Cathode Materials and Batteries

Abstract

A positive electrode material 1000 according to the present disclosure comprises a positive electrode active substance 110 and a covering layer 120 that covers the positive electrode active substance 110. The covering layer 120 contains niobium and carbon. The positive electrode active substance 110 and the covering layer 120 constitute a covered active substance 130. The atomic ratio Nb / C of the niobium content relative to the carbon content in the surface layer part of the covered active substance 130 is 0.11 or greater.

Description

[Technical Field]

[0001] The present disclosure relates to positive electrode materials and batteries. [Background technology]

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

[0003] [Patent Document 1] International Publication No. 2019 / 135322 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, further improvement in the discharge voltage of batteries is desired. [Means for solving the problem]

[0005] In one embodiment of the present disclosure, the positive electrode material is a positive electrode active material; a coating layer that coats the positive electrode active material; A positive electrode material comprising: the coating layer comprises niobium and carbon; the positive electrode active material and the coating layer constitute a coated active material, In the surface layer portion of the coated active material, the ratio of the niobium content to the carbon content, Nb / C, is 0.11 or more in terms of atomic ratio. [Effects of the Invention]

[0006] According to the present disclosure, the discharge voltage of a battery can be improved. [Brief explanation of the drawings]

[0007] [Figure 1]FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 1000 according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Summary of one aspect of the present disclosure) The positive electrode material according to the first aspect of the present disclosure is a positive electrode active material; a coating layer that coats the positive electrode active material; A positive electrode material comprising: the coating layer comprises niobium and carbon; the positive electrode active material and the coating layer constitute a coated active material, In the surface layer portion of the coated active material, the ratio of the niobium content to the carbon content, Nb / C, is 0.11 or more in terms of atomic ratio.

[0009] According to the first aspect, the discharge voltage of the battery can be improved.

[0010] In a second aspect of the present disclosure, for example, the positive electrode material according to the first aspect may further include a solid electrolyte, which can improve ionic conductivity in the positive electrode.

[0011] In a third aspect of the present disclosure, for example, in the positive electrode material according to the second aspect, the solid electrolyte is Li α M β X γ where α, β, and γ may each independently be greater than 0, M may include at least one element selected from the group consisting of metal elements and metalloid elements other than Li, and X may include at least one element selected from the group consisting of F, Cl, Br, and I. According to the third aspect, the output density of the battery can be improved. In addition, the thermal stability of the battery can be improved, and the generation of harmful gases such as hydrogen sulfide can be suppressed.

[0012] In a fourth aspect of the present disclosure, for example, in the positive electrode material according to the third aspect, the M may contain yttrium.

[0013] In the fifth embodiment of the present disclosure, for example, in the positive electrode material according to the third or fourth embodiment, 2.5≦α≦3, 1≦β≦1.1, and γ=6 may be satisfied.

[0014] In a sixth aspect of the present disclosure, for example, in the positive electrode material according to any one of the third to fifth aspects, the X may include at least one selected from the group consisting of Cl and Br.

[0015] According to the fourth to sixth aspects, the ionic conductivity of the solid electrolyte can be further improved, thereby improving the output density of the battery.

[0016] In a seventh aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to sixth aspects, the coating layer may contain a lithium niobate compound, which can further improve the charge / discharge efficiency of the battery.

[0017] In an eighth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to seventh aspects, the positive electrode active material may contain Li and at least one element selected from the group consisting of Mn, Co, Ni, and Al. According to the eighth aspect, the energy density of the battery can be further increased.

[0018] A battery according to a ninth aspect of the present disclosure includes: a positive electrode comprising the positive electrode material according to any one of the first to eighth aspects; a negative electrode; an electrolyte layer disposed between the positive electrode and the negative electrode; Equipped with.

[0019] According to the ninth aspect, the discharge voltage of the battery can be improved.

[0020] In a tenth aspect of the present disclosure, for example, in the battery according to the ninth aspect, the cathode material may further contain a solid electrolyte, and the electrolyte layer may contain a solid electrolyte having the same composition as the solid electrolyte contained in the cathode material. According to the tenth aspect, the charge / discharge efficiency of the battery can be further improved.

[0021] In an eleventh aspect of the present disclosure, for example, in the battery according to the ninth or tenth aspect, the cathode 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 cathode material. According to the eleventh aspect, the output density and charge / discharge efficiency of the battery can be improved.

[0022] In a 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 contain a sulfide solid electrolyte. According to the twelfth aspect, a low-potential negative electrode material such as graphite or metallic lithium can be used, thereby improving the energy density of the battery.

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0024] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 1000 according to the first embodiment.

[0025] The positive electrode material 1000 in the first embodiment includes a coated active material 130 and a solid electrolyte 100 .

[0026] 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.

[0027] In the surface layer portion of the coated active material 130, the ratio of the niobium content to the carbon content, Nb / C, is 0.11 or more in 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 a position at which composition information can be obtained by a surface composition analysis method. For example, when the coating layer 120 has a thickness that exceeds the penetration depth of soft X-rays or electron beams used in composition analysis, the coating layer 120 is considered to be 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 soft X-rays or electron beams used in composition analysis, a portion 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."

[0028] The positive electrode active material 110 is separated from the solid electrolyte 100 by the coating layer 120. The positive electrode active material 110 does not need to be in direct contact with the solid electrolyte 100. This is because the coating layer 120 has ion conductivity.

[0029] According to the above configuration, the discharge voltage of the battery can be improved.

[0030] Patent Document 1 mentions that an oxidative decomposition side reaction occurs during charging, in which electrons are extracted from the solid electrolyte in contact with the positive electrode active material, and that this causes the formation of an oxide layer with poor lithium ion conductivity between the positive electrode active material and the solid electrolyte, resulting in an increase in interfacial resistance. It also mentions that providing a coating layer between the positive electrode active material and the solid electrolyte can suppress the formation of the oxide layer and thus the increase in interfacial resistance. However, the surface composition of the coating layer is not disclosed.

[0031] On the other hand, as a result of intensive research, the present inventors discovered a problem in that, when a battery is operated, the composition of the surface layer of the coated active material, including the coating layer and the positive electrode active material, changes, increasing the interface resistance and decreasing the discharge voltage. After further detailed investigation, the present inventors discovered that the discharge voltage can be improved by intentionally increasing the ratio of the niobium content to the carbon content (Nb / C) in the surface layer of the coated active material. This is thought to be because the reduction in the carbon impurity content in the niobium compound (e.g., lithium niobium oxide) contained in the coating layer improves the ionic conductivity (e.g., lithium ion conductivity) of the coating layer, thereby reducing the interface resistance of the electrode reaction.

[0032] The effect of improving the potential stability of the coating layer 120 is expected to not only suppress the formation of an oxide layer on the solid electrolyte but also suppress oxidation of the electrolyte solution, and therefore the technology of the present disclosure is considered to be effective in batteries containing an electrolyte solution.

[0033] The method for controlling the ratio (Nb / C) is not particularly limited. For example, the coated active material 130 may be heat-treated in an oxygen atmosphere, and then recovered after the heat treatment in an atmosphere with a dew point of −30° C. or lower. The oxygen atmosphere may be a pure oxygen atmosphere. The heat treatment conditions and the atmospheric conditions for removing the coated active material 130 from the heat treatment device after the heat treatment can be appropriately selected based on the compositions of the positive electrode active material 110 and the coating layer 120.

[0034] X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and the like can be used to analyze the surface composition of the coated active material 130. The surface composition analysis method is appropriately selected depending on the composition of the coating material contained in the coating layer 120 and the coating state of the positive electrode active material 110. Surface composition analysis using XPS is less likely to be a localized analysis and can evaluate a relatively wide area of ​​the material surface. Furthermore, XPS is suitable as a surface composition analysis method because it can obtain average surface composition information from a depth of 10 nm from the outermost surface, facilitating quality control of the material.

[0035] The ratio (Nb / C) may 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 are not too small, and appropriate electronic conductivity is ensured. This makes it possible to suppress an increase in the internal resistance of the positive electrode material 1000. By suppressing an increase in the internal resistance of the positive electrode material 1000, high-power operation of the battery becomes possible. The ratio (Nb / C) may be 0.11 or more and 0.18 or less. When the ratio (Nb / C) is within this range, both electronic conductivity and ionic conductivity of the coating layer 120 can be achieved. As a result, the discharge voltage of the battery is further improved.

[0036] The solid electrolyte 100 may be a halide solid electrolyte.

[0037] The halide solid electrolyte is represented, for example, by the following composition formula (1): In composition formula (1), α, β, and γ each independently have a value greater than 0. M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li. X includes at least one element selected from the group consisting of F, Cl, Br, and I.

[0038] Li α M β X γ ...Equation (1)

[0039] Metalloid elements include B, Si, Ge, As, Sb, and Te. Metal elements include all elements in groups 1 to 12 of the periodic table except for hydrogen, and all elements in groups 13 to 16 except for B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming inorganic compounds with halides.

[0040] Examples of halide solid electrolytes that can be used include Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, and Li3(Al,Ga,In)X6.

[0041] The above configuration can improve the power density of the battery, as well as the thermal stability of the battery and suppress the generation of harmful gases such as hydrogen sulfide.

[0042] In this disclosure, when an element in a formula is expressed as "(Al, Ga, In)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(Al, Ga, In)" is synonymous with "at least one element selected from the group consisting of Al, Ga, and In". The same applies to other elements. Halide solid electrolytes exhibit excellent ionic conductivity. Note that halide solid electrolytes do not necessarily need to contain sulfur.

[0043] In the composition formula (1), M may contain Y (=yttrium). That is, the solid electrolyte 100 may contain Y as a metal element.

[0044] The composition formula (1) may satisfy 2.5≦α≦3, 1≦β≦1.1, and γ=6.

[0045] In the composition formula (1), X may include at least one selected from the group consisting of Cl and Br.

[0046] The above configuration can further improve the ionic conductivity of the solid electrolyte 100. This improves the power density of the battery.

[0047] The halide solid electrolyte containing Y may be a compound represented by the following composition formula (2).

[0048] Li a M b Y c X6...Formula (2)

[0049] Composition formula (2) satisfies a+mb+3c=6 and c>0. In composition formula (2), M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Y. m is the valence of M. X includes at least one element selected from the group consisting of F, Cl, Br, and I. M includes 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. Specific examples of Y-containing halide solid electrolytes include Li3YF6, Li3YCl6, Li3YBr6, Li3YI6, Li3YBrCl5, Li3YBr3Cl3, Li3YBr5Cl, Li3YBr5I, Li3YBr3I3, Li3YBrI5, Li3YClI5, Li3YCl3I3, Li3YCl5I, Li3YBr2Cl2I2, Li3YBrCl4I, Li 2.7 Y 1.1 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 Y 0.3 Zr 0.7 Cl6 and the like can be used.

[0050] According to the above configuration, the output density of the battery can be further improved.

[0051] The solid electrolyte 100 may include a sulfide solid electrolyte.

[0052] Sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These can be used in addition to LiX, Li2O, MO q , Li p MO q The element X in "LiX" is at least one element selected from the group consisting of F, Cl, Br, and I. q " and "Li pMO q "The element M is at least one element selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q " p and q in this expression are independent natural numbers.

[0053] According to the above configuration, the output density of the battery can be improved.

[0054] The solid electrolyte 100 may include at least one selected from the group consisting of an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0055] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element-substituted LISICON-type solid electrolytes, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those substituted with LiN and its element, LiN and its H-substituted compounds, LiPO4 and its N-substituted compounds, and glass or glass ceramics containing a base material containing Li-BO compounds such as LiBO2 and LiBO3 to which a material such as LiSO4 or LiCO3 has been added can be used.

[0056] As the polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain a large amount of lithium salt, thereby further increasing ionic conductivity. As the lithium salt, LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc. can be used. As the lithium salt, one type of lithium salt selected from these may be used alone, or a mixture of two or more types of lithium salts selected from these may be used.

[0057] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0058] According to the above configuration, the output density of the battery can be improved.

[0059] Possible materials for the positive electrode active material 110 in the first embodiment include, for example, lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material 110, the manufacturing cost can be reduced and the average discharge voltage can be increased.

[0060] The positive electrode active material 110 may contain Li and at least one element selected from the group consisting of Mn, Co, Ni, and Al. Examples of such materials include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2.

[0061] Positive electrode active material 110 may include a single active material, or may include multiple active materials having different compositions.

[0062] In the first embodiment, the positive electrode active material 110 may be Li(NiCoMn)O2.

[0063] According to the above configuration, the energy density of the battery can be further increased.

[0064] The positive electrode active material 110 has, for example, a particle shape. There are no particular limitations on the shape of the particles of the positive electrode active material 110. The shape of the particles of the positive electrode active material 110 may be spherical, oval, scaly, or fibrous.

[0065] A material with low electron conductivity can be used as the coating material contained in the coating layer 120. Examples of the coating material that can be used include oxide materials, oxide solid electrolytes, and carbonates.

[0066] Examples of oxide materials that can be used include SiO2, Al2O3, TiO2, B2O3, Nb2O5, WO3, and ZrO2. Examples of oxide solid electrolytes include Li-Nb-O compounds such as LiNbO3, Li-BO compounds such as LiBO2 and Li3BO3, Li-Al-O compounds such as LiAlO2, Li-Si-O compounds such as Li4SiO4, Li-SO compounds such as Li2SO4, and Li4Ti5O. 12 Li-Ti-O compounds such as Li2ZrO3, Li-Zr-O compounds such as Li2MoO3, Li-VO compounds such as LiV2O5, and Li-WO compounds such as Li2WO4 can be used.

[0067] In the first embodiment, the coating material may be an oxide solid electrolyte.

[0068] Oxide solid electrolytes have high ionic conductivity and high potential stability, and therefore, by using oxide solid electrolytes, the charge / discharge efficiency of batteries can be further improved.

[0069] In the first embodiment, the coating layer 120 may contain a lithium niobate-based compound as a coating material. The coating material may be LiNbO3. The lithium niobate-based compound is a compound containing lithium, niobium, and oxygen.

[0070] LiNbO3 has higher ionic conductivity and higher high-potential stability, so the use of LiNbO3 can further improve the charge / discharge efficiency of the battery.

[0071] The thickness of the covering layer 120 may be 1 nm or more and 100 nm or less.

[0072] By making the thickness of the coating layer 120 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, thereby improving the charge / discharge efficiency.

[0073] By setting the thickness of the coating layer 120 to 100 nm or less, the thickness of the coating layer 120 does not become too thick. This allows the internal resistance of the battery to 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 slicing the coated active material 130 by a method such as ion milling and observing the cross section of the coated active material 130 with a transmission electron microscope.

[0074] The coating layer 120 may uniformly coat the particles of the positive electrode active material 110. This prevents direct contact between the particles of the positive electrode active material 110 and the particles of the solid electrolyte 100, thereby suppressing side reactions in the solid electrolyte 100. This improves charge / discharge efficiency.

[0075] Alternatively, the coating layer 120 may cover only a portion of the surface of the particles of the positive electrode active material 110. The particles of the positive electrode active material 110 come into direct contact with each other through the portion not having the coating layer 120, thereby improving the electronic conductivity between the particles of the positive electrode active material 110. This enables the battery to operate at high power output.

[0076] The shape of solid electrolyte 100 in embodiment 1 is not particularly limited and may be, for example, needle-like, spherical, oval-spherical, etc. For example, solid electrolyte 100 may be in the form of particles.

[0077] For example, when solid electrolyte 100 in the first embodiment is in the form of particles (for example, spheres), the median diameter may be 100 μm or less.

[0078] 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 be well dispersed in the positive electrode material 1000. This improves the charge / discharge characteristics of the battery.

[0079] In the first embodiment, the median diameter of solid electrolyte 100 may be 10 μm or less.

[0080] According to the above configuration, in the positive electrode material 1000, the coated active material 130 and the solid electrolyte 100 can be well dispersed.

[0081] In the first embodiment, the median diameter of the solid electrolyte 100 may be smaller than the median diameter of the coated active material 130 .

[0082] According to the above configuration, the solid electrolyte 100 and the coated active material 130 can be dispersed in the positive electrode material 1000 in a better state.

[0083] The median diameter of the coated active material 130 may be 0.1 μm or more and 100 μm or less.

[0084] 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 be well dispersed in the positive electrode material 1000. As a result, the charge / discharge characteristics of the battery are improved.

[0085] When the median diameter of the coated active material 130 is 100 μm or less, a sufficient diffusion rate of lithium is ensured within the coated active material 130. This enables the battery to operate at high power output.

[0086] The median diameter of the coated active material 130 may be larger than the median diameter of the solid electrolyte 100. This allows the coated active material 130 and the solid electrolyte 100 to form a good dispersed state.

[0087] In the positive electrode material 1000 of the first embodiment, the particles of the solid electrolyte 100 and the particles of the coated active material 130 may be in contact with each other, as shown in Fig. 1. In this case, the coating layer 120 and the positive electrode active material 110 are in contact with each other.

[0088] The positive electrode material 1000 in the first embodiment may include a plurality of particles of the solid electrolyte 100 and a plurality of particles of the coated active material 130 .

[0089] In the positive electrode material 1000, the content of the solid electrolyte 100 and the content of the coated active material 130 may be the same or different from each other.

[0090] As used herein, the term "median diameter" refers to the particle size when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measurement device or an image analysis device.

[0091] Next, a method for producing the positive electrode material 1000 will be described.

[0092] 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, a plurality of raw material powders are mixed and fired to obtain the powder of the positive electrode active material 110. In addition, powders of the positive electrode active material 110 with various compositions are commercially available and can be easily obtained.

[0093] Next, the coating layer 120 is formed on the surface of the particles of the positive electrode active material 110. There are no particular limitations on the method for forming the coating layer 120. Methods for forming the coating layer 120 include a liquid-phase coating method and a vapor-phase coating method.

[0094] For example, in the liquid-phase coating method, a precursor solution of an ion-conductive material is applied to the surface of the positive electrode active material 110. When forming a coating layer 120 containing LiNbO3, the precursor solution can be a mixed solution (sol solution) of a solvent, lithium alkoxide, and niobium alkoxide. Examples of lithium alkoxide include lithium ethoxide. Examples of niobium alkoxide include niobium ethoxide. The solvent is, for example, an alcohol such as ethanol. The amounts of lithium alkoxide and niobium alkoxide are adjusted depending on the target composition of the coating layer 120. Water may be added to the precursor solution if necessary. The precursor solution may be acidic or alkaline.

[0095] The method for applying the precursor solution to the surface of the positive electrode active material 110 is not particularly limited. For example, the precursor solution can be applied to the surface of the positive electrode active material 110 using a tumbling fluidized granulation coating device. With the tumbling fluidized granulation coating device, the precursor solution can be sprayed onto the positive electrode active material 110 while tumbling and fluidizing the positive electrode active material 110, thereby applying the precursor solution to the surface of the positive electrode active material 110. In this way, a precursor coating is formed on the surface of the positive electrode active material 110. The positive electrode active material 110 coated with the precursor coating is then heat-treated. The heat treatment promotes gelation of the precursor coating, forming a coating layer 120. This results in a coated active material 130. At this point, the coating layer 120 covers substantially the entire surface of the positive electrode active material 110. The thickness of the coating layer 120 is generally uniform.

[0096] Vapor-phase coating methods include pulsed laser deposition (PLD), vacuum evaporation, sputtering, thermal chemical vapor deposition (CVD), and plasma chemical vapor deposition. For example, in the PLD method, a target made of an ion-conductive material is irradiated with a high-energy pulse laser (e.g., a KrF excimer laser, wavelength: 248 nm), and the sublimated ion-conductive material is deposited on the surface of the positive electrode active material 110. When forming the LiNbO3 coating layer 120, highly sintered LiNbO3 is used as the target.

[0097] Next, the coated active material 130 is treated 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 may be a pure oxygen atmosphere. The heat treatment conditions and the atmospheric conditions when removing the coated active material 130 from the heat treatment device 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 higher and 72 hours or lower. After the heat treatment, the coated active material 130 may be re-pulverized. For example, as the heat treatment temperature increases, the ratio (Nb / C) tends to increase.

[0098] The pure oxygen atmosphere can be formed, for example, by the following method: the interior of the chamber is replaced with oxygen gas of 99% or higher purity, and the volume concentration of gases other than oxygen gas is less than 1%. The pressure of the pure oxygen atmosphere is, for example, equal to atmospheric pressure.

[0099] Through the above steps, a positive electrode material 1000 exhibiting a desired ratio (Nb / C) is obtained.

[0100] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0101] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the second embodiment.

[0102] The battery 2000 in the second embodiment includes a positive electrode 201 , an electrolyte layer 202 , and a negative electrode 203 .

[0103] The positive electrode 201 includes a positive electrode material 1000 .

[0104] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0105] According to the above configuration, the discharge voltage of the battery 2000 can be improved.

[0106] The volume ratio "v1:100-v1" of the coated active material 130 to the solid electrolyte 100 contained in the positive electrode 201 may satisfy 30≦v1≦95. When 30≦v1 is satisfied, the energy density of the battery 2000 is sufficiently ensured. Furthermore, when v1≦95 is satisfied, high-power operation is possible.

[0107] The thickness of the positive electrode 201 may 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, high-power operation is possible.

[0108] The electrolyte layer 202 is a layer containing an electrolyte. The electrolyte is, for example, a solid electrolyte. That is, the electrolyte layer 202 may be a solid electrolyte layer. As the solid electrolyte, the materials exemplified in the first embodiment may be used. That is, the electrolyte layer 202 may contain a solid electrolyte having the same composition as the solid electrolyte contained in the positive electrode material 1000.

[0109] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be further improved.

[0110] Alternatively, the electrolyte layer 202 may include a halide solid electrolyte having a different composition than the composition of the solid electrolyte included in the cathode material 1000 .

[0111] According to the above configuration, the output density and charge / discharge efficiency of the battery 2000 can be improved.

[0112] The electrolyte layer 202 may include a sulfide solid electrolyte.

[0113] According to the above configuration, since the battery contains a sulfide solid electrolyte with excellent reduction stability, a low potential negative electrode material such as graphite or metallic lithium can be used, and the energy density of the battery 2000 can be improved.

[0114] As the sulfide solid electrolyte for the electrolyte layer 202, the sulfide solid electrolyte exemplified in the first embodiment can be used.

[0115] The electrolyte layer 202 may contain at least one selected from the group consisting of an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. Examples of these materials are also as described in the first embodiment.

[0116] The electrolyte layer 202 may contain only one solid electrolyte selected from the above-mentioned group of solid electrolytes, or may contain two or more solid electrolytes selected from the above-mentioned group of solid electrolytes. The multiple solid electrolytes have different compositions. For example, the electrolyte layer 202 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0117] The thickness of the electrolyte layer 202 may 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 less likely to short-circuit. When the thickness of the electrolyte layer 202 is 300 μm or less, high-output operation is possible.

[0118] The negative electrode 203 includes a material having the property of absorbing and releasing metal ions (for example, lithium ions). The negative electrode 203 includes, for example, a negative electrode active material.

[0119] The negative electrode active material may be a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, or the like. The metal material may be a simple metal. Alternatively, the metal material may be an alloy. Examples of the metal material include lithium metal and lithium alloys. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds are preferably used.

[0120] The negative electrode 203 may contain a solid electrolyte. The above configuration increases the lithium ion conductivity inside the negative electrode 203, enabling high-power operation. The materials exemplified in the first embodiment may be used as the solid electrolyte.

[0121] The median diameter of the negative electrode active material may 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 be well dispersed in the negative electrode 203. This improves the charge / discharge characteristics of the battery 2000. Furthermore, 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. This enables the battery 2000 to operate at high power.

[0122] The median diameter of the negative electrode active material may be larger than the median diameter of the solid electrolyte contained in the negative electrode 203. This allows the negative electrode active material and the solid electrolyte to be well dispersed.

[0123] When the volume ratio of the negative electrode active material to the solid electrolyte in the negative electrode 203 is expressed as "v2:100-v2", the volume ratio v2 of the negative electrode active material may satisfy 30≦v2≦95. When 30≦v2 is satisfied, the energy density of the battery 2000 is sufficiently ensured. Furthermore, when v2≦95 is satisfied, high-power operation is possible.

[0124] The thickness of the negative electrode 203 may 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, high-power operation is possible.

[0125] At least one of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder to improve adhesion between particles. The binder is used to improve the binding properties of the materials constituting the electrodes. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. The binder may be a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Alternatively, a mixture of two or more materials selected from these may be used as the binder.

[0126] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives that can be used include graphites (natural graphite or artificial graphite), carbon blacks (acetylene black, ketjen black, etc.), conductive fibers (carbon fiber or metal fiber, etc.), metal powders (carbon fluoride, aluminum, etc.), conductive whiskers (zinc oxide, potassium titanate, etc.), conductive metal oxides (titanium oxide, etc.), and conductive polymer compounds (polyaniline, polypyrrole, polythiophene, etc.). Using a carbon conductive additive can reduce costs.

[0127] The battery 2000 in the second embodiment can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type. [Example]

[0128] Hereinafter, the present disclosure will be described in detail using examples and comparative examples.

[0129] <<Example 1>> [Preparation of halide solid electrolytes] In an argon glove box with a dew point below -60°C, LiCl powder, LiBr powder, and YCl powder were weighed out in a molar ratio of LiCl:LiBr:YCl = 1:2:1. These were ground and mixed in a mortar to obtain a mixture. The mixture was then milled in a planetary ball mill at 600 rpm for 12 hours.

[0130] As a result of the above, a halide solid electrolyte powder of Example 1 represented by the composition formula Li3YBr2Cl4 was obtained.

[0131] [Preparation of coated active material] Li(NiCoMn)O2 (hereafter referred to as NCM) powder was dried in vacuum at 100°C for 2 weeks, and then removed from the drying apparatus in a dry atmosphere with a dew point of -30°C or less.

[0132] In an argon glove box with a dew point of -60°C or less, ethoxylithium (manufactured by Kojundo Chemical Co., Ltd.) and pentaethoxyniobium (manufactured by Kojundo Chemical Co., Ltd.) were weighed out in a molar ratio of 1:1 and dissolved in ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating solution.

[0133] A tumbling fluidized bed granulation coating device (FD-MP-01E, manufactured by Powrex Corporation) was used to form a coating layer on the surface of the dried NCM particles.

[0134] The amount of NCM added, stirring speed, and coating solution delivery rate were 1 kg, 400 rpm, and 6.59 g / min, respectively. The amount of coating solution added was adjusted so that the LiNbO3 film thickness was 6 nm. The amount of coating solution added was calculated using the specific surface area of ​​the active material and the density of LiNbO3. The series of processes using the tumbling fluidized bed granulation coating equipment was carried out in a dry atmosphere with a dew point of -30°C or below.

[0135] After the treatment for forming the coating layer was completed, the obtained powder was placed in an alumina crucible and heat-treated at 350°C for 1 hour in a pure oxygen atmosphere.

[0136] The heat-treated powder was taken out into a dry atmosphere with a dew point of −30° C. or less and re-pulverized in an agate mortar, thereby obtaining the coated active material of Example 1 (NCM coated with a coating layer).

[0137] The coating material contained in the coating layer was LiNbO3.

[0138] [Preparation of cathode material] In an argon glove box with a dew point of −60° C. or less, the carbon conductive additive, the halide solid electrolyte of Example 1, and the coated active material of Example 1 were weighed out in a weight ratio of 2:18:82. These were mixed in an agate mortar to produce the positive electrode material of Example 1.

[0139] <<Example 2>> [Preparation of halide solid electrolytes] The halide solid electrolyte (NCM) powder of Example 2 was obtained by the same method as in Example 1.

[0140] [Preparation of coated active material] The NCM powder was vacuum dried at 100°C for two weeks. Then, the NCM powder was heat-treated in a nitrogen atmosphere at 400°C for one hour to dry the surface of the NCM particles. The NCM powder was then removed from the drying apparatus in a dry atmosphere with a dew point of -30°C or less.

[0141] A coating layer was formed on the surface of the NCM particles in the same manner as in Example 1, except that the amount of coating solution added was adjusted so that the LiNbO3 film thickness was 2 nm. This resulted in the coated active material of Example 2.

[0142] [Preparation of cathode material] The positive electrode material of Example 2 was obtained in the same manner as in Example 1, except that the coated active material of Example 2 was used.

[0143] <<Example 3>> The positive electrode material of Example 3 was obtained in the same manner as in Example 2, except that the amount of coating solution added was adjusted so that the LiNbO3 film thickness was 6 nm.

[0144] <<Example 4>> The positive electrode material of Example 4 was obtained in the same manner as in Example 2, except that the amount of coating solution added was adjusted so that the LiNbO3 film thickness was 12 nm.

[0145] <<Comparative Example 1>> [Preparation of halide solid electrolytes] A halide solid electrolyte (NCM) powder of Comparative Example 1 was obtained by the same method as in Example 1.

[0146] [Preparation of coated active material] The NCM powder was dried in a vacuum at 100°C for two weeks, and then removed from the drying apparatus in a dry atmosphere with a dew point of -30°C or less.

[0147] In an argon glove box with a dew point of -60°C or less, ethoxylithium (manufactured by Kojundo Chemical Co., Ltd.) and pentaethoxyniobium (manufactured by Kojundo Chemical Co., Ltd.) were weighed out in a molar ratio of 1:1 and dissolved in ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating solution.

[0148] A tumbling fluidized bed granulation coating device (FD-MP-01E, manufactured by Powrex Corporation) was used to form a coating layer on the surface of the dried NCM particles.

[0149] The amount of NCM added, stirring speed, and coating solution delivery rate were 1 kg, 400 rpm, and 6.59 g / min, respectively. The amount of coating solution added was adjusted so that the LiNbO3 film thickness was 2 nm. The amount of coating solution added was calculated using the specific surface area of ​​the active material and the density of LiNbO3. The series of processes using the tumbling fluidized bed granulation coating equipment was carried out in a dry atmosphere with a dew point of -30°C or below.

[0150] After the treatment for forming the coating layer was completed, the obtained powder was placed in an alumina crucible and subjected to heat treatment in an air atmosphere at 350°C for 1 hour.

[0151] The powder after the heat treatment was taken out into the air and re-pulverized in an agate mortar, thereby obtaining a coated active material of Comparative Example 1.

[0152] The coating material contained in the coating layer was LiNbO3.

[0153] [Preparation of cathode material] In an argon glove box with a dew point of −60° C. or less, the carbon conductive additive, the halide solid electrolyte of Comparative Example 1, and the coated active material of Comparative Example 1 were weighed out in a weight ratio of 2:18:82. These were mixed in an agate mortar to produce the positive electrode material of Comparative Example 1.

[0154] <<Comparative Example 2>> The positive electrode material of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that the amount of coating solution added was adjusted so that the LiNbO3 film thickness was 6 nm.

[0155] [Preparation of sulfide solid electrolyte] In an argon glove box with an Ar atmosphere and a dew point of -60°C or less, Li2S powder and P2S5 powder were weighed out to a molar ratio of Li2S:P2S5 = 75:25. These were ground and mixed in a mortar to obtain a mixture. The mixture was then milled for 10 hours at 510 rpm using a planetary ball mill (Fritsch, P-7 model). This yielded a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated in an inert atmosphere at 270°C for 2 hours. This yielded a glass-ceramic sulfide solid electrolyte.

[0156] [Secondary battery production] Secondary batteries were fabricated using the halide solid electrolyte of Example 1, the positive electrode materials of Examples 1 to 4 and Comparative Examples 1 and 2, and the sulfide solid electrolyte.

[0157] First, 80 mg of sulfide solid electrolyte, 20 mg of halide solid electrolyte, and 18 mg of cathode material were stacked in this order in an insulating outer cylinder. The resulting stack was press-molded at a pressure of 720 MPa to obtain the cathode and electrolyte layer.

[0158] Next, metal In (200 μm thick), metal Li (300 μm thick), and metal In (200 μm thick) were laminated in this order on the electrolyte layer opposite to the side in contact with the positive electrode. The resulting laminate was press-molded at a pressure of 80 MPa to produce a laminate consisting of a positive electrode, an electrolyte layer, and a negative electrode.

[0159] Next, stainless steel current collectors were placed on the top and bottom of the laminate, and current collecting leads were attached to each current collector.

[0160] Finally, the insulating outer cylinder was sealed using an insulating ferrule to isolate the inside of the outer cylinder from the outside atmosphere, and batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were fabricated.

[0161] [Charge / discharge test] Using the batteries of Examples 1 to 4 and Comparative Examples 1 and 2, charge / discharge tests were carried out under the following conditions.

[0162] The battery was placed in a thermostatic chamber at 25°C.

[0163] The battery was charged at a constant current of 140 μA, which corresponds to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, and charging was completed at a voltage of 3.7 V.

[0164] Next, the battery was discharged at a current value of 140 μA, which was also a 0.05 C rate, and the discharge was completed at a voltage of 1.9 V.

[0165] As described above, the average discharge voltage was measured for each of the batteries of Examples 1 to 4 and Comparative Examples 1 and 2. The results are shown in Table 1 below.

[0166] [Surface composition analysis] The coated active materials of Examples 1 to 4 and Comparative Examples 1 and 2 were used to carry out the following measurements.

[0167] The surface composition analysis was performed using a QuanteraSXM (manufactured by ULVAC-PHI, Inc.) under the following measurement conditions:

[0168] X-ray source: Al monochromator (25W, 15kV) Analysis area: 300μm×800μm(Area) Electron / ion neutralization gun: ON Photoelectron take-off angle: 45 degrees

[0169] The binding energy scan range was from 0 eV to 1250 eV. The atomic concentrations of elements were calculated using the software “MultiPak” manufactured by ULVAC-PHI.

[0170] The elements selected for measurement were Li (scan range: 45-65 eV), C (scan range: 275-295 eV), O (scan range: 522-542 eV), Mn (scan range: 632-662 eV), Co (scan range: 770-810 eV), Ni (scan range: 848-888 eV), and Nb (scan range: 195-215 eV). The atomic concentrations of the elements were calculated from the integrated peak area ratio based on the peaks observed in each element's scan range. The ratio (Nb / C) was then calculated as the atomic ratio between the calculated surface Nb concentration and the calculated surface C concentration.

[0171] As a result, the atomic ratio (Nb / C) of the niobium (Nb) content to the carbon (C) content in the region from the outermost surface to a depth of 10 nm of the coated active material was obtained. The results are shown in Table 1 below.

[0172] Carbon (C) is derived from ethoxylithium and pentaethoxyniobium, which are raw materials for the coating layer.

[0173] [Table 1]

[0174] <<Considerations>> As shown in Table 1, the coated active materials of Examples 1 to 4 had atomic ratios (Nb / C) of 0.18, 0.11, 0.15, and 0.15, respectively. All of the coated active materials of Examples 1 to 4 had atomic ratios (Nb / C) of 0.11 or more. The average discharge voltages of the batteries of Examples 1 to 4 were 3.624 V or more. It was confirmed that the discharge voltage of the battery was improved by using a positive electrode material in which the atomic ratio (Nb / C) of the niobium content to the carbon content was 0.11 or more in the surface layer portion of the coated active material.

[0175] In contrast, the atomic ratios (Nb / C) of the coated active materials of Comparative Examples 1 and 2 were less than 0.01 and 0.08, respectively, which were significantly lower than the values ​​of Examples 1 to 4. The average discharge voltages of the batteries of Comparative Examples 1 and 2 were both 3.586 V or less. [Industrial Applicability]

[0176] The battery of the present disclosure can be used, for example, as an all-solid-state battery. [Explanation of symbols]

[0177] 1000 cathode materials 100 solid electrolyte 110 Cathode active material 120 Covering layer 130 Coated active material 2000 batteries 201 Positive electrode 202 Electrolyte layer 203 Negative electrode

Claims

1. a positive electrode active material; a coating layer that coats the positive electrode active material; a solid electrolyte; A positive electrode material comprising: the coating layer contains a lithium niobate-based compound and carbon, the positive electrode active material and the coating layer constitute a coated active material, the positive electrode active material includes a lithium-containing transition metal oxide, a positive electrode material, wherein, when niobium and carbon contained in a surface layer portion of the coated active material are quantified by surface composition analysis using XPS to a depth of 10 nm from the outermost surface, the ratio of the niobium content to the carbon content, Nb / C, in terms of atomic ratio, is 0.11 or more and 0.18 or less.

2. The solid electrolyte is represented by the following composition formula (1): Li α M β X γ ... Formula (1) where α, β, and γ are each independently a value greater than 0; M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li, 2. The cathode material of claim 1, wherein X comprises at least one selected from the group consisting of F, Cl, Br, and I.

3. 3. The cathode material of claim 2, wherein M comprises yttrium.

4. The positive electrode material according to claim 2 or 3, wherein 2.5≦α≦3, 1≦β≦1.1, and γ=6 are satisfied.

5. 5. The positive electrode material according to claim 2, wherein X comprises at least one selected from the group consisting of Cl and Br.

6. The positive electrode material according to claim 1 , wherein the positive electrode active material contains Li and at least one element selected from the group consisting of Mn, Co, Ni, and Al.

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

8. the positive electrode material comprises a solid electrolyte; 8. The battery of claim 7, wherein the electrolyte layer includes a solid electrolyte having the same composition as the solid electrolyte included in the positive electrode material.

9. the positive electrode material comprises a solid electrolyte; 9. The battery according to claim 7, wherein the electrolyte layer includes a halide solid electrolyte having a composition different from the composition of the solid electrolyte included in the positive electrode material.

10. 10. The battery of claim 7, wherein the electrolyte layer comprises a sulfide solid electrolyte.

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