Negative electrode active material and battery

Abstract

A negative electrode active material according to the present disclosure includes Li, V, M, and O. M is at least one selected from tetravalent metalloid elements and tetravalent metal elements other than V. The electron conductivity of the negative electrode active material is 7.0×10-13 S / cm or more.

Description

Negative electrode active material and battery

[0001] The present disclosure relates to a negative electrode active material and a battery.

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

[0003] JP 2008-77847 A

[0004] In the prior art, there is a need to improve the charge / discharge efficiency of batteries that use lithium vanadium oxide as the negative electrode active material.

[0005] An object of the present disclosure is to provide a negative electrode active material and a battery that improve the charge / discharge efficiency of the battery.

[0006] In one embodiment of the present disclosure, the negative electrode active material contains Li, V, M, and O, where M is at least one selected from tetravalent metal elements and tetravalent metalloid elements excluding V, and has an electronic conductivity of 7.0×10 -13 S / cm or more.

[0007] The negative electrode active material of the present disclosure can improve the charge / discharge efficiency of a battery.

[0008] Fig. 1 is a schematic cross-sectional view showing a negative 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 schematic cross-sectional view showing a pressure forming die used to evaluate the electronic conductivity of the negative electrode active material. Fig. 5 is a graph showing the measurement results of a charge-discharge test of batteries using the negative electrode active materials of Examples 1 to 3 and Comparative Example 1.

[0009] (Findings that Form the Basis of the Present Disclosure) The present inventors have conducted extensive research into the causes that prevent improvement in the charge-discharge efficiency of batteries that use a negative electrode active material containing lithium vanadium oxide. As a result, the present inventors have found that when the negative electrode active material has an electronic conductivity below a certain value, sufficient charge-discharge efficiency cannot be obtained, which led to the present disclosure.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiments.

[0011] First Embodiment A negative electrode active material 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 electronic conductivity of the negative electrode active material is 7.0×10 -13 S / cm or more. With this configuration, the charge / discharge efficiency of a battery using the negative electrode active material can be improved.

[0012] The electron conductivity of the negative electrode active material according to the first embodiment is 8.0×10 -11 According to this configuration, a battery using the negative electrode active material can obtain good energy density and input / output characteristics. The electronic conductivity of the negative electrode active material according to the first embodiment may be 1.0×10 -2 S / cm or less, and may be 1.0 × 10 -6 The electronic conductivity of the negative electrode active material is a value measured without adding an additional component that improves electronic conductivity to the negative electrode active material. Examples of additional components that improve electronic conductivity include carbon coated on the surface of the negative electrode active material and a conductive additive attached to the surface of the negative electrode active material.

[0013] The negative electrode active material according to the first embodiment may be, for example, Li 3+x V 1-x M x O4, and has a composition represented by composition formula (1), where 0<x<1 is satisfied. With such a configuration, insertion and desorption of Li into and from the negative electrode active material is facilitated, thereby improving the capacity of a battery using the negative electrode active material. The content x of M may satisfy 0<x≦0.2. With such a configuration, the capacity of a battery using the negative electrode active material is further improved. The content x of M may satisfy 0<x<0.1. With such a configuration, the capacity of a battery using the negative electrode active material is further improved. The content x of M may satisfy 0<x<0.08. With such a configuration, the capacity of a battery using the negative electrode active material is further improved.

[0014] 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 in a range 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, which are crystalline phases of the lithium vanadium oxide constituting the negative electrode active material, 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 negative electrode active material.

[0015] 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. With this configuration, the negative electrode active material is more likely to maintain a high theoretical capacity. M may include Ti. With this configuration, the negative electrode active material is more likely to maintain a high theoretical capacity. Note that M may be Ti. With this configuration, the negative electrode active material is more likely to maintain a high theoretical capacity.

[0016] The negative electrode active material according to the first embodiment may include both the β phase and the γ phase as crystalline phases.

[0017] The β phase is a crystalline phase that can be generated in lithium vanadium oxide and has 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 a negative electrode 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.

[0018] The γ phase is a crystalline phase that can be produced in lithium vanadium oxide and has a crystalline structure belonging to the space group Pcmn. Specifically, the crystalline structure of the γ phase, like the crystalline structure of the β phase, has LiO tetrahedra and VO tetrahedra. In the γ phase, the LiO tetrahedra and VO 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 a direction opposite to the one direction (the −c-axis direction, which is one side of the crystal lattice), with approximately half of the tetrahedra present. In the γ phase crystal structure, LiO tetrahedra share vertices and one side with adjacent LiO tetrahedra, and VO tetrahedra share vertices with adjacent LiO tetrahedra or VO tetrahedra. The γ phase can be stably obtained by partially substituting 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 lithium vanadium oxide as a negative electrode active material.

[0019] When the negative electrode active material according to the first embodiment contains both the β phase and the γ phase, it maintains both the high theoretical capacity that is an advantage of the β phase and the low expansion / shrinkage rate that is an advantage of the γ phase.

[0020] In the negative electrode active material 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 such a configuration, a mixed phase of β phase and γ phase is likely to be generated. Furthermore, if the firing temperature during production of the negative electrode active material is high, the γ phase is likely to be generated. Furthermore, if raw materials with low melting points are selected as raw materials for the negative electrode active material, the γ phase is likely to be generated at lower firing temperatures. 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 production of the negative electrode active material, and the type of raw material for the negative electrode active material.

[0021] The volume ratio of the β phase to the γ phase is not limited. Since the volume ratio of the β phase to the γ phase correlates with the results of X-ray diffraction measurement of the negative electrode active material, the results of the 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 attributable to the (101) plane of the β phase to the intensity of the diffraction peak attributable to the (011) plane of the γ phase is 0.1 or more and 10.0 or less. The ratio of the intensity of the diffraction peaks 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 negative electrode active material is used in a battery.

[0022] 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°" of 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 account 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 diffraction angle 2θ range of 22.4°±0.1° may be 0.1 to 10.0. The ratio of the intensities of the diffraction peaks may be 0.1 to 7.0.

[0023] The shape of the negative electrode active material according to the first embodiment is not limited. Examples of the shape include an acicular shape, a spherical shape, or an oval spherical shape. The negative electrode active material according to the first embodiment may be in the form of particles, pellets, or plates.

[0024] When the negative electrode active material according to the first embodiment is particulate (e.g., spherical), the negative electrode active material may have a median diameter of 0.1 μm to 100 μm, or may have a median diameter of 0.5 μm to 10 μm. This allows the negative electrode active material 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 a volume-based particle size distribution. The volume-based particle size distribution may be measured using a laser diffraction measurement device or an image analyzer.

[0025] <Method for Manufacturing Negative Electrode Active Material> The negative electrode active material according to the first embodiment can be manufactured by the following method. Raw material powder is prepared so as to have a target composition. Examples of the 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 negative electrode active material having a composition represented by 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 an air atmosphere or an inert gas atmosphere. The inert atmosphere is, for example, an argon atmosphere or a nitrogen atmosphere. The raw material mixture may be fired in a reducing atmosphere. The reducing atmosphere is, for example, an ammonia atmosphere, a methane atmosphere, or a hydrogen sulfide atmosphere. The temperature increase rate when firing the raw material mixture is, for example, 1°C / min or more and 10°C / min or less. The temperature decrease rate when firing the raw material mixture is, for example, 1°C / min or more and 10°C / min or less. The electronic conductivity of the negative electrode active material tends to increase as the raw materials of the negative electrode active material are fired at a higher temperature.

[0028] The negative electrode active material may be obtained by mechanochemically reacting a mixture of raw material powders with each other in a mixing device such as a planetary ball mill (using a mechanochemical milling method). By these methods, the negative electrode active material according to the first embodiment can be obtained.

[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 negative electrode active material 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 anode material 100 according to the second embodiment. The anode material 100 includes an anode active material 111 and a solid electrolyte 112. The anode material 100 may include a conductive additive 113 for the purpose of enhancing electronic conductivity. The anode active material 111, the solid electrolyte 112, and the conductive additive 113 are, for example, each in a particulate form. The anode active material 111 includes the anode active material according to the first embodiment. As described above, the anode active material according to the first embodiment has electronic conductivity equal to or higher than a certain level.

[0033] The negative electrode active material 111 may contain the negative electrode active material according to the first embodiment as a main component. "Containing the negative electrode active material according to the first embodiment as a main component" means that the component contained in the largest amount by mass is the negative electrode active material according to the first embodiment. The negative electrode active material 111 may consist solely of the negative electrode active material according to the first embodiment.

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

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

[0036] The negative electrode material 100 according to the second embodiment contains the negative electrode active material according to the first embodiment, and therefore, a negative electrode suitable for improving the charge / discharge efficiency of a battery can be obtained.

[0037] Third Embodiment A third embodiment will be described below, and the matters described in the first and second embodiments will be omitted as appropriate.

[0038] 2 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.

[0039] The positive electrode 101 includes a positive electrode active material and a solid electrolyte.

[0040] The electrolyte layer 102 includes an electrolyte material, such as a solid electrolyte material.

[0041] The negative electrode 103 includes a negative electrode active material 111 and a solid electrolyte 112 .

[0042] The negative electrode active material 111 is a particle containing the negative electrode active material according to the first embodiment. The negative electrode active material 111 may be a particle containing the negative electrode active material according to the first embodiment as a main component. "Particles containing the negative electrode active material according to the first embodiment as a main component" means particles in which the component contained most abundantly by mass is the negative electrode active material according to the first embodiment. The negative electrode active material 111 may be a particle consisting solely of the negative electrode active material according to the first embodiment.

[0043] 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 negative electrode 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 diffusion rate of lithium in the negative electrode active material 111 improves. This allows the battery 1000 to operate at high power.

[0044] The negative electrode active material 111 may have a larger median diameter than the solid electrolyte 112. This allows the negative electrode active material 111 and the solid electrolyte 112 to be dispersed well.

[0045] 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 negative electrode active material 111 to the total volume of the negative electrode active material 111 and the solid electrolyte 112 may be 0.30 or more and 0.95 or less.

[0046] 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.

[0047] 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.

[0048] 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 containing a halogen element but not sulfur. The halide solid electrolyte may contain not only a halogen element but also oxygen.

[0049] 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 GeP2S12 is.

[0050] Examples of halide solid electrolytes include Li a Me b Y c It is a compound having a composition represented by the composition formula 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.

[0051] 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).

[0052] 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.

[0053] Another example of a halide solid electrolyte is Li α M β O γ X δ The compound has a composition represented by the following composition formula: where 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.

[0054] 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 ZnGeO16 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.

[0055] 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 a composite compound of polyethylene oxide and a lithium salt. An example of such a polymer solid electrolyte is lithium bis(trifluoromethanesulfonyl)imide.

[0056] 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.

[0057] The positive electrode 101 includes a material capable of absorbing and releasing metal ions such as lithium ions, and includes, for example, a positive electrode active material (for example, particles of a positive electrode active material).

[0058] Examples of the positive electrode active material include a lithium-containing transition metal oxide, a transition metal fluoride, a polyanionic material, a fluorinated polyanionic material, a transition metal sulfide, a transition metal oxysulfide, or a transition metal oxynitride. Examples of the lithium-containing transition metal oxide include Li(Ni,Co,Al)O, Li(Ni,Co,Mn)O, or LiCoO.

[0059] In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

[0060] From the viewpoint of cost and safety of the battery 1000, lithium phosphate may be used as the positive electrode active material.

[0061] 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 positive electrode 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.

[0062] 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.

[0063] In order to improve the energy density and output of the battery 1000, the ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte in the positive electrode 101 may be 0.30 or more and 0.95 or less.

[0064] A coating layer may be formed on the surface of the positive 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.

[0065] 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. With this configuration, the battery 1000 has high charge / discharge efficiency.

[0066] 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.

[0067] 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.

[0068] The electrolyte layer 102 includes an electrolyte material. The electrolyte material is, for example, a solid electrolyte material. The electrolyte layer 102 may be an electrolyte layer made of a solid electrolyte. 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.

[0069] 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.

[0070] FIG. 3 shows a battery 2000, which 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. For example, 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The ionic liquid may include a lithium salt.

[0080] 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.

[0081] 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. A mixture of two or more of the above materials may also be used as binders.

[0082] 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.

[0083] 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.

[0084] The positive electrode 101 constituting the battery 1000 shown in Fig. 2 may contain not only a positive electrode 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 a positive electrode active material but also a conductive additive.

[0085] 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 negative electrode active material 111. This increases the contact area between the conductive additive 113 and the negative electrode active material 111. As a result, the battery resistance decreases, and 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 positive electrode active material. The positive electrode 201 of the battery 2000 shown in FIG. 3 may also be configured in the same manner as above.

[0086] In the negative electrode 103 of the battery 1000 shown in FIG. 2 , the ratio of the volume of the conductive additive 113 to the sum of the volume of the negative electrode 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 FIG. 3 may also be configured in the same manner as above. In the positive electrode 101 of the battery 1000 shown in FIG. 2 , the ratio of the volume of the conductive additive to the sum of the volume of the positive electrode 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 FIG. 3 may also be configured in the same manner as above.

[0087] The negative electrode material 100 shown in FIG. 1 may be included in the negative electrode 103 of the battery 1000 shown in FIG. 2. A coating layer may be formed on the surface of the negative electrode active material 111 to prevent the solid electrolyte 112 from reacting with the negative electrode active material 111. With this configuration, the battery 1000 has high charge / discharge efficiency. Similarly, the negative electrode material 100 shown in FIG. 1 may be included in the negative electrode 203 of the 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 negative electrode active material.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0093] (Technology 1) A composition containing Li, V, M, and O, wherein M is at least one selected from tetravalent metal elements and tetravalent metalloid elements excluding V, and wherein the electronic conductivity is 7×10 -13 2. A negative electrode active material having a specific resistance of 200 s / cm or more.

[0094] According to the present disclosure, the negative electrode active material is 7×10 -13 By having an electronic conductivity of 100 S / cm or more, the charge / discharge efficiency of a battery using the negative electrode active material is improved.

[0095] (Technology 2) Li 3+x V 1-x M x The negative electrode active material according to Technology 1 has a composition represented by O4 and satisfies 0<x<1. According to this configuration, a battery using the negative electrode active material has good charge / discharge characteristics.

[0096] (Technology 3) The negative electrode active material according to Technology 2, which satisfies 0<x≦0.2. According to this configuration, a battery using the negative electrode active material has even better charge / discharge characteristics.

[0097] (Technology 4) The negative electrode active material according to any one of Technologies 1 to 3, wherein M contains Ti. According to this configuration, the charge / discharge efficiency of a battery using the negative electrode active material is further improved.

[0098] (Technology 5) The negative electrode active material according to any one of Technologies 1 to 4, wherein the negative electrode active material includes both a β phase and a γ phase as crystalline phases. According to this configuration, the negative electrode active material includes both a β phase and a γ phase as crystalline phases, and therefore, when the negative electrode active material is used in a battery, a battery that achieves both high capacity and durability can be obtained.

[0099] (Technology 6) Electronic conductivity is 8.0 × 10 -11 6. The negative electrode active material according to any one of techniques 1 to 5, wherein the electrical conductivity is 100 S / cm or more. According to this configuration, when the negative electrode active material is used in a battery, a battery having good energy density and input / output characteristics can be obtained.

[0100] (Technology 7) A battery comprising a positive electrode, a negative electrode containing the negative electrode active material according to any one of Technologies 1 to 6, and an electrolyte layer disposed between the positive electrode and the negative electrode. According to this configuration, the negative electrode active material contained in the negative electrode is 7×10 -13 By having an electronic conductivity of 100 S / cm or more, the charge / discharge efficiency of the battery is improved.

[0101] (Technology 8) The battery according to Technology 7, 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.

[0102] Hereinafter, the present disclosure will be described in detail using examples and comparative examples. Note that the negative electrode active material and battery of the present disclosure are not limited to the following examples.

[0103] Example 1 Preparation of Negative Electrode Active Material The negative electrode active material of Example 1 was prepared as follows. Raw material powders containing Li2CO3, VO, and TiO2 were prepared in a molar ratio of Li2CO3:VO:TiO2 = 1.525:0.475:0.05. Li2CO3 was added in an amount 10% by mass in excess of the mass of Li2CO3 corresponding to the Li2CO3 molar ratio. These raw material powders were mixed in a mortar to obtain a mixed powder. The mixed powder was pre-fired at 600°C for 3 hours in the air. The pre-fired powder was then fired at 940°C for 15 hours in the air. The temperature was increased at an average rate of 5°C / min and decreased at an average rate of 3°C / min. In this manner, the negative electrode active material of Example 1 was prepared.

[0104] Example 2 A negative electrode active material of Example 2 was produced in the same manner as in Example 1, except that the temperature for main baking was changed to 985°C.

[0105] Example 3 A negative electrode active material of Example 3 was produced in the same manner as in Example 1, except that the temperature for main baking was changed to 965°C.

[0106] Comparative Example 1: Li2CO3 and VO were prepared as raw material powders in a molar ratio of Li2CO3:VO5 = 1.5:0.5. Li2CO3 was added in an amount 3 mass% in excess of the mass of Li2CO3 corresponding to the Li2CO3 in the above molar ratio. The mixed powder was fired in the same manner as in Example 1, except that the firing temperature was changed to 800°C, to produce a negative electrode active material of Comparative Example 1.

[0107] [X-ray Diffraction Measurement] In a dry atmosphere having a dew point of −45° C. or less, an X-ray diffractometer (MiniFlex 600, manufactured by RIGAKU Corporation) was used to measure X-ray diffraction of the negative electrode active materials of Examples 1 to 3 and Comparative Example 1. Cu-Kα radiation (wavelengths 1.5405 Å and 1.5444 Å) was used as the X-ray source.

[0108] The X-ray diffraction patterns of the negative electrode active materials of Examples 1 to 3 had both diffraction peaks attributable to the crystal planes of the β phase and diffraction peaks attributable to the crystal planes of the γ phase. That is, the negative electrode active materials of Examples 1 to 3 each contained both the β phase and the γ phase as crystalline phases. The X-ray diffraction pattern of the negative electrode active material of Comparative Example 1 had only diffraction peaks attributable to the crystal planes of the β phase. That is, the negative electrode active material of Comparative Example 1 contained only the β phase.

[0109] [Analysis by ICP Optical Emission Spectroscopy] The Ti composition ratios of the negative electrode active materials according to Examples 1 to 3 were 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 negative electrode active materials according to Examples 1 to 3, x in composition formula (1) was 0.05 in all cases.

[0110] [Measurement of Electronic Conductivity of Negative Electrode Active Material] Fig. 4 schematically shows a pressure-molding die 300 used to evaluate the electronic conductivity of a negative electrode active material. The pressure-molding die 300 includes an upper punch 301, a frame 302, and a lower punch 303. The frame 302 is made of insulating polycarbonate. The upper punch 301 and the lower punch 303 are both made of stainless steel having electronic conductivity.

[0111] The electronic conductivity of the negative electrode active material was measured by the following method using a pressure molding die 300 shown in FIG.

[0112] In a dry atmosphere, the powder of the negative electrode active material 111 was filled into the pressure molding die 300. Inside the pressure molding die 300, the powder of the negative electrode active material 111 was compressed between the upper punch 301 and the lower punch 303, thereby applying a pressure of 720 MPa to the negative electrode active material 111. While the pressure was still applied, the upper punch 301 and the lower punch 303 were each connected to a potentiostat (VersaSTAT4, manufactured by Princeton Applied Research) equipped with a frequency response analyzer. The upper punch 301 was connected to a working electrode and a potential measurement terminal. The lower punch 303 was connected to a counter electrode and a reference electrode.

[0113] A voltage was applied to the working electrode relative to the reference electrode, and the current value was read. A graph of the IV characteristics was obtained by plotting the current value against the change in potential value, and the electronic conductivity was calculated from the slope. The negative electrode active materials of Examples 1 to 3 and Comparative Example 1 were each used as the negative electrode active material 111 in FIG. 3 and measured for electronic conductivity at room temperature using a pressure molding die 300. The electronic conductivity was measured in a state where the negative electrode active material 111 did not contain a coating such as carbon or the conductive additive described above. The measurement results of the electronic conductivity of the negative electrode active materials of Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0114] [Diffusion Coefficient] The diffusion coefficient of Li ions was determined by constant current intermittent titration for each of the secondary batteries of Examples 1 to 3 and Comparative Example 1. The diffusion coefficients of Li ions for Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0115] [Fabrication of Negative Electrode] Li3PS4 (hereinafter referred to as "LPS") was prepared as the solid electrolyte. The negative electrode active material of Example 1 was prepared as the negative electrode active material. LPS, negative electrode active material, conductive additive, binder-containing solvent, and 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. Next, a negative electrode was stacked on the side of the solid electrolyte layer opposite to the side in contact with 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 sulfide 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 stacked structure in the above order was compressed and molded at a pressure of 80 MPa to produce a laminate 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 and 3, and Comparative Example 1 were fabricated using the same method as Example 1.

[0120] [Charge / Discharge Test] The batteries of Examples 1 to 3 and Comparative Example 1 were placed in a thermostatic chamber maintained at 25°C. Each battery was charged with a constant current at a 0.05C rate (20-hour rate) based on the theoretical capacity of the battery. The end-of-charge voltage was 3.6V. Next, each battery was discharged at a current value corresponding to a 0.05C rate until the voltage reached 1.0V.

[0121] 5 shows the results of charge / discharge tests on the batteries of Examples 1 to 3 and Comparative Example 1. The discharge capacity and charge / discharge efficiency at 0.05 C obtained by the charge / discharge tests are shown in Table 1. The charge / discharge efficiency was calculated by measuring the charge capacity during charging and the discharge capacity during discharging, and then calculating the ratio of the discharge capacity to the charge capacity.

[0122]

[0123] As shown in the results of Examples 1 to 3, the negative electrode active material containing a mixed phase of β and α phases exhibited high electronic conductivity and diffusion coefficient. Batteries using such negative electrode active materials exhibited high discharge capacity and charge / discharge efficiency.

[0124] The negative electrode active material of Comparative Example 1 contained only the β phase. Therefore, the negative electrode active material of Comparative Example 1 exhibited low electronic conductivity and diffusion coefficient. A battery using such a negative electrode active material exhibited low discharge capacity and charge / discharge efficiency.

[0125] As shown by the results of Examples 1 to 3 and Comparative Example 1, the electronic conductivity of the negative electrode active material was 6.7 × 10 -13 When the negative electrode active material had a charge / discharge efficiency of more than 76.5%, the battery using the negative electrode active material had a charge / discharge efficiency of more than 76.5%.

[0126] As described above, the negative electrode active material of the present disclosure exhibits high electronic conductivity, and a battery containing this negative electrode active material in the negative electrode is suitable for improving charge / discharge efficiency.

[0127] The negative electrode active material and battery of the present disclosure can be used, for example, in lithium ion secondary batteries.

[0128] REFERENCE SIGNS LIST 100 Negative electrode material 111 Negative electrode 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 300 Pressure molding die 301 Upper punch 302 Frame 303 Lower punch 1000, 2000 Battery

Claims

1. A compound containing Li, V, M, and O, where M is at least one selected from tetravalent metal elements other than V and tetravalent metalloid elements, and has an electronic conductivity of 7.0×10 -13 S / cm or more.

2. Li 3+x V 1-x M x The negative electrode active material according to claim 1 , having a composition represented by O4, and satisfying 0<x<1.

3. The negative electrode active material according to claim 2, wherein 0<x≦0.2 is satisfied.

4. The negative electrode active material according to claim 1, wherein M contains Ti.

5. The negative electrode active material according to claim 1, wherein the negative electrode active material contains both a β phase and a γ phase as crystal phases.

6. Electronic conductivity is 8.0 x 10 -11 The negative electrode active material according to claim 1 , wherein the electrical conductivity is 1.0 S / cm or more.

7. A battery comprising: a positive electrode; a negative electrode containing the negative electrode active material according to any one of claims 1 to 6; and an electrolyte layer disposed between the positive electrode and the negative electrode.

8. The battery according to claim 7, wherein the negative electrode contains a conductive additive.

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