Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing the positive electrode active material, and non-aqueous electrolyte secondary battery

Abstract

This invention provides a positive electrode active material that, when used in the positive electrode of a non-aqueous electrolyte secondary battery, particularly an all-solid-state battery, exhibits high initial discharge capacity and high durability. [Solution] The invention comprises lithium transition metal composite oxide particles and a coating layer covering at least a portion of the surface of the particles, wherein the particles have a molar ratio of Li:Ni:Co:Mn:M=s:x:y:(1-xyz):z (where M is at least one element selected from V, Mg, Mo, Nb, Ti, W, Zr, and Al, 1.3≦s<1.6, 0.05≦x≦0.3, 0.1≦y≦0.4, 0≦z≦0.1) and a niobium solid solution layer in which niobium is solid-dissolved on the surface, the coating layer contains niobium and has an average thickness of 2 nm to 1 μm, and the niobium content in the niobium solid solution layer and the coating layer is greater than 1.0 mol% and less than or equal to 2.0 mol% relative to the total of Ni, Co, Mn, and element M.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the positive electrode active material, and a non-aqueous electrolyte secondary battery using the positive electrode active material. [Background technology]

[0002] In recent years, with the spread of electric vehicles, there has been a strong demand for the development of small, lightweight rechargeable batteries with high energy density. One such rechargeable battery is the lithium-ion battery, which is a non-aqueous electrolyte rechargeable battery.

[0003] In typical non-aqueous electrolyte secondary batteries, lithium transition metal composite oxides such as LiCoO2, LiNiO2, and LiMn2O4 are used as the positive electrode active material, lithium metal, lithium alloys, metal oxides, and carbon are used as the negative electrode active material, and a non-aqueous electrolyte is used which is prepared by dissolving Li salts such as LiClO4 and LiPF6 as supporting salts in organic solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0004] Among the components of non-aqueous electrolyte secondary batteries, the non-aqueous electrolyte, in particular, is a limiting factor in battery performance such as fast charging, thermal stability, and lifespan due to its chemical properties including heat resistance and potential window. Therefore, research and development are currently actively underway on all-solid-state batteries, which improve battery performance by using a solid electrolyte instead of a non-aqueous electrolyte.

[0005] Japanese Patent Publication No. 2014-056661 states that sulfide solid electrolytes exhibit high lithium ion conductivity during charging and discharging, and that using sulfide solid electrolytes as solid electrolytes can increase the energy density of all-solid-state batteries. However, when sulfide solid electrolytes come into contact with positive electrode active materials made of oxides, a reaction occurs at the interface between the solid electrolyte and the positive electrode active material during charging and discharging, generating a high-resistance phase that hinders the operation of the all-solid-state battery.

[0006] On the other hand, in Japanese Patent Application Laid-Open No. 2010-170715, regarding the positive electrode active material used in all-solid-state batteries, it has been proposed to provide a coating layer made of LiNbO3 on the surface of the positive electrode active material in order to suppress the formation of a high-resistance phase. More specifically, this document proposes that a raw material composition obtained by adding ethanol to a mixed solution of lithium ethoxide and pentaethoxynbium is applied onto the surface of LiCoO2 using a rolling fluid coating device and heat-treated to obtain a positive electrode active material provided with a coating layer of a predetermined thickness.

[0007] On the other hand, in non-aqueous electrolyte secondary batteries using conventional non-aqueous electrolytes, from the viewpoint of increasing their energy density, it is considered preferable to use positive electrode active materials with a high nickel content such as LiNiO2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] When examining the applicability of the above-described positive electrode active materials with a high nickel content to all-solid-state batteries, it has been found that in all-solid-state batteries, the energy density obtained from these positive electrode active materials is lower than the energy density expected from non-aqueous electrolyte secondary batteries using conventional non-aqueous electrolytes.

[0010] This disclosure aims to provide a positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter also referred to as "positive electrode active material") and a method for manufacturing the same, which, when used as the positive electrode of a non-aqueous electrolyte secondary battery (hereinafter also referred to as "positive electrode active material") with a high manganese content instead of a positive electrode active material with a high nickel content, will have high initial discharge capacity and high durability, regardless of whether it is used as the positive electrode of a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte solution or an all-solid-state battery using a solid electrolyte (hereinafter, "non-aqueous electrolyte solution" and "solid electrolyte" are collectively referred to as "non-aqueous electrolyte secondary battery"), or a non-aqueous electrolyte secondary battery (hereinafter, "non-aqueous electrolyte secondary battery using a non-aqueous electrolyte solution" and "all-solid-state battery" are collectively referred to as "non-aqueous electrolyte secondary battery"). Furthermore, this disclosure aims to provide a non-aqueous electrolyte secondary battery with high initial discharge capacity and high durability by using such a positive electrode active material as the positive electrode. [Means for solving the problem]

[0011] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of this disclosure comprises particles of a lithium transition metal composite oxide and a coating layer covering at least a portion of the surface of the particles. The lithium transition metal composite oxide particles contain Li, Ni, Co, Mn, and element M in a molar ratio of Li:Ni:Co:Mn:M=s:x:y:(1-xyz):z (where M is at least one element selected from the group consisting of V, Mg, Mo, Nb, Ti, W, Zr, and Al, with 1.3≦s<1.6, 0.05≦x≦0.3, 0.1≦y≦0.4, 0≦z≦0.1), and are provided with a niobium solid solution layer having an average thickness of 0.5 nm to 20 nm, in which niobium is solid-dissolved in at least a portion of the surface. The coating layer comprises a compound containing lithium and niobium, has an average thickness of 2 nm to 1 μm, and The niobium content in the niobium solid solution layer and the coating layer is greater than 1.0 mol% and less than or equal to 2.0 mol% relative to the total amount of Ni, Co, Mn, and element M constituting the particles of the lithium transition metal composite oxide, and the lithium content in the coating layer is between 1.0 and 2.0 in molar ratio to the niobium contained in the coating layer. It is characterized by the following:

[0012] The aforementioned lithium and niobium-containing compound preferably contains at least lithium niobate, and more preferably contains at least one of Li3NbO4, LiNbO3, LiNb3O8, and Li8Nb2O9.

[0013] The lithium content in the coating layer is preferably 1.0 mol% to 3.0 mol% relative to the total amount of Ni, Co, Mn, and element M that constitute the particles of the lithium transition metal composite oxide.

[0014] The aforementioned compound containing lithium and niobium is preferably amorphous.

[0015] A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes: depositing a coating solution containing lithium and niobium onto the surface of lithium transition metal composite oxide particles as a base material to form a coating layer precursor; heat-treating the lithium transition metal composite oxide particles on which the coating layer precursor is formed to form a niobium solid solution layer in which niobium is solid-dissolved in at least a portion of the surface of the lithium transition metal composite oxide particles, and forming a coating layer that covers at least a portion of the surface of the lithium transition metal composite oxide particles; The coating solution comprises a niobium peroxo complex, lithium ions, hydrogen peroxide, and ammonia, and The niobium content in the coating solution is greater than 1.0 mol% and 2.2 mol% or less relative to the total amount of Ni, Co, Mn, and element M constituting the particles of the lithium transition metal composite oxide, and the molar ratio of lithium to niobium in the peroxo complex in the coating solution is 1.0 or more and 2.0 or less (1.0 ≤ Li / Nb ≤ 2.0). It is characterized by the following:

[0016] It is preferable that the lithium content in the coating layer be 1.0 mol% or more and 3.0 mol% or less relative to the total amount of Ni, Co, Mn, and element M that constitute the particles of the lithium transition metal composite oxide.

[0017] It is preferable to apply the coating solution to the lithium transition metal composite oxide particles using a rolling flow coating apparatus.

[0018] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of this disclosure can be suitably applied to a positive electrode for an all-solid-state battery in which a solid electrolyte is used as the non-aqueous electrolyte.

[0019] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte (a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte), or comprises a positive electrode, a negative electrode, and a solid electrolyte (an all-solid-state battery), characterized in that the positive electrode active material for a non-aqueous electrolyte secondary battery of the present disclosure is used as the positive electrode active material used in the positive electrode. [Effects of the Invention]

[0020] In a positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of this disclosure, even with a positive electrode active material having a high manganese content, the formation of a high-resistance phase due to reactions at the interface between the non-aqueous electrolyte, which consists of a non-aqueous electrolyte or a solid electrolyte, particularly a sulfide solid electrolyte, and the positive electrode active material is sufficiently suppressed. Therefore, the positive electrode active material according to one aspect of this disclosure can achieve high initial discharge capacity and high durability. Thus, by applying the positive electrode active material according to one aspect of this disclosure, it is possible to provide a non-aqueous electrolyte secondary battery, including an all-solid-state battery, that has high initial discharge capacity and high durability. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a schematic diagram showing the structure of a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic process diagram showing a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. [Figure 3]Figures 3(A) to 3(C) are schematic diagrams showing the state of particles in each step of the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. [Figure 4] This figure shows the results of STEM-EDS surface analysis of the positive electrode active material of Example 1. [Figure 5] Figure 5 is a schematic cross-sectional view showing the configuration of the test battery used to evaluate its characteristics. [Modes for carrying out the invention]

[0022] A preferred embodiment of the present disclosure is described below. However, the present disclosure is not limited to the following embodiment, and various modifications and improvements can be made to the following embodiment without departing from the scope of the present disclosure.

[0023] (1) Positive electrode active material for non-aqueous electrolyte secondary batteries A positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises lithium transition metal composite oxide particles and a coating layer covering at least a portion of the surface of the particles. In particular, the positive electrode active material of this example is characterized by comprising a niobium solid solution layer in which niobium is solid-dissolved in at least a portion of the surface of the lithium transition metal composite oxide particles, and a coating layer containing a compound containing lithium and niobium, thereby improving the initial discharge capacity (battery capacity) and initial charge-discharge efficiency in a non-aqueous electrolyte secondary battery, especially an all-solid-state battery.

[0024] Figure 1 is a schematic diagram of the positive electrode active material of this example. The positive electrode active material 1 has lithium transition metal composite oxide particles 2. The lithium transition metal composite oxide particles 2 have a niobium solid solution layer 3 formed on their surface. The positive electrode active material 1 of this example further comprises a coating layer 4 that covers at least a portion of the surface of the lithium transition metal composite oxide particles 2. The lithium transition metal composite oxide particles 2 contain lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn), or optionally contain element M. In addition to these elements, niobium (Nb) is also present in the niobium solid solution layer 3. The coating layer 4 is composed of a compound containing lithium and niobium (hereinafter also referred to as "lithium niobium compound").

[0025] <Particles of lithium transition metal composite oxides> The lithium transition metal composite oxide particles 2 constituting the positive electrode active material 1 in this example contain lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and an arbitrary element M, excluding niobium (Nb) which is dissolved in the niobium solid solution layer 3, in a molar ratio of Li:Ni:Co:Mn:M=s:x:y:(1-xyz):z.

[0026] Furthermore, the values ​​of s, x, y, and z, which represent the molar ratios, satisfy the following conditions: 1.3 ≤ s < 1.6, 0.05 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, and 0 ≤ z ≤ 0.1.

[0027] The value of s, which indicates the lithium content constituting particle 2 of the lithium transition metal composite oxide, is 1.3 or more and less than 1.6. Preferably, the value of s is 1.35 or more and 1.55 or less, and more preferably 1.4 or more and 1.5 or less.

[0028] If the s value, which indicates the lithium content, is less than 1.3, the parts of the lithium transition metal composite oxide particle crystal that should be occupied by lithium may be occupied by other elements, which can reduce the charge and discharge capacity in a non-aqueous electrolyte secondary battery. On the other hand, if the s value is 1.6 or higher, there may be excess lithium compounds that do not contribute to charging and discharging, which can increase the positive electrode resistance (reaction resistance) or reduce the battery capacity.

[0029] Nickel in the lithium transition metal composite oxide particles 2 is an element that contributes to increasing the capacity of non-aqueous electrolyte secondary batteries. The value of x, which indicates the nickel content, is between 0.05 and 0.3. Preferably, the value of x is between 0.1 and 0.25, and more preferably between 0.15 and 0.2.

[0030] Cobalt is an element that contributes to achieving high battery capacity and improving cycle characteristics in non-aqueous electrolyte secondary batteries. The value of y, which indicates the cobalt content, is preferably between 0.1 and 0.4. The value of x is preferably between 0.15 and 0.35.

[0031] Manganese is an element that contributes to achieving high battery capacity and improving thermal stability in non-aqueous electrolyte secondary batteries. The (1-xyz) value, which indicates the manganese content, is between 0.2 and 0.85. Preferably, the (1-xyz) value is between 0.4 and 0.8, and more preferably between 0.6 and 0.7.

[0032] The lithium transition metal composite oxide particles 2 may contain element M as an additional optional additive. The type of element M and its content are appropriately selected depending on the application and required performance of the non-aqueous electrolyte secondary battery to which the positive electrode active material of this example is applied.

[0033] Element M is at least one element selected from vanadium (V), magnesium (Mg), molybdenum (Mo), niobium (Nb), titanium (Ti), tungsten (W), zirconium (Zr), and aluminum (Al). In this example, niobium as element M is treated separately from the niobium present in the coating layer 4 and the niobium dissolved in the niobium solid solution layer 3.

[0034] The value of z indicating the content of element M is, for example, 0 or more and 0.1 or less. The positive electrode active material can contain a small amount of elements other than Ni, Co, Mn, and element M as long as the effects according to the present disclosure are not inhibited.

[0035] As the composition excluding the niobium dissolved in the niobium solid solution layer 3 and the lithium and niobium present in the coating layer 4 in the particles 2 of the lithium transition metal composite oxide, that is, the positive electrode active material 1, the general formula: Li s Ni x Co y Mn (1-x-y-z) M z O 2+α (M is at least one element selected from V, Mg, Mo, Nb, Ti, W, Zr, and Al, 1.3 ≦ s < 1.6, 0.05 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.1, 0 ≦ α ≦ 0.2) can be adopted. In the above general formula, α is a coefficient that changes according to the valence of the metal element other than lithium contained in the lithium transition metal composite oxide and the atomic ratio of lithium to the metal element other than lithium.

[0036] The particles 2 of the lithium transition metal composite oxide preferably have a layered crystal structure. Also, in the particles 2, the portion excluding the niobium solid solution layer 3 can have a uniform composition, or there may be a concentration gradient in the concentration of nickel, cobalt, manganese, and / or element M in the direction from the outermost surface to the inside of the particles 2.

[0037] The lithium transition metal composite oxide particles 2 may include secondary particles formed by the aggregation of multiple primary particles, or they may include a single primary particle. They may also be a mixture of a single primary particle and a secondary particle.

[0038] <Niobium solid solution layer> The niobium solid solution layer 3, together with the coating layer 4, has the function of suppressing the formation of a high-resistance phase due to reactions at the interface between the non-aqueous electrolyte, particularly the sulfide solid electrolyte, and the positive electrode active material 1. The niobium solid solution layer 3 refers to at least a part of the surface layer (from the outermost surface of the particle to the interior of the particle) of the lithium transition metal composite oxide particle 2, where the presence of niobium (Nb) is confirmed. Furthermore, the surface layer of particle 2 refers to the layer extending from the outermost surface of particle 2 to the interior of the particle along that outermost surface.

[0039] If the lithium transition metal composite oxide particles 2 are composed of, for example, secondary particles formed by the aggregation of multiple primary particles, niobium can be dissolved in solid solution on the surface of the secondary particles. If the lithium transition metal composite oxide particles 2 are composed of a single primary particle, niobium can be dissolved in solid solution on the surface of the primary particle.

[0040] The presence of niobium in the niobium solid solution layer 3 can be confirmed, for example, by STEM-EDS surface / line analysis using a scanning transmission electron microscope (STEM) and an energy-dispersive X-ray spectrometer (EDS) attached to the STEM (see Figure 4).

[0041] The average thickness of the niobium solid solution layer 3 is between 0.5 nm and 20 nm. If the average thickness of the niobium solid solution layer 3 is less than 0.5 nm, the function of suppressing the formation of the high-resistance phase is not fully exhibited. On the other hand, if the average thickness of the niobium solid solution layer 3 is greater than 20 nm, it may hinder the increase in capacity of the non-aqueous electrolyte secondary battery. From the viewpoint of improving battery characteristics, the average thickness of the niobium solid solution layer 3 is preferably between 1 nm and 20 nm, more preferably between 1 nm and 15 nm, even more preferably between 1 nm and 10 nm, and most preferably between 1 nm and 5 nm. The average thickness of the niobium solid solution layer 3 may be 3 nm or less, or 2 nm or less.

[0042] The average thickness of the niobium solid solution layer 3 can be confirmed, for example, by performing STEM-EDS surface / line analysis on the surface of the positive electrode active material 1. Note that if there is variation in the thickness of the niobium solid solution layer 3 depending on the measurement site, the average thickness of the niobium solid solution layer 3 refers to the average value obtained from measurements of multiple sites.

[0043] The niobium solid solution layer 3 may be formed partially (for example, in island-like formations) on a portion of the surface of the lithium transition metal composite oxide particles 2, but it is preferable that it is formed across the entire surface of the particle 2, as shown in Figure 1. Furthermore, there may be a concentration gradient of niobium in the direction from the outermost surface toward the interior of the lithium transition metal composite oxide particles 2.

[0044] <Coating layer> The coating layer 4 covers at least a portion of the surface of the lithium transition metal composite oxide particles 2. The lithium and niobium-containing compounds constituting the coating layer 4 have the function of suppressing the reaction between the lithium transition metal composite oxide and the sulfide solid electrolyte. Therefore, by arranging the coating layer 4, it is possible to suppress the increase in interfacial resistance between the positive electrode active material 1 and the solid electrolyte in non-aqueous electrolyte secondary batteries, especially all-solid-state batteries.

[0045] Lithium niobium compounds are compounds containing lithium atoms and niobium atoms, preferably containing lithium niobate. Lithium niobate is a composite oxide of niobium and lithium, and examples of lithium niobate include Li3NbO4, LiNbO3, LiNb3O8, and Li8Nb2O9. These lithium niobates fully exhibit the function of suppressing the formation of a high-resistance phase without hindering the conductivity of lithium ions in the coating layer. It is more preferable that the lithium niobium compound contains at least one of these. Lithium niobate also includes mixed forms such as Li3NbO4, LiNbO3, LiNb3O8, and Li8Nb2O9. Furthermore, from the viewpoint of more appropriately exhibiting the function of the lithium niobium compound, it is effective to have a balanced ratio of lithium to niobium. For example, if there is an excess of niobium in the ratio of lithium to niobium, the lithium conductivity of the coating layer may deteriorate. Therefore, among these lithium niobate compounds, Li3NbO4 and / or LiNbO3 are more preferred. The type of lithium niobium compound is determined by the molar ratio of lithium to niobium in the niobium peroxo complex contained in the coating solution containing lithium and niobium, the method of applying the coating solution to the base material 5, and the conditions of the subsequent heat treatment of the base material 5 with the coating layer precursor 6.

[0046] The presence and type of lithium niobium compound constituting the coating layer 4 can be confirmed, for example, by X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and STEM-EDS surface / line analysis using an energy-dispersive X-ray spectrometer (EDS) attached to the STEM.

[0047] Lithium niobium compounds may be amorphous or have a crystalline structure. When the lithium niobium compound is amorphous, lithium ion conductivity is improved, further reducing the positive electrode resistance in non-aqueous electrolyte secondary batteries. The crystallinity of the lithium niobium compound can be confirmed by X-ray diffraction (XRD) measurement.

[0048] The coating layer 4 can be formed on a portion of the lithium transition metal composite oxide particles 2 that come into contact with the electrolyte, or on the entire surface thereof. If the particles 2 consist of secondary particles or primary particles, the coating layer 4 can be formed on a portion of the surface of the secondary particles or a portion of the surface of the primary particles, but it is preferable that it be formed on the entire surface of the secondary particles or the entire surface of the primary particles. However, if the particles 2 are secondary particles, the coating layer 4 may be formed on the surface of the primary particles that constitute the secondary particles. Furthermore, if the particles 2 consist of secondary particles, the coating layer 4 may be formed on the surface of the primary particles exposed on the surface of the secondary particles, or on the surface of the primary particles inside the secondary particles.

[0049] The average thickness of the coating layer 4 is between 2 nm and 1 μm. Furthermore, from the viewpoint of further improving battery characteristics, the average thickness of the coating layer 4 is preferably between 2 nm and 100 nm, more preferably between 2 nm and 50 nm, even more preferably between 2 nm and 20 nm, and most preferably between 5 nm and 10 nm. The average thickness of the coating layer 4 can be confirmed, for example, by performing STEM-EDS surface analysis / line analysis on the surface of the positive electrode active material 1. Note that if there is variation in the thickness of the coating layer 4 depending on the measurement site, the average thickness of the coating layer 4 refers to the average value obtained when measuring multiple sites.

[0050] As shown in Figure 1, the coating layer 4 may be formed over the entire surface of the lithium transition metal composite oxide particles 2, or partially (for example, in island-like formations) on a portion of the surface, but it is preferable that it be formed uniformly over the entire surface. Furthermore, the average thickness of the niobium solid solution layer 3 relative to the average thickness of the coating layer 4 (average thickness of the niobium solid solution layer 3 / average thickness of the coating layer 4) is not particularly limited, but may be 0.1 or more, preferably greater than 0.1, more preferably 0.15 or more, and even more preferably 0.2 or more.

[0051] <Niobium content> The niobium content in the positive electrode active material 1, excluding the niobium added to the lithium transition metal composite oxide particles 2 as element M, corresponds to the total amount of niobium contained in the niobium solid solution layer 3 and the coating layer 4. This niobium content is greater than 1.0 mol% and less than or equal to 2.0 mol% relative to the total amount of Ni, Co, Mn, and element M in the lithium transition metal composite oxide particles 2. If the niobium content is 1.0 mol% or less, the effect of suppressing the formation of a high-resistance layer during repeated charging and discharging becomes less effective. On the other hand, if the niobium content exceeds 2.0 mol%, the lithium ratio in the coating layer decreases relatively, which worsens the lithium conductivity of the coating layer and causes the battery resistance to increase during charging and discharging. It is more preferable that the niobium content is between 1.2 mol% and 2.0 mol%. Furthermore, from the viewpoint of further improving battery characteristics, the amount of niobium contained in the lithium niobium compound constituting the coating layer 4 is preferably 1.3 mol% to 1.9 mol%, and more preferably 1.3 mol% to 1.8 mol%.

[0052] Furthermore, if the lithium transition metal composite oxide particles 2 contain niobium as element M, the difference in niobium content before and after coating can be used as the niobium content (the total amount of niobium contained in the niobium solid solution layer 3 and the coating layer 4).

[0053] <Lithium content> The lithium content in the coating layer 4, that is, the lithium content in the lithium niobium compound constituting the coating layer 4, is 1.0 or more and 2.0 or less in molar ratio to niobium contained in the coating layer 4. The type of lithium niobium compound constituting the coating layer 4 is determined according to the lithium content in the coating layer 4. If the molar ratio to niobium, which indicates the lithium content, is less than 1.0 or exceeds 2.0, problems arise in that the initial discharge capacity (battery capacity) and initial charge-discharge efficiency cannot be sufficiently improved. From the viewpoint of uniformly forming the niobium solid solution layer 3, it is more preferable that the molar ratio to niobium, which indicates the lithium content, is 1.2 or more and 1.8 or less, and even more preferable that it is 1.4 or more and 1.6 or less.

[0054] The lithium content in the coating layer 4 is 1.0 mol% to 3.0 mol% relative to the total amount of Ni, Co, Mn, and element M in the lithium transition metal composite oxide particles 2. The lithium content is preferably 1.3 mol% to 2.6 mol%, and more preferably 0.14 mass% to 0.16 mass%.

[0055] In the positive electrode active material 1 of this example, lithium is introduced into the coating layer 4, forming a lithium niobium compound. Compared to a coating layer 4 formed solely of niobium compounds, lithium ion conductivity is improved. Therefore, the coating layer 4 is less likely to hinder the intercalation / deintercalation reaction of lithium to the lithium transition metal composite oxide particles 2. This reduces the internal resistance of the non-aqueous electrolyte secondary battery and suppresses the decrease in its discharge capacity.

[0056] <Volume-average particle size MV> The volume-average particle size MV of the lithium transition metal composite oxide particles 2 constituting the positive electrode active material 1 is, for example, 5 μm or more and 30 μm or less, preferably 5 μm or more and 20 μm or less. If the volume-average particle size MV of the lithium transition metal composite oxide particles 2 is less than 5 μm, the specific surface area of ​​the positive electrode active material 1 increases, resulting in higher output in a non-aqueous electrolyte secondary battery. However, the packing density of the positive electrode decreases, reducing the charge / discharge capacity per unit volume, and the dispersibility of the conductive agent and positive electrode active material may deteriorate when preparing the electrode paste. Furthermore, the voltage applied to individual positive electrode active material particles within the electrode becomes non-uniform, and particles to which high voltage is applied degrade with repeated charging and discharging, potentially reducing the charge / discharge capacity of the non-aqueous electrolyte secondary battery. Conversely, if the volume-average particle size MV of the lithium transition metal composite oxide particles 2 exceeds 30 μm, the specific surface area of ​​the positive electrode active material 1 decreases, reducing the interface with the electrolyte and thus reducing the pathways for lithium ions to enter and exit. This can increase the resistance of the positive electrode and degrade the output characteristics of the battery. Note that the volume-average particle size (MV) is a value measured by laser diffraction scattering.

[0057] <Breadth of particle size distribution> [(d90-d10) / volume average particle size MV], an index indicating the spread of the particle size distribution of the lithium transition metal composite oxide particles 2 constituting the positive electrode active material 1, is not particularly limited, but from the viewpoint of having high packing efficiency, it is preferably 0.70 or higher, and more preferably 0.70 or higher and 1.2 or lower. d10 refers to the particle size at which the cumulative volume, calculated by accumulating the number of particles at each particle size from the smallest particle size, is 10% of the total volume of all particles. Similarly, d90 refers to the particle size at which the cumulative volume, calculated by accumulating the number of particles, is 90% of the total volume of all particles. Furthermore, d10 and d90 can be determined from the volume integrated values ​​measured with a laser diffraction scattering particle size analyzer, similar to the average particle size.

[0058] The BET specific surface area of ​​the lithium transition metal composite oxide particles 2 constituting the positive electrode active material is preferably 0.3 m². 2 / g or more 1.8m 2 It is preferable that it be less than or equal to / g, and 0.5m 2 / g or more 1.5m 2 It is more preferable that the BET specific surface area is less than or equal to / g. When the BET specific surface area is within the above range, the contact area with the solid electrolyte can be made sufficient, thereby reducing the positive electrode resistance and obtaining sufficient output characteristics. The BET specific surface area is measured by the BET method using nitrogen gas adsorption.

[0059] <Average particle size of primary particles> When the lithium transition metal composite oxide particles 2 constituting the positive electrode active material 1 include secondary particles composed of multiple primary particles, the average particle size of the primary particles is preferably, for example, 0.2 μm or more and 1.0 μm or less, and more preferably 0.3 μm or more and 0.7 μm or less. When the average particle size of the primary particles is within the above range, higher output characteristics, battery capacity, and even higher cycle characteristics can be obtained when used as the positive electrode of a non-aqueous electrolyte secondary battery. If the average particle size of the primary particles is less than 0.2 μm, firing may be insufficient, and sufficient battery performance may not be obtained. Also, if the average particle size of the primary particles exceeds 1.0 μm, high output characteristics and high cycle characteristics may not be obtained.

[0060] The positive electrode active material 1 may contain lithium transition metal composite oxides other than the lithium transition metal composite oxide particles 2 described above, to the extent that they do not impair the effects of this disclosure.

[0061] (2) Method for producing positive electrode active material for non-aqueous electrolyte secondary batteries The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to one example of the embodiments of this disclosure is not particularly limited, but it is preferable to use the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to one example of an embodiment of this disclosure described below.

[0062] Figure 2 is a schematic process diagram showing the manufacturing method of the positive electrode active material in this example. Figures 3(A) to 3(C) are schematic diagrams showing the state of particles in each step of the manufacturing method of a positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

[0063] As shown in Figure 2, the method for manufacturing the positive electrode active material in this example comprises the steps of: attaching a coating solution containing lithium and niobium to the surface of lithium transition metal composite oxide particles (hereinafter also referred to as "base material 5") as a base material 5 to form a coating layer precursor 6 (attachment step: step S1); and heat-treating the base material 5 on which the coating layer precursor 6 has been formed to form a niobium solid solution layer 3, thereby obtaining a positive electrode active material 1 comprising lithium transition metal composite oxide particles 2 with the niobium solid solution layer 3 and a coating layer 4 (heat treatment step: step S2). The positive electrode active material 1 in this example can be easily and productively manufactured on an industrial scale using the manufacturing method of this example.

[0064] <First Process [Adhesion Process: Step S1]> The adhesion step (step S1) is a step in which a coating solution containing lithium and niobium is applied to the surface of the base material 5 to form a coating layer precursor 6 (see Figure 3(B)). By using a coating solution containing lithium together with niobium in the adhesion step (step S1), the formation of a lithium-niobium compound can be reliably ensured even when there is only a trace amount of excess lithium on the surface of the base material 5. Furthermore, in the heat treatment step, a lithium-niobium compound is formed by the lithium and niobium present in the coating layer precursor 6, and a portion of the niobium is solid-dissolved on the surface of the base material 5. As a result, a niobium solid-solution layer 3 can be suitably formed in the positive electrode active material 1 finally obtained after the heat treatment step.

[0065] (Coating solution containing lithium and niobium) The coating solution containing lithium and niobium (hereinafter also referred to as "coating solution") is not particularly limited as long as it is a solution capable of forming the lithium niobium compound that ultimately constitutes the desired coating layer 4.

[0066] The coating solution can be obtained, for example, by mixing a lithium compound, a niobium compound, and a solvent. Furthermore, from the viewpoint of uniformly coating the surface of the base material 5, the coating solution is preferably liquid at room temperature, and the lithium compound and niobium compound used as raw materials are preferably low-melting-point compounds that melt with low-temperature heat treatment.

[0067] The coating solution may be prepared, for example, by mixing a lithium compound and a niobium compound in a single solvent, or by separately preparing a solution containing a dissolved lithium compound (hereinafter also referred to as "lithium solution") and a solution containing a dissolved niobium compound (hereinafter also referred to as "niobium solution") and mixing them. Alternatively, the lithium solution and niobium solution can be sprayed separately onto the base material 5 to form a coating solution on the surface of the base material 5.

[0068] This example is characterized by the use of a coating solution containing a niobium peroxo complex, lithium ions with a molar ratio of lithium to niobium in the peroxo complex (Li / Nb) of 1.0 ≤ Li / Nb ≤ 2.0, hydrogen peroxide, and ammonia. Specifically, by using hydrogen peroxide and ammonia as solvents, the niobium peroxo complex is formed in the coating solution. By using such a coating solution, it is possible to ensure a sufficient amount of lithium in the coating layer 4 while increasing the niobium content in the niobium solid solution layer 3 and the coating layer 4, given that the average thickness of the niobium solid solution layer 3 and the average thickness of the coating layer 4 are the same. This makes it possible to provide a positive electrode active material that enables higher initial discharge capacity (battery capacity) and initial charge-discharge efficiency in non-aqueous electrolyte secondary batteries, especially all-solid-state batteries.

[0069] Niobium peroxocomplexes can be obtained by adding aqueous ammonia to a niobium compound, followed by the addition of hydrogen peroxide. Specifically, adding aqueous ammonia to the niobium compound makes the system alkaline, which allows for the rapid dissolution of the niobium compound, particularly niobium oxide or niobium hydroxide. Furthermore, aqueous ammonia, in particular, forms an ammine complex, which facilitates the dissolution of the niobium compound. On the other hand, since it is desirable that the oxidation state of niobium does not change in order to maintain the peroxoacid form, adding aqueous hydrogen peroxide makes it possible to easily maintain the oxidation state of niobium at pentavalent.

[0070] (Niobium compounds) The type of niobium compound used in the coating solution is not particularly limited, but examples include niobium hydroxide, niobium oxide, niobium nitrate, niobium pentachloride, and niobium nitrate, with niobium hydroxide being preferred among these. The niobium compound may be used individually or in a mixture of two or more types.

[0071] To form a niobium peroxo complex, for example, niobic acid (diniobium pentoxide hydrate) can be suitably used.

[0072] The niobium compound used to prepare the coating solution may consist of at least one of a single primary particle and a secondary particle comprising multiple primary particles.

[0073] By using a coating solution containing a niobium peroxo complex, lithium ions with a molar ratio of lithium to niobium in the peroxo complex (Li / Nb) of 1.0 ≤ Li / Nb ≤ 2.0, hydrogen peroxide, and ammonia, the reactivity between the niobium peroxo complex and lithium ions is excellent. This allows for the formation of a coating layer precursor 6 consisting of a lithium niobium compound that is more uniform on the surface of the base material 5 and has a sufficiently high niobium content. Ultimately, this enables the formation of a more uniform coating layer 4 on the surface of the lithium transition metal composite oxide particles 2, and allows for a more sufficient niobium content in both the niobium solid solution layer 3 and the coating layer 4.

[0074] (Lithium compounds) The type of lithium compound used in the coating solution is not particularly limited, but examples include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate. Among these, lithium hydroxide is preferred because of its high reactivity and ability to reduce impurities. The lithium compound may be used alone or in a mixture of two or more types.

[0075] (base material) The composition and particle structure of the base material 5 are the same as those of the lithium transition metal composite oxide particles 2, except for the niobium solid solution layer 3 and the presence of niobium due to the niobium solid solution layer 3. The method for producing the base material 5 is not particularly limited, and for example, it can be obtained by mixing nickel composite hydroxide particles obtained by crystallization, or nickel composite oxide particles obtained by roasting the nickel composite hydroxide, with a lithium compound, and then firing. Furthermore, either a batch method or a continuous method can be applied as the method for producing the nickel composite hydroxide particles, and from the viewpoint of cost and obtaining nickel composite hydroxide particles with a wider particle size distribution, it is more preferable to apply a continuous method in which nickel composite hydroxide particles that overflow from the reaction vessel are continuously recovered.

[0076] (Method of attachment) In the adhesion process (S1), the BET specific surface area of ​​the base material 5 is measured, and the coating solution can be prepared according to the target amount of niobium in the niobium solid solution layer 3 and coating layer 4 per unit area of ​​the surface of the lithium transition metal composite oxide particles 2.

[0077] The niobium content in the coating solution is preferably adjusted so that when the coating solution is applied to the surface of the base material 5, the niobium content is greater than 1.0 mol% and less than or equal to 2.2 mol% relative to the total amount of Ni, Co, Mn, and element M in the lithium transition metal composite oxide particles 2. From the viewpoint of further improving battery characteristics, it is even more preferable to prepare the coating solution so that the niobium content is between 1.2 mol% and 2.0 mol%. By regulating the niobium content in the coating solution in this way, the niobium content in the niobium solid solution layer 3 and the coating layer 4 of the positive electrode active material 1 can be set to greater than 1.0 mol% and less than or equal to 2.0 mol% relative to the total amount of Ni, Co, Mn, and element M in the lithium transition metal composite oxide particles 2.

[0078] The lithium ion content in the coating solution is preferably adjusted so that when the coating solution is applied to the surface of the base material 5, the lithium ion content is between 1.0 mol% and 3.0 mol% relative to the total amount of Ni, Co, Mn, and element M in the lithium transition metal composite oxide particles 2. From the viewpoint of appropriately forming the lithium niobium compound constituting the coating layer 4, that is, appropriately defining the lithium content contained in the coating layer 4, and from the viewpoint of uniformly forming the niobium solid solution layer 3, the molar ratio of lithium to niobium in the coating solution is preferably 1.0 ≤ Li / Nb ≤ 2.0, more preferably 1.2 ≤ Li / Nb ≤ 1.8, and even more preferably 1.4 ≤ Li / Nb ≤ 1.6.

[0079] Furthermore, the base material 5 may contain lithium compounds as excess lithium, and lithium derived from the excess lithium in the base material 5 can react with niobium in the coating solution to form part of the lithium-niobium compound (coating layer 4). However, if the coating solution does not contain lithium, it becomes difficult to form a coating layer 4 with a uniform thickness and to stably form the niobium solid solution layer 3.

[0080] Next, the coating liquid is applied to the surface of the base material 5. The device used for application is not particularly limited, as long as it can uniformly coat the surface of the base material 5 with the coating liquid. For example, a general mixer can be used to mix the base material 5 and the coating liquid and then apply it.

[0081] From the viewpoint of forming a more uniform coating layer precursor 6, it is preferable to carry out the application of the coating liquid by spraying and the drying of the coating liquid after application in parallel. For this reason, it is preferable to use a rolling flow coating apparatus to carry out the application of the coating liquid by spraying and the drying of the coating liquid after application in parallel. By using a rolling flow coating apparatus, heated airflow is generated inside the container, the base material 5 is put into a flow state, and the application of the coating liquid by spraying and the drying after application are carried out in parallel, making it possible to uniformly apply the coating liquid to the surface of the base material 5.

[0082] The coating solution may shrink upon drying, and if only one spraying step and one drying step are performed, gaps are likely to form between the lithium transition metal composite oxide particles 2 and the coating layer 4. Therefore, it is preferable to repeat the process of spraying the coating solution and drying it in parallel multiple times. When using a rolling flow coating apparatus, the coating solution can be sprayed onto the base material 5, which is flowing due to a heated airflow inside the apparatus's container. As a result, spraying and drying are automatically repeated, and a uniform coating layer precursor 6 can be formed across the entire surface of the base material 5.

[0083] Drying can be carried out at a temperature sufficient to remove solvents and other contaminants from the coating agent. For example, the supply air temperature in a rolling flow coating apparatus can be set to 80°C or higher and less than 300°C, or it may be set to less than 200°C. In addition, after the adhesion process (S1), additional drying may be performed separately using a stationary dryer or the like.

[0084] The atmosphere during drying is not particularly limited, but it is preferable to use air supplied from a compressor equipped with a dryer, or to create an inert atmosphere using nitrogen gas or argon gas, in order to prevent the base material 5 from reacting with moisture in the atmosphere.

[0085] <Second process [Heat treatment process: Step S2]> The heat treatment step (step S2) is a step (step S2) in which the lithium transition metal composite oxide particles (base material 5) on which the coating layer precursor 6 is formed are heat-treated to form the niobium solid solution layer 3 and the coating layer 4. By performing the heat treatment step (step S2), a portion of the niobium in the coating layer precursor 6 solid-solves into at least a portion (inside) of the surface layer of the base material 5, forming a niobium solid solution layer 3 having a specific thickness (see Figure 3(C)), and firmly bonding the coating layer 4 and the lithium transition metal composite oxide particles 2.

[0086] The heat treatment conditions in the heat treatment step (step S2) are not particularly limited, as long as they are conditions under which the desired niobium solid solution layer 3 is formed.

[0087] The heat treatment atmosphere can be an oxygen-containing atmosphere, such as an air atmosphere. The oxygen concentration in the oxygen-containing atmosphere is preferably equal to or greater than the oxygen concentration in the air atmosphere, i.e., an oxygen concentration of 20% by volume or more. By making the oxygen-containing atmosphere during heat treatment equal to or greater than the oxygen concentration in the air atmosphere, the occurrence of oxygen defects in the resulting positive electrode active material 1 can be suppressed. Since an oxygen atmosphere can also be used, the upper limit of the oxygen concentration in the oxygen-containing atmosphere is 100% by volume.

[0088] The heat treatment temperature is arbitrary as long as it allows for the formation of the niobium solid solution layer 3 and the coating layer 4. For example, the heat treatment temperature can be 100°C to 600°C, preferably 200°C to 500°C. However, a heat treatment temperature of 300°C or higher is preferable because it particularly suppresses the retention of impurities contained in the coating solution within the positive electrode active material. Furthermore, a heat treatment temperature of 600°C or lower is preferable because it suppresses excessive diffusion of the components of the coating layer precursor 6 (lithium, niobium, and other components), and allows for the favorable maintenance of the niobium solid solution layer 3 and the coating layer 4.

[0089] The heat treatment time is, for example, between 1 hour and 5 hours. By making the heat treatment time 1 hour or longer, the retention of impurities contained in the coating solution within the positive electrode active material 1 can be particularly suppressed. Furthermore, even if the heat treatment time is longer than 5 hours, no significant change is observed in the resulting positive electrode active material 1, so from the viewpoint of energy efficiency, it is preferable to make the heat treatment time 5 hours or less.

[0090] After the heat treatment step (step S2), the material is cooled to room temperature to obtain a positive electrode active material 1, which is the final product, in which a coating layer 4 is formed on the surface of lithium transition metal composite oxide particles 2 having a niobium solid solution layer 3. If slight sintering is observed in the positive electrode active material 1 obtained after the heat treatment step (step S2), a further crushing treatment may be performed.

[0091] (3) Non-aqueous electrolyte secondary battery An example of the configuration of a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure will be described. The non-aqueous electrolyte secondary battery in this example has a configuration comprising a positive electrode using a positive electrode active material according to one embodiment of the present disclosure, a negative electrode, and a non-aqueous electrolyte (solid electrolyte or non-aqueous electrolyte solution).

[0092] <Positive electrode> The positive electrode is formed by molding a positive electrode mixture. The positive electrode is then processed as appropriate according to the battery being used. For example, pressure compression using a press may be performed to increase electrode density.

[0093] The positive electrode mixture used in all-solid-state batteries is formed by mixing a powdered positive electrode active material with a solid electrolyte.

[0094] Solid electrolytes are added to electrodes to provide them with appropriate ionic conductivity. The material of the solid electrolyte is not particularly limited, but examples include Li3PS4 and Li7P3S. 11 Li 10 GeP2S 12 Sulfide solid electrolytes such as Li7La3Zr2O 12 Li 0.34 La 0.51 TiO 2.94 Oxide solid electrolytes such as PEO and polymer-based electrolytes such as PEO can be used.

[0095] Binding agents and conductive additives may also be added to the positive electrode mixture. Conductive additives are added to provide the electrode with appropriate conductivity. The material of the conductive additive is not particularly limited, but for example, graphite such as natural graphite, artificial graphite, and expanded graphite, or carbon black-based materials such as acetylene black and Ketjenblack (registered trademark) can be used. The content of the conductive additive is not particularly limited and is appropriately determined according to the performance of the battery to be used. For example, if the total solid content of the positive electrode mixture is 100% by mass, the content of the conductive additive can be 0.5% by mass or more and 20% by mass or less, preferably 1% by mass or more and 10% by mass or less.

[0096] The binder plays the role of holding the positive electrode active material together. The binder used in the positive electrode mixture is not particularly limited, but for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic acid, etc., can be used. The binder content is not particularly limited and is appropriately determined according to the performance of the battery to be used. For example, if the total solid content of the positive electrode mixture is 100% by mass, the binder content can be 1% by mass or more and 30% by mass or less, preferably 2% by mass or more and 15% by mass or less.

[0097] The mixing ratio of the positive electrode active material to the solid electrolyte in the positive electrode mixture is not particularly limited. For example, per 100 parts by mass of the positive electrode mixture, the content of the positive electrode active material can be 50 parts by mass or more and 90 parts by mass or less, and the content of the solid electrolyte can be 10 parts by mass or more and 50 parts by mass or less.

[0098] The cathode mixture may also contain other additives (such as thickeners).

[0099] In this example, even when a sulfide solid electrolyte is included as the solid electrolyte constituting the positive electrode, the positive electrode active material 1 comprises a niobium solid solution layer 3 and a coating layer 4, which makes direct contact between the positive electrode active material and the sulfide solid electrolyte difficult, and sufficiently suppresses the increase in resistance caused by the reaction between the positive electrode active material and the sulfide solid electrolyte.

[0100] The positive electrode mixture paste used in non-aqueous electrolyte secondary batteries is prepared by mixing a positive electrode active material with a binder and a conductive additive, and further adding activated carbon, viscosity adjusters, and other solvents as needed, and then kneading the mixture to create the paste. The mixing ratio of each component in the positive electrode mixture paste can be, for example, if the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material can be 60 parts by mass or more and 95 parts by mass or less, the content of the conductive additive can be 1 part by mass or more and 20 parts by mass or less, and the content of the binder can be 1 part by mass or more and 20 parts by mass or less.

[0101] In this case, the resulting positive electrode mixture paste is applied to the surface of a current collector, for example, made of aluminum foil, and dried to allow the solvent to evaporate. If necessary, pressure is applied using a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode is produced.

[0102] Furthermore, the configuration and manufacturing method of the positive electrode are not limited to those exemplified above, and any other known configuration and manufacturing method for the positive electrode can also be applied.

[0103] <Negative electrode> The negative electrode is formed by molding a negative electrode mixture. Although the components and their proportions of the negative electrode mixture differ, the negative electrode is essentially formed by the same manufacturing method as the positive electrode described above, and various treatments are performed as needed, just as with the positive electrode.

[0104] The negative electrode mixture used in all-solid-state batteries can be prepared by mixing a negative electrode active material with a solid electrolyte. The negative electrode mixture used in non-aqueous electrolyte secondary batteries is prepared by mixing a binder with the negative electrode active material, adding a suitable solvent to form a paste, applying the paste to the surface of a metal foil current collector such as copper, drying it, and compressing it as needed. As the negative electrode active material, for example, an intercalating material capable of intercalating and deintercalating lithium ions can be used.

[0105] The absorbed material is not particularly limited, but for example, one or more selected from natural graphite, artificial graphite, calcined organic compounds such as phenolic resin, and powdered carbon materials such as coke can be used. When such an absorbed material is used as the negative electrode active material, a sulfide electrolyte such as Li3PS4 can be used as the solid electrolyte, similar to the positive electrode.

[0106] Furthermore, the negative electrode can also be composed of a sheet-like member made of a material containing a metal that alloys with lithium, such as metallic lithium or indium.

[0107] <Non-aqueous electrolytes> Among non-aqueous electrolytes, solid electrolytes consist of solids that are lithium-ion conductive and possess the property of being able to withstand high voltages. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

[0108] Inorganic solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes.

[0109] The sulfide solid electrolyte is not particularly limited and can be used as long as it contains sulfur (S) and has lithium ion conductivity and electronic insulating properties. Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, and LiI-Li3PO4-P2S5.

[0110] The oxide solid electrolyte is not particularly limited and can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulating properties. Examples of oxide solid electrolytes include lithium phosphate (Li3PO4) and Li3PO4N. X LiBO2N X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≦X≦1), Li 1+X Al X Ge 2-X (PO4)3(0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≦X≦2 / 3), Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P0.4 Examples include O4.

[0111] In addition, inorganic solid electrolytes other than those mentioned above may be used; for example, Li3N, LiI, Li3N-LiI-LiOH, etc., can also be used.

[0112] The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity; for example, polyethylene oxide, polypropylene oxide, or copolymers thereof can be used. The organic solid electrolyte may also contain a supporting salt (lithium salt).

[0113] Among non-aqueous electrolytes, non-aqueous electrolytes can be prepared by dissolving a lithium salt, which is a supporting salt, in an organic solvent. Organic solvents used in non-aqueous electrolytes can be selected from the following: cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethylmethyl sulfone and butanesultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One of these can be used alone or in mixtures of two or more.

[0114] As supporting salts, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and composite salts thereof can be used. The non-aqueous electrolyte may also contain radical scavengers, surfactants, and flame retardants.

[0115] <Shape and structure of non-aqueous electrolyte secondary batteries> This section describes examples of the arrangement and configuration of components in the non-aqueous electrolyte secondary battery of this example. The non-aqueous electrolyte secondary battery of this example, which comprises a positive electrode, a negative electrode, and a solid electrolyte or non-aqueous electrolyte, can take on various shapes, such as coin-type or stacked type. In any case, a structure can be adopted in which the positive electrode and negative electrode are stacked with a solid electrolyte in between, or a structure in which the positive electrode and negative electrode are stacked with a separator in between to form an electrode body, and the resulting electrode body is impregnated with a non-aqueous electrolyte. The positive electrode current collector and the positive electrode terminal that is open to the outside, and the negative electrode current collector and the negative electrode terminal that is open to the outside are connected using current collector leads, etc., and the battery can be sealed in a battery case to form a non-aqueous electrolyte secondary battery.

[0116] <Characteristics of non-aqueous electrolyte secondary batteries> The non-aqueous electrolyte secondary battery of this example, using the positive electrode active material 1 according to one embodiment of the present disclosure, can exhibit high initial discharge capacity (battery capacity) and initial charge-discharge efficiency.

[0117] Specifically, a test battery was constructed using the positive electrode active material 1 from this example as the positive electrode, and the current density was set to 0.2 mA / cm². 2 Preferably, the initial discharge capacity, which is the discharge capacity when charged to a cutoff voltage of 3.7V (vs. Li-In), discharged to a cutoff voltage of 1.9V (vs. Li-In) after a 1-hour rest, is 165mAh / g or more, more preferably 170mAh / g or more, and even more preferably 172mAh / g.

[0118] Furthermore, the initial charge-discharge efficiency, which is the ratio (%) of the discharge capacity to the charge capacity when charging and discharging under the above conditions, is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more.

[0119] Furthermore, the current density for the positive electrode is 0.2 mA / cm². 2Preferably, the capacity retention rate after 50 cycles, which is the ratio of the discharge capacity to the initial discharge capacity after 50 cycles of charging to 3.7V and discharging to 1.9V, is 75% or higher, and more preferably 80% or higher.

[0120] The applications of the non-aqueous electrolyte secondary battery in this example are not particularly limited and can be suitably used in applications requiring various power sources. Furthermore, even when an all-solid-state battery is used as the non-aqueous electrolyte secondary battery in this example, it has the same charge / discharge capacity as a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte, and can be miniaturized. Therefore, the non-aqueous electrolyte secondary battery in this example, whether an all-solid-state battery or a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte is used, is suitable as a power source for electric vehicles where mounting space is limited. [Examples]

[0121] A positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery according to an example of one embodiment of this disclosure will be described in detail with reference to examples in which these are applied to an all-solid-state battery. This disclosure is not limited to these examples. The analytical methods for the metals contained in the positive electrode active material and the various evaluation methods for the positive electrode active material in the examples and comparative examples are as follows.

[0122] [composition] The composition of the lithium transition metal composite oxide was measured using an ICP emission spectrometer (VARIAN 725ES).

[0123] [BET specific surface area, volume-average particle size (MV), and particle size distribution of the base material] The volume-average particle size (MV), D10, and D90, which are indicators of the particle size distribution of lithium transition metal composite oxide particles (matrix), were measured using a laser diffraction particle size analyzer (manufactured by Nikkiso Co., Ltd., product name: Microtrac). Using the measured values, a variability index expressed as [(D90-D10) / MV] was calculated. In addition, the BET specific surface area of ​​the lithium transition metal composite oxide particles (matrix) was obtained by calculating the BET method from the measurement results obtained by the gas adsorption method.

[0124] [Coating layer and niobium solid solution layer] The presence and type of the niobium solid solution layer 3 and coating layer 4 were confirmed by STEM-EDS surface / line analysis using a scanning transmission electron microscope (STEM, JEOL Ltd., JEM-ARM500F) and an energy-dispersive X-ray spectrometer (EDS, JEOL Ltd., JED-2300T) attached to the STEM. The portion of the surface of the positive electrode active material 1 that contained only Nb and no Ni was identified as coating layer 4, while the portion containing both Nb and Ni was identified as the niobium solid solution layer 3. Furthermore, the crystallinity of the lithium niobium compound was confirmed by XRD measurement using an X-ray diffractometer (XRD, Rigaku Corporation, SmartLab SE).

[0125] The thickness of the coating layer 4 was measured by observing the cathode active material 1, which had been thinned using a cryo-ion slicer (JEOL Ltd., IB-09060CIS), with a TEM. The thickness of the niobium solid solution layer 3 was confirmed by STEM-EDS surface / line analysis.

[0126] The molar ratio of Li / Nb in the coating layer 4, the niobium content in the coating layer 4 and the niobium solid solution layer 3, and the lithium content were determined from the type of lithium compound constituting the coating layer 4, as well as the molar ratio of Li / Nb, niobium content, and lithium content in the coating solution.

[0127] [Structure of the test battery] To evaluate the capacity of the obtained positive electrode active material, a battery with the structure shown in Figure 5 (hereinafter referred to as the "test battery") was used. The test battery 7 consists of a case 8 and compacted powder cells 9 housed within the case 8.

[0128] Case 8 comprises a hollow negative electrode can 10 with one end open, and a positive electrode can 11 positioned at the opening of the negative electrode can 10. When the positive electrode can 11 is positioned at the opening of the negative electrode can 10, a space for housing the compacted powder cell 9 is formed between the positive electrode can 11 and the negative electrode can 10. The positive electrode can 11 is fixed to the negative electrode can 10 with a wing nut 12 and a nut 13.

[0129] The negative electrode can 10 is equipped with a negative terminal (not shown), and the positive electrode can 11 is equipped with a positive terminal (not shown). The case 8 is equipped with an insulating sleeve 14, which fixes the negative electrode can 10 and the positive electrode can 11 in a non-contact state.

[0130] A pressure screw 15 is provided at one closed end of the negative electrode can 10. After fixing the positive electrode can 11 to the negative electrode can 10, the pressure screw 15 is tightened toward the compacted powder cell housing space, thereby holding the compacted powder cell 9 under pressure through the hemispherical washer 16. A screw-in plug 17 is provided at the end of the negative electrode can 10 where the pressure screw 15 is located. O-rings 18 are provided between the negative electrode can 10 and the positive electrode can 11, and between the negative electrode can 10 and the plug 17, sealing the gap between the negative electrode can 10 and the positive electrode can 11 and maintaining airtightness within the case 8.

[0131] The compacted cell 9 is composed of pellets stacked in the order of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The positive electrode layer is housed in the case 8 so as to contact the inner surface of the positive electrode can 11 through the lower current collector 19, and the negative electrode layer is housed in the case 8 so as to contact the inner surface of the negative electrode can 10 through the upper current collector 20, a hemispherical washer 16, and a pressure screw 15. The lower current collector 19, the compacted cell 9, and the upper current collector 20 are protected by a sleeve 21 so as not to electrically contact the positive and negative electrode layers.

[0132] [Preparation of test batteries] A test battery 7 like this was manufactured as follows.

[0133] First, 80 mg of the synthesized solid electrolyte was pressurized at 25 MPa using a pellet former to obtain a solid electrolyte pellet. Next, 70 mg of the positive electrode active material and 30 mg of the solid electrolyte were mixed in a mortar. The solid electrolyte pellet and 15 mg of the mixture of positive electrode active material and solid electrolyte were placed in the pellet former and pressurized at 360 MPa to form a positive electrode layer on the solid electrolyte pellet. The electrodes were stacked in the following order from bottom to top: the lower electrode, the pellet with the positive electrode layer facing downwards, the indium foil, and the upper electrode, and pressed with 9 kN to form the electrode. The electrode was sealed in a case and the pressure screw was tightened with a torque of 6 N·m to 7 N·m. Test battery 7 was fabricated in a glove box with an Ar atmosphere where the dew point was controlled to -80°C.

[0134] [Initial discharge capacity] The charge and discharge capacity of the fabricated test battery 7 was evaluated as follows: The initial discharge capacity of the all-solid-state battery was determined by leaving the test battery, which used indium foil as the negative electrode, for about 24 hours after fabrication, until the open circuit voltage (OCV) stabilized, and then measuring the current density to the positive electrode at 0.2 mA / cm². 2 The discharge capacity (initial discharge capacity) was evaluated by measuring the discharge capacity after charging to a cutoff voltage of 3.7V (vs. Li-In), letting it sit for 1 hour, and then discharging it to a cutoff voltage of 1.9V (vs. Li-In).

[0135] [Initial charge / discharge efficiency] The initial charge-discharge capacity obtained in the measurement of the initial discharge capacity described above, and the ratio of the initial charge-discharge capacity (=initial discharge capacity / initial charge-discharge capacity × 100 (%)) were calculated as the initial charge-discharge efficiency.

[0136] [Capacity retention rate after 50 cycles] The capacitance retention rate after 50 cycles is calculated based on a current density of 0.2 mA / cm² relative to the positive electrode. 2 The capacity retention rate after 50 cycles was calculated by determining the ratio of the discharged capacity to the initial discharged capacity after 50 cycles of charging to 3.7V and discharging to 1.9V.

[0137] [Example 1] (Preparation of the base material) As a base material, a hydroxide powder mainly composed of Mn and lithium hydroxide were mixed and then calcined to obtain lithium transition metal composite oxide particles. The obtained lithium transition metal composite oxide particles are Li 1.5 Ni 0.15 Co 0.17 Mn 0.68 It has a composition represented by O2, a volume-average particle size MV of 7.0 μm, a ratio of [(d90-d10) / volume-average particle size MV] of 1.1, and a BET specific surface area of ​​1.24 m². 2 The concentration was / g. The lithium transition metal composite oxide particles contained secondary particles composed of multiple primary particles, and the average particle size of the primary particles was 0.2 μm. The obtained lithium transition metal composite oxide particles were used as the base material.

[0138] (Preparation of coating solution) For 500 g of lithium transition metal composite oxide particles (base material), 15.6 g of niobium hydroxide (Nb2O5·nH2O, Nb2O5 equivalent concentration 53% by mass) was used to prepare a coating solution for lithium niobate, more specifically, a coating solution containing a niobium peroxo complex, lithium ions with a molar ratio of Li / Nb = 1.0 to 1 mole of niobium in the peroxo complex, hydrogen peroxide, and ammonia.

[0139] (Adhesion process) The coating solution was applied by spraying it onto 500g of base material using a rolling flow coating device (MP-01, manufactured by Powrec Co., Ltd.). Specifically, 500g of base material was sprayed with air heated to 120°C at a flow rate of 0.3m 3 The material was flowed into the chamber at a rate of / min, and the coating solution was sprayed onto this base material at a rate of 1 ml / min.

[0140] (Heat treatment process) After spraying the entire amount of coating solution, the lithium transition metal composite oxide particles to which the coating solution had adhered were recovered from inside the chamber and subjected to heat treatment at 300°C for 2 hours under oxygen flow (100% oxygen concentration) in an atmospheric firing furnace.

[0141] Subsequently, the material was cooled to room temperature to obtain lithium transition metal composite oxide particles having a coating layer that served as the positive electrode active material. The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0142] Figure 4 shows the results of STEM-EDS surface / line analysis of the positive electrode active material of Example 1. From left to right, the images show the STEM image, the distribution of Ni by STEM-EDS, and the distribution of Nb by STEM-EDS. As shown in Figure 4, Nb exists on the surface of the lithium transition metal composite oxide particles (the portion that coincides with the distribution of Ni inside the surface) and as a coating layer covering the surface (surface layer).

[0143] XRD analysis of the positive electrode active material obtained in Example 1 did not yield a clear peak for lithium niobium compounds. Therefore, it is considered that the lithium niobium compound present on the surface (coating layer) of the positive electrode active material is in an amorphous state. Furthermore, STEM-EDS surface / line analysis confirmed that the lithium compound constituting the coating layer 4 is LiNbO3.

[0144] [Example 2] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 1.5. XRD measurement did not yield a clear peak for the lithium niobium compound. Furthermore, STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4 (mostly LiNbO3, but with some Li3NbO4). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0145] [Example 3] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 2.0. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4 (a mixture of LiNbO3 and Li3NbO4). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Table 1.

[0146] [Example 4] As a base material, the composition is Li 1.5 Ni 0.3 Co 0.3 Mn 0.4 It has a composition represented by O2, and its secondary particles have a volume-average particle size MV of 6.8 μm, a ratio of [(d90-d10) / volume-average particle size MV] of 1.2, and a BET specific surface area of ​​0.86 m². 2 The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that lithium transition metal composite oxide particles were used as the base material. XRD measurement did not yield a clear peak for lithium niobium compounds. Furthermore, STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3. The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0147] [Example 5] The positive electrode active material was obtained and evaluated in the same manner as in Example 4, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 1.5. XRD measurement did not yield a clear peak for the lithium niobium compound. Furthermore, STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4 (mostly LiNbO3, but with some Li3NbO4). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0148] [Example 6] The positive electrode active material was obtained and evaluated in the same manner as in Example 4, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 2.0. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4 (a mixture of LiNbO3 and Li3NbO4). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0149] [Comparative Example 1] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that no coating treatment was applied to the base material. The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0150] [Comparative Example 2] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 0.8. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-LiNb3O8 (composed of LiNbO3 and a smaller amount of LiNb3O8). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0151] [Comparative Example 3] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 2.5. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4-Li8Nb2O9 (composed of LiNbO3, a larger amount of Li3NbO4, and a small amount of Li8Nb2O9). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Table 1.

[0152] [Comparative Example 4] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 4.0. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was Li3NbO4-Li8Nb2O9 (a mixture of Li3NbO4 and Li8Nb2O9). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0153] [Comparative Example 5] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the coating solution was prepared using 31.2 g of niobium hydroxide (Nb2O5·nH2O, Nb2O5 equivalent concentration 53% by mass) so that the niobium content of the coating layer was 2.6% by mass for 500 g of lithium transition metal composite oxide particles (base material), 4.4 g of anhydrous lithium hydroxide (LiOH) so that the Li / Nb molar ratio of the coating layer was 1.5, 50 ml of 35% hydrogen peroxide solution, and 50 ml of 28% ammonia solution. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4 (mostly LiNbO3, but with some Li3NbO4). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0154] [Comparative Example 6] The positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the coating solution was prepared using 9.6 g of niobium hydroxide (Nb2O5·nH2O, Nb2O5 equivalent concentration 53% by mass) so that the niobium content of the coating layer was 0.8% by mass for 500 g of lithium transition metal composite oxide particles (base material), 1.35 g of anhydrous lithium hydroxide (LiOH) so that the Li / Nb molar ratio of the coating layer was 1.5, 50 ml of 35% hydrogen peroxide solution, and 50 ml of 28% ammonia solution. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4 (mostly LiNbO3, but with some Li3NbO4). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0155] [Comparative Example 7] The positive electrode active material was obtained and evaluated in the same manner as in Example 4, except that no coating treatment was applied to the base material. The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0156] [Comparative Example 8] The positive electrode active material was obtained and evaluated in the same manner as in Example 4, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 0.8. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-LiNb3O8 (composed of LiNbO3 and a smaller amount of LiNb3O8). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0157] [Comparative Example 9] The positive electrode active material was obtained and evaluated in the same manner as in Example 4, except that the amount of lithium hydroxide in the coating solution was adjusted so that the Li / Nb molar ratio was 2.5. XRD measurement did not yield a clear peak for the lithium niobium compound. STEM-EDS surface analysis confirmed that the lithium compound constituting the coating layer 4 was LiNbO3-Li3NbO4 (composed of LiNbO3 and a larger amount of Li3NbO4). The manufacturing conditions and evaluation results of the obtained positive electrode active material are shown in Tables 1 and 2.

[0158] [Table 1]

[0159] [Table 2]

[0160] [evaluation] The non-aqueous electrolyte secondary batteries (all-solid-state batteries) using the positive electrode active materials of Examples 1 to 6, despite using positive electrode active materials with a high manganese content, exhibited high initial discharge capacity and high capacity retention after 50 cycles, demonstrating improved durability. This is thought to be because the presence of a coating layer and niobium solid solution layer with a sufficiently high niobium content suppressed side reactions between the positive electrode active material, which consists of lithium transition metal composite oxides, and the non-aqueous electrolyte (solid electrolyte), thereby suppressing degradation.

[0161] The positive electrode active materials of Comparative Examples 1 and 7 did not contain niobium, resulting in low initial discharge capacity and low capacity retention after 50 cycles. The positive electrode active materials of Comparative Examples 2 and 8 had low lithium content, resulting in improved initial discharge capacity compared to the positive electrode active material of Comparative Example 1, but lower initial discharge capacity and capacity retention after 50 cycles compared to the positive electrode active materials of Examples 1-6. Furthermore, the positive electrode active materials of Comparative Examples 3, 4, and 9 had excessively high lithium content, resulting in improved initial discharge capacity compared to the positive electrode active material of Comparative Example 1, but lower initial discharge capacity and capacity retention after 50 cycles compared to the positive electrode active materials of Examples 1-6.

[0162] Furthermore, the positive electrode active material of Comparative Example 6 had a low niobium content, resulting in improved initial discharge capacity compared to the positive electrode active material of Comparative Example 1. However, compared to the positive electrode active materials of Examples 1 to 6, its initial discharge capacity and capacity retention rate after 50 cycles were lower. The positive electrode active material of Comparative Example 5 had an excessive niobium content. Although its initial discharge capacity improved compared to the positive electrode active material of Comparative Example 1, it also had a lower initial discharge capacity and capacity retention rate after 50 cycles compared to the positive electrode active materials of Examples 1 to 6.

[0163] From the results above, it has been shown that the positive electrode active material according to one embodiment of the present disclosure has a coating layer and a niobium solid solution layer with a sufficiently high niobium content, and the lithium content in the coating layer is sufficient, thereby having a high battery capacity and achieving improved capacity retention rate (durability) after 50 cycles. [Explanation of Symbols]

[0164] 1 Cathode active material 2. Particles of lithium transition metal composite oxides 3. Niobium solid solution layer 4 Covering layer 5. Particles of lithium transition metal composite oxide (matrix material) 6 Coating layer precursor 7 Test batteries 8 cases 9. Compacted powder cell 10 Negative electrode cans 11 Positive electrode can 12 wing nuts 13 nuts 14 Insulating sleeves 15 Pressure screw 16 Hemispherical Washer 17 plugs 18 O-rings 19 Lower current collector 20 Upper current collector 21 sleeves

Claims

1. The material comprises particles of a lithium transition metal composite oxide and a coating layer covering at least a portion of the surface of the particles. The lithium transition metal composite oxide particles contain Li, Ni, Co, Mn, and element M in a molar ratio of Li:Ni:Co:Mn:M = s:x:y:(1-x-y-z):z (where M is at least one element selected from the group consisting of V, Mg, Mo, Nb, Ti, W, Zr, and Al, with 1.3 ≤ s < 1.6, 0.05 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.1), and are provided with a niobium solid solution layer having an average thickness of 0.5 nm to 20 nm, in which niobium is solid-dissolved in at least a portion of the surface. The coating layer comprises a compound containing lithium and niobium, has an average thickness of 2 nm or more and 1 μm or less, and The niobium content in the niobium solid solution layer and the coating layer is greater than 1.0 mol% and less than or equal to 2.0 mol% relative to the total amount of Ni, Co, Mn, and element M constituting the particles of the lithium transition metal composite oxide, and the lithium content in the coating layer is between 1.0 and 2.0 in molar ratio to the niobium contained in the coating layer. Positive electrode active material for non-aqueous electrolyte secondary batteries.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the compound comprising lithium and niobium comprises at least lithium niobate.

3. The aforementioned compound containing lithium and niobium is Li ３ NboO ４ LiNbo ３ LiNb ３ O ８ , and Li ８ Nb ２ O ９ A positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, comprising at least one of the following.

4. The lithium content in the coating layer is 1.0 mol% or more and 3.0 mol% or less relative to the total amount of Ni, Co, Mn, and element M constituting the particles of the lithium transition metal composite oxide, as described in claim 1.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the compound containing lithium and niobium is amorphous.

6. A method for obtaining a positive electrode active material for a non-aqueous electrolyte secondary battery as described in claim 1, The method includes: applying a coating solution containing lithium and niobium to the surface of lithium transition metal composite oxide particles as a base material to form a coating layer precursor; heat-treating the lithium transition metal composite oxide particles on which the coating layer precursor is formed to form a niobium solid solution layer in which niobium is solid-dissolved in at least a portion of the surface of the lithium transition metal composite oxide particles, and forming a coating layer that covers at least a portion of the surface of the lithium transition metal composite oxide particles; The coating solution comprises a niobium peroxo complex, lithium ions, hydrogen peroxide, and ammonia, and The niobium content in the coating solution is greater than 1.0 mol% and 2.2 mol% or less relative to the total amount of Ni, Co, Mn, and element M constituting the particles of the lithium transition metal composite oxide, and the molar ratio of lithium to niobium in the peroxo complex in the coating solution is 1.0 or more and 2.0 or less (1.0 ≤ Li / Nb ≤ 2.0). A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

7. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the lithium content in the coating layer is 1.0 mol% or more and 3.0 mol% or less with respect to the total amount of Ni, Co, Mn, and element M constituting the particles of the lithium transition metal composite oxide.

8. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6, wherein the coating liquid is applied to the lithium transition metal composite oxide particles using a rolling flow coating apparatus.

9. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, applicable to the positive electrode of an all-solid-state battery in which a solid electrolyte is used as the non-aqueous electrolyte.

10. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte, or comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode active material used in the positive electrode is the positive electrode active material for a non-aqueous electrolyte secondary battery described in claim 1.

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