Coated active material, electrode mixture, battery, and coat solution

Abstract

To provide a coated active material capable of suppressing a resistance increase even when an electrode active material having a high nickel ratio and a coating layer containing phosphorus are combined with each other.SOLUTION: In the present disclosure, there is provided a coated active material including an electrode active material and a coating layer that covers the electrode active material. The electrode active material includes an Li element, an M element (M is a metal other than Li and at least contains Ni), and an O element, a molar ratio (Ni / M) of the Ni to the M is 80% or more, the coating layer includes a B element, a P element, an La element, and an O element, and a molar ratio (La / P) of the La element to the P element is 0.005 or more and 0.15 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a coated active material, an electrode composite material, a battery, and a coating solution.

Background Art

[0002] In recent years, the development of batteries has been actively carried out. For example, in the automotive industry, the development of batteries used in battery electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), or hybrid electric vehicles (HEVs) has been promoted. Further, it is known to coat the surface of an electrode active material used in a battery with a phosphorus-based coating solution.

[0003] For example, Patent Document 1 discloses composite particles including positive electrode active material particles and a coating film that covers at least a part of the surface of the positive electrode active material particles and contains a phosphorus compound. Further, Patent Document 1 discloses that composite particles are manufactured by mixing positive electrode active material particles and an aqueous coating solution containing phosphorus (aqueous coating solution) and drying them.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Electrode active materials with a high nickel ratio are promising from the viewpoint of increasing the capacity. On the other hand, when an aqueous coating solution containing phosphorus comes into contact with an electrode active material with a high nickel ratio, an exchange reaction between H + and Li + is presumed to occur, and high-resistance NiO is generated. As a result, an increase in resistance occurs. This is a problem peculiar to the case of combining an electrode active material with a high nickel ratio and an aqueous coating solution containing phosphorus (coating layer containing phosphorus).

[0006] The present disclosure has been made in view of the above circumstances, and the main object is to provide a coated active material capable of suppressing an increase in resistance even when combined with an electrode active material having a high nickel ratio and a coating layer containing phosphorus.

Means for Solving the Problems

[0007] [1] A coated active material having an electrode active material and a coating layer that coats the electrode active material, wherein the electrode active material has Li element, M element (M is a metal other than Li and contains at least Ni), and O element, the molar ratio of Ni to M (Ni / M) is 80% or more, the coating layer contains B element, P element, La element and O element, a coated active material in which the molar ratio of La to P (La / P) with respect to the P element is 0.005 or more and 0.15 or less.

[0008] [2] The coated active material according to [1], wherein La / P is 0.01 or more and 0.11 or less.

[0009] [3] The coated active material according to [1] or [2], wherein the molar ratio of B to P (B / P) with respect to the P element is 0.5 or more and 2.0 or less.

[0010] [4] The coated active material according to any one of [1] to [3], wherein the coating rate of the coating layer with respect to the electrode active material is 75% or more.

[0011] [5] The coated active material according to any one of [1] to [4], wherein M further contains at least one of Co, Mn, and Al.

[0012] [6] An electrode composite material containing the coated active material according to any one of [1] to [5] and at least one of a conductive material and a binder.

[0013] [7] The electrode composite material according to [6], wherein the electrode composite material contains a solid electrolyte.

[0014] [8] The electrode composite material according to [7], wherein the solid electrolyte is a sulfide solid electrolyte.

[0015] [9] A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, The battery, wherein the positive electrode layer or the negative electrode layer contains the electrode composite material according to any one of [6] to [8].

[0016]

[10] The battery according to [9], wherein the positive electrode layer contains the electrode composite material.

[0017]

[11] The battery according to [9] or

[10] , wherein the electrolyte layer contains a solid electrolyte.

[0018]

[12] A coating liquid for forming the coating layer in the coated active material according to any one of [1] to [8], The coating liquid contains a solute containing B element, P element and La element, and water as a solvent, The molar ratio (La / P) of the La element to the P element is 0.001 or more and 0.100 or less, The coating liquid having an absorbance of 0.1 or less.

Effect of the Invention

[0019] The coated active material in the present disclosure has an effect of suppressing an increase in resistance even when combined with an electrode active material having a high nickel ratio and a coating layer containing phosphorus.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0021] Hereinafter, the coated active material, electrode binder, battery, and coating solution in the present disclosure will be described in detail.

[0022] A. Coated active material FIG. 1 is a schematic cross-sectional view illustrating a coated active material in the present disclosure. The coated active material 10 shown in FIG. 1 has an electrode active material 1 and a coating layer 2 that coats the electrode active material 1. The electrode active material 1 has Li element, M element (M is a metal other than Li and contains at least Ni), and O element. Further, the molar ratio of Ni to M (Ni / M) is 80% or more. On the other hand, the coating layer 2 contains B element, P element, La element, and O element, and the molar ratio of La element to P element (La / P) is 0.005 or more and 0.15 or less.

[0023] According to the present disclosure, by adding La element to the coating layer, even when combined with an electrode active material having a high nickel ratio and a coating layer containing phosphorus, a coated active material capable of suppressing an increase in resistance can be obtained. As described above, Patent Document 1 discloses that composite particles are produced by mixing a positive electrode active material particle and an aqueous coating solution containing phosphorus and drying. On the other hand, an electrode active material having a high nickel ratio is promising from the viewpoint of increasing the capacity. When an aqueous coating solution containing phosphorus comes into contact with an electrode active material having a high nickel ratio, an exchange reaction between H + and Li + is presumed to occur, and high-resistance NiO is generated. As a result, an increase in resistance occurs. For example, when the electrode active material is LiNiO2, the following reaction is presumed to occur. LiNiO2 + H + → NiOOH + Li+ NiOOH → NiO + 0.5H2O + 0.25O2

[0024] In particular, when an aqueous coating solution containing phosphorus is used, it is presumed that the presence of P element makes it easier for moisture to stay in the coating layer, and the above exchange reaction is promoted. On the contrary, in the present disclosure, by adding La element having a high affinity with P element, it is presumed that the retention of moisture in the coating layer is suppressed, and as a result, the above exchange reaction is suppressed. Therefore, an increase in resistance can be suppressed. Further, since the coating layer contains P element, the chemical stability of the coating layer is improved. Furthermore, since the coating layer contains B element in addition to P element, the ionic conductivity of the coating layer can be improved while improving the chemical stability of the coating layer.

[0025] 1. Coating layer The coating layer in the present disclosure is a layer that coats the electrode active material. Further, the coating layer contains B element, P element and O element. The coating layer may further contain Li element. Further, the coating layer preferably contains a PO4 structure.

[0026] In the coating layer, the molar ratio of La element to P element (La / P) is usually 0.005 or more and 0.15 or less, and may be 0.01 or more and 0.11 or less. If La / P is too small, the resistance suppression effect by La element may not be sufficiently obtained. On the other hand, if La / P is too large, the manufacturing may become difficult.

[0027] In the coating layer, the molar ratio of B element to P element (B / P) is not particularly limited. For example, it is 0.5 or more and 2.0 or less, and may be 0.8 or more and 1.25 or less, or may be 0.9 or more and 1.11 or less. Further, when the coating layer further contains Li element, the molar ratio of Li element to the total of P element and B element (Li / (P + B)) is not particularly limited. For example, it is 0.3 or more and 1.2 or less, and may be 0.5 or more and 1.0 or less.

[0028] The coating rate of the coating layer on the electrode active material is not particularly limited, but for example, it is 75% or more, and may be 80% or more. If the coating rate is too low, it may not be possible to sufficiently suppress the increase in resistance due to the high-resistance layer generated by the reaction between the electrode active material and the electrolyte. On the other hand, the coating rate may be 100% or less than 100%. In the present disclosure, the coating rate is determined as the ratio of the elements contained in the coating layer to the total of the elements contained in the electrode active material and the elements contained in the coating layer, by calculating the element ratio from the intensity ratio of the main elements based on X-ray photoelectron spectroscopy (XPS) measurement.

[0029] The thickness of the coating layer is not particularly limited, but for example, it is 1 nm or more and 100 nm or less, may be 5 nm or more and 50 nm or less, or may be 10 nm or more and 30 nm or less. The thickness of the coating layer is obtained, for example, as the average value of the thicknesses of a plurality of samples (for example, 100 or more samples) observed by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0030] 2. Electrode active material The electrode active material in the present disclosure usually has Li element, M element, and O element. M is a metal other than Li (including semimetals) and contains at least Ni. M other than Ni may be a transition metal or a metal (including semimetals) belonging to Groups 13 to 16 of the periodic table. Also, M other than Ni may be one kind of metal or two or more kinds of metals. Among them, it is preferable that M other than Ni is at least one of Co, Mn, Al, V, and Fe.

[0031] The molar ratio of Ni to M (Ni / M) is usually 80% or more, and may be 85% or more, or may be 90% or more. On the other hand, Ni / M may be 100% or less than 100%.

[0032] In addition to Li element, M element, and O element, the electrode active material may contain non-metallic elements such as P element. Also, the crystal structure of the electrode active material is not particularly limited, and examples thereof include a rock salt layered structure, a spinel structure, and an olivine structure.

[0033] As an example of the composition of the electrode active material, LiNi x Co y Al z O2 (0.80 ≦ x, 0 ≦ y, 0 ≦ z, x + y + z = 1) can be mentioned. x is usually 0.80 or more, may be 0.85 or more, and may be 0.90 or more. y may be 0, or may be greater than 0. Also, y is, for example, 0.20 or less. z may be 0, or may be greater than 0. Also, z is, for example, 0.10 or less.

[0034] As another example of the composition of the electrode active material, LiNi a Co b Mn c O2 (0.80 ≦ a, 0 ≦ b, 0 ≦ c, a + b + c = 1) can be mentioned. a is usually 0.80 or more, may be 0.85 or more, and may be 0.90 or more. b may be 0, or may be greater than 0. Also, b is, for example, 0.20 or less. c may be 0, or may be greater than 0. Also, c is, for example, 0.20 or less.

[0035] The shape of the electrode active material is usually particulate. The particle diameter D of the electrode active material 50 is, for example, 100 nm or more, may be 1 μm or more, and may be 5 μm or more. On the other hand, the particle diameter D of the electrode active material 50 is, for example, 50 μm or less, and may be 20 μm or less. In the present disclosure, the particle diameter D 50 corresponds to the particle diameter corresponding to the cumulative 50 volume% measured by a laser diffraction particle size distribution measuring device.

[0036] 3. Coating active material The coating active material in the present disclosure is usually used in a battery. The electrode active material in the coating active material may be a positive electrode active material or a negative electrode active material, but the former is preferred. Further, the method for producing the coating active material is not particularly limited. For example, a method having a preparation step of preparing an electrode active material and a coating liquid, and a coating layer forming step of forming a coating layer by coating the electrode active material with the coating liquid and drying it can be mentioned.

[0037] In the preparation step, an electrode active material and a coating liquid are prepared. The electrode active material is the same as described in the above "A. Coating active material". On the other hand, the coating liquid will be described in "D. Coating liquid" described later. In the coating layer forming step, a coating layer is formed by coating the electrode active material with the coating liquid and drying it. As a method of coating the electrode active material with the coating liquid and drying it, for example, a spray drying method can be mentioned. In the present disclosure, it is also possible to provide a method for producing a coating active material having the above-described preparation step and coating layer forming step.

[0038] B. Electrode composite The electrode composite in the present disclosure contains the above-described coating active material and at least one of a conductive material and a binder.

[0039] According to the present disclosure, by using the above-described coating active material, even when combined with an electrode active material having a high nickel ratio and a coating layer containing phosphorus, an electrode composite capable of suppressing an increase in resistance can be obtained.

[0040] The electrode composite contains the coating active material and at least one of a conductive material and a binder. The coating active material is the same as described in the above "A. Coating active material". The electrode active material in the coating active material may be a positive electrode active material or a negative electrode active material, but the former is preferred. That is, the electrode composite may be a positive electrode composite or a negative electrode composite, but the former is preferred.

[0041] The proportion of the coating active material in the electrode composite material is, for example, 20% by weight or more, and may be 30% by weight or more, or may be 40% by weight or more. If the proportion of the coating active material is too small, sufficient energy density may not be obtained. On the other hand, the proportion of the coating active material is, for example, 80% by weight or less, and may be 70% by weight or less, or may be 60% by weight or less. If the proportion of the coating active material is too large, the ionic conductivity and electronic conductivity in the electrode composite material may relatively decrease.

[0042] The electrode composite material contains at least one of a conductive material and a binder. Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of the binder include rubber-based binders and fluoride-based binders.

[0043] The electrode composite material may further contain a solid electrolyte. The solid electrolyte may be an organic solid electrolyte such as a gel electrolyte, or an inorganic solid electrolyte such as a sulfide solid electrolyte or an oxide solid electrolyte. Among them, the solid electrolyte is preferably a sulfide solid electrolyte because of its high ionic conductivity.

[0044] The sulfide solid electrolyte usually contains at least Li element and S element. The sulfide solid electrolyte preferably further contains a Me element (Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In). The sulfide solid electrolyte may also contain a halogen element such as F, Cl, Br, or I.

[0045] The sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide solid electrolyte may have a crystalline phase. Examples of the crystalline phase include a Thio-LISICON type crystalline phase, an argyrodite type crystalline phase, and an LGPS type crystalline phase.

[0046] The composition of the sulfide solid electrolyte is not particularly limited, and examples include xLi2S·(1-x)P2S5 (0.5≦x<1), yLiI·zLiBr·(100-y-z)(xLi2S·(1-x)P2S5) (0.5≦x<1, 0≦y≦30, 0≦z≦30). In these compositions, it is preferable that x satisfies 0.7≦x≦0.8. Also, as other examples of the composition of the sulfide solid electrolyte, Li 7-x-2y PS 6-x-y X y is included. X is at least one of F, Cl, Br, and I, and x and y satisfy 0≦x, 0≦y. Also, as other examples of the composition of the sulfide solid electrolyte, Li 4-x Me 1-x P x S4 (0<x<1) is included. Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0047] C. Battery FIG. 2 is a schematic cross-sectional view illustrating the battery in the present disclosure. The battery 20 shown in FIG. 2 includes a positive electrode layer 11, a negative electrode layer 12, an electrolyte layer 13 disposed between the positive electrode layer 11 and the negative electrode layer 12, a positive electrode current collector 14 that collects current from the positive electrode layer 11, and a negative electrode current collector 15 that collects current from the negative electrode layer 12. In the present disclosure, the positive electrode layer 11 or the negative electrode layer 12 contains the electrode composite material described in the above "B. Electrode Composite Material".

[0048] According to the present disclosure, by using the above-described electrode composite material, even when combined with a high-nickel ratio electrode active material and a coating layer containing phosphorus, a battery with suppressed resistance increase can be obtained. As described above, the electrode composite material may be a positive electrode composite material or a negative electrode composite material, but the former is preferred. Hereinafter, when the electrode composite material is a positive electrode composite material, the details of the battery will be described.

[0049] 1. Positive electrode layer The positive electrode layer in the present disclosure contains the above-described electrode composite material (positive electrode composite material). Since the description of the electrode composite material is the same as that described in "B. Electrode composite material" above, the description here is omitted. Further, the positive electrode layer may contain an electrolyte as necessary. The description of the electrolyte is the same as that described in "3. Electrolyte layer". The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or may be 0.1 μm or more and 100 μm or less. Further, as a method for forming the positive electrode layer, for example, a method of coating the electrode composite material (positive electrode composite material) on a positive electrode current collector can be mentioned.

[0050] 2. Negative electrode layer The negative electrode layer is a layer containing at least a negative electrode active material. Further, the negative electrode layer may contain at least one of an electrolyte, a conductive material, and a binder as necessary.

[0051] Examples of the negative electrode active material include metal active materials such as Li, Si-based active materials, carbon active materials such as graphite, and oxide active materials such as Li4Ti5O 12 and the like.

[0052] The negative electrode active material is preferably a Si-based active material because it can achieve a higher capacity of the battery. The Si-based active material is an active material mainly composed of Si. The Si-based active material may be single-crystalline Si, an Si alloy, or an Si oxide. Further, the Si-based active material may have a diamond-type crystal phase, a clathrate I-type crystal phase, or a clathrate II-type crystal phase. In the clathrate I-type or II-type crystal phase, a polyhedron (cage) containing a pentagon or a hexagon is formed by a plurality of Si elements. Since this polyhedron has a space inside that can enclose Li ions, volume changes due to charge and discharge can be suppressed.

[0053] Examples of the shape of the negative electrode active material include particulate. The particle diameter D of the negative electrode active material 50 is not particularly limited, but is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the particle diameter D of the negative electrode active material 50 is, for example, 50 μm or less, and may be 20 μm or less.

[0054] The electrolyte used for the negative electrode layer is the same as the content described in "3. Electrolyte layer". Further, since the conductive material and the binder used for the negative electrode layer are the same as the content described in the above "B. Electrode composite material", the description here is omitted. The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less, may be 0.1 μm or more and 500 μm or less, or may be 0.1 μm or more and 100 μm or less.

[0055] 3. Electrolyte layer The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer and contains at least an electrolyte. The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolyte solution).

[0056] Regarding the solid electrolyte, since it is the same as the content described in the above "B. Electrode composite material", the description here is omitted. On the other hand, the electrolytic solution preferably contains a supporting salt and a solvent. Examples of the supporting salt (lithium salt) of the electrolytic solution having lithium ion conductivity include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAsF6, etc., and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, LiC(CF3SO2)3, etc. Examples of the solvent used in the electrolytic solution include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc., and chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. The electrolytic solution preferably contains two or more solvents.

[0057] The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or may be 0.1 μm or more and 100 μm or less.

[0058] 4. Other configurations The battery in the present disclosure preferably has a positive electrode current collector for collecting current of the positive electrode layer and a negative electrode current collector for collecting current of the negative electrode layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon.

[0059] The battery in the present disclosure may further include a restraining jig that applies a restraining pressure along the thickness direction to the positive electrode layer, the electrolyte layer, and the negative electrode layer. In particular, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply a restraining pressure in order to form good ion conduction paths and electron conduction paths. The restraining pressure is, for example, 0.1 MPa or more, may be 1 MPa or more, and may be 5 MPa or more. On the other hand, the restraining pressure is, for example, 100 MPa or less, may be 50 MPa or less, and may be 20 MPa or less.

[0060] 5. Battery The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. Further, the battery in the present disclosure may be a liquid battery containing an electrolytic solution as the electrolyte layer, or may be a solid battery having a solid electrolyte layer as the electrolyte layer. The solid battery may be a semi-solid battery or a all-solid battery. Further, the battery in the present disclosure may be a primary battery or a secondary battery, but among them, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery.

[0061] Examples of the uses of the battery include power sources for vehicles such as hybrid vehicles (HEV), plug-in hybrid vehicles (PHEV), battery electric vehicles (BEV), gasoline vehicles, and diesel vehicles. In particular, it is preferably used as a driving power source for a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), or a battery electric vehicle (BEV). Further, the battery may be used as a power source for mobile bodies other than vehicles (for example, railways, ships, and aircraft), or may be used as a power source for electrical products such as information processing devices.

[0062] D. Coating Liquid The coating liquid in the present disclosure is a coating liquid for forming the coating layer in the coating active material described in the above "A. Coating active material". The coating liquid contains a solute containing B element, P element and La element, and water as a solvent. The molar ratio (La / P) of the La element to the P element is 0.001 or more and 0.100 or less. Further, the absorbance of the coating liquid is 0.1 or less.

[0063] According to the present disclosure, by adding the La element so as to obtain a predetermined absorbance, even when combined with an electrode active material having a high nickel ratio, a coating liquid capable of suppressing an increase in resistance can be obtained.

[0064] The coating liquid contains a solute containing B element, P element and La element, and water as a solvent. The solute may further contain an O element. Among them, the solute preferably contains a PO4 structure. Further, the coating liquid may further contain a Li element.

[0065] In the coating liquid, the molar ratio (La / P) of the La element to the P element is usually 0.001 or more and 0.100 or less, and may be 0.003 or more and 0.080 or less. If La / P is too small, the resistance suppression effect by the La element may not be sufficiently obtained. On the other hand, if La / P is too large, the production may become difficult.

[0066] In the coating liquid, the molar ratio (B / P) of the B element to the P element is not particularly limited. For example, it may be 0.5 or more and 2.0 or less, may be 0.8 or more and 1.25 or less, and may be 0.9 or more and 1.11 or less. Further, when the coating liquid further contains a Li element, the molar ratio (Li / (P + B)) of the Li element to the total of the P element and the B element is not particularly limited. For example, it may be 0.3 or more and 1.2 or less, and may be 0.5 or more and 1.0 or less.

[0067] The absorbance of the coating liquid is usually 0.1 or less, may be 0.05 or less, and may be 0.001 or less. The method for measuring the absorbance is as described in the examples described later.

[0068] The method for preparing the coating liquid is not particularly limited. For example, a method of dissolving a solute containing a B source, a P source, and a La source in water as a solvent can be mentioned. The B source is not particularly limited as long as it is a simple substance or compound having a B element. For example, boric acid (H3BO3) can be mentioned. The P source is not particularly limited as long as it is a simple substance or compound having a P element. For example, orthophosphoric acid (H3PO4), metaphosphoric acid (HPO3) can be mentioned. Further, the coating liquid preferably has an O source. Examples of the O source include the O element contained in the above-mentioned B source or P source. Further, the above solute may contain a Li source. The Li source is not particularly limited as long as it is a simple substance or compound having a Li element. For example, lithium hydroxide monohydrate (LiOH·H2O) can be mentioned.

[0069] Note that the present disclosure is not limited to the above embodiments. The above embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same operational effects is included in the technical scope of the present disclosure.

Example

[0070] [Comparative Example 1] (Preparation of Coating Liquid) Metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and ion-exchanged water were mixed at a ratio of metaphosphoric acid:ion-exchanged water = 4.52:191.8 (weight ratio) to obtain an aqueous solution. Boric acid (manufactured by Nacalai Tesque) was added to the obtained aqueous solution so that the molar ratio of B element to P element (B / P) became 1.0 and dissolved. Thereby, a coating liquid was obtained.

[0071] (Preparation of Coated Active Material) To the obtained coating liquid, active material particles (LiNi 0.81 Co 0.15 Al 0.04 O2, particle diameter D 50A slurry was prepared by dispersing 3 (with a particle size of 4.5 μm). The solid content concentration of the slurry was 69% by weight. Next, a coating layer was formed on the surface of the active material particles by drying the slurry using a spray dryer "Product Name: Mini Spray Dryer B-290" manufactured by BUCHI. The air supply temperature of the spray dryer was 200 °C, and the air supply volume was 0.45 m

[0072] [Example 1] Metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) and ion-exchanged water were mixed at a ratio of metaphosphoric acid:ion-exchanged water = 4.52:191.8 (weight ratio) to obtain an aqueous solution. Boric acid (manufactured by Nacalai Tesque) was added to the obtained aqueous solution so that the molar ratio of B element to P element (B / P) was 1.0 and dissolved. Further, lanthanum oxide (manufactured by Fujifilm Wako Pure Chemical Corporation) was added so that the molar ratio of La element to P element (La / P) was 0.003 and dissolved. Thereby, a coating solution was obtained. A coated active material was obtained in the same manner as in Comparative Example 1 except that the obtained coating solution was used.

[0073] [Examples 2 - 5] A coating solution was obtained in the same manner as in Example 1 except that the molar ratio of La element to P element (La / P) was changed to 0.006, 0.01, 0.05, and 0.075, respectively. A coated active material was obtained in the same manner as in Comparative Example 1 except that the obtained coating solution was used.

[0074] [Comparative Example 2] A coating solution was obtained in the same manner as in Example 1 except that the molar ratio of La element to P element (La / P) was changed to 0.100. A coated active material was obtained in the same manner as in Comparative Example 1 except that the obtained coating solution was used.

[0075] [Evaluation] (Absorbance measurement) The absorbances of the coating liquids obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were measured. Specifically, 3.5 mL of the coating liquid was added to a quartz cell (10 mm × 10 mm × 45 mm), and the absorbance was measured using an ultraviolet-visible spectrophotometer (product name: UV-1280, manufactured by Shimadzu Corporation). When the absorbance at a wavelength of 660 nm was measured, it was confirmed that the concentration of insoluble fine particles present in the coating liquids in Examples 1 to 5 and Comparative Example 1 was extremely low (see, for example, JIS-K0101). On the other hand, in Comparative Example 2, since the coating liquid was visibly turbid, the absorbance measurement was not performed. The results are shown in Table 1.

[0076] (Measurement of Coating Rate and La / P) The coating rates of the coating active materials obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were measured by X-ray photoelectron spectroscopy (XPS). Specifically, surface elemental analysis of the coating active material was performed using an X-ray photoelectron spectrometer (manufactured by ULVAC-PHI, PHI X-tool). The pass energy was set to 224 eV, and narrow scan analysis was performed. Thereafter, the elemental ratio was calculated from the intensity values of C1s, O1s, P2p, Ni2p3, Co2p3, Al2p, B1s, and La3d3 detected by analysis software (MultiPak, manufactured by ULVAC-PHI), and the value [%] of (La + P + B) / (La + P + B + Ni + Co + Al) was determined as the coating rate. Also, the molar ratio of La element to P element (La / P) was determined from the above elemental ratio. The results are shown in Table 1.

[0077] (Resistance Measurement) Using the coating active materials obtained in Examples 1 to 5 and Comparative Examples 1 and 2 as the positive electrode active material, batteries were fabricated and resistance measurements were performed.

[0078] First, a positive electrode slurry was prepared by mixing a positive electrode active material (coated active material), a sulfide solid electrolyte (10LiI - 15LiBr - 75Li3PS4), a conductive material (VGCF), a binder (SBR), and a dispersion medium (heptane). The mixing ratio of the positive electrode active material to the sulfide solid electrolyte was positive electrode active material:sulfide solid electrolyte = 6:4 (volume ratio). The compounding amounts of the conductive material and the binder were each 3 parts by weight with respect to 100 parts by weight of the positive electrode active material. The positive electrode slurry was sufficiently stirred by an ultrasonic homogenizer, and the positive electrode slurry was applied to the surface of a positive electrode current collector (Al foil) to form a coating film. The coating film was dried at 100 °C for 30 minutes using a hot plate. Thereby, a positive electrode raw sheet was obtained. A disk-shaped positive electrode was cut out from the positive electrode raw sheet. The area of the positive electrode was 1 cm 2 was obtained.

[0079] Next, a negative electrode and a solid electrolyte layer were prepared. The negative electrode active material was graphite. The same kind of sulfide solid electrolyte was used between the positive electrode, the solid electrolyte layer, and the negative electrode. In a cylindrical jig, a laminate was formed by laminating the positive electrode, the solid electrolyte layer, and the negative electrode in this order. By pressing the laminate, a power generation element was formed. By connecting terminals to the power generation element, a battery (all-solid-state battery) was obtained. After adjusting the open circuit voltage (OCV) of the obtained all-solid-state battery to 2.03 V, constant current discharge was performed, and the voltage drop in 5 seconds was divided by the current amount to measure the battery resistance. The discharge current rate was 2.5C. Based on the resistance of the battery of Comparative Example 1 as a reference (1.00), the resistances of the batteries of each example and each example were relativized and evaluated. The results are shown in Table 1 and Figure 3.

[0080]

Table 1

[0081] As shown in Table 1, in Examples 1 to 5 and Comparative Example 1, the La / P value in the coating layer became larger than the La / P value in the coating solution. This is presumably because La was segregated. Also, as shown in Table 1 and FIG. 3, it was confirmed that Examples 1 to 5 had lower resistance than Comparative Example 1. Thus, it was confirmed that even when an electrode active material with a high nickel ratio was combined with a coating layer containing phosphorus, the addition of La to the coating layer could suppress an increase in resistance. On the other hand, in Comparative Example 2, it was confirmed that the coating solution became turbid and was a dispersion rather than a solution. Therefore, a compositional deviation occurred and the desired coated active material could not be obtained.

Explanation of Signs

[0082] 1 … Electrode active material 2 … Coating layer 10 … Coated active material 11 … Positive electrode layer 12 … Negative electrode layer 13 … Electrolyte layer 14 … Positive electrode current collector 15 … Negative electrode current collector 20 … Battery

Claims

1. A coated active material having an electrode active material and a coating layer covering the electrode active material, wherein the electrode active material has Li element, M element (M is a metal other than Li and contains at least Ni), and O element, the molar ratio of Ni to M (Ni / M) is 80% or more, the coating layer contains B element, P element, La element and O element, the molar ratio of La element to P element (La / P) in the coating active material is 0.005 or more and 0.15 or less.

2. The coated active material according to Claim 1, wherein La / P is 0.01 or more and 0.11 or less.

3. The coated active material according to Claim 1, wherein the molar ratio of B element to P element (B / P) is 0.5 or more and 2.0 or less.

4. The coated active material according to Claim 1, wherein the coating rate of the coating layer with respect to the electrode active material is 75% or more.

5. The coated active material according to Claim 1, wherein M further contains at least one of Co, Mn, and Al.

6. An electrode composite material containing the coated active material according to any one of Claims 1 to 5 and at least one of a conductive material and a binder.

7. The electrode composite material according to Claim 6, wherein the electrode composite material contains a solid electrolyte.

8. The electrode composite material according to Claim 7, wherein the solid electrolyte is a sulfide solid electrolyte.

9. A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer or the negative electrode layer contains the electrode composite material according to Claim 6.

10. The battery according to Claim 9, wherein the positive electrode layer contains the electrode composite material.

11. The battery according to Claim 9, wherein the electrolyte layer contains a solid electrolyte.

12. A coating solution for forming the coating layer in the coated active material according to any one of Claims 1 to 5, wherein the coating solution contains a solute containing B element, P element and La element and water as a solvent, the molar ratio of La element to P element (La / P) is 0.001 or more and 0.100 or less, and the absorbance of the coating solution is 0.1 or less.

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