Active material composite particles and batteries

Abstract

In active material composite particles in which a coating layer is provided on active material particles, the coverage and durability of the coating layer are improved. [Solution] The battery includes active material particles (141) and a coating layer (142) in contact with at least a portion of the surface of the active material particles. The coating layer contains a first component (142a) made of an oxide-based ion conductor containing at least a crystalline phase, and a second component (142b) different from the first component. The particles constituting the first component have higher particle strength than the particles constituting the second component. The second component contains at least an amorphous phase, and has a higher amorphous phase content than the first component.

Description

[Technical Field]

[0001] This disclosure relates to active material composite particles and batteries using the same. [Background technology]

[0002] Patent Document 1 discloses a method for suppressing the reaction between active material particles, which are made of oxide-based ceramic particles, by forming a coating layer containing lithium niobate (LiNbO3) on the surface of the active material particles, which are made of oxide-based ceramic particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6380221 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the LiNbO3 used in the coating layer in the above-mentioned Patent Document 1 has high ion conduction resistance, and the coating layer needs to be made thin to reduce its resistance. In this case, the mechanical strength of the coating layer decreases and it peels off from the active material particles, the coverage rate of the active material particles by the coating layer decreases, and the solid electrolyte and active material particles come into contact more easily.

[0005] In view of the above points, this disclosure aims to improve the coverage rate and durability of the coating layer in active material composite particles in which an active material particle is provided with a coating layer. [Means for solving the problem]

[0006] To achieve the above objective, the first and second embodiments of this disclosure include an active material particle (141) and a coating layer (142) in contact with at least a portion of the surface of the active material particle, wherein the coating layer contains a first component (142a) made of an oxide-based ion conductor containing at least a crystalline phase and a second component (142b) different from the first component.

[0007] The crystalline first component contained in the coating layer functions as an anchor and a filler. Thereby, the adhesion and contact of the coating layer to the active material particles can be improved, and the durability of the coating layer can be improved.

[0008] In the first aspect of the present disclosure, the particles constituting the first component have higher particle strength than the particles constituting the second component Furthermore, the second component contains at least an amorphous phase, the oxide-based ion conductor is a pyrochlore-type oxide, and the particles constituting the first component have a smaller particle size than the active material particles. Thus, since the coating layer contains a second component having a lower particle strength than the first component, the second component is more likely to deform than the first component. Therefore, the contact between the active material particles and the coating layer can be improved, and the coverage rate of the active material particles by the coating layer can be improved.

[0009] In the second aspect of the present disclosure, the second component contains at least an amorphous phase, and the content ratio of the amorphous phase is higher than that of the first component Furthermore, the oxide-based ion conductor is a pyrochlore-type oxide, and the particles constituting the first component have a smaller particle size than the active material particles. Thereby, the second component having a high content ratio of the amorphous phase is more likely to deform than the first component. Therefore, the contact between the active material particles and the coating layer can be improved, and the coverage rate of the active material particles by the coating layer can be improved.

[0010] Note that the reference numerals in parentheses for each of the above components indicate the correspondence with the specific means described in the embodiments described later.

Brief Description of Drawings

[0011] [Figure 1] It is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of the present disclosure. [Figure 2] It is a diagram showing a specific example of a positive electrode active material and a coating layer. [Figure 3] It is a diagram showing a specific example of a positive electrode active material and a coating layer. [Figure 4] It is a diagram showing a specific example of a positive electrode active material and a coating layer. [Figure 5] It is a diagram showing the crystal structure of a pyrochlore-type oxide. [Figure 6]This diagram shows the manufacturing process for pyrochlore-type oxides. [Figure 7] This is an SEM image of the coating layer. [Figure 8] This is a SEM image of the active material composite particles. [Figure 9] This is a SEM image of the active material composite particles. [Figure 10] This is a SEM image of the active material composite particles. [Figure 11] This figure shows the coverage rate, discharge characteristics, and durability characteristics of the active material composite particles of the examples and comparative examples. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In this embodiment, the active material composite particles 140 are applied as the positive electrode active material of the secondary battery 10. The secondary battery 10 in this embodiment is a lithium-ion battery in which lithium ions are conducted as conductive ions.

[0013] As shown in Figure 1, the secondary battery 10 comprises a negative electrode current collector 11, a negative electrode 12, a positive electrode current collector 13, a positive electrode 14, and an electrolyte layer 15.

[0014] An electrolyte layer 15 is sandwiched between the positive electrode 14 and the negative electrode 12. The negative electrode 12 and the electrolyte layer 15 are in contact. The positive electrode 14 and the electrolyte layer 15 are in contact. The negative electrode 12 and the positive electrode 14 are connected via the electrolyte layer 15. In this embodiment, the secondary battery 10 is charged and discharged by lithium ions moving between the negative electrode 12 and the positive electrode 14 via the electrolyte layer 15.

[0015] The negative electrode current collector 11 and the positive electrode current collector 13 can be made of any material suitable for use as a current collector in a lithium-ion battery. In this embodiment, Cu is used as the negative electrode current collector 11 and Al is used as the positive electrode current collector 13.

[0016] The negative electrode material constituting the negative electrode 12 can be any material that can be used as a negative electrode active material for lithium-ion batteries. Examples of negative electrode materials include carbon-based negative electrode materials, oxide-based negative electrode materials, and metal-based negative electrode materials.

[0017] The positive electrode 14 releases lithium ions when the secondary battery 10 is charged and accepts lithium ions when the secondary battery 10 is discharged. The positive electrode 14 contains active material composite particles 140. The positive electrode 14 may also contain a conductive additive and a binder. Furthermore, the positive electrode 14 may also contain an electrolyte and a polymer. The active material composite particles 140 will be described in detail later.

[0018] The electrolyte layer 15 is ionic conductive and can move lithium ions between the negative electrode 12 and the positive electrode 14. In this embodiment, a solid electrolyte is used as the electrolyte material of the electrolyte layer 15. As the solid electrolyte, for example, oxide-based solid electrolytes or sulfide-based solid electrolytes can be used. The electrolyte layer 15 may contain a binder. Furthermore, the electrolyte layer 15 may contain an electrolyte solution or a polymer. As the electrolyte solution, for example, ethylene carbonate can be used. The electrolyte solution may also be an ionic liquid. As the polymer, for example, polyethylene oxide can be used.

[0019] Next, the active material composite particles 140 of this embodiment will be described. Figures 2 to 4 show different embodiments of the coating layer 142 in the active material composite particles 140.

[0020] As shown in Figures 2 to 4, the active material composite particle 140 is a ceramic composite particle containing an active material particle 141 and a coating layer 142 that covers the active material particle 141. The coating layer 142 only needs to be in contact with at least a portion of the surface of the active material particle 141 and only needs to cover at least a portion of the surface of the active material particle 141.

[0021] The active material particles 141 are the positive electrode active material. The active material particles 141 are ceramic particles that undergo a redox reaction and release or accept lithium ions, which are conductive ions, through the redox reaction.

[0022] As the active material particles 141, any material that can be used as a positive electrode active material for a lithium-ion battery can be employed. For example, layered rock salt type active materials, olivine type active materials, and spinel type active materials can be used. As the layered rock salt type active material, for example, LiNi x Co y Mn z O2 (NCM), LiNi x Co y Al z O2 (NCA) and other ternary positive electrode materials can be used. As the olivine type active material, for example, LiFePO4 (LFP), LiMn 1-x Fe x PO4 (LMFP), LiMnPO4 (LMP), LiCoPO4 (LCP), LiNiPO4 (LNP) can be used. As the spinel type active material, for example, LiMn2O4 (LMO), LiNi 0.5 Mn 1.5 O4 (LNMO) can be used. Further, as the active material particles 141, Li 1.3 Nb 0.3 Mn 0.4 O2 containing Nb or Li2MnO 1.5 F 1.5 containing F can be used.

[0023] The coating layer 142 is a composite having a plurality of components including at least a first component 142a and a second component 142b. The first component 142a and the second component 142b are each particulate components. The first component 142a can be referred to as the first phase, and the second component 142b can be referred to as the second phase. The coating layer 142 contains at least one compound composed of an amorphous phase.

[0024] In this embodiment, the first component 142a is a crystalline oxide-based ionic conductor, and the second component 142b is at least one of an amorphous ionic conductor or an amorphous electron conductor. The amorphous ionic conductor used as the second component 142b is a different type of ionic conductor from the crystalline ionic conductor used as the first component 142a.

[0025] The coating layer 142 may contain a third component different from the first component 142a and the second component 142b, and may contain three or more components. If the coating layer 142 contains a third component, the first component 142a may be a crystalline oxide-based ionic conductor, one of the second component 142b and the third component may be an amorphous ionic conductor, and the other may be an amorphous electron conductor.

[0026] The oxide-based ionic conductor constituting the first component 142a may contain at least a crystalline phase, may be entirely crystalline, or may be a mixture of amorphous and crystalline phases. The amorphous ionic conductor constituting the second component 142b may contain at least an amorphous phase, may be entirely amorphous, or may be a mixture of amorphous and crystalline phases. If the constituent material of the second component 142b contains both amorphous and crystalline phases, it is desirable that the volume ratio of the amorphous phase is equal to or greater than the volume ratio of the crystalline phase. The second component 142b has a higher amorphous phase content than the first component 142a.

[0027] The crystalline first component 142a contained in the coating layer 142 exhibits an anchoring effect on the active material particles 141. Furthermore, the first component 142a acts as a filler. This improves the adhesion and contact of the coating layer 142 with respect to the active material particles 141, thereby improving the durability of the coating layer 142.

[0028] The amorphous second component 142b contained in the coating layer 142 is more easily deformed than the crystalline first component 142a. Therefore, the contact between the active material particles 141 and the coating layer 142 can be improved, and the coverage rate of the active material particles 141 by the coating layer 142 can be improved.

[0029] As the crystalline oxide-based ion conductor constituting the first component 142a, for example, a pyrochlore-type oxide can be suitably used. For example, Li 1.25 La 0.58 Nb2O6F(LLNOF) and Li 1.25 La 0.58 Ta2O6F(LLTOF) can be used. The pyrochlore-type oxide of this embodiment has high ionic conductivity. Pyrochlore-type oxides will be described in detail later.

[0030] As the amorphous ionic conductor used as the second component 142b, for example, amorphous LiNbO3 or amorphous LiF can be used. As the amorphous electron conductor used as the second component 142b, for example, amorphous carbon can be used, and amorphous carbon such as carbon black can be used.

[0031] As shown in Figures 2, 3, and 4, the first component 142a and the second component 142b can be provided in various forms in the coating layer 142 of the active material composite particle 140. In form 1 of Figure 2, form 2 of Figure 3, and form 3 of Figure 4, the configuration of the first component 142a and the second component 142b differs inside the coating layer 142 of the active material composite particle 140. Among the forms of the active material composite particle 140 shown in Figures 2, 3, and 4, the random structure shown in Figure 2 is the most preferred form from the viewpoint of increasing the contact ratio between the second component 142b and the active material 141 and the first component 142a.

[0032] The coating layer 142 in Embodiment 1 shown in Figure 2 has a random structure in which the first component 142a and the second component 142b are randomly mixed. The coating layer 142 is exposed as the outer surface of the active material particles 141. In Embodiment 1, the outer surface of the active material particles 141 is in contact with the first component 142a and the second component 142b of the coating layer 142. In Embodiment 1, the entire outer surface of the active material particles 141 is covered by the coating layer 142 as the random structured coating layer 142 comes into contact with the entire outer surface of the active material particles 141. The first component 142a in Embodiment 1 is particulate, and the area around the first component 142a is covered with the second component 142b. The random structured coating layer 142 exists in a dispersed state in which the particles of the first component 142a and the second component 142b are dispersed and compounded.

[0033] The coating layer 142 in Embodiment 2 shown in Figure 3 is composed of core-shell particles, each having a core structure where the outer surface of a particulate first component 142a is coated with a shell-like second component 142b, which overlaps with the active material particles 141. In Embodiment 2, the active material particles 141 are in contact with the second component 142b of the core-shell particles. Also, in Embodiment 2, the entire outer surface of the active material particles 141 is covered with the coating layer 142. In Embodiment 2, the particulate first component 142a is individually coated with the second component 142b, forming core-shell particles. The coating layer 142 with a core-shell structure exists in a layered state where the first component 142a and the second component 142b overlap.

[0034] The coating layer 142 of form 3 shown in Figure 4 is a laminated structure in which a first component 142a and a second component 142b are formed in layers. In form 3, the outer surface of the active material particle 141 is covered by the first component 142a, and the outer surface of the first component 142a is covered by the second component 142b. In Figure 4, the first component 142a and the second component 142b are shown as being stacked separately in layers, but the second component 142b exists to fill the gaps in the first component 142a.

[0035] The first component 142a is the main component of the coating layer 142. The volume ratio of the first component 142a in the coating layer 142 is greater than or equal to the volume ratio of the other components, and the volume ratio of the first component 142a in the coating layer 142 is 50% or more. In other words, the volume ratio of the first component 142a in the coating layer 142 is greater than or equal to the volume ratio of the second component 142b. If the coating layer 142 contains a third component, the volume ratio of the first component 142a in the coating layer 142 is greater than or equal to the combined volume ratio of the second component 142b and the third component. By increasing the volume ratio of the first component 142a, which has high ionic conductivity, in the coating layer 142, the ionic conductivity of the coating layer 142 can be made as high as possible.

[0036] In this embodiment, the particle strength of the active material particles 141 is higher than that of the first component 142a and the second component 142b of the coating layer 142. The crystalline first component 142a is usually stronger than the amorphous second component 142b. Therefore, the particle strengths of the active material particles 141, the first component 142a, and the second component 142b have the relationship: active material particles 141 > first component 142a > second component 142b. The particle strengths of the active material particles 141, the first component 142a, and the second component 142b can be measured by the "Method for measuring the fracture strength and deformation strength of fine particles" specified in JIS Z8844.

[0037] For example, the particle strength of the active material particles 141 is preferably in the range of 200 MPa to 250 MPa. An example of the active material particles 141 having the above particle strength is NCM. The particle strength of the first component 142a of the coating layer 142 is preferably in the range of 130 MPa to 180 MPa. An example of the first component 142a having the above particle strength is LLNOF. The particle strength of the second component 142b of the coating layer 142 is preferably 50 MPa or less. For reference, the particle strength of LLZ, an oxide-based ion conductor, is about 300 MPa.

[0038] Because the particle strength of the active material particles 141 is greater than the particle strength of the first component 142a and the second component 142b of the coating layer 142, when stress is applied to the active material composite particles 140, the coating layer 142 will preferentially break before the active material particles 141. This suppresses the breakage of the active material particles 141 when stress is applied to the active material composite particles 140.

[0039] Furthermore, in the coating layer 142, the second component 142b, which has lower particle strength than the first component 142a, is more easily deformable than the first component 142a, thereby improving the contact between the active material particles 141 and the coating layer 142. This improves the coverage rate of the active material particles 141 by the coating layer 142.

[0040] It is desirable that the particle size of the first component 142a of the coating layer 142 is smaller than the particle size of the active material particles 141. By making the particle size of the first component 142a smaller than that of the active material particles 141, the contact area between the first component 142a and the particle surface of the active material particles 141 can be increased, thereby improving the coverage rate of the positive electrode active material 141 by the coating layer 142.

[0041] Furthermore, it is desirable that the first component 142a of the coating layer 142 has a larger BET specific surface area than the active material particles 141. The BET specific surface area is the specific surface area calculated by the BET method, which measures the amount of gas physically adsorbed on the particle surface at low temperatures. Having a larger BET specific surface area for the first component 142a of the coating layer 142 than for the active material particles 141 can achieve the same effect as when the particle diameter of the first component 142a of the coating layer 142 is smaller than that of the active material particles 141. In other words, having a larger BET specific surface area for the first component 142a of the coating layer 142 than for the active material particles 141 can increase the contact area between the first component 142a and the particle surface of the active material particles 141, thereby improving the coverage rate of the positive electrode active material 141 by the coating layer 142.

[0042] The coating layer 142 is in contact with at least a portion of the surface of the active material particles 141. By contacting the active material particles 141, the coating layer 142 covers at least a portion of the active material particles 141. By covering the surface of the active material particles 141, the coating layer 142 can suppress the active material particles 141 from coming into contact with and reacting with other materials, such as the electrolyte in the electrolyte layer 15.

[0043] The coating layer 142 may cover the entire surface of the active material particles 141, or it may cover only a portion of the surface of the active material particles 141. To suppress the active material particles 141 from coming into contact with the electrolyte layer 15 and reacting with it, it is desirable that the coverage rate of the outer surface of the active material particles 141 by the coating layer 142 be as high as possible. In this embodiment, the coverage rate of the active material particles 141 by the coating layer 142 is set to 70% or more.

[0044] In the positive electrode 14, it is desirable to maximize the volume ratio of the active material particles 141 from the viewpoint of battery capacity. On the other hand, if the volume ratio of the coating layer 142 is reduced, the coverage rate of the active material particles 141 by the coating layer 142 decreases. In this embodiment, the volume ratio of the coating layer 142 to the active material particles 141 is set within the range of 5 to 50%.

[0045] To increase the volume ratio of the active material particles 141, it is desirable that the thickness of the coating layer 142 be as thin as possible. On the other hand, if the thickness of the coating layer 142 is thin, the coverage rate of the active material particles 141 by the coating layer 142 decreases. In this embodiment, the thickness of the coating layer 142 is set to a range of 1 to 100 nm.

[0046] It is desirable that at least one of the first component 142a and the second component 142b of the coating layer 142 is a compound containing the same element as the element contained in the active material particles 141. Examples of elements contained in the first component 142a and the second component 142b of the coating layer 142 that are the same as the elements contained in the active material particles 141 include Li and Nb.

[0047] When LLNOF or LLTOF is used as the first component 142a and LiNbO3 is used as the second component 142b, Li is contained in both the first component 142a and the second component 142b of the coating layer 142. In this case, the lithium ion conductivity can be improved by including Li in the active material particles 141 and the coating layer 142.

[0048] When LLNOF is used as the first component 142a and LiNbO3 is used as the second component 142b, Nb is contained in both the first component 142a and the second component 142b of the coating layer 142. In this case, the presence of Nb in both the active material particles 141 and the coating layer 142 can improve the adhesion and contact of the coating layer 142 to the active material particles 141 through diffusion between the same elements.

[0049] Next, we will describe the pyrochlore-type oxide used as the first component 142a. The pyrochlore-type oxide used in this embodiment has the composition formula "Aa 2-α Ab (1+α) / 3 B2O 7-β X γ It has a pyrochlore structure represented by the above compositional formula. In the above compositional formula, O is an oxygen atom, and Aa, Ab, B, and X represent any element or group. Aa, Ab, and B are each different types of cations, and O and X are each different types of anions. Aa is an alkali metal cation. Pyrochlore-type oxides contain multiple cations in their composition, consisting of the alkali metal cation Aa and multiple cations Ab and B other than the alkali metal cation Aa. In other words, pyrochlore-type oxides contain multiple cations in their composition, including the alkali metal cation Aa.

[0050] As shown in Figure 5, pyrochlore-type oxides have a crystalline structure in which a three-dimensional octahedral network of BO6 (NbO6, TaO6) is formed. In BO6, cation B is at the center, with oxygen atoms at its vertices, and these vertices are shared with adjacent BO6 molecules. Within the three-dimensional network of BO6 molecules, hexagonal tunnel structures are formed in which cation A and anion X are arranged.

[0051] In the above compositional formula, 0.6 < α < 2.0, 0 < β ≤ 1, and 0 < γ ≤ 1. A change in α alters the compositional ratio of Aa and Ab, and a change in β and γ alters the compositional ratio of O and X.

[0052] Cation Aa is an alkali metal cation. Any of Li, Na, K, Rb, or Cs can be used as the alkali metal represented by Aa. Alternatively, Mg or H, which are not alkali metals, may be used as cation Aa. In other words, cation Aa contains at least one selected from Li, Na, K, Rb, Cs, Mg, and H. In this embodiment, Li is used as Aa. The composition ratio (2-α) of Aa is in the range of 0 < (2-α) < 1.4.

[0053] The cation Ab contains at least one lanthanide. At least one of La, Ce, Nd, or Sm can be used as the lanthanide represented by Ab. In this embodiment, La is used as Ab. The composition ratio of Ab (1+α) / 3 is in the range of 0.53 < (1+α) / 3 < 1.

[0054] The basic structure of the cation Ab consists of lanthanides, and some of the lanthanides constituting Ab may be substituted with alkaline earth metals (such as Ca, Mg, and Sr). In this embodiment, the pyrochlore-type oxide has a pyrochlore structure where 0.6 < α < 2.0 and 0 < β ≤ 1. It is thought that the inclusion of lanthanides in this pyrochlore structure creates defects in the crystal structure, thereby improving ionic conductivity. In this embodiment, La is used as Ab.

[0055] In this embodiment, the pyrochlore-type oxide has a composite cation consisting of lithium metal and a lanthanide, where cation A is located in the typical pyrochlore structure's compositional formula "A2B2O7". This is thought to contribute to the improved ionic conductivity of the pyrochlore-type oxide.

[0056] Cation B is a metallic cation distinct from Aa and Ab, and is a transition metal or a metal selected from group 13 to 15 elements. In the crystal, B forms an octahedron surrounded by six oxygen atoms. As the transition metal represented by B, group 4 or group 5 transition metals can be used, and more specifically, at least one of Nb, Ta, Ti, Zr, Hf, or V can be used. As the group 13 element represented by B, Al, Ga, or In can be used; as the group 14 element, Ge or Sn can be used; and as the group 15 element, Sb or Bi can be used. In this embodiment, Nb or Ta is used as B.

[0057] Anion X is a substituteable anion for the oxygen atoms constituting the pyrochlore structure. X has different electronegativity and polarizability from the oxygen atoms. At least one of O, F, Cl, Br, I, S, OH, or P can be used as the anion represented by X. The composition ratio γ of X is in the range of 0 < γ ≤ 1, and at least some of the oxygen atoms constituting the pyrochlore structure are substituted with X. In this embodiment, F is used as X.

[0058] The pyrochlore-type oxide of this embodiment has a defect structure in which lattice defects are included in the crystal, as some of the oxygen atoms constituting the pyrochlore structure are replaced by anions with different electronegativity and polarizability from the oxygen atoms. It is believed that the ionic conductivity of the pyrochlore-type oxide of this embodiment is improved because the pyrochlore structure contains defect structures.

[0059] In the pyrochlore-type oxide of this embodiment, a portion of Aa and Ab is missing as a defect structure. The composition formula of a typical pyrochlore structure is "A2B2O7", and the composition ratio of cation A is 2. In contrast, in the pyrochlore-type oxide of this embodiment, the composition ratios of Aa and Ab are "2-α" and "(1+α) / 3", respectively, and since 0.6 < α < 2.0, the sum of the composition ratios of Aa and Ab is less than 2. In other words, in the crystal structure of the pyrochlore-type oxide of this embodiment, a portion of at least one of Aa and Ab is missing. The composition ratio corresponding to the missing portions of Aa and Ab is (2α-1) / 3.

[0060] In addition to deviations in compositional ratios, defect structures can also be formed by making the sum of the valencies of the cations consisting of Aa, Ab, and B and the anions consisting of O and X in the above compositional formula negative.

[0061] Furthermore, the pyrochlore-type oxide of this embodiment is a complex anionic compound in which multiple anions such as O and X are contained in the pyrochlore structure. Because the anion represented by X is present in the BO6 coordination octahedron structure, the alkali metal Aa can be located in the center of the space between the BO6 coordination octahedron and the BO6 coordination octahedron without being confined to it. Therefore, it is believed that the pyrochlore-type oxide of this embodiment exhibits high ionic conductivity when used with an electric field applied, such as in a battery.

[0062] Furthermore, since α, β, and γ in the above compositional formula affect lattice defects and ionic conductivity, it is desirable to use them within an appropriate range. Larger values ​​of α, β, and γ increase the defect concentration in the crystal lattice, but beyond a certain amount, the concentration of alkali metals represented by Aa decreases, and the ionic conductivity declines. For this reason, it is desirable to control α within the range of 0.6 < α < 2.0, β within the range of 0 < β ≤ 1, and γ within the range of 0 < γ ≤ 1.

[0063] In this embodiment, "Li" is used as the pyrochlore-type oxide. 1.25 La 0.58 Nb2O6F(LLNOF) or Li1.25 La 0.58 The pyrochlore-type oxide represented as "Ta2O6F(LLTOF)" is used. Specifically, Li is used as cation Aa, La as cation Ab, Nb or Ta as cation B, and F as anion X, with α=0.75, β=1, and γ=1.

[0064] The pyrochlore-type oxide of this embodiment is 1 × 10 -3 Ionic conductivity of S / cm or higher has been achieved. The pyrochlore-type oxide of this embodiment exhibits significantly higher ionic conductivity than other oxide-type solid electrolytes such as garnet-type oxides.

[0065] Next, the method for producing the pyrochlore-type oxide of this embodiment will be described. When amorphous LiF is used as the second component 142b of the coating layer 142 in the active material composite particle 140, amorphous LiF can be formed simultaneously when producing the pyrochlore-type oxide. For example, in the pyrochlore-type oxide production process, by adding LiF, which is the raw material for producing the pyrochlore-type oxide, in excess of the required amount, amorphous phase LiF as the second component 142b can be formed on the surface of the pyrochlore-type oxide as the first component 142a.

[0066] Figure 6 shows the method for producing pyrochlore-type oxide according to this embodiment. In the method for producing pyrochlore-type oxide, the first mixing step S10, the first calcination step S11, the second mixing step S12, the molding step S13, and the second calcination step S14 are carried out in order.

[0067] First, a lanthanum source, a lithium source, and either a niobium source or a tantalum source are prepared as raw materials for the pyrochlore-type oxide, and a first mixing step S10 is performed in which these are mixed. As the lanthanum source, lithium source, niobium source, and tantalum source, metal oxides and metal carbon oxides can be used. In this embodiment, La2O3 is used as the lanthanum source, Li2CO3 as the lithium source, Nb2O5 as the niobium source, and Ta2O5 as the tantalum source. In the first mixing step, La2O3, Li2CO3, and either Nb2O5 or Ta2O5 are mixed in a predetermined ratio.

[0068] Next, the first calcination step S11 is performed to calcine the mixture prepared in the first mixing step. The first calcination step S11 consists of two stages. In the first stage, the mixture is calcined in air at 500°C for 6 hours. Calcination removes moisture and other substances from the mixture, thereby increasing its reactivity. Following the calcination, the mixture is calcined in air at 1200°C for 4 hours. This process yields Li, a precursor of the target product. 0.5 La 0.5 Nb2O6 or Li 0.5 La 0.5 One of the following can be obtained: Ta2O6.

[0069] Next, a second mixing step S12 is performed in which a fluorine source is prepared as a raw material and mixed with the precursor. Metal fluorides can be used as the fluorine source. In this embodiment, LiF and LaF3 are used as the fluorine source. LiF is both a fluorine source and a lithium source, and LaF3 is both a fluorine source and a lanthanum source. In the second mixing step, LiF and LaF3 are mixed with the precursor in a predetermined ratio. When amorphous LiF is used as the second component 142b of the coating layer 142, an excess amount of LiF is added, more than the amount required to produce the pyrochlore-type oxide.

[0070] Next, the mixture of the precursor, LiF, and LaF3 is processed into pellets and subjected to a molding process S13 under pressure of 100 MPa. This process forms the mixture of the precursor, LiF, and LaF3 into pellets.

[0071] Next, a second calcination step S14 is performed in which the precursor, LiF, and LaF3 mixture is calcined. In the second calcination step S14, the precursor, LiF, and LaF3 mixture is heated at 1000°C for 6 hours under a nitrogen atmosphere. In the second calcination step S14, in order to suppress compositional shifts due to the volatilization of Li and F elements, calcination may be performed in a sealed state or in a state covered with mother powder.

[0072] By cooling the product from the second calcination process, the composition formula "Li 1.25 La 0.58 Nb2O6F(LLNOF) or "Li 1.25 La 0.58 A pyrochlore-type oxide represented as "Ta2O6F(LLTOF)" is obtained. The generated pyrochlore-type oxide is particulate. If an excess of LiF is added in the second mixing step S12, the outer surface of the pyrochlore-type oxide is coated with LiF, and particles with a core-shell structure having a pyrochlore-type oxide core phase and a LiF shell phase can be obtained.

[0073] By controlling the cooling conditions after the second firing process, the amorphous nature of LiF can be promoted. Specifically, increasing the cooling rate of the product can promote the amorphous nature of LiF, thereby increasing the volume ratio of amorphous material.

[0074] By changing the mixing ratio of La2O3, Li2CO3, Nb2O5 or Ta2O5, LiF, and LaF3 in the above manufacturing process, "Li 2-α La (1+α) / 3 Nb2O 7-β F γ " or "Li 2-α La (1+α) / 3 Ta2O 7-β F γA pyrochlore-type solid electrolyte represented by can be obtained. By changing the mixing ratio of La2O3, Li2CO3, either Nb2O5 or Nb2O5, LiF, and LaF3, the α, β, and γ in the composition formula can be adjusted. Furthermore, when calcination is performed, a portion of the material sublimes. Therefore, α, β, and γ can also be adjusted by changing the calcination conditions, calcination furnace atmosphere, and calcination furnace size in the first and second calcination processes.

[0075] Figure 7 shows SEM images of crystalline LLNOF and amorphous LiF, which are pyrochlore-type oxides. In Figure 7, the left side shows a random structure in which crystalline LLNOF and amorphous LiF are randomly mixed, and the right side shows a core-shell structure in which crystalline LLNOF is covered with amorphous LiF. The manufacturing method of this embodiment yields the composite of crystalline LLNOF and amorphous LiF shown in Figure 7.

[0076] Next, a method for producing the active material composite particles 140 will be described. For example, a mechanochemical method or a rolling flow method can be used to produce the active material composite particles 140.

[0077] First, we will explain the case where amorphous LiNbO3 is used as the second component 142b of the coating layer 142. When amorphous LiNbO3 is used as the second component 142b of the coating layer 142, the following steps are performed in order: a first coating step in which crystalline LLNOF is coated onto particulate active material particles 141 by a mechanochemical method; a second coating step in which a LiNbO3 precursor is coated onto the particles produced in the first coating step by a rolling flow method; and a heat treatment step in which amorphous LiNbO3 is obtained from the precursor.

[0078] In the first coating step, in which crystalline LLNOF particles are coated onto the active material particles 141, the active material particles and pyrochlore-type oxide particles are mixed in a predetermined ratio, and a strong shearing treatment is performed at 10,000 rpm for 5 minutes using a mechanochemical apparatus. The treatment conditions vary depending on the type of mechanochemical apparatus. The first coating step yields composite particles in which the active material particles 141 are coated with crystalline LLNOF particles.

[0079] When coating by a mechanochemical method, it is desirable that there be a significant size difference between the coating particles constituting the coating layer 142 and the coated particles constituting the active material particles 141. Specifically, it is desirable that the coating particles have a particle size of 1 / 10 or less of the coated particles.

[0080] Since the active material particles 141, which are the particles to be coated, are generally in the range of 1 to 10 μm, the coating particles must be at most 1 μm or less. However, if 1 μm coating particles are used, the thickness of the coating layer 142 increases, leading to an increase in resistance. Therefore, in order to form a coating layer 142 of 100 nm or less, it is more desirable for the coating particles to be 100 nm or less.

[0081] Following the first coating step, a second coating step is performed in which a LiNbO3 precursor is coated onto the composite particles obtained in the first coating step using a rolling flow method. In the second coating step, an alkoxide solution is prepared by mixing and stirring ethoxylithium and pentaethoxyniobium in ethanol so that the elemental ratio of lithium to niobium is 1:1. Then, using a rolling flow apparatus, a predetermined proportion of active material particles are spray-coated onto the particles obtained in the first coating step using the alkoxide solution in air at 80°C.

[0082] Next, a heat treatment step is performed to obtain LiNbO3 from the LiNbO3 precursor. In this heat treatment step, active material particles coated with the LiNbO3 precursor are heat-treated at 300°C in air for 2 hours to obtain LiNbO3 containing an amorphous phase.

[0083] Next, we will describe the case where amorphous carbon particles (amorphous carbon) are used as the second component 142b of the coating layer 142. When carbon particles are used as the second component 142b of the coating layer 142, a first coating step is performed in which crystalline LLNOF is coated onto particulate active material particles 141 by a mechanochemical method, and a second coating step is performed in which carbon particles, which are the second component 142b, are sequentially coated onto the particles produced in the first coating step by a mechanochemical method. The first coating step can be performed in the same manner as when amorphous LiNbO3 is used as the second component 142b.

[0084] Following the first coating step, a second coating step is performed in which carbon particles are coated using a mechanochemical method. In the second coating step, the composite particles obtained in the first coating step and the carbon particles are mixed in a predetermined ratio, and then subjected to a strong shearing treatment at 5000 rpm for 3 minutes using a mechanochemical apparatus. The treatment conditions vary depending on the type of mechanochemical apparatus.

[0085] Figures 8, 9, and 10 are SEM images of the active material composite particles 140. Figures 8 and 9 show SEM images of the active material composite particles 140 of this embodiment. Figure 10 shows an SEM image of the active material composite particles 140 of a comparative example. Figure 8 shows a cross-section of the active material composite particles 140. Figures 9 and 10 show the external appearance of the active material composite particles 140 in the upper section and a cross-section of the active material composite particles 140 in the lower section.

[0086] The active material composite particle 140 in Figure 8 uses NCM as the active material particle 141, crystalline LLNOF as the first component 142a of the coating layer 142, and amorphous LiF as the second component 142b. The coating layer 142 has a random structure in which the first component 142a and the second component 142b are randomly mixed. The configuration of the active material composite particle 140 in Figure 8 corresponds to Example 4 described later.

[0087] The active material composite particle 140 shown on the left side of Figure 9 uses NCM as the active material particle 141, crystalline LLNOF as the first component 142a of the coating layer 142, and amorphous LiNbO3 as the second component 142b. The configuration of the active material composite particle 140 shown on the left side of Figure 9 corresponds to Example 1 described later.

[0088] The active material composite particle 140 shown on the right side of Figure 9 uses NCM as the active material particle 141, crystalline LLNOF as the first component 142a of the coating layer 142, amorphous LiF as the second component 142b, and amorphous carbon as the third component. The configuration of the active material composite particle 140 shown on the right side of Figure 9 corresponds to Example 8 described later.

[0089] The active material composite particle 140 shown on the left side of Figure 10 uses NCM as the active material particle 141 and amorphous LiNbO3 as the second component 142b of the coating layer 142. The configuration of the active material composite particle 140 shown on the left side of Figure 10 corresponds to Comparative Example 1 described later.

[0090] The active material composite particle 140 shown on the right side of Figure 10 uses NCM as the active material particle 141 and crystalline LLNOF as the first component 142a of the coating layer 142. The configuration of the active material composite particle 140 shown on the right side of Figure 10 corresponds to Comparative Example 2 described later.

[0091] Next, the coverage rate of the active material composite particles 140 and the discharge characteristics and durability characteristics of the secondary battery 10 using the active material composite particles 140 will be explained using the examples and comparative examples shown in Figure 11.

[0092] Examples 1-10 and Comparative Examples 1-8 differ in the type of active material particles 141 or the type of coating layer 142. The coverage rate in Figure 11 is the percentage of the total surface area of ​​the active material particles 141 that is covered by the coating layer 142. The discharge characteristics in Figure 11 are the discharge time until the lower limit voltage is reached when the secondary battery 10 is discharged at 5C. The durability characteristics in Figure 11 show the battery capacity retention rate of the secondary battery 10 after a cycle charge-discharge test at 60°C and 0.5C. In Figure 11, the coverage rate, discharge characteristics, and durability characteristics are shown as relative values ​​with the value of Comparative Example 1 set to 100%.

[0093] Examples 1-6, 8-10, and Comparative Examples 1-8 use LiNi as the active material particle 141. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is used. Example 7 uses LiMn as the active material particle 141. 0.6 Fe 0.4 PO4(LMFP) is used.

[0094] In Examples 1-10 and Comparative Examples 2-3 and 5-8, a crystalline ion conductor is used as the first component 142a of the coating layer 142. In Comparative Examples 1 and 4, the first component 142a of the coating layer 142 is not provided.

[0095] In Examples 1-5, 7-10, and Comparative Examples 2, 6, and 7, crystalline LLNOF was used as the first component 142a of the coating layer 142. In Example 6 and Comparative Example 3, crystalline LLTOF was used as the first component 142a of the coating layer 142. In Comparative Examples 5 and 8, crystalline LLZ was used as the first component 142a of the coating layer 142.

[0096] In Examples 1-9 and Comparative Examples 1, 6, and 8, an amorphous ionic conductor is used as the second component 142b of the coating layer 142. In Example 10, an amorphous electron conductor is used as the second component 142b of the coating layer 142. In Comparative Examples 4 and 7, a crystalline ionic conductor is used as the second component 142b of the coating layer 142. In Comparative Examples 2, 3, and 5, the second component 142b of the coating layer 142 is not provided.

[0097] In Examples 1-3 and 9, amorphous LiNbO3 is used as the second component 142b of the coating layer 142. In Example 4, amorphous LiF is used as the second component 142b of the coating layer 142. In Example 5, LiF containing both crystalline and amorphous materials is used as the second component 142b of the coating layer 142. In Example 10, amorphous carbon is used as the second component 142b of the coating layer 142.

[0098] In Examples 8 and 9, the coating layer 142 contains a third component. In Examples 8 and 9, amorphous carbon is used as the third component of the coating layer 142.

[0099] In Examples 1, 4-7, and 10, the volume ratio of the first component 142a to the second component 142b of the coating layer 142 is 90:10. In Example 2, the volume ratio of the first component 142a to the second component 142b of the coating layer 142 is 70:30. In Example 3, the volume ratio of the first component 142a to the second component 142b of the coating layer 142 is 50:50. In Examples 8 and 9, the volume ratio of the first component 142a, the second component 142b, and the third component of the coating layer 142 is 89:8:3.

[0100] In Comparative Examples 1 and 4, the volume ratio of the first component 142a to the second component 142b of the coating layer 142 is 0:100. In Comparative Examples 2, 3, and 5, the volume ratio of the first component 142a to the second component 142b of the coating layer 142 is 100:0. In Comparative Examples 6 to 8, the volume ratio of the first component 142a to the second component 142b of the coating layer 142 is 90:10.

[0101] Examples 1-10 and Comparative Examples 2, 3, and 5 having the first component 142a of the coating layer 142. 、7、 In case 8, the particle size of the active material particles 141 exceeds the particle size of the first component 142a of the coating layer 142. In Comparative Example 6, the particle size of the first component 142a of the coating layer 142 is larger than the particle size of the active material particles 141.

[0102] In Examples 1-10 and Comparative Examples 6 and 7, the particle strengths are in the following order: active material particle 141 > first component 142a > second component 142b. In Comparative Examples 1 and 4, the particle strengths are in the following order: active material particle 141 > second component 142b. In Comparative Examples 2 and 3, the particle strengths are in the following order: active material particle 141 > first component 142a. In Comparative Example 5, the particle strengths are in the following order: first component 142a > active material particle 141. In Comparative Example 8, the particle strengths are in the following order: first component 142a > active material particle 141 > second component 142b.

[0103] As shown in Figure 11, Examples 1 to 10 exceeded 100% in coverage, discharge characteristics, and durability characteristics. In contrast, Comparative Examples 2, 3, 4 to 8 fell below 100% in coverage, discharge characteristics, and durability characteristics. In Comparative Examples 4 and 8, although the coverage exceeded 100%, the discharge characteristics and durability characteristics fell below 100%.

[0104] In Examples 1 to 10, it is believed that a high coverage rate was obtained because the coating layer 142 contains a second component 142b with lower particle strength than the first component 142a, and because the coating layer 142 contains a second component 142b with a higher proportion of amorphous phase than the first component 142a.

[0105] Furthermore, in Examples 1 to 10, it is believed that high discharge characteristics were obtained because the coating layer 142 contained a first component 142a, which is an ion conductor, and a second component 142b, which is at least one of an ion conductor and an electron conductor.

[0106] Furthermore, in Examples 1 to 10, it is believed that high durability was achieved because the crystalline first component 142a contained in the coating layer 142 functions as an anchor and filler.

[0107] As described above, the coating layer 142 of the active material composite particles 140 contains a crystalline first component 142a and a second component 142b with lower particle strength than the first component 142a, or an amorphous second component 142b, thereby improving the durability and coverage of the coating layer 142. Peeling of the coating layer 142 from the active material particles 141 is likely to occur during mixing during electrode fabrication or during expansion and contraction of the secondary battery 10 due to charging and discharging. In contrast, by using the active material composite particles 140 of this embodiment, the coating layer 142 can effectively suppress the reaction of the active material particles 141 with other materials.

[0108] The coating layer 142 contains a first component 142a, which is a crystalline ion conductor, and this first component 142a functions as an anchor and filler. This improves the adhesion and contact of the coating layer 142 to the active material particles 141, thereby improving the durability of the coating layer 142. Furthermore, by using a material with high ionic conductivity as the first component 142a, the ionic conductivity of the coating layer 142 can be improved, thereby improving the discharge characteristics.

[0109] Furthermore, because the coating layer 142 contains a second component 142b with lower particle strength than the first component 142a, the second component 142b is more easily deformed than the first component 142a. This improves the contact between the active material particles 141 and the coating layer 142, thereby improving the coverage rate of the active material particles 141 by the coating layer 142.

[0110] Furthermore, because the coating layer 142 contains amorphous second component 142b, the amorphous second component 142b is more easily deformed than the crystalline first component 142a. Therefore, the contact between the active material particles 141 and the coating layer 142 can be improved, and the coverage of the active material particles 141 by the coating layer 142 can be improved.

[0111] In other words, the coating layer 142 contains a crystalline first component 142a and a second component 142b that is different from the first component. The durability and coverage of the coating layer 142 can be improved by having the second component 142b have lower particle strength than the first component 142a, or by having the second component 142b be amorphous.

[0112] Furthermore, in this embodiment, the particle strength of the active material particles 141 is higher than the particle strength of the first component 142a and the second component 142b of the coating layer 142. As a result, when stress is applied to the active material composite particles 140, the coating layer 142 will be preferentially damaged over the active material particles 141, thereby suppressing damage to the active material particles 141.

[0113] Furthermore, the coating layer 142 of this embodiment contains a compound (e.g., LiNbO3, LiF) consisting of an amorphous phase component having ionic conductivity as the second component 142b, which improves the ionic conductivity of the coating layer 142 and thus improves the lithium ion conductivity of the positive electrode 14.

[0114] Furthermore, according to this embodiment, the coating layer 142 contains a compound that contains the same element as the element contained in the active material particles 141. For example, if the coating layer 142 contains a compound that contains Li as the same element as the element contained in the active material particles 141, the lithium ion conductivity of the coating layer 142 can be improved. If the coating layer 142 contains a compound that contains Nb as the same element as the element contained in the active material particles 141, the adhesion and contact of the coating layer 142 to the active material particles 141 can be improved by diffusion between the same elements.

[0115] Furthermore, according to this embodiment, by using a pyrochlore-type oxide as the crystalline ion conductor constituting the first component 142a of the coating layer 142, the ionic conductivity of the coating layer 142 can be improved.

[0116] Furthermore, according to this embodiment, the particle size of the first component 142a of the coating layer 142 is made smaller than the particle size of the active material particles 141. This makes it possible to increase the contact area between the first component 142a and the particle surface of the active material particles 141, thereby improving the coverage rate of the positive electrode active material 141 by the coating layer 142.

[0117] Furthermore, according to this embodiment, the BET specific surface area of ​​the first component 142a of the coating layer 142 is made larger than that of the active material particles 141. This also increases the contact area between the first component 142a and the particle surface of the active material particles 141, thereby improving the coverage rate of the positive electrode active material 141 by the coating layer 142.

[0118] Furthermore, according to this embodiment, the volume ratio of the first component 142a in the coating layer 142 is greater than or equal to the volume ratio of the other components. By increasing the volume ratio of the first component 142a, which has high ionic conductivity, in the coating layer 142, the ionic conductivity of the coating layer 142 can be made as high as possible.

[0119] Furthermore, in this embodiment, the active material composite particles 140 are applied to the secondary battery 10. Active material particles are prone to degradation during charging of the secondary battery 10. Therefore, by using the active material composite particles 140 of this embodiment in the secondary battery 10, the degradation of the active material particles 141 during charging can be effectively suppressed.

[0120] Furthermore, when a sulfide-based solid electrolyte is used as the electrolyte layer 15, the active material particles 141 are prone to degradation. Therefore, in a secondary battery 10 using a sulfide-based solid electrolyte as the electrolyte layer 15, using the active material composite particles 140 of this embodiment can effectively suppress the degradation of the active material particles 141.

[0121] (Other embodiments) This disclosure is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of this disclosure. Furthermore, the means disclosed in each of the embodiments described above may be combined as appropriate to the extent that they are feasible.

[0122] For example, in the above embodiment, an example was described in which the active material composite particles of the present disclosure were applied to the active material of a secondary battery, but the active material composite particles of the present disclosure can also be applied to the active material of a primary battery.

[0123] Furthermore, although the above embodiments described an example in which the active material composite particles of this disclosure are applied to a lithium-ion battery in which the conductive ions are lithium ions, they may also be applied to secondary batteries with different conductive ions. Specifically, the active material composite particles of this disclosure can be applied to potassium-ion batteries in which potassium ions conduct, sodium-ion batteries in which sodium ions conduct, and the like.

[0124] Furthermore, in the above embodiment, an example was described in which the active material composite particles 140 of the present disclosure are applied to the positive electrode 14 and the positive electrode active material is used as the active material particle 141 of the active material composite particles 140. However, the active material composite particles of the present disclosure may also be applied to the negative electrode 12 and the negative electrode active material may be used as the active material particle of the active material composite particles.

[0125] Furthermore, although the above embodiment describes an example in which the active material composite particles of the present disclosure are applied to a secondary battery 10 that is pre-equipped with a negative electrode 12, the active material composite particles of the present disclosure may also be applied to an anode-free battery. In an anode-free battery, the negative electrode 12 is not formed on the negative electrode current collector 11 in the initial state, and lithium metal is deposited on the negative electrode current collector 11 by lithium ions that move from the positive electrode 14 during charging, thereby forming the negative electrode 12. Then, the lithium metal constituting the negative electrode 12 moves to the positive electrode 14 as lithium ions during discharge.

[0126] Furthermore, although the above embodiment describes an example in which the active material composite particles 140 of this disclosure are applied to an all-solid-state battery using a solid electrolyte as the electrolyte layer 15, the active material composite particles 140 of this disclosure can be applied to different types of secondary batteries.

[0127] For example, the active material composite particles 140 of this disclosure may be applied to a liquid-type secondary battery provided with an electrolyte and a separator. As the electrolyte, for example, ethylene carbonate or an ionic liquid can be used. As the separator, for example, a porous material can be used.

[0128] Furthermore, the active material composite particles 140 of this disclosure may be applied to a semi-solid battery. Examples of semi-solid batteries include gel polymer type batteries using a gelled electrolyte, clay type batteries in which the electrolyte is kneaded into a clay-like substance, and liquid-added type batteries in which a small amount of electrolyte is impregnated into the electrode members.

[0129] Furthermore, the active material composite particles 140 of this disclosure may be applied to a bipolar battery. A bipolar battery has a structure in which multiple battery cells are stacked and connected in series, and adjacent battery cells share a current collector. That is, the current collector that contacts the positive electrode of one adjacent battery cell contacts the negative electrode of the other adjacent battery cell.

[0130] The characteristics of the active material composite particles and batteries disclosed herein are as follows: (Item 1) Active material particles (141), The active material particles are further comprising a coating layer (142) that is in contact with at least a portion of the surface of the active material particles, The coating layer contains a first component (142a) which is an oxide-based ion conductor containing at least a crystalline phase, and a second component (142b) which is different from the first component. The particles constituting the first component are active material composite particles having a higher particle strength than the particles constituting the second component. (Item 2) Active material particles (141), The active material particles are further comprising a coating layer (142) that is in contact with at least a portion of the surface of the active material particles, The coating layer contains a first component (141a) which is an oxide-based ion conductor containing at least a crystalline phase, and a second component (142b) which is different from the first component. The second component comprises at least an amorphous phase, and the proportion of the amorphous phase is higher than that of the first component, in an active material composite particle. (Item 3) The active material composite particles described in item 2, wherein the particles constituting the first component have a higher particle strength than the particles constituting the second component. (Item 4) The active material particles are active material composite particles according to any one of items 1 to 3, wherein the particle strength is higher than that of the particles constituting the first component. (Item 5) The active material composite particle according to any one of items 1 to 4, wherein the second component is at least one of an ionic conductor or an electronic conductor. (Item 6) The active material composite particle according to any one of items 1 to 5, wherein the first component and the second component exist in a layered state or a dispersed state within the coating layer. (Item 7) The active material composite particle according to any one of items 1 to 6, wherein the coating layer contains a compound containing the same element as the element contained in the active material particle. (Item 8) The oxide-based ion conductor is a pyrochlore-type oxide, as described in any one of items 1 to 7. (Item 9) The compositional formula of the pyrochlore-type oxide is Aa 2-α Ab (1+α) / 3 B2O 7-β X γ The active material composite particle according to item 8, wherein Aa is an alkali metal, Ab contains at least a lanthanide, B is a cation different from Aa and Ab, X is an anion that can be replaced by an O atom constituting the pyrochlore-type oxide, and in the composition formula, α is in the range of 0.6 < α < 2.0, β is in the range of 0 < β ≤ 1, γ is in the range of 0 < γ ≤ 1, and includes a defect structure. (Item 10) The particles constituting the first component are active material composite particles according to any one of items 1 to 9, wherein the particle size is smaller than that of the active material particles. (Item 11) The particles constituting the first component are active material composite particles according to any one of items 1 to 10, having a BET specific surface area higher than the active material particles. (Item 12) The active material composite particle according to any one of items 1 to 11, wherein the volume ratio of the first component in the coating layer is equal to or greater than the volume ratio of components other than the first component in the coating layer. (Item 13) The active material composite particle described in item 1 or 3, wherein the particle strength of the particles constituting the first component is in the range of 130 MPa to 180 MPa, and the particle strength of the particles constituting the second component is 50 MPa or less. (Item 14) The device comprises a positive electrode (14) having a positive electrode active material and a negative electrode (12) having a negative electrode active material. A battery in which an active material composite particle described in any one of items 1 to 13 is used as at least one of the positive electrode active material and the negative electrode active material. [Explanation of symbols]

[0131] 12 Negative electrode 14 Positive electrode 140 Active material composite particles 141 Active material particles 142 Coat Layers 142a Component 1 142b Second component

Claims

1. Active material particles (141), The active material particles are further comprising a coating layer (142) that is in contact with at least a portion of the surface of the active material particles, The coating layer contains a first component (142a) which is an oxide-based ion conductor containing at least a crystalline phase, and a second component (142b) which is different from the first component. The particles constituting the first component have a higher particle strength than the particles constituting the second component. The second component comprises at least an amorphous phase, The aforementioned oxide-based ionic conductor is a pyrochlore-type oxide. The particles constituting the first component are active material composite particles having a smaller particle size than the active material particles.

2. Active material particles (141), The active material particles are further comprising a coating layer (142) that is in contact with at least a portion of the surface of the active material particles, The coating layer contains a first component (141a) which is an oxide-based ion conductor containing at least a crystalline phase, and a second component (142b) which is different from the first component. The second component contains at least an amorphous phase, and the proportion of the amorphous phase is higher than that of the first component. The aforementioned oxide-based ionic conductor is a pyrochlore-type oxide. The particles constituting the first component are active material composite particles having a smaller particle size than the active material particles.

3. The active material composite particle according to claim 2, wherein the particles constituting the first component have a higher particle strength than the particles constituting the second component.

4. The active material composite particle according to claim 1 or 2, wherein the active material particles have a particle strength higher than the particles constituting the first component.

5. The active material composite particle according to claim 1 or 2, wherein the second component is at least one of an ion conductor or an electron conductor.

6. The active material composite particle according to claim 1 or 2, wherein the first component and the second component exist in a layered state or a dispersed state within the coating layer.

7. The active material composite particle according to claim 1 or 2, wherein the coating layer contains a compound containing the same element as the element contained in the active material particle.

8. The compositional formula of the pyrochlore-type oxide is Aa ２－α Ab （１＋α）／３ B ２ O ７－β X γ The active material composite particle according to claim 1 or 2, wherein Aa is an alkali metal, Ab contains at least a lanthanide, B is a cation different from Aa and Ab, X is an anion that can be replaced with an O atom constituting the pyrochlore-type oxide, and in the composition formula, α is in the range of 0.6 < α < 2.0, β is in the range of 0 < β ≤ 1, γ is in the range of 0 < γ ≤ 1, and includes a defect structure.

9. The active material composite particle according to claim 1 or 2, wherein the particles constituting the first component have a BET specific surface area higher than the active material particles.

10. The active material composite particle according to claim 1 or 2, wherein the volume ratio of the first component in the coating layer is equal to or greater than the volume ratio of components other than the first component in the coating layer.

11. The active material composite particle according to claim 1 or 3, wherein the particle strength of the particles constituting the first component is in the range of 130 MPa to 180 MPa, and the particle strength of the particles constituting the second component is 50 MPa or less.

12. The active material composite particle according to claim 5, wherein the particles constituting the second component are selected from at least one of amorphous LiNbO3, amorphous LiF, and amorphous carbon.

13. The active material composite particle according to claim 1 or 2, wherein the coating layer has a third component that includes at least an amorphous phase.

14. The active material composite particle according to claim 13, wherein the particles constituting the third component have lower particle strength than the first and second components.

15. The active material composite particle according to claim 13, wherein the volume ratio of the first component in the coating layer is equal to or greater than the combined volume ratio of the second component and the third component.

16. The active material composite particle according to claim 13, wherein the third component is amorphous carbon.

17. The device comprises a positive electrode (14) having a positive electrode active material and a negative electrode (12) having a negative electrode active material. A battery in which the active material composite particles according to claim 1 or 2 are used as at least one of the positive electrode active material and the negative electrode active material.

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