Composite positive electrode active material particles, method for manufacturing composite positive electrode active material particles, and solid-state battery

Abstract

To provide composite positive electrode active material particles that can suppress the rate of resistance increase of a battery, a method for manufacturing composite positive electrode active material particles, and a solid-state battery. [Solution] A composite positive electrode active material particle, a method for producing the composite positive electrode active material particle, and a solid-state battery, comprising positive electrode active material particles, a first coating layer covering at least a portion of the positive electrode active material particles, and a second coating layer covering at least a portion of the first coating layer, wherein the first coating layer contains an oxide, the second coating layer contains a sulfide solid electrolyte, the sulfide solid electrolyte contains an argyrodite-type sulfide, and the 10% particle size D10 in the volume-based cumulative particle size distribution is 3.3 μm or less.

Description

Technical Field

[0001] The present disclosure relates to composite positive electrode active material particles, a method for manufacturing the composite positive electrode active material particles, and a solid battery.

Background Art

[0002] In recent years, the demand for secondary batteries has been increasing, and in addition to secondary batteries equipped with an electrolytic solution, the development of solid batteries using a solid electrolyte has been promoted. An all-solid battery, which is an example of a solid battery, is a battery having a solid electrolyte layer instead of an electrolytic solution, and since it does not use a flammable organic solvent, simplification of safety devices can be achieved, and it is excellent in manufacturing cost and productivity.

[0003] As positive electrode active material particles capable of reducing resistance even when the binding force of the battery is small or the blending amount of the positive electrode active material particles is high, positive electrode composite active material particles in which at least a part of the surface of positive electrode active material particles made of a lithium-containing oxide is coated with a coating material containing a sulfide solid electrolyte are known (Patent Document 1). The above coating is a glass-ceramics.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a solid battery using positive electrode active material particles coated with glass-ceramics as the positive electrode, the resistance increase rate may become high with the use of the battery.

[0006] The problem to be solved by one embodiment of the present disclosure is to provide composite positive electrode active material particles, a method for manufacturing the composite positive electrode active material particles, and a solid battery capable of suppressing the resistance increase rate of the battery.

Means for Solving the Problems

[0007] The means for solving the problems include the following aspects. <1> Composite positive electrode active material particles including positive electrode active material particles, a first coating layer covering at least a part of the positive electrode active material particles, and a second coating layer covering at least a part of the first coating layer, the first coating layer containing an oxide, the second coating layer containing a sulfide solid electrolyte, the sulfide solid electrolyte containing an argyrodite-type sulfide, and the 10% particle diameter D10 in the volume-based cumulative particle size distribution being 3.3 μm or less. <2> The positive electrode active material particles are the composite positive electrode active material particles according to <1>, containing Ni at a ratio of 80 mol% or more. <3> The first coating layer is the composite positive electrode active material particles according to <1> or <2> composed of an oxide. <4> The first coating layer is the composite positive electrode active material particles according to any one of <1> to <3> composed of a phosphoric oxide. <5> The composite positive electrode active material particles according to any one of <1> to <4>, wherein the 10% particle diameter D10 in the volume-based cumulative particle size distribution is 2.5 μm or less. <6> The composite positive electrode active material particles according to any one of <1> to <5>, wherein the 10% particle diameter D10 in the volume-based cumulative particle size distribution is 1.9 μm or more. <7> A method for manufacturing the composite positive electrode active material particles according to any one of <1> to <6>, including a step of forming positive electrode active material particles coated with the first coating layer by spray-drying a mixed liquid containing a solution containing elements constituting the first coating layer and positive electrode active material particles, and a step of forming positive electrode active material particles further coated with the second coating layer by mixing the positive electrode active material particles coated with the first coating layer and a dispersion liquid containing an argyrodite-type sulfide using a kneading device. <8> A solid battery including a positive electrode containing the composite positive electrode active material particles according to any one of <1> to <6>, a negative electrode, and a sulfide solid electrolyte. <9> The solid battery according to <8>, wherein the sulfide solid electrolyte contains an argyrodite-type sulfide.

Advantages of the Invention

[0008] According to one embodiment of this disclosure, a composite positive electrode active material particle that can suppress the rate of resistance increase of a battery, a method for manufacturing the composite positive electrode active material particle, and a solid-state battery are provided. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a cross-sectional view of a composite cathode active material particle, schematically showing its structure. [Figure 2] Figure 2 is a schematic cross-sectional view showing an example of an electrode stacking structure. [Modes for carrying out the invention]

[0010] In this disclosure, a numerical range indicated using "~" means a range that includes the numbers written before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, unless otherwise specified, the amount of each component refers to the total amount of multiple substances if there are multiple substances corresponding to each component. In this disclosure, when embodiments are described with reference to the drawings, the configuration of such embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each figure are conceptual, and the relative relationships between the sizes of the components are not limited thereto.

[0011] In this disclosure, "10% particle size D10" refers to the average particle size corresponding to the cumulative frequency of smaller diameters at 10% in the volume-based cumulative particle size distribution, and "50% particle size D50" refers to the average particle size corresponding to the cumulative frequency of smaller diameters at 50% in the volume-based cumulative particle size distribution. For example, if D10 is 5 μm in the volume distribution, it means that the volume of all particles smaller than 5 μm accounts for 10% of the total. In this disclosure, the particle size in the volume-based cumulative particle size distribution is a value measured by laser diffraction-scattering.

[0012] <Composite positive electrode active material particles> Hereinafter, an embodiment of the composite cathode active material particles of this disclosure will be described with reference to Figures 1 and 2. A composite positive electrode active material particle, which is one embodiment of the present disclosure, comprises positive electrode active material particles, a first coating layer covering at least a portion of the positive electrode active material particles, and a second coating layer covering at least a portion of the first coating layer, wherein the 10% particle size D10 (hereinafter also referred to as particle size D10) in the volume-based cumulative particle size distribution is 3.3 μm or less. The first coating layer contains an oxide. The second coating layer contains a sulfide solid electrolyte, and the sulfide solid electrolyte contains an argyrodite-type sulfide.

[0013] Secondary batteries include secondary batteries equipped with an electrolyte and solid batteries equipped with a solid electrolyte. Solid batteries also include all-solid batteries using a solid electrolyte and semi-solid batteries having a gel layer containing an electrolyte and a polymer between the electrode and the solid electrolyte, and the solid electrolyte may contain less than 10% by mass of the electrolyte relative to the total amount of electrolyte. The solid electrolyte may also be a composite solid electrolyte containing an inorganic solid electrolyte and a polymer electrolyte. In this disclosure, all-solid batteries are preferred as solid batteries. For certain applications, high-capacity solid-state batteries are desired. For example, if a rechargeable battery in a car has a high capacity, it can travel a longer distance on a single charge, improving convenience. By ensuring a longer driving range, the frequency of charging is reduced, lessening the burden on the user.

[0014] To increase the capacity of solid-state batteries, for example, it is conceivable to use positive electrode active material particles with a high elemental ratio of Ni, from the viewpoint of electron transfer capability and lithium storage capacity. However, when positive electrode active material particles with a high elemental ratio of Ni are used in solid-state batteries equipped with a sulfide solid electrolyte, the volume change of the active material particles during charging and discharging is relatively large, and the resistance increase rate may be high. Suppressing the resistance increase rate leads to a longer battery life. Furthermore, if the resistance increase rate in the low SOC (State of Charge) region can be suppressed, it is particularly desirable for automotive secondary batteries, backup secondary batteries, etc., where operation in the low SOC region is expected.

[0015] The inventors investigated how to suppress the increase in resistance even when using a positive electrode active material with a high elemental ratio of Ni, and focused on the composition of the positive electrode active material particles. They found that in a battery using composite positive electrode active material particles having specific first and second coating layers, and in which the particle diameter D10 in the volume-based cumulative particle size distribution is a specific value, the increase in resistance is suppressed.

[0016] Although the mechanism by which the above effects are achieved is not clear, it is presumed that composite positive electrode active material particles having specific first and second coating layers and a particle diameter D10 of a specific value possess chemical stability, such as suppressing the formation of a high-resistance layer at the interface between the positive electrode active material and the solid electrolyte, and mechanical stability, such as having a strong interface between the positive electrode active material and the solid electrolyte that is not easily lost.

[0017] As shown in Figure 1, the composite positive electrode active material particles 10 include a first coating layer 12 that covers the core positive electrode active material particles 11, and a second coating layer 13 that covers the first coating layer 12. The composite positive electrode active material particles 10 vary in size, shape, etc., and the composite positive electrode active material particles as a whole have a particle size distribution. Note that "particles" can refer to individual particles or to the particles as a whole. In addition, although Figure 1 shows an embodiment in which the positive electrode active material particles 11 or the first coating layer 12 are covered over their entire surface, it is not necessarily required that the entire surface be covered, and the positive electrode active material particles 11 and the first coating layer 12 may be covered in a manner in which only a part of them is covered.

[0018] (Cathode active material particles) The positive electrode active material particles vary in size, shape, etc., and may be secondary particles formed by the aggregation of primary particles. The positive electrode active material particles as a whole have a particle size distribution. In order to keep the particle diameter D10 of the composite positive electrode active material particles within a specific range, it is preferable to use relatively small particle sizes as the positive electrode active material particles. The 50% particle diameter D50 (hereinafter also referred to as particle diameter D50) in the volume-based cumulative particle size distribution of the positive electrode active material particles is preferably 1.0 μm to 20.0 μm, more preferably 2.0 μm to 6.0 μm, and even more preferably 3.0 μm to 5.0 μm.

[0019] In composite cathode active material particles, the 50% particle size D50 in the volume-based cumulative particle size distribution is a value measured by laser diffraction-scattering. Particle size obtained by laser diffraction-scattering can be measured using a corresponding particle size distribution analyzer.

[0020] In this disclosure, the laser diffraction and scattering method is performed using a Shimadzu SALD-7500nano laser. 1.0 g of composite positive electrode active material particles and 3.0 g of 1,2,3,4-tetrahydronaphthalene as a solvent are placed in a PP container. The mixture is then mixed and stirred for 60 seconds using an ultrasonic homogenizer (SMT UH-50, output setting level 9, constant mode) to disperse the particles in the solvent. The mixture is then weighed into a batch cell and the particle size distribution is measured. During the measurement, the refractive index was set to 1.40 for the real part and 0.02i for the imaginary part.

[0021] The composition of the positive electrode active material particles is preferably that which contains a lithium composite oxide. The lithium composite oxide may contain at least one element selected from the group consisting of F, Cl, N, S, Br, and I. The lithium composite oxide may also have a crystal structure belonging to at least one space group selected from the space groups R-3m, Immmm, and P63-mmc (also called P63mc or P6 / mmc). Furthermore, the lithium composite oxide may have an O2-type structure in which the main arrangement of the transition metal, oxygen, and lithium is also appropriate.

[0022] Examples of lithium composite oxides having a crystal structure belonging to R-3m include Li x Me y O α X β Examples of compounds represented by (Me represents at least one selected from the group consisting of Mn, Co, Ni, Fe, Al, Cu, V, Nb, Mo, Ti, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, Ag, Ru, W, B, Si, and P, and X represents at least one selected from the group consisting of F, Cl, N, S, Br, and I, satisfying 0.5≦x≦1.5, 0.5≦y≦1.0, 1≦α<2, and 0<β≦1) include.

[0023] Examples of lithium composite oxides having a crystal structure belonging to Immm include Li x1 M 1 A 1 2(satisfying 1.5 ≤ x1 ≤ 2.3, M 1contains at least one selected from the group consisting of Ni, Co, Mn, Cu and Fe, and A 1 contains at least oxygen, and A 1 the ratio of oxygen in A is 85 atomic% or more. ) The composite oxide represented by (specific examples include Li2NiO2), Li x1 M 1A 1-x2 M 1B x2 O 2-y A 2 y (0 ≦ x2 ≦ 0.5, 0 ≦ y ≦ 0.3, and at least one of x2 and y is not 0, and M 1A represents at least one selected from the group consisting of Ni, Co, Mn, Cu and Fe, and M 1B represents at least one selected from the group consisting of Al, Mg, Sc, Ti, Cr, V, Zn, Ga, Zr, Mo, Nb, Ta and W, and A2 represents at least one selected from the group consisting of F, Cl, Br, S and P. ) The composite oxide represented by is mentioned.

[0024] As the lithium composite oxide having a crystal structure belonging to P63 - mmc, for example, M1 x M2 y O2 (M1 represents an alkali metal (at least one of Na and K is preferred), M2 represents a transition metal (at least one selected from the group consisting of Mn, Ni, Co and Fe is preferred), and x + y satisfies 0 < x + y ≦ 2. ) The composite oxide represented by is mentioned.

[0025] As the lithium composite oxide having an O2 - type structure, for example, Li x [Li α (Mn a Co b M c ) 1-α O2 (0.5 < x < 1.1, 0.1 < α < 0.33, 0.17 < a < 0.93, 0.03 < b < 0.50, 0.04 < c < 0.33, and M represents at least one selected from the group consisting of Ni, Mg, Ti, Fe, Sn, Zr, Nb, Mo, W and Bi. ) The composite oxide represented by is mentioned, and as a specific example, Li 0.744[Li 0.145 Mn 0.625 Co 0.115 Ni 0.115 Examples include O2.

[0026] The positive electrode active material particles preferably contain Ni at a ratio of 80 mol% or more. By using positive electrode active material particles with a high Ni elemental ratio, the performance of the battery, such as high capacity, can be improved, and the resistance increase rate is relatively low, making it possible to create a battery with a long lifespan. Examples of positive electrode active materials with a high Ni elemental ratio include NMC811(LiNi 0.8 Mn 0.1 Co 0.1 O2), NMC90 / 5 / 5 (LiNi 0.9 Mn 0.05 Co 0.05 O2), NCA(LiNi 0.83 Co 0.13 Al 0.04 Examples include O2. Materials doped with elements such as Zr, F, and Ti may also be used.

[0027] (1st coating layer) The first coating layer directly coats the positive electrode active material particles and has the function of preventing reaction with sulfides contained in the solid electrolyte. The first coating layer covers at least a portion of the surface of the positive electrode active material particles, preferably covering as wide a surface as possible, and more preferably covering the entire surface of the positive electrode active material particles. The coverage rate, as measured by X-ray photoelectron spectroscopy, may be, for example, 83% or more. A coverage rate of 83% or more is expected to reduce the initial resistance.

[0028] The first coating layer is preferably uniform in composition and is preferably a relatively thin film. The first coating layer may be, for example, 5 nm to 100 nm thick. The thickness of the first coating layer covering the surface of the positive electrode active material particles is determined by observing cross-sectional SEM images and taking the average value of 200 thickness points (10 particles, 20 points each) measured arbitrarily.

[0029] The first coating layer is preferably an oxide layer composed of oxides. By having the first coating layer composed of oxides, it is possible to suppress the formation of a high-resistance layer at the interface between the positive electrode active material and the solid electrolyte, which leads to a suppression of the resistance increase rate.

[0030] The oxide contained in the first coating layer only needs to have the function of preventing reaction with the sulfides contained in the solid electrolyte, and conventionally known oxides can be used. Examples of oxides include niobium oxides such as LiNbO3 and phosphorus oxides. The first coating layer is preferably composed of phosphorus oxide. This is because phosphorus oxide is stable at high potential and therefore does not easily degrade the sulfide solid electrolyte contained in the second coating layer.

[0031] The method for forming the first coating layer is not limited. Examples include preparing a processing solution containing a precursor for the first coating layer, preparing a mixed solution such as a slurry in which positive electrode active material particles are dispersed in the processing solution, and then firing or spray-drying the mixed solution using a spray dryer; using a rolling flow coating apparatus; the method described in Japanese Patent Application Publication No. 2022-047501; Japanese Patent Application Publication No. 2023-122200; and Japanese Patent Application Publication No. 2023-137657. Among these, the spray-drying method is preferred because it allows for a uniform composition of the first coating layer and the formation of a relatively thin film over the entire surface of the positive electrode active material particles.

[0032] (2nd coating layer) The second coating layer covers at least a portion of the first coating layer. The second coating layer contains a sulfide solid electrolyte. The sulfide solid electrolyte contains argyrodite-type sulfides. The second coating layer may also contain particulate argyrodite-type sulfides. Because the second coating layer consists of a sulfide solid electrolyte containing argyrodite-type sulfides, a high-resistance layer is less likely to form at the interface between the positive electrode active material particles and the solid electrolyte, and a chemically stable interface is formed. Therefore, by using a positive electrode active material with a high elemental ratio of Ni, the resistance increase rate can be suppressed even when the volume change associated with charging and discharging is large.

[0033] The second coating layer preferably covers the entire surface of the first coating layer. The second coating layer may partially cover the surface of the positive electrode active material particles. The second coating layer may form the outermost layer of the composite positive electrode active material particles. The second coating layer is preferably a layer with a uniform film thickness. The second coating layer may have a thickness of, for example, 5 nm to 3000 nm. The thickness, range, etc. of the second coating layer covering the surface of the positive electrode active material particles or the first coating layer is determined as the average value of 200 measured thickness points (10 particles, 20 points each) by observing a cross-sectional SEM image and arbitrarily measuring.

[0034] As the composition of the all-dielectric type sulfide, it is preferable that the all-dielectric type sulfide contains sulfur (S) as the main component of the anion element, and in addition to S, it is preferably further contains, for example, Li element, A element, and S element. The A element is at least one selected from the group consisting of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of the halogen element (X) include F, Cl, Br, I, etc. The composition of the sulfide solid electrolyte is not particularly limited, and examples include xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30). The sulfide solid electrolyte may have a composition represented by the following general formula (1).

[0035] Li 4-x Ge 1-x P x S4(0 < x < 1) Formula (1)

[0036] In formula (1), at least a portion of Ge may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. Also, at least a portion of P may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. A portion of Li may be substituted with at least one selected from the group consisting of Na, K, Mg, Ca, and Zn. A portion of S may be substituted with a halogen. The halogen is at least one of F, Cl, Br, and I. Specifically, the argyrodite-type sulfide has the composition Li6PS5X, and the halogen element represented by X is Cl, Br, or I.

[0037] Argyrodite-type sulfides also include compounds in which properties are imparted by the inclusion of other elements that substitute for some of these elements. For example, other elements such as Ge, Si, and Sn may be included to improve electrochemical properties and stability. Furthermore, the sulfide solid electrolyte contained in the second coating layer may be mainly composed of argyrodite-type sulfides and compounded with other components. Other components include oxides, nitrides, carbides, or fluorides. In addition, the second coating layer may contain fragments of extremely active material particles generated during manufacturing, fragments of the first coating layer, etc.

[0038] The method for forming the second coating layer is not limited. For example, one method involves preparing a dispersion of sulfide solid electrolyte, kneading it with positive electrode active material particles having the first coating layer in a kneading device, and removing the solvent component. It is preferable to form the second coating layer by kneading in a wet state, as shear force can make the thickness of the second coating layer uniform.

[0039] (Particle size distribution of composite positive electrode active material particles) The composite positive electrode active material particles have a 10% particle size D10 in the volume-based cumulative particle size distribution of 3.3 μm or less. By adopting a particle size D10, and furthermore by having a particle size D10 below a specific value, the number of interfaces between the positive electrode active material particles and the solid electrolyte becomes relatively large, the expansion and contraction rate per reaction field becomes relatively small, and a strong interface is easily formed. As a result, the formed solid electrolyte interface is less likely to be lost, resulting in an interface with high mechanical stability. Therefore, by using a positive electrode active material with a high elemental ratio of Ni, the resistance increase rate can be suppressed even when the volume change associated with charging and discharging is large.

[0040] The particle size D10 of the composite positive electrode active material particles is preferably 3.0 μm or less, and more preferably 2.5 μm or less. This makes it possible to suppress the rate of resistance increase in the low SOC region. The low SOC region may refer to, for example, the region with an SOC of 30 or less, the region with an SOC of 20 or less, etc.

[0041] The particle size D10 is preferably 1.9 μm or larger, more preferably 2.1 μm or larger, and even more preferably 2.4 μm. This allows for sufficient coverage of both the first and second coating layers, making it easy to manufacture high-quality composite cathode active materials.

[0042] The 10% particle size D10 of the composite cathode active material particles in the volume-based cumulative particle size distribution is measured by laser diffraction and scattering. The laser diffraction and scattering method is the same as described above.

[0043] In composite cathode active material particles, the particle size D10 can be adjusted to a specific value by using relatively small-sized cathode active material particles during the manufacturing process.

[0044] One embodiment of the composite positive electrode active material particles, having the above configuration, is less likely to form a high-resistance layer at the interface between the positive electrode active material particles and the solid electrolyte, resulting in a chemically stable interface. Furthermore, the formed solid electrolyte interface tends not to be lost easily, resulting in a mechanically stable interface. Therefore, it is a composite positive electrode active material particle that can suppress the resistance increase rate of the battery. For example, by using a positive electrode active material with a high elemental ratio of Ni, the resistance increase rate can be suppressed even when there is a large volume change due to charging and discharging. In addition, the resistance increase rate in the low SOC region can be suppressed. Therefore, it is particularly preferable in secondary batteries where a long battery life is required, automotive secondary batteries where operation in the low SOC region is expected, backup secondary batteries, etc.

[0045] <Method for manufacturing composite positive electrode active material particles> A method for producing composite cathode active material particles according to one embodiment of the present disclosure is a method for producing composite cathode active material particles having the above configuration according to one embodiment of the present disclosure, and includes a first coating layer formation step and a second coating layer formation step. The first coating layer formation step forms cathode active material particles coated with a first coating layer by spray-drying a mixture containing a solution containing elements constituting the first coating layer and cathode active material particles. The second coating layer formation step forms cathode active material particles further coated with a second coating layer by mixing the cathode active material particles coated with the first coating layer and a dispersion containing an argyrodite-type sulfide using a kneading device. According to the method for producing composite cathode active material particles according to one embodiment of the present disclosure, composite cathode active material particles having the above configuration according to one embodiment of the present disclosure can be produced stably.

[0046] (First coating layer formation step) In the first coating layer formation step, a mixture of a treatment solution containing the elements constituting the first coating layer and a slurry containing positive electrode active material particles is spray-dried. Spray drying allows for the uniform formation of a relatively thin film.

[0047] The solution containing the elements constituting the first coating layer is a solution corresponding to the oxide contained in the first coating layer, and is a treatment solution containing precursors of the oxide contained in the first coating layer. The oxide contained in the first coating layer is as described above. When the oxide is a phosphorus oxide, the elements constituting the first coating layer are P, Li, O, C, etc., and the treatment solution contains a phosphoric acid compound and a solvent. Examples of phosphoric acid compounds include metaphosphoric acid and polyphosphoric acid. The type of oxide constituting the first coating layer, the composition ratio, etc. can be controlled by adjusting the proportion of elements and compounds contained in the treatment solution.

[0048] (Second coating layer formation process) In the second coating layer formation process, the cathode active material particles coated with the first coating layer and a dispersion containing argyrodite-type sulfide are mixed using a kneading device. By mixing with a dispersion that has relatively high viscosity and is wet, an appropriate shear force is generated, making it possible to form the second coating layer with a uniform composition and film thickness.

[0049] A dispersion containing argyrodite-type sulfides comprises a sulfide solid electrolyte containing argyrodite-type sulfides and a solvent. The solvent is preferably a nonpolar solvent suitable for hydrophobic particles, and preferably a solvent that can provide a hydrophobic environment to prevent aggregation of composite cathode active material particles. For example, dehydrated 1,2,3,4-tetrahydronaphthalene can be preferably used.

[0050] As a mixing device, an ultrasonic homogenizer can preferably be used to prevent aggregation of the composite positive electrode active material particles and to form a uniform composition and film thickness of the second coating layer.

[0051] <Solid battery> A solid-state battery according to one embodiment of the present disclosure includes a positive electrode containing composite positive electrode active material particles according to one embodiment of the present disclosure, a negative electrode, and a sulfide solid electrolyte. Because the solid-state battery according to one embodiment of the present disclosure has a low resistance increase rate, it can provide a long-life solid-state battery. Furthermore, because the resistance increase rate in the low SOC region can be kept low, it is suitable for applications such as secondary batteries where a long battery life is required, automotive secondary batteries that are expected to operate in the low SOC region, and backup secondary batteries.

[0052] A solid-state battery has an electrode stack structure comprising a positive electrode, a sulfide solid electrolyte layer, and a negative electrode in that order. The positive electrode includes a positive electrode current collector and a positive electrode layer, and the negative electrode includes a negative electrode current collector and a positive electrode layer. In this disclosure, an all-solid-state battery is preferred as the solid-state battery.

[0053] (Current collector) The type of current collector used in the positive electrode current collector and negative electrode current collector constituting the electrode stacked structure is not particularly limited as long as it is used in solid-state batteries, and can be selected from known current collectors. Specifically, the material of the current collector can be a metal selected from Ag, Cu, Au, Al, Ni, Fe, and Ti, or an alloy containing these metals. The thickness of the current collector is not particularly limited and can be selected considering the type and scale of the battery obtained using the current collector. The total thickness of the current collector may be, for example, 5 μm or more, 10 μm or more, or 20 μm or more. The total thickness of the current collector may be, for example, 120 μm or less, 80 μm or less, or 60 μm or less.

[0054] (electrode layer) Of the positive electrode layer and negative electrode layer constituting the electrode stacked structure, the positive electrode layer includes composite positive electrode active material particles, which are one embodiment of the present disclosure, as the electrode active material. The composite positive electrode active material particles are as described above. The electrode layer, including the positive electrode layer and the negative electrode layer, contains at least the electrode active material and may optionally include a binder, conductive material, solid electrolyte, etc.

[0055] The negative electrode layer is not particularly limited as an electrode active material used in solid-state batteries, and can be selected from known electrode active materials. Specific examples of electrode active materials for the negative electrode layer include carbon materials, active materials containing Si elements, metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides, transition metal nitrides, etc.

[0056] Examples of carbon materials include graphite materials, amorphous carbon materials, carbon black, and activated carbon. Examples of graphite materials include natural graphite and artificial graphite. Examples of amorphous carbon materials include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch carbon fiber (MCF). Graphite materials may be coated with metal or amorphous carbon.

[0057] Active materials containing the Si element include elemental silicon, silicon alloys (for example, alloys of Si with one or more metals selected from the group consisting of Sn, Ti, Fe, Ni, Cu, Co, and Al), porous silicon, silicon clathrate compounds, silicon oxides, and the like.

[0058] The electrode active material contained in the electrode layer may be a single type or a combination of two or more types. The form of the electrode active material may be, for example, fibrous, spherical, or flake-like. For the negative electrode active material, the volume-average particle size may be selected from, for example, a range of 5 μm to 50 μm. The volume-average particle size of the negative electrode active material is defined as the value (D50) at which the cumulative amount from the smallest diameter side in the volume-based particle size distribution obtained using the laser diffraction-scattering method becomes 50%.

[0059] Examples of binders include polyvinylidene fluoride (PVdF), polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethylcellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, polymethacrylate, and polytetrafluoroethylene (PTFE).

[0060] Examples of conductive materials include carbon materials, metals, conductive oxides, and conductive nitrides. Specific examples of carbon materials include graphite, carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes (CNTs), carbon nanofibers (CNFs), and vapor-grown carbon fibers (VGCFTMs). A single conductive material may be used, or two or more may be used in combination.

[0061] The solid electrolyte is a sulfide solid electrolyte. The sulfide solid electrolyte may be an argyrodite-type sulfide solid electrolyte used in the second coating layer, or it may be another type, such as a glass-ceramic-type sulfide solid electrolyte. The sulfide solid electrolyte is as described above. One type of solid electrolyte may be used, or two or more types may be used in combination.

[0062] (Sulfide solid electrolyte layer) The sulfide solid electrolyte layer is a layer containing a sulfide solid electrolyte. The thickness of the sulfide solid electrolyte layer is not particularly limited and may be selected from, for example, a range of 1 μm to 30 μm.

[0063] The type of sulfide solid electrolyte contained in the sulfide solid electrolyte layer is not particularly limited. For example, it may be selected and used from the sulfide solid electrolytes that may be contained in the electrode layer described above. In this case, the types of solid electrolytes contained in each layer may be the same or different. Furthermore, it may be the same type as the sulfide solid electrolyte contained in the second coating layer of the composite positive electrode active material particles, or it may be a different type.

[0064] Figure 2 shows an example of an all-solid-state battery. As shown in Figure 2, the all-solid-state battery 20 has a stacked structure of positive electrode / sulfide solid electrolyte layer / negative electrode. The all-solid-state battery 20 has a negative electrode including a negative electrode current collector 113 and a negative electrode active material layer A, a sulfide solid electrolyte layer B, and a positive electrode including a positive electrode current collector 115 and a positive electrode active material layer C. The sulfide solid electrolyte layer B may have a two-layer structure.

[0065] The negative electrode active material layer A includes a negative electrode active material 101, a conductive additive 105, and a binder 109. The positive electrode active material layer C includes composite positive electrode active material particles 103, a conductive additive 107, and a binder 111.

[0066] The sulfide solid electrolyte layer B contains sulfide solid electrolyte 102. The solid electrolyte may contain less than 10% by mass of electrolyte relative to the total amount of electrolyte. The solid electrolyte may also be a composite solid electrolyte containing an inorganic solid electrolyte and a polymer electrolyte.

[0067] All-solid-state batteries may be constructed by sealing the laminated ends (sides) of a positive electrode / solid electrolyte layer / negative electrode with resin. The current collector of the electrode may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer on its surface.

[0068] (Exterior) An all-solid-state battery, which is one embodiment of the present disclosure, may further include an outer casing. The outer casing at least houses the electrode laminate described above. Examples of outer casings include laminate-type outer casings and case-type outer casings. A laminate-type outer casing may be formed from a laminate (laminate film) having a metal layer containing a metal such as aluminum and a heat-seal layer containing a resin that melts upon heating.

[0069] (Restraining member) An all-solid-state battery, which is one embodiment of the present disclosure, may further include a restraining member. The restraining member applies a restraining pressure in the thickness direction to the electrode stack described above. The restraining pressure applied in the thickness direction to the electrode stack may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. The restraining pressure applied in the thickness direction to the electrode stack may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0070] The applications of the all-solid-state battery, which is one embodiment of the present disclosure, are not particularly limited. Typical applications include power sources for vehicles, electronic equipment, and electrical storage systems. It may also be used as a power source for mobile devices other than vehicles (e.g., railways, ships, aircraft), or as a power source for electrical products such as information processing devices. Among these, the application of the all-solid-state battery, which is one embodiment of the present disclosure, is preferably as a power source for vehicles, and more preferably as a power source for hybrid vehicles, plug-in hybrid vehicles, or electric vehicles. Examples of vehicles include electric four-wheeled vehicles, electric two-wheeled vehicles, gasoline vehicles, diesel vehicles, etc. Examples of electric four-wheeled vehicles include electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid vehicles (HEVs). Examples of electric two-wheeled vehicles include electric motorcycles and electric assist bicycles. [Examples]

[0071] Embodiments of this disclosure will be described below with reference to examples. However, this disclosure is not limited to these examples. Details of the materials indicated by abbreviations are as follows. NCA:LiNi 0.81 Co 0.15 Al 0.04 Positive electrode active material represented by the composition formula of O2 VGCF: Vapor-phase grown carbon fiber SBR: Styrene-butadiene rubber

[0072] <Example 1> (Preparation of composite positive electrode active material particles) (First coating layer formation) NCA was prepared as the positive electrode active material particles. The particle size D50 of the positive electrode active material particles was 5.0 μm. The specific surface area of ​​the positive electrode active material particles was 0.45 m². 2 The concentration was / g. The treatment solution for the first coating layer was prepared as follows: 1.97 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in 191.8 parts by mass of deionized water to obtain an aqueous solution. Furthermore, the molar concentration ratio C B / C P A predetermined amount of boric acid (manufactured by Nacalai Tesque) was dissolved in an aqueous solution so that the ratio of molars to concentrations C was 1.0. Finally, the molar concentration ratio C was calculated. Li / (C B +C P Lithium hydroxide monohydrate was added to the treatment solution for the first coating layer so that the ratio was 0.9. B This is the amount of substance of B (boron), and C p This is the amount of substance of P (phosphorus), and C Li This represents the amount of substance of Li (lithium).

[0073] (Particle size D50) The particle size distribution of the obtained positive electrode active material particles was measured using a laser diffraction / scattering particle size distribution analyzer (Shimadzu Corporation, SALD-7500nano), and the particle size D50 was calculated. The calculated particle size D50 of the positive electrode active material particles is shown in Table 1. The measurement method was the same as described above.

[0074] A slurry was prepared by dispersing positive electrode active material particles in the processing solution for the first coating layer. The solid content concentration of the slurry was 60% by mass relative to the entire slurry. A spray dryer manufactured by BUCHI (product name: "Mini Spray Dryer B-290") was prepared. The slurry was dried by spray drying by supplying it to the spray dryer. The air supply temperature of the spray dryer was 200°C, and the air supply flow rate was 0.45 m³. 3 The value was / min. Positive electrode active material particles having a dried first coating layer were heat-treated in air. The heat treatment was performed at a treatment temperature of 200°C for a treatment time of 5 hours.

[0075] (Second coating layer formation) A dispersion was prepared by dispersing 40.2 parts by mass of sulfide solid electrolyte in 93.7 parts by mass of solvent using an ultrasonic homogenizer. The sulfide solid electrolyte used was an argyrodite-type sulfide represented by the chemical formula LiPS5Cl (abbreviated as argyrodite in Table 1), and the solvent was 1,2,3,4-tetrahydronaphthalene that had been previously dehydrated. 31.2 parts by mass of the dispersion obtained above was supplied to a kneading device (Hibismix, manufactured by Primix Corporation) with 350 parts by mass of positive electrode active material particles having a first coating layer. The mixture was kneaded at 30 rpm for 5 minutes, 70 rpm for 5 minutes, and 100 rpm for 300 minutes. Subsequently, the solvent was removed by vacuum drying to obtain positive electrode active material particles coated with a first and a second coating layer.

[0076] (Measurement of composite positive electrode active material particles) (Particle size D10) The particle size distribution of the obtained composite cathode active material particles was measured using a Shimadzu SALD-7500nano. 1.0 g of composite cathode active material particles and 3.0 g of 1,2,3,4-tetrahydronaphthalene as a solvent were taken and weighed into a batch cell. The particles were dispersed in the solvent by mixing and stirring for 60 seconds using an ultrasonic homogenizer. The refractive index was set to a real part of 1.40 and an imaginary part of 0.02i. The particle size distribution was measured and the particle size D10 was calculated. The calculated particle size D10 of the composite cathode active material particles is listed in Table 1.

[0077] By performing X-ray diffraction measurements on composite particles under an atmosphere-blocked state, we were able to confirm diffraction peaks originating from the argyrodite-type structure in addition to peaks originating from the layered cathode active material. Measurements were performed using a Rigaku SmartLabII at a measurement angle of 10° to 80°, with a Cu tube, tube voltage of 45kV, and current of 200mA. The step size was set to 0.02°, and scanning was performed at 2° / min.

[0078] <Example 2> Composite cathode active material particles were prepared in the same manner as in Example 1, except that the cathode active material particles had a particle size D50 of 4.6 μm, and the concentration of the treatment solution was adjusted in the formation of the first coating layer by adjusting the amount of metaphosphoric acid used in proportion to the specific surface area of ​​the cathode active material used. The particle size D50 of the cathode active material particles and the particle size D10 of the composite cathode active material particles are shown in Table 1, respectively. The thicknesses of the first and second coating layers were the same as in Example 1.

[0079] <Examples 3 to 6> Composite cathode active material particles were prepared in the same manner as in Example 1, except that the particle size D50 of the cathode active material particles was 3.0 μm, and the concentration of the treatment solution was adjusted in the formation of the first coating layer by adjusting the amount of metaphosphoric acid used in proportion to the specific surface area of ​​the cathode active material used. The particle size D50 of the cathode active material particles and the particle size D10 of the composite cathode active material particles are shown in Table 1, respectively. The thicknesses of the first and second coating layers were the same as in Example 1.

[0080] <Comparative Example 1 to Comparative Example 4> Composite cathode active material particles having a first coating layer but lacking a second coating layer were prepared in the same manner as in Example 1, except that the cathode active material particles with particle size D50 as listed in Table 1 were used, the concentration of the treatment solution was adjusted by adjusting the amount of metaphosphoric acid used so as to be proportional to the specific surface area of ​​the cathode active material used, and a second coating layer was not formed. The particle size D50 of the cathode active material particles and the particle size D10 of the composite cathode active material particles are listed in Table 1, respectively.

[0081] <Comparative Example 5 to Comparative Example 6> Composite cathode active material particles were prepared in the same manner as in Example 1, except that a second coating layer containing glass ceramics was formed. The second coating layer was formed as follows. Specifically, it was formed in the same manner as in Example 1, except that the sulfide solid electrolyte used was a glass ceramic represented by the compositional formula 10LiI-15LiBr-75Li3PS4. The particle size D50 of the active material particles and the particle diameter D10 of the composite positive electrode active material particles are shown in Table 1, respectively.

[0082] <Rating> (Manufacturing of all-solid-state batteries) The following materials were prepared. Sulfide solid electrolyte: 10LiI-15LiBr-75Li3PS4 Conductive material: VGCF Binder: SBR Dispersion medium: heptane Positive electrode current collector: Al foil Negative electrode current collector: Ni foil

[0083] A positive electrode slurry was prepared by mixing the composite positive electrode active material particles obtained in Example 1, a sulfide solid electrolyte to be added later, a conductive material, a binder, and a dispersion medium. The mixing ratio was 75 / 25 (volume ratio) for the composite positive electrode active material particles including the first coating layer / (total of the second coating layer and sulfide solid electrolyte from the later addition). The amount of conductive material was 3 parts by mass per 100 parts by mass of composite positive electrode active material particles. The amount of binder was 3 parts by mass per 100 parts by mass of composite positive electrode active material particles. The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer. A positive electrode layer was formed by coating the positive electrode slurry onto the surface of the positive electrode current collector. The positive electrode layer was dried on a hot plate at 100°C for 30 minutes. This produced a raw material sheet. A disc-shaped positive electrode layer was cut from the raw material sheet. The area of ​​the positive electrode layer was 1 cm². 2 That was the case.

[0084] A negative electrode layer and a sulfide solid electrolyte layer were prepared. The negative electrode layer was made of graphite. The same type of sulfide solid electrolyte was used between the positive electrode layer, the sulfide solid electrolyte layer, and the negative electrode layer. An electrode stacked structure was formed by stacking the positive electrode layer, the sulfide solid electrolyte layer, and the negative electrode layer in this order within a cylindrical jig. The electrode stacked structure was pressed. An evaluation cell (all-solid-state battery) was formed by connecting terminals to the pressed electrode stacked structure.

[0085] The state of charge (SOC) of the evaluation cell was adjusted to 20%. The evaluation cell was discharged for 5 seconds at a current rate of 2.5C. The battery resistance (initial resistance) was calculated using the following formula. The initial resistance is listed in Table 1.

[0086] R = ΔV / I

[0087] R: Battery resistance ΔV: Voltage drop during a 5-second discharge. I: discharge current

[0088] As part of the durability test, after measuring the initial resistance, charge-discharge cycles were repeated at a current rate of 1.0C in a temperature environment of 60°C. After 100 cycles, the battery resistance (resistance after durability) was measured again under the same conditions as above. The resistance increase rate was calculated using the following formula. The resistance increase rate is expressed as a percentage (%). The resistance after durability and the resistance increase rate are listed in Table 1.

[0089] ΔR = (R1 / R0) × 100

[0090] ΔR: Resistance increase rate R0: Initial resistance R1: Resistance after durability

[0091] Except for using the composite positive electrode active material particles obtained in Examples 2-6 and Comparative Examples 1-6, the initial resistance at SOC 20%, the resistance after durability testing, and the resistance increase rate were measured in the same manner as described above, and are shown in Table 1.

[0092] [Table 1] [Explanation of symbols]

[0093] 10, 103 Composite positive electrode active material particles 11 Positive electrode active material particles 12 First coating layer 13 Second coating layer 20 All-solid-state battery 101 Negative electrode active material 102 Sulfide solid electrolyte 105, 107 Conductive additives 109, 111 binders 113 Negative electrode current collector 115 Positive electrode current collector A negative electrode active material layer B Sulfide solid electrolyte layer C positive electrode active material layer

Claims

1. Positive electrode active material particles, A first coating layer covering at least a portion of the positive electrode active material particles, The first coating layer comprises a second coating layer that covers at least a portion of the first coating layer, The first coating layer contains an oxide, The second coating layer contains a sulfide solid electrolyte, The sulfide solid electrolyte comprises an argyrodite-type sulfide, The 10% particle size D10 in the volume-based cumulative particle size distribution is 3.3 μm or less. Composite positive electrode active material particles.

2. The composite positive electrode active material particles according to claim 1, wherein the positive electrode active material particles contain Ni in a proportion of 80 mol% or more.

3. The composite cathode active material particles according to claim 1, wherein the first coating layer is composed of an oxide.

4. The composite cathode active material particles according to claim 1, wherein the first coating layer is composed of a phosphoric acid.

5. The composite cathode active material particles according to claim 1, wherein the 10% particle size D10 in the volume-based cumulative particle size distribution is 2.5 μm or less.

6. The composite cathode active material particles according to claim 1, wherein the 10% particle diameter D10 in the volume-based cumulative particle size distribution is 1.9 μm or larger.

7. A method for producing composite positive electrode active material particles according to any one of claims 1 to 6, A step of forming the positive electrode active material particles coated with the first coating layer by spray-drying a mixture containing a solution containing the elements constituting the first coating layer and the positive electrode active material particles, The process includes a step of further forming positive electrode active material particles coated with a second coating layer by mixing the positive electrode active material particles coated with the first coating layer and the dispersion containing the argyrodite-type sulfide using a kneading device, A method for producing composite cathode active material particles.

8. A positive electrode comprising composite positive electrode active material particles according to any one of claims 1 to 6, The negative electrode and, A sulfide solid electrolyte, solid state battery.

9. The solid battery according to claim 8, wherein the sulfide solid electrolyte comprises an argyrodite-type sulfide.

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