Composite cathode active material, cathode material, and battery

Abstract

A composite positive electrode active material 100 according to the present disclosure comprises a positive electrode active material 101 and a coating layer 102 that covers at least a part of the surface of the positive electrode active material 101. The coating layer 102 contains a first coating material and a second coating material; the first coating material is composed of a solid fluoride electrolyte; and the second coating material is composed of a material that produces at least one substance that is selected from the group consisting of lithium oxide and lithium fluoride after being reacted with at least one substance that is selected from the group consisting of water and hydrogen fluoride.

Description

Technical Field

[0001] The present disclosure relates to a composite positive electrode active material, a positive electrode material, and a battery.

Background Art

[0002] Patent Document 1 discloses an all-solid-state lithium battery including a positive electrode active material coated with a sulfide solid electrolyte.

[0003] Patent Document 2 discloses a positive electrode material including a positive electrode active material coated with a halide solid electrolyte and a solid electrolyte. The halide solid electrolyte contains lithium, yttrium, and chlorine and / or bromine.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] The present disclosure is a positive electrode active material, a coating layer that coats at least a part of the surface of the positive electrode active material, and wherein the coating layer includes a first coating material containing a fluoride solid electrolyte and a second coating material, the second coating material is a material that generates at least one selected from the group consisting of lithium oxide and lithium fluoride after reacting with at least one selected from the group consisting of water and hydrogen fluoride. A composite positive electrode active material is provided.

[0007] According to this disclosure, it is possible to suppress the increase in the output resistance of the battery when heat is applied. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a cross-sectional view showing the schematic configuration of the composite positive electrode active material in Embodiment 1. [Figure 2] Figure 2 illustrates the actions and effects of the composite positive electrode active material shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view showing the schematic configuration of the cathode material in Embodiment 2. [Figure 4] Figure 4 is a cross-sectional view showing the schematic configuration of the battery in Embodiment 3. [Modes for carrying out the invention]

[0009] Embodiments of the present disclosure will be described below with reference to the drawings.

[0010] The following descriptions are either comprehensive or specific examples. The numerical values, compositions, shapes, film thicknesses, electrical properties, secondary battery structures, electrode materials, etc., shown below are examples and are not intended to limit this disclosure. In addition, any components not described in the independent claim representing the highest-level concept are optional components.

[0011] (Knowledge that forms the basis of this disclosure) In Patent Document 1, the positive electrode active material is coated with a sulfide solid electrolyte. Although sulfide solid electrolytes are materials with high ionic conductivity, they have problems with oxidation resistance.

[0012] Patent Document 2 uses a halogenated solid electrolyte containing chlorine and / or bromine. As a result of diligent research, the present inventors have found that when a halogenated solid electrolyte containing chlorine and / or bromine is included in the positive electrode material, the halogenated solid electrolyte undergoes oxidative decomposition during battery charging, and consequently, the battery's charge and discharge efficiency decreases.

[0013] Specifically, when a solid electrolyte containing chlorine or bromine is used in combination with a positive electrode active material having an average lithium potential of 3.7V or higher, the solid electrolyte may decompose during charging due to an oxidation reaction, and the resulting oxidative decomposition products may function as a resistive layer. Here, oxidation refers to a side reaction in which, in addition to the normal charging reaction in which lithium and electrons are extracted from the positive electrode active material in the positive electrode material, electrons are also extracted from the solid electrolyte in contact with the positive electrode active material. This oxidation reaction is thought to lead to the formation of a resistive layer of oxidative decomposition products with poor lithium ion conductivity between the positive electrode active material and the solid electrolyte, and this resistive layer is thought to function as a large interfacial resistance.

[0014] The inventors investigated techniques to suppress the formation of a high-resistance layer between the positive electrode active material and the solid electrolyte. As a result of their investigation, it was found that batteries using a positive electrode active material coated with a fluoride solid electrolyte exhibit excellent oxidation resistance and can suppress the increase in the internal resistance of the battery during charging. The details of the mechanism are not clear, but it is presumed to be as follows: Fluorine has the highest electronegativity among halogen elements and therefore strongly bonds with cations in the fluoride solid electrolyte. As a result, the oxidation reaction of fluorine, i.e., the side reaction in which electrons are extracted from fluorine, does not proceed easily. Therefore, fluoride solid electrolytes exhibit excellent oxidation resistance.

[0015] Furthermore, the inventors investigated the thermal stability of positive electrode active material coated with a fluoride solid electrolyte. As a result of the investigation, they found that when the positive electrode active material undergoes a thermal history of 100°C or higher, the output resistance of the battery during discharge increases. The details of the mechanism are not clear, but it is presumed to be as follows: When the positive electrode active material undergoes a thermal history, water is generated from some of the water, hydrates, and hydroxides present in the positive electrode active material. Hydrogen fluoride is generated when the generated water reacts with the fluoride solid electrolyte. Furthermore, water is generated again when the hydrogen fluoride reacts with the positive electrode active material. As these reactions are repeated, a resistance layer is formed at the interface between the positive electrode active material and the fluoride solid electrolyte.

[0016] Based on the above findings, the inventors conducted thorough research and discovered that coating the positive electrode active material with a specific material can suppress the increase in the battery's output resistance when heat is applied.

[0017] (Summary of one aspect of this disclosure) The composite cathode active material relating to the first aspect of this disclosure is Positive electrode active material and, A coating layer covering at least a portion of the surface of the positive electrode active material, Equipped with, Here, the coating layer includes a first coating material and a second coating material, The first coating material is a fluoride solid electrolyte, The second coating material is a material that, after reacting with at least one selected from the group consisting of water and hydrogen fluoride, produces at least one selected from the group consisting of lithium oxide and lithium fluoride.

[0018] The composite cathode active material relating to the second aspect of this disclosure is Positive electrode active material and, A coating layer covering at least a portion of the surface of the positive electrode active material, Equipped with, Here, the coating layer comprises Li, Ti, M, P, O, and F. M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr.

[0019] The composite positive electrode active material of this disclosure can suppress the increase in the output resistance of the battery when heat is applied.

[0020] In a third aspect of this disclosure, for example, in a composite positive electrode active material according to the second aspect, the coating layer may include a first coating material and a second coating material, the first coating material may include Li, Ti, M, and F, and the second coating material may include Li, P, and O. With such a configuration, the reaction between the coating material and water, and the reaction between the coating material and hydrogen fluoride can be effectively suppressed.

[0021] In a fourth aspect of this disclosure, for example, in a composite cathode active material according to the first or third aspect, the first coating material may be represented by the following compositional formula (1), where α, β, and γ satisfy α + 4β + 3γ = 6 and γ > 0. Such a configuration can improve the ionic conductivity of the coating material. Li α Ti β M γ F6...Formula (1)

[0022] In a fifth aspect of this disclosure, for example, in the composite cathode active material according to either the second or fourth aspect, M may be Al. Such a configuration can improve the ionic conductivity of the coating material.

[0023] In a sixth aspect of this disclosure, for example, in the composite cathode active material according to the fourth aspect, γ may satisfy 0.5 ≤ γ < 1. Such a configuration can further improve the ionic conductivity of the coating material.

[0024] In a seventh aspect of this disclosure, for example, in a composite cathode active material according to the fourth or sixth aspect, α, β, and γ may satisfy α=2.7, β=0.3, and γ=0.7. Such a configuration can further improve the ionic conductivity of the coating material.

[0025] In the eighth aspect of this disclosure, for example, in the composite cathode active material according to the first, third, fourth, sixth, or seventh aspect, the second coating material may contain lithium phosphate. Li3PO4 reacts with water and hydrogen fluoride to produce lithium oxide and lithium fluoride, thereby halting the continued reaction.

[0026] In the ninth aspect of this disclosure, for example, in the composite cathode active material according to the first, third, fourth, sixth, seventh, or eighth aspect, the ratio of the volume of the second coating material to the volume of the first coating material may be in the range of 2% or more and less than 100%. When this ratio is appropriately adjusted, the ionic conductivity of the coating material can be ensured while suppressing continuous reactions involving the cathode active material, fluoride solid electrolyte, water, and hydrogen fluoride.

[0027] In the tenth aspect of this disclosure, for example, in the composite positive electrode active material according to the ninth aspect, the ratio may be in the range of 2% or more and 50% or less. With such a configuration, the increase in the output resistance of the battery can be further suppressed.

[0028] In an eleventh aspect of this disclosure, for example, in a composite positive electrode active material according to any one of the first to tenth aspects, the ratio of the volume of the coating layer to the volume of the positive electrode active material may be in the range of 1% or more and 10% or less. When this ratio is appropriately adjusted, the surface of the positive electrode active material is covered with an appropriate amount of coating material.

[0029] In a twelfth aspect of this disclosure, for example, in a composite positive electrode active material according to any one of the first to eleventh aspects, the positive electrode active material may contain lithium nickel cobalt aluminate. Such a configuration can increase the energy density of the battery.

[0030] The cathode material relating to the 13th aspect of this disclosure is A composite positive electrode active material according to any one of the first to twelfth embodiments, The first solid electrolyte, It is equipped with.

[0031] The composite cathode active material imparts the desired effect to the cathode material.

[0032] In a fourteenth aspect of this disclosure, for example, in the cathode material according to the thirteenth aspect, the first solid electrolyte may include a halide solid electrolyte. Halide solid electrolytes have excellent oxidation resistance.

[0033] In a 15th aspect of this disclosure, for example, in a cathode material according to the 13th or 14th aspect, the first solid electrolyte may include a sulfide solid electrolyte. Sulfide solid electrolytes have excellent ionic conductivity and flexibility.

[0034] The battery relating to the 16th aspect of this disclosure is A positive electrode comprising a positive electrode material according to any one of the 13th to 15th embodiments, The negative electrode and, An electrolyte layer disposed between the positive electrode and the negative electrode, It is equipped with.

[0035] Since the positive electrode material contains the composite positive electrode active material of this disclosure, the desired effect is brought to the battery.

[0036] In a 17th aspect of this disclosure, for example, in a battery according to the 16th aspect, the electrolyte layer may include a second solid electrolyte, and the second solid electrolyte may include a solid electrolyte having the same composition as the solid electrolyte contained in the first solid electrolyte. Such a configuration can further improve the output characteristics of the battery.

[0037] In the eighteenth aspect of this disclosure, for example, in the battery according to the sixteenth aspect, the electrolyte layer may include a second solid electrolyte, and the second solid electrolyte may include a halide solid electrolyte having a different composition from the solid electrolyte contained in the first solid electrolyte. Such a configuration can further improve the output characteristics of the battery.

[0038] In a 19th aspect of this disclosure, for example, in a battery according to the 16th aspect, the electrolyte layer may contain a second solid electrolyte, and the second solid electrolyte may contain a sulfide solid electrolyte. When a sulfide solid electrolyte with excellent reduction stability is included in the electrolyte layer, a low-potential negative electrode material such as graphite or metallic lithium can be used for the negative electrode.

[0039] A method for producing a composite cathode active material according to the 20th aspect of this disclosure is: A method for producing a composite positive electrode active material according to any one of the first to twelfth embodiments, The manufacturing method includes treating a mixture containing the positive electrode active material and the material constituting the coating layer by a dry particle compounding method. The dry particle compounding method includes applying mechanical energy such as impact, compression, and shear to the mixture.

[0040] According to the dry particle compounding method, the composite cathode active material of this disclosure can be efficiently manufactured.

[0041] Embodiments of the present disclosure will be described below with reference to the drawings.

[0042] (Embodiment 1) (Composite positive electrode active material) Figure 1 is a cross-sectional view showing the schematic configuration of the composite positive electrode active material in Embodiment 1. The composite positive electrode active material 100 comprises a positive electrode active material 101 and a coating layer 102. The coating layer 102 covers at least a portion of the surface of the positive electrode active material 101. The coating layer 102 includes a first coating material and a second coating material. The first coating material is a fluoride solid electrolyte. The second coating material is a material that, after reacting with at least one selected from the group consisting of water and hydrogen fluoride, produces at least one selected from the group consisting of lithium oxide and lithium fluoride. In this specification, the materials constituting the coating layer 102 may be referred to as "coating material". When simply referred to as "coating material", it means both the first coating material and the second coating material. The coating layer 102 is formed by the coating material being located on at least a portion of the surface of the positive electrode active material 101. With this configuration, the increase in the output resistance of the battery when heat is applied can be suppressed.

[0043] The coating layer 102 may contain Li, Ti, M, P, O, and F. M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. With such a configuration, the composite positive electrode active material 100 can suppress the increase in the output resistance of the battery when heat is applied.

[0044] In this embodiment, the coating layer 102 includes a first coating material and a second coating material. The first coating material includes Li, Ti, M, and F. The second coating material includes Li, P, and O. With this configuration, the reaction between the coating material and water, and the reaction between the coating material and hydrogen fluoride can be effectively suppressed. This suppresses the increase in the output resistance of the battery when heat is applied.

[0045] Figure 2 illustrates the action and effects of the composite positive electrode active material 100. First, as shown in STEP 1, when heat is applied to the composite positive electrode active material 100, water (H2O) is generated from water, hydrates, and hydroxides present inside or on the surface of the positive electrode active material 101. Next, as shown in equation (a) of STEP 2, hydrogen fluoride (HF) is generated by the reaction of the generated water with the fluoride solid electrolyte (LiMF6) contained in the coating layer 102. Furthermore, as shown in equation (b) of STEP 3, the hydrogen fluoride reacts with the positive electrode active material 101, causing the surface of the positive electrode active material 101 to be eroded or fluorinated. Also, hydrogen fluoride is released from the positive electrode active material 101 (LiM'O x ) reacts with to generate water. When the reactions from STEP 1 to STEP 3 are repeated, a resistive layer is formed at the interface between the positive electrode active material 101 and the coating layer 102. The resistive layer typically contains an acid fluoride containing oxygen and fluorine as anions.

[0046] Here, when the above-described second coating material is included in the coating layer 102, the reaction of STEP2.1 occurs in competition with the reaction of STEP2. That is, as shown in formula (c) of STEP2.1, a compound such as Li3PO4 reacts with water, lithium oxide (Li2O) is generated, and the reaction stops. Also, the reaction of STEP3.1 occurs in competition with the reaction of STEP3. That is, as shown in formula (d) of STEP3.1, a compound such as Li3PO4 reacts with hydrogen fluoride, lithium fluoride (LiF) is generated, and the reaction stops. As a result, the formation of the resistance layer is prevented, so that an increase in the output resistance of the battery when heat is applied is suppressed. In the reactions of STEP2.1 and STEP3.1, in addition to lithium oxide and lithium fluoride, lithium hydrogen phosphate (Li x H y PO4), phosphoric acids (PO x H y ) etc. may be generated.

[0047] The first coating material may be represented by the following compositional formula (1). In compositional formula (1), α, β, and γ satisfy α + 4β + 3γ = 6 and γ > 0. According to such a configuration, the ionic conductivity of the coating material can be improved.

[0048] Li α Ti β M γ F6 ··· Formula (1)

[0049] In compositional formula (1), M can be Al. According to such a configuration, the ionic conductivity of the coating material can be improved.

[0050] In compositional formula (1), γ may satisfy 0.5 ≤ γ < 1. According to such a configuration, the ionic conductivity of the coating material can be further improved. At the same time, an increase in the output resistance of the battery is likely to be suppressed.

[0051] In compositional formula (1), α, β, and γ may satisfy α=2.7, β=0.3, and γ=0.7. With such a configuration, the ionic conductivity of the coating material can be further improved. In addition, the increase in the output resistance of the battery is more easily suppressed.

[0052] The second coating material is a material that, after reacting with at least one selected from the group consisting of water and hydrogen fluoride, produces at least one selected from the group consisting of lithium oxide and lithium fluoride. The second coating material is typically a lithium-containing phosphate. Examples of the second coating material include Li3PO4, LiMe2(PO4)3, LiFePO4, and their elemental substitutions. Me is at least one selected from the group consisting of Ti, Zr, Ge, and Si. One or more of these can be used as the second coating material. The appropriate second coating material can suppress the continuous reaction involving the positive electrode active material, fluoride solid electrolyte, water, and hydrogen fluoride. This prevents the formation of a resistance layer at the interface between the positive electrode active material 101 and the coating layer 102. Examples of the elemental substitutions of the lithium-containing phosphate mentioned above include Li 1+x Ti 2-x Al x (PO4)3, Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ge 2-x Examples include (PO4)3. Specific compositions include Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1.3 Al 0.3 Zr 1.7 (PO4)3, Li 1.3 Al 0.3 Ge 1.7 Examples include (PO4)3.

[0053] The second coating material is typically lithium phosphate (Li3PO4). As illustrated with reference to Figure 2, Li3PO4 reacts with water and hydrogen fluoride to produce lithium oxide and lithium fluoride, thereby halting the continued reaction.

[0054] The term "coating material" is not limited to materials that strictly satisfy the above compositional formula. Materials containing trace amounts of impurities in addition to the constituent elements shown in the compositional formula are also included in the definition of "coating material." For example, the amount of impurities in the coating layer 102 other than the constituent elements shown in the compositional formula is 5% by mass or less of the total amount of the coating layer 102.

[0055] The ratio of the total mass of impurities contained in the first coating material and the second coating material to the total mass of the coating layer 102 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0056] The coating layer 102 may consist substantially of the first coating material and the second coating material, or it may consist solely of the first coating material and the second coating material. The phrase "consistently of..." means excluding other components that alter the essential characteristics of the materials mentioned. The phrase "consisting solely of..." means that no other components, other than unavoidable impurities, have been intentionally added.

[0057] The first and second coating materials do not necessarily have to contain sulfur. In this case, the generation of hydrogen sulfide gas can be prevented.

[0058] In the coating layer 102, the ratio of the volume of the second coating material to the volume of the first coating material is, for example, in the range of 2% or more and less than 100%. When this ratio is appropriately adjusted, the ionic conductivity of the coating material can be ensured while suppressing the continuous reaction involving the positive electrode active material, fluoride solid electrolyte, water, and hydrogen fluoride. This effectively suppresses the formation of a resistive layer between the positive electrode active material 101 and the coating layer 102, and consequently suppresses the increase in the output resistance of the battery when heat is applied. The ratio of the volume of the second coating material to the volume of the first coating material may be 50% or less.

[0059] The ratio of the volume of the second coating material to the volume of the first coating material is an average value calculated from a large number of particles of the composite cathode active material 100. This ratio can be determined by the following method: For example, the elemental ratio of cations constituting the coating layer 102 is calculated from the XPS spectrum of the composite cathode active material 100 obtained by X-ray photoelectron spectroscopy (XPS). From the elemental ratio, the molar ratios of the first and second coating materials are calculated. The ratio of the volume of the second coating material to the volume of the first coating material can be calculated from the molar mass and density of the first and second coating materials, respectively.

[0060] The ratio of the volume of the coating layer 102 to the volume of the positive electrode active material 101 is, for example, in the range of 1% or more and 10% or less. When this ratio is appropriately adjusted, the surface of the positive electrode active material 101 is covered with an appropriate amount of coating material. In this case, the formation of a resistive layer between the positive electrode active material 101 and the coating layer 102 can be effectively suppressed, and consequently, the increase in the output resistance of the battery can be suppressed. The transfer of electrons between the particles of the positive electrode active material 101 is also smooth. This also contributes to suppressing the increase in the output resistance of the battery.

[0061] The ratio of the volume of the coating layer 102 to the volume of the positive electrode active material 101 can be determined by the following method. For example, it can be determined by calculating the volume ratio for 20 arbitrarily selected cross-sectional SEM images of the composite positive electrode active material 100 obtained by a scanning electron microscope (SEM), and then calculating the average value of these ratios. When the volume of the positive electrode active material 101 is defined as V1 and the volume of the composite positive electrode active material 100 is defined as V2, the ratio of the volume of the coating layer 102 (V2-V1) to the volume of the positive electrode active material 101 (V1) can be calculated by (V2-V1) / V1. The volume V1 of the positive electrode active material 101 can be calculated by the following method. The area of ​​the positive electrode active material 101 is calculated from the contour of the positive electrode active material 101 extracted from the cross-sectional SEM image. The radius (equivalent diameter) r1 of a circle having an area equivalent to this area is calculated. Assuming that the positive electrode active material 101 is a perfect sphere with an equivalent diameter r1, the volume V1 of the positive electrode active material 101 can be calculated from the equivalent diameter r1. The volume of the coating layer 102 can be calculated as the value obtained by subtracting the volume V1 of the positive electrode active material 101 from the volume V2 of the composite positive electrode active material 100 (V2-V1). The volume V2 of the composite positive electrode active material 100 can be calculated by the following method: Add the average thickness of the coating layer 102 to the equivalent diameter r1 of the positive electrode active material 101 calculated from the cross-sectional SEM image, and consider this to be the equivalent diameter r2 of the composite positive electrode active material 100. Assuming that the composite positive electrode active material 100 is a perfect sphere with an equivalent diameter r2, the volume V2 of the composite positive electrode active material 100 can be calculated from the equivalent diameter r2. The average thickness of the coating layer 102 can be determined, for example, by measuring the thickness of the coating layer 102 at any 16 points on each particle for 20 arbitrarily selected cross-sectional SEM images of the composite positive electrode active material 100, and then calculating the average value from these measurements.

[0062] The coating layer 102 can be a single layer. With this configuration, the coating layer 102 is easy to form, and the increase in the manufacturing cost of the composite positive electrode active material 100 can be suppressed. In addition, the desired effect can be obtained uniformly throughout the entire coating layer 102.

[0063] The coating layer 102 comprises a mixture of the first coating material and the second coating material. With this configuration, the desired effect can be uniformly obtained throughout the coating layer 102.

[0064] The coating layer 102 has a substantially uniform composition. That is, the first coating material and the second coating material are uniformly mixed in the coating layer 102. With this configuration, the desired effect can be obtained uniformly throughout the entire coating layer 102.

[0065] The coating layer 102 may be composed of multiple layers. The coating layer 102 can be formed by coating the surface of the positive electrode active material 101 with a second coating material, and then coating it with a first coating material. That is, the coating layer 102 may have a first coating layer that covers at least a portion of the surface of the positive electrode active material 101 with the second coating material, and a second coating layer that covers at least a portion of the surface of the positive electrode active material 101 with the first coating layer with the first coating material. If the first coating layer made of the second coating material is located largely on the surface of the positive electrode active material 101, continuous reactions involving the positive electrode active material, fluoride solid electrolyte, water, and hydrogen fluoride can be efficiently suppressed. As a result, the formation of a resistance layer at the interface between the positive electrode active material 101 and the coating layer 102 can be effectively suppressed, and consequently, the increase in the output resistance of the battery when heat is applied can be further suppressed.

[0066] The thickness of the coating layer 102 is, for example, 1 nm or more and 300 nm or less. The thickness of the coating layer 102 can be measured by the method described above.

[0067] The composite positive electrode active material 100 has, for example, a particle shape. The particle shape of the composite positive electrode active material 100 is not particularly limited. The particle shape of the composite positive electrode active material 100 may be needle-shaped, flake-shaped, spherical, or ellipsoidal.

[0068] (Method of manufacturing coating material) The first coating material can be manufactured, for example, by the following method.

[0069] Prepare the raw material powders so that they match the desired composition ratio. For example, Li2.7 Al 0.7 Ti 0.3 To prepare F6, LiF, AlF3, and TiF4 are prepared in a molar ratio of 2.7:0.7:0.3. Furthermore, the values ​​"α", "β", and "γ" in the above compositional formula (1) can be adjusted by adjusting the raw materials, mixing ratios, and synthesis process.

[0070] After mixing the raw material powders, the powders are mixed, pulverized, and reacted using a mechanochemical milling method. Alternatively, after mixing the raw material powders, they may be calcined in a vacuum or an inert atmosphere. For example, calcination is carried out at a temperature range of 100°C to 800°C for at least one hour. This yields a first coating material having the composition described above.

[0071] The composition of the crystalline phase (crystal structure) in the first coating material can be determined by adjusting the reaction method and reaction conditions of the raw material powders.

[0072] The second coating material can be manufactured, for example, by the following method.

[0073] Prepare the raw material powders in a ratio that matches the desired composition. For example, to produce Li3PO4, prepare Li2CO3 and NH4H2PO4 in a molar ratio of 3:2.

[0074] After mixing the raw material powders, the mixture is calcined in air. For example, calcination is performed at a temperature range of 500°C to 900°C for at least one hour. This yields Li3PO4 as the second coating material. Alternatively, commercially available Li3PO4 reagents can also be used.

[0075] The composition of the crystalline phase (crystal structure) in the second coating material can be determined by adjusting the reaction method and reaction conditions of the raw material powders.

[0076] The coating material can be manufactured, for example, by the following method.

[0077] Prepare the first and second coating materials to achieve the desired volume ratio. For example, Li as the first coating material. 2.7 Al 0.7 Ti 0.3 F6 is used, and Li3PO4 is used as the second coating material. When adjusting the ratio of the volume of the second coating material to the volume of the first coating material to 50%, Li 2.7 Al 0.7 Ti 0.3 F6 and Li3PO4 are prepared in a 1:1 volume ratio. By mixing these raw material powders, the desired coating material is obtained. The composition of the coating material can be adjusted by adjusting the volume ratio of the first coating material and the second coating material.

[0078] (Cathode active material) The positive electrode active material 101 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). Examples of positive electrode active material 101 include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Examples of lithium-containing transition metal oxides include Li(Ni,Co,Al)O2, Li(Ni,Co,Mn)O2, and LiCoO2. When a lithium-containing transition metal oxide is used as the positive electrode active material 101, the manufacturing cost of the positive electrode can be reduced, and the average discharge voltage of the battery can be increased.

[0079] To increase the energy density of the battery, the positive electrode active material 101 may be lithium nickel-cobalt aluminate. The positive electrode active material 101 may also be Li(Ni,Co,Al)O2.

[0080] As the positive electrode active material 101, a positive electrode active material having a film containing a lithium metal oxide on its surface may be used. That is, a film made of lithium metal oxide may be provided between the positive electrode active material 101 and the coating layer 102. Examples of lithium metal oxides include LiNbO3 (lithium niobate). By providing a film containing lithium metal oxide on the surface of the positive electrode active material 101, side reactions between the positive electrode active material 101 and the coating layer 102 during charging are suppressed. Therefore, with this configuration, the formation of a resistive layer on the surface of the positive electrode active material 101 can be further suppressed.

[0081] The positive electrode active material 101 has, for example, a particle shape. The particle shape of the positive electrode active material 101 is not particularly limited. The particle shape of the positive electrode active material 101 may be spherical, ellipsoidal, flaky, or fibrous.

[0082] (Method for manufacturing composite positive electrode active material) The composite positive electrode active material 100 can be manufactured, for example, by the following method.

[0083] A mixture is obtained by mixing the powder of the positive electrode active material 101 and the powder of the coating material in an appropriate ratio. The mixture is milled to impart mechanical energy to it. A mixing device such as a ball mill can be used for the milling process. To suppress oxidation of the materials, the milling process may be carried out in a dry and inert atmosphere.

[0084] The composite cathode active material 100 may be manufactured by a dry particle compounding method. The dry particle compounding method involves stirring while applying mechanical energy such as impact, compression, and shear to a mixture containing the cathode active material 101 and a coating material. The dry particle compounding method allows for the efficient manufacture of the composite cathode active material 100.

[0085] The equipment used in the coating process is not particularly limited and can be any equipment capable of imparting mechanical energy to the mixture, such as impact, compression, or shear. Examples of equipment capable of imparting mechanical energy include ball mills, compression-shear type processing equipment (particle compounding equipment) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) and "Nobilta" (manufactured by Hosokawa Micron Corporation). Among these, "Mechanofusion" and "Nobilta" are preferred, with "Nobilta" being even more preferred.

[0086] "Mechanofusion" is a particle compounding device that uses a dry mechanical compounding technology that applies strong mechanical energy to multiple different material particles. In mechanofusion, the raw material powder, which is fed between a rotating container and a press head, is subjected to mechanical energy such as compression, shear, and friction, causing particle compounding to occur.

[0087] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced particle compounding technology, to compound nanoparticles as raw materials. "Nobilta" employs a technology that produces composite particles by applying mechanical energy such as impact, compression, and shear to multiple raw material powders.

[0088] In "Nobilta," a rotor rotates at high speed within a horizontal cylindrical mixing container, positioned to maintain a predetermined gap between itself and the inner wall of the container. This process repeatedly forces the raw material particles through the gap. This applies impact, compression, and shear forces to the mixture, enabling the creation of composite particles of the positive electrode active material 101 and the coating material. Conditions such as the rotor's rotation speed, processing time, and the amount of material to be charged can be adjusted as needed.

[0089] The types and amounts of elements contained in the composite positive electrode active material 100 can be determined by known chemical analysis methods.

[0090] (Embodiment 2) (Positive electrode material) Figure 3 is a cross-sectional view showing the schematic configuration of the cathode material in Embodiment 2.

[0091] The positive electrode material 110 includes the composite positive electrode active material 100 and the first solid electrolyte 103 of Embodiment 1. The composite positive electrode active material 100 provides the positive electrode material 110 with the effects described in Embodiment 1.

[0092] The first solid electrolyte 103 may contain a halide solid electrolyte. Halide solid electrolytes have excellent oxidation resistance. Examples of halide solid electrolytes include Li3(Ca,Y,Gd)X6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li3(Al,Ga,In)X6, and LiI. X is at least one selected from the group consisting of Cl, Br, and I. In this disclosure, when an element in a formula is represented as "(Al,Ga,In)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(Al,Ga,In)" is synonymous with "at least one selected from the group consisting of Al, Ga, and In". The same applies to other elements. The halide solid electrolyte does not have to contain sulfur.

[0093] The first solid electrolyte 103 may contain a sulfide solid electrolyte. Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These can be used. These include LiX, Li2O, and MO q Li p MO q The following may be added. Here, X is at least one selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q In ", element M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MOq In this example, p and q are independent natural numbers.

[0094] The first solid electrolyte 103 may contain a sulfide solid electrolyte. Sulfide solid electrolytes have excellent ionic conductivity and flexibility. For example, the sulfide solid electrolyte may contain lithium sulfide and phosphorus sulfide. The sulfide solid electrolyte may also be Li2S-P2S5.

[0095] The first solid electrolyte 103 has, for example, a particle shape. The particle shape of the first solid electrolyte 103 is not particularly limited. The particle shape of the first solid electrolyte 103 can be spherical, ellipsoidal, flaky, or fibrous.

[0096] If the shape of the first solid electrolyte 103 is particulate (for example, spherical), the median diameter may be 100 μm or less. When the median diameter of the first solid electrolyte 103 is 100 μm or less, the composite positive electrode active material 100 and the first solid electrolyte 103 can form a good dispersion state in the positive electrode material 110. This improves the charge and discharge characteristics of the battery. The median diameter of the first solid electrolyte 103 may also be 10 μm or less.

[0097] The median diameter of the first solid electrolyte 103 may be smaller than the median diameter of the composite positive electrode active material 100. With this configuration, the composite positive electrode active material 100 and the first solid electrolyte 103 can form a good dispersion state in the positive electrode material 110.

[0098] The median diameter of the composite positive electrode active material 100 may be 0.1 μm or more and 100 μm or less. When the median diameter of the composite positive electrode active material 100 is 0.1 μm or more, the composite positive electrode active material 100 and the first solid electrolyte 103 tend to form a good dispersion state in the positive electrode material 110. As a result, the charge and discharge characteristics of the battery are improved. When the median diameter of the composite positive electrode active material 100 is 100 μm or less, the lithium diffusion rate inside the positive electrode active material 101 is sufficiently fast. Therefore, the battery can operate at high power.

[0099] The median diameter of the composite positive electrode active material 100 may be larger than the median diameter of the first solid electrolyte 103. This allows the composite positive electrode active material 100 and the first solid electrolyte 103 to form a good dispersion state.

[0100] In this specification, "median diameter" means the particle size at which the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction analyzer or an image analyzer.

[0101] In the positive electrode material 110, the first solid electrolyte 103 and the composite positive electrode active material 100 may be in contact with each other. In this case, the coating layer 102 and the first solid electrolyte 103 are also in contact with each other. The particles of the first solid electrolyte 103 may fill the spaces between the particles of the composite positive electrode active material 100.

[0102] The positive electrode material 110 may contain a plurality of particles of the first solid electrolyte 103 and a plurality of particles of the composite positive electrode active material 100.

[0103] In the positive electrode material 110, the content of the first solid electrolyte 103 and the content of the composite positive electrode active material 100 may be the same or different.

[0104] (Embodiment 3) Embodiment 3 will now be described. Descriptions that overlap with Embodiments 1 and 2 described above will be omitted as appropriate.

[0105] Figure 4 is a cross-sectional view showing the schematic configuration of the battery in Embodiment 3.

[0106] The battery 200 comprises a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The electrolyte layer 202 is located between the positive electrode 201 and the negative electrode 203.

[0107] The positive electrode 201 includes the positive electrode material 110 described in Embodiment 2. Since the positive electrode material 110 contains the composite positive electrode active material 100, the effects described in Embodiment 1 are brought to the battery 200.

[0108] The volume of the positive electrode active material 101 is defined as v1. The total volume of the coating layer 102 and the first solid electrolyte 103 is defined as (100-v1). Volume v1 represents the volume of the positive electrode active material 101 when the total volume of the positive electrode active material 101, coating layer 102, and first solid electrolyte 103 is defined as 100. When the ratio of volume v1 to the total volume (100-v1) is defined as "v1:100-v1", the condition 30≦v1≦95 may be satisfied. If 30≦v1 is satisfied, the energy density of the battery 200 is more likely to be secured. If v1≦95 is satisfied, the battery 200 may operate at high power.

[0109] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. If the thickness of the positive electrode 201 is 10 μm or more, the energy density of the battery 200 is sufficiently ensured. If the thickness of the positive electrode 201 is 500 μm or less, the battery 200 can operate at high power.

[0110] The electrolyte layer 202 is a layer containing an electrolyte. This electrolyte is, for example, a solid electrolyte. That is, the electrolyte layer 202 may be a solid electrolyte layer. Hereinafter, the solid electrolyte contained in the electrolyte layer 202 may be referred to as the "second solid electrolyte".

[0111] As the second solid electrolyte, at least one selected from the group consisting of halogenated solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes may be used.

[0112] The second solid electrolyte may contain a solid electrolyte having the same composition as the solid electrolyte contained in the first solid electrolyte 103.

[0113] For example, the second solid electrolyte may contain a halogen solid electrolyte having the same composition as the halogen solid electrolyte contained in the first solid electrolyte 103. That is, the electrolyte layer 202 may contain a halogen solid electrolyte having the same composition as the halogen solid electrolyte contained in the first solid electrolyte 103. With such a configuration, the output characteristics of the battery 200 can be further improved.

[0114] The second solid electrolyte may contain a halogen solid electrolyte having a different composition from the halogen solid electrolyte contained in the first solid electrolyte 103. That is, the electrolyte layer 202 may contain a halogen solid electrolyte having a different composition from the halogen solid electrolyte contained in the first solid electrolyte 103. With such a configuration, the output characteristics of the battery 200 can be further improved.

[0115] The second solid electrolyte may contain a sulfide solid electrolyte. The second solid electrolyte may contain a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte contained in the first solid electrolyte 103. That is, the electrolyte layer 202 may contain a sulfide solid electrolyte having the same composition as the sulfide solid electrolyte contained in the first solid electrolyte 103. If a sulfide solid electrolyte with excellent reduction stability is contained in the electrolyte layer 202, a low-potential negative electrode material such as graphite or metallic lithium can be used for the negative electrode 203. This can improve the energy density of the battery 200. Furthermore, if the electrolyte layer 202 contains a sulfide solid electrolyte with the same composition as the sulfide solid electrolyte contained in the first solid electrolyte 103, the output characteristics of the battery 200 can be further improved.

[0116] The second solid electrolyte may contain an oxide solid electrolyte. Examples of oxide solid electrolytes include NASICON-type solid electrolytes represented by LiTi2(PO4)3 and its elemental substitutions, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGe4O 16, LISICON-type solid electrolytes represented by Li4SiO4, LiGeO4 and their elemental substitutions, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those represented by elemental substitutions thereof, Li3PO4 and its N-substituted derivatives, and glass or glass ceramics can be used, which are based on Li-BO compounds such as LiBO2 and Li3BO3 to which materials such as Li2SO4 and Li2CO3 are added.

[0117] The second solid electrolyte may contain a polymer solid electrolyte. As the polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may have an ethylene oxide structure. Polymer compounds having an ethylene oxide structure can contain a large amount of lithium salt. Therefore, the ionic conductivity can be further increased. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used.

[0118] The second solid electrolyte may contain a complex hydride solid electrolyte. Examples of complex hydride solid electrolytes that can be used include LiBH4-LiI and LiBH4-P2S5.

[0119] The electrolyte layer 202 may contain a second solid electrolyte as its main component. That is, the electrolyte layer 202 may contain 50% or more (i.e., 50% by mass or more) of the second solid electrolyte in terms of mass ratio to the total mass of the electrolyte layer 202. With such a configuration, the output characteristics of the battery 200 can be further improved.

[0120] The electrolyte layer 202 may contain 70% or more (i.e., 70% by mass or more) of the second solid electrolyte in terms of mass ratio to the total mass of the electrolyte layer 202. With such a configuration, the output characteristics of the battery 200 can be further improved.

[0121] The electrolyte layer 202 mainly contains a second solid electrolyte, but may also contain unavoidable impurities, or starting materials, by-products, and decomposition products used in the synthesis of the second solid electrolyte.

[0122] The electrolyte layer 202 may contain 100% (i.e., 100% by mass) of the second solid electrolyte in terms of mass relative to the total mass of the electrolyte layer 202, excluding unavoidable impurities. With such a configuration, the output characteristics of the battery 200 can be further improved.

[0123] The electrolyte layer 202 may consist only of the second solid electrolyte.

[0124] The electrolyte layer 202 may contain only one solid electrolyte selected from the group of solid electrolytes described above, or it may contain two or more solid electrolytes selected from the group of solid electrolytes described above. The multiple solid electrolytes may have different compositions from each other. For example, the electrolyte layer 202 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0125] The thickness of the electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the positive electrode 201 and the negative electrode 203 can be reliably separated. When the thickness of the electrolyte layer 202 is 300 μm or less, the battery 200 can operate at high output. By appropriately adjusting the thickness of the electrolyte layer 202, it is possible to achieve both safety and output characteristics.

[0126] The negative electrode 203 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). The negative electrode 203 includes, for example, a negative electrode active material.

[0127] The negative electrode active material can be a metallic material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, or the like. The metallic material may be a pure metal or an alloy. Examples of metallic materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, carbon in the process of graphitization, carbon fibers, spheroidal carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, or tin compounds can be used.

[0128] The negative electrode 203 may contain a solid electrolyte (third solid electrolyte). With such a configuration, the lithium ion conductivity inside the negative electrode 203 is increased, allowing the battery 200 to operate at high power. As the third solid electrolyte, the materials listed as examples of the second solid electrolyte can be used.

[0129] The median diameter of the negative electrode active material particles may be larger than the median diameter of the third solid electrolyte particles contained in the negative electrode 203. This allows for the formation of a good dispersion state between the negative electrode active material and the third solid electrolyte.

[0130] Let v2 be the volume of the negative electrode active material. Let (100-v2) be the volume of the third solid electrolyte. Volume v2 represents the volume of the negative electrode active material when the total volume of the negative electrode active material and the third solid electrolyte is defined as 100. When the ratio of volume v2 to volume (100-v2) is defined as "v2:100-v2", the condition 30≦v2≦95 may be satisfied. If 30≦v2 is satisfied, the energy density of battery 200 is likely to be secured. If v2≦95 is satisfied, battery 200 may operate at high power.

[0131] The thickness of the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 203 is 10 μm or more, the energy density of the battery 200 is sufficiently ensured. When the thickness of the negative electrode 203 is 500 μm or less, the battery 200 can operate at high power.

[0132] At least one selected from the group consisting of a positive electrode 201, an electrolyte layer 202, and a negative electrode 203 may contain a binder for the purpose of improving the adhesion between particles. The binder is used to improve the bonding properties of the materials constituting the electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl polyacrylate, polyethyl polyacrylate, polyhexyl polyacrylate, polymethacrylic acid, polymethyl polymethacrylate, polyethyl polymethacrylate, polyhexyl polymethacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethylcellulose. Furthermore, a copolymer of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene may be used as a binder. Alternatively, two or more materials selected from these may be mixed and used as a binder.

[0133] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive for the purpose of enhancing electronic conductivity. Possible conductive additives include graphites such as natural graphite and artificial graphite; carbon blacks such as acetylene black and Ketjenblack; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce the cost of the battery 200.

[0134] Battery 200 can be configured as batteries of various shapes, such as coin-type, cylindrical, prismatic, sheet-type, button-type, flat-type, and stacked-type.

[0135] The battery 200 can be manufactured by the following method. First, a positive electrode material 110, a material for forming the electrolyte layer 202, and a material for forming the negative electrode 203 are prepared. A laminate is fabricated in which the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 are arranged in this order by a known method. This yields the battery 200. [Examples]

[0136] The present disclosure will be described in more detail below with reference to examples.

[0137] (Samples 1 to 3) [Preparation of coating material A] In a glove box with an argon atmosphere, dew point below -60°C and oxygen level below 5 ppm, the raw material powders LiF, AlF3, and TiF4 were weighed in a molar ratio of LiF:AlF3:TiF4 = 2.7:0.7:0.3. These raw material powders were mixed in an agate mortar to obtain a mixture. Next, the mixture was milled using a planetary ball mill (Fritsch, P-7 type) for 12 hours at 500 rpm. As a result, Li 2.7 Al 0.7 Ti 0.3 A compound represented by the compositional formula of F6 (hereinafter referred to as LTAF) was obtained. The compound was mixed with an appropriate amount of solvent and milled using a planetary ball mill at 20 minutes and 200 rpm. The solvent was then removed by drying. This yielded LTAF powder with an average particle size of 0.5 μm, to be used as the first coating material.

[0138] A mixture was obtained by mixing Li3PO4 (hereinafter referred to as LPO) powder with an appropriate amount of solvent. The mixture was milled using a planetary ball mill at 200 rpm for 20 minutes. After that, the solvent was removed by drying. This yielded LPO powder with an average particle size of 0.5 μm to be used as the second coating material.

[0139] Next, LPO and LTAF were weighed in a volume ratio of 1:2. These were mixed in an agate mortar. This prepared coating material A.

[0140] The average particle size of the coating material was calculated from planar SEM images of the coating material taken with a scanning electron microscope (KEYENCE VE-8800, 3D Real Surface View Microscope, 5000x magnification). Specifically, the average equivalent diameter of 50 arbitrarily selected particles in the planar SEM image of the coating material was used to calculate the average particle size.

[0141] [Cathode active material] As the positive electrode active material, Li(NiCoAl)O2 (hereinafter referred to as NCA) with an average particle size of 5 μm was used.

[0142] [Fabrication of composite cathode active materials] The coating of coating material A onto the positive electrode active material was performed using a particle compounding apparatus (Nobilta, NOB-MINI, manufactured by Hosokawa Micron Corporation). 49.1 g of NCA and 0.9 g of coating material A were placed in the NOB-MINI container. The NCA and coating material A were compounded under conditions of a rotation speed of 6000 rpm, an operating time of 60 minutes, and a power value of 550 W to 740 W. This yielded composite positive electrode active materials for samples 1 to 3. The ratio of the volume of coating material A to the volume of the positive electrode active material was 3 volume%.

[0143] [Thermal treatment of composite cathode active materials] The following heat treatment process was performed using the composite cathode active materials of Samples 1 to 3. The powder of the composite cathode active material was placed in an alumina crucible in a glove box with an argon atmosphere, dew point below -60°C, and oxygen level below 5 ppm. Next, the crucible was placed in an electric furnace and the composite cathode active material was heat-treated for 1 hour. The heat treatment temperatures were 100°C for Sample 1, 200°C for Sample 2, and 300°C for Sample 3. The powder after heat treatment was re-ground in an agate mortar. This yielded the composite cathode active materials (heat-treated) of Samples 1 to 3.

[0144] (Samples 4 to 6) Coating material B was prepared using the same method as sample 1, except that the volume ratio of LPO to LTAF was changed to 1:1.

[0145] 48.8 g of NCA and 1.2 g of coating material B were placed in a NOB-MINI container. The NCA and coating material B were compounded under the conditions of a rotation speed of 6000 rpm, an operating time of 60 minutes, and a power value of 550 W to 740 W. This resulted in the creation of composite cathode active materials for samples 4 to 6. The ratio of the volume of coating material B to the volume of cathode active material was 4 volume%.

[0146] The composite cathode active materials of Samples 4 to 6 were subjected to the same heat treatment process as Samples 1 to 3. The heat treatment temperatures were 100°C for Sample 4, 200°C for Sample 5, and 300°C for Sample 6. The powder after heat treatment was re-ground in an agate mortar. This yielded the composite cathode active materials (heat-treated) of Samples 4 to 6.

[0147] (Samples 7 to 9) Coating material C was prepared using the same method as in Sample 1, except that the volume ratio of LPO to LTAF was changed to 2:98.

[0148] 46.8 g of NCA and 3.2 g of coating material C were placed in a NOB-MINI container. The NCA and coating material C were compounded under conditions of a rotation speed of 6000 rpm, an operating time of 60 minutes, and a power value of 550 W to 740 W. This resulted in the creation of composite cathode active materials for samples 7 to 9. The ratio of the volume of coating material C to the volume of cathode active material was 10 volume%.

[0149] The composite cathode active materials of samples 7 to 9 were subjected to the same heat treatment process as samples 1 to 3. The heat treatment temperatures were 100°C for sample 7, 200°C for sample 8, and 300°C for sample 9. The powder after heat treatment was re-ground in an agate mortar. This yielded the composite cathode active materials (heat-treated) of samples 7 to 9.

[0150] (Samples 10 to 12) As coating material D, we prepared the LTAF powder used in Sample 1.

[0151] 49.4 g of NCA and 0.6 g of coating material D were placed in a NOB-MINI container. The NCA and coating material D were compounded under conditions of a rotation speed of 6000 rpm, an operating time of 60 minutes, and a power value of 550 W to 740 W. This resulted in the creation of 10 to 12 composite cathode active materials. The ratio of the volume of coating material D to the volume of cathode active material was 2 volume%.

[0152] The composite cathode active materials of samples 10 to 12 were subjected to the same heat treatment process as for samples 1 to 3. The heat treatment temperatures were 100°C for sample 10, 200°C for sample 11, and 300°C for sample 12. The powder after heat treatment was re-ground in an agate mortar. This yielded the composite cathode active materials (heat-treated) of samples 10 to 12.

[0153] (Samples 13 to 15) As coating material D, we prepared the LTAF powder used in Sample 1.

[0154] 46.8 g of NCA and 3.2 g of coating material D were placed in a NOB-MINI container. The NCA and coating material D were compounded under conditions of a rotation speed of 6000 rpm, an operating time of 60 minutes, and a power value of 550 W to 740 W. This resulted in the creation of composite cathode active materials for samples 13 to 15. The ratio of the volume of coating material D to the volume of cathode active material was 10 volume%.

[0155] The composite cathode active materials of samples 13 to 15 were subjected to the same heat treatment process as samples 1 to 3. The heat treatment temperatures were 100°C for sample 13, 200°C for sample 14, and 300°C for sample 15. The powder after heat treatment was re-ground in an agate mortar. This yielded the composite cathode active materials (heat-treated) of samples 13 to 15.

[0156] (Sample 16) The composite cathode active material for Sample 16 was prepared using the same method as for Sample 1, except that the composite cathode active material was not heat-treated.

[0157] (Sample 17) The composite cathode active material for Sample 17 was prepared using the same method as for Sample 4, except that the composite cathode active material was not heat-treated.

[0158] (Sample 18) The composite cathode active material for Sample 18 was prepared using the same method as for Sample 7, except that the composite cathode active material was not heat-treated.

[0159] (Sample 19) The composite cathode active material for Sample 19 was prepared using the same method as for Sample 10, except that the composite cathode active material was not heat-treated.

[0160] (Sample 20) The composite cathode active material for Sample 20 was prepared using the same method as for Sample 13, except that the composite cathode active material was not heat-treated.

[0161] [Manufacturing of secondary batteries] The following steps were performed using the composite cathode active material of Sample 1. The composite cathode active material and Li2S-P2S5 were weighed in a glove box under an argon atmosphere with a dew point of -60°C or lower and an oxygen value of 5 ppm or lower. The amounts of the composite cathode active material and Li2S-P2S5 were adjusted so that the volume ratio (cathode active material):(coating material + Li2S-P2S5) = 75:25 was satisfied. Furthermore, a conductive additive (VGCF-H, manufactured by Showa Denko Corporation) was weighed to 1.5% by mass relative to the mass of the cathode active material. These were mixed in an agate mortar. This prepared the cathode material of Sample 1. "VGCF" is a registered trademark of Showa Denko Corporation.

[0162] 60 mg of Li2S-P2S5 was placed inside an insulating outer casing and pressure-molded at 80 MPa to form an electrolyte layer. Next, 15.6 mg of the positive electrode material from Sample 1 (calculated as the mass of the positive electrode active material) was placed inside the insulating outer casing and pressure-molded at 720 MPa to form the positive electrode. Next, metallic Li (200 μm thick) was placed on the surface of the electrolyte layer on the negative electrode side. The laminate of the positive electrode, electrolyte layer, and metallic Li was pressure-molded at 80 MPa to form the negative electrode. Next, stainless steel current collectors were placed above and below the laminate, and current collector leads were attached to the current collectors. Finally, the insulating outer casing was sealed with an insulating ferrule so that the inside of the insulating outer casing was isolated from the outside atmosphere. Through these steps, the battery of Sample 1 was obtained. The inner diameter of the insulating outer casing was 9.5 mm, and the projected area of ​​the electrodes was 0.71 cm². 2 That was the case.

[0163] Twenty batteries were fabricated from Sample 2 using the same method as Sample 1.

[0164] [Evaluation of output resistance] The batteries from sample 1 to 20 were evaluated under the following conditions.

[0165] The battery was placed in a constant temperature bath at 25°C.

[0166] The battery is charged with a constant current of 319 μA, which corresponds to a 0.1C rate (10-hour rate) relative to its theoretical capacity, and the voltage is 4.3 V (Li / Li). + Charging was terminated at the reference voltage. Next, constant voltage charging was performed at 4.3V, and charging was terminated when the current value fell below 31.9μA, which corresponds to a 0.01C rate. After a 20-minute rest, constant current discharge was performed at a current value of 319μA, which corresponds to a 0.1C rate, and the voltage was 3.62V (Li / Li +Discharge was terminated at the reference voltage. Next, constant voltage discharge was performed at 3.62V, and the discharge was terminated when the current value fell below 31.9μA, which corresponds to a 0.01C rate. After a 10-minute pause, the output resistance was calculated from the voltage drop using Ohm's law (R=ΔV / 0.00463) by discharging for 10 seconds at a current value of 4.63mA, which corresponds to a 1.45C rate. Next, constant current discharge was performed at a current value of 319μA, which corresponds to a 0.1C rate, and the voltage was 2.5V (Li / Li + Discharge was terminated at the reference voltage. Finally, constant voltage discharge was performed at 2.5V, and the discharge was terminated when the current value fell below 31.9μA, which corresponds to a 0.01C rate. Based on the above, the output resistance of batteries 1 to 20 was determined. The results are shown in Table 1.

[0167] [Table 1]

[0168] As shown in Table 1, when comparing samples that had undergone a thermal history of 100°C or higher, the output resistance of batteries 1 to 3 was lower than that of batteries 10 to 12. The output resistance of batteries 4 to 6 was also lower than that of batteries 10 to 12. In particular, when comparing samples that had undergone a thermal history of 300°C or higher, the output resistance of batteries 3 and 6 was lower than that of sample 12. Furthermore, when the ratio of the volume of the coating layer to the volume of the positive electrode active material was the same, the output resistance of batteries 7 to 9 was lower than that of batteries 13 to 15.

[0169] As shown in Table 1, the addition of LPO suppressed the increase in the battery's output resistance when heat was applied. According to Table 1, when the ratio of the volume of the second coating material, LPO, to the volume of the first coating material, LTAF, was in the range of 2% or more and less than 100% (more precisely, when the ratio of the volume of LPO to the total volume of LPO and LTAF was 2% or more and 50% or less), the increase in the battery's output resistance when heat was applied was sufficiently suppressed. As can be seen by comparing the results of samples 1 to 3 with the results of samples 4 to 6, the battery's output resistance decreased slightly as the ratio of the volume of LPO increased. From this, it can be said that the ratio of the volume of LPO to the volume of LTAF may be 50% or less. Furthermore, when the ratio of the volume of the coating layer to the volume of the positive electrode active material was in the range of 1% or more and 10% or less, the increase in the battery's output resistance when heat was applied was sufficiently suppressed.

[0170] It is presumed that the same trend would be observed when using fluoride solid electrolytes (LTMF) other than LTAF as the first coating material. This is because the excellent oxidation resistance of LTMF is mainly due to the effect of fluorine. [Industrial applicability]

[0171] The technology disclosed herein is useful for batteries such as all-solid-state lithium secondary batteries. [Explanation of Symbols]

[0172] 100 Composite positive electrode active material 101 Cathode active material 102 Covering layer 103 First solid electrolyte 110 Cathode Material 200 batteries 201 Positive electrode 202 Electrolyte layer 203 Negative electrode

Claims

1. Positive electrode active material and, A coating layer covering at least a portion of the surface of the positive electrode active material, Equipped with, Here, the coating layer includes a first coating material and a second coating material. The first coating material is a fluoride solid electrolyte, The second coating material contains lithium phosphate, Composite positive electrode active material.

2. Positive electrode active material and, A coating layer covering at least a portion of the surface of the positive electrode active material, Equipped with, The coating layer comprises a first coating material and a second coating material, The first coating material comprises Li, Ti, M, and F. The second coating material comprises Li, P, and O. M is at least one selected from the group consisting of Ca, Mg, Al, Y, and Zr. Composite positive electrode active material.

3. The first coating material is represented by the following compositional formula (1): Li α Ti β M γ F 6 ... Formula (1) Here, α, β, and γ satisfy α + 4β + 3γ = 6 and γ > 0. The composite positive electrode active material according to claim 1.

4. M is Al, The composite positive electrode active material according to claim 2 or 3.

5. γ satisfies 0.5 ≤ γ < 1. The composite cathode active material according to claim 3.

6. α, β, and γ satisfy α = 2.7, β = 0.3, and γ = 0.

7. The composite cathode active material according to claim 3.

7. The ratio of the volume of the second coating material to the volume of the first coating material is in the range of 2% or more and less than 100%. The composite positive electrode active material according to claim 1 or 2.

8. The aforementioned ratio is in the range of 2% or more and 50% or less. The composite positive electrode active material according to claim 7.

9. The ratio of the volume of the coating layer to the volume of the positive electrode active material is in the range of 1% or more and 10% or less. The composite positive electrode active material according to claim 1 or 2.

10. The positive electrode active material contains lithium nickel cobalt aluminate. The composite positive electrode active material according to claim 1 or 2.

11. A composite positive electrode active material according to claim 1 or 2, The first solid electrolyte and, A positive electrode material possessing the following characteristics.

12. The first solid electrolyte includes a halogenated solid electrolyte. The positive electrode material according to claim 11.

13. The first solid electrolyte includes a sulfide solid electrolyte. The positive electrode material according to claim 11.

14. A positive electrode comprising the positive electrode material described in claim 11, The negative electrode and, An electrolyte layer disposed between the positive electrode and the negative electrode, A battery equipped with a battery.

15. The electrolyte layer includes a second solid electrolyte, The second solid electrolyte includes a solid electrolyte having the same composition as the solid electrolyte contained in the first solid electrolyte. The battery according to claim 14.

16. The electrolyte layer includes a second solid electrolyte, The second solid electrolyte includes a halogenated solid electrolyte having a composition different from that of the solid electrolyte contained in the first solid electrolyte. The battery according to claim 14.

17. The electrolyte layer includes a second solid electrolyte, The second solid electrolyte comprises a sulfide solid electrolyte. The battery according to claim 14.

18. A method for producing a composite positive electrode active material according to claim 1 or 2, The manufacturing method includes treating a mixture containing the positive electrode active material and the material constituting the coating layer by a dry particle compounding method. The dry particle compounding method includes applying mechanical energy such as impact, compression, and shear to the mixture. A method for producing a composite cathode active material.

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