Composite particles, electrode for secondary battery, and secondary battery

Abstract

Provided are: active material particles (101); a carbon layer (102) covering at least a portion of surfaces of the active material particles; and at least one type of ceramic particles (103) containing oxygen. At least a portion of the ceramic particles is in contact with one of the carbon layer and the active material particles. By coating positive electrode active material particles with the carbon layer, electrical conductivity of the composite particles can be improved. The ceramic particles are in contact with at least one of the carbon layer and the positive electrode active material particles (101), and therefore, the effect of promoting the insertion and desorption of conductive ions into and from the active material particles can be improved. This makes it possible to reduce resistance of a secondary battery in which the composite particles are used in an electrode.

Description

Composite particle, electrode for secondary battery, and secondary battery Cross-Reference to Related Applications

[0001] The present application is based on Japanese Patent Application No. 2025-67892 filed on April 17, 2025, the contents of which are incorporated herein by reference.

[0002] The present invention relates to a composite particle, an electrode for a secondary battery, and a secondary battery.

[0003] Patent Document 1 proposes a composite particle including a plurality of active material particles, a plurality of oxide-type solid electrolyte particles present between the active material particles, and a conductive material for the purpose of improving battery output.

[0004] Japanese Patent No. 6098612

[0005] However, in Patent Document 1, the conductive material is only mixed into the composite particles, and it is difficult to obtain favorable conductivity. For this reason, the internal resistance of the battery increases, making it difficult to improve battery performance. In particular, when an olivine-type active material with low conductivity is used, the resistance tends to increase. Furthermore, since the composite particles of Patent Document 1 have low ion diffusivity, the resistance tends to increase.

[0006] In view of the above points, the present invention aims to provide a composite particle capable of reducing the resistance of a secondary battery.

[0007] To achieve the above object, one aspect of the present disclosure includes: active material particles, a carbon layer covering at least a part of the surface of the active material particles, and at least one or more types of ceramic particles containing an oxygen element. At least a part of the ceramic particles is in contact with at least one of the carbon layer or the active material particles.

[0008] According to the present disclosure, since the positive electrode active material particles are covered with the carbon layer, the conductivity of the composite particles can be improved. Furthermore, since the ceramic particles are in contact with at least one of the carbon layer or the positive electrode active material particles, the effect of promoting the insertion and desorption of conductive ions into and from the active material particles can be enhanced. Thereby, the resistance of a secondary battery using the composite particles in an electrode can be reduced, and the battery performance can be improved.

[0009] Furthermore, since the ceramic particles are in contact with at least one of the carbon layer and the positive electrode active material particles, when the composite particles are used in an electrode of a secondary battery, the ceramic particles can be arranged at positions where the highest effect can be obtained. Thereby, the effect of promoting the insertion and desorption of conductive ions into and from the active material particles can be maximized with the minimum amount of ceramic particles.

[0010] FIG. 2 is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of the present disclosure. FIG. 3 is a schematic diagram of a granule composed of composite particles. FIG. 4 is a schematic diagram of a composite particle. FIG. 5 is an SEM image of composite particles. FIG. 6 is a chart showing Examples and Comparative Examples of composite particles.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The secondary battery 10 of the present embodiment is a lithium ion battery in which lithium ions conduct as conductive ions.

[0012] As shown in FIG. 1, the secondary battery 10 includes, as constituent elements, a negative electrode current collector 11, a negative electrode layer 12, a positive electrode current collector 13, a positive electrode layer 14, a separator 15, and an electrolytic solution 16. The negative electrode current collector 11, the negative electrode layer 12, the positive electrode current collector 13, the positive electrode layer 14, and the separator 15 constitute a laminate stacked along a predetermined stacking direction. The positive electrode layer 14 corresponds to the electrode for a secondary battery of the present disclosure.

[0013] The separator 15 is sandwiched between a pair of electrode layers 12 and 14 composed of the negative electrode layer 12 and the positive electrode layer 14. The negative electrode layer 12 and the separator 15 are in contact with each other. The positive electrode layer 14 and the separator 15 are in contact with each other. The negative electrode layer 12 and the positive electrode layer 14 are connected via the separator 15. The secondary battery 10 is charged and discharged as lithium ions move between the negative electrode layer 12 and the positive electrode layer 14 via the separator 15.

[0014] For the negative electrode current collector 11 and the positive electrode current collector 13, any material that can be used as a current collector for lithium ion batteries can be used. In the present embodiment, Cu is used for the negative electrode current collector 11, and Al is used for the positive electrode current collector 13.

[0015] The negative electrode layer 12 is provided with a negative electrode active material. Any material usable as a negative electrode active material for lithium-ion batteries can be used as the negative electrode active material. Examples of negative electrode active materials include carbon-based negative electrode materials such as graphite, amorphous carbon, fullerene, and carbon nanotubes, lithium metal materials, metal-based negative electrode materials such as silicon and tin, and Nb ２ O ５ YaTiO ２ Oxide-based negative electrodes such as those mentioned above, or composites thereof, can be used.

[0016] The negative electrode layer 12 may contain a conductive additive, a binder, and a polymer. The conductive additive can be, for example, a carbon material such as acetylene black or carbon black. As the binder, an aqueous binder such as a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose) can be used.

[0017] The positive electrode layer 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 layer 14 is provided with composite particles 100. The composite particles 100 in this embodiment have high electrical conductivity and high ionic conductivity. The composite particles 100 will be described in detail later.

[0018] The positive electrode layer 14 may contain a conductive additive, a binder, and a polymer. The conductive additive can be, for example, a carbon material such as acetylene black or carbon black. As the binder included in the positive electrode layer 14, for example, an organic binder can be used. As an organic solvent binder, for example, polyvinylidene fluoride (PVdF), an acrylic binder, or a urethane binder can be used. As the polymer, for example, polyethylene oxide can be used.

[0019] The separator 15 is positioned between the negative electrode layer 12 and the positive electrode layer 14, separating them. The separator 15 is an insulating ion-permeable film that prevents physical contact between the negative electrode layer 12 and the positive electrode layer 14, thereby suppressing electrical short circuits, while also allowing ions to pass through.

[0020] The separator 15 is formed from a porous material such as a porous membrane, woven fabric, or nonwoven fabric made of resin. Examples of materials that can be used for the separator 15 include polyolefin resins such as polypropylene and polyethylene, and nonwoven fabrics such as cellulose, aramid, and polyester.

[0021] The separator 15 may be surface-coated with a dissimilar material. Examples of dissimilar materials include mixtures of ceramic materials such as alumina, titania, boehmite, magnesium hydroxide, and barium sulfate with binders such as PVDF, PTFE, acrylic copolymers, and PVA, and mixtures of resin materials such as methaluminium and paraaramid with the above-mentioned binders.

[0022] As shown by the dashed line in Figure 1, the electrolyte 16 is provided extending from the negative electrode layer 12 to the positive electrode layer 14. The electrolyte 16 is provided so as to permeate into the interior of the negative electrode layer 12, the positive electrode layer 14, and the separator 15.

[0023] The electrolyte 16 has lithium-ion conductivity and conducts conductive ions between the negative electrode layer 12 and the positive electrode layer 14. Any electrolyte usable in lithium-ion batteries can be used as the electrolyte 16.

[0024] The electrolyte 16 contains an electrolyte salt and a solvent for dissolving the electrolyte salt. The electrolyte salt contains conductive ions, and in this embodiment, a lithium salt containing lithium is used as the electrolyte salt. For example, LiPF ６ These can be used. As the solvent for the electrolyte 16, an organic electrolyte, an ionic liquid, a gel polymer, etc., can be used. As the organic electrolyte, ethylene carbonate, diethyl carbonate, propylene carbonate, etc., can be used. These solvents may be used individually or in combination.

[0025] Here, the composite particles 100 of the positive electrode layer 14 will be explained using Figures 2 and 3. Figure 2 shows an example in which multiple composite particles 100 aggregate to form secondary particles and constitute a granulated body. Figure 3 shows two bonded composite particles 100.

[0026] As shown in Figure 2 and Figure 3, the composite particle 100 includes positive electrode active material particles 101, a carbon layer 102, and ceramic particles 103. The positive electrode active material particles 101, the carbon layer 102, and the ceramic particles 103 are each fixed to constitute the composite particle 100, and are configured not to be easily separated.

[0027] As shown in Figure 3, in adjacent composite particles 100, the mutual carbon layers 102 are connected and integrated. That is, the respective carbon layers 102 covering the adjacent active material particles 101 are formed integrally and continuously. In this case, it can be said that the adjacent composite particles 100 are crosslinked by the carbon layer 102.

[0028] As the positive electrode active material particles 101, any material that can be used for positive electrode active materials for lithium ion batteries can be used. As the positive electrode active material particles 101, for example, an olivine-type active material, a layered rock salt-type active material, or a spinel-type active material can be used. As the olivine-type active material, for example, LiFePO ４ (LFP), LiMn ｘ Fe １－ｘ PO ４ (LMFP), LiMnPO ４ (LMP), LiCoPO ４ (LCP), LiNiPO ４ (LNP) can be used. As the layered rock salt-type active material, for example, LiNi ｘ Co ｙ Mn ｚ O ２ (NCM), LiNi ｘ Co ｙ Al ｚ O ２ A ternary positive electrode material such as (NCA) can be used. As the spinel-type active material, for example, LiMn ２ O ４ (LMO), LiNi ０．５ Mn １．５ O ４ (LNMO) can be used.

[0029] In this embodiment, LMFP, an olivine-type active material having an olivine-type structure, is used as the positive electrode active material particle 101. Olivine-type active materials are active materials with low conductivity, and among them, LMFP containing Mn has particularly low conductivity. Therefore, when LMFP is used as the positive electrode active material particle 101, the effect of improving the conductivity of the composite particle 100 is enhanced.

[0030] The LMFP used as the positive electrode active material particle 101 has the composition formula LiMn ｘ Fe １－ｘ PO ４ It is desirable that x be within the range of 0.65 to 0.8, where x is 0 < x < 1. LMFPs with x greater than 0.65 have low conductivity, and the effect of improving conductivity according to this embodiment is enhanced. Furthermore, if x exceeds 0.8, ion diffusion becomes poor, and even if the effect of improving conductivity according to this embodiment is obtained, ion diffusion becomes the rate-limiting process, making it difficult to improve battery performance.

[0031] Since LMFP used as positive electrode active material particles 101 has lower ion diffusion properties than other positive electrode materials, it is desirable to reduce the particle size to compensate for the low ion diffusion properties. On the other hand, if the particle size of the LMFP is too small, aggregation and moisture adsorption are more likely to occur during electrode fabrication, leading to a decrease in battery performance. For this reason, the particle size of the LMFP used as positive electrode active material particles 101 is preferably in the range of 0.5 to 15 μm, more preferably in the range of 1 to 10 μm, and even more preferably in the range of 1 to 3 μm.

[0032] The carbon layer 102 is a carbon material that covers at least a portion of the surface of the positive electrode active material particles 101. The carbon layer 102 is a conductive material and can improve the conductivity of the composite particles 100.

[0033] The carbon layer 102 can be obtained by carbonizing the positive electrode active material particles 101 while a carbon precursor is coated on them. The carbon precursor is the carbon source for the carbon layer 102, and can be sugars such as glucose, sucrose, and lactose, or organic compounds such as glycerin, ascorbic acid, lauric acid, stearic acid, and citric acid.

[0034] The degree of crystallinity (graphitization) of carbon materials can be evaluated by the G / D ratio, which is the ratio of peak intensities originating from the D band and the G band in the Raman spectrum measured by Raman spectroscopy. The D band of the Raman spectrum is 1350–1360 cm⁻¹. －１ These are peaks observed in the vicinity, attributed to carbon atoms with defects or dangling bonds such as amorphous carbon. The G-band of the Raman spectrum is 1580 cm⁻¹. －１ This is a peak observed in the vicinity, and it is attributed to graphite.

[0035] Raman spectra can be obtained, for example, using a Raman spectrometer HR800 manufactured by Horiba, Ltd., equipped with an argon laser (λ = 532 nm), at a range of 200 to 1800 cm⁻¹. －１ It can be measured within the range.

[0036] Generally, a higher G / D ratio improves the crystallinity of carbon and thus improves conductivity, but it also decreases mechanical strength. For this reason, it is desirable to keep the G / D ratio of the carbon layer 102 within a predetermined range. The G / D ratio of the carbon layer 102 can be changed, for example, by adjusting the firing temperature when carbonizing the carbon precursor. In this embodiment, the G / D ratio of the carbon layer 102 is set within the range of 0.8 to 15 to achieve both conductivity and mechanical strength.

[0037] To improve the conductivity of the composite particles 100, it is desirable to maximize the coverage rate of the positive electrode active material particles 101 by the carbon layer 102. The coverage rate of the positive electrode active material particles 101 by the carbon layer 102 is preferably 50% or more, and more preferably 70% or more. The coverage rate of the positive electrode active material particles 101 by the carbon layer 102 is the ratio of the surface area of ​​the positive electrode active material particles 101 to the area covered by the carbon layer 102.

[0038] In the composite particle 100, it is desirable that the weight ratio of the carbon layer 102 to the positive electrode active material particles 101 be within a predetermined range. If the weight ratio of the carbon layer 102 to the positive electrode active material particles 101 is too low, the coverage rate of the positive electrode active material particles 101 by the carbon layer 102 will be low, and sufficient conductivity may not be obtained. On the other hand, if the weight ratio of the carbon layer 102 to the positive electrode active material particles 101 is too high, the specific surface area of ​​the carbon layer 102 will increase, which may promote side reactions such as the decomposition of the electrolyte 16 and cause a decrease in battery capacity. Furthermore, if the weight ratio of the carbon layer 102 to the positive electrode active material particles 101 is too high, the amount of positive electrode active material particles 101 in the positive electrode layer 14 will decrease, which may cause a decrease in energy density.

[0039] Therefore, in the composite particle 100, the weight ratio of the carbon layer 102 to the positive electrode active material particles 101 is preferably in the range of 0.5 to 5%, more preferably in the range of 1 to 2.5%, and even more preferably in the range of 1.3 to 2%.

[0040] The ceramic particles 103 are oxides containing the element oxygen and are oxide-based ion conductors having ionic conductivity. The ceramic particles 103 may be one type of oxide or multiple types of oxides.

[0041] The ceramic particles 103 are dielectrics with dielectric properties, and their high dielectric properties attract lithium ions, thereby promoting the insertion and removal of lithium ions from the positive electrode active material particles 101.

[0042] As shown in Figure 3, in the composite particle 100, at least a portion of the ceramic particle 103 is in contact with at least one of the carbon layer 102 or the positive electrode active material particle 101. The ceramic particle 103 may be in contact only with the carbon layer 102, or only with the positive electrode active material 101, or in contact with both the carbon layer 102 and the positive electrode active material 101. Furthermore, a portion of the ceramic particle 103 may be covered with the carbon layer 102, or the entire ceramic particle 103 may be covered with the carbon layer 102.

[0043] By having at least a portion of the ceramic particles 103 in contact with at least one of the carbon layer 102 or the positive electrode active material particles 101, the ceramic particles 103 can be positioned as close as possible to the positive electrode active material particles 101. By having the ceramic particles 103 at the three-phase interface between the positive electrode active material particles 101, the carbon layer 102, and the electrolyte 16, the effect of promoting the insertion and removal of lithium ions to and from the positive electrode active material particles 101 can be enhanced. To enhance the effect of promoting the insertion and removal of lithium ions to and from the positive electrode active material particles 101, it is more desirable for the ceramic particles 103 to be in contact with the positive electrode active material particles 101.

[0044] As the dielectric oxide-based ion conductor 14b, for example, pyrochlore-type oxides, NASICON-type oxides, garnet-type solid electrolytes, etc. can be used. As a pyrochlore-type oxide, for example Li ２－ｘ La （１＋ｘ）／３ Nb ２ O ６ F (LLNOF), Li ２－ｘ La （１＋ｘ）／３ Ta ２ O ６ F (LLTOF) can be used. These pyrochlore-type oxides have a defect structure, are acid fluorides, and are Lewis acidic. As for NASICON-type oxides, for example Li １＋ｘ Al ｘ Ti ２－ｘ (PO ４ ) ３ (LATP) can be used. As a garnet-type solid electrolyte, for example, LLZ(Li ７ La ３ Zr ２ O １２ ) can be used.

[0045] The higher the dielectric constant of the ceramic particles 103, the greater the effect of promoting the insertion and removal of lithium ions. For this reason, the relative permittivity of the ceramic particles 103 is preferably 10 or higher, more preferably 90 or higher, and even more preferably 200 or higher. LLZ has a relative permittivity of 10 or higher, LATP has a relative permittivity of 90 or higher, and LLNOF has a relative permittivity of 200 or higher.

[0046] Pyrochlore-type oxides have high ionic conductivity. Therefore, when pyrochlore-type oxides are used as ceramic particles 103, the ionic conductivity of the secondary battery 10 can be improved. Pyrochlore-type oxides will be explained later.

[0047] In the composite particle 100, it is desirable that the weight ratio of ceramic particles 103 to positive electrode active material particles 101 be within the range of 0.2 to 10%. If the weight ratio of ceramic particles 103 to positive electrode active material particles 101 is less than 0.2%, a sufficient effect in promoting the insertion and removal of lithium ions from the positive electrode active material particles 101 cannot be obtained. On the other hand, if the weight ratio of ceramic particles 103 to positive electrode active material particles 101 exceeds 10%, it will cause a decrease in battery performance due to a decrease in conductivity. Furthermore, if the weight ratio of ceramic particles 103 to positive electrode active material particles 101 exceeds 10%, the amount of positive electrode active material particles 101 in the positive electrode layer 14 will decrease, which may cause a decrease in energy density.

[0048] If the particle size of the ceramic particles 103 is too large compared to the positive electrode active material particles 101, there is a risk that the ceramic particles 103 will not be evenly dispersed among the positive electrode active material particles 101 contained in the positive electrode layer 14. If the ceramic particles 103 are not evenly dispersed, there will be active material particles 101 in which the ceramic particles 103 are located close together, and active material particles 101 in which the ceramic particles 103 are not located close together.

[0049] Therefore, it is desirable that the particle size of the ceramic particles 103 be smaller than that of the positive electrode active material particles 101, and it is even more desirable that the particle size of the ceramic particles 103 be 50% or less of that of the positive electrode active material particles 101. This makes it easier to position the ceramic particles 103 in the vicinity of the positive electrode active material particles 101, thereby enhancing the insertion and deinsertion effect of lithium ions on the positive electrode active material particles 101.

[0050] Furthermore, if the particle size of the ceramic particles 103 is too small compared to the positive electrode active material particles 101, the ceramic particles 103 tend to aggregate during the manufacturing process of the composite particles 100, which raises manufacturing concerns. For this reason, it is desirable that the particle size of the ceramic particles 103 be 1% or more of the particle size of the positive electrode active material particles 101.

[0051] The particle diameter of the positive electrode active material particles 101 and the ceramic particles 103 is the particle median diameter D50. The particle median diameter D50 represents the volume-based particle diameter when the volume is integrated from the smallest particle in the particle diameter distribution and reaches 50% of the total particle volume. In other words, the particle median diameter D50 represents the particle diameter corresponding to the median of the particle diameter distribution.

[0052] Here, we will describe the pyrochlore-type oxide used as the ceramic particle 103. The pyrochlore-type oxide in this embodiment has the composition formula "Aa ２－α Ab （１＋α）／３ B ２ O 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 an 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.

[0053] 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.

[0054] Cation Aa is an alkali metal cation. As the alkali metal represented by Aa, any of Li, Na, K, Rb, or Cs can be used. Alternatively, Mg or H, other than 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.

[0055] The cation Ab contains at least one lanthanide. At least one of La, Ce, Nd, and 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.

[0056] The basic structure of the cation Ab consists of lanthanides, and some of the lanthanides constituting Ab may be substituted with alkaline earth metals (Ca, Mg, Sr, etc.). In this embodiment, the pyrochlore-type oxide is thought to have improved ionic conductivity because defects are created in the crystal structure by the inclusion of lanthanides in the pyrochlore structure where 0.6 < α < 2.0 and 0 < β ≤ 1 in the above composition formula. In this embodiment, La is used as Ab.

[0057] Cation B is a metallic cation distinct from Aa and Ab, and is a transition metal or a metal selected from Group 13 to Group 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 Group 13 elements represented by B, Al, Ga, and In can be used; as Group 14 elements, Ge and Sn can be used; and as Group 15 elements, Sb and Bi can be used.

[0058] Anion X is a substituteable anion for the oxygen (O) atoms that make up the pyrochlore structure. X has different electronegativity and polarizability from the oxygen atom. 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 that make up the pyrochlore structure are substituted with X.

[0059] 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.

[0060] Pyrochlore-type oxides are preferably halogen-containing oxides in which a halogen element is used as anion X. Pyrochlore-type oxides containing halogen elements are more likely to exhibit electron conductivity because defects are easily formed in the crystal structure, facilitating the insertion and removal of Li. Among halogen elements, it is particularly desirable to use F as anion X. In other words, pyrochlore-type oxides are preferably acid fluorides in which some of the O is substituted with F.

[0061] In the pyrochlore-type oxide of this embodiment, a portion of Aa and Ab is missing as a defect structure. The compositional formula of a typical pyrochlore structure is "A ２ B ２ O ７ In this case, 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, at least a portion of either Aa or Ab is missing. The composition ratio corresponding to the missing portions of Aa and Ab is (2α-1) / 3.

[0062] In addition to deviations in composition 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 composition formula negative.

[0063] 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 metal 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.

[0064] As a pyrochlore-type oxide, "Li １．２５ La ０．５８ Nb ２ O ６ An example is "F (LLNOF)". LLNOF uses Li as cation Aa, La as cation Ab, Nb as cation B, and F as anion X, with α = 0.75, β = 1, and γ = 1.

[0065] The pyrochlore-type oxide of this embodiment is 1 × 10 －３ Ionic conductivity of S / cm or higher has been obtained. The pyrochlore-type oxide of this embodiment exhibits significantly higher ionic conductivity than other oxide-based solid electrolytes such as garnet-type oxides.

[0066] Next, a method for manufacturing the composite particles 100 of this embodiment will be described. As a method for manufacturing the composite particles 100, one can use a method in which positive electrode active material particles 101, a carbon source for generating a carbon layer 102, and ceramic particles 103 are mixed, and then the carbon source is carbonized to generate the carbon layer 102, or a method in which active material particles 101 coated with the carbon layer 102 and ceramic particles 103 are mixed.

[0067] As a method for producing the composite particles 100 of this embodiment, for example, mechanical milling, spray drying, CVD, etc., can be used.

[0068] In the mechanical milling method, composite particles 100 can be produced by mixing ceramic particles 103 with composite particles consisting of positive electrode active material particles 101 and a carbon source. Specifically, ceramic particles 103 of a predetermined size are mixed with the composite particles of positive electrode active material particles 101 and a carbon source, and coating is performed at 10,000 rpm for 1 to 5 minutes using the particle design device "CompoS" manufactured by Nippon Coke Industries Co., Ltd.

[0069] When using the spray drying method, composite particles 100 can be produced by performing a slurry preparation step, an aggregate preparation step, and a carbonization step. In the slurry preparation step, a first pattern can be adopted in which ceramic particles 103 are mixed before coating the positive electrode active material particles 101 with the carbon layer 102, and a second pattern can be adopted in which ceramic particles 103 are mixed after coating the positive electrode active material particles 101 with the carbon layer 102.

[0070] In the first pattern of the spray drying method, a slurry is prepared by mixing positive electrode active material particles 101, water, a carbon source, and ceramic particles 103. After that, aggregates are obtained by spray drying and then fired at 600°C for 2 to 12 hours in an inert atmosphere. This makes it possible to produce the composite particles 100 of this embodiment.

[0071] In the second spray drying method, a slurry is prepared by mixing positive electrode active material particles 101 coated with a carbon layer 102 and ceramic particles 103. After obtaining aggregates by spray drying, the slurry is fired at 400-550°C for 1 hour in an inert atmosphere. This allows for the production of the composite particles 100 of this embodiment.

[0072] In the second pattern, if the firing temperature is too low, the bonding force between the positive electrode active material particles 101, the carbon layer 102, and the ceramic particles 103 in the composite particle 100 weakens, increasing the likelihood of the ceramic particles 103 separating from the composite particle 100 during the electrode fabrication process. For this reason, a firing temperature of 400°C or higher is desirable. On the other hand, if the firing temperature is too high, there is a high possibility that the positive electrode active material particles 101 and the ceramic particles 103 will react during firing. For this reason, a firing temperature of 550°C or lower is desirable.

[0073] By using the composite particles 100 produced by the above manufacturing method, and manufacturing an electrode together with a conductive additive and a binder, a positive electrode layer 14 containing the composite particles 100 of this embodiment can be obtained.

[0074] The upper left image of Figure 4 is an SEM image of the composite particles 100 of this embodiment. The upper right image of Figure 4 is an SEM image showing a cross-section of an electrode manufactured using the composite particles 100 of this embodiment. The lower part of Figure 4 is an SEM image of composite particles 100 manufactured without mixing ceramic particles 103, and is shown as a comparative example. The composite particles 100 shown in Figure 4 are manufactured by a spray drying method and are granulated bodies formed by the aggregation of multiple composite particles 100. Note that the carbon layer 102 is not shown in the SEM image of Figure 4.

[0075] As shown in the upper SEM image of Figure 4, it has been confirmed that the composite particle 100 of this embodiment contains ceramic particles 103. The ceramic particles 103 may be present on the surface of the composite particle 100 or may be present inside the composite particle 100.

[0076] Next, examples and comparative examples of the composite particles 100 of this embodiment will be described with reference to Figure 5. Figure 5 shows the results of measuring the battery resistance when secondary batteries 10 were fabricated using composite particles 100 with different types of positive electrode active material particles 101, presence or absence of carbon layer 102, and types of ceramic particles 103 in Examples 1 to 9 and Comparative Examples 1 to 7.

[0077] The secondary batteries 10 of Examples 1-9 and Comparative Examples 1-7 shown in Figure 5 were manufactured as coin cells having the following common configuration: Lithium metal was used as the negative electrode layer 12. The positive electrode layer 14 used a composite particle 100, a conductive additive consisting of acetylene black, and a binder consisting of PVdF. LiPF was used as the electrolyte 16 in a solvent of ethylene carbonate and diethyl carbonate mixed in a 1:1 ratio. ６ An electrolyte solution was used in which LiPF was dissolved in electrolyte solution 16. ６ The concentration was set to 1 M.

[0078] The positive electrode layer 14 can be manufactured by the following procedure. Composite particles 100, a conductive additive, and a binder are mixed, and NMP (N-methylpyrrolidone) is added to prepare a paste. This paste is applied to the positive electrode current collector 13 made of Al foil and dried. Then, it is pressed to a predetermined thickness and cut to a predetermined electrode size to produce the positive electrode layer 14.

[0079] In Comparative Examples 2 and 3, the composite particle 100 contains positive electrode active material particles 101 and ceramic particles 103, but does not contain a carbon layer 102. In Comparative Examples 1, 4, 6, and 7, the composite particle 100 contains positive electrode active material particles 101 and a carbon layer 102, but does not contain ceramic particles 103.

[0080] Comparative Examples 6 and 7 use a composite particle 100 containing only positive electrode active material particles 101 and a carbon layer 102, and a positive electrode layer 14 made by mixing ceramic particles. The ceramic particles in Comparative Examples 6 and 7 do not constitute the composite particle 100 and are not included in the composite particle 100.

[0081] As the positive electrode active material particles 101, LMFP with a particle size of 2 μm was used in Examples 1 to 4, 6 to 9, and Comparative Examples 1, 2, 5, and 6, while LFP with a particle size of 10 μm was used in Example 5, Comparative Examples 3, 4, and 7.

[0082] The weight ratio of the carbon layer 102 to the positive electrode active material particles 101 was 1.5% in Examples 1-4, 6-9, and Comparative Examples 1 and 5-7, and 1.0% in Example 5 and Comparative Example 4. In these examples and comparative examples, the weight ratio of the carbon layer 102 to the positive electrode active material particles 101 falls within the range of 0.5-5%. In Comparative Examples 2 and 3, the composite particles 100 were not provided with a carbon layer 102.

[0083] As ceramic particles 103, LLNOF was used in Examples 1-6, 8, and Comparative Examples 2, 3, 6, and 7; LATP was used in Example 7; LLZ was used in Example 9; and Al was used in Comparative Example 5. ２ O ３ In Comparative Examples 1 and 4, composite particles 100 that did not contain ceramic particles 103 were used.

[0084] The particle size of the ceramic particles 103 used in Examples 1-5, 7-9, and Comparative Examples 2, 3, and 5-7 was 0.1 μm, while the particle size of the ceramic particles 103 used in Example 6 was 1 μm. In Example 6, the particle size of the ceramic particles 103 was 50% of the particle size of the positive electrode active material particles 101. In Examples 1-4, 7-9, and Comparative Examples 2, 5, and 6, the particle size of the ceramic particles 103 was 5% of the particle size of the positive electrode active material particles 101. In Example 5, and Comparative Examples 3 and 7, the particle size of the ceramic particles 103 was 1% of the particle size of the positive electrode active material particles 101.

[0085] The weight ratio of ceramic particles 103 to positive electrode active material particles 101 was 2% in Examples 1, 5-7, 9, and Comparative Examples 2, 3, 5-7, 1% in Example 2, 5% in Example 3, 10% in Example 4, and 0.5% in Example 8. In these examples and comparative examples, the weight ratio of ceramic particles 103 to positive electrode active material particles 101 falls within the range of 0.2-10%.

[0086] The relative permittivity of the ceramic particles 103 in Examples 1-9 and Comparative Examples 2, 3, and 5-7 is the measured dielectric constant ε' of the ceramic particles 103 compared to the dielectric constant ε of vacuum. ０ It was calculated by dividing by ε. Permittivity of vacuum ε ０ is 8.85 x 10 －１２ The dielectric constant was set to (F / m). The dielectric constant ε' of the ceramic particle 103 was measured as follows.

[0087] The ceramic particle 103 to be measured was compressed and molded into pellets. The ceramic particle 103 pellets were then sintered at a high temperature. The sintering conditions differed for each type of ceramic particle 103. For example, LLNOF was wrapped in Pt foil to prevent fluorine volatilization, sealed in an alumina crucible, and heated at 1000°C for 6 hours. The sintered ceramic particle 103 pellets were removed, and electrodes were formed by sputtering Ag onto both sides of the pellets to a thickness of 300 nm to prepare a sample for dielectric constant measurement.

[0088] The measurement sample was placed in a 25°C constant temperature bath and connected to a high-frequency impedance measuring device, and the dielectric constant was measured in voltage mode (PEIS). Impedance measurements were performed with a voltage amplitude of 10 mV and a frequency range of 100 MHz to 20 Hz.

[0089] The dielectric constant ε' of the measurement sample was calculated using the impedance measurement value according to the following formula (1).

[0090]

[0091] However, z' = real part of impedance, z'' = imaginary part of impedance, ω = 2πf, and f = frequency at the time of impedance measurement, which is specifically 11 MHz. ０ This represents the electrical capacitance when no measurement sample is available, and was calculated using the following formula (2).

[0092]

[0093] However, ε ０ = permittivity of vacuum, S = area of ​​the electrode, d = distance between electrodes.

[0094] Furthermore, the measured dielectric constant may have an error of up to ±10%. This error can be caused by variations in the sintering density of the pellet sample during firing, variations in the contact properties of the Ag electrode in the sample, and other factors. In addition, pyrochlore-type oxides such as LLNOF tend to have larger errors when measuring the dielectric constant because halogens and lithium are desorbed during sintering, causing variations in the content of these elements.

[0095] The measured relative permittivity of LLNOF used in Examples 1-6, 8, and Comparative Examples 2, 3, 6, and 7 was 215. The measured relative permittivity of LATP used in Example 7 was 93. The measured relative permittivity of LLZ used in Example 9 was 35. The Al used in Comparative Example 5 ２ O ３ The measured relative permittivity of was less than 10. In other words, LLZ is a dielectric with a relative permittivity of 10 or more, LATP is a dielectric with a relative permittivity of 90 or more, and LLNOF is a dielectric with a relative permittivity of 200 or more.

[0096] The battery resistance shown in Figure 5 was measured using the following procedure. The secondary battery 10 prepared using the composite particles 100 of the examples and comparative examples was placed in a constant temperature bath at 25°C, and then adjusted to a State of Charge (SOC) of 50%. An SOC of 50% can be achieved, for example, by adjusting the voltage of the secondary battery 10 to an Open Circuit Voltage (OCV) corresponding to an SOC of 50%, or by fully charging the secondary battery 10 (SOC 100%) and then discharging a capacity equivalent to 50% of the previously measured full discharge capacity.

[0097] After adjusting the secondary battery 10 to a state of charge (SOC) of 50%, the DC internal resistance (DCIR) was measured. The DCIR of the secondary battery 10 was calculated by discharging it for 10 seconds at a 1C rate current and dividing the voltage change during that time by the applied current.

[0098] The battery resistance shown in Figure 5 is expressed as a relative value with Comparative Example 1, which uses composite particles 100 without ceramic particles 103, set to 100%.

[0099] Examples 1-4 and 7-9 use the same positive electrode active material particles 101 as Comparative Example 1, and ceramic particles 103 are added to the composite particles 100. In Examples 1-4 and 7-9, the resistance of the secondary battery 10 is 86-97%, which is lower than that of Comparative Example 1. In other words, by using composite particles 100 containing dielectric ceramic particles 103, the resistance of the secondary battery 10 can be reduced.

[0100] Furthermore, Examples 1 to 4 and 8 differ in the weight ratio of ceramic particles 103 to positive electrode active material particles 101. According to Examples 1 to 4 and 8, the higher the weight ratio of ceramic particles 103, the lower the resistance of the secondary battery 10. In other words, increasing the weight ratio of ceramic particles 103 can enhance the effect of reducing the resistance of the secondary battery 10.

[0101] Furthermore, Examples 1, 7, and 9 use ceramic particles 103 with different dielectric constants. According to Examples 1, 7, and 9, the higher the relative dielectric constant of the ceramic particles 103 used, the lower the resistance of the secondary battery 10. In other words, the higher the dielectric constant of the ceramic particles 103, the greater the effect of promoting the insertion and removal of lithium ions from the positive electrode active material particles 101, and the greater the effect of reducing resistance.

[0102] Furthermore, in Examples 1 and 6, the ratio of the particle diameter of the ceramic particles 103 to the particle diameter of the positive electrode active material particles 101 is different. According to Examples 1 and 6, a smaller particle diameter of the ceramic particles 103 is more effective in reducing the resistance of the secondary battery 10.

[0103] Comparative Example 5 is a ceramic particle (Al) with a relative permittivity of less than 10. ２ O ３ ) was used, and the resistance of the secondary battery 10 increased compared to Comparative Example 1. In other words, the composite particle 100 using ceramic particles with a relative permittivity of less than 10 did not produce the effect of reducing resistance.

[0104] Furthermore, the resistance of the secondary battery 10 in Example 1 is lower than that of Comparative Example 6. In other words, the configuration in Example 1, in which LLNOF is part of the composite particles 100, is more effective in reducing the resistance of the secondary battery 10 than the configuration in Comparative Example 6, in which composite particles 100 consisting of positive electrode active material particles 101 and a carbon layer 102 are mixed with LLNOF to produce the positive electrode layer 14.

[0105] Furthermore, the resistance of the secondary battery 10 in Example 5 is lower than that of Comparative Example 7. In other words, the configuration in Example 5, in which LFP is part of the composite particles 100, is more effective in reducing the resistance of the secondary battery 10 than the configuration in Comparative Example 7, in which composite particles 100 consisting of positive electrode active material particles 101 and a carbon layer 102 are mixed with LFP to produce the positive electrode layer 14.

[0106] Furthermore, in Comparative Examples 6 and 7, electrodes are fabricated using fine ceramic particles, which raises concerns about the electrode fabrication process, specifically the occurrence of aggregation during slurry preparation. In contrast, in Examples 1 and 5, electrodes are fabricated using composite particles 100, which are composite ceramic particles 103, thus preventing aggregation during slurry preparation and simplifying the electrode fabrication process.

[0107] Furthermore, in Comparative Example 2, the resistance of the secondary battery 10 is significantly increased compared to Comparative Example 1. In other words, in a configuration where the carbon layer 102 is not provided on the positive electrode active material particles 101, the conductivity decreases, and the resistance of the secondary battery 10 increases significantly. Similarly, in Comparative Example 3, where the carbon layer 102 is not provided on the positive electrode active material particles 101, the resistance of the secondary battery 10 is significantly increased compared to Comparative Example 1, and the resistance could not be measured.

[0108] The composite particle 100 of this embodiment described above comprises positive electrode active material particles 101, a carbon layer 102 covering the positive electrode active material particles 101, and ceramic particles 103 in which at least a portion is in contact with at least one of the carbon layer 102 or the positive electrode active material particles 101. The positive electrode active material particles 101 are covered with the carbon layer 102, which improves the conductivity of the composite particle 100. Furthermore, the ceramic particles 103 are in contact with at least one of the carbon layer 102 or the positive electrode active material particles 101, which allows the ceramic particles 103 to be positioned as close as possible to the positive electrode active material particles 101, thereby increasing the effect of promoting the insertion and removal of lithium ions from the positive electrode active material particles 101. As a result, the resistance of the secondary battery 10 using the composite particle 100 as an electrode can be reduced, and the battery performance can be improved.

[0109] Furthermore, since the ceramic particles 103 can be placed at the three-phase interface of the positive electrode active material particles 101, the carbon layer 102, and the electrolyte 16, the ceramic particles 103 can be placed in the location in the positive electrode layer 14 where the highest effect can be obtained. This maximizes the effect of promoting the insertion and removal of lithium ions into and out of the positive electrode active material particles 101 with a minimum amount of ceramic particles 103. As a result, the amount of ceramic particles 103 used can be reduced, and the decrease in the energy density of the battery associated with the addition of ceramic particles 103 can be suppressed.

[0110] Furthermore, according to the composite particles 100 of this embodiment, even when using an olivine-type active material with low conductivity, conductivity can be improved, thereby improving battery performance. Moreover, even when using LMFP, which has low conductivity among olivine-type active materials, conductivity can be effectively improved.

[0111] Furthermore, in this embodiment, by using a dielectric material with a high dielectric constant as the ceramic particles 103, the effect of promoting the insertion and removal of lithium ions into and out of the positive electrode active material particles 101 can be enhanced. In particular, pyrochlore-type oxides such as LLNOF have a high dielectric constant, and can further enhance the effect of promoting the insertion and removal of lithium ions into and out of the positive electrode active material particles 101.

[0112] Furthermore, because pyrochlore-type oxides have high ionic conductivity, using pyrochlore-type oxides as ceramic particles 103 in composite particles 100 can improve the ionic conductivity of the secondary battery 10, thereby improving battery performance.

[0113] The present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of the invention. Furthermore, the means disclosed in each of the above embodiments may be combined as appropriate to the extent that they are feasible.

[0114] For example, it is not necessary for all of the positive electrode active material in the positive electrode layer 14 to be positive electrode active material particles 101 that constitute the composite particles 100 of the present invention; it is sufficient if at least a portion of the positive electrode active material in the positive electrode layer 14 is positive electrode active material particles 101 that constitute the composite particles 100 of the present invention. For example, even if the composite particles 100 of the present invention and other positive electrode active materials that do not constitute the composite particles 100 (e.g., NCM) are mixed in the positive electrode layer 14, the resistance reduction effect of the secondary battery 10 according to the present invention can still be achieved.

[0115] Furthermore, the shape of the secondary battery 10 is not limited to the form described in the above embodiment, and can be used in various forms such as cylindrical, rectangular, or pouch-type (laminated).

[0116] Furthermore, the secondary battery 10 described in the above embodiment may be configured as 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. In other words, the current collector that contacts the positive electrode of one adjacent battery cell contacts the negative electrode of the other adjacent battery cell.

[0117] Furthermore, the secondary battery 10 described in the above embodiment may be configured as an anode-free battery. In an anode-free battery, the negative electrode layer 12 is not formed on the negative electrode current collector 11 in its initial state. During charging, lithium ions move from the positive electrode layer 14, causing lithium metal to deposit on the negative electrode current collector 11 and forming the negative electrode layer 12. The lithium metal constituting the negative electrode layer 12 then moves to the positive electrode layer 14 as lithium ions during discharge.

[0118] The composite particles, electrodes for secondary batteries, and secondary batteries disclosed herein have the following features: (Item 1) A composite particle comprising: active material particles (101); a carbon layer (102) covering at least a portion of the surface of the active material particles; and at least one type of ceramic particles (103) containing an oxygen element, wherein at least a portion of the ceramic particles is in contact with at least one of the carbon layer or the active material particles. (Item 2) The composite particle according to Item 1, wherein each of the carbon layers covering adjacent active material particles is formed integrally and continuously. (Item 3) The composite particle according to Item 1 or 2, wherein the weight ratio of the carbon layer to the active material particles is 0.5% to 5%. (Item 4) The composite particle according to any one of Items 1 to 3, wherein the weight ratio of the ceramic particles to the active material particles is 0.2% to 10%. (Item 5) The composite particle according to any one of Items 1 to 4, wherein the ceramic particles are dielectrics. (Item 6) The composite particle according to Item 5, wherein the relative permittivity of the ceramic particles is 90 or more. (Item 7) The composite particle according to Item 6, wherein the ceramic particles have a pyrochlore structure. (Item 8) The composite particle according to any one of Items 1 to 7, wherein the ceramic particles have a particle diameter smaller than the active material particles. (Item 9) The composite particle according to Item 8, wherein the particle diameter of the ceramic particles is 50% or less of the particle diameter of the active material particles. (Item 10) The composite particle according to any one of Items 1 to 9, wherein the active material particles have an olivine-type structure. (Item 11) The active material particles are LiMn ｘ Fe １－ｘ PO ４ (Item 12) A composite particle according to item 10, wherein (0 < x < 1). (Item 12) A composite particle according to any one of items 1 to 11, wherein the G / D ratio, which is the degree of crystallinity of the carbon layer, is 0.8 to 15. (Item 13) An electrode for a secondary battery comprising the composite particle (100) according to any one of items 1 to 12. (Item 14) A secondary battery comprising the electrode (14) for a secondary battery according to item 13.

[0119] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, while various combinations and forms are shown in this disclosure, other combinations and forms that include one, more, or fewer of those elements also fall within the scope and concept of this disclosure.

Claims

1. A composite particle comprising: active material particles (101); a carbon layer (102) covering at least a portion of the surface of the active material particles; and at least one type of ceramic particles (103) containing the element oxygen, wherein at least a portion of the ceramic particles is in contact with at least one of the carbon layer or the active material particles.

2. The composite particle according to claim 1, wherein each of the carbon layers coating adjacent active material particles is formed integrally and continuously.

3. The composite particle according to claim 1, wherein the weight ratio of the carbon layer to the active material particles is 0.5% to 5%.

4. The composite particle according to claim 1, wherein the weight ratio of the ceramic particles to the active material particles is 0.2 to 10%.

5. The composite particle according to claim 1, wherein the ceramic particles are dielectrics.

6. The composite particle according to claim 5, wherein the relative permittivity of the ceramic particles is 90 or more.

7. The composite particle according to claim 6, wherein the ceramic particles have a pyrochlore structure.

8. The composite particle according to claim 1, wherein the ceramic particles have a smaller particle size than the active material particles.

9. The composite particle according to claim 8, wherein the particle diameter of the ceramic particles is 50% or less of the particle diameter of the active material particles.

10. The composite particle according to claim 1, wherein the active material particle has an olivine-type structure.

11. The active material particles are LiMn ｘ Fe １－ｘ PO ４ The composite particle according to claim 10, wherein (0 < x < 1).

12. The composite particle according to claim 1, wherein the G / D ratio, which is the degree of crystallinity of the carbon layer, is 0.8 to 15.

13. An electrode for a secondary battery comprising composite particles (100) according to any one of claims 1 to 12.

14. A secondary battery comprising the electrode (14) for a secondary battery according to claim 13.

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