Lithium-ion battery

Abstract

To provide a lithium-ion battery capable of suppressing the increase of resistance at high potential.SOLUTION: The lithium-ion battery includes a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer. At least one of the positive electrode active material layer and the electrolyte layer includes a sulfide. The positive electrode active material layer includes an active material composite. The active material composite has a positive electrode active material and a reaction-suppressing part formed in at least a part of the surface of the positive electrode active material. The positive electrode active material is in contact with the sulfide via the reaction-suppressing part. The reaction-suppressing part includes oxides that have at least Li, Nb, P, and O as constituent elements.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application discloses a lithium-ion battery. [Background technology]

[0002] Patent Document 1 discloses an all-solid-state battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, wherein at least one of the positive electrode active material layer and the solid electrolyte layer contains a sulfide solid electrolyte material, and the positive electrode active material layer contains an active material composite, and the active material composite has a positive electrode active material and a reaction suppressor provided on at least a portion of a surface of the positive electrode active material, the positive electrode active material being in contact with the sulfide solid electrolyte material via the reaction suppressor, and the reaction suppressor contains a first lithium ion conductor and a second lithium ion conductor, wherein the first lithium ion conductor is LiNbO3 and the second lithium ion conductor is a Li-containing compound having a polyanion structure containing at least one of B, Si, P, Ti, Zr, Al, and W. Patent Document 2 also discloses an active material composite particle comprising an active material and a lithium niobate layer formed on the surface of the active material, the lithium niobate layer containing nitrogen. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-026003 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-170973 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, active material composites having reaction suppression parts containing lithium niobate are used in lithium ion batteries. However, lithium ion batteries constructed using such active material composites are prone to increase in resistance, for example, when charged and discharged at a high potential (when the positive electrode potential becomes high). [Means for solving the problem]

[0005] As one of the means for solving the above problems, the present application provides: A lithium ion battery comprising a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, at least one of the positive electrode active material layer and the electrolyte layer contains a sulfide, the positive electrode active material layer contains an active material composite, the active material composite has a positive electrode active material and a reaction suppressor provided on at least a portion of a surface of the positive electrode active material, the positive electrode active material is in contact with the sulfide via the reaction suppression unit, The reaction suppression portion contains an oxide having at least Li, Nb, P, and O as constituent elements. Lithium-ion battery Disclose.

[0006] In the lithium ion battery of the present disclosure, the molar ratio Nb / P of Nb to P in the oxide may be 1 or more and 9 or less.

[0007] In the lithium-ion battery of the present disclosure, at least one of the positive electrode active material layer and the electrolyte layer may contain a sulfide solid electrolyte as the sulfide.

[0008] The lithium ion battery of the present disclosure may be an all-solid-state battery. [Effects of the Invention]

[0009] The lithium-ion battery of the present disclosure is less likely to experience an increase in resistance even when the positive electrode potential is high. This is thought to be because the use of an oxide containing P in addition to Li, Nb, and O in the reaction suppression section of the active material composite increases the decomposition voltage of the oxide compared to when LiNbO, which does not contain P, and improves the voltage resistance of the reaction suppression section. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows a schematic cross-sectional configuration of a lithium-ion battery. [Figure 2] 1 shows the results of measuring the resistance of the lithium ion battery according to the example after a cycle test. [Figure 3] 1 shows the results of measuring the resistance after a cycle test for a lithium ion battery according to a comparative example. [Figure 4] 1 shows the results of measuring the resistance of the lithium ion battery according to the example after a durability test. [Figure 5] 1 shows the results of measuring the resistance after a durability test for a lithium ion battery according to a comparative example. [Figure 6] The decomposition voltage of oxides (LiNbO3 or P-substituted LiNbOx) calculated by first principles is shown. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1. Lithium-ion battery FIG. 1 shows a schematic configuration of a lithium-ion battery 100 according to one embodiment. As shown in FIG. 1, the lithium-ion battery 100 includes a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30. At least one of the positive electrode active material layer 10 and the electrolyte layer 20 contains a sulfide 15. The positive electrode active material layer 10 includes an active material composite 11. The active material composite 11 includes a positive electrode active material 11a and a reaction suppression portion 11b provided on at least a portion of the surface of the positive electrode active material 11a. The positive electrode active material 11a is in contact with the sulfide 15 via the reaction suppression portion 11b. The reaction suppression portion 11b contains an oxide having at least Li, Nb, P, and O as constituent elements.

[0012] 1.1 Cathode active material layer The positive electrode active material layer 10 includes an active material composite 11. The positive electrode active material layer 10 may optionally include an electrolyte, a conductive additive, a binder, and the like. The contents of the active material, electrolyte, conductive additive, binder, and the like in the positive electrode active material layer 10 may be appropriately determined depending on the desired battery performance. For example, when the entire positive electrode active material layer 10 (total solid content) is taken as 100 mass%, the content of the active material composite 11 may be 30 mass% or more, 40 mass% or more, or 50 mass% or more, or 100 mass% or less, 95 mass% or less, 90 mass% or less, or 85 mass% or less. The shape of the positive electrode active material layer 10 is not particularly limited and may be, for example, a substantially flat sheet. The thickness of the positive electrode active material layer 10 is not particularly limited and may be, for example, 0.1 μm or more or 1 μm or more, and 2 mm or less or 1 mm or less.

[0013] 1.1.1 Active material composite The active material composite 11 has a positive electrode active material 11a and a reaction suppression portion 11b provided on at least a portion of the surface of the positive electrode active material 11a. In the active material composite 11, the reaction suppression portion 11b may be provided on at least a portion of the surface of the positive electrode active material 11a, and may cover 70% or more or 90% or more of the surface of the positive electrode active material 11a. The upper limit of the coverage is not particularly limited, and may be 100%. The coverage of the reaction suppression portion 11b on the surface of the positive electrode active material 11a can be calculated based on a scanning electron microscope (SEM) image of a cross section of the active material composite 11, or can be calculated by calculating the element ratio on the surface of the active material composite 11 using X-ray photoelectron spectroscopy (XPS).

[0014] (Cathode active material) The positive electrode active material 11a may be a known positive electrode active material for lithium ion batteries. The positive electrode active material 11a may be, for example, a lithium-containing oxide. Specifically, the lithium-containing oxide serving as the positive electrode active material 11a may contain at least Li, at least one transition metal element selected from Co, Ni, and Mn, and O. Alternatively, the lithium-containing oxide serving as the positive electrode active material 11a may contain Ti or Fe as a transition metal element. The lithium-containing oxide serving as the positive electrode active material 11a may also contain an element other than a transition metal element, such as Al or Mg. Furthermore, lithium metal phosphates (such as LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4) containing at least Li, the transition metal element, P, and O may also be included in the lithium-containing oxide serving as the positive electrode active material 11a. In particular, the technology of the present disclosure can be expected to have a more effective effect when the lithium-containing oxide serving as the positive electrode active material 11a contains at least Li, at least one transition metal element selected from Co, Ni, and Mn, and O. Specific examples of such lithium-containing oxides include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and oxides in which some elements of these oxides are substituted with other elements, such as Li a Mn x Ni y Co z O 2±δ(0 < a ≤ 1.5, 0 ≤ x ≤ 1.5, 0 ≤ y ≤ 1.5, 0 ≤ z ≤ 1.5, 0 < x + y + z < 1.5), etc. are included. The lithium-containing oxide as the positive electrode active material 11a may, for example, have an O2-type structure, an O3-type structure, or a crystal structure other than these. Only one type of the positive electrode active material 11a may be used alone, or two or more types may be combined and used.

[0015] The shape of the positive electrode active material 11a is not particularly limited. For example, the positive electrode active material 11a may be particulate, or may have other shapes (such as layered or film-like). When the positive electrode active material 11a is particulate, the particles may be solid particles or hollow particles. When the positive electrode active material 11a is particulate, the particles may be primary particles or secondary particles formed by aggregation of a plurality of primary particles. When the positive electrode active material 11a is particulate, the average particle diameter (D50) of the particles may be, for example, 1 nm or more, 5 nm or more, 10 nm or more, 50 nm or more, 100 nm or more, or 500 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Further, when the positive electrode active material 11a is particulate, the BET specific surface area of the particles may be, for example, 0.1 m 2 / g or more or 0.2 m 2 / g or more, and may also be 5.0 m 2 / g or less or 2.0 m 2 / g or less. Incidentally, the average particle diameter D50 is the particle diameter (median diameter) at the integrated value of 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0016] (Reaction suppression part) The reaction suppression unit 11b has a function of suppressing a reaction between the positive electrode active material 11a and the sulfide 15 due to direct contact therebetween, for example, and protects the positive electrode active material 11a by covering at least a portion of the surface of the positive electrode active material 11a. The reaction suppression unit 11b includes an oxide having at least Li, Nb, P, and O as constituent elements. The oxide may have a composition in which a portion of the Nb in lithium niobate is substituted with P, for example. The oxide may also include some doping element other than Li, Nb, P, and O, as long as the effect of the oxide is not impaired. The oxide may be amorphous or crystalline. The reaction suppression unit 11b may also include components other than the oxide as long as the effect of the oxide is not impaired. Alternatively, the reaction suppression unit 11b may be substantially free of components other than the oxide.

[0017] In the lithium-ion battery 100, the oxide constituting the reaction suppression unit 11b contains P in addition to Li, Nb, and O, improving the voltage resistance of the reaction suppression unit 11b (increasing the decomposition potential of the reaction suppression unit 11b). This makes it difficult for the reaction suppression unit 11b to decompose, and the battery resistance is unlikely to increase, even when the positive electrode potential becomes high due to charging and discharging at a high potential. For example, the decomposition potential of LiNbO3, which does not contain P, is calculated to be 3.4 V (vs. Li + / Li), whereas the decomposition potential is 3.4V (vs. Li) due to substitution with P. + In this regard, the lithium ion battery 100 of the present disclosure can be improved significantly to a predetermined potential exceeding 3.4 V (vs. Li) at the end-of-charge potential. + / Li). The charge and discharge of the lithium ion battery may be controlled by a known control means.

[0018] Although the ratio of each element in an oxide having at least Li, Nb, P, and O as constituent elements is not particularly limited, when the molar ratio Nb / P of Nb to P in the oxide is 1 or more and 9 or less (i.e., when the molar ratio Nb:P is 5:5 to 9:1), the voltage resistance of reaction suppression unit 11b is more likely to be improved. The molar ratio Li / (Nb+P) of Li to the sum of Nb and P is not particularly limited, but may be, for example, 0.5 or more or 0.8 or more, or 1.5 or less or 1.2 or less. Furthermore, the molar ratio O / (Nb+P) of O to the sum of Nb and P is not particularly limited, but may be, for example, 2.5 or more or 2.8 or more, and 3.5 or less or 3.2 or less.

[0019] The reaction suppression unit 11b may be formed as a layer on the surface of the positive electrode active material 11a. That is, the reaction suppression unit 11b may be a coating layer that covers at least a portion of the surface of the positive electrode active material 11a. The thickness of the coating layer is not particularly limited and may be, for example, 0.1 nm or more, 0.5 nm or more, or 1 nm or more, or 500 nm or less, 300 nm or less, 100 nm or less, 50 nm or less, or 20 nm or less.

[0020] 1.1.2 Electrolytes The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolytic solution). For example, when the lithium ion battery 100 is an all-solid-state battery, the positive electrode active material layer 10 may contain a solid electrolyte as the electrolyte. When the lithium ion battery 100 is an electrolyte solution battery, the positive electrode active material layer 10 may contain an electrolyte solution as the electrolyte.

[0021] (solid electrolyte) The solid electrolyte may be any known solid electrolyte for lithium ion batteries. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have higher ionic conductivity than organic polymer electrolytes. They also have superior heat resistance than organic polymer electrolytes. Examples of inorganic solid electrolytes include lithium lanthanum zirconate, LiPON, and Li 1+X Al X Ge 2-X Examples of suitable solid electrolytes include oxide solid electrolytes such as (PO4)3, Li-SiO-based glass, and Li-Al-SO-based glass; and sulfide solid electrolytes such as Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, and Li2S-P2S5-GeS2. Sulfide solid electrolytes, especially sulfide solid electrolytes containing Li2S-P2S5, exhibit high performance. The positive electrode active material layer 10 may contain a sulfide solid electrolyte as the sulfide 15. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be, for example, particulate. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0022] (electrolyte) The electrolyte may contain, for example, lithium ions as carrier ions. The electrolyte may be an aqueous electrolyte or a non-aqueous electrolyte. The composition of the electrolyte may be the same as that of known electrolytes for lithium ion batteries. For example, the electrolyte may be a carbonate-based solvent in which a lithium salt is dissolved at a predetermined concentration. Examples of carbonate-based solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC). Examples of lithium salts include LiPF6.

[0023] 1.1.3 Conductive additives Examples of the conductive additive include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metal materials such as nickel, aluminum, and stainless steel. The conductive additive may be, for example, in the form of particles or fibers, and its size is not particularly limited. Only one type of conductive additive may be used alone, or two or more types may be used in combination.

[0024] 1.1.4 Binder Examples of binders include butadiene rubber (BR)-based binders, butylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, etc. Only one type of binder may be used alone, or two or more types may be used in combination.

[0025] 1.1.5 Other ingredients In addition to the above components, the positive electrode active material layer 10 may contain other components, such as various additives and positive electrode active materials other than the above active material composites.

[0026] 1.2 Electrolyte layer The electrolyte layer 20 contains at least an electrolyte. When the lithium-ion battery 100 is an all-solid-state battery, the electrolyte layer 20 contains a solid electrolyte and may further contain an optional binder or the like. In this case, the contents of the solid electrolyte and binder or the like in the electrolyte layer 20 are not particularly limited. On the other hand, when the lithium-ion battery 100 is an electrolyte battery, the electrolyte layer 20 contains an electrolyte solution and may further have a separator or the like for retaining the electrolyte solution and preventing contact between the positive electrode active material layer 10 and the negative electrode active material layer 30. The thickness of the electrolyte layer 20 is not particularly limited and may be, for example, 0.1 μm or more or 1 μm or more, or 2 mm or less or 1 mm or less.

[0027] The solid electrolyte, the electrolyte solution, the binder, and the like are as described above. As described above, the electrolyte layer 20 may contain a sulfide 15. For example, the electrolyte layer 20 may contain a sulfide solid electrolyte as the sulfide 15. The separator may be any separator commonly used in lithium-ion batteries, such as a separator made of a resin such as polyethylene (PE), polypropylene (PP), polyester, or polyamide. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a two-layer structure of PE / PP, or a three-layer structure of PP / PE / PP or PE / PP / PE. The separator may be made of a nonwoven fabric such as a cellulose nonwoven fabric, a resin nonwoven fabric, or a glass fiber nonwoven fabric.

[0028] 1.3 Negative electrode active material layer The negative electrode active material layer 30 contains a negative electrode active material. The negative electrode active material layer 30 may also optionally contain an electrolyte, a conductive additive, and a binder. The contents of the active material, electrolyte, conductive additive, binder, and the like in the negative electrode active material layer 30 may be appropriately determined depending on the desired battery performance. For example, when the entire negative electrode active material layer 30 (total solid content) is taken as 100 mass%, the content of the negative electrode active material may be 30 mass% or more, 40 mass% or more, or 50 mass% or more, or 100 mass% or less, 95 mass% or less, 90 mass% or less, or 85 mass% or less. The shape of the negative electrode active material layer 30 is not particularly limited and may be, for example, a substantially flat sheet. The thickness of the negative electrode active material layer 30 is not particularly limited and may be, for example, 0.1 μm or more or 1 μm or more, and 2 mm or less or 1 mm or less. The thickness and area of the negative electrode active material layer 30 may be determined so that the negative electrode capacity is greater than the positive electrode capacity.

[0029] 1.3.1 Negative electrode active material The negative electrode active material may be any of those known as negative electrode active materials for lithium ion batteries, and may include various materials whose potential for absorbing and releasing lithium ions (charge / discharge potential) is lower than that of the positive electrode active material 11a. Examples of such materials include silicon-based active materials such as Si, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium and lithium alloys. The negative electrode active materials may be used singly or in combination of two or more.

[0030] The shape of the negative electrode active material may be any shape commonly used for negative electrode active materials in lithium ion batteries. For example, the negative electrode active material may be in the form of particles. The negative electrode active material particles may be primary particles or secondary particles formed by aggregation of multiple primary particles. The average particle diameter (D50) of the negative electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

[0031] 1.3.2 Electrolytes, Conductive Aids and Binders Examples of electrolytes that can be contained in the anode active material layer 30 include the above-mentioned solid electrolytes and electrolytic solutions. When the lithium-ion battery 100 is an all-solid-state battery, the performance of the battery is likely to be improved when the anode active material layer 30 contains a solid electrolyte, particularly a sulfide solid electrolyte, and even more particularly a sulfide solid electrolyte containing Li2S-P2S5. Examples of conductive additives that can be contained in the anode active material layer 30 include the above-mentioned carbon materials and metal materials. The binder that can be contained in the anode active material layer 30 may be appropriately selected from, for example, the binders that can be contained in the above-mentioned cathode active material layer 10.

[0032] 1.4 Positive electrode current collector As shown in FIG. 1 , the lithium-ion battery 100 may include a positive electrode current collector 40 in contact with the positive electrode active material layer 10. Any common positive electrode current collector for lithium-ion batteries can be used as the positive electrode current collector 40. The positive electrode current collector 40 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The positive electrode current collector 40 may be made of a metal foil or metal mesh. Metal foils are particularly easy to handle. The positive electrode current collector 40 may be made of multiple foils. Metals constituting the positive electrode current collector 40 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, the positive electrode current collector 40 may contain Al to ensure oxidation resistance. The positive electrode current collector 40 may have a coating layer on its surface for purposes such as adjusting resistance. The positive electrode current collector 40 may be a metal foil or a substrate plated or vapor-deposited with the above metal. When the positive electrode current collector 40 is made of multiple metal foils, some layer may be present between the multiple metal foils. The thickness of the positive electrode current collector 40 is not particularly limited. For example, it may be 0.1 μm or more, 1 μm or more, or 1 mm or less, or 100 μm or less.

[0033] 1.5 Negative electrode current collector As shown in FIG. 1 , the lithium-ion battery 100 may include a negative electrode current collector 50 in contact with the negative electrode active material layer 30. The negative electrode current collector 50 may be any of those commonly used as negative electrode current collectors for lithium-ion batteries. The negative electrode current collector 50 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The negative electrode current collector 50 may be a metal foil, a metal mesh, or a carbon sheet. Metal foils are particularly advantageous in terms of ease of handling. The negative electrode current collector 50 may be composed of multiple foils or sheets. Examples of metals constituting the negative electrode current collector 50 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, from the viewpoints of ensuring reduction resistance and being less likely to alloy with lithium, the negative electrode current collector 50 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 50 may have some kind of coating layer on its surface for the purpose of adjusting the resistance, etc. Alternatively, the negative electrode current collector 50 may be a metal foil or a substrate on which the above metal is plated or vapor-deposited. Alternatively, when the negative electrode current collector 50 is made of multiple sheets of metal foil, some kind of layer may be present between the multiple sheets of metal foil. The thickness of the negative electrode current collector 50 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0034] 1.6 Supplementary Information The lithium ion battery 100 may have other general battery components in addition to the components described above. For example, the lithium ion battery 100 may have each of the components described above housed inside an exterior body. Any known battery exterior body can be used as the exterior body. Furthermore, a plurality of lithium ion batteries 100 may be electrically connected and stacked in any manner to form an assembled battery. In this case, the assembled battery may be housed inside a known battery case. The lithium ion battery 100 may also have other obvious components such as necessary terminals. The lithium ion battery 100 may have, for example, a coin type, a laminate type, a cylindrical type, a prismatic type, or the like in its shape.

[0035] Although the lithium-ion battery 100 shown in FIG. 1 includes a configuration in which the sulfide 15 (e.g., a sulfide solid electrolyte) is contained in both the positive electrode active material layer 10 and the electrolyte layer 20, the technology of the present disclosure is not limited to this configuration. When the sulfide 15 is contained in at least one of the positive electrode active material layer 10 and the electrolyte layer 20, the active material composite 11 included in the positive electrode active material layer 10 comes into contact with the sulfide 15. The sulfide 15 is not limited to that contained as the sulfide solid electrolyte. The sulfide 15 may be contained as a sulfur-based or sulfide-based positive electrode active material, or may be contained as a constituent of other positive electrode materials. The sulfide 15 that can be contained in the electrolyte layer 20 is also not limited to that contained as a sulfide solid electrolyte, and may be a sulfur-based or sulfide-based battery material other than a sulfide solid electrolyte.

[0036] 2. Cathode materials The technology of the present disclosure also has an aspect as a positive electrode material (positive electrode mixture). That is, the positive electrode material of the present disclosure includes the above-described active material composite 11 and sulfide 15, and the positive electrode active material 11a is in contact with the sulfide 15 via the reaction suppression portion 11b. Details of the active material composite 11 are as described above. The sulfide 15 may be the above-described sulfide solid electrolyte. The positive electrode material may be obtained by mixing the active material composite 11 and the sulfide 15.

[0037] 3. Method for manufacturing active material composite The technology of the present disclosure also has an aspect as a method for producing an active material composite. That is, the method for producing an active material composite of the present disclosure includes the following steps: Preparing a positive electrode active material 11a; and At least a part of the surface of the positive electrode active material 11a is coated with an oxide having at least Li, Nb, P, and O as constituent elements, thereby forming a reaction suppression portion 11b on at least a part of the surface of the positive electrode active material 11a. Includes.

[0038] 3.1 Preparation of positive electrode active material The positive electrode active material 11a is as described above. For example, particles having a desired chemical composition and crystal structure may be synthesized as the positive electrode active material 11a. Alternatively, a film or layer having a desired chemical composition and crystal structure may be prepared.

[0039] 3.2 Formation of reaction suppression part When forming reaction suppression portion 11b on at least a portion of the surface of positive electrode active material 11a, various methods are possible for coating at least a portion of the surface of positive electrode active material 11a with an oxide containing at least Li, Nb, P, and O as constituent elements. For example, a coating liquid containing a Li source, an Nb source, and a P source may be brought into contact with and adhered to the surface of positive electrode active material 11a, followed by drying and optionally heating (firing), thereby forming reaction suppression portion 11b made of a desired oxide on the surface of positive electrode active material 11a.

[0040] The coating liquid containing the Li source, the Nb source, and the P source may be an aqueous solution or a solution using an organic solvent such as alcohol. In the coating liquid, the Li source, the Nb source, and the P source may each be present in an ionic state or in a state other than an ionic state.

[0041] The method for contacting and adhering the coating liquid to the surface of the positive electrode active material 11a and the method for drying the coating liquid are not particularly limited. For example, a tumbling fluidized coating device, a spray dryer, or the like can be used to contact and adsorb the coating liquid containing a Li source, an Nb source, and a P source to the surface of the positive electrode active material 11a, and then the coating liquid can be dried. The precursor obtained after drying can be optionally fired to form the reaction suppression portion 11b on at least a portion of the surface of the positive electrode active material 11a. In this case, the thickness and coverage (coverage area) of the reaction suppression portion 11b on the surface of the positive electrode active material 11a can be controlled by adjusting the tumbling fluidized coating conditions and the spray drying conditions.

[0042] Alternatively, a layer made of an oxide containing Li, Nb, P, and O may be formed by sputtering on the surface of the positive electrode active material 11a using an oxide as a sputtering target. In addition, a reaction suppression portion can be formed on at least a portion of the surface of the positive electrode active material by various other methods.

[0043] 4. Lithium-ion battery manufacturing method The technology of the present disclosure also has an aspect of a method for manufacturing a lithium ion battery. That is, the method for manufacturing a lithium ion battery of the present disclosure includes the following steps: Obtaining an active material composite 11 by a method for producing an active material composite according to the present disclosure; forming a positive electrode active material layer 10 using the active material composite 11; forming an electrolyte layer 20; and forming a negative electrode active material layer 30; Including, At least one of the positive electrode active material layer 10 and the electrolyte layer 20 contains a sulfide 15; Includes.

[0044] The positive electrode active material layer 10, the electrolyte layer 20, and the negative electrode active material layer 30 can be easily formed by, for example, dry or wet molding a mixture containing the various components described above. The method for manufacturing a lithium ion battery according to the present disclosure may employ the same steps as those for manufacturing conventional lithium ion batteries, except for using the active material composite 11 described above. Such manufacturing steps are self-evident, and therefore will not be described in detail here. [Example]

[0045] The technology of the present disclosure will be described in more detail below with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0046] 1. Example 1.1 Coating of positive electrode active material by barrel sputtering Cathode active material (LiMn 1 / 3 Ni 1 / 3 Co 1 / 3An active material composite was obtained by coating 10 g of particles (having an O3 type structure with O2 as the main phase) with a first sputtering target so that the coating layer, which serves as a reaction suppressor, was 10 nm thick. Here, the first sputtering target contained Li, Nb, P, and O as constituent elements.

[0047] 1.2 Identifying the composition of the coating layer After 24 hours of deposition on the Al foil using the first sputtering target, the composition of the coating layer was identified by ICP measurement. As a result, the coating layer formed by the first sputtering target was found to be composed of LiNb 0.9 P 0.1 O x (x is undefined)

[0048] 1.3 Preparation of the positive electrode active material layer A PVDF binder (manufactured by Kureha Corporation), the active material composite obtained above, a solid electrolyte (Li2S-P2S5-based glass ceramics), a conductive additive (vapor-grown carbon fiber, VGCF, manufactured by Showa Denko), and a solvent were added to a polypropylene (PP) container and stirred for 30 seconds using an ultrasonic disperser (UH-50 manufactured by SMT). The PP container was then shaken for 3 minutes using a shaker (TTM-1 manufactured by Shibata Scientific Co., Ltd.) and further stirred for 30 seconds using the ultrasonic disperser to obtain a coating solution. The resulting coating solution was applied to an Al foil (manufactured by Nippon Foil Co., Ltd.) substrate using an applicator by the blade method. After air drying, the mixture was dried on a hot plate at 100 °C for 30 minutes to obtain transfer material A, which had a positive electrode active material layer on one surface of the Al foil substrate.

[0049] 1.4 Preparation of the positive electrode current collector Carbon black and a PVDF-based binder were weighed out in a mass ratio of 30:70, and a solvent was added to obtain a coating solution. Using an applicator, the coating solution was applied to an Al foil (thickness: 15 μm) by the blade method, allowed to air dry, and then dried on a hot plate at 100°C for 30 minutes. This resulted in a positive electrode current collector having a 2 μm-thick carbon layer on one surface of the Al foil. The resulting positive electrode current collector was punched out to a size larger than the positive electrode active material layer obtained above.

[0050] 1.5 Preparation of the negative electrode A PVDF binder (manufactured by Kureha Corporation), anode active material (lithium titanate (LTO)), the above-mentioned solid electrolyte, and a solvent were added to a PP container and stirred for 30 seconds using an ultrasonic disperser (UH-50 manufactured by SMT) to obtain a coating solution. Next, the obtained coating solution was applied to a Cu foil (anode current collector) by a blade method using an applicator. After air drying, the foil was dried on a hot plate at 100°C for 30 minutes. This formed a cathode active material layer on one surface of the Cu foil. Subsequently, the same treatment was performed to form a cathode active material layer on the other surface of the Cu foil (anode current collector), obtaining a cathode.

[0051] 1.6 Preparation of electrolyte layer Butyl butyrate and the above-mentioned solid electrolyte were added to a PP container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). Next, the PP container was shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Technology) and further stirred for 30 seconds using the ultrasonic disperser to obtain a coating solution. The obtained coating solution was applied to an Al foil (Nippon Foil Co., Ltd.) substrate using an applicator by the blade method, and after natural drying, it was dried on a hot plate at 100°C for 30 minutes to obtain transfer material B having a solid electrolyte layer on one surface of the Al foil substrate.

[0052] 1.7 Fabrication of Lithium-ion Battery for Evaluation Two transfer materials B were prepared, each placed on the negative electrode active material layer formed on both sides of the negative electrode current collector and pressed, and the Al foil substrate of transfer material B was peeled off. This resulted in a laminate having a structure consisting of a solid electrolyte layer / negative electrode active material layer / negative electrode current collector / negative electrode active material layer / solid electrolyte layer. The resulting laminate was punched out to a size larger than the positive electrode current collector obtained above. Next, two transfer materials A were prepared, each placed on the solid electrolyte layer and pressed, and the Al foil substrate of transfer material A was peeled off and further pressed. This resulted in an electrode laminate having a structure consisting of a positive electrode active material layer / solid electrolyte layer / negative electrode active material layer / negative electrode current collector / negative electrode active material layer / solid electrolyte layer / positive electrode active material layer.

[0053] Next, positive electrode current collectors were attached to both sides of the electrode laminate using a binder. This resulted in an all-solid-state lithium-ion battery with a two-layer cell structure in which positive electrode current collectors were formed on both sides of the electrode laminate. At this time, the carbon layer side of the positive electrode current collector was arranged to contact the positive electrode active material layer of the electrode laminate. Furthermore, multiple two-layer cell structures were stacked, terminals were welded, and the stack was sealed with a laminate film to obtain a battery for evaluation.

[0054] 2. Comparative Example A test battery was obtained in the same manner as in the example, except that a second sputtering target was used instead of the first sputtering target. The second sputtering target contained Li, Nb, and O as constituent elements, but did not contain P. After 24 hours of film formation on an Al foil using the second sputtering target, the composition of the coating layer was determined by ICP measurement. The coating layer formed by the second sputtering target had a composition represented by LiNbO3.

[0055] 3. Measurement of Initial Resistance The resistance (cell resistance) of each evaluation battery according to the examples and comparative examples was measured. Specifically, the battery was charged at a constant current and constant voltage of 0.33 C at 25°C within the range of 1.5 to 3.0 V, then discharged at a constant current and constant voltage to an SOC of 40%, and then discharged at a rate of 3 C for 5 seconds. The resistance was calculated from the voltage drop (ΔV).

[0056] 4. Resistance measurement after cycle testing Each evaluation battery (prepared differently from the one used to measure initial resistance) according to the examples and comparative examples was repeatedly charged and discharged in a constant-current (CC) chamber at 25°C with a discharge cutoff potential of 1.5 V (vs. Li / Li+), a charge cutoff potential of 4.5 V (vs. Li / Li+), and a current density of 0.1 C. After 1, 2, 3, 4, 5, and 10 cycles of charge and discharge, each battery was discharged at 0.33 C to 1.5 V. After discharge, the battery was charged at a constant current and voltage of 25°C and 0.33 C, and then discharged at a constant current and voltage to 40% SOC. Resistance was calculated from the voltage drop (ΔV) after discharging at a rate of 3 C for 5 seconds.

[0057] 5. Resistance measurement after endurance test A durability test was conducted in a constant temperature bath at 60°C for each evaluation battery (prepared differently from the batteries used to measure the initial resistance and resistance after the cycle test) according to the examples and comparative examples. The batteries were charged to 4.5 V, 4.8 V, or 5.0 V at a constant current charge rate of 0.1 C, and then held at that potential for two weeks. After holding for two weeks, the batteries were discharged at 0.33 C to 1.5 V. After discharge, the batteries were charged at a constant current and voltage of 25°C at 0.33 C, and then discharged at a constant current and voltage to 40% SOC. Resistance was calculated from the voltage drop (ΔV) observed when the batteries were discharged at a rate of 3 C for five seconds.

[0058] 6. Amorphous structure creation, voltage resistance evaluation, and Li diffusion coefficient evaluation Using VASP (Vienna Ab initio Simulation Package), (1) amorphous structure creation, (2) voltage endurance evaluation, and (3) Li diffusion coefficient evaluation were performed. The calculation methods and conditions are as follows. Calculation method: Density Functional Theory (DFT) Calculation conditions: The exchange-correlation potential between electrons uses the PBE functional of the generalized gradient approximation (GGA). Cutoff energy for (1) and (2): 500 eV Cutoff energy at (3): 400 eV

[0059] 7. Evaluation Results 7.1 Resistance measurement results FIG. 2 shows the results of measuring the resistance after a cycle test for the evaluation battery according to the example. FIG. 3 shows the results of measuring the resistance after a cycle test for the evaluation battery according to the comparative example. FIG. 4 shows the results of measuring the resistance after a durability test for the evaluation battery according to the example. Furthermore, FIG. 5 shows the results of measuring the resistance after a durability test for the evaluation battery according to the comparative example. As is clear from the results shown in FIGS. 2 to 5, the use of LiNb as a reaction suppressing portion in the active material composite 0.9 P 0.1 O x The test battery according to the example employing LiNbO3 as the reaction suppressing portion of the active material composite showed a suppressed increase in resistance both after the cycle test and after the durability test, compared to the test battery according to the comparative example employing LiNbO3 as the reaction suppressing portion of the active material composite.

[0060] 7.2 Voltage resistance evaluation results based on first-principles calculations Figure 6 shows the oxides (LiNbO3 or P-substituted LiNbO x ) shows the decomposition voltage of the oxide. The horizontal axis is the substitution rate with P, and for example, a substitution rate of "50" means that the molar ratio of Nb to P in the oxide is 5:5. As is clear from the results shown in FIG. 6, by substituting a portion of the Nb in LiNbO3 with P, the decomposition voltage of the oxide increases, and it is thought that the voltage resistance improves. In the evaluation battery according to the example, the use of an oxide with such a high decomposition voltage is thought to have suppressed the increase in resistance both after the cycle test and after the durability test.

[0061] 8. Summary From the above results, it can be said that lithium-ion batteries having the following configurations (1) to (6) have improved voltage resistance and are less likely to increase resistance even when charged and discharged up to high potentials compared to conventional batteries that use LiNbO3 as the reaction suppression section of the active material composite. This is thought to be because the reaction suppression section of the active material composite uses an oxide containing P in addition to Li, Nb, and O, which improves the voltage resistance of the reaction suppression section.

[0062] (1) The device comprises a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer. (2) At least one of the positive electrode active material layer and the electrolyte layer contains a sulfide. (3) The positive electrode active material layer contains an active material composite. (4) The active material composite has a positive electrode active material and a reaction suppressor provided on at least a portion of the surface of the positive electrode active material. (5) The positive electrode active material is in contact with the sulfide via the reaction suppressor. (6) The reaction suppressor contains an oxide having at least Li, Nb, P, and O as constituent elements.

[0063] In the above examples, LiMn was used as the positive electrode active material. 1 / 3 Ni 1 / 3 Co 1 / 3 Although the present disclosure illustrates the use of particles having an O3-type structure with O2 as the main phase, the technology of the present disclosure can also be applied to cases where other positive electrode active materials are used. Furthermore, in the above examples, an all-solid-state lithium-ion battery was used as an example of the battery to be evaluated. However, the technology of the present disclosure can be widely applied to batteries in which the positive electrode active material comes into contact with sulfides via a reaction suppression unit, and it is believed that it can also be applied to, for example, electrolyte batteries. However, even greater effects can be expected in all-solid-state batteries, particularly all-solid-state batteries using a sulfide solid electrolyte. Furthermore, the types and forms of the electrolyte layer, negative electrode active material layer, and current collector are not limited to those shown in the above examples. [Explanation of symbols]

[0064] 10 Cathode active material layer 11 Active material composite 11a Cathode active material 11b Reaction suppression section 15 Sulfide 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector 100 Lithium-ion batteries

Claims

1. A lithium ion battery comprising a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, at least one of the positive electrode active material layer and the electrolyte layer contains a sulfide, the positive electrode active material layer contains an active material composite, the active material composite has a positive electrode active material and a reaction suppressor provided on at least a portion of a surface of the positive electrode active material, the positive electrode active material is in contact with the sulfide via the reaction suppression unit, The positive electrode active material is in particulate form and has a particle size of 0.1 m ２ / g or more 5.0m ２ / g or less BET specific surface area, the reaction suppressor includes an oxide having at least Li, Nb, P, and O as constituent elements, The oxide has a composition in which part of Nb in lithium niobate is substituted with P. Lithium-ion battery.

2. The molar ratio Nb / P of Nb to P in the oxide is 1 or more and 9 or less. The lithium ion battery of claim 1.

3. At least one of the positive electrode active material layer and the electrolyte layer contains a sulfide solid electrolyte as the sulfide. The lithium ion battery according to claim 1 or 2.

4. It is an all-solid-state battery. The lithium ion battery according to any one of claims 1 to 3.

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