Cathode Material and Battery

Abstract

The positive electrode material (1000) of the present disclosure includes a positive electrode active material (110) and a coating layer (120) that coats the positive electrode active material (110). The coating layer (120) contains niobium and carbon. The positive electrode active material (110) and the coating layer (120) form a coated active material (130). In the surface layer portion of the coated active material (130), the ratio (Nb / C) of the niobium content to the carbon content is 0.11 or more in terms of atomic ratio.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode material and a battery. Background Art

[0002] Patent Document 1 discloses an all-solid-state battery that uses a positive electrode active material coated with a coating material.

[0003] Prior Art Documents

[0004] Patent Document 1: International Publication No. 2019 / 135322 Summary of the Invention

[0005] In the prior art, it has been desired to further increase the discharge voltage of the battery.

[0006] The positive electrode material according to one aspect of the present disclosure includes:

[0007] a positive electrode active material, and

[0008] a coating layer that coats the positive electrode active material,

[0009] the coating layer contains niobium and carbon,

[0010] the positive electrode active material and the coating layer constitute a coated active material,

[0011] in the surface layer portion of the coated active material, the ratio Nb / C of the niobium content to the carbon content is 0.11 or more in terms of atomic ratio.

[0012] According to the present disclosure, the discharge voltage of the battery can be increased. Brief Description of the Drawings

[0013] Figure 1 It is a cross-sectional view showing a schematic structure of the positive electrode material 1000 of Embodiment 1.

[0014] Figure 2 It is a cross-sectional view showing a schematic structure of the battery 2000 of Embodiment 2. Detailed Description of the Embodiments

[0015] (Overview of One Aspect of the Present Disclosure)

[0016] The positive electrode material according to the first aspect of the present disclosure includes:

[0017] a positive electrode active material, and

[0018] a coating layer that coats the positive electrode active material,

[0019] the coating layer contains niobium and carbon,

[0020] the positive electrode active material and the coating layer constitute a coated active material,

[0021] In the surface layer portion of the coated active material, the ratio Nb / C of the niobium content to the carbon content is 0.11 or more in terms of atomic ratio.

[0022] According to the first aspect, the discharge voltage of the battery can be increased.

[0023] In the second aspect of the present disclosure, for example, in the positive electrode material of the first aspect, the solid electrolyte may further be included. According to the second aspect, the ionic conductivity of the positive electrode can be increased.

[0024] In the third aspect of the present disclosure, for example, in the positive electrode material of the second aspect, the solid electrolyte may be represented by the compositional formula Li α M β X γ where α, β, and γ may each independently be values greater than 0, M may contain at least one element selected from metal elements and metalloid elements other than Li, and X may contain at least one selected from F, Cl, Br, and I. According to the third aspect, the output density of the battery can be increased. In addition, the thermal stability of the battery can be increased, and the generation of harmful gases such as hydrogen sulfide can be suppressed.

[0025] In the fourth aspect of the present disclosure, for example, in the positive electrode material of the third aspect, M may contain yttrium.

[0026] In the fifth aspect of the present disclosure, for example, in the positive electrode material of the third or fourth aspect, 2.5 ≤ α ≤ 3, 1 ≤ β ≤ 1.1, and γ = 6 may be satisfied.

[0027] In the sixth aspect of the present disclosure, for example, in the positive electrode material of any one of the third to fifth aspects, X may contain at least one selected from Cl and Br.

[0028] According to the fourth to sixth aspects, the ionic conductivity of the solid electrolyte can be further increased. Thereby, the output density of the battery is increased.

[0029] In the seventh aspect of the present disclosure, for example, in the positive electrode material of any one of the first to sixth aspects, the coating layer may contain a lithium niobate-based compound. According to the seventh aspect, the charge-discharge efficiency of the battery can be further increased.

[0030] In the eighth aspect of the present disclosure, for example, in the positive electrode material of any one of the first to seventh aspects, the positive electrode active material may contain Li and at least one element selected from Mn, Co, Ni, and Al. According to the eighth aspect, the energy density of the battery can be further increased.

[0031] The battery according to the ninth aspect of the present disclosure includes:

[0032] The positive electrode comprising the positive electrode material according to any one of the first to eighth aspects,

[0033] a negative electrode, and

[0034] an electrolyte layer disposed between the positive electrode and the negative electrode.

[0035] According to the ninth aspect, the discharge voltage of the battery can be increased.

[0036] In the tenth aspect of the present disclosure, for example, in the battery according to the ninth aspect, the positive electrode material may further include a solid electrolyte, and the electrolyte layer may include a solid electrolyte having the same composition as the solid electrolyte contained in the positive electrode material. According to the tenth aspect, the charge and discharge efficiency of the battery can be further improved.

[0037] In the eleventh aspect of the present disclosure, for example, in the battery according to the ninth or tenth aspect, the positive electrode material may further include a solid electrolyte, and the electrolyte layer may include a halide solid electrolyte having a composition different from that of the solid electrolyte contained in the positive electrode material. According to the eleventh aspect, the output density and charge and discharge efficiency of the battery can be increased.

[0038] In the twelfth aspect of the present disclosure, for example, in the battery according to any one of the ninth to eleventh aspects, the electrolyte layer may include a sulfide solid electrolyte. According to the twelfth aspect, a low-potential negative electrode material such as graphite or metallic lithium can be used, and the energy density of the battery can be increased.

[0039] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0040] (Embodiment 1)

[0041] Figure 1 FIG. is a cross-sectional view schematically showing the structure of the positive electrode material 1000 of Embodiment 1.

[0042] The positive electrode material 1000 of Embodiment 1 includes a coated active material 130 and a solid electrolyte 100.

[0043] The coated active material 130 includes a positive electrode active material 110 and a coating layer 120. The coating layer 120 is provided on the surface of the positive electrode active material 110. The coating layer 120 is a layer containing a coating material. The positive electrode active material 110 is coated with the coating material. The coating layer 120 contains niobium and carbon.

[0044] In the surface layer portion of the coated active material 130, the ratio Nb / C of the niobium content to the carbon content is 0.11 or more in terms of atomic ratio. The "surface layer portion of the coated active material 130" refers to the portion from the outermost surface of the coated active material 130 to a predetermined depth position. The "predetermined depth position" may be the position of the compositional information obtained by the analysis method of the surface composition. For example, when the thickness of the coating layer 120 exceeds the penetration depth of the soft X-ray or electron beam used in the composition analysis, the coating layer 120 is regarded as the "surface layer portion of the coated active material 130". When the thickness of the coating layer 120 is less than the penetration depth of the soft X-ray or electron beam used in the composition analysis, a part of the positive electrode active material 110 and the coating layer 120 are included in the "surface layer portion of the coated active material 130".

[0045] The positive electrode active material 110 is separated from the solid electrolyte 100 by the coating layer 120. The positive electrode active material 110 may not be in direct contact with the solid electrolyte 100. Since the coating layer 120 has ion conductivity.

[0046] According to the above structure, the discharge voltage of the battery can be increased.

[0047] Patent Document 1 mentions that during charging, an oxidative decomposition side reaction occurs in which electrons are extracted from the solid electrolyte in contact with the positive electrode active material. Along with this, an oxide layer lacking lithium ion conductivity is formed between the positive electrode active material and the solid electrolyte, and the interfacial resistance increases. In addition, it is mentioned that by providing a coating layer between the positive electrode active material and the solid electrolyte, the formation of the oxide layer can be suppressed, and the increase in the interfacial resistance can be suppressed. However, the surface composition of the coating layer is not clear.

[0048] On the other hand, as a result of the intensive research by the present inventors, the following problem has been found. If the battery is operated, the composition of the surface layer portion of the coated active material including the coating layer and the positive electrode active material changes, the interfacial resistance increases, and the discharge voltage decreases. As a result of further detailed investigation, the present inventors have found that by intentionally increasing the ratio (Nb / C) of the niobium content to the carbon content in the surface layer portion of the coated active material, the discharge voltage increases. It is considered that this is because the carbon impurity content in the niobium compound (for example, lithium niobium oxide) contained in the coating layer decreases, whereby the ion conductivity (for example, lithium ion conductivity) of the coating layer increases, and the interfacial resistance of the electrode reaction decreases.

[0049] It is expected that the effect of improving the potential stability of the coating layer 120 not only suppresses the formation of the oxide layer of the solid electrolyte but also suppresses the oxidation of the electrolyte. Therefore, it is considered that the technology of the present disclosure is also effective in a battery including an electrolyte.

[0050] The method for controlling the ratio (Nb / C) is not particularly limited. For example, a method of heat-treating the coated active material 130 in an oxygen atmosphere and recovering the coated active material 130 in an atmosphere with a dew point of -30°C or lower after the heat treatment can be cited. The oxygen atmosphere can be a pure oxygen atmosphere. The heat treatment conditions and the atmosphere conditions when the coated active material 130 is taken out from the heat treatment apparatus after the heat treatment can be appropriately selected based on the compositions of the positive electrode active material 110 and the coating layer 120.

[0051] As an analysis method for the surface composition of the coated active material 130, X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), etc. can be used. The analysis method for the surface composition is appropriately selected according to the composition of the coating material contained in the coating layer 120 and the coating state of the positive electrode active material 110. The surface composition analysis using XPS is not easily a local analysis and can evaluate a relatively wide area of the material surface. In addition, since the average surface composition information with a depth of 10 nm from the outermost surface can be obtained and the material quality is easy to manage, XPS is suitable as an analysis method for the surface composition.

[0052] The ratio (Nb / C) can be 0.11 or more and 10 or less. When the ratio (Nb / C) is 10 or less, the carbon impurities in the coating layer 120 will not become too few, and the electronic conductivity can be appropriately ensured. Thereby, an increase in the internal resistance of the positive electrode material 1000 can be suppressed. By suppressing the increase in the internal resistance of the positive electrode material 1000, the battery can operate at a high output. The ratio (Nb / C) can be 0.11 or more and 0.18 or less. If the ratio (Nb / C) falls within such a range, the electronic conductivity and the ionic conductivity of the coating layer 120 can be achieved simultaneously. As a result, the discharge voltage of the battery is further increased.

[0053] As the solid electrolyte 100, a halide solid electrolyte can be used.

[0054] The halide solid electrolyte is represented by the following compositional formula (1), for example. In the compositional formula (1), α, β, and γ are each independently a value greater than 0. M contains at least one element selected from metal elements other than Li and metalloid elements. X contains at least one selected from F, Cl, Br, and I.

[0055] Li α M β X γ Formula (1)

[0056] Metalloid elements include B, Si, Ge, As, Sb, and Te. Metallic elements include all elements contained in Groups 1 to 12 of the periodic table except hydrogen, and all elements contained in Groups 13 to 16 except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. That is, metallic elements are a group of elements that can become cations when forming halogen compounds and inorganic compounds.

[0057] As the halide solid electrolyte, Li 3 YX 6 , Li 2 MgX 4 , Li 2 FeX 4 , Li(Al,Ga,In)X 4 , Li 3 (Al,Ga,In)X 6 etc.

[0058] Based on the above structure, the output density of the battery can be increased. In addition, the thermal stability of the battery can be improved, and the generation of harmful gases such as hydrogen sulfide can be suppressed.

[0059] In the present disclosure, when the elements in the formula are represented in the form of "(Al,Ga,In)", this representation method means at least one element selected from the group of elements in the parentheses. That is, "(Al,Ga,In)" has the same meaning as "at least one selected from Al, Ga, and In". The same applies to other elements. The halide solid electrolyte exhibits excellent ionic conductivity. Furthermore, the halide solid electrolyte may not contain sulfur.

[0060] In the composition formula (1), M may contain Y (= yttrium). That is, the solid electrolyte 100 may contain Y as a metallic element.

[0061] The composition formula (1) may satisfy 2.5 ≤ α ≤ 3, 1 ≤ β ≤ 1.1, and γ = 6.

[0062] In the composition formula (1), X may contain at least one selected from Cl and Br.

[0063] Based on the above structure, the ionic conductivity of the solid electrolyte 100 can be further improved. Thereby, the output density of the battery is increased.

[0064] The Y-containing halide solid electrolyte may be a compound represented by the following composition formula (2).

[0065] Li a M b Y c X 6 Formula (2)

[0066] The compositional formula (2) satisfies a + mb + 3c = 6 and c > 0. In the compositional formula (2), M contains at least one element selected from metal elements and metalloid elements other than Li and Y. m is the valence of M. X contains at least one selected from F, Cl, Br, and I. M contains at least one selected from Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. Specifically, as the Y-containing halogen solid electrolyte, Li 3 YF 6 、Li 3 YCl 6 、Li 3 YBr 6 、Li 3 YI 6 、、Li 3 YBrCl 5 、Li 3 YBr 3 Cl 3 、、Li 3 YBr 5 Cl、Li 3 YBr 5 I、Li 3 YBr 3 I 3 、Li 3 YBrI 5 、Li 3 YClI 5 、Li 3 YCl 3 I 3 、Li 3 YCl 5 I、Li 3 YBr 2 Cl 2 I 2 、Li 3 YBrCl 4 I、Li 2.7 Y 1.1 Cl 6 、Li 2.5 Y 0.5 Zr 0.5 Cl 6 、Li 2.5 Y 0.3 Zr 0.7 Cl 6 etc.

[0067] Based on the above structure, the output density of the battery can be further improved.

[0068] The solid electrolyte 100 may include a sulfide solid electrolyte.

[0069] As the sulfide solid electrolyte, Li 2 S-P 2 S 5 、Li 2 S-SiS 2 、Li 2 S-B 2 S 3 、Li 2 S-GeS 2 、Li 3.25 Ge 0.25 P 0.75 S 4 、Li 10 GeP 2 S 12 etc. LiX, Li 2 O, MO q 、Li p MO q etc. can be added thereto. Here, the element X in "LiX" is at least one element selected from F, Cl, Br, and I. The element M in "MO q " and "Li p MO q " is at least one element selected from P, Si, Ge, B, Al, Ga, In, Fe, and Zn. The p and q in "MO q " and "Li p MO q " are each independent natural numbers.

[0070] According to the above structure, the output density of the battery can be improved.

[0071] The solid electrolyte 100 may include at least one selected from an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0072] As the oxide solid electrolyte, for example, NASICON-type solid electrolytes represented by LiTi 2 (PO 4 ) 3 and its element substituents, (LaLi)TiO 3 -series perovskite-type solid electrolytes, LISICON-type solid electrolytes represented by Li 14 ZnGe 4 O 16 、Li 4 SiO 4 、LiGeO 4 and its element substituents, and Li 7La 3 Zr 2 O 12 and garnet-type solid electrolytes represented by their elemental substituents, Li 3 N and its H substituents, Li 3 PO 4 and its N substituents, in a substrate containing LiBO 2 、Li 3 BO 3 and other Li-B-O compounds, Li 2 SO 4 、Li 2 CO 3 and other materials such as glass or glass ceramics.

[0073] As a polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound can have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain many lithium salts, so the ionic conductivity can be further improved. As the lithium salt, LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiSO 3 CF 3 、LiN(SO 2 CF 3 ) 2 、LiN(SO 2 C 2 F 5 ) 2 、LiN(SO 2 CF 3 )(SO 2 C 4 F 9 )、LiC(SO 2 CF 3 ) 3 etc. As the lithium salt, one lithium salt selected from them can be used alone, or a mixture of two or more lithium salts selected from them can be used.

[0074] As a complex hydride solid electrolyte, for example, LiBH 4 -LiI, LiBH 4 -P 2 S 5 etc. can be used.

[0075] According to the above structure, the output density of the battery can be improved.

[0076] As the positive electrode active material 110 of Embodiment 1, for example, a lithium-containing transition metal oxide, a transition metal fluoride, a polyanion material, a fluorinated polyanion material, a transition metal sulfide, a transition metal oxysulfide, a transition metal oxynitride, etc. can be used. In particular, when using a lithium-containing transition metal oxide as the positive electrode active material 110, the manufacturing cost can be reduced and the average discharge voltage can be increased.

[0077] The positive electrode active material 110 may contain Li and at least one element selected from Mn, Co, Ni, and Al. As such a material, Li(NiCoAl)O 2 , Li(NiCoMn)O 2 , LiCoO 2 , etc. can be cited.

[0078] The positive electrode active material 110 may contain a single active material or may contain a plurality of active materials having different compositions.

[0079] In Embodiment 1, the positive electrode active material 110 may be Li(NiCoMn)O 2 .

[0080] According to the above structure, the energy density of the battery can be further increased.

[0081] The positive electrode active material 110 has a particle shape, for example. The particle shape of the positive electrode active material 110 is not particularly limited. The particle shape of the positive electrode active material 110 may be spherical, ellipsoidal, scaly, or fibrous.

[0082] As the coating material contained in the coating layer 120, a material with low electronic conductivity can be used. As the coating material, an oxide material, an oxide solid electrolyte, a carbonate, etc. can be used.

[0083] As the oxide material, for example, SiO 2 , Al 2 O 3 , TiO 2 , B 2 O 3 , Nb 2 O 5 , WO 3 , ZrO 2 , etc. can be used. As the oxide solid electrolyte, for example, Li-Nb-O compounds such as LiNbO 3 , LiBO 2 , Li 3 BO 3 , etc. Li-B-O compounds, LiAlO 2 , etc. Li-Al-O compounds, Li 4 SiO4 Li-Si-O compounds such as Li 2 SO 4 Li-S-O compounds such as Li 4 Ti 5 O 12 Li-Ti-O compounds such as Li 2 ZrO 3 Li-Zr-O compounds such as Li 2 MoO 3 Li-Mo-O compounds such as LiV 2 O 5 Li-V-O compounds such as Li 2 WO 4 Li-W-O compounds, etc.

[0084] In Embodiment 1, the coating material may be an oxide solid electrolyte.

[0085] The oxide solid electrolyte has high ionic conductivity and high potential stability. Therefore, by using the oxide solid electrolyte, the charge-discharge efficiency of the battery can be further improved.

[0086] In Embodiment 1, the coating layer 120 may contain a lithium niobate-based compound as the coating material. The coating material may be LiNbO 3 . The lithium niobate-based compound is a compound containing lithium, niobium, and oxygen.

[0087] LiNbO 3 has higher ionic conductivity and higher potential stability. Therefore, by using LiNbO 3 , the charge-discharge efficiency of the battery can be further improved.

[0088] The thickness of the coating layer 120 may be 1 nm or more and 100 nm or less.

[0089] By the thickness of the coating layer 120 being 1 nm or more, direct contact between the positive electrode active material 110 and the solid electrolyte 100 can be suppressed, and side reactions of the solid electrolyte can be suppressed. Therefore, the charge-discharge efficiency can be improved.

[0090] By the thickness of the coating layer 120 being 100 nm or less, the thickness of the coating layer 120 does not become too thick. Therefore, the internal resistance of the battery can be sufficiently reduced. As a result, the energy density of the battery can be increased. The thickness of the coating layer 120 can be determined by thinning the coated active material 130 using a method such as ion milling and observing the cross-section of the coated active material 130 with a transmission electron microscope.

[0091] The coating layer 120 can similarly coat the particles of the positive electrode active material 110. It is possible to suppress the direct contact between the particles of the positive electrode active material 110 and the particles of the solid electrolyte 100, and suppress side reactions of the solid electrolyte 100. Therefore, the charge-discharge efficiency can be improved.

[0092] Alternatively, the coating layer 120 may also coat only a part of the surface of the particles of the positive electrode active material 110. By the particles of the plurality of positive electrode active materials 110 being in direct contact with each other via the portion without the coating layer 120, the electron conductivity between the particles of the positive electrode active material 110 is improved. Therefore, the battery can operate with high output.

[0093] The shape of the solid electrolyte 100 in Embodiment 1 is not particularly limited, and may be, for example, needle-shaped, spherical, ellipsoidal, etc. For example, the shape of the solid electrolyte 100 may be granular.

[0094] For example, when the shape of the solid electrolyte 100 in Embodiment 1 is granular (e.g., spherical), the median diameter may be 100 μm or less.

[0095] When the median diameter of the solid electrolyte 100 is 100 μm or less, the coated active material 130 and the solid electrolyte 100 can form a good dispersion state in the positive electrode material 1000. Thereby, the charge-discharge characteristics of the battery are improved.

[0096] In Embodiment 1, the median diameter of the solid electrolyte 100 may be 10 μm or less.

[0097] According to the above structure, the coated active material 130 and the solid electrolyte 100 can form a good dispersion state in the positive electrode material 1000.

[0098] In Embodiment 1, the median diameter of the solid electrolyte 100 may be smaller than the median diameter of the coated active material 130.

[0099] According to the above structure, the solid electrolyte 100 and the coated active material 130 can form a better dispersion state in the positive electrode material 1000.

[0100] The median diameter of the coated active material 130 may be 0.1 μm or more and 100 μm or less.

[0101] When the median diameter of the coated active material 130 is 0.1 μm or more, the coated active material 130 and the solid electrolyte 100 can form a good dispersion state in the positive electrode material 1000. As a result, the charge-discharge characteristics of the battery are improved.

[0102] When the median diameter of the coated active material 130 is 100 μm or less, the lithium diffusion rate within the coated active material 130 is sufficiently ensured. Therefore, the battery can operate at high output.

[0103] The median diameter of the coated active material 130 can be larger than the median diameter of the solid electrolyte 100. Thereby, the coated active material 130 and the solid electrolyte 100 can form a good dispersion state.

[0104] In the positive electrode material 1000 of Embodiment 1, the particles of the solid electrolyte 100 and the particles of the coated active material 130 can be in contact with each other as Figure 1 shown. At this time, the coating layer 120 and the positive electrode active material 110 are in contact with each other.

[0105] The positive electrode material 1000 of Embodiment 1 may include a plurality of particles of the solid electrolyte 100 and a plurality of particles of the coated active material 130.

[0106] The content of the solid electrolyte 100 and the content of the coated active material 130 in the positive electrode material 1000 may be the same or different from each other.

[0107] In this specification, the "median diameter" refers to the particle diameter at which the cumulative volume in the particle size distribution based on volume is equal to 50%. The particle size distribution based on volume is measured, for example, by a laser diffraction measuring device or an image analysis device.

[0108] Next, a method for manufacturing the positive electrode material 1000 will be described.

[0109] First, a powder of the positive electrode active material 110 is prepared. The powder of the positive electrode active material 110 is synthesized, for example, by a solid-phase method. In the solid-phase method, the powder of the positive electrode active material 110 is obtained by mixing and firing a plurality of raw material powders. In addition, powders of the positive electrode active material 110 with various compositions are commercially available and easily obtained.

[0110] Next, a coating layer 120 is formed on the surface of the particles of the positive electrode active material 110. The method for forming the coating layer 120 is not particularly limited. As the method for forming the coating layer 120, a liquid-phase coating method and a gas-phase coating method can be cited.

[0111] For example, in the liquid-phase coating method, a precursor solution of an ion-conductive material is coated on the surface of the positive electrode active material 110. When forming a coating containing LiNbO 3In the case of the coating layer 120, the precursor solution may be a mixed solution (sol solution) of a solvent, lithium alkoxide, and niobium alkoxide. Examples of the lithium alkoxide include lithium ethoxide. Examples of the niobium alkoxide include niobium ethoxide. The solvent is, for example, an alcohol such as ethanol. The amounts of the lithium alkoxide and the niobium alkoxide are adjusted according to the target composition of the coating layer 120. If necessary, water may be added to the precursor solution. The precursor solution may be acidic or basic.

[0112] The method of coating the precursor solution on the surface of the positive electrode active material 110 is not particularly limited. For example, a tumbling granulation coating apparatus may be used to coat the precursor solution on the surface of the positive electrode active material 110. With the tumbling granulation coating apparatus, while the positive electrode active material 110 is being rolled and flowed, the precursor solution is sprayed onto the positive electrode active material 110 to coat the precursor solution on the surface of the positive electrode active material 110. Thereby, a precursor film is formed on the surface of the positive electrode active material 110. Then, the positive electrode active material 110 coated with the precursor film is heat-treated. The gelation of the precursor film is promoted by the heat treatment to form the coating layer 120. Thereby, the coated active material 130 is obtained. At this point in time, the coating layer 120 almost covers the entire surface of the positive electrode active material 110. The thickness of the coating layer 120 is substantially uniform.

[0113] Examples of the vapor coating method include a pulsed laser deposition (PLD) method, a vacuum evaporation method, a sputtering method, a chemical vapor deposition (CVD) method, and a plasma chemical vapor deposition method. For example, in the PLD method, a high-energy pulsed laser (e.g., a KrF excimer laser, wavelength: 248 nm) is irradiated onto an ion conductive material as a target, and the sublimated ion conductive material is deposited on the surface of the positive electrode active material 110. In the case of forming the coating layer 120 of 3 LiNbO 3 sintered at a high density is used as the target.

[0114] Next, the coated active material 130 is processed to adjust the ratio (Nb / C). For example, the coated active material 130 is heat-treated in an oxygen atmosphere, and after the heat treatment, the coated active material 130 is recovered in an atmosphere with a dew point of -30°C or lower. The oxygen atmosphere can be a pure oxygen atmosphere. The heat treatment conditions and the atmosphere conditions when the coated active material 130 is taken out of the heat treatment apparatus after the heat treatment can be appropriately selected based on the compositions of the positive electrode active material 110 and the coating layer 120. The heat treatment temperature is, for example, 150°C or higher and 1000°C or lower. The heat treatment time is, for example, 1 hour or longer and 72 hours or shorter. After the heat treatment, a treatment for re-crushing the coated active material 130 can be performed. For example, there is a tendency that the ratio (Nb / C) increases as the heat treatment temperature increases.

[0115] The pure oxygen atmosphere can be formed, for example, by the following method. That is, the inside of the chamber is replaced with oxygen having a purity of 99% or more, and the volume concentration of gases other than oxygen is made less than 1%. The pressure of the pure oxygen atmosphere is, for example, equal to the atmospheric pressure.

[0116] Through the above respective steps, a positive electrode material 1000 showing the desired ratio (Nb / C) is obtained.

[0117] (Embodiment 2)

[0118] Hereinafter, Embodiment 2 will be described. Descriptions that are the same as those in the above Embodiment 1 will be appropriately omitted.

[0119] Figure 2 FIG. is a cross-sectional view showing a schematic structure of the battery 2000 according to Embodiment 2.

[0120] The battery 2000 according to Embodiment 2 includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203.

[0121] The positive electrode 201 contains the positive electrode material 1000.

[0122] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203.

[0123] According to the above structure, the discharge voltage of the battery 2000 can be increased.

[0124] Regarding the volume ratio "v1: 100 - v1" of the coated active material 130 contained in the positive electrode 201 to the solid electrolyte 100, 30 ≤ v1 ≤ 95 can be satisfied. When 30 ≤ v1 is satisfied, the energy density of the battery 2000 is sufficiently ensured. In addition, when v1 ≤ 95 is satisfied, it is possible to operate with a high output.

[0125] The thickness of the positive electrode 201 can be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 is 10 μm or more, the energy density of the battery 2000 is sufficiently ensured. When the thickness of the positive electrode 201 is 500 μm or less, it can operate at a high output.

[0126] The electrolyte layer 202 is a layer containing an electrolyte. This electrolyte is, for example, a solid electrolyte. That is, the electrolyte layer 202 can be a solid electrolyte layer. As the solid electrolyte, the materials exemplified in Embodiment 1 can be used. That is to say, the electrolyte layer 202 can contain a solid electrolyte having the same composition as the solid electrolyte contained in the positive electrode material 1000.

[0127] According to the above structure, the charge-discharge efficiency of the battery 2000 can be further improved.

[0128] Alternatively, the electrolyte layer 202 can contain a halide solid electrolyte having a composition different from that of the solid electrolyte contained in the positive electrode material 1000.

[0129] According to the above structure, the output density and charge-discharge efficiency of the battery 2000 can be improved.

[0130] The electrolyte layer 202 can contain a sulfide solid electrolyte.

[0131] According to the above structure, since it contains a sulfide solid electrolyte with excellent reduction stability, it is possible to use a negative electrode material with a low potential such as graphite or metallic lithium, and the energy density of the battery 2000 can be improved.

[0132] As the sulfide solid electrolyte for the electrolyte layer 202, the sulfide solid electrolyte exemplified in Embodiment 1 can be used.

[0133] The electrolyte layer 202 can contain at least one selected from oxide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes. Examples of these materials are also as described in Embodiment 1.

[0134] The electrolyte layer 202 can contain only 1 type of solid electrolyte selected from the above solid electrolytes, or can contain 2 or more types of solid electrolytes selected from the above solid electrolytes. The compositions of the multiple solid electrolytes are different from each other. For example, the electrolyte layer 202 can contain a halide solid electrolyte and a sulfide solid electrolyte.

[0135] The thickness of the electrolyte layer 202 can be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the positive electrode 201 and the negative electrode 203 are not easily short-circuited. When the thickness of the electrolyte layer 202 is 300 μm or less, it can operate at a high output.

[0136] The negative electrode 203 contains a material having the property of occluding and releasing metal ions (such as lithium ions). The negative electrode 203 contains, for example, a negative electrode active material.

[0137] As the negative electrode active material, a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, etc. can be used. The metal material can be a single metal. Alternatively, the metal material can be an alloy. Examples of the metal material include lithium metal, lithium alloy, etc. Examples of the carbon material include natural graphite, coke, semi-graphitized carbon, carbon fiber, spherical carbon, artificial graphite, amorphous carbon, etc. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds can be preferably used.

[0138] The negative electrode 203 can contain a solid electrolyte. According to the above structure, the lithium ion conductivity inside the negative electrode 203 can be improved to operate at a high output. As the solid electrolyte, the materials exemplified in Embodiment 1 can be used.

[0139] The median diameter of the negative electrode active material can be 0.1 μm or more and 100 μm or less. When the median diameter of the negative electrode active material is 0.1 μm or more, the negative electrode active material and the solid electrolyte can form a good dispersion state in the negative electrode 203. Thereby, the charge-discharge characteristics of the battery 2000 are improved. In addition, when the median diameter of the negative electrode active material is 100 μm or less, the diffusion rate of lithium in the negative electrode active material is sufficiently ensured. Therefore, the battery 2000 can operate at a high output.

[0140] The median diameter of the negative electrode active material can be larger than the median diameter of the solid electrolyte contained in the negative electrode 203. Thereby, the negative electrode active material and the solid electrolyte can form a good dispersion state.

[0141] When the volume ratio of the negative electrode active material to the solid electrolyte in the negative electrode 203 is represented by "v2: 100 - v2", the volume ratio v2 of the negative electrode active material can satisfy 30 ≤ v2 ≤ 95. When 30 ≤ v2 is satisfied, the energy density of the battery 2000 is sufficiently ensured. In addition, when v2 ≤ 95 is satisfied, it can operate at a high output.

[0142] The thickness of the negative electrode 203 can be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 203 is 10 μm or more, the energy density of the battery 2000 is sufficiently ensured. When the thickness of the negative electrode 203 is 500 μm or less, it can operate at a high output.

[0143] For the purpose of improving the adhesion between particles, at least one of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder. The binder is used to improve the adhesiveness of the materials constituting the electrode. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, methyl polyacrylate, ethyl polyacrylate, hexyl polyacrylate, polymethacrylic acid, methyl polymethacrylate, ethyl polymethacrylate, hexyl polymethacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropropylene, styrene-butadiene rubber, carboxymethyl cellulose, etc. In addition, as the binder, a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, trichloroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene can be used. In addition, two or more selected from them can be mixed and used as the binder.

[0144] For the purpose of improving electron conductivity, at least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive. As the conductive additive, for example, graphite-based materials such as natural graphite or artificial graphite, carbon black-based materials such as acetylene black and Ketjen black, conductive fiber-based materials such as carbon fiber or metal fiber, carbon fluoride, metal powder-based materials such as aluminum, conductive whisker-based materials such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene can be used. When using a carbon conductive additive, the cost can be reduced.

[0145] The battery 2000 of Embodiment 2 can be formed into various shapes such as coin type, cylindrical type, square type, sheet type, button type, flat type, and laminated type.

[0146] Examples

[0147] Hereinafter, the details of the present disclosure will be described using examples and comparative examples.

[0148] 《Example 1》

[0149] [Production of Halide Solid Electrolyte]

[0150] In an argon glove box with a dew point of -60°C or lower, LiCl powder, LiBr powder, and YCl 3 were weighed in a molar ratio of LiCl:LiBr:YCl 3 = 1:2:1. They were pulverized and mixed in a mortar to obtain a mixture. Then, using a planetary ball mill, the mixture was subjected to a grinding treatment at 600 rpm for 12 hours.

[0151] As described above, Li 3YBr 2 Cl 4 Powder of the halide solid electrolyte of Example 1 represented by the compositional formula.

[0152] [Production of Coated Active Material]

[0153] Li(NiCoMn)O 2 (hereinafter referred to as NCM) powder was vacuum dried at 100 °C for 2 weeks. Then, the NCM powder was taken out from the drying device in a drying atmosphere with a dew point of -30 °C or lower.

[0154] In an argon glove box with a dew point of -60 °C or lower, lithium ethoxide (manufactured by Kanto Chemical Co., Inc.) and niobium pentaethoxide (manufactured by Kanto Chemical Co., Inc.) were weighed so that their molar ratio was 1:1, and they were dissolved in ultradehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating solution.

[0155] A tumbling granulation coating device (manufactured by POWREX Corporation, FD-MP-01E) was used to form a coating layer on the surface of the dried NCM particles.

[0156] The NCM input amount, stirring speed, and feeding rate of the coating solution were 1 kg, 400 rpm, and 6.59 g / min, respectively. The input amount of the coating solution was adjusted so that the film thickness of LiNbO 3 was 6 nm. The input amount of the coating solution was calculated using the specific surface area of the active material and the density of LiNbO 3 . A series of processes using the tumbling granulation coating device were carried out in a drying atmosphere with a dew point of -30 °C or lower.

[0157] After the treatment for forming the coating layer was completed, the obtained powder was put into an alumina crucible and heat-treated at 350 °C for 1 hour in a pure oxygen atmosphere.

[0158] The heat-treated powder was taken out in a drying atmosphere with a dew point of -30 °C or lower and pulverized again with an agate mortar. Thus, the coated active material of Example 1 (NCM coated with a coating layer) was obtained.

[0159] The coating material contained in the coating layer is LiNbO 3 .

[0160] [Production of Cathode Material]

[0161] A carbon conductive additive, the halide solid electrolyte of Example 1, and the coated active material of Example 1 were weighed in a weight ratio of 2:18:82 in an argon glove box with a dew point of -60 °C or lower. By mixing them in an agate mortar, the cathode material of Example 1 was prepared.

[0162] 《Example 2》

[0163] [Fabrication of Halide Solid Electrolyte]

[0164] The halide solid electrolyte (NCM) powder of Example 2 was obtained by the same method as in Example 1.

[0165] [Fabrication of Coated Active Material]

[0166] The NCM powder was vacuum dried at 100 °C for 2 weeks. Then, the NCM powder was heat-treated at 400 °C for 1 hour in a nitrogen atmosphere to dry the surface of the NCM particles. The NCM powder was taken out from the drying device in a drying atmosphere with a dew point of -30 °C or lower.

[0167] Adjust the input amount of the coating solution so that the film thickness of LiNbO 3 is 2 nm. Except for this, a coating layer was formed on the surface of the NCM particles by the same method as in Example 1. Thus, the coated active material of Example 2 was obtained.

[0168] [Fabrication of Cathode Material]

[0169] Using the coated active material of Example 2, except for this, the cathode material of Example 2 was obtained by the same method as in Example 1.

[0170] 《Example 3》

[0171] Adjust the input amount of the coating solution so that the film thickness of LiNbO 3 is 6 nm. Except for this, the cathode material of Example 3 was obtained by the same method as in Example 2.

[0172] 《Example 4》

[0173] Adjust the input amount of the coating solution so that the film thickness of LiNbO 3 is 12 nm. Except for this, the cathode material of Example 4 was obtained by the same method as in Example 2.

[0174] 《Comparative Example 1》

[0175] [Fabrication of Halide Solid Electrolyte]

[0176] The halide solid electrolyte (NCM) powder of Comparative Example 1 was obtained by the same method as in Example 1.

[0177] [Fabrication of Coated Active Material]

[0178] The NCM powder was vacuum dried at 100 °C for 2 weeks. Then, the NCM powder was taken out from the drying device in a drying atmosphere with a dew point of -30 °C or lower.

[0179] Weigh lithium ethoxide (manufactured by High Purity Chemical Co., Ltd.) and niobium pentaethoxide (manufactured by High Purity Chemical Co., Ltd.) in an argon glove box below the dew point of -60 °C so that the molar ratio is 1:1, and dissolve them in ultradehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating solution.

[0180] When forming a coating layer on the surface of the dried NCM particles, a tumbling granulation coating device (POWREX Co., Ltd., FD-MP-01E) is used.

[0181] The NCM input amount, stirring speed, and feeding rate of the coating solution are 1 kg, 400 rpm, and 6.59 g / min, respectively. Adjust the input amount of the coating solution so that the film thickness of LiNbO 3 is 2 nm. The input amount of the coating solution is calculated using the specific surface area of the active material and the density of LiNbO 3 . A series of processes using the tumbling granulation coating device are carried out in a dry atmosphere below the dew point of -30 °C.

[0182] After the treatment for forming the coating layer is completed, the obtained powder is put into an alumina crucible and heat-treated at 350 °C for 1 hour in an air atmosphere.

[0183] Take out the heat-treated powder in an air atmosphere and pulverize it again with an agate mortar. Thus, the coated active material of Comparative Example 1 is obtained.

[0184] The coating material contained in the coating layer is LiNbO 3 .

[0185] [Fabrication of the positive electrode material]

[0186] Weigh a carbon conductive additive, the halide solid electrolyte of Comparative Example 1, and the coated active material of Comparative Example 1 in an argon glove box below the dew point of -60 °C at a weight ratio of 2:18:82. Mix them in an agate mortar to fabricate the positive electrode material of Comparative Example 1.

[0187] [Comparative Example 2]

[0188] Adjust the input amount of the coating solution so that the film thickness of LiNbO 3 is 6 nm. Except for this, the positive electrode material of Comparative Example 2 is obtained in the same manner as in Comparative Example 1.

[0189] [Fabrication of the sulfide solid electrolyte]

[0190] In an argon glove box under an Ar atmosphere at the dew point of -60 °C, weigh Li 2 S powder and P 2 S 5 powder so that the molar ratio is Li 2 S:P2 S 5 = 75:25. They were pulverized and mixed in a mortar to obtain a mixture. Then, using a planetary ball mill (manufactured by Fritsch, model P-7), the mixture was ground under the conditions of 10 hours and 510 rpm. Thus, a glassy solid electrolyte was obtained. The glassy solid electrolyte was heat-treated at 270 °C for 2 hours in an inert atmosphere. Thus, a glass-ceramic sulfide solid electrolyte was obtained.

[0191] [Fabrication of Secondary Battery]

[0192] Using the halide solid electrolyte of Example 1, the positive electrode materials of Examples 1 to 4 and Comparative Examples 1 to 2, and the sulfide solid electrolyte, secondary batteries were fabricated.

[0193] First, in an insulating outer cylinder, 80 mg of sulfide solid electrolyte, 20 mg of halide solid electrolyte, and 18 mg of positive electrode material were sequentially laminated. By pressing the obtained laminate at a pressure of 720 MPa, a positive electrode and an electrolyte layer were obtained.

[0194] Next, on the side opposite to the side in contact with the positive electrode, metal In (thickness 200 μm), metal Li (thickness 300 μm), and metal In (thickness 200 μm) were sequentially laminated on the electrolyte layer. By pressing the obtained laminate at a pressure of 80 MPa, a laminate composed of a positive electrode, an electrolyte layer, and a negative electrode was fabricated.

[0195] Next, stainless steel current collectors were disposed above and below the laminate. Current collecting leads were attached to each current collector.

[0196] Finally, by using an insulating ferrule to seal the insulating outer cylinder and separating the inside of the outer cylinder from the external gas atmosphere, the batteries of Examples 1 to 4 and Comparative Examples 1 to 2 were fabricated respectively.

[0197] [Charge and Discharge Tests]

[0198] Using the batteries of Examples 1 to 4 and Comparative Examples 1 to 2, charge and discharge tests were carried out under the following conditions.

[0199] The batteries were placed in a thermostat at 25 °C.

[0200] Constant current charging was carried out at a current value of 140 μA at a rate of 0.05 C (20-hour rate) relative to the theoretical capacity of the battery, and charging was terminated at a voltage of 3.7 V.

[0201] Next, similarly, discharging was carried out at a current value of 140 μA at a rate of 0.05 C, and discharging was terminated at a voltage of 1.9 V.

[0202] As described above, the average discharge voltage of each of the batteries of Examples 1 to 4 and Comparative Examples 1 and 2 was measured. The results are shown in Table 1 below.

[0203] [Surface composition analysis]

[0204] The following measurements were carried out using the coated active materials of Examples 1 to 4 and Comparative Examples 1 and 2.

[0205] For the surface composition analysis by XPS, Quantera SXM (manufactured by ULVAC-PHI) was used. The measurement conditions are as follows.

[0206] X-ray source: Al monochromatic (25 W, 15 kV)

[0207] Analysis area: 300 μm × 800 μm (region)

[0208] Electron / ion neutralization gun: ON

[0209] Photoelectron extraction angle: 45 degrees

[0210] The scanning range of the binding energy was 0 eV to 1250 eV. The atomic concentration of the elements was calculated using the software "MultiPak" manufactured by ULVAC-PHI.

[0211] As the elements to be measured, Li (scanning range: 45 - 65 eV), C (scanning range: 275 - 295 eV), O (scanning range: 522 - 542 eV), Mn (scanning range: 632 - 662 eV), Co (scanning range: 770 - 810 eV), Ni (scanning range: 848 - 888 eV), and Nb (scanning range: 195 - 215 eV) were selected. The atomic concentration of the elements was calculated based on the peaks observed in the scanning range of each element, and the surface concentration of each element was calculated according to the integrated peak area ratio. Then, the ratio (Nb / C) was calculated in the form of an atomic ratio from the calculated surface Nb concentration and the calculated surface C concentration.

[0212] As described above, in the region from the outermost surface to a depth of 10 nm of the coated active material, the atomic ratio (Nb / C) of the niobium (Nb) content to the carbon (C) content was obtained. The results are shown in Table 1 below.

[0213] Carbon (C) is derived from lithium ethoxide and niobium pentaethoxide, which are raw materials for the coating layer.

[0214] Table 1

[0215]

[0216] <Examination>

[0217] As shown in Table 1, the coated active materials of Examples 1 to 4 have atomic ratios (Nb / C) of 0.18, 0.11, 0.15, and 0.15, respectively. The coated active materials of Examples 1 to 4 all have an atomic ratio (Nb / C) of 0.11 or more. The average discharge voltage of the batteries of Examples 1 to 4 is 3.624 V or more. It was confirmed that the discharge voltage of the battery increases by using a positive electrode material in which the atomic ratio (Nb / C) of the niobium content to the carbon content in the surface layer portion of the coated active material is 0.11 or more.

[0218] In contrast, the atomic ratios (Nb / C) of the coated active materials of Comparative Examples 1 and 2 are less than 0.01 and 0.08, respectively, which are significantly lower than those of Examples 1 to 4. The average discharge voltages of the batteries of Comparative Examples 1 and 2 are both 3.586 V or less.

[0219] Industrial Applicability

[0220] The battery of the present disclosure can be used as, for example, an all-solid battery.

[0221] Description of Reference Numerals

[0222] 1000 Positive electrode material

[0223] 100 Solid electrolyte

[0224] 110 Positive electrode active material

[0225] 120 Coating layer

[0226] 130 Coated active material

[0227] 2000 Battery

[0228] 201 Positive electrode

[0229] 202 Electrolyte layer

[0230] 203 Negative electrode

Claims

1. A positive electrode material, comprising: a positive electrode active material, and a coating layer covering the positive electrode active material, the coating layer containing niobium and carbon, the positive electrode active material and the coating layer constituting a coated active material, in the surface layer portion of the coated active material, the ratio Nb / C of the niobium content to the carbon content is 0.11 or more and 0.18 or less in terms of atomic ratio, when the thickness of the coating layer exceeds the penetration depth of the soft X-ray or electron beam used in compositional analysis, the coating layer is regarded as the surface layer portion of the coated active material, and when the thickness of the coating layer is less than the penetration depth of the soft X-ray or electron beam used in compositional analysis, a part of the positive electrode active material and the coating layer are included in the surface layer portion of the coated active material.

2. The positive electrode material according to claim 1, further comprising a solid electrolyte.

3. The positive electrode material according to claim 2, wherein the solid electrolyte is represented by the following compositional formula (1), Li α M β X γ Formula (1) wherein, α, β, and γ are each independently a value greater than 0, M contains at least one element selected from metal elements other than Li and metalloid elements, X contains at least one selected from F, Cl, Br, and I.

4. The positive electrode material according to claim 3, wherein the M contains yttrium.

5. The positive electrode material according to claim 3 or 4, satisfying 2.5 ≤ α ≤ 3, 1 ≤ β ≤ 1.1, and γ = 6.

6. The positive electrode material according to claim 3 or 4, wherein the X contains at least one selected from Cl and Br.

7. The positive electrode material according to any one of claims 1 to 3, wherein the coating layer contains a lithium niobate-based compound.

8. The positive electrode material according to any one of claims 1 to 3, wherein the positive electrode active material contains Li and at least one element selected from Mn, Co, Ni, and Al.

9. A battery, comprising: a positive electrode containing the positive electrode material according to any one of claims 1 to 8, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode.

10. The battery according to claim 9, the positive electrode material contains a solid electrolyte, the electrolyte layer contains a solid electrolyte having the same composition as the solid electrolyte contained in the positive electrode material.

11. The battery according to claim 9 or 10, the positive electrode material contains a solid electrolyte, the electrolyte layer contains a halide solid electrolyte having a composition different from that of the solid electrolyte contained in the positive electrode material.

12. The battery according to claim 9 or 10, wherein the electrolyte layer contains a sulfide solid electrolyte.

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