Positive electrode active material particles, method for manufacturing positive electrode active material particles, positive electrode, and all-solid-state battery

Abstract

Cathode active material particles that achieve both extended lifespan and low resistance. [Solution] A positive electrode active material particle having a core particle and a coating layer covering the surface of the core particle, wherein the core particle is formed of a first composite oxide, the first composite oxide comprising lithium and at least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus, the coating layer is formed of a second composite oxide, the second composite oxide comprising lithium and at least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, the coverage rate of the coating layer over the core particle calculated by observing the positive electrode active material particle using a scanning electron microscope is 90.0 area% or more, the average thickness of the coating layer is 15.0 nm or less, and the maximum thickness of the coating layer is 15.0 nm or less.

Description

[Technical Field]

[0001] This disclosure relates to positive electrode active material particles that can be used in secondary batteries, a method for producing positive electrode active material particles, a positive electrode, and an all-solid-state battery. [Background technology]

[0002] Lithium-ion batteries are rechargeable batteries with excellent energy density and cycle characteristics. In recent years, all-solid-state batteries, which use a solid instead of a conventional organic solvent as the electrolyte, have been developed and are expected to achieve higher safety than conventional batteries. In particular, sulfide-based solid electrolytes containing sulfur have achieved high conductivity, but a challenge remains in that the formation of a high-resistance layer at the interface due to a side reaction between the positive electrode active material and the sulfide-based solid electrolyte reduces the battery life. To address these issues, Patent Document 1 discloses a measure to suppress side reactions with the sulfide solid electrolyte by providing a coating layer on the positive electrode active material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-170715 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the inventors have recognized that the coating state of the coating layer significantly affects the performance of the battery. Specifically, if the coating layer has a low coverage rate, the effect of suppressing side reactions between the positive electrode active material and the solid electrolyte is reduced, which may decrease the battery life. On the other hand, if the coating layer is thick, the resistance increases, which may decrease the conductivity of lithium ions.

[0005] This disclosure provides positive electrode active material particles that can achieve both long lifespan and low resistance by having a coating layer. This disclosure also provides a method for manufacturing the above positive electrode active material particles. Furthermore, this disclosure provides a positive electrode and an all-solid-state battery using the above positive electrode active material particles. [Means for solving the problem]

[0006] This disclosure relates to positive electrode active material particles having a core particle and a coating layer covering the surface of the core particle, The core particles are formed of a first composite oxide, The above-mentioned first composite oxide is Lithium and, At least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus, Includes, The coating layer is formed of a second composite oxide, The second composite oxide described above is Lithium and, At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, Includes, In a 50,000x backscattered electron image obtained by observing the positive electrode active material particles using a scanning electron microscope, the sum of the areas of the area corresponding to the coating layer and the area corresponding to the core particles when the area corresponding to the coating layer and the area corresponding to the core particles are binarized. When the ratio of the area of ​​the portion corresponding to the coating layer to the core particles (area %) is defined as the coverage rate of the coating layer to the core particles, the coverage rate is 90.0 area % or more, The average thickness of the coating layer is 15.0 nm or less. The maximum thickness of the coating layer is 15.0 nm or less. Regarding positive electrode active material particles.

[0007] This disclosure relates to a method for producing positive electrode active material particles, The manufacturing method is Step (i) of obtaining a mixed solution 1 by mixing an alkoxide monomer and / or its oligomer with an organic solvent; Step (ii) of obtaining a mixed solution 2 by mixing the mixed solution 1 with the core particles; and, Step (iii) of mixing the mixed solution 2 with a hydrolyzing agent, hydrolyzing and dehydrating and condensing the alkoxide monomer and / or its oligomer contained in the mixed solution 2, and depositing it on the surface of the core particles to form the coating layer and obtaining the positive electrode active material particles; having wherein the alkoxide monomer and / or its oligomer contains lithium and at least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum and tungsten; relates to a method for producing positive electrode active material particles. The present disclosure relates to a positive electrode of an all-solid-state battery,

[0008] where the positive electrode is a molded body of a positive electrode composite material containing positive electrode active material particles, and relates to a positive electrode in which the positive electrode active material particles are the above positive electrode active material particles.

[0009] The present disclosure relates to an all-solid-state battery, where the all-solid-state battery has at least a positive electrode layer, a solid electrolyte layer and a negative electrode layer in this order, and relates to an all-solid-state battery in which the positive electrode layer contains the above positive electrode active material particles.

Advantages of the Invention

[0010] According to the present disclosure, positive electrode active material particles capable of achieving both long life and low resistance can be provided. Further, according to the present disclosure, a method for producing the above positive electrode active material particles can be provided. Further, according to the present disclosure, a positive electrode and an all-solid-state battery using the above positive electrode active material particles can be provided. <00….109>

Brief Description of the Drawings

[0011] [Figure 1]Figure 1 shows an example of a cross-sectional image and line analysis of positive electrode active material particles. [Figure 2] Figure 2 shows an example of a profile obtained by line analysis of elements contained in the coating layer. [Modes for carrying out the invention]

[0012] In this disclosure, descriptions of numerical ranges such as "XX or greater and YY or less" or "XX to YY" mean a numerical range that includes the lower and upper limits, unless otherwise specified. When numerical ranges are described in steps, the upper and lower limits of each numerical range can be any combination. Also, in this disclosure, a description such as "at least one selected from the group consisting of XX, YY, and ZZ" means any of the following: XX, YY, ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Note that if XX is a group, multiple values ​​may be selected from XX, and the same applies to YY and ZZ. That is the case.

[0013] The embodiments of this disclosure will be described in more detail below, but this disclosure is not limited to these embodiments.

[0014] This disclosure relates to positive electrode active material particles having a core particle and a coating layer covering the surface of the core particle, The core particles are formed of a first composite oxide, The above-mentioned first composite oxide is Lithium and, At least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus, Includes, The coating layer is formed of a second composite oxide, The second composite oxide described above is Lithium and, At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, Includes, When observing the positive electrode active material particles using a scanning electron microscope and obtaining a 50,000x backscattered electron image, the ratio of the area of ​​the coating layer to the sum of the areas of the coating layer and the core particles (area %) is defined as the coverage rate of the coating layer over the core particles, and the coverage rate is 90.0 area % or more. The average thickness of the coating layer is 15.0 nm or less. The maximum thickness of the coating layer is 15.0 nm or less. Regarding positive electrode active material particles.

[0015] The inventors believe that the effects of this disclosure can be obtained by fulfilling the above conditions as follows. As mentioned above, the coating condition of the coating layer can significantly affect battery performance. If the coating layer has low coverage, the effect of suppressing side reactions between the positive electrode active material and the solid electrolyte is reduced, which may shorten the battery life. On the other hand, if the coating layer is thick, the resistance increases, which may reduce the conductivity of lithium ions.

[0016] Patent Document 1 discloses a positive electrode active material having a reaction suppression portion with a coverage rate of 90% and an average thickness of 9.5 nm in an example. However, when the present inventors examined the positive electrode active material described in Patent Document 1, they found that the resistance value remained high even when a coating layer with a high coverage rate was provided. It is thought that even if the average thickness is controlled, areas with a thick coating layer remain, resulting in high resistance. The present inventors conducted further investigations and found that in order to achieve both a long lifespan and low resistance of positive electrode active material particles, it is not sufficient to control only the coverage rate and average thickness of the coating layer, but it is also important to control the maximum thickness.

[0017] This disclosure relates to positive electrode active material particles having a core particle and a coating layer covering the surface of the core particle. Then, using a scanning electron microscope (SEM), the positive electrode active material particles are observed, and in the 50,000x magnified backscattered electron image obtained, the portion corresponding to the coating layer and the portion corresponding to the core particles are binarized. The ratio of the area of ​​the portion corresponding to the coating layer to the sum of the areas of the portions corresponding to the coating layer and the portions corresponding to the core particles (area %) is defined as the coverage rate of the coating layer over the core particles. In this case, if the coverage rate of the coating layer over the core particles is 90.0 area % or more, It is necessary that the average thickness of the coating layer is 15.0 nm or less, and the maximum thickness of the coating layer is 15.0 nm or less.

[0018] By providing a coating layer covering the core particles of the coating layer with a coverage rate of 90.0 area or more, side reactions at the contact interface between the positive electrode active material and the solid electrolyte can be suppressed. As a result, the capacity retention rate after repeated charge-discharge tests is high, and a longer lifespan can be achieved. Furthermore, by controlling the average thickness of the coating layer to 15.0 nm or less, and the maximum thickness to 15.0 nm or less, low resistance can be maintained, thereby suppressing a decrease in lithium ion conductivity.

[0019] If the coverage rate of the coating layer over the core particles is less than 90.0 area%, the area of ​​direct contact between the core particles and the solid electrolyte increases, leading to the formation of a resistive layer due to side reactions at the interface, and shortening the lifespan. From the viewpoint of increasing the capacity retention rate after repeated charge-discharge tests and extending the lifespan, the coverage rate of the coating layer over the core particles is preferably 92.0 area% or more, more preferably 93.0 area% or more, and even more preferably 94.0 area% or more.

[0020] A higher coverage rate is preferable, and there is no particular upper limit, but preferred coverage rates include 100.0 area% or less, 99.0 area% or less, 98.0 area% or less, and 97.0 area% or less. Preferred coverage rates are, for example, 90.0 to 100.0 area%, 92.0 to 100.0 area%, 93.0 to 99.0 area%, 94.0 to 98.0 area%, and 94.0 to 97.0 area%.

[0021] The coverage rate of the coating layer can be determined by the manufacturing method used to coat the core particles, the method of preparing the coating material, specifically the amount of coating material added, the type of solvent used, etc. The coverage rate can be easily increased by adopting the manufacturing methods described in steps (i) to (iii) below, or by increasing the amount of coating material added.

[0022] Furthermore, if the average thickness of the coating layer is greater than 15.0 nm, the coating layer will increase the resistance. Also, even if the average thickness of the coating layer can be controlled to be 15.0 nm or less, if the maximum thickness of the coating layer is greater than 15.0 nm, the resistance value will increase, making it difficult to achieve both long lifespan and low resistance. This is thought to be because even if the average thickness is controlled to be low, the resistance will increase in areas where the coating layer is thicker.

[0023] Therefore, the average thickness of the coating layer is 15.0 nm or less, and the maximum thickness of the coating layer is 15.0 nm or less. From the viewpoint of making it easier to achieve low resistance, the average thickness is preferably 10.0 nm or less, and more preferably 9.0 nm or less. The average thickness of the coating layer is, for example, 5.0 to 15.0 nm, preferably 6.0 to 10.0 nm, and more preferably 7.5 to 9.0 nm.

[0024] Furthermore, from the viewpoint of making it easier to achieve low resistance, the maximum thickness of the coating layer is preferably 12.0 nm or less, more preferably 11.0 nm or less, and even more preferably 9.8 nm or less. The maximum thickness of the coating layer is, for example, 6.0 to 15.0 nm, preferably 7.0 to 12.0 nm, more preferably 7.5 to 11.0 nm, and even more preferably 7.5 to 9.8 nm.

[0025] The average and maximum thickness of the coating layer can be controlled by the manufacturing method used to coat the core particles, the method of preparing the coating material, specifically the amount of coating material added, the type of solvent, etc. To control the average and maximum thickness of the coating layer to 15.0 nm or less, the manufacturing methods described in steps (i) to (iii) below are recommended. In coating methods using a rolling fluidized bed, as shown in Patent Document 1, even if the average thickness can be controlled to 15.0 nm or less, the maximum thickness of the coating layer may exceed 15.0 nm.

[0026] As described above, by setting the coating layer on the positive electrode active material particles to 90.0 area or more, and controlling both the average and maximum thickness of the coating layer to 15.0 nm or less, it is possible to achieve both a longer lifespan and lower resistance for the positive electrode active material particles.

[0027] Furthermore, the difference between the maximum thickness and the minimum thickness of the coating layer (maximum thickness - minimum thickness) is, for example, 6.5 nm or less, preferably 5.0 nm or less, more preferably 4.2 nm or less, even more preferably 2.5 nm or less, and even more preferably 1.5 nm or less. The lower limit is not particularly limited as a smaller value is preferable, and examples include 0 nm or more and 0.1 nm or more.

[0028] By keeping the difference between the maximum and minimum thickness of the coating layer to 5.0 nm or less, it is possible to suppress non-uniformity in the lithium ion conductivity path between relatively thick and thin areas of the coating layer, thereby making it easier to achieve lower resistance. The difference between the maximum and minimum thickness of the coating layer can be controlled by the manufacturing method when coating the core particles, the method of adjusting the coating material, specifically the amount of coating material added, the type of solvent, etc.

[0029] The amount of coating layer per 100 parts by mass of core particles is, for example, 1.20 parts by mass or less, preferably 1.00 parts by mass or less, more preferably 0.90 parts by mass or less, even more preferably 0.70 parts by mass or less, and even more preferably 0.50 parts by mass or less. By having a ratio of 1.00 part by mass or less of the coating layer to the core particles, the ratio of the coating layer to the core particles can be reduced, making it easier to lower the resistance and thus easier to maintain a high conductivity of lithium ions.

[0030] The content of the coating layer with respect to 100 parts by mass of the core particles is, for example, 0.10 to 1.20 parts by mass, preferably 0.20 to 1.00 parts by mass, more preferably 0.20 to 0.90 parts by mass, even more preferably 0.20 to 0.70 parts by mass, and even more preferably 0.25 to 0.50 parts by mass. The ratio of the coating layer to the core particles can be adjusted by the addition amount of the coating material when coating the core particles.

[0031] Next, the core particles formed of the first composite oxide in the positive electrode active material particles will be described. The core particles formed of the first composite oxide contain lithium and at least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus. The core particles preferably contain at least one selected from the group consisting of manganese, cobalt, and nickel and lithium.

[0032] The core particles formed of the first composite oxide include, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. In addition, “(NiCoMn)” and “(NiCoAl)” in “Li(NiCoMn)O2” and “Li(NiCoAl)O2” indicate that the total of the composition ratios in the parentheses is 1. As long as the total is 1, the individual component amounts are arbitrary. Li(NiCoMn)O2 is, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, etc. may be included.

[0033] The core particles are preferably Li(NiCoMn)O2. Commercially available Li(NiCoMn)O2 may be used. For example, LiNi 0.8 Co0.1 Mn 0.1 O2 (product name PO5038, manufactured by MSE Supplies) is one example.

[0034] The coating layer is formed of a second composite oxide. The second composite oxide contains lithium and also contains at least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten. For example, from the viewpoint of reducing resistance, the second composite oxide is preferably a composite oxide containing lithium and niobium. The second composite oxide may contain, for example, lithium niobate.

[0035] The following describes a preferred method for producing positive electrode active material particles. A method for manufacturing positive electrode active material particles is, for example, (i) A step of mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1. (ii) A step of mixing the aforementioned mixture 1 with the core particles formed of the first composite oxide to obtain a mixture 2, and (iii) A step of mixing the aforementioned mixture 2 with a hydrolyzing agent, hydrolyzing the alkoxide monomer and / or its oligomer contained in the mixture 2, dehydrating and condensing it, and depositing it on the surface of the core particles to form the coating layer and obtain the positive electrode active material particles, It holds. And the alkoxide monomer and / or its oligomer, Lithium and, At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, Includes.

[0036] In the above manufacturing method, after obtaining mixture 2 in step (ii), a hydrolyzing agent is added in step (iii) to initiate hydrolysis. This manufacturing method allows the coating reaction to begin from a state in which the core particles and the alkoxide monomers and / or their oligomers, which are the materials for the coating layer, are uniformly dispersed. Therefore, it becomes easier to obtain positive electrode active material particles with a high coating rate, less variation in the thickness of the coating layer, and a small difference between the maximum thickness and the minimum thickness of the coating layer.

[0037] The alkoxide monomer and / or its oligomer is preferably an alkoxide monomer. Step (i) is preferably a mixture of lithium alkoxide, at least one alkoxide selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, and an organic solvent. The number of carbon atoms in the alkoxy group of the alkoxide is, for example, 1 to 6, preferably 1 to 3, and more preferably 1 or 2.

[0038] At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten is preferably niobium, and more preferably niobium. The organic solvent is not particularly limited, and known solvents such as 2-propanol, toluene, THF, methanol, ethanol, and 1-butanol may be used. The purity of the organic solvent is preferably 99.9% or higher, and more preferably 99.99% or higher.

[0039] In step (i), the amount of lithium alkoxide and / or its oligomer is, for example, 50.0 to 500.0 mg or 100.0 to 350.0 mg per 100 ml of organic solvent. In addition, in step (i), the amount of at least one alkoxide and / or its oligomer selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten is, for example, 0.10 to 2.00 ml or 0.50 to 1.80 ml per 100 ml of organic solvent, and in terms of mass, for example, 0.13 to 2.60 g or 0.65 to 2.30 g.

[0040] Furthermore, when using multiple alkoxide monomers with different reaction rates, reflux may be added in the step of obtaining the mixture 1 in order to improve the uniformity of the composition of the coating layer. In addition, a chelating material may be added in order to control the reaction rate of the alkoxide and obtain a uniform coating layer. There are no particular restrictions on the chelating material used, but examples include acetylacetone.

[0041] In step (ii), mixture 1 and core particles formed from the first composite oxide are mixed to obtain mixture 2. The core particles can be those described above. From the viewpoint of material dispersion, it is preferable to mix mixture 1 and core particles while continuing to stir. The amounts of mixture 1 and core particles should be controlled so as to yield the desired amount of coating layer.

[0042] In step (iii), the mixture 2 and the hydrolyzing agent are mixed. For example, the hydrolyzing agent is added to the mixture 2. The alkoxide monomer and / or its oligomer contained in the mixture 2 are then hydrolyzed, dehydrated and condensed, and precipitated on the surface of the core particles to form a coating layer. The hydrolyzing agent only needs to be able to hydrolyze the alkoxide monomer and / or its oligomer. The hydrolyzing agent may include, for example, water (H2O).

[0043] The amount of hydrolyzing agent is not particularly limited, as long as it is sufficient to hydrolyze the alkoxide monomer and / or its oligomer. For example, the amount of hydrolyzing agent is, for example, 1.00 to 15.00 ml, preferably 1.00 to 10.00 ml, and more preferably 2.00 to 8.00 ml, per 100 ml of organic solvent in step (i).

[0044] From the viewpoint of material dispersion, step (iii) should be carried out while continuing stirring. Also, from the viewpoint of minimizing thickness variations in the coating layer, it is preferable not to hydrolyze the alkoxide monomer and / or its oligomer up to step (iii). For example, it is preferable not to substantially add a hydrolyzing agent up to step (iii).

[0045] "Substantially omitting hydrolysants" means intentionally omitting hydrolysants, and trace amounts of hydrolysants that inevitably become mixed in small amounts during the production of positive electrode active material particles are acceptable. For example, trace amounts of water that are inevitably contained in organic solvents, or amounts of water that are too small to exert a hydrolytic effect, are acceptable. For example, the content ratio of hydrolysants in mixture 1 and mixture 2 is 0.1% by mass or less, preferably 0.05% by mass or less, more preferably 0.01% by mass or less, and even more preferably 0.001% by mass or less. For example, when 2-propanol and ethanol with a purity of 99.9% are used, the frequency of contact between water and alkoxide can be extremely reduced, so it is considered that no hydrolytic effect will occur.

[0046] From the viewpoint of reducing thickness variations in the coating layer, after adding the hydrolyzing agent, the reaction is preferably carried out for 1 to 48 hours or 2 to 24 hours while continuing to stir. Through this reaction, the alkoxide monomer and / or its oligomer are hydrolyzed and precipitated on the core particle surface through dehydration condensation, forming a coating layer and obtaining positive electrode active material particles.

[0047] Furthermore, the obtained positive electrode active material particles may be dried and sintered at approximately 200°C to 800°C for the purpose of removing residual carbon and controlling the crystal structure of the coating layer. The particle size of the positive electrode active material particles is not particularly limited and can be set according to the application. Examples of volume-based median diameters (D50) of the positive electrode active material particles include 1-100 μm, 2-50 μm, 3-20 μm, and 5-15 μm.

[0048] (All-solid-state battery) This disclosure can provide all-solid-state batteries. A solid-state battery has at least a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order. The positive electrode layer contains the above-mentioned positive electrode active material particles. Current collectors may be provided in the positive electrode layer and the negative electrode layer.

[0049] The positive electrode layer contains positive electrode active material particles. If necessary, the positive electrode composite material used in the positive electrode layer may contain conductive additives such as carbon black and a solid electrolyte. The same solid electrolyte as that used in the solid electrolyte layer may be used. The amounts of conductive additives and solid electrolytes are not particularly limited and can be set appropriately according to the desired positive electrode.

[0050] This disclosure can provide a positive electrode for an all-solid-state battery. The positive electrode is a molded body of a positive electrode composite containing positive electrode active material particles, wherein the positive electrode active material particles are the positive electrode active material particles described above. The means for obtaining the positive electrode or positive electrode layer are not particularly limited. For example, a positive electrode mixture containing positive electrode active material particles, a conductive additive and a solid electrolyte as needed, can be molded by pressurizing it, for example, using a press machine.

[0051] A solid electrolyte layer is, for example, made by solidifying solid electrolyte particles. The solid electrolyte particles are not particularly limited, and ion-conducting solids commonly used in all-solid-state batteries can be used. For example, sulfide-based solid electrolytes (Li6PS5Cl, Li7P3S 11 Li3PS4, Li8P2S9, Li 13 GeP3S 16 Li 10 GeP2S 12 (etc.), Li-B oxide-based solid electrolyte particles, Li-Yb oxide-based solid electrolyte particles, NASCICON-type solid electrolyte particles (LiAlTi(PO4)3, LiAlGe(PO4)3, etc.), perovskite-type oxide-based solid electrolyte particles (Li x La (1-x) / 3 TiO3, LixLa (1-x) / 3 (e.g., NbO3), garnet-type oxide solid electrolyte particles (Li7La3Zr2O 12 Examples include Li-PO-based solid electrolyte particles (such as Li3PO4 and LiPON (particles in which some of the O in Li3PO4 is replaced with N)).

[0052] The negative electrode layer contains a negative electrode active material. The negative electrode active material is not particularly limited, and known materials that can be used in all-solid-state batteries may be used. Examples of negative electrode active materials include carbon materials, Li materials, Si materials, etc. For example, metals such as metallic lithium, metallic indium, metallic silicon, or metallic aluminum, or alloys thereof, can be used. All-solid-state batteries can be manufactured by molding the materials for the positive electrode layer, solid electrolyte layer, and negative electrode layer using a known press machine or the like.

[0053] The measurement methods relating to this disclosure are described below. <Method for calculating the coverage ratio of the coating layer to the core particles> (Method for obtaining backscattered electron images of the surface of positive electrode active material particles) The coverage rate of the coating layer over the core particles is calculated using the backscattered electron image of the surface of the positive electrode active material particles. Backscattered electron images of positive electrode active material particles are acquired using a scanning electron microscope (SEM). The backscattered electron images obtained from the SEM are also called "compositional images," and particles with smaller atomic numbers appear darker, while those with larger atomic numbers appear brighter.

[0054] The difference in atomic numbers between the elements in the positive electrode active material particles and the elements in the coating layer creates a contrast between the core particle area and the coating layer area. For example, if the core particles are an oxide containing cobalt, nickel, and manganese, and the coating layer is an oxide containing niobium, the backscattered electron image obtained from the SEM will show the core particles as dark areas and the coating layer as bright areas.

[0055] The SEM equipment and observation conditions are as follows: Equipment used: Carl Zeiss Microscopy Co., Ltd. GeminiSEM 560 Acceleration voltage: 1.0kV WD: 4.0mm Aperture Size: 20.0 μm Detection signal: EsB (Energy-selective backscattered electrons) EsB Grid: 600V Observation magnification: 5,000x (adjust the magnification as needed to allow one particle to be observed within the field of view, depending on the particle size) Contrast: 63.0 ± 5.0% (reference value) Brightness: 38.0 ± 5.0% (reference value) Image size: 1024 pixels x 768 pixels Pretreatment: Cathode active material particles are scattered onto carbon tape (no vapor deposition is performed). Contrast and brightness should be set appropriately according to the condition of the equipment being used. The acceleration voltage and EsB grid should be set to achieve objectives such as acquiring structural information of the outermost surface of the positive electrode active material particles, preventing charge buildup in undeposited samples, and selectively detecting high-energy backscattered electrons. The observation field should be selected near where the curvature of the positive electrode active material particles is small.

[0056] (Method for identifying elements in the region observed in backscattered electron images) The elements observed in the backscattered electron image are confirmed by overlaying the elemental mapping image obtained by energy-dispersive X-ray spectroscopy (EDS), which can be acquired with a scanning electron microscope (SEM), with the backscattered electron image.

[0057] The SEM / EDS equipment and observation conditions are as follows: Equipment used (SEM): GeminiSEM manufactured by Carl Zeiss Microscopy Co., Ltd. 560 Equipment used (EDS): NORAN manufactured by Thermo Fisher Scientific Co., Ltd. System 7 Detector (EDS): Ultra Dry (Windowless type) Acceleration voltage: 1.0kV WD: 5.0mm Aperture Size: 30.0 μm Detection signal: SE2 (secondary electrons) Observation magnification: 5,000x (adjust the magnification as needed to allow one particle to be observed within the field of view, depending on the particle size) Mode: Spectral Imaging Pretreatment: Cathode active material particles are scattered onto carbon tape (no vapor deposition is performed). The mapping image obtained using this method is superimposed with the backscattered electron image, and atoms contained in the bright and dark areas of the backscattered electron image are identified to determine the core particles and coating layer. For example, if the niobium atoms in the mapping image coincide with the bright areas of the backscattered electron image, it can be identified that the bright areas of the backscattered electron image are coated with an oxide containing niobium.

[0058] (Coverage rate of the coating layer relative to the core particles) To calculate the coverage rate, first, using the same method as for obtaining backscattered electron images of the surface of the positive electrode active material particles described above, the observation magnification is adjusted appropriately so that there are about 10 particles in the observation field, and backscattered electron images are obtained. Next, for each particle in the observation field, an image is obtained at an observation magnification of 50,000x so that the center of the particle is at the center of the observation field. Using the above method, an image processing software, ImageJ (developed by Wayne Rashand), is used to calculate the coverage rate S, which is the ratio (area %) of the area of ​​the coating layer to the sum of the areas of the coating layer and the core particles. The procedure is as follows.

[0059] First, convert the backscattered electron image to 8-bit using the Image menu's Type option. Next, reduce image noise by setting the Median diameter to 2.0 pixels using the Process menu's Filters option. Next, use the Straight Line tool on the toolbar to select the scale bar in the observation conditions display area shown at the bottom of the backscattered electron image. With the scale bar selected, select Set Scale from the Analyze menu. A new window will open, and the pixel distance of the selected line will be entered in the Distance in Pixels field.

[0060] Enter the value of the scale bar (e.g., 100) in the Known Distance field of the aforementioned window, enter the unit of the scale bar (e.g., nm) in the Unit of Measurement field, and click OK to complete the scale setting. Next, after excluding the observation conditions display area shown at the bottom of the backscattered electron image, estimate the image center and use the Rectangle Tool on the toolbar to select a 1.5 μm square area from the center of the backscattered electron image.

[0061] Next, select Set Measurements from the Analyze menu and check Area. Select Measure from the Analyze menu, check Display Result, and click OK to perform the domain analysis. The area of ​​the analyzed portion (Area) obtained from the newly opened Results window is defined as S1, which is the sum of the area of ​​the portion corresponding to the coating layer and the area of ​​the portion corresponding to the core particles. Next, select Threshold from Adjust. In manual operation, choose 128 as the threshold, which is the midpoint between black and white in an 8-bit image, and click Apply to obtain the binarized image.

[0062] If the coating layer is a niobium-containing oxide, the coating layer is observed as a bright area, and this operation will display the pixels corresponding to the coating domain D in black. Again, after excluding the observation conditions display area shown at the bottom of the backscattered electron image, estimate the image center and use the Rectangle Tool on the toolbar to select a 1.5 μm square area from the center of the backscattered electron image.

[0063] Next, select Set Measurements from the Analyze menu and check Area. Then, select Measure from the Analyze menu, check Display Result, and click OK to perform the domain analysis. The area obtained from the newly opened Results window is defined as the area S2 of the portion corresponding to the coating layer.

[0064] The coverage ratio S is calculated from the sum of the areas S1 (area of ​​the portion corresponding to the coating layer and the area of ​​the portion corresponding to the core particles) and the area S2 (area of ​​the portion corresponding to the coating layer) using the following formula. S(area%)=S2 / S1×100 The above procedure is performed on each particle that can be observed when approximately 10 particles are initially placed in the observation field, and the coverage S of each particle is calculated. This operation is repeated until there are more than 50 positive electrode active material particles, and the arithmetic mean of the coverage S of all observed particles is used as the coverage.

[0065] <Method for calculating the average thickness, maximum thickness, and the difference between the maximum and minimum thickness of the coating layer> The average thickness, maximum thickness, and the difference between the maximum and minimum thicknesses of the coating layer are calculated using cross-sectional images obtained with a transmission electron microscope (TEM). Cross-sectional observation of positive electrode active material particles is performed using the following method. The specific method for observing the cross-section of positive electrode active material particles is as follows: First, the positive electrode active material powder is processed using a focused ion / electron beam processing system "Helios G4UC" (manufactured by FI Japan) under acceleration voltage conditions of 30kV (sampling) and 8kV (finishing) to cut out a thin section sample with a thickness of approximately 100nm. The extracted sample is observed cross-sectionally using a transmission electron microscope and elemental mapping is performed using EDS. The mapped image allows for the identification of atoms contained in the core particles and the coating layer.

[0066] The observation conditions are as follows: Equipment used (TEM): JEOL JEM-2800 Equipment used (EDS detector): JEOL Ltd. JED-2300T Dry SD100GV detector (detection element area: 100 mm²) 2 ) Equipment used (EDS analyzer): Thermo Fisher Scientific NORAN System 7 Acceleration voltage: 200kV Observation magnification: 1,000,000x Probe size: 1.0mm STEM image size: 1024 pixels x 1024 pixels EDS mapping size: 256 pixels x 256 pixels Number of frames: 1000 Aperture Size: 40.0 μm Detection signal: STEM-DF

[0067] Based on the obtained cross-sectional mapping image, line analysis is performed on the elements contained in the coating layer in the direction normal to the particles. The conditions for line analysis are as follows: STEM magnification: 1,000,000x Line length: 100nm Points: 100 Figure 1 shows an example of a cross-sectional image and line analysis of the highly active material particles. Line analysis is performed on the coating layer in the direction normal to the particles, i.e., in the direction of the arrow in Figure 1. Figure 2 shows an example of a profile obtained by line analysis. The full width at half maximum (FWHM) of the obtained X-ray intensity peak is taken as the thickness of the coating layer at the corresponding location. A similar line analysis is performed at 20 locations on a single cross-sectional image. The analysis locations are spaced equally apart. The same analysis is performed on 50 cross-sectional images, and the arithmetic mean of locations where a thickness of 0.5 nm or more is observed is taken as the average thickness of the coating layer. Furthermore, the maximum value among the 1000 obtained coating layer thicknesses is taken as the maximum thickness, and the minimum value among locations where a thickness of 0.5 nm or more was observed is taken as the minimum thickness, and the difference between these two values ​​is calculated.

[0068] <Method for calculating the ratio of the coating layer to the core particles> The content of the coating layer relative to the core particles is determined by the fundamental parameter (FP) method using X-ray fluorescence. For example, if the core particles are LiNi 0.8 Co 0.1 Mn 0.1In the case of O2 and a coating layer of lithium niobate, the Ni in the core particles is quantified as nickel oxide, and the Nb in the coating layer is quantified as niobium pentoxide. This is then converted to parts by mass of the coating layer per 100 parts by mass of the core particles. If the powder sample can be formed into pellets, the measurement should be performed under a vacuum atmosphere. If pellet formation is not possible, the measurement should be performed in a helium atmosphere using a special cup and film while the sample remains in powder form. Furthermore, if there are elements that are not detected by X-ray fluorescence (elements lighter than oxygen), the calculation should be performed after setting the balance components.

[0069] An example of the measurement is shown below. Equipment used: X-ray fluorescence analyzer Zetium (manufactured by Spectris Corporation) Sample adjustment A 6.0 μm thick Mylar film (manufactured by Chemplex Industries) was mounted in a 29 mm inner diameter P2 plastic liquid sample cup (manufactured by Spectris Co., Ltd.), and 2.0 g of the sample was poured into it, leveling it to a uniform thickness. Measurement conditions X-ray tube: Rh target Tube output: 2.4kW Measurement diameter: 27mm Atmosphere: Helium Analysis conditions FP Quantitative Software: Omnian Element: Oxide Balanced ingredients: Li [Examples]

[0070] The present disclosure will be described in detail below with reference to examples and comparative examples, but the present disclosure is not limited to these examples.

[0071] Examples relating to the positive electrode active material particles of this disclosure will be described below. <Example of manufacturing of positive electrode active material particles 1> [Preparation of Mixture 1] In a container equipped with a stirring device, 100.0 ml of 2-propanol (super-dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. While stirring, 260.0 mg of LiOC2H5 (manufactured by Kojunkagaku Co., Ltd.) as a lithium alkoxide and 1.25 ml of Nb(OC2H5)5 (manufactured by Kojunkagaku Co., Ltd.) as a niobium alkoxide were added. The mixture was then refluxed at 85°C overnight. This was designated as mixture 1.

[0072] [Preparation of Mixture 2] While continuing to stir the mixture 1, LiNi is added as core particles containing the first composite oxide. 0.8 Co 0.1 Mn 0.1 30g of O2 (PO5038, manufactured by MSE Supplies) was added to obtain mixture 2.

[0073] Next, 4.50 ml of H2O was added to the mixture 2 as a hydrolyzing agent while continuing to stir, and stirring was continued overnight to hydrolyze the alkoxide monomer, causing dehydration condensation and deposition on the core particle surface to form a coating layer. Subsequently, the material was recovered by filtration, vacuum-dried at 80°C for 4 hours, and sintered at 350°C for 1 hour to obtain positive electrode active material particles 1 having a core-shell structure. The physical properties of positive electrode active material particles 1 are shown in Table 2.

[0074] <Examples of manufacturing processes for positive electrode active material particles 2-8> In the example of producing positive electrode active material particle 1, positive electrode active material particles 2 to 8 are obtained in the same manner, except that the solvent type, Li alkoxide LiOC2H5, Nb alkoxide Nb(OC2H5)5, and H2O are changed as shown in Table 1. The physical properties of positive electrode active material particles 2 to 8 are shown in Table 2.

[0075] <Cathode active material particles 9> LiNi coated with LiNbO3 0.8 Co 0.1 Mn 0.1 O2(MSE PO0185 (manufactured by Supplies Inc.) was used as the positive electrode active material particle 9.

[0076] <Example of manufacturing of positive electrode active material particles 10> Add 100.0 ml of ethanol (super-dehydrated) (99.5%) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a container equipped with a stirring device, and while stirring, add 816.4 mg of LiOC2H5 (manufactured by Kojunkagaku Co., Ltd.) as a lithium alkoxide and 3.92 ml of Nb(OC2H5)5 (manufactured by Kojunkagaku Co., Ltd.) as a niobium alkoxide. While continuing to stir, 30g of PO5038 manufactured by MSE Supplies was added. Then, 1.00ml of H2O was added, and stirring was continued overnight. After that, the ethanol was evaporated, and sintering was performed at 500°C for 3 hours to obtain positive electrode active material particles 10. The physical properties of positive electrode active material particles 10 are shown in Table 2.

[0077] <Example of manufacturing of positive electrode active material particles 11> To 1.00 kg of ethanol (super-dehydrated) (99.5%) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 8.16 g of LiOC2H5 and 39.2 ml of Nb(OC2H5)5 were added and stirred to obtain a coating material composition. The raw material composition is applied to the surface of MSE Supplies' PO5038 using a coating apparatus with a rolling fluidized bed. At this time, the ratio of the coating raw material composition to the core particles is adjusted so that there are 0.0525 mg of the coating raw material composition per 1 g of core particles. Then, a sintering treatment is performed at 350°C to obtain positive electrode active material particles 11. The physical properties of the positive electrode active material particles 11 are shown in Table 2.

[0078] <Cathode active material particles 12> PO5038 manufactured by MSE Supplies is used as the positive electrode active material particle 12.

[0079] [Table 1]

[0080] [Table 2]

[0081] In the table, the amount of the coating layer is shown as the amount of the coating layer (parts by mass) per 100 parts by mass of core particles.

[0082] [Measurement of resistance value and measurement of capacitance retention rate] Solid-state batteries were fabricated using the prepared positive electrode active material particles 1 and 9 by the following method, and their resistance and capacity retention rates were measured. The measured resistance and capacity retention rates are shown in Table 3. Solid-state batteries were fabricated using the same method for positive electrode active material particles 2-8 and 10-12, and their resistance and capacity retention rates were measured. The resistance and capacity retention rates are shown in Table 3.

[0083] <Fabrication of all-solid-state batteries> The following operations were performed inside a glove box under an argon atmosphere. (Preparation of positive electrode composite material) A cathode composite material was prepared by mixing 65.0 mg of cathode active material particles obtained by the method described above, 5.0 mg of conductive additive (acetylene black), and 30.0 mg of solid electrolyte (Li6PS5Cl) in a mortar for 5 minutes.

[0084] (Battery cell manufacturing) Next, 85.0 mg of solid electrolyte (Li6PS5Cl) was placed inside a solid-state battery cell (HSSC-05, manufactured by Hosen Co., Ltd., electrode size Φ10 mm), and the solid electrolyte layer was formed by pressurizing it at 30 MPa using a press machine.

[0085] Next, after releasing the pressure, the upper punch was withdrawn, and 10.6 mg of the aforementioned cathode composite material was placed on top of the solid electrolyte layer formed in the cell. The upper punch was then reinserted, and pressure was applied at 200 MPa using a press machine to form the cathode layer on top of the solid electrolyte layer. After that, the upper punch was removed, a SUS foil (Φ10mm x 0.5mm thick) was inserted on top of the positive electrode layer, and the upper punch was reinserted and pressed in by hand.

[0086] The all-solid-state battery cell was inverted, the punch on the side opposite the positive electrode layer was removed, and lithium metal foil (200 μm thick) and indium foil (100 μm thick), punched out to a diameter of Φ8 mm, were sequentially inserted on top of the solid electrolyte layer as the negative electrode layer. Next, a SUS foil (Φ10mm x 0.5mm thick) was inserted on top of the negative electrode, a punch was made, and pressure was applied to 90MPa using a press machine. After depressurization, the case screws were tightened so that the internal restraining pressure of the cell was 200MPa.

[0087] A glass desiccator with airtightness, capable of connecting electrical wiring to the inside and outside, was prepared. The aforementioned battery cells were placed in the container, and the wiring of each electrode plate of the cell was connected to the desiccator before sealing, thereby fabricating the battery cells. The completed battery cells were removed from the glove box and evaluated as follows.

[0088] <Resistance measurement> The prototype battery cells underwent two charge-discharge tests under the following conditions. ·Equipment: Bio Logic VMP-3e ·Temperature: 25℃ ·Charging potential: 3.6V • Discharge potential: 2.0V • Current rate: 0.1C • Cutoff current rate: 0.01C (or 60 minutes)

[0089] Next, AC impedance measurements were performed under the following conditions, and a Cole-Cole plot was obtained. ·Equipment: Bio Logic VMP-3e ·Temperature: 25℃ • SOC 100% (calculated from the discharge capacity of the second cycle) • Measurement frequency: 1MHz~10mHz A circular arc was fitted to the obtained Cole-Cole plot, and the distance between the two intersection points of the fitted circular arc and the real axis was measured as the resistance value.

[0090] <Measurement of volume retention rate> For battery cells after resistance measurement, the capacity retention rate was measured as the ratio of the discharge capacity after 25 cycles to the discharge capacity after 1 cycle when further charge-discharge tests were performed under the following conditions. ·Equipment: Bio Logic VMP-3e ·Temperature: 25℃ ·Charging potential: 3.6V • Discharge potential: 2.0V • Current rate: 0.1C • Cutoff current rate: None

[0091] Table 3 shows the resistance values ​​and capacity retention rates of each battery cell containing the positive electrode active material particles described in Table 3, as Examples 1 to 9 and Comparative Examples 1 to 4.

[0092] [Table 3]

[0093] This disclosure relates to the following configuration and method. (Composition 1) A positive electrode active material particle having a core particle and a coating layer covering the surface of the core particle, The core particles are formed of a first composite oxide, The above-mentioned first composite oxide is Lithium and, At least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus, Includes, The coating layer is formed of a second composite oxide, The second composite oxide described above is Lithium and, At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, Includes, When observing the positive electrode active material particles using a scanning electron microscope and obtaining a 50,000x backscattered electron image, the ratio of the area of ​​the coating layer to the sum of the areas of the coating layer and the core particles (area %) is defined as the coverage rate of the coating layer over the core particles, and the coverage rate is 90.0 area % or more. The average thickness of the coating layer is 15.0 nm or less. The maximum thickness of the coating layer is 15.0 nm or less. Positive electrode active material particles characterized by the above. (Configuration 2) The positive electrode active material particles according to configuration 1, wherein the difference between the maximum thickness and the minimum thickness of the coating layer is 5.0 nm or less. (Composition 3) The positive electrode active material particle according to configuration 1 or 2, wherein the content of the coating layer relative to 100 parts by mass of the core particles is 1.00 part by mass or less. (Composition 4) The content of the coating layer relative to 100 parts by mass of the core particles is 0.20 to 0.90 parts by mass. The positive electrode active material particles are those described in any of configurations 1 to 3. (Composition 5) The positive electrode active material particles according to any one of configurations 1 to 4, wherein the second composite oxide comprises lithium and niobium. (Method 6) A method for producing positive electrode active material particles according to any of the configurations 1 to 5, The manufacturing method is (i) A step of mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1. (ii) A step of mixing the aforementioned mixed liquid 1 with the core particles to obtain a mixed liquid 2, and (iii) A step of mixing the aforementioned mixture 2 with a hydrolyzing agent, hydrolyzing the alkoxide monomer and / or its oligomer contained in the mixture 2, dehydrating and condensing it, and depositing it on the surface of the core particles to form the coating layer and obtain the positive electrode active material particles, It has, The alkoxide monomer and / or its oligomer, Lithium and, At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, including, A method for producing positive electrode active material particles, characterized by the above. (Composition 7) The positive electrode of an all-solid-state battery, The positive electrode is a molded body of a positive electrode composite material containing positive electrode active material particles. The positive electrode active material particles are positive electrode active material particles according to any of the configurations 1 to 5. A positive electrode characterized by the following features. (Composition 8) All-solid-state battery, The all-solid-state battery has at least a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order. The positive electrode layer contains positive electrode active material particles according to any of the configurations 1 to 5. A solid-state battery characterized by the following features.

Claims

1. A positive electrode active material particle having a core particle and a coating layer covering the surface of the core particle, The core particles are formed of a first composite oxide, The first composite oxide described above is Lithium and, At least one selected from the group consisting of manganese, cobalt, nickel, aluminum, iron, and phosphorus, Includes, The coating layer is formed of a second composite oxide, The second composite oxide is Lithium and, At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, Includes, When observing the positive electrode active material particles using a scanning electron microscope and obtaining a 50,000x backscattered electron image, the ratio of the area of ​​the part corresponding to the coating layer to the sum of the areas of the parts corresponding to the coating layer and the core particles, when the parts corresponding to the coating layer and the core particles are binarized, the coverage rate of the coating layer over the core particles is defined as the ratio of the area of ​​the part corresponding to the coating layer to the sum of the areas of the parts corresponding to the coating layer and the core particles, and the coverage rate is 90.0 area% or more, The average thickness of the coating layer is 15.0 nm or less. The maximum thickness of the coating layer is 15.0 nm or less. Positive electrode active material particles characterized by the above.

2. The positive electrode active material particle according to claim 1, wherein the difference between the maximum thickness and the minimum thickness of the coating layer is 5.0 nm or less.

3. The positive electrode active material particle according to claim 1 or 2, wherein the content of the coating layer relative to 100 parts by mass of the core particles is 1.00 part by mass or less.

4. The positive electrode active material particle according to claim 1 or 2, wherein the content of the coating layer relative to 100 parts by mass of the core particles is 0.20 to 0.90 parts by mass.

5. The positive electrode active material particles according to claim 1 or 2, wherein the second composite oxide comprises lithium and niobium.

6. A method for producing positive electrode active material particles according to claim 1 or 2, The manufacturing method is (i) A step of mixing an alkoxide monomer and / or its oligomer with an organic solvent to obtain a mixed solution 1. (ii) A step of mixing the aforementioned mixed liquid 1 and the core particles to obtain a mixed liquid 2, (iii) A step of mixing the aforementioned mixture 2 with a hydrolyzing agent to hydrolyze the alkoxide monomer and / or its oligomer contained in the mixture 2, dehydrate and condense it, precipitate it on the surface of the core particles to form the coating layer, and obtain the positive electrode active material particles. It has, The alkoxide monomer and / or its oligomer, Lithium and, At least one selected from the group consisting of niobium, boron, phosphorus, zirconium, titanium, aluminum, lanthanum, and tungsten, including, A method for producing positive electrode active material particles, characterized by the above.

7. The positive electrode of an all-solid-state battery, The positive electrode is a molded body of a positive electrode composite material containing positive electrode active material particles. The positive electrode active material particles are the positive electrode active material particles described in claim 1 or 2. A positive electrode characterized by the following features.

8. All-solid-state battery, The all-solid-state battery has at least a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order. The positive electrode layer contains positive electrode active material particles according to claim 1 or 2. A solid-state battery characterized by the following features.

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