Nb complex aqueous solution, method for manufacturing positive electrode active material for all-solid-state lithium ion battery, method for manufacturing positive electrode for all-solid-state lithium ion battery, and method for manufacturing all-solid-state lithium ion battery

Abstract

Provided are an aqueous Nb complex solution capable of producing a positive electrode active material for an all-solid-state lithium-ion battery having good battery characteristics, a method for producing a positive electrode active material for an all-solid-state lithium-ion battery using the same, a method for producing a positive electrode for an all-solid-state lithium-ion battery, and a method for producing an all-solid-state lithium-ion battery. [Solution] An aqueous solution of a Nb complex containing Li, Nb, and one or more elements M selected from P, Si, B, and W, wherein the molar ratio of Li to Nb: Li / Nb is 2.85 or more, and the molar ratio of Li to M: Li / M is 0.5 to 10.

Description

[Technical Field]

[0001] The present invention relates to an aqueous Nb complex solution, a method for producing a positive electrode active material for an all-solid-state lithium ion battery, a method for producing a positive electrode for an all-solid-state lithium ion battery, and a method for producing an all-solid-state lithium ion battery. [Background technology]

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become important. Among these batteries, lithium-ion secondary batteries have attracted attention from the viewpoint of their high energy density. In addition to liquid-type lithium-ion secondary batteries that use an electrolyte solution, lithium-ion secondary batteries also include all-solid-state lithium-ion batteries that use a solid electrolyte, which have been attracting attention in recent years.

[0003] An aqueous solution of Nb peroxo complex containing Li is used as a coating solution for the positive electrode active material of all-solid-state batteries. 3- ) requires a counter cation, typically an ammonium ion (NH4 + ) is used.

[0004] Patent Document 1 discloses a solution containing lithium and niobium, the solution having a D90 of 200 nm or less, based on the light scattering intensity measured by dynamic light scattering. Furthermore, ammonia water is added to a suspension containing niobium and mixed to produce a transparent solution containing a peroxo complex of niobium. It also describes that this configuration can provide a solution containing lithium and niobium, in which the presence of fine particles between the positive electrode active material and the solid electrolyte is reduced, and a method for producing the same.

[0005] Patent Document 2 discloses a solution containing lithium, a metal complex that is at least one of a niobium complex and a titanium complex, and ammonia, wherein the amount of the ammonia in the solution is 1% by mass or less and the content of hydrogen peroxide in the solution is 1% by mass or less. It also describes that such a configuration makes it possible to provide a solution containing lithium, at least one of a niobium complex and a titanium complex, which itself suppresses corrosiveness and has excellent storage stability, and is suitable for forming a coating layer that can improve the battery characteristics of an active material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7593792 [Patent Document 2] Patent No. 6882912 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, Patent Documents 1 and 2 describe coating solutions for forming a coating layer on a positive electrode active material, but both use solutions containing ammonia. However, if a coating solution with an increased amount of ammonium ions is used to coat the surface of a positive electrode active material, the battery performance of the positive electrode active material may be reduced. This is thought to be due to ammonium ions remaining in the coating layer formed on the surface of the positive electrode active material or volatilizing from the coating layer, causing the coating layer to become non-uniform and reducing performance. Furthermore, when the coating solution and the positive electrode active material must be slurried together to coat the surface of the positive electrode active material, as in the continuous coating method, an ammine complex is formed in which ammonia molecules (NH3) coordinate with Ni and Co in the positive electrode active material, which may lead to the elution of Ni and Co, resulting in a reduction in battery performance.

[0008] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an Nb complex aqueous solution capable of producing a positive electrode active material for an all-solid-state lithium-ion battery having good battery characteristics, a method for producing a positive electrode active material for an all-solid-state lithium-ion battery using the same, a method for producing a positive electrode for an all-solid-state lithium-ion battery, and a method for producing an all-solid-state lithium-ion battery. [Means for solving the problem]

[0009] The present invention, which was completed based on the above findings, is defined below. 1. Contains Li, Nb, and one or more elements M selected from P, Si, B, and W, The molar ratio of Li to Nb: Li / Nb is 2.85 or more, An aqueous solution of a Nb complex, in which the molar ratio of Li to M: Li / M is 0.5 to 10. 2. The aqueous Nb complex solution according to 1 above, wherein the molar ratio of Li to Nb: Li / Nb is 3.0 or more. 3. The aqueous Nb complex solution according to 1 or 2 above, wherein the molar ratio of Li to M: Li / M is 1.5 to 7.0. 4. The Nb complex aqueous solution according to any one of 1 to 3 above, wherein the Li concentration is 0.06 to 5 mol / L, the Nb concentration is 0.02 to 1 mol / L, and the M concentration is 0.02 to 1 mol / L. 5. The aqueous solution of an Nb complex according to any one of 1 to 4 above, wherein the Nb complex has a peroxy group. 6. A method for producing a positive electrode active material for an all-solid-state lithium ion battery, comprising a step of forming a coating layer containing an oxide of Li, Nb, and M on a surface of a positive electrode active material particle of the positive electrode active material for a lithium ion battery, using the Nb complex aqueous solution described in any one of 1 to 5 above. 7. The method for producing a positive electrode active material for an all-solid-state lithium-ion battery according to 6 above, wherein a coating layer containing the oxide of Li and Nb and the M is formed using a tumbling fluidized bed coating apparatus. 8. A method for producing a positive electrode for an all-solid-state lithium ion battery, comprising producing a positive electrode for an all-solid-state lithium ion battery using a positive electrode active material for an all-solid-state lithium ion battery obtained by the method according to 6 or 7 above. 9. A method for producing an all-solid-state lithium ion battery, comprising producing an all-solid-state lithium ion battery using a positive electrode for an all-solid-state lithium ion battery obtained by the method described in 8 above. [Effects of the Invention]

[0010] The present invention can provide an Nb complex aqueous solution capable of producing a positive electrode active material for an all-solid-state lithium-ion battery having good battery characteristics, a method for producing a positive electrode active material for an all-solid-state lithium-ion battery using the same, a method for producing a positive electrode for an all-solid-state lithium-ion battery, and a method for producing an all-solid-state lithium-ion battery. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of an all-solid-state lithium-ion battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0013] (Nb complex aqueous solution) The Nb complex aqueous solution according to the embodiment of the present invention is used as a coating solution for forming a coating layer on the surface of a positive electrode active material for a lithium-ion battery, as described below. The Nb complex aqueous solution according to the embodiment of the present invention is an aqueous solution containing Li, Nb, and one or more elements M selected from P, Si, B, and W. The Nb complex aqueous solution is not particularly limited as long as it contains Li, Nb, and one or more elements M selected from P, Si, B, and W. Examples of the Nb complex aqueous solution include an aqueous solution containing one or more of lithium hydroxide monohydrate, lithium carbonate, and lithium nitrate as a lithium source, one or more of niobium oxide, niobium hydroxide, and niobium oxalate as a niobium source, one or more of phosphoric acid, polyphosphoric acid, diphosphorus pentoxide, and phosphates as a phosphorus source, one or more of lithium silicate and silicon dioxide as a silicon source, one or more of boric acid and boron oxide as a boron source, one or more of tungsten oxide, tungstic acid, and tungstates as a tungsten source, and one or more of pure water and hydrogen peroxide.

[0014] Conventionally, in the coating solution for forming a coating layer containing Nb on the surface of the positive electrode active material for lithium-ion batteries, a peroxo complex of Nb ([Nb(O2)4] 3- ) must be prepared, which requires the use of ammonium ions (NH4 + ) has been used. However, if the coating solution contains ammonia, ammonium ions may remain in the coating layer formed on the surface of the positive electrode active material, or ammonium ions may volatilize from the coating layer, causing the coating layer to become non-uniform and resulting in a decrease in performance. In contrast, the Nb complex aqueous solution according to the embodiment of the present invention has a molar ratio of Li to Nb: Li / Nb controlled to 2.85 or more. Since the Nb complex aqueous solution according to the embodiment of the present invention has a molar ratio of Li to Nb: Li / Nb of 2.85 or more, the Nb peroxo complex ([Nb(O2)4] 3-) can be obtained. If the Nb complex aqueous solution does not contain ammonia, the resulting coating layer will not contain ammonia. As a result, ion conduction is less likely to be inhibited, and non-uniformity in the coating layer due to volatilization of ammonia does not occur. This improves the contact between the positive electrode active material / coating layer and the coating layer / solid electrolyte, thereby improving battery characteristics. Furthermore, when forming the coating layer, if the positive electrode active material is slurried with an ammonia-free Nb complex aqueous solution, there is also the effect of reducing the elution of Ni and Co from the positive electrode active material. Therefore, a positive electrode active material for an all-solid-state lithium-ion battery with good battery characteristics can be produced. The Nb complex aqueous solution according to the embodiment of the present invention may contain a trace amount of ammonia as long as the above-mentioned effects are not impaired. The Nb complex aqueous solution according to the embodiment of the present invention may contain ammonia at a concentration of 0.0050 mol / L or less, for example, 0.0001 to 0.0050 mol / L. The Nb complex aqueous solution according to the embodiment of the present invention may contain ammonia at a concentration of 0.0030 mol / L or less, for example, 0.0001 to 0.0030 mol / L. The Nb complex aqueous solution according to the embodiment of the present invention may not contain ammonia, that is, the ammonia concentration may be 0 mol / L.

[0015] The Nb complex aqueous solution according to the embodiment of the present invention preferably has a molar ratio of Li to Nb: Li / Nb of 3.0 or more. The Nb complex aqueous solution according to the embodiment of the present invention may have a molar ratio of Li to Nb: Li / Nb of 3.0 to 4.0, or may have a molar ratio of Li to Nb of 3.0 to 3.5.

[0016] The Nb complex aqueous solution according to the embodiment of the present invention has a molar ratio of Li to one or more elements M selected from P, Si, B, and W, Li / M, of 0.5 to 10. This configuration can prevent the precipitation of compounds with low ionic conductivity, such as lithium hydroxide, lithium oxide, and lithium carbonate, making it possible to obtain a coating layer with relatively high ionic conductivity. The Nb complex aqueous solution according to the embodiment of the present invention preferably has a molar ratio of Li to M, Li / M, of 1.5 to 7.0. The elements contained in the Nb complex aqueous solution can be measured using an inductively coupled plasma optical emission spectrometer (ICP-OES) after diluting it appropriately.

[0017] The Nb complex aqueous solution according to the embodiment of the present invention preferably has a Li concentration of 0.06 to 5 mol / L, a Nb concentration of 0.02 to 1 mol / L, and an M concentration of 0.02 to 1 mol / L. This configuration makes it possible to more reliably obtain a coating layer made of an oxide of Li and Nb on the surface of the positive electrode active material particles. The Nb complex aqueous solution according to the embodiment of the present invention more preferably has a Li concentration of 0.3 to 1.2 mol / L, a Nb concentration of 0.05 to 0.3 mol / L, and an M concentration of 0.05 to 0.3 mol / L.

[0018] The Nb complex aqueous solution according to the embodiment of the present invention is specifically an Nb complex aqueous solution containing Li and M. The Nb complex aqueous solution according to the embodiment of the present invention may be a peroxo complex aqueous solution in which the Nb complex has a peroxy group. Here, the term "peroxo complex" refers to a complex having a peroxy group (-OO-) on the niobium, but not all of the groups bonded to the niobium may be peroxy groups. For example, most of the groups bonded to the niobium may be peroxy groups, while some may remain as oxygen (oxy groups).

[0019] Niobium peroxo complexes can be obtained by adding hydrogen peroxide to niobic acid (niobium pentoxide hydrate). When preparing niobium peroxo complexes, it is preferable to add hydrogen peroxide in large excess relative to the niobic acid. Specifically, the molar ratio is 10 moles or more, preferably 30 moles or more, and more preferably 50 moles or more of hydrogen peroxide per mole of niobium atoms. This configuration can prevent hydrolysis of the peroxo complex from prevailing over the formation of the peroxo complex, ensuring the production of the desired niobium peroxo complex.

[0020] (Cathode active material for all-solid-state lithium-ion batteries) A positive electrode active material for an all-solid-state lithium ion battery according to an embodiment of the present invention includes a positive electrode active material for a lithium ion battery, and a coating layer containing an oxide of Li and Nb and M, which is provided on the surface of positive electrode active material particles of the positive electrode active material for a lithium ion battery.

[0021] The composition of the positive electrode active material for a lithium ion battery of the all-solid-state lithium ion battery according to the embodiment of the present invention is not particularly limited, but may be represented by the composition shown in the following formula (1). Li a Ni b Co c Mn d M e O f (1) (In formula (1), M is Ta and / or W, and 1.0≦a≦1.07, 0.60≦b≦0.92, b+c+d+e=1, 1.8≦f≦2.2, and 0.000≦e / (b+c+d+e)≦0.007.)

[0022] In the positive electrode active material for lithium ion batteries, in the above formula (1), a, which indicates the lithium composition, satisfies the condition of 1.0≦a≦1.07. Because a, which indicates the lithium composition, is 1.0 or more, it is possible to suppress the reduction of nickel due to lithium deficiency. Furthermore, because a, which indicates the lithium composition, is 1.07 or less, it is possible to suppress residual alkaline components, such as lithium carbonate and lithium hydroxide, present on the surface of the positive electrode active material particles, which may become resistance components when the battery is formed.

[0023] In the positive electrode active material for lithium-ion batteries, the sum of b, which represents the nickel composition, c, which represents the cobalt composition, d, which represents the manganese composition, and e, which represents the composition of the dopant M, in the above formula (1) is controlled to be b+c+d+e=1, i.e., 0.08≦c+d+e≦0.4, thereby improving cycle characteristics and reducing the expansion and contraction behavior of the crystal lattice due to lithium insertion and extraction during charge and discharge. When c+d+e is 0.08 or greater, the effects of the above cycle characteristics and expansion and contraction behavior are more easily achieved, and when c+d+e is 0.4 or less, the decrease in initial discharge capacity is suppressed.

[0024] The positive electrode active material for a lithium ion battery has the form of a secondary particle formed by the aggregation of a plurality of primary particles. The shape of the primary particles constituting the secondary particle is not particularly limited and may be various shapes, such as substantially spherical, substantially elliptical, substantially plate-like, or substantially needle-like. The form of the aggregate of a plurality of primary particles is also not particularly limited and may be various shapes, such as a randomly oriented aggregate or a substantially uniformly radially oriented aggregate from a center to form a substantially spherical or substantially elliptical secondary particle. In an embodiment of the present invention, the primary particle refers to a region in which grain boundaries are observed in part or all of the periphery when a cross section of the positive electrode active material is observed with a transmission electron microscope (TEM).

[0025] In the positive electrode active material for a lithium ion battery according to an embodiment of the present invention, the above formula (1) satisfies 0.000≦e / (b+c+d+e)≦0.007. That is, the positive electrode active material for a lithium ion battery does not need to contain the dopant element M (Ta and / or W). On the other hand, when the dopant element is dissolved in the positive electrode active material, it has the effect of reducing the expansion and contraction behavior of the crystal lattice due to the insertion and extraction of lithium during charge and discharge. Therefore, by including the dopant element M (Ta and / or W), the positive electrode active material for a lithium ion battery improves the cycle characteristics. On the other hand, this element does not contribute to charge compensation during charge and discharge. Therefore, when the composition ratio of the dopant element M, e / (b+c+d+e), is 0.007 or less, it has the effect of suppressing a decrease in discharge capacity. Furthermore, it is preferable that 0.0035≦e / (b+c+d+e)≦0.0055.

[0026] One known effect of doping with heterogeneous elements is the reduction of lattice volume changes during charge-discharge cycling. Doping with elements with large ionic radii and strong oxygen bonding prevents interlayer expansion due to charge repulsion between oxygen ions, even when Li is lost during charging. In the case of positive electrode active material particles without heterogeneous element doping, the number of neighboring particles increases, causing distortion at the grain boundaries due to particle expansion and contraction during charge and discharge, leading to the problem of grain boundary cracking after a certain number of cycles. Changing the shape of the primary particles to a more elongated, almost columnar shape by doping with heterogeneous elements reduces the number of neighboring particles, potentially reducing grain boundary cracking due to the accumulation of strain at the primary particle interfaces. Therefore, efficient doping of positive electrode active materials with element M, which has a high affinity for oxygen, improves battery performance.

[0027] The positive electrode active material for a lithium ion battery according to an embodiment of the present invention preferably has a 50% cumulative volume particle size D50 of 5 to 8 μm. Here, the 50% cumulative volume particle size D50 is the volume particle size at 50% accumulation in a volume-based cumulative particle size distribution curve. When the positive electrode active material for a lithium ion battery has a 50% cumulative volume particle size D50 of 5 μm or more, the specific surface area can be reduced, and the amount of coating of Li and Nb oxides can be reduced. When the positive electrode active material for a lithium ion battery has a 50% cumulative volume particle size D50 of 8 μm or less, the specific surface area can be prevented from becoming excessively small. The positive electrode active material for a lithium ion battery more preferably has a 50% cumulative volume particle size D50 of 5 to 7 μm.

[0028] The 50% cumulative volume particle size D50 can be measured, for example, as follows. First, 100 mg of the positive electrode active material powder was dispersed using a Microtrac laser diffraction particle size analyzer "MT3300EXII" at a 50% flow rate by irradiating it with 40 W ultrasonic waves for 60 seconds, and then the particle size distribution was measured to obtain a volume-based cumulative particle size distribution curve. Next, the volume particle size at 50% accumulation in the obtained cumulative particle size distribution curve was taken as the 50% cumulative volume particle size D50 of the positive electrode active material powder. The aqueous solvent used in the measurement was passed through a filter, with a solvent refractive index of 1.333, particle permeability conditions of transparent, particle refractive index of 1.81, and shape of aspherical. The measurement range was 0.021 to 2000 μm, and the measurement time was 30 seconds.

[0029] The coating layer of the cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention is provided on the surface of a cathode active material particle, and contains an oxide of Li and Nb and M. The oxide of Li and Nb constituting the coating layer may contain lithium niobate (LiNbO3) or may be LiNbO3. The coating layer of the cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention does not contain ammonia, and therefore ion conduction is less likely to be inhibited. Furthermore, since non-uniformity in the coating layer due to volatilization of ammonia does not occur, contact between the cathode active material / coating layer and the coating layer / solid electrolyte is improved, resulting in improved battery characteristics.

[0030] The thickness of the coating layer of the positive electrode active material for an all-solid-state lithium-ion battery according to the embodiment of the present invention is preferably 10 nm or less, more preferably 6 nm or less. When the thickness of the coating layer is 6 nm or less, adverse effects such as the inhibition of Li ion migration can be more effectively avoided. The lower limit of the thickness of the coating layer is not particularly limited, but is typically 4 nm or more, preferably 5 nm or more. The thickness of the coating layer can be measured by elemental mapping analysis and line analysis using a scanning transmission electron microscope (STEM).

[0031] (Method of manufacturing positive electrode active material for all-solid-state lithium-ion batteries) In the method for producing a cathode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, first, the surfaces of cathode active material particles of the cathode active material for a lithium-ion battery are coated with an Nb complex aqueous solution (coating solution) according to an embodiment of the present invention. In this case, a coating device having a tumbling fluidized bed (tumbling fluidized bed coating device) is preferably used as the coating method. By using the tumbling fluidized bed coating device, it is possible to coat uniformly while controlling the thickness. This allows the formation of an ammonia-free coating layer made of oxides of Li and Nb on the surfaces of the cathode active material particles.

[0032] (Cathode for all-solid-state lithium-ion batteries and all-solid-state lithium-ion batteries) A positive electrode can be formed using the positive electrode active material for an all-solid-state lithium-ion battery according to an embodiment of the present invention, and the positive electrode can be used as a positive electrode layer to fabricate an all-solid-state lithium-ion battery including the positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The solid electrolyte layer and the negative electrode layer constituting the all-solid-state lithium-ion battery according to an embodiment of the present invention are not particularly limited and can be formed from known materials and can have a known configuration as shown in FIG. 1. The positive electrode for a lithium-ion battery may have a structure in which a positive electrode mixture prepared by mixing the positive electrode active material for an all-solid-state lithium-ion battery, a conductive additive, and a binder is provided on one or both sides of a current collector.

[0033] The positive electrode layer of the all-solid-state lithium-ion battery can be a layer of a positive electrode mixture obtained by mixing the positive electrode active material for all-solid-state lithium-ion batteries according to the embodiment of the present invention with a solid electrolyte. The content of the positive electrode active material in the positive electrode layer is, for example, preferably 50% by mass or more and 99% by mass or less, and more preferably 60% by mass or more and 90% by mass or less.

[0034] Examples of the conductive additive include carbon-based conductive additives (graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, and thermal lamp black)). These conductive additives may be used alone or in combination of two or more. These conductive additives may also be particulate ceramic materials or resin materials coated with a conductive material (preferably a metal one of the above-mentioned conductive additives) by plating or the like. The shape (form) of the conductive additive is not limited to particulate form, and may be a form other than particulate form, or may be a form that is in practical use as a so-called filler-based conductive additive, such as carbon nanofibers or carbon nanotubes.

[0035] Examples of binders include substances commonly used in positive electrode composites for lithium-ion batteries, but copolymers or homopolymers having a structure derived from vinylidene fluoride (PVDF), tetrafluoroethylene (TEF), and hexafluoropropylene (HFP) are preferred. Specific examples include PVDF-HFP, PVDF-HFP-TEF, PVDF-TEF, and TEF-HFP.

[0036] The positive electrode mixture may be made into a slurry by adding a solvent. As the solvent for the positive electrode mixture slurry, known organic solvents, such as hydrocarbon organic solvents, amide compounds, lactam compounds, urea compounds, organic sulfur compounds, and cyclic organic phosphorus compounds, can be used alone or as a mixed solvent. As the hydrocarbon organic solvent, saturated hydrocarbons, unsaturated hydrocarbons, or aromatic hydrocarbons can be used. Examples of saturated hydrocarbons include hexane, pentane, 2-ethylhexane, heptane, decane, and cyclohexane. Examples of unsaturated hydrocarbons include hexene, heptene, and cyclohexene. Examples of aromatic hydrocarbons include toluene, xylene, decalin, and 1,2,3,4-tetrahydronaphthalene. Of these, toluene and xylene are particularly preferred.

[0037] The average thickness of the positive electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately designed depending on the purpose. The average thickness of the positive electrode layer of the all-solid-state lithium ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0038] The method for forming the positive electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the positive electrode layer of the all-solid-state lithium ion battery include a method of compression molding a positive electrode active material for an all-solid-state lithium ion battery.

[0039] A lithium-ion battery using a positive electrode for an all-solid-state lithium-ion battery may be constructed by combining a negative electrode as a counter electrode, housing the negative electrode together with a separator in a cell container, injecting an electrolyte, and sealing the cell container. Alternatively, the battery may be obtained by forming a positive electrode on one side of a current collector and a negative electrode on the other side to prepare a bipolar electrode, stacking the bipolar electrode with a separator, housing the bipolar electrode in a cell container, injecting an electrolyte, and sealing the cell container.

[0040] Examples of the separator include known separators for lithium ion batteries, such as porous films made of polyethylene or polypropylene, laminated films of porous polyethylene film and porous polypropylene, nonwoven fabrics made of synthetic fibers (polyester fibers, aramid fibers, etc.) or glass fibers, and those having ceramic fine particles such as silica, alumina, or titania attached to the surface thereof.

[0041] The negative electrode layer of the all-solid-state lithium ion battery may be formed by layering known negative electrode active materials for all-solid-state lithium ion batteries. Examples of negative electrode active materials for all-solid-state lithium ion batteries include carbon-based materials (graphite, non-graphitizable carbon, amorphous carbon, burned resins (e.g., phenolic resins, furan resins, etc., which are burned and carbonized), cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), and carbon fibers), silicon-based materials (silicon, silicon oxide (SiO x), silicon-carbon composites (carbon particles whose surfaces are coated with silicon and / or silicon carbide, silicon particles or silicon oxide particles whose surfaces are coated with carbon and / or silicon carbide, silicon carbide, etc.), silicon alloys (silicon-aluminum alloys, silicon-lithium alloys, silicon-nickel alloys, silicon-iron alloys, silicon-titanium alloys, silicon-manganese alloys, silicon-copper alloys, silicon-tin alloys, etc.), conductive polymers (e.g., polyacetylene and polypyrrole), metals (tin, aluminum, zirconium, titanium, etc.), metal oxides (titanium oxide, lithium-titanium oxide, etc.), metal alloys (e.g., lithium-tin alloys, lithium-aluminum alloys, lithium-aluminum-manganese alloys, etc.), and mixtures of these with carbon-based materials. The conductive additive may be the same as that used for the positive electrode.

[0042] The negative electrode layer may be a layer of a negative electrode mixture obtained by mixing a known negative electrode active material for all-solid-state lithium-ion batteries with a solid electrolyte. The content of the negative electrode active material in the negative electrode layer is, for example, preferably 10% by mass or more and 99% by mass or less, and more preferably 20% by mass or more and 90% by mass or less.

[0043] The average thickness of the negative electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. The average thickness of the negative electrode layer of the all-solid-state lithium ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0044] The method for forming the negative electrode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the negative electrode layer of the all-solid-state lithium ion battery include a method of compression molding negative electrode active material particles and a method of vapor-depositing a negative electrode active material.

[0045] The solid electrolyte may be a known solid electrolyte for all-solid-state lithium ion batteries, such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0046] Sulfide-based solid electrolytes generally have high lithium ion conductivity and low grain boundary resistance, resulting in good battery performance. Specific examples of sulfide-based solid electrolytes include, but are not limited to, Li 10 GeP2S 12 (LGPS series), Li 9.5 AlP2S 12 (LAPS series), Li7P3S 11 (LPS type), Li6PS5Cl (Argyrodite type), etc.

[0047] Oxide-based solid electrolytes are easy to handle because they have high chemical stability and do not easily react with water. Specific examples of oxide-based solid electrolytes include, but are not limited to, Li7La3Zr2O 12 (LLZO series), Li 3x La 2 / 3-x TiO3 (LLTO system), Li 1-x Al x Ti 2-x (PO4)3 (LATP system), etc.

[0048] The average thickness of the solid electrolyte layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately designed depending on the purpose. The average thickness of the solid electrolyte layer of the all-solid-state lithium ion battery may be, for example, 50 μm to 500 μm, or 50 μm to 100 μm.

[0049] The method for forming the solid electrolyte layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of the method for forming the solid electrolyte layer of the all-solid-state lithium ion battery include sputtering using a target material for the solid electrolyte and compression molding of the solid electrolyte.

[0050] Other components constituting the all-solid-state lithium-ion battery are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a positive electrode current collector, a negative electrode current collector, and a battery case.

[0051] The size and structure of the positive electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. Examples of materials for the positive electrode current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, as well as baked carbon, conductive polymer materials, and conductive glass. Among these, aluminum is more preferred from the viewpoints of weight reduction, corrosion resistance, and high conductivity. Furthermore, the current collector is preferably a resin current collector made of a conductive polymer material. The positive electrode current collector may be in the form of, for example, a foil, a plate, a mesh, etc. Alternatively, it may be a deposited layer made of fine particles of the above-mentioned materials. The average thickness of the positive electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0052] The size and structure of the negative electrode current collector are not particularly limited and can be appropriately selected depending on the purpose. Examples of materials for the negative electrode current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, as well as baked carbon, conductive polymer materials, and conductive glass. Among these, aluminum is more preferred from the viewpoints of weight reduction, corrosion resistance, and high conductivity. Furthermore, the current collector is preferably a resin current collector made of a conductive polymer material. The negative electrode current collector may be in the form of, for example, a foil, a plate, a mesh, etc. Alternatively, it may be a deposited layer made of fine particles of the above-mentioned materials. The average thickness of the negative electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0053] The battery case is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include known laminate films that can be used in conventional all-solid-state lithium-ion batteries, such as resin laminate films and films in which metal is vapor-deposited on resin laminate films. The shape of the battery is not particularly limited and can be appropriately selected depending on the purpose. Examples include cylindrical, square, button, coin, and flat types. [Example]

[0054] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0055] Example 1 2.4 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 12.8 g of hydrogen peroxide (30 mass%). 3.5 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 2.2 g of phosphoric acid (H3PO4, 85 mass%) was then added to obtain a transparent Nb complex solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.9 Co 0.07 Mn 0.03 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0056] Example 2 2.4 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 12.8 g of hydrogen peroxide (30 mass%). 3.5 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 5.5 g of lithium silicate aqueous solution (Li content 1.0 mass%, Si content 9.5 mass%) was then added to obtain a transparent Nb complex aqueous solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.894 Co 0.069 Mn 0.030 Ta 0.007 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0057] Example 3 1.6 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 8.5 g of hydrogen peroxide (30 mass%). 2.3 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 1.5 g of boric acid (H3BO3) was then added to obtain a transparent Nb complex solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.894 Co 0.069 Mn 0.030 Ta 0.007 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0058] Example 4 2.4 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 12.8 g of hydrogen peroxide (30 mass%). 3.5 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 4.3 g of tungsten oxide (WO3) was then added to obtain a transparent Nb complex solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.9 Co 0.07 Mn 0.03 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0059] Example 5 5.5 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 12.8 g of hydrogen peroxide (30 mass%). 3.5 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 4.3 g of tungsten oxide (WO3) was then added to obtain a transparent Nb complex solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.894 Co 0.069 Mn 0.030 Ta 0.007 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0060] Example 6 2.4 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 12.8 g of hydrogen peroxide (30 mass%). 3.5 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 4.3 g of tungsten oxide (WO3) was then added to obtain a transparent Nb complex solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.816 Co 0.149 Mn 0.030 Ta 0.005 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0061] Example 7 2.4 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 12.8 g of hydrogen peroxide (30 mass%). 3.5 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 4.3 g of tungsten oxide (WO3) was then added to obtain a transparent Nb complex solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.597 Co 0.199 Mn 0.199 Ta 0.005 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0062] Example 8 2.8 g of lithium hydroxide monohydrate was dissolved in a mixed solution of 200 g of pure water and 15.0 g of hydrogen peroxide (30 mass%). 4.1 g of niobic acid (Nb2O5·nH2O, Nb content 49.8 mass%) was then dissolved. 2.6 g of tungsten oxide (WO3) and 1.3 g of lithium silicate aqueous solution (Li content 1.0 mass%, Si content 9.5 mass%) were then added to obtain a transparent Nb complex aqueous solution. Next, the obtained Nb complex aqueous solution was used as a coating liquid to coat the positive electrode active material particles (composition formula: LiNi 0.894 Co 0.069 Mn 0.030 Ta 0.007 O2) was coated on its surface. Next, the material was heat-treated at 250°C in an oxygen stream to obtain a positive electrode active material for an all-solid-state lithium-ion battery with a coating layer formed on the surface.

[0063] (Comparative Example 1) A cathode active material for lithium-ion batteries without a coating layer on the surface (composition formula: LiNi 0.9 Co 0.07 Mn 0.03 O2) was prepared.

[0064] (Battery characteristics) <Method for manufacturing all-solid-state lithium-ion batteries> The positive electrode active material for all-solid-state lithium ion batteries obtained in Examples 1 to 8 and the positive electrode active material for lithium ion batteries obtained in Comparative Example 1 were mixed with a sulfide-based solid electrolyte (75Li2S-25P2S5), acetylene black, and a binder in a mass ratio of 60:35:5:1.5 in this order, and anisole was added as a solvent so that the solid content of the slurry was 65 mass%, and the mixture was mixed with a Mazerustar for 400 seconds to form a positive electrode mixture slurry, which was then applied to the surface of a 0.03 mm thick aluminum foil positive electrode current collector. At this time, the positive electrode mixture slurry was applied to the surface of the positive electrode current collector by moving the applicator at a speed of 15 mm / s using an applicator with a gap of 400 μm. Next, the positive electrode current collector with the positive electrode composite slurry coated on its surface was dried on a hot plate at 100°C for 30 minutes to remove the solvent, thereby forming a positive electrode composite layer on the surface of the positive electrode current collector. Next, the above-mentioned positive electrode composite layer was placed on a sulfide-based solid electrolyte having the same composition as the sulfide-based solid electrolyte used in producing the positive electrode composite layer, and pressed at 333 MPa to produce a laminate of solid electrolyte layer / positive electrode composite layer / positive electrode current collector. Next, a metallic Li-In alloy was pressed onto the negative electrode side of the solid electrolyte layer at 37 MPa to form a negative electrode layer. The laminate thus prepared was placed in a battery test cell made of SUS304 and subjected to a confining pressure to form an all-solid-state secondary battery. The all-solid-state secondary battery formed by applying the confining pressure was then placed in a sealed container to block the air.

[0065] <Evaluation of initial discharge capacity> The discharge capacity of the above-mentioned all-solid-state lithium-ion battery was evaluated by measuring the impedance to determine the resistance after the initial charge at 0.1 C at 55°C, and then discharging at 0.1 C. The test conditions and evaluation results are shown in Tables 1 and 2. In Table 1, "M1" and "M2" represent the element M. Furthermore, "M1 added amount" and "M2 added amount" represent "the added amount of a substance containing M1" and "the added amount of a substance containing M2," respectively.

[0066] [Table 1]

[0067] [Table 2]

[0068] (Evaluation results) According to the above test results, in all of Examples 1 to 8, the initial discharge capacity (battery characteristics) was good because the positive electrode active material for an all-solid-state lithium-ion battery was prepared using an Nb complex aqueous solution containing Li, Nb, and one or more elements M selected from P, Si, B, and W, in which the molar ratio of Li to Nb: Li / Nb was 2.85 or more and the molar ratio of Li to M: Li / M was 0.5 to 10. Note that the composition of the obtained positive electrode active material was calculated from the content of elements contained in the raw materials because it was unlikely to change from the content of elements contained in the raw materials.

[0069] In Comparative Example 1, the initial discharge capacity was inferior to Examples 1 to 8 because no coating layer was formed.

[0070] According to one embodiment of the present invention, there are provided an aqueous solution of Nb complex capable of producing a cathode active material for an all-solid-state lithium-ion battery with excellent battery characteristics, a method for producing the cathode active material for an all-solid-state lithium-ion battery using the same, a method for producing a cathode for an all-solid-state lithium-ion battery, and a method for producing an all-solid-state lithium-ion battery. These methods may lead to the widespread use of non-fossil fuels, reduce the use of fossil fuels such as oil and gas, which currently account for the majority of energy generation, and contribute to the prevention of global warming. Furthermore, the primary materials used in the method are environmentally friendly materials such as lithium, carbon, manganese, nickel, and cobalt, and do not contain hazardous substances such as cadmium, lead, or mercury, potentially reducing the environmental impact. Therefore, one embodiment of the present invention may contribute to the achievement of Goal 7 of the United Nations-led Sustainable Development Goals (SDGs), "Ensure access to affordable, reliable, sustainable, and modern energy for all," Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation," and Goal 12, "Ensure sustainable consumption and production patterns."

Claims

1. Contains Li, Nb, and one or more elements M selected from Si, B, and W, The molar ratio of Li to Nb: Li / Nb is 2.85 or more, An aqueous Nb complex solution, wherein the molar ratio of Li to M: Li / M is 0.5 to 10.

2. 2. The Nb complex aqueous solution according to claim 1, wherein the molar ratio of Li to Nb: Li / Nb is 3.0 or more.

3. 2. The Nb complex aqueous solution according to claim 1, wherein the molar ratio of Li to M: Li / M is 1.5 to 7.

0.

4. 2. The Nb complex aqueous solution according to claim 1, wherein the concentration of Li is 0.06 to 5 mol / L, the concentration of Nb is 0.02 to 1 mol / L, and the concentration of M is 0.02 to 1 mol / L.

5. The Nb complex aqueous solution according to claim 1 , wherein the Nb complex has a peroxy group.

6. A method for producing a positive electrode active material for an all-solid-state lithium ion battery, comprising: forming a coating layer containing an oxide of Li, the Nb, and the M on a surface of a positive electrode active material particle of the positive electrode active material for a lithium ion battery using the Nb complex aqueous solution according to any one of claims 1 to 5.

7. 7. The method for producing a positive electrode active material for an all-solid-state lithium ion battery according to claim 6, wherein a coating layer containing the oxide of Li and the Nb and the M is formed by a tumbling fluidized bed coating apparatus.

8. A method for producing a positive electrode for an all-solid-state lithium ion battery, comprising producing a positive electrode for an all-solid-state lithium ion battery using the positive electrode active material for an all-solid-state lithium ion battery obtained by the method according to claim 6.

9. A method for producing an all-solid-state lithium ion battery, comprising producing an all-solid-state lithium ion battery using a positive electrode for an all-solid-state lithium ion battery obtained by the method according to claim 8.

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