Fig. 3 may also contain a binder.

[0082] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. Copolymers may also be used as binders. Examples of such binders include copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Mixtures of two or more materials selected from the above materials may also be used.

[0083] The negative electrode 103 constituting the battery 1000 shown in Fig. 2 may contain a conductive additive 113 for the purpose of increasing electronic conductivity. The negative electrode 203 constituting the battery 2000 shown in Fig. 3 may also contain a conductive additive.

[0084] Examples of the conductive additive include: (i) graphites such as natural graphite or artificial graphite, (ii) carbon blacks such as acetylene black or ketjen black, (iii) conductive fibers such as carbon fiber or metal fiber, (iv) carbon fluoride, (v) metal powders such as aluminum, (vi) conductive whiskers such as zinc oxide or potassium titanate, (vii) conductive metal oxides such as titanium oxide, or (viii) conductive polymer compounds such as polyaniline, polypyrrole, or polythiophene. To reduce costs, the conductive additives (i) or (ii) may be used.

[0085] The positive electrode 101 constituting the battery 1000 shown in Fig. 2 may contain not only an active material but also a conductive additive. Examples of materials for the conductive additive are as described above. The positive electrode 201 constituting the battery 2000 shown in Fig. 3 may also contain not only an active material but also a conductive additive.

[0086] In the negative electrode 103 of the battery 1000 shown in FIG. 2 , the conductive additive 113 may cover at least a portion of the surface of the active material 111. This increases the contact area between the conductive additive 113 and the active material 111. As a result, the battery resistance decreases and the output can be increased. The negative electrode 203 of the battery 2000 shown in FIG. 3 may also be configured in the same manner as above. In the positive electrode 101 shown in FIG. 2 , the conductive additive may also cover at least a portion of the surface of the active material. The positive electrode 201 of the battery 2000 shown in FIG. 3 may also be configured in the same manner as above.

[0087] In the negative electrode 103 of the battery 1000 shown in Figure 2, the ratio of the volume of the conductive additive 113 to the sum of the volume of the active material 111 and the volume of the conductive additive 113 may be 0.01 or more and 0.4 or less. The negative electrode 203 of the battery 2000 shown in Figure 3 may also be configured in the same manner as above. In the positive electrode 101 of the battery 1000 shown in Figure 2, the ratio of the volume of the conductive additive to the sum of the volume of the active material and the volume of the conductive additive may also be 0.01 or more and 0.4 or less. The positive electrode 201 of the battery 2000 shown in Figure 3 may also be configured in the same manner as above.

[0088] The electrode material 100 shown in FIG. 1 may be included in the negative electrode 103 shown in FIG. 2. When the electrode material 100 is included in the negative electrode 103, a coating layer may be formed on the surface of the active material 111 to prevent the solid electrolyte 112 from reacting with the active material 111. This allows the battery to have high charge / discharge efficiency. Similarly, the electrode material 100 shown in FIG. 1 may be included in the negative electrode 203 of a battery 2000 shown in FIG. 3. In the battery 2000 shown in FIG. 3, a coating layer may be formed on the surface of the active material of the negative electrode.

[0089] Examples of the coating material contained in the coating layer include a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a halide solid electrolyte.

[0090] An example of a sulfide solid electrolyte is Li2S-P2S5. An example of an oxide solid electrolyte is trilithium phosphate. An example of a polymer solid electrolyte is a composite compound of polyethylene oxide and a lithium salt. An example of such a polymer solid electrolyte is lithium bis(trifluoromethanesulfonyl)imide.

[0091] Examples of the shape of the battery according to the third embodiment include a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, and a laminate type.

[0092] The battery according to the third embodiment may be manufactured, for example, by preparing a material for forming a positive electrode, a material for forming an electrolyte layer, and a material for forming a negative electrode, and by a known method, fabricating a laminate in which the positive electrode, the electrolyte layer, and the negative electrode are arranged in this order.

[0093] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0094] (Technology 1) A lithium vanadium oxide containing Li, V, M, and O, wherein M is at least one selected from tetravalent metal elements other than V and tetravalent metalloid elements, and the lithium vanadium oxide contains both a β phase and a γ phase as crystalline phases.

[0095] According to the present disclosure, lithium vanadium oxide contains both the β-phase and the γ-phase as crystalline phases, so that a battery using the lithium vanadium oxide as an active material can achieve both high capacity and durability.

[0096] (Technology 2) Li 3+x V 1-x M x The lithium vanadium oxide according to Technology 1 has a composition represented by O4 and satisfies 0 < x < 1. According to this configuration, the capacity of a battery using the lithium vanadium oxide as an active material is improved.

[0097] (Technology 3) The lithium vanadium oxide according to Technology 2, which satisfies 0<x≦0.2. According to this configuration, the capacity of the battery is further improved by using the lithium vanadium oxide as an active material.

[0098] (Technology 4) The lithium vanadium oxide according to any one of Technologies 1 to 3, wherein M contains Ti. According to this configuration, when the lithium vanadium oxide is used as an active material, the active material tends to maintain a high theoretical capacity.

[0099] (Technology 5) The lithium vanadium oxide according to any one of Technologies 1 to 4, wherein in an X-ray diffraction pattern obtained using Cu-Kα radiation as a radiation source, the ratio of the intensity of the diffraction peak assigned to the (101) plane of the β phase to the intensity of the diffraction peak assigned to the (011) plane of the γ phase is 0.1 or more and 10.0 or less. With this configuration, when the lithium vanadium oxide is used as an active material in a battery, a battery having good charge-discharge characteristics can be realized.

[0100] (Technology 6) The lithium vanadium oxide according to any one of Technologies 1 to 4, wherein in an X-ray diffraction pattern obtained using Cu-Kα radiation as a radiation source, the ratio of the intensity of a diffraction peak appearing at a diffraction angle 2θ of 22.7°±0.2° to the intensity of a diffraction peak appearing in a diffraction angle 2θ range of 22.4°±0.2° is 0.1 or more and 10.0 or less. With this configuration, when the lithium vanadium oxide is used as an active material in a battery, a battery having good charge / discharge characteristics can be realized.

[0101] (Technology 7) A negative electrode active material containing the lithium vanadium oxide according to any one of Technologies 1 to 6. According to this configuration, the negative electrode active material contains both the β phase and the γ phase as crystalline phases, thereby making it possible to obtain a battery that achieves both high capacity and durability.

[0102] (Technology 8) A battery comprising a positive electrode, a negative electrode containing the negative electrode active material according to Technology 7, and an electrolyte disposed between the positive electrode and the negative electrode. With this configuration, the negative electrode active material contains both the β phase and the γ phase as crystalline phases, thereby making it possible to obtain a battery that achieves both capacity and durability.

[0103] (Technology 9) The battery according to Technology 8, wherein the negative electrode contains a conductive additive. According to this configuration, the negative electrode contains the conductive additive, thereby improving the conductivity of the negative electrode.

[0104] Hereinafter, the present disclosure will be described in detail using examples and comparative examples. Note that the lithium vanadium oxide, negative electrode active material, and battery are not limited to the following examples.

[0105] Example 1 Preparation of Lithium Vanadium Oxide The lithium vanadium oxide of Example 1 was prepared as follows. As raw material powders, Li2CO3 (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%), VO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%), and TiO2 (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) were prepared in a molar ratio of Li2CO3:VO5:TiO2 = 1.525:0.475:0.05. However, Li2CO3 was prepared in an amount 10% by mass in excess of the above composition. In other words, Li2CO3 was prepared so that it was 10% by mass in excess of the mass of Li2CO3 whose molar ratio was determined as described above. These raw material powders were mixed in a mortar to obtain a mixed powder. The obtained mixed powder was calcined in air at 600°C for 3 hours. The obtained calcined powder was subjected to main calcination in the air at 965°C for 15 hours, where the temperature was increased at an average rate of 5°C / min and decreased at an average rate of 3°C / min, thereby obtaining the lithium vanadium oxide of Example 1.

[0106] Example 2 Lithium vanadium oxide of Example 2 was produced in the same manner as in Example 1, except that the temperature of the main firing was changed to 900°C.

[0107] Example 3: Li2CO3, VO, and TiO2 were prepared as raw material powders in a molar ratio of Li2CO3:VO:TiO2 = 1.525:0.475:0.05. However, Li2CO3 was also prepared in an amount 3 mass% in excess of the mass of Li2CO3 whose molar ratio was determined as described above. The mixed powder obtained by mixing these raw material powders was pre-fired in the same manner as in Example 1, and then fired in air at 800°C for 15 hours. In this manner, the lithium vanadium oxide of Example 3 was produced.

[0108] Comparative Example 1: Li2CO3 and VO were prepared as raw material powders in a molar ratio of Li2CO3:VO5 = 1.5:0.5. However, Li2CO3 was also prepared so that it was 3 mass% in excess of the mass of Li2CO3 whose molar ratio was determined as described above. The mixed powder obtained by mixing these raw material powders was pre-fired in the same manner as in Example 1, and then fired in air at 800°C for 15 hours. In this manner, the lithium vanadium oxide of Comparative Example 1 was produced.

[0109] Comparative Example 2 Lithium vanadium oxide of Comparative Example 2 was produced in the same manner as in Example 1, except that the molar ratio of the raw material powders was changed to Li2CO3:V2O5:TiO2 = 1.55:0.45:0.10.

[0110] [X-ray Diffraction Measurement] X-ray diffraction measurements of the lithium vanadium oxides of Example 1, Comparative Example 1, and Comparative Example 2 were carried out using an X-ray diffractometer (MiniFlex 600, manufactured by RIGAKU Corporation) in a dry atmosphere having a dew point of −45° C. or less. Cu-Kα radiation (wavelengths 1.5405 Å and 1.5444 Å) was used as the X-ray source.

[0111] Fig. 4 is a graph showing the X-ray diffraction patterns of Example 1, Comparative Example 1, and Comparative Example 2. As shown in Fig. 4, the diffraction pattern of the lithium vanadium oxide of Example 1 had both a diffraction peak attributable to the crystal planes of the β phase and a diffraction peak attributable to the crystal planes of the γ phase. Although not shown in Fig. 4, the diffraction patterns of the lithium vanadium oxides of Examples 2 and 3 had both a diffraction peak attributable to the crystal planes of the β phase and a diffraction peak attributable to the crystal planes of the γ phase, similar to Example 1. That is, the lithium vanadium oxides of Examples 1 to 3 each contained both the β phase and the γ phase as crystal phases.

[0112] In the diffraction peaks obtained from the lithium vanadium oxide of Example 1, the I(β phase) / I(γ phase) value, which is the ratio of the diffraction peak intensity attributable to the (011) plane of the γ phase appearing at 2θ=22.7° to the diffraction peak intensity attributable to the (101) plane of the γ phase appearing at 2θ=22.4°, was 0.41. In the diffraction peaks obtained from the lithium vanadium oxide of Example 2, the I(β phase) / I(γ phase) value was 0.83. In the diffraction peaks obtained from the lithium vanadium oxide of Example 3, the I(β phase) / I(γ phase) value was 2.28.

[0113] As shown in Fig. 4, the diffraction pattern of the lithium vanadium oxide of Comparative Example 1 had only diffraction peaks attributable to crystal planes of the β phase. That is, the lithium vanadium oxide of Comparative Example 1 contained only the β phase. Furthermore, the diffraction pattern of the lithium vanadium oxide of Comparative Example 2 had only diffraction peaks attributable to crystal planes of the γ phase. That is, the lithium vanadium oxide of Comparative Example 2 contained only the γ phase.

[0114] [Analysis by ICP Optical Emission Spectroscopy] The Ti composition ratio of the lithium vanadium oxide according to Example 1 was analyzed using ICP optical emission spectroscopy. An ICP optical emission spectroscopy analyzer (PS3520VDDII, manufactured by Hitachi High-Tech Science Corporation) was used for the analysis. In the lithium vanadium oxide according to Example 1, x in composition formula (1) was 0.05. The Ti composition ratios of the lithium vanadium oxides according to Examples 2, 3, and Comparative Example 2 were analyzed using the same method as in Example 1. In the lithium vanadium oxides according to Examples 2 and 3, x in composition formula (1) was 0.05. In the lithium vanadium oxide according to Comparative Example 2, x in composition formula (1) was 0.1. When the lithium vanadium oxides calculated from the compositions of Examples 1 to 3 and Comparative Examples 1 and 2 were used as active materials, the theoretical capacities of the active materials are shown in Table 1.

[0115] [Fabrication of Negative Electrode] Li3PS4 (hereinafter referred to as "LPS") was prepared as the solid electrolyte. Lithium vanadium oxide according to Example 1 was prepared as the negative electrode active material. LPS, the negative electrode active material, a conductive additive, a solvent containing a binder, and an organic solvent were added to a polypropylene container, and these materials were stirred using an ultrasonic homogenizer. The negative electrode slurry was applied to a current collector foil to form a coating film. The current collector foil with the coating film was placed on a hot plate, and the organic solvent was removed from the coating film in an argon atmosphere. This resulted in a negative electrode. The negative electrode was pre-dried at 70°C for 20 minutes, followed by main drying at 110°C for 30 minutes.

[0116] [Preparation of Positive Electrode] LPS was prepared as the solid electrolyte. Lithium nickel cobalt aluminum oxide (hereinafter referred to as "NCA") was prepared as the positive electrode active material. LPS, NCA, a conductive additive, a solvent containing a binder, and an organic solvent were added to a polypropylene container, and these materials were stirred using an ultrasonic homogenizer. The positive electrode slurry was applied to a current collector foil to form a coating film. The current collector foil with the coating film was placed on a hot plate, and the organic solvent was removed from the coating film in an argon atmosphere. This resulted in a positive electrode. The positive electrode was pre-dried at 70°C for 20 minutes, followed by final drying at 120°C for 30 minutes.

[0117] [Fabrication of Secondary Battery] In an insulating outer cylinder, a 550 μm thick (80 mg) sulfide solid electrolyte Li2S-P2S5 and a positive electrode were stacked in this order. After the positive electrode was fabricated as described above, it was punched out to a size of φ9.2 mm and stacked on the sulfide solid electrolyte material. Next, a negative electrode was stacked on the side of the solid electrolyte layer opposite the side that contacts the positive electrode. After the negative electrode was fabricated as described above, it was punched out to a size of φ9.2 mm and stacked on the solid electrolyte layer. The positive electrode and negative electrode were combined so that the theoretical capacity of the negative electrode was 1.2 times the theoretical capacity of the positive electrode. The films stacked in the above order were pressure-molded at a pressure of 80 MPa to produce a stack consisting of a positive electrode, a solid electrolyte layer, and a negative electrode.

[0118] Next, stainless steel current collectors were attached to the positive and negative electrodes, respectively, and current collecting leads were attached to the respective current collectors.

[0119] Finally, an insulating ferrule was used to isolate the inside of the insulating outer cylinder from the outside atmosphere, sealing the inside of the cylinder. As described above, the battery of Example 1 was fabricated. Batteries of Examples 2, 3, Comparative Examples 1, and 2 were fabricated using the same method as Example 1.

[0120] [Charge / Discharge Test] The batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were each placed in a thermostatic chamber maintained at 25°C. The batteries were charged with a constant current at a 0.05C rate (20-hour rate) relative to the theoretical capacity of the battery. The end-of-charge voltage was 3.6V. Next, the batteries were discharged at a current value corresponding to a 0.05C rate until the voltage reached 1.0V. After two cycles of charge / discharge at a 0.05C rate, a durability test was conducted. At the C rate, which was the durability test condition, 100 cycles of charge / discharge were conducted at a current value corresponding to a 1C (1-hour rate).

[0121] 5 shows the discharge capacity retention rates up to 100 cycles for the batteries of Examples 1 to 3 and Comparative Example 1. Table 1 shows the discharge capacity retention rates after 100 cycles for the batteries of Examples 1 to 3 and Comparative Example 1. Here, the "discharge capacity retention rate after 100 cycles" means the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle of charge and discharge.

[0122]

[0123] (Discussion) As shown by the results of Examples 1 to 3, by doping with Ti, a negative electrode active material composed of lithium vanadium oxide containing β-phase and γ-phase was obtained while maintaining a high theoretical capacity. The negative electrode active material composed of lithium vanadium oxide of Example 3 had a high β / γ ratio and exhibited a mixed phase state in which the β-phase was dominant. Nevertheless, the battery of Example 3 exhibited a high discharge capacity retention rate.

[0124] The negative electrode active material composed of lithium vanadium oxide in Comparative Example 1 contained only the β phase. Therefore, the discharge capacity retention rate of the battery in Comparative Example 1 was low. As shown by the results of Comparative Example 2, it is possible to produce a single γ phase by increasing the ratio of the amount of V to the total amount of V and M up to 10%. However, increasing the amount of Ti significantly reduces the theoretical capacity, which may prevent the advantages of lithium vanadium oxide from being fully utilized.

[0125] As described above, the lithium vanadium oxide according to the present disclosure is suitable for providing a battery that can achieve both high capacity and durability.

[0126] The lithium vanadium oxide of the present disclosure can be used, for example, as an active material in a lithium ion secondary battery.

[0127] REFERENCE SIGNS LIST 100 Electrode material 111 Active material 112 Solid electrolyte 113 Conductive additive 101, 201 Positive electrode 102, 202 Electrolyte layer 103, 203 Negative electrode 212 First electrolyte layer 222 Second electrolyte layer 1000, 2000 Battery

Claims

1. A lithium vanadium oxide comprising Li, V, M, and O, wherein M is at least one selected from tetravalent metal elements other than V and tetravalent metalloid elements, and the lithium vanadium oxide comprises both a β phase and a γ phase as crystal phases.

2. Li 3+x V 1-x M x The lithium vanadium oxide according to claim 1, having a composition represented by O4, satisfying 0<x<1.

3. The lithium vanadium oxide according to claim 2, wherein 0<x≦0.2 is satisfied.

4. The lithium vanadium oxide according to claim 1, wherein M includes Ti.

5. The lithium vanadium oxide according to claim 1, wherein in an X-ray diffraction pattern using Cu-Kα radiation as a radiation source, the ratio of the intensity of the diffraction peak assigned to the (101) plane of the β phase to the intensity of the diffraction peak assigned to the (011) plane of the γ phase is 0.1 or more and 10.0 or less.

6. The lithium vanadium oxide according to claim 1, wherein in an X-ray diffraction pattern obtained using Cu-Kα radiation as a radiation source, the ratio of the intensity of a diffraction peak appearing at a diffraction angle 2θ of 22.7°±0.2° to the intensity of a diffraction peak appearing in a range of a diffraction angle 2θ of 22.4°±0.2° is 0.1 or more and 10.0 or less.

7. A negative electrode active material comprising the lithium vanadium oxide according to any one of claims 1 to 6.

8. A battery comprising: a positive electrode; a negative electrode containing the negative electrode active material according to claim 7; and an electrolyte disposed between the positive electrode and the negative electrode.

9. The battery according to claim 8, wherein the negative electrode contains a conductive additive.

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