Coated positive electrode active material, positive electrode material, and battery

Abstract

This coated positive electrode active substance contains a positive electrode active substance and a coating material that coats at least a part of the surface of the positive electrode active substance, wherein the coating material contains Al2Ox (O<x<3). A positive electrode material 1000 contains the coated positive electrode active substance 150 and a first solid electrolyte material 100. The first solid electrolyte material 100 contains Li, M, and X, wherein M is at least one element selected from the group consisting of the metalloid elements and the metallic elements other than Li, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

Description

Technical Field

[0001] The present disclosure relates to a coated positive electrode active material, a positive electrode material, and a battery.

Background Art

[0002] Patent Document 1 discloses a battery including a halide, an electrode active material, and a coating material located on the surface of the electrode active material.

[0003] Patent Document 2 discloses a negative electrode active material having a coating portion composed of aluminum oxide on its surface.

[0004] Patent Document 3 discloses an all-solid-state battery in which a metal layer having an apparent average thickness of 0.05 μm or more is provided on the surface of active material particles.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document ③

Summary of the Invention

[0006] The present disclosure provides a positive electrode active material capable of improving the cycle characteristics of a battery.

[0007] The coated positive electrode active material of the present disclosure includes a positive electrode active material and a coating material that coats at least a part of the surface of the positive electrode active material, and the coating material includes Al2O x (0 < x < 3).

[0008] The present disclosure provides a positive electrode active material capable of improving the cycle characteristics of a battery.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 1000 in Embodiment 2. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 in Embodiment 3. [Figure 3] FIG. 3 shows a schematic diagram of a compression molding die 300 used to evaluate the ionic conductivity of a solid electrolyte material. [Figure 4] FIG. 4 shows peaks attributed to Al 2p in the X-ray photoelectron spectra of the surfaces of the coated positive electrode active materials of Example 1 and Comparative Example 2 measured by X-ray photoelectron spectroscopy and Al2O3. [Figure 5] FIG. 5 is a graph showing charge-discharge curves indicating the initial charge-discharge characteristics of the batteries in Examples 1 to 3 and Comparative Examples 1 to 2.

Modes for Carrying Out the Invention

[0010] (Findings on which the present disclosure is based) In conventional all-solid-state lithium-ion secondary batteries, there have been problems with cycle characteristics because the solid electrolyte undergoes oxidative decomposition. A method of coating the surface of a positive electrode active material has been reported to suppress the above problems. However, the oxide that coats the surface of the positive electrode active material may inhibit the conduction of lithium ions and electrons and cause capacity degradation or the like. Therefore, it is difficult for a battery provided with a positive electrode active material whose surface is coated with a coating material to maintain battery characteristics such as cycle characteristics. Also, a method of coating a metal on the surface of the active material has been reported, but it cannot sufficiently suppress the oxidative decomposition of the solid electrolyte.

[0011] (Outline of one aspect according to the present disclosure) The coated positive electrode active material according to the first aspect of the present disclosure is a positive electrode active material, A coating material that coats at least a part of the surface of the positive electrode active material, including the coating material contains Al2O x (0 < x < 3).

[0012] In the coated positive electrode active material according to the first aspect, at least a part of the surface is coated with a coating material containing Al2O x (0 < x < 3). Therefore, while effectively suppressing the oxidative decomposition of the solid electrolyte due to the contact between the solid electrolyte and the positive electrode active material in the battery, it is possible to suppress the inhibition of lithium ion conduction on the surface of the positive electrode active material. Therefore, the coated positive electrode active material according to the first aspect can effectively suppress the oxidative decomposition of the solid electrolyte and suppress the increase in internal resistance, so that the cycle characteristics of the battery can be improved.

[0013] In the second aspect of the present disclosure, for example, in the coated positive electrode active material according to the first aspect, the coating material consists essentially of Al and O, and in the spectrum obtained by X-ray photoelectron spectroscopy measurement of the surface, the full width at half maximum of the peak attributed to Al2p may exceed 1.80 eV.

[0014] The coated positive electrode active material according to the second aspect can improve the cycle characteristics of the battery.

[0015] In the third aspect of the present disclosure, for example, in the coated positive electrode active material according to the first or second aspect, the positive electrode active material may have a composition represented by the following compositional formula (2). LiNi α Co β Me 1-α-β O2 ··· Formula (2) Here, α and β satisfy 0 ≤ α < 1, 0 ≤ β ≤ 1, and 0 ≤ 1 - α - β ≤ 0.35, and Me is at least one selected from the group consisting of Al and Mn.

[0016] The coated positive electrode active material according to the third aspect can improve the charge-discharge capacity of the battery.

[0017] In a fourth aspect of the present disclosure, for example, the coated positive electrode active material according to the third aspect may satisfy at least one selected from the group consisting of the following (A) and (B). (A) On the surface of the coated positive electrode active material, the Al / Ni atomic ratio is 2.9 or less. (B) On the surface of the coated positive electrode active material, the Al / Co atomic ratio is 4.6 or less.

[0018] The coated positive electrode active material according to the fourth aspect can further improve the cycle characteristics of the battery.

[0019] The positive electrode material according to the fifth aspect of the present disclosure includes a coated positive electrode active material according to any one of the first to fourth aspects, a first solid electrolyte material, and the first solid electrolyte material contains Li, M, and X, M is at least one selected from the group consisting of metal elements and metalloid elements other than Li, X is at least one selected from the group consisting of F, Cl, Br, and I.

[0020] The positive electrode material according to the fifth aspect can improve the cycle characteristics of the battery.

[0021] The battery according to the sixth aspect of the present disclosure includes a positive electrode, a negative electrode, a solid electrolyte layer provided between the positive electrode and the negative electrode, and the positive electrode includes the positive electrode material according to the fifth aspect.

[0022] The battery according to the sixth aspect has improved cycle characteristics.

[0023] (Embodiment 1) The coated positive electrode active material according to Embodiment 1 of the present disclosure includes a positive electrode active material and a coating material that covers at least a part of the surface of the positive electrode active material, and the coating material contains Al2O x (0 < x < 3).

[0024] Al2O x (0 < x < 3) makes lithium diffusion in the coating material likely to occur. Furthermore, by covering at least a part of the surface of the positive electrode active material with the coating material, electron conduction that is a factor in the decomposition of the solid electrolyte can be suppressed. Therefore, the cycle characteristics of the battery can be improved.

[0025] x may satisfy 2 ≤ x < 3. By doing so, lithium diffusion in the coating material is likely to occur, and furthermore, electron conduction that is a factor in the oxidative decomposition of the solid electrolyte can be suppressed. Therefore, the cycle characteristics of the battery can be improved.

[0026] Al2O x (0 < x < 3) can be confirmed, for example, in the X-ray photoelectron spectrum obtained by X-ray photoelectron spectroscopy, by the full width at half maximum of the peak attributed to Al2p being wider than that (1.80 eV) in the X-ray photoelectron spectrum obtained by X-ray photoelectron spectroscopy of Al2O3. This is considered to be due to the coexistence of the valences of Al.

[0027] The coating material may consist substantially of Al and O, and in the spectrum obtained by X-ray photoelectron spectroscopy of the surface of the coated positive electrode active material, the full width at half maximum of the peak attributed to Al2p may exceed 1.80 eV.

[0028] "The coating material consists substantially of Al and O" means that the ratio (i.e., molar fraction) of the total amount of the substances of Al and O to the total amount of the substances of all the elements constituting the coating material is 90% or more. As an example, the ratio may be 95% or more. The ratio of the total amount of the substances of Al and O may be 98% or more, or 99% or more.

[0029] The coating material may contain unavoidably incorporated elements. An example of such an element is Li that diffuses into the coating material by repeated use of the lithium-ion secondary battery including the coated cathode active material of the present disclosure.

[0030] The coating material may consist of Al and O.

[0031] The coating material may contain Al2O x (0 < x < 3) as a main component. Here, the "main component" means the component contained most in terms of mass ratio.

[0032] According to the above configuration, the cycle characteristics of the battery can be further improved.

[0033] The coating material may contain Al2O x and may be composed only of (0 < x < 3).

[0034] The coating material may cover 30% or more, 60% or more, or 90% or more of the surface of the cathode active material. The coating material may substantially cover the entire surface of the cathode active material.

[0035] The coating material may be in direct contact with the surface of the cathode active material.

[0036] The thickness of the coating material may be, for example, 100 nm or less, or 10 nm or less. The coating material may be formed in an island shape on the surface of the cathode active material. Note that the coating material may be in a trace amount close to the detection limit. When the presence of Al2O x (0 < x < 3) can be confirmed on the cathode, it is presumed that Al2O x (0 < x < 3) adheres to some extent to the cathode active material, and the improvement effect of the cycle characteristics corresponding thereto is recognized. In particular, when the thickness of the coating material is 10 nm or less, lithium conduction is not inhibited and capacity degradation is suppressed. The thickness of the coating material may be 5 nm or less. If the thickness of the coating material is 5 nm or less, capacity degradation is further suppressed.

[0037] If the thickness of the coating material is 5 nm or less, when the surface of the coated cathode active material is analyzed by X-ray photoelectron spectroscopy, peaks of elements originating from the cathode active material as well as those from the coating material will be observed.

[0038] The thickness of the coating material may be 1 nm or more. If the thickness is 1 nm or more, the surface of the positive electrode active material can be sufficiently coated, and the effect of suppressing the decomposition of the solid electrolyte can be obtained.

[0039] The method for measuring the thickness of the coating material is not particularly limited, but for example, it can be determined by directly observing the thickness of the coating material using a transmission electron microscope.

[0040] The coated positive electrode active material according to Embodiment 1 of this disclosure may satisfy at least one selected from the group consisting of (A) and (B) below. (A) The Al / Ni atomic ratio on the surface of the coated positive electrode active material is 2.9 or less. (B) The Al / Co atomic ratio on the surface of the coated positive electrode active material is 4.6 or less.

[0041] The Al / Ni atomic ratio and Al / Co atomic ratio can be calculated, for example, by X-ray photoelectron spectroscopy.

[0042] (Method for coating the surface of the positive electrode active material) The coating material can be formed on the surface of the positive electrode active material by the following method. The following description is not limited to the method of preparing the coated positive electrode active material.

[0043] The coating material is formed, for example, by depositing Al on the surface of the positive electrode active material using a vapor phase method such as sputtering or electron beam deposition in an oxygen-containing atmosphere with controlled oxygen levels. Alternatively, the coating material may be formed by depositing Al on the surface of the positive electrode active material using the aforementioned vapor phase method or plating method, and then heating it in an oxygen atmosphere.

[0044] The positive electrode active material may include a lithium-containing transition metal composite oxide. The transition metal included in the lithium-containing transition metal composite oxide may be at least one selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), chromium (Cr), titanium (Ti), niobium (Nb), zirconium (Zr), vanadium (V), tantalum (Ta), and molybdenum (Mo).

[0045] Lithium-containing transition metal composite oxides can be obtained, for example, by mixing a lithium compound with a transition metal-containing compound obtained by coprecipitation or the like, and then calcining the resulting mixture under predetermined conditions. Lithium-containing transition metal composite oxides typically form secondary particles that are aggregates of multiple primary particles. The average particle size (D50) of lithium-containing transition metal composite oxide particles is, for example, between 1 μm and 20 μm. Note that the average particle size (D50) refers to the particle size at which the integrated volume value in the volume-based particle size distribution measured by laser diffraction scattering (volume-average particle size).

[0046] A lithium-containing transition metal composite oxide may also contain metals other than transition metals. These non-transition metals may include at least one selected from the group consisting of aluminum (Al), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), and silicon (Si). Furthermore, the composite oxide may also contain other elements besides metals, such as boron (B).

[0047] From the viewpoint of increasing capacity, the transition metal may include at least one selected from the group consisting of Ni and Co. The lithium-containing transition metal composite oxide may include Ni and at least one selected from the group consisting of Co, Mn, Al, Ti, and Fe. From the viewpoint of increasing capacity and power output, in particular, the lithium-containing transition metal composite oxide may include Ni and at least one selected from the group consisting of Co, Mn, and Al, or Ni and at least one selected from the group consisting of Co, Mn, and Al. When the lithium-containing transition metal composite oxide further includes Co in addition to Li and Ni, the phase transition of the composite oxide containing Li and Ni is suppressed during charging and discharging, the stability of the crystal structure is improved, and the cycle characteristics are easily improved. When the lithium-containing transition metal composite oxide further includes at least one selected from the group consisting of Mn and Al, thermal stability is improved.

[0048] From the viewpoint of improving cycle characteristics and increasing power output, the lithium-containing transition metal composite oxide in the positive electrode active material may include a lithium-containing transition metal composite oxide having a layered rock salt type crystal structure and containing at least one selected from the group consisting of Ni and Co, or it may include a lithium-containing transition metal composite oxide having a spinel type crystal structure and containing Mn. From the viewpoint of increasing capacity, the lithium-containing transition metal composite oxide may be a composite oxide (hereinafter also referred to as nickel-based composite oxide) having a layered rock salt type crystal structure, containing Ni and a metal other than Ni, and having an atomic ratio of Ni to the metal other than Ni of 0.3 or more.

[0049] The positive electrode active material may have a layered rock salt-type crystalline structure and a composition represented by the following compositional formula (1). LiRing α Me' 1-α O2...Equation (1) Here, α satisfies 0 ≤ α < 1, and Me' is at least one element selected from the group consisting of Co, Mn, Al, Ti, and Fe.

[0050] In compositional formula (1), when α is within the above range, a good balance is obtained between the effect of increasing capacity due to Ni and the effect of improving stability due to the element Me'.

[0051] In compositional formula (1), α may be 0.5 or greater, or 0.75 or greater.

[0052] The positive electrode active material may include a material represented by the following composition formula (2). LiRing α Co β Me 1-α-β O2...Equation (2) Here, α and β satisfy 0 ≤ α < 1, 0 ≤ β ≤ 1, and 0 ≤ 1 - α - β ≤ 0.35, and Me is at least one selected from the group consisting of Al and Mn.

[0053] (Embodiment 2) Figure 1 is a cross-sectional view showing the schematic configuration of the positive electrode material 1000 in Embodiment 2. The positive electrode material 1000 according to Embodiment 2 of this disclosure includes the coated positive electrode active material 150 and the first solid electrolyte material 100 in Embodiment 1. The coated positive electrode active material 150 includes a positive electrode active material 110 and a coating material 120 that covers at least a portion of the surface of the positive electrode active material 110. The first solid electrolyte material 100 includes Li, M, and X, where M is at least one selected from the group consisting of metal elements other than Li and metalloid elements, and X is at least one selected from the group consisting of F, Cl, Br, and I.

[0054] The first solid electrolyte material 100 contains a halide solid electrolyte as described above. The first solid electrolyte material 100 may consist substantially of Li, M, and X. "The first solid electrolyte material 100 consists substantially of Li, M, and X" means that in the first solid electrolyte material 100, the ratio (i.e., mole fraction) of the total amount of substance of Li, M, and X to the total amount of substance of all elements constituting the first solid electrolyte material is 90% or more. As an example, this ratio (i.e., mole fraction) may be 95% or more. The first solid electrolyte material 100 may consist only of Li, M, and X. The first solid electrolyte material 100 does not have to contain sulfur.

[0055] To increase ionic conductivity, M may include at least one element selected from the group consisting of Group 1 elements, Group 2 elements, Group 3 elements, Group 4 elements, and lanthanide elements.

[0056] Furthermore, M may include elements from Group 5, Group 12, Group 13, and Group 14.

[0057] Examples of Group 1 elements are Na, K, Rb, or Cs. Examples of Group 2 elements are Mg, Ca, Sr, or Ba. Examples of Group 3 elements are Sc or Y. Examples of Group 4 elements are Ti, Zr, or Hf. Examples of lanthanide elements are La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu.

[0058] Examples of Group 5 elements are Nb or Ta. Examples of Group 12 elements are Zn. Examples of Group 13 elements are Al, Ga, and In. Examples of Group 14 elements are Sn.

[0059] To further enhance ionic conductivity, M may include at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ba, Sc, Y, Zr, Hf, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0060] To further enhance ionic conductivity, M may include at least one element selected from the group consisting of Mg, Ca, Sr, Y, Sm, Gd, Dy, and Hf. To further enhance ionic conductivity, X may include at least one element selected from the group consisting of Br, Cl, and I.

[0061] To further enhance ionic conductivity, X may include at least one element selected from the group consisting of Br, Cl, and I.

[0062] To further enhance ionic conductivity, X may contain Br, Cl, and I.

[0063] The first solid electrolyte material 100 may be Li3YX6. The first solid electrolyte material 100 may be Li3YBr6. The first solid electrolyte material 100 may be Li3YBr x1 Cl 6-x1 (0 ≤ x1 < 6) may also be the case. The first solid electrolyte material 100 is Li3YBr x2 Cl y2 I 6-x2-y2 (0≦x², 0≦y², 0≦x²+y²≦6) is also acceptable.

[0064] The first solid electrolyte material 100 may be Li3YBr6, Li3YBr2Cl4, or Li3YBr2Cl2I2.

[0065] The first solid electrolyte material 100 may further include a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte.

[0066] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12Li6PS5Cl and the like can be used. In addition, LiX', Li2O, MOq, LipM'Oq, etc. may be added to these. Here, X' is at least one selected from the group consisting of F, Cl, Br, and I, M' is at least one selected from P, Si, Ge, B, Al, Ga, In, Fe, and Zn, and p and q are independent natural numbers.

[0067] Examples of oxide solid electrolytes include NASICON-type solid electrolytes represented by LiTi2(PO4)3 and its elemental substitutions, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGe4O 16 , LiSICON-type solid electrolytes such as Li4SiO4, LiGeO4 and their elemental substitutions, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those represented by their elemental substitutions, Li-BO compounds such as Li3N and its H-substituted derivatives, Li3PO4 and its N-substituted derivatives, LiBO2, Li3BO3, and Li2SO4, Li2CO3, can be used as a base for glass, glass ceramics, etc., to which Li2SO4, Li2CO3, etc., can be added.

[0068] As a 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. Polymer solid electrolytes having an ethylene oxide structure can contain a large amount of lithium salt, thus increasing ionic conductivity. Examples of lithium salts that can be used include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc. One lithium salt selected from these can be used alone. Alternatively, a mixture of two or more lithium salts selected from these can be used.

[0069] Examples of complex hydride solid electrolytes that can be used include LiBH4-LiI and LiBH4-P2S5.

[0070] Furthermore, the shape of the first solid electrolyte material 100 is not particularly limited and may be, for example, needle-shaped, spherical, ellipsoidal, etc. For example, the shape of the first solid electrolyte material 100 may be particles.

[0071] For example, if the shape of the first solid electrolyte material 100 is particulate (e.g., spherical), the median diameter of the first solid electrolyte material 100 may be 100 μm or less. When the median diameter of the first solid electrolyte material 100 is 100 μm or less, the coated positive electrode active material 150 and the first solid electrolyte material 100 can form a good dispersion state in the positive electrode material 1000. As a result, the charge and discharge characteristics of the battery using the positive electrode material 1000 are improved.

[0072] The median diameter of the first solid electrolyte material 100 may be 10 μm or less. With this configuration, the coated positive electrode active material 150 and the first solid electrolyte material 100 can form a better dispersion state in the positive electrode material 1000.

[0073] The median diameter of the first solid electrolyte material 100 may be smaller than the median diameter of the coated positive electrode active material 150. With this configuration, the coated positive electrode active material 150 and the first solid electrolyte material 100 can form a better dispersion state in the positive electrode material 1000.

[0074] The median diameter of the coated positive electrode active material 150 may be 0.1 μm or more and 100 μm or less.

[0075] If the median diameter of the coated positive electrode active material 150 is 0.1 μm or more, the coated positive electrode active material 150 and the first solid electrolyte material 100 can form a good dispersion state in the positive electrode material 1000. As a result, the charge and discharge characteristics of the battery using the positive electrode material 1000 are improved. Furthermore, if the median diameter of the coated positive electrode active material 150 is 100 μm or less, the lithium diffusion rate within the coated positive electrode active material 150 is improved. Therefore, the battery using the positive electrode material 1000 can operate at high power.

[0076] The median diameter of the coated positive electrode active material 150 may be larger than the median diameter of the first solid electrolyte material 100. This allows the coated positive electrode active material 150 and the first solid electrolyte material 100 to form a good dispersion state.

[0077] (Embodiment 3) Embodiment 3 will now be described. Descriptions that overlap with Embodiments 1 and 2 described above will be omitted as appropriate.

[0078] Figure 2 is a cross-sectional view showing the schematic configuration of the battery 2000 in Embodiment 3.

[0079] The battery 2000 in Embodiment 3 comprises a positive electrode 201 containing the positive electrode material 1000 described in Embodiment 2 above, a negative electrode 203, and a solid electrolyte layer 202 provided between the positive electrode 201 and the negative electrode 203.

[0080] Battery 2000 may be an all-solid-state battery.

[0081] (Positive electrode 201) The positive electrode 201 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The positive electrode 201 includes a coated positive electrode active material 150 and a first solid electrolyte material 100.

[0082] The volume ratio Vp, which represents the volume of the positive electrode active material 110 relative to the total volume of the positive electrode active material 110 and the first solid electrolyte material 100 contained in the positive electrode 201, may be between 0.3 and 0.95. When the volume ratio Vp is 0.3 or higher, it is easier to ensure a sufficient energy density of the battery 2000. When the volume ratio Vp is 0.95 or lower, it becomes easier to operate the battery 2000 at high power.

[0083] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less.

[0084] When the thickness of the positive electrode 201 is 10 μm or more, sufficient energy density of the battery 2000 can be ensured. Furthermore, when the thickness of the positive electrode 201 is 500 μm or less, high-power operation of the battery 2000 can be achieved.

[0085] The positive electrode 201 may contain a binder. The binder is used to improve the bonding properties of the materials constituting the positive electrode 201. 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, carboxymethylcellulose, and the like. Furthermore, a copolymer of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene may be used as a binder. Two or more of these may be mixed and used as a binder.

[0086] The positive electrode 201 may contain a conductive additive. The conductive additive is used to enhance electronic conductivity. Examples of conductive additives include graphites such as natural or artificial graphite, carbon blacks such as acetylene black and Ketjenblack, conductive fibers such as carbon fibers or metal fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs. Conductive additives may be used individually or in combination of two or more.

[0087] The positive electrode 201 may further include a positive electrode current collector.

[0088] For example, a metal foil may be used as the positive electrode current collector. Examples of metals that make up the positive electrode current collector include aluminum, titanium, alloys containing these metal elements, and stainless steel. The thickness of the positive electrode current collector is not particularly limited, but for example, it is 3 μm or more and 50 μm or less. The metal foil may be coated with carbon or the like.

[0089] (Negative electrode 203) The negative electrode 203 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The negative electrode 203 includes, for example, a negative electrode active material. The negative electrode 203 may also include a negative electrode active material 130 and a second solid electrolyte material 140.

[0090] The negative electrode active material 130 may contain a carbon material that intercepts and releases lithium ions. Examples of carbon materials that intercept and release lithium ions include graphite (natural graphite, artificial graphite), easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). Among these, graphite is preferable because it has excellent charge-discharge stability and low irreversible capacity.

[0091] The negative electrode active material 130 may include an alloying material. An alloying material is a material containing at least one metal that can form an alloy with lithium, and examples include silicon, tin, indium, silicon alloys, tin alloys, indium alloys, silicon compounds, etc. As the silicon compound, a composite material comprising a lithium ion conducting phase and silicon particles dispersed in that phase may be used. As the lithium ion conducting phase, a silicate phase such as a lithium silicate phase, a silicon oxide phase having 95% or more by mass as silicon dioxide, a carbon phase, etc., may be used.

[0092] Furthermore, when a lithium alloy or lithium storage metal is used as the negative electrode active material 130, the negative electrode 203 may not contain the second solid electrolyte material 140 and may consist of the negative electrode active material 130 alone.

[0093] The negative electrode active material 130 may contain lithium titanium oxide. The lithium titanium oxide is Li4Ti5O 12 Li7Ti5O 12 It may also include at least one material selected from LiTi2O4.

[0094] The negative electrode active material 130 may be an alloy material and a carbon material, or a combination of lithium titanium oxide and a carbon material.

[0095] In the negative electrode 203, the content of the second solid electrolyte material 140 may be the same as or different from the content of the negative electrode active material 130.

[0096] In the negative electrode 203, the volume ratio Vn, which represents the volume of the negative electrode active material 130 to the total volume of the negative electrode active material 130 and the second solid electrolyte material 140, may be between 0.3 and 0.95. When the volume ratio Vn is 0.3 or higher, it is easier to ensure a sufficient energy density of the battery 2000. When the volume ratio Vn is 0.95 or lower, it becomes easier to operate the battery 2000 at high power.

[0097] The second solid electrolyte material 140 may have the same composition as the first solid electrolyte material 100 described above, or it may have a different composition.

[0098] The second solid electrolyte material 140 may be the material listed as the first solid electrolyte material 100. The second solid electrolyte material 140 may have the same composition as the first solid electrolyte material 100, or it may have a different composition from the first solid electrolyte material 100.

[0099] The thickness of the negative electrode 203 may be 10 μm or more and 500 μm or less.

[0100] When the thickness of the negative electrode 203 is 10 μm or more, sufficient energy density of the battery 2000 can be ensured. Furthermore, when the thickness of the negative electrode 203 is 500 μm or less, high-power operation of the battery 2000 can be achieved.

[0101] The negative electrode 203 may further include a negative electrode current collector. The same material used for the positive electrode current collector may be used for the negative electrode current collector. The thickness of the negative electrode current collector is not particularly limited, but for example, it is 3 to 50 μm. Also, when a lithium alloy or lithium storage metal is used as the negative electrode active material 130, the lithium storage alloy can be used as both the negative electrode active material and the negative electrode current collector.

[0102] The negative electrode 203 may comprise a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector. The negative electrode mixture layer can be formed, for example, by dispersing a negative electrode slurry (a mixture of negative electrode active material 130 and second solid electrolyte material 140) in a dispersion medium on the surface of the negative electrode current collector and drying it. The dried coating may be rolled if necessary. The negative electrode mixture layer may be formed on one surface of the negative electrode current collector or on both surfaces.

[0103] The negative electrode mixture may further contain a binder, a conductive additive, and a thickener. The binder and conductive additive can be the same as those used in the positive electrode 201.

[0104] (Solid electrolyte layer 202) The solid electrolyte layer 202 is placed between the positive electrode 201 and the negative electrode 203.

[0105] The solid electrolyte layer 202 is a layer containing a solid electrolyte material.

[0106] The solid electrolyte material included in the solid electrolyte layer 202 may be the materials exemplified as the first solid electrolyte material 100 and the second solid electrolyte material 140. The solid electrolyte layer 202 may contain a solid electrolyte material having the same composition as the first solid electrolyte material 100, or a solid electrolyte material having the same composition as the second solid electrolyte material 140. The solid electrolyte layer 202 may also use materials different from the first solid electrolyte material 100 and the second solid electrolyte material 140.

[0107] The solid electrolyte layer 202 may contain two or more of the materials listed as solid electrolyte materials. For example, the solid electrolyte layer may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0108] The solid electrolyte layer 202 may include a first electrolyte layer and a second electrolyte layer, the first electrolyte layer being located between the positive electrode 201 and the negative electrode 203, and the second electrolyte layer being located between the first electrolyte layer and the negative electrode 203. The first electrolyte layer may contain a material having the same composition as the first solid electrolyte material 100. The second electrolyte layer may contain a material having a different composition than the first solid electrolyte material 100. The second electrolyte layer may contain a material having the same composition as the second solid electrolyte material 140.

[0109] The solid electrolyte layer 202 may contain a binder as appropriate. The same binder as that used in the positive electrode 201 can be used.

[0110] The solid electrolyte layer 202 may be formed from the materials exemplified as the first solid electrolyte material 100 and the second solid electrolyte material 140.

[0111] The solid electrolyte layer 202 can be formed, for example, by drying a solid electrolyte slurry (a solid electrolyte material dispersed in a dispersion medium) to form a sheet, and then transferring it to the surface of the positive electrode 201 or the negative electrode 203. Alternatively, it can also be formed by directly coating the surface of the positive electrode 201 or the negative electrode 203 with the solid electrolyte slurry and drying it.

[0112] Although a method for forming the positive electrode 201, negative electrode 203, and solid electrolyte layer 202 using a slurry has been described, the manufacturing method of the battery 2000 is not limited to coating. The battery 2000 according to Embodiment 3 may be manufactured, for example, by preparing a material for forming the positive electrode, a material for forming the electrolyte layer, and a material for forming the negative electrode, and then creating a laminate in which the positive electrode, electrolyte layer, and negative electrode are arranged in this order by a known method. For example, the battery 2000 can also be formed by compacting a positive electrode containing a positive electrode active material 110, a first solid electrolyte material 100, and a conductive material, a solid electrolyte layer, and a negative electrode containing a negative electrode active material 130, a second solid electrolyte material 140, and a conductive material, and then bonding them together. [Examples]

[0113] The present disclosure will be described in detail below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0114] (Example 1) (Preparation of the first solid electrolyte material) Under an argon atmosphere with a dew point of -80°C and an oxygen concentration of approximately 10 ppm (hereinafter referred to as "dry argon atmosphere"), the raw material powders LiBr, YBr3, LiCl, and YCl3 were weighed in a molar ratio of Li:Y:Br:Cl = 3:1:2:4. These were ground and mixed in a mortar. Then, the mixture was milled using a planetary ball mill at 600 rpm for 25 hours. As a result, the powder of Li3YBr2Cl4, the first solid electrolyte material of Example 1, was obtained.

[0115] (Evaluation of the composition of the first solid electrolyte material) The composition of the first solid electrolyte material of Example 1 was evaluated by ICP emission spectroscopy using an inductive coupled plasma (ICP) emission spectrometer (ThermoFisher Scientific, iCAP7400). As a result, the molar ratio of Li / Y deviated from the initial composition by less than 3%. In other words, the composition of the raw material powder prepared using a planetary ball mill and the composition of the first solid electrolyte material obtained in Example 1 were almost identical.

[0116] (Evaluation of ionic conductivity of the first solid electrolyte material) Figure 3 shows a schematic diagram of a pressure-molding die 300 used to evaluate the ionic conductivity of the first solid electrolyte material.

[0117] The pressure forming die 300 comprised a punch upper section 301, a frame 302, and a punch lower section 303. The frame 302 was formed from insulating polycarbonate. Both the punch upper section 301 and the punch lower section 303 were formed from electronically conductive stainless steel. The frame 302 was formed from insulating polycarbonate.

[0118] Using the pressure molding die 300 shown in Figure 3, the ionic conductivity of the first solid electrolyte material according to Example 1 was measured by the following method.

[0119] In a dry atmosphere having a dew point of -30°C or lower, the powder of the first solid electrolyte material according to Example 1 (solid electrolyte material powder 101 in Figure 3) was filled into the inside of a pressure molding die 300. Inside the pressure molding die 300, a pressure of 300 MPa was applied to the solid electrolyte material according to Example 1 using the upper part of the punch 301 and the lower part of the punch 303.

[0120] While pressure was being applied, the upper punch 301 and the lower punch 303 were connected to a potentiostat (Princeton Applied Research, VersaSTAT4) equipped with a frequency response analyzer. The upper punch 301 was connected to the working electrode and the potential measurement terminal. The lower punch 303 was connected to the counter electrode and the reference electrode. The impedance of the first solid electrolyte material was measured at room temperature by an electrochemical impedance measurement method to measure the ionic conductivity.

[0121] The ionic conductivity of the first solid electrolyte material according to Example 1 measured at 22°C was 1.5×10 -3 S / cm. The same first solid electrolyte material was also used in Examples 2 to 3 and Comparative Examples 1 to 2.

[0122] (Preparation of Coated Cathode Active Material) As the cathode active material, composite oxide particles (average particle size (D50) 4.4 μm) having a composition of layered rock salt type LiNi 0.5 Co 0.3 Mn 0.2 O2 (hereinafter referred to as NCM) were used.

[0123] The method of coating Al2O x (0 < x < 3) on the surface of the cathode active material is shown below, but the method is not limited to the following.

[0124] By sputtering, using Al as the target, setting the target film thickness to 5 nm, and adjusting the oxygen flow rate, a coating material was formed on the cathode active material. The cathode active material was enclosed in a gauge covered with a metal mesh, and the gauge was rotated so that the coating material was formed while the cathode active material was constantly stirred.

[0125] Surface analysis was performed using X-ray photoelectron spectroscopy. Fig. 4 shows the peaks attributed to Al2p in the X-ray photoelectron spectra of the surface of the coated cathode active material of Example 1 measured by X-ray photoelectron spectroscopy and of the Al2O3 powder. The full width at half maximum of the peak attributed to Al2p of Example 1 is wider than that of the peak attributed to Al2p of the spectrum in which the Al2O3 powder was measured. From this, it can be seen that the valence of Al has changed. As described above, it was confirmed that a film containing Al2O x (0 < x < 3) was formed.

[0126] Also, as a result of surface analysis using X-ray photoelectron spectroscopy, the Al / Ni atomic ratio on the surface of the coated cathode active material of Example 1 was 2.89, and the Al / Co atomic ratio was 4.56. These atomic ratios were calculated from the peak intensities and sensitivity coefficients of the respective elements. The surface analysis was performed using an X-ray photoelectron spectrometer (manufactured by ULVAC-PHI, Inc., Quantera).

[0127] (Preparation of Cathode Composite Material) Under a dry argon atmosphere, the first solid electrolyte material, the coated cathode active material, and vapor-grown carbon fiber (VGCF (manufactured by Showa Denko K.K.)) as a conductive assistant were weighed at a weight ratio of 34:64:2. By mixing these in an agate mortar, a cathode composite material was prepared. Note that VGCF is a registered trademark of Showa Denko K.K.

[0128] (Preparation of Battery) Inside an insulating outer casing, 13.1 mg of positive electrode composite material, 80 mg of first solid electrolyte material, and 80 mg of solid electrolyte material Li6PS5Cl (manufactured by MSE) were layered in sequence. This was pressure-molded at a pressure of 720 MPa to produce a laminate consisting of a positive electrode and a solid electrolyte layer. Next, on the side of the solid electrolyte layer opposite to the side in contact with the positive electrode, metallic In (thickness 200 μm), metallic Li (thickness 300 μm), and metallic In (thickness 200 μm) were layered in sequence. This was pressure-molded at a pressure of 80 MPa to produce a laminate consisting of a positive electrode, a solid electrolyte layer, and a negative electrode. Next, stainless steel current collectors were placed above and below the laminate, i.e., at the positive and negative electrodes, and current collector leads were attached to the current collectors. Finally, the battery according to Example 1 was fabricated by sealing the inside of the insulating outer casing from the outside atmosphere using an insulating ferrule.

[0129] (Charge / Discharge Test) Using the battery from Example 1 described above, a charge-discharge test was performed as follows.

[0130] The battery was placed in a constant temperature bath at 25°C.

[0131] Constant current charging was performed at a current of 130 μA until the potential relative to Li / In reached 3.68 V. After that, constant voltage charging was performed with the current at the end of the constant voltage charging period set to 26 μA.

[0132] Next, a constant current discharge was performed at a current of 130 μA until the potential relative to Li / In reached 1.88 V. After that, a constant voltage discharge was performed with the current at the end of the constant voltage discharge set to 26 μA.

[0133] The above charging and discharging process constituted one cycle, and a cycle test was conducted. Table 1 shows the discharge capacity after the first cycle and the discharge retention rate after 50 cycles for the battery of Example 1.

[0134] The discharge retention rate at 50 cycles is the ratio of the discharge capacity at 50 cycles to the discharge capacity at 1 cycle. A discharge retention rate exceeding 100% at 50 cycles is due to a decrease in resistance and an increase in capacity during the first few cycles.

[0135] Figure 5 shows the charge-discharge curve illustrating the initial charge-discharge characteristics of the battery in Example 1.

[0136] (Example 2) In the preparation of the positive electrode active material whose surface is coated with a coating material, the battery of Example 2 was fabricated using the same method as the battery of Example 1, except that the target film thickness was set to 1 nm.

[0137] A charge-discharge test was conducted in the same manner as in Example 1. Table 1 shows the discharge capacity of the battery in Example 2 after 1 cycle and the discharge retention rate after 50 cycles. Figure 5 shows the charge-discharge curve illustrating the initial charge-discharge characteristics of the battery in Example 2.

[0138] (Example 3) In the preparation of the positive electrode active material whose surface is coated with a coating material, the battery of Example 3 was fabricated using the same method as the battery of Example 1, except that the target film thickness was set to 3 nm.

[0139] A charge-discharge test was conducted in the same manner as in Example 1. Table 1 shows the discharge capacity after the first cycle and the discharge retention rate after 50 cycles for the battery of Example 3. Figure 5 shows the charge-discharge curve illustrating the initial charge-discharge characteristics of the battery of Example 3.

[0140] (Comparative Example 1) The positive electrode mixture for Comparative Example 1 was prepared by weighing the positive electrode active material NCM, the first solid electrolyte material, and the conductive additive VGCF in a mass ratio of 34:64:2 and mixing them in a mortar. In other words, the positive electrode active material used in Comparative Example 1 was not coated with a coating material. Except as described above, the battery of Comparative Example 1 was prepared in the same manner as the battery of Example 1.

[0141] A charge-discharge test was conducted in the same manner as in Example 1. Table 1 shows the discharge capacity at the first cycle and the discharge retention rate at 50 cycles for the battery of Comparative Example 1. Figure 5 shows the charge-discharge curve illustrating the initial charge-discharge characteristics of the battery of Comparative Example 1.

[0142] In Comparative Example 1, the discharge retention rate at 50 cycles is lower compared to the batteries in Examples 1 to 3. This is because, since the positive electrode material does not contain a coating material, the resistance increases due to oxidative decomposition of the solid electrolyte, and the discharge capacity decreases. As shown in Figure 5, the initial charge capacity of the battery in Comparative Example 1 is larger compared to the batteries in Examples 1 to 3. This is because oxidative decomposition of the solid electrolyte occurs during the initial charging of the battery in Comparative Example 1, and this oxidation reaction increases the apparent charge capacity.

[0143] (Comparative Example 2) Using sputtering, a coating material was deposited on the positive electrode active material NCM with Al as the target, a target film thickness of 2 nm, and while adjusting the oxygen flow rate.

[0144] Surface analysis of the coated cathode active material of Comparative Example 2 was performed using X-ray photoelectron spectroscopy. Figure 4 shows the peaks attributed to Al2p in the X-ray photoelectron spectra of the surface of the coated cathode active material of Comparative Example 2 and the Al2O3 powder, as measured by X-ray photoelectron spectroscopy. The full width at half maximum of the peaks attributed to Al2p was approximately the same as the full width at half maximum of the peaks attributed to Al2p in the spectrum measured for the Al2O3 powder. Thus, it was confirmed that an Al2O3 coating was formed on the surface of the cathode active material of Comparative Example 2.

[0145] The battery of Comparative Example 2 was fabricated using the same method as the battery of Example 1.

[0146] A charge-discharge test was conducted in the same manner as in Example 1. Table 1 shows the discharge capacity after the first cycle and the discharge retention rate after 50 cycles for Comparative Example 2. Figure 5 shows the charge-discharge curve illustrating the initial charge-discharge characteristics of the battery in Comparative Example 2.

[0147] In Comparative Example 2, the discharge capacity at the first cycle and the discharge retention rate at 50 cycles are lower compared to the batteries in Examples 1 to 3. Furthermore, Figure 5 shows that the charge capacity and discharge voltage of the battery in Comparative Example 2 are lower compared to the battery in Comparative Example 1. These findings indicate that, compared to Comparative Example 1, the coating suppresses the oxidative decomposition of the solid electrolyte during charging, but an increase in resistance occurs due to the Al2O3 coating.

[0148] [Table 1]

[0149] Example 1 shows a higher discharge maintenance rate at 50 cycles than Example 2. This is likely because the surface of the positive electrode active material was sufficiently coated, effectively suppressing the oxidative decomposition of the solid electrolyte. [Industrial applicability]

[0150] The all-solid-state battery described herein is suitably used, for example, as a power source for mobile devices such as smartphones, a power source for vehicles such as electric vehicles, a power source for various in-vehicle equipment, and a storage device for natural energy such as solar power. [Explanation of Symbols]

[0151] 1000 Cathode Materials 110 Cathode active material 100 First solid electrolyte material 120 Coating material 130 Negative electrode active material 140 Second solid electrolyte material 150 Coated positive electrode active material 2000 batteries 201 Positive electrode 202 Solid electrolyte layer 203 Negative electrode 300 pressure molding dies 301 Punch Top 302 Frame type 303 Punch bottom 101 Powder of solid electrolyte material

Claims

1. Positive electrode active material and, A coating material that covers at least a portion of the surface of the positive electrode active material, A coated positive electrode active material containing, First solid electrolyte material and Includes, The aforementioned coating material is Al 2 O x (Including 0 < x < 3), The positive electrode active material includes a material represented by the following composition formula (2): LiNi α Co β Me 1-α-β O 2 ...Formula (2) Here, α and β satisfy 0 ≤ α < 1, 0 ≤ β ≤ 1, and 0 ≤ 1 - α - β ≤ 0.35, and Me is at least one selected from the group consisting of Al and Mn. The first solid electrolyte material comprises Li, M, and X, M is at least one selected from the group consisting of metallic elements and metalloid elements other than Li. X is at least one selected from the group consisting of F, Cl, Br, and I. Cathode material.

2. The coating material is substantially composed of Al and O, and in the spectrum obtained by X-ray photoelectron spectroscopy of the surface of the coating cathode active material, the full width at half maximum of the peak attributed to Al2p exceeds 1.80 eV. The positive electrode material according to claim 1.

3. Satisfying at least one selected from the following groups (A) and (B): The positive electrode material according to claim 1. (A) The Al / Ni atomic ratio on the surface of the coated positive electrode active material is 2.9 or less. (B) The Al / Co atomic ratio on the surface of the coated positive electrode active material is 4.6 or less.

4. Positive electrode and, The negative electrode and, A solid electrolyte layer is provided between the positive electrode and the negative electrode, Equipped with, The positive electrode includes the positive electrode material described in any one of claims 1 to 3. battery.

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