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

Abstract

The present invention provides a positive electrode composite material, a positive electrode, an all-solid-state battery, and a method for manufacturing the positive electrode composite material that can suppress the deterioration of battery characteristics. [Solution] The positive electrode composite material for an all-solid-state battery according to this embodiment includes a positive electrode active material, a solid electrolyte, a first conductive material, and a second conductive material having lower crystallinity than the first conductive material, wherein the first conductive material is largely distributed in the vicinity of the positive electrode active material.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a positive electrode composite material, a positive electrode, an all-solid-state battery, and a method for manufacturing a positive electrode composite material. This application claims priority under Japanese Patent Application No. 2024-177996, filed on October 10, 2024, and all information disclosed in the specification and drawings of said application is incorporated herein. [Background technology]

[0002] Currently, lithium-ion secondary batteries using liquid electrolytes are widely used. However, when using liquid electrolytes, deformation or external impact can cause short circuits, potentially leading to overheating or explosion. To improve the safety of lithium-ion secondary batteries, all-solid-state batteries, which do not use organic electrolytes, have recently attracted attention as next-generation batteries, and various research and development efforts are underway.

[0003] A technique is known for adding conductive materials such as acetylene black or carbon nanotubes to electrode materials for all-solid-state batteries (see Patent Document 1). Such conductive materials can assist in the movement of electrons in the electrode material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2020-507893 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The inventors focused on the problem that while conductive materials play a role in assisting electron transfer between active materials, they also promote the decomposition of solid electrolytes during charging and discharging, thereby degrading battery characteristics.

[0006] The problem that this invention aims to solve is to provide a positive electrode composite material, a positive electrode, an all-solid-state battery, and a method for manufacturing a positive electrode composite material that can suppress the deterioration of battery characteristics. [Means for solving the problem]

[0007] The inventors focused on the relationship between the adverse effects of conductive materials on solid electrolytes and the crystallinity of the conductive materials, and conceived the idea that the decomposition of solid electrolytes by conductive materials could be suppressed by using a combination of highly crystalline and low-crystalline conductive materials. After diligent research, the inventors found that the degradation of battery characteristics could be suppressed by distributing a large amount of highly crystalline conductive material near the positive electrode active material.

[0008] The present invention may include the following embodiments. [1] A positive electrode composite material for an all-solid-state battery, comprising a positive electrode active material, a solid electrolyte, a first conductive material, and a second conductive material having lower crystallinity than the first conductive material, wherein the first conductive material is largely distributed in the vicinity of the positive electrode active material. [2] The positive electrode composite material according to [1], wherein the first conductive material comprises a linear carbon material. [3] The second conductive material is a positive electrode composite material as described in [1] or [2], comprising a linear carbon material. [4] The first conductive material is a cathode composite material according to any one of [1] to [3], comprising carbon nanotubes. [5] The second conductive material is a cathode composite material according to any one of [1] to [4], comprising carbon nanofibers. [6] The first conductive material and the second conductive material are both carbon materials, and in the Raman spectrum they show 1560 cm⁻¹. -1 ~1600cm -1 The maximum peak intensity within the range is I G , 1310cm -1 ~1350cm -1 The maximum peak intensity within the range is I D In this case, the G / D ratio of the first conductive material (I G / I D ) is a positive electrode composite material according to any one of [1] to [5], wherein the G / D ratio of the second conductive material is greater. [7] The positive electrode composite material according to [6], wherein the G / D ratio of the first conductive material is 10 or more and 100 or less when a diffraction grating of 300 gr / mm is used. [8] The first conductive material is included in the positive electrode composite material in an amount of 0.01% by mass or more and 1% by mass or less, based on the total mass of the positive electrode active material, as described in any one of [1] to [7]. [9] The second conductive material is included in the positive electrode mixture in an amount of 0.1% by mass or more and 5% by mass or less, based on the total mass of the positive electrode mixture, as described in any one of [1] to [8].

[10] The positive electrode composite material according to any one of [1] to [9], wherein the second conductive material is distributed substantially homogeneously with respect to the positive electrode active material.

[11] The positive electrode composite material according to any one of [1] to

[10] , wherein the abundance of the first conductive material in the first region near the positive electrode active material is greater than the abundance of the first conductive material in the second region outside the first region.

[12] The presence rate of the second conductive material in the second region outside the first region near the positive electrode active material is greater than the presence rate of the first conductive material in the second region, according to any one of [1] to

[11] . A positive electrode containing a positive electrode composite material described in any one of

[13] [1] to

[12] . All-solid-state battery, including the positive electrode described in

[14]

[13] .

[15] A method for producing a positive electrode composite, comprising the steps of: mixing a positive electrode active material and a first conductive material to prepare a positive electrode active material / first conductive material mixture; and mixing the positive electrode active material / first conductive material mixture with a solid electrolyte and a second conductive material having lower crystallinity than the first conductive material. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a positive electrode composite material, a positive electrode, an all-solid-state battery, and a method for manufacturing a positive electrode composite material that can suppress the deterioration of battery characteristics. [Brief explanation of the drawing]

[0010] [Figure 1]Schematic diagram showing the microscopic structure of the positive electrode composite material according to the embodiment. [Figure 2] Schematic diagram showing the structure of the all-solid-state battery according to the embodiment. [Figure 3] Graph showing the change in discharge capacity with respect to the discharge rate for Examples 1 to 7 and Comparative Examples 1 to 9. [Figure 4] Graph showing the rate characteristics of Examples 1 to 7 and Comparative Examples 1 to 9.

Mode for Carrying Out the Invention

[0011] Hereinafter, the positive electrode composite material, positive electrode, all-solid-state battery, and method for manufacturing the positive electrode composite material according to the embodiment will be described. Note that the following embodiments show one aspect of the present invention, do not limit the present invention, and can be arbitrarily changed within the scope of the technical idea of the present invention. In addition, each configuration and each feature of the embodiment can be arbitrarily combined.

[0012] Hereinafter, a singular expression is used in the sense of "one or more" unless it clearly refers only to the singular in the context.

[0013] In this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only the case where it is "directly above" the other part but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, plate, etc. is described as being "under" another part, this includes not only the case where it is "directly below" the other part but also the case where there is another part in between. Also, in this specification, being "disposed on" can include not only the upper part but also the case of being disposed below.

[0014] In this specification, the average particle size (D 50 ) is defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve of the particles. The average particle size (D 50The particle size can be measured, for example, using the laser diffraction method. Laser diffraction can generally measure particle sizes from the submicron range to several millimeters in size, and can provide highly reproducible and high-resolution results.

[0015] In this specification, "carbon nanotube" (CNT) means a carbon material having a tubular structure formed from a single or multiple layers of graphene sheets and having a diameter less than 1 μm. "Carbon nanofiber" (CNF) means a carbon material having a diameter less than 1 μm and being formed in a fibrous manner by stacking graphene sheets.

[0016] In this specification, "single-walled carbon nanotube" (SWCNT) refers to a carbon nanotube in which the tubular wall made of carbon atoms is composed of a single atomic layer (i.e., one layer of graphene sheet). "Multi-walled carbon nanotube" (MWCNT) refers to a carbon nanotube in which the tubular wall made of carbon atoms is composed of multiple atomic layers (i.e., multiple layers of graphene sheet).

[0017] <1. Cathode composite material> The positive electrode composite material according to this embodiment includes a positive electrode active material, a solid electrolyte, a first conductive material, and a second conductive material having lower crystallinity than the first conductive material, wherein the first conductive material is mixed so that it is distributed in large quantities near the positive electrode active material.

[0018] Figure 1 is a schematic diagram showing the microscopic structure of the positive electrode composite material. The positive electrode composite material includes positive electrode active material particles 10, solid electrolyte particles 12, a first conductive material 14, and a second conductive material 16. In Figure 1, the solid electrolyte particles 12 are smaller than the positive electrode active material particles 10 and are scattered around the positive electrode active material particles 10. During the charge-discharge process, lithium ions move between the positive electrode active material particles 10 and the solid electrolyte particles 12, which are in contact with each other. In conjunction with this lithium ion conduction, electrons move between the positive electrode active material particles 10 and the electrode current collector (not shown). The first conductive material 14 and the second conductive material 16 are entangled with the positive electrode active material particles 10. Some of the first conductive material 14 and the second conductive material 16 are in contact with multiple positive electrode active material particles 10. During the charging and discharging process, the first conductive material 14 and the second conductive material 16 can form electron conduction paths from the positive electrode active material particles 10 to other particles 10 or the current collector. In Figure 1, the second conductive material 16 has a shape that is thicker and longer than the first conductive material 14, but it is not limited to this.

[0019] The first conductive material 14 is not randomly distributed within the positive electrode mixture, but rather is unevenly distributed around the positive electrode active material particles 10. Specifically, the first conductive material 14 may be distributed more in the vicinity of the positive electrode active material 10. In this specification, "nearby" means at a distance of 50 nm or less. For example, the vicinity of the positive electrode active material 10 refers to the region within 50 nm of the particle surface of the positive electrode active material 10. For example, the first conductive material 14 may be distributed more in the vicinity of the positive electrode active material 10 than in the vicinity of the solid electrolyte 12.

[0020] The distribution of the first conductive material 14 can be investigated by the following procedure (1) to (5). (1) Identify the positive electrode active material particles 10 and the first conductive material 14 in the scanning electron microscope (SEM) image (this may also be a transmission electron microscope (TEM) image or a micro-Raman image, etc. Hereinafter simply referred to as "SEM image"). (2) Determine the area S10 of the first region that is near the particles 10 of the positive electrode active material in the SEM image, and the area S20 of the second region other than the first region (that is, the region that is not near the particles 10 of the positive electrode active material in the SEM image). Here, the first region consists of a region within 50 nm from the surface of the particles 10 of the positive electrode active material in the SEM image. The second region is a region farther than 50 nm from the surface of the particles 10 of the positive electrode active material in the SEM image. (3) In the SEM image, determine the area S11 of the region where the first conductive material 14 exists in the first region, and the area S21 of the region where the first conductive material 14 exists in the second region. (4) Calculate the abundance ratio E11 of the first conductive material 14 in the first region by E11 = S11 / S10. Similarly, calculate the abundance ratio E21 of the first conductive material 14 in the second region by E21 = S21 / S20. (5) If E11 > E21, it can be said that the first conductive material 14 is more distributed in the first region than in the second region. That is, it can be evaluated that the first conductive material 14 is more distributed near the positive electrode active material 10. Conversely, if E11 < E21, it can be said that the first conductive material 14 is more distributed in the second region than in the first region. That is, it can be evaluated that the first conductive material 14 is more distributed in the region other than near the positive electrode active material 10.

[0021] The absolute values of the abundance ratios E11 and E21 of the first conductive material 14 vary depending on the addition amount of the first conductive material 14, manufacturing conditions, etc. In this embodiment, the magnitude relationship is E11 > E21. That is, the abundance ratio E11 of the first conductive material 14 in the first region (that is, near the particles 10 of the positive electrode active material) is larger than the abundance ratio E21 of the first conductive material 14 in the second region (the other region). For example, the abundance ratio E11 of the first conductive material 14 in the first region is greater than 0 and less than or equal to 1, greater than or equal to 0.01 and less than or equal to 0.9, greater than or equal to 0.1 and less than or equal to 0.8, greater than or equal to 0.2 and less than or equal to 0.7, or greater than or equal to 0.3 and less than or equal to 0.5. For example, the abundance ratio E 21 of the first conductive material 14 in the second region is greater than or equal to 0 and less than 1, greater than or equal to 0.01 and less than or equal to 0.8, greater than or equal to 0.1 and less than or equal to 0.5, or greater than or equal to 0.2 and less than or equal to 0.3.

[0022] As an index representing the degree of uneven distribution, the ratio of the abundance of the first conductive material 14 in the first and second regions, R1 = E21 / E11, can be defined. The abundance ratio R1 is preferably between 0 and 1, for example, between 0.1 and 0.8, between 0.2 and 0.6, or between 0.3 and 0.5.

[0023] On the other hand, the second conductive material 16 may be distributed substantially homogeneously with respect to the positive electrode active material particles 10. Preferably, the second conductive material 16 may be distributed substantially homogeneously with respect to the positive electrode active material particles 10 and the solid electrolyte particles 12. For example, the second conductive material 16 may be randomly distributed in the positive electrode mixture. However, the second conductive material 16 may be unevenly distributed in the positive electrode mixture. Thus, the second conductive material 16 may have a different distribution from the first conductive material 14. For example, the difference in the distribution of the first conductive material 14 and the second conductive material 16 can be evaluated using the above-mentioned ratio of abundance by the following procedure (1) to (5). (1) In addition to the positive electrode active material particles 10 and the first conductive material 14, the second conductive material 16 in the SEM image is identified. (2) Determine the area S12 of the region in the SEM image where the second conductive material 16 is present in the first region (i.e., the region near the positive electrode active material particles 10), and the area S22 of the region in the SEM image where the second conductive material 16 is present in the second region (i.e., the region in the SEM image that is not near the positive electrode active material particles 10). (3) The abundance E12 of the second conductive material 16 in the first region is calculated using E12 = S12 / S10. Similarly, the abundance E22 of the second conductive material 16 in the second region is calculated using E22 = S22 / S20. (4) Calculate the ratio of the second conductive material 16 in the first and second regions, R2 = E22 / E12. (5) The abundance ratio R1 of the first conductive material 14 and the abundance ratio R2 of the second conductive material 16 are compared. If the difference between R2 and R1 is 0.1 or more, the second conductive material 16 can be evaluated as having a different distribution from the first conductive material 14. The abundance ratio R2 of the second conductive material 16 is preferably 0.5 or more and 1.5 or less, for example, 0.8 or more and 1.2 or less, or 0.9 or more and 1.1 or less.

[0024] Preferably, the abundance ratio E11 of the first conductive material 14 in the first region is greater than the abundance ratio E12 of the second conductive material 16 in the first region (E11 > E12). As a result, the contribution of the first conductive material 14 to electron conduction in the first region can be greater than that of the second conductive material 16 (for example, in the first region, electron conduction by the first conductive material 14 may be dominant). Preferably, the abundance ratio E22 of the second conductive material 16 in the second region is greater than the abundance ratio E21 of the first conductive material 14 in the second region (E21 < E22). As a result, the contribution of the second conductive material 16 to electron conduction in the second region can be greater than that of the first conductive material 14 (for example, in the second region, electron conduction by the second conductive material 16 may be dominant). However, the mode of electron conduction is not limited to the above example, and in the first region and / or the second region, both conductive materials 14 and 16 may contribute significantly to electron conduction.

[0025] <1-1. Positive electrode active material> During charge and discharge, the positive electrode active material cooperates with the negative electrode active material described later to release and occlude lithium ions at the positive electrode.

[0026] The positive electrode active material may be one that is generally used as a positive electrode active material in the relevant technical field. The positive electrode active material may be any compound capable of reversible insertion (intercalation) and desorption (deintercalation) of lithium, and its type is not particularly limited. For example, the positive electrode active material is a lithium metal composite oxide. Specific examples include, for example, lithium metal composite oxides containing one or more metals such as cobalt, manganese, nickel, copper, vanadium, and aluminum and lithium, particularly lithium transition metal oxides. More specifically, such lithium metal composite oxides include lithium-manganese-based oxides (for example, LiMnO2, LiMnO3, LiMn2O3, LiMn2O4, etc.); lithium-cobalt-based oxides (for example, LiCoO2, etc.); lithium-nickel-based oxides (for example, LiNiO2, etc.); lithium-copper-based oxides (for example, Li2CuO2, etc.); lithium-vanadium-based oxides (for example, LiV3O8, etc.); lithium-nickel-manganese-based oxides (for example, LiNi 1-z Mn z O2(0 < z < 1), LiMn 2-z Ni z O4(0 < z < 2), etc.); lithium-nickel-cobalt-based oxides (for example, LiNi 1-y Co y O2(0 < y < 1), etc.); lithium-manganese-cobalt-based oxides (for example, LiCo 1-z Mn z O2(0 < z < 1), LiMn 2-y Co y O4(0 < y < 2), etc.); lithium-nickel-manganese-cobalt-based oxides (for example, Li(Ni x Co y Mn z )O2(0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1), Li(Ni x Co y Mn z )O4(0 < x < 2, 0 < y < 2, 0 < z < 2, x + y + z = 2), etc.); lithium-nickel-cobalt-metal (M) oxides (for example, Li(Ni x Co y Mn z Mw )O2 (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < w < 1, x + y + z + w = 1), etc.); Li-excess solid solution cathode (e.g., pLi2MnO3-(1-p)Li(Ni x Co y Mn z )O2 (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1, 0 < p < 1); Examples include compounds in which the transition metal element in these compounds is partially substituted with one or two or more other metal elements. The positive electrode active material layer can contain any one or two or more of these compounds. However, it is not limited to only these.

[0027] Particularly, in the lithium transition metal oxide with a high nickel content effective for increasing the battery capacity, the lithium transition metal oxide preferably contains 50 mol% or more of nickel based on the total amount of transition metals. Examples of such lithium transition metal oxides include Li a NiO2 (0.5 ≦ a ≦ 1.5); Li a (Ni x Co y Mn z )O2 (0.5 ≦ a ≦ 1.5, 0.5 ≦ x < 1, 0 < y < 0.5, 0 < z < 0.5, x + y + z = 1); Li a (Ni x Co y Mn z )O2 (0.7 ≦ x < 1, 0 < y < 0.3, 0 < z < 0.3, x + y + z = 1); Li a (Ni x Co y Mn z )O2 (0.8 ≦ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z = 1); Li a (Ni x Co y Mn z )O2 (0.9 ≦ x < 1, 0 < y < 0.1, 0 < z < 0.1, x + y + z = 1); Li a Ni 1-y Co y O2 (0.5 ≦ a ≦ 1.5, 0 < y ≦ 0.5); Li a Ni 1-zMn z O2 (0.5 ≤ a ≤ 1.5, 0 < z ≤ 0.5); Li a (Ni x Co y Mn z )O4 (0.5 ≤ a ≤ 1.5, 1 ≤ x < 2, 0 < y < 1, 0 < z < 1, x + y + z = 2); Li a (Ni x Co y M w )O2 (M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga, and In, 0.5 ≤ a ≤ 1.5, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < w < 0.5, x + y + w = 1); Li a (Ni x Co y Mn z M w )O2 (M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga, and In, 0.5 ≤ a ≤ 1.5, 0.5 ≤ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 < w < 0.5, x + y + z + w = 1); Compounds in which at least part of the transition metal atoms in these compounds are substituted with one or more other metal elements (for example, one or more of Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga, and In); Compounds in which oxygen atoms in these compounds are partially substituted with one or more other non-metal elements (for example, one or more of P, F, S, and N), etc. are included. Preferably, the lithium transition metal oxide is Li a Ni x M yO2 (M is one or more metal elements other than Ni, for example, one or more elements selected from the group consisting of Al, Fe, Co, Mn, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga, and In, 0 < a ≤ 1.05, x + y = 1), where the value of x can be, for example, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, and 0.9 or more, and can be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less. The positive electrode active material can include one or more of the above, but is not limited thereto. Also, even within the same particle, there may be a concentration distribution of substitution between the inside and the surface layer. It may also be coated on the surface of the particle. For example, there are surfaces coated with metal oxides, lithium transition metal oxides, polymers, etc., but it is not limited thereto.

[0028] Particularly, in terms of improving the capacity characteristics and stability of the battery, Li a NiO2, Li a (Ni 0.5 Mn y Co z )O2 (y + z = 0.5), Li a (Ni 0.6 Mn y Co z )O2 (y + z = 0.4), Li a (Ni 0.7 Mn y Co z )O2 (y + z = 0.3), Li a (Ni 0.8 Mn y Co z )O2 (y + z = 0.2), Li a (Ni 0.8 Co y Mn z Al w )O2 (y + z + w = 0.2), Li a (Ni 0.85 Co y Mn z )O2 (y + z = 0.15), Li a (Ni 0.85 Co y Mn z Al w)O2(y+z+w=0.15), Li a (Ni 0.9 Co y Mn z )O2(y+z=0.1), Li a (Ni 0.9 Co y Mn z Al w )O2(y+z+w=0.1), Li a (Ni 0.9 Co y Mn z )O2(y+z=0.1), Li a (Ni 0.95 Co y Mn z Al w )O2(y+z+w=0.05) is preferred. Here, the value of a is, for example, 0.5≦a≦1.5, and preferably 1.0≦a≦1.5.

[0029] More specifically, LiNiO2, Li(Ni 0.5 Mn 0.3 Co 0。2 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05 )O2, Li(Ni 0.8 Co 0.1 Mn 0.05 Al 0.05 )O2, Li(Ni 0.85 Co 0.10 Mn 0.05 )O2, Li(Ni 0.85 Co 0.10 Mn 0.03 Al 0.02 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O 2、 Li(Ni) 0.9 Co 0.05Al 0.05 )O2, Li(Ni 0.95 Co 0.03 Mn 0.02 )O2, Li(Ni 0.95 Co 0.03 Al 0.02 ) O2 is preferred.

[0030] The particle size of the positive electrode active material particles 10 is, for example, 10 nm to 20 μm, 50 nm to 18 μm, 100 nm to 15 μm, 200 nm to 13 μm, 500 nm to 12 μm, or 1 μm to 10 μm. If the particle size of the positive electrode active material particles 10 is 10 nm or larger, surface degradation of the particles can be suppressed. If the particle size of the positive electrode active material particles 10 is 20 μm or smaller, the lithium diffusion path will not become excessively long, and electron conduction paths by the first conductive material 14 and the second conductive material 16 can be efficiently formed.

[0031] Preferably, a coating containing a metal oxide is formed on the particle surface of the positive electrode active material. The metal oxide may be at least one selected from the group consisting of LiNbO2, LiNbO3, LiCoO2, and Li2TiO3. More preferably, a coating containing LiNbO2 is formed on the particle surface of lithium transition metal oxide. Such a coating can reduce the internal resistance of the positive electrode. When the positive electrode active material particles 10 have the above coating, the first conductive material 14 and the second conductive material 16 may be located outside the coating.

[0032] <1-2. Solid electrolyte> The solid electrolyte assists in the transfer of lithium ions between the positive electrode active material and the negative electrode active material. The solid electrolyte particles 12 can mediate the transfer of lithium ions by coming into contact with the positive electrode active material particles 10, the negative electrode active material particles, or other solid electrolyte particles 12.

[0033] Solid electrolytes primarily serve to transport lithium ions within the electrode, and therefore require materials with high ionic conductivity (for example, materials with an ionic conductivity of 10). -5 s / m or more, preferably 10 -4 Any of the following can be used (s / m or higher), and are not limited to specific components.

[0034] The solid electrolyte may be one or more selected from the group consisting of, for example, sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes. The polymer-based solid electrolyte may be a polymer solid electrolyte formed by adding a polymer resin to a solventized lithium salt, or a polymer gel electrolyte containing an organic electrolyte, ionic liquid, monomer, or oligomer containing an organic solvent and a lithium salt in a polymer resin. On the other hand, sulfide-based solid electrolytes have high ionic conductivity, and oxide-based solid electrolytes have excellent electrochemical stability. Therefore, an appropriate solid electrolyte component can be selected and used depending on the characteristics of the solid electrolyte and the intended use of the battery. Preferably, the solid electrolyte is a sulfide-based solid electrolyte.

[0035] Sulfide-based solid electrolytes contain sulfur (S) and have ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table. Examples of sulfide-based solid electrolytes include Li-PS glass or Li-PS glass ceramics. Sulfide-based solid electrolytes include glassy solid electrolytes, crystalline solid electrolytes, and glass ceramic solid electrolytes. Specifically, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, argyrodite-based solid electrolytes (e.g., Li6PS5X(X:Cl,Br,I)), LGPS-based solid electrolytes (Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc., Li7P3S 11 Examples include, but are not limited to, the above. For example, the solid electrolyte may contain one or more compounds selected from the group consisting of the above compounds.

[0036] Oxide-based solid electrolytes contain oxygen (O) and possess the ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table. Examples of oxide-based solid electrolytes include LLTO compounds and Li6La2CaTa2O 12 Li6La2ANb2O 12 (A: Ca or Sr), Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (Here, 0≦x≦1, 0≦y≦1), LiAl x Zr 2-x (PO4)3 (where 0≦x≦1, 0≦y≦1), LiTi x Zr 2-x Examples of such compounds include (PO4)3 (0≦x≦1, 0≦y≦1), LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, and LLZO compounds, but are not limited to these. For example, a solid electrolyte may contain one or more compounds selected from the group consisting of the above compounds.

[0037] Polymeric solid electrolytes may include, for example, polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxysane polymers, phosphagen polymers, polyethylene derivatives, alkylene oxide derivatives such as PEO (polyethylene oxide) and PPO (polypropylene oxide), phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups. For example, a solid electrolyte may contain one or more compounds selected from the group consisting of the above compounds.

[0038] The solid electrolyte content may be, for example, 1% to 70% by mass, 5% to 50% by mass, 10% to 45% by mass, or 20% to 40% by mass, based on the total mass of the positive electrode active material. If the solid electrolyte particle content is 1% by mass or more, the solid electrolyte particles surround the surface of the lithium transition metal oxide particles, thereby sufficiently forming a conduction path for lithium ions. If the solid electrolyte particle content is 50% by mass or less, it is possible to suppress the solid electrolyte particles from separating from the lithium transition metal oxide and aggregating.

[0039] The particle size of the solid electrolyte particles 12 is, for example, 10 nm to 10 μm, 50 nm to 5 μm, 100 nm to 1 μm, or 200 nm to 500 nm. If the particle size of the solid electrolyte particles 12 is within the above range, lithium ions can be smoothly transferred between the active material and the solid electrolyte particles at an appropriate electrode density and tap density.

[0040] <1-3. First conductive material> The first conductive material 14 is mainly distributed around the particle surface of the positive electrode active material and contributes to the formation of a conductive network between the particles of the positive electrode active material or between the positive electrode active material particles and the positive electrode current collector.

[0041] Examples of the first conductive material 14 include, but are not limited to, carbon materials, metallic materials, conductive metal oxides, and conductive polymers. Preferably, the first conductive material 14 includes a carbon material. Examples of carbon materials include carbon nanotubes, carbon nanofibers, artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and carbon fibers. The first conductive material 14 may be a mixture of multiple materials. More preferably, the first conductive material 14 includes carbon nanotubes. The first conductive material 14 may be carbon nanotubes. The first conductive material 14 may include a linear carbon material. Compared to a spherical carbon material, the linear carbon material can form a continuous electron conduction path within the electrode. This formation of a continuous conduction network facilitates electron transfer and is more stable than a conduction network based on spherical particles that depend on point contact. Furthermore, when the first conductive material 14 includes a linear carbon material, the active material within the electrode reacts uniformly, which can improve the bottleneck phenomenon in ion diffusion that occurs under high-rate charge-discharge conditions. Therefore, when the first conductive material 14 includes a linear carbon material, the initial efficiency and rate characteristics can be improved.

[0042] The carbon nanotubes contained in the first conductive material 14 may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs). Single-walled carbon nanotubes have superior electronic conductivity compared to multi-walled carbon nanotubes. On the other hand, multi-walled carbon nanotubes are easier to manufacture than single-walled carbon nanotubes and are therefore more cost-effective.

[0043] The first conductive material 14 has higher crystallinity than the second conductive material 16. When the first conductive material 14 contains carbon material, the peak intensity ratio (G / D ratio) in the Raman spectrum can be used as an indicator of the crystallinity of the carbon material. Specifically, the carbon material contained in the first conductive material 14 has a peak intensity of 1560 cm⁻¹ in the Raman spectrum. -1 ~1600cm -1 The maximum peak intensity within the range is I G , 1310cm -1 ~1350cm -1 The maximum peak intensity within the range is I D The G / D ratio in this case (I G / I D ) is greater than the G / D ratio of the carbon material contained in the second conductive material 16. For example, the G / D ratio of the carbon material contained in the first conductive material 14 may be 5 to 100, 10 to 80, or 20 to 70 when using a diffraction grating of 300 gr / mm. In general, the Raman spectrum of carbon materials is 1580 cm⁻¹. -1A peak (called the G-band) originating from the graphite structure was observed nearby, at 1350 cm. -1 A peak (called the D band) originating from defects in the graphite structure is observed nearby. Carbon materials with a larger G / D ratio have fewer defects in the graphite structure and higher crystallinity. If the G / D ratio is 10 or higher, the defects in the graphite structure of the carbon material are sufficiently few, allowing for sufficient electron conduction paths to be formed during the charge-discharge process.

[0044] Here, the decomposition of solid electrolyte particles 12 is thought to proceed most rapidly on the surface of the positive electrode material, and it is common practice to apply a Li conductor coating such as LiNBO3 to the positive electrode surface. During charging and discharging at high temperatures and high voltages, smoother insertion and removal of Li is required. Therefore, by placing a first conductive material 14 with high crystallinity and high conductivity near the positive electrode material, electrons can be smoothly transferred to the positive electrode material during Li insertion and removal. Generally, conductive materials are thought to have a tendency to react with solid electrolyte particles, so if the first conductive material 14 comes into contact with the solid electrolyte particles 12, there is a possibility that the solid electrolyte particles 12 will decompose due to a reaction with the first conductive material 14. However, as shown in Figure 1, if the first conductive material 14 is located closer to the positive electrode active material particles 10 than to the solid electrolyte particles 12, the proportion of electrons consumed in the oxidation-reduction of the positive electrode material before the decomposition of the solid electrolyte particles 12 increases. Therefore, the decomposition of solid electrolyte particles 12 by the first conductive material 14 can be relatively suppressed.

[0045] The average length of the carbon nanotubes contained in the first conductive material 14 is, for example, 0.5 μm to 200 μm, 1 μm to 100 μm, 2 μm to 50 μm, or 5 μm to 10 μm. Here, "average length" refers to the average length of the top 100 objects (in this case, carbon nanotubes) and the bottom 100 objects (in this case, carbon nanotubes) observed by SEM. Carbon nanotubes with a length of 1 μm to 500 μm can efficiently form electron conduction paths between active material particles or between active material particles and current collectors without excessive aggregation among the carbon nanotubes themselves during electrode fabrication.

[0046] The first conductive material 14 may have a length sufficient to come into contact with a plurality of positive electrode active material particles 10 having an average particle size of 1 μm to 20 μm.

[0047] The average diameter of the carbon nanotubes contained in the first conductive material 14 is not particularly limited, but for example, it may be between 1 nm and less than 1 μm, between 5 nm and 500 nm, between 10 nm and 200 nm, or between 20 nm and 100 nm. Here, "average diameter" refers to the average value of the diameters of the top 100 objects (in this case, carbon nanotubes) and the bottom 100 objects (in this case, carbon nanotubes) observed by SEM. If the average diameter of the carbon nanotubes is between 1 nm and less than 1 μm, the carbon nanotubes will disperse easily in the positive electrode without excessive aggregation.

[0048] The content of the first conductive material 14 is, for example, 0.01% by mass or more and 1% by mass or less, 0.02% by mass or more and 0.5% by mass or less, 0.025% by mass or more and 0.2% by mass or less, or 0.05% by mass or more and 0.1% by mass or less, based on the total mass of the positive electrode active material. If the content of the first conductive material 14 is 0.01% by mass or more, a conductive network can be efficiently formed within the positive electrode. If the content of the first conductive material 14 is 1% by mass or less, the decomposition of the solid electrolyte particles 12 by the first conductive material 14 can be suppressed while maintaining the dispersibility and stability of the conductive material.

[0049] <1-4. Second conductive material> The second conductive material 16, like the first conductive material 14, mainly contacts the particle surface of the positive electrode active material and / or the positive electrode current collector, and contributes to the formation of a conductive network between the particles of the positive electrode active material or between the positive electrode active material particles and the positive electrode current collector.

[0050] Examples of the second conductive material 16 include, but are not limited to, carbon materials, metal materials, conductive metal oxides, and conductive polymers. Preferably, the second conductive material 16 includes a carbon material. Examples of carbon materials include carbon nanotubes, carbon nanofibers, artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and carbon fibers. The second conductive material 16 may be a mixture of multiple materials. More preferably, the second conductive material 16 includes carbon nanofibers. The second conductive material 16 may be carbon nanofibers. The second conductive material 15 may include a linear carbon material. Compared to a spherical carbon material, the linear carbon material can form a continuous electron conduction path within the electrode. This formation of a continuous conduction network facilitates electron transfer and is more stable than a conduction network based on spherical particles that depend on point contact. Furthermore, when the second conductive material 15 includes a linear carbon material, the active material within the electrode reacts uniformly, which can improve the bottleneck phenomenon for ion diffusion that occurs under high-rate charge-discharge conditions. Therefore, when the second conductive material 15 includes a linear carbon material, the initial efficiency and rate characteristics can be improved.

[0051] The second conductive material 16 has lower crystallinity than the first conductive material 14. When both the first conductive material 14 and the second conductive material 16 contain carbon material, the G / D ratio of the first conductive material 14 is greater than the G / D ratio of the second conductive material 16. When the second conductive material 16 contains carbon material, the G / D ratio of the carbon material contained in the second conductive material 16 may be, for example, 1 to 10, 1.5 to 6, or 2 to 5. If the G / D ratio is 10 or less, certain defects exist in the graphite structure of the carbon material, which reduces the reactivity of the carbon material and suppresses the decomposition of the solid electrolyte particles 12 by the second conductive material 16. For example, when the second conductive material 16 contains carbon nanofibers with low crystallinity, the conductivity on the sides of the carbon nanofibers is low, so even if the carbon nanofibers come into contact with the solid electrolyte particles 12, the decomposition reaction of the solid electrolyte particles 12 is unlikely to occur.

[0052] The average length of the carbon nanofibers contained in the second conductive material 16 is, for example, 1 μm to 500 μm, 2 μm to 100 μm, 5 μm to 50 μm, or 6 μm to 15 μm. Preferably, the average length of the carbon nanofibers contained in the second conductive material 16 is greater than the average length of the first conductive material 14, for example, greater than the average length of the carbon nanotubes contained in the first conductive material 14. Carbon nanofibers with a length of 1 μm to 500 μm can efficiently form electron conduction paths between active material particles or between active material particles and current collectors without excessive aggregation of carbon nanofibers during electrode fabrication.

[0053] The second conductive material 16 may have a length sufficient to contact, for example, a plurality of positive electrode active material particles 10 having an average particle size of 1 μm to 20 μm. For example, when observed by SEM, it is preferable that 50% (on a number basis), 60%, 70%, 80%, 90%, or 100% of the second conductive material 16 in the positive electrode composite material are in contact with both the positive electrode active material particles 10 and the electrode current collector, or are in contact with a plurality of positive electrode active material particles 10.

[0054] It is preferable that the average length of the second conductive material 16 is greater than the average particle size of the positive electrode active material particles 10, as this allows the second conductive material 16 to easily come into contact with multiple positive electrode active material particles 10. For example, the average length of the second conductive material 16 is 1 or more, 2 or more, 5 or more, or 10 or more times the average particle size of the positive electrode active material particles 10.

[0055] The average diameter of the carbon nanofibers contained in the second conductive material 16 is not particularly limited, but for example, it may be between 10 nm and less than 1 μm, between 20 nm and 500 nm, between 50 nm and 300 nm, or between 100 nm and 200 nm. If the average diameter of the carbon nanofibers is between 10 nm and less than 1 μm, the carbon nanofibers will disperse easily in the positive electrode without excessive aggregation.

[0056] The content of the second conductive material 16 is, for example, 0.1% to 5% by mass, 0.5% to 4% by mass, or 1% to 3% by mass, based on the total mass of the positive electrode composite material. If the content of the second conductive material 16 is 0.1% by mass or more, a conductive network can be efficiently formed within the positive electrode. If the content of the second conductive material 16 is 5% by mass or less, a decrease in the energy density of the battery can be prevented. When the content of the second conductive material 16 is based on the total mass of the positive electrode active material, the content of the second conductive material 16 is, for example, 0.1% to 10% by mass, 0.5% to 8% by mass, 1% to 5% by mass, or 2% to 4% by mass.

[0057] <1-5. Formation of electron conduction paths> Since the first conductive material 14 and the second conductive material 16 have high electronic conductivity, electron conduction paths are formed between the active material particles and the electrode current collector, or between the active material particles themselves. The first conductive material 14, which is abundantly distributed near the positive electrode active material particles 10, mainly forms electron conduction paths around the positive electrode active material particles 10. On the other hand, the second conductive material 16 mainly forms electron conduction paths between multiple positive electrode active material particles 10, or between the positive electrode active material particles 10 and the electrode current collector.

[0058] As described above, the second conductive material 16 has lower crystallinity than the first conductive material 14. Since the highly crystalline first conductive material 14 is unevenly distributed near the positive electrode active material particles 10, the second conductive material 16, which has lower crystallinity than the first conductive material 14, is more abundant near the solid electrolyte particles 12 compared to the distribution of the first conductive material 14. If the second conductive material 16 has a longitudinal shape with sides and cross-sections (i.e., end faces, edges), and its crystallinity is lower than that of the first conductive material 14, then the second conductive material 16 will have more defects, especially on its sides, and electrons are thought to flow more easily between the cross-sections (edges) than between the sides of the second conductive material 16. Since the second conductive material 16 has lower crystallinity than the first conductive material 14, it is relatively less likely to decompose the solid electrolyte particles 12. Therefore, the positive electrode composite as a whole can suppress the decomposition reaction of the solid electrolyte particles 12 while forming electron conduction paths with both the first conductive material 14 and the second conductive material 16.

[0059] When viewed from the perspective of the positive electrode active material particles, it is preferable that electron conduction paths are formed with the electrode current collector or other active material particles. For example, when observed with a SEM, it is preferable that 50% (on a number basis), 60% or more, 70% or more, 80% or more, 90% or more, or 100% of the positive electrode active material particles in the positive electrode composite material are in contact with the first conductive material 14 or the second conductive material 16. Furthermore, when observed with a SEM, it is preferable that 50% (on a number basis), 60% or more, 70% or more, 80% or more, 90% or more, or 100% of the positive electrode active material particles in the positive electrode composite material are in contact with the first conductive material 14 or the second conductive material 16, and that the first conductive material 14 or the second conductive material 16 is also in contact with the electrode current collector or other positive electrode active material particles.

[0060] As described above, the first conductive material 14 and the second conductive material 16 can form electron conduction paths between active material particles that are not in contact with each other and the electrode current collector, and between multiple active material particles that are not in contact with each other. This facilitates electron conduction within the positive electrode, allowing the active material particles within the positive electrode to participate uniformly in the charge-discharge reaction. As a result, the battery capacity can be improved. Furthermore, since the first conductive material 14 and the second conductive material 16 have excellent electron conductivity, energy losses such as heat generation under high current can be suppressed. As a result, rate characteristics (especially high-speed charge-discharge characteristics) can be improved.

[0061] Furthermore, the first conductive material 14 or the second conductive material 16 does not necessarily have to be in direct contact with the positive electrode active material. For example, if the surface of the positive electrode active material particles is coated with a conductive material such as carbon, the first conductive material 14 or the second conductive material 16 will be in contact with the positive electrode active material particles through the coating, but even in that case, an electron conduction path will be formed. Therefore, the contact between the first conductive material 14 or the second conductive material 16 and the positive electrode active material particles does not have to be direct contact, but may be indirect contact through another configuration, as long as the first conductive material 14 or the second conductive material 16 forms an electron conduction path that mediates electron conduction between the positive electrode active material particles. In addition, the first conductive material 14 or the second conductive material 16 may support the positive electrode active material particles by adsorption or the like, but it does not have to support the positive electrode active material particles if it is merely in contact with them. For example, the first conductive material 14 or the second conductive material 16 does not have to be adsorbed with the positive electrode active material particles.

[0062] <2. Method for manufacturing positive electrode composite material> The method for manufacturing a positive electrode composite material for an all-solid-state battery according to this embodiment includes the following steps. (a) A step of mixing the positive electrode active material and the first conductive material to prepare a positive electrode active material / first conductive material mixture. (b) A step of mixing the positive electrode active material / first conductive material mixture, a solid electrolyte, and a second conductive material having lower crystallinity than the first conductive material.

[0063] As described in steps (a) and (b) above, by performing stepwise mixing, the first conductive material 14 can be distributed in large quantities near the positive electrode active material particles 10. That is, in step (a), only the positive electrode active material particles 10 and the first conductive material 14 are mixed, so the positive electrode active material / first conductive material mixture obtained in step (a) has a particle arrangement structure in which the first conductive material 14 is located around the positive electrode active material particles 10. For example, some or all of the first conductive material 14 may be physically bonded to the surface of the positive electrode active material particles 10 by intermolecular forces or the like. Next, in step (b), the positive electrode active material / first conductive material mixture, solid electrolyte particles 12, and second conductive material 16 are mixed. The particle arrangement structure obtained in step (a), in which the first conductive material 14 is located around the positive electrode active material particles 10, can be maintained to some extent even during the mixing in step (b). For example, if the first conductive material 14 undergoes the mixing process in step (b) while physically bonded to the surface of the positive electrode active material particles 10, a certain number of the first conductive material 14 may remain physically bonded to the surface of the positive electrode active material particles 10 even after step (b). As a result, a positive electrode composite material is obtained in which the first conductive material 14 is unevenly distributed near the positive electrode active material particles 10.

[0064] However, the above method is merely one example of a method for unevenly distributing the first conductive material 14 in the positive electrode mixture. A positive electrode mixture having an uneven distribution of the first conductive material 14 as described above may be manufactured by methods other than those described above. For example, the positive electrode active material particles 10 or the first conductive material 14 may be chemically modified to facilitate bonding between the positive electrode active material particles 10 and the first conductive material 14.

[0065] The above mixing can be carried out using, but is not limited to, dry mixers, agitators, shakers such as orbital shakers, mortar mixers, milling machines such as planetary ball mills, etc., which are generally used for mixing powders. The mixing method is not limited to dry mixing, but may also be wet mixing using any liquid medium. In addition, other additives may be added.

[0066] <3. All-solid-state battery> The all-solid-state battery according to this embodiment comprises a positive electrode containing the positive electrode composite material, a negative electrode, and a solid electrolyte layer between the positive and negative electrodes. The all-solid-state battery may be a lithium-ion secondary battery.

[0067] Figure 2 is a schematic diagram showing the structure of an all-solid-state battery 100 according to an embodiment. As shown in Figure 2, the all-solid-state battery 100 includes a positive electrode 110, a solid electrolyte layer 120, and a negative electrode 130 in this order. The positive electrode 110 includes a positive electrode current collector 112 and a positive electrode composite layer 114. The negative electrode 130 includes a negative electrode material layer 132 and a negative electrode current collector 134. However, if the negative electrode is formed solely of metallic lithium, for example, the negative electrode material layer 132 and the negative electrode current collector 134 are provided integrally. Overall, the all-solid-state battery 100 is formed by stacking the positive electrode current collector 112, positive electrode composite layer 114, solid electrolyte layer 120, negative electrode material layer 132, and negative electrode current collector 134 in this order.

[0068] <3-1. Positive electrode> In the all-solid-state battery 100 according to this embodiment, the positive electrode 110 includes a positive electrode current collector 112 and a positive electrode active material layer 114 formed on one or both surfaces of the positive electrode current collector 112. The positive electrode active material layer 114 may be formed on the entire surface of the positive electrode current collector 112 or on only a portion of it.

[0069] <3-1-1. Positive electrode current collector> The positive electrode current collector 112 used in the positive electrode 110 is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel; aluminum; nickel; titanium; calcined carbon; or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. can be used as the positive electrode current collector 112.

[0070] The positive electrode current collector 112 may have a thickness of, for example, 3 μm to 500 μm. Fine irregularities can also be formed on the surface of the positive electrode current collector 112 to increase its adhesion to the positive electrode active material. The positive electrode current collector 112 may have various forms, such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0071] <3-1-2. Positive electrode active material layer> The positive electrode active material layer 114 may include the above-mentioned positive electrode mixture. In addition to the above-mentioned positive electrode mixture, the positive electrode active material layer 114 may also include a binder and any additives.

[0072] The thickness of the positive electrode active material layer 114 may be, for example, 1 μm or more and 500 μm or less, 5 μm or more and 250 μm or less, 10 μm or more and 200 μm or less, 20 μm or more and 150 μm or less, or 50 μm or more and 100 μm or less.

[0073] <3-1-3. Binder> The positive electrode active material layer 114 may further contain a binder. The binder is for ensuring adhesion between positive electrode active material particles or between positive electrode active material particles and the current collector. Any binder commonly used in the art can be used, and the type is not particularly limited. Examples of binders include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. These materials may be used individually or in mixtures of two or more.

[0074] The binder content may be, for example, 10% by mass or less, and preferably 0.1% to 5% by mass, based on the total mass of the positive electrode active material layer 114. When the binder content satisfies the above range, excellent electrode adhesion can be achieved while minimizing the increase in electrode resistance.

[0075] <3-2. Negative electrode> The negative electrode 130 may be composed of lithium metal alone, or it may include a negative electrode current collector 134 and a negative electrode active material layer 132 formed on one or both surfaces of the negative electrode current collector 134. The negative electrode active material layer 132 may be formed on the entire surface of the negative electrode current collector 134, or only on a portion of it.

[0076] <3-2-1. Negative electrode current collector> The negative electrode current collector 134 used in the negative electrode is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys may be used as the negative electrode current collector 134.

[0077] The negative electrode current collector 134 may have a thickness of 3 μm to 500 μm. Fine irregularities can also be formed on the surface of the negative electrode current collector 134 to increase its adhesion to the negative electrode active material. The negative electrode current collector 134 may have various forms, such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0078] <3-2-2. Negative electrode active material layer> The negative electrode active material layer 132 comprises a negative electrode active material and a solid electrolyte. The negative electrode active material layer 132 may optionally contain a conductive material, a binder, and other optional additives. The conductive material is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. The solid electrolyte and binder are the same as those described above and are therefore omitted here.

[0079] Examples of negative electrode active materials include lithium metal; lithium alloys; lithium metal composite oxides; lithium-containing titanium composite oxides (LTO); carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO2. v(0 < v < 2), SnO₂, vanadium oxide, lithium vanadate, Li x Fe₂O₃ (0 < x ≤ 1), Li x Metal oxides capable of lithium doping and undoping, such as WO₂ (0 < x ≤ 1); composites containing the above metallic compounds and carbonaceous materials, such as Si - C composites and Sn - C composites, etc. These may be used alone or as a mixture of two or more.

[0080] The negative electrode active material may be contained at 70% to 100% by mass, preferably 80% to 99% by mass, based on the total mass of the negative electrode active material layer 132. When the content of the electrode active material satisfies the above range, excellent energy density, electrode adhesion, and electrical conductivity can be realized.

[0081] <3 - 3. Solid electrolyte layer> The solid electrolyte layer 120 is disposed between the positive electrode 110 and the negative electrode 130 to mediate the transfer of lithium ions between the positive electrode active material and the negative electrode active material. The solid electrolyte layer 120 also functions as a separator layer that prevents short - circuiting between the electrodes by physically separating the positive electrode 110 and the negative electrode 130.

[0082] The solid electrolyte layer 120 is, for example, a layer formed of the same material as the solid electrolyte contained in the above positive electrode composite material. In this case, the solid electrolyte particles 12 are included in all of the positive electrode active material layer 114, the negative electrode active material layer 132, and the solid electrolyte layer 120. However, the solid electrolyte layer 120 may further contain another solid electrolyte or additive, or may be formed of another solid electrolyte.

[0083] <4. Manufacturing method of all - solid - state battery> The manufacturing method of the all - solid - state battery 100 is not particularly limited. For example, the all - solid - state battery 100 may be manufactured by sequentially putting the constituent materials of the battery into a cylindrical mold and pressing them. Alternatively, after separately molding each layer of the all - solid - state battery 100, the all - solid - state battery 100 may be manufactured by laminating and pressing these. Other arbitrary methods are available.

[0084] <5. Effects> With the positive electrode composite material described above, by using a first conductive material with high crystallinity and a second conductive material with low crystallinity in combination, an electron conduction network can be formed between the positive electrode active material particles and the positive electrode current collector, and between the positive electrode active material particles themselves. At the same time, by unevenly distributing the first conductive material, which easily decomposes solid electrolyte particles, near the positive electrode active material particles, the decomposition of solid electrolyte particles can be suppressed. This improves the charge / discharge efficiency and lifespan characteristics of the battery. [Examples]

[0085] Examples and comparative examples are described below, but the present invention is not limited thereto. Furthermore, the considerations described below are merely illustrative inferences to aid in understanding the invention and do not limit the present invention in any way.

[0086] <Manufacturing Example 1> (Manufacturing of positive electrode composite material) Positive electrode active material LiNi with an average particle size of approximately 5 μm 0.8 Co 0.1 Mn 0.1 To 100 parts by mass of O2 powder, an N-methylpyrrolidone (NMP) solution containing 0.1 parts by mass of single-walled carbon nanotubes (SWCNTs) as the first conductive material was added, and the mixture was mixed for 3 minutes in a rotation-orbit mixer (2000 rpm). The resulting slurry was dried at 130°C for 12 hours to obtain a cathode active material / SWCNT mixture.

[0087] 63 parts by mass of the obtained positive electrode active material / SWCNT mixture was mixed with 35 parts by mass of argyrodite-based solid electrolyte Li6PS5Cl powder. Then, 2 parts by mass of carbon nanofiber (CNF, average length 12 μm) was added as a second conductive material, and the mixture was homogenized in a mortar to obtain a positive electrode composite material.

[0088] (Manufacturing of all-solid-state batteries) A solid-state battery 100 was manufactured by stacking and compressing a positive electrode current collector (SUS plate) 112, a positive electrode composite layer 114, a sulfide-based solid electrolyte separator layer 120, a negative electrode Li metal layer 132, and a negative electrode current collector (SUS430 plate) 134 in the order shown in Figure 2.

[0089] <Manufacturing Example 2> All-solid-state battery 100 was manufactured in the same manner as in Manufacturing Example 1, except that the mass ratio of the positive electrode active material / SWCNT mixture, the argyrodite-based solid electrolyte, and the second conductive material (CNF) was set to 78:20:2.

[0090] <Manufacturing Example 3> A solid-state battery 100 was manufactured in the same manner as in Manufacturing Example 2, except that the amount of the first conductive material (SWCNT) added to 100 parts by mass of the positive electrode active material was 0.05 parts by mass.

[0091] <Manufacturing Example 4> A solid-state battery 100 was manufactured in the same manner as in Manufacturing Example 2, except that the amount of the first conductive material (SWCNT) added to 100 parts by mass of the positive electrode active material was 0.025 parts by mass.

[0092] <Manufacturing Example 5> All-solid-state battery 100 was manufactured in the same manner as in Manufacturing Example 1, except that the first conductive material (SWCNT) was not added.

[0093] <Manufacturing Example 6> All-solid-state battery 100 was manufactured in the same manner as in Manufacturing Example 1, except that a second conductive material (CNF) was not added. <Manufacturing Example 7> All-solid-state battery 100 was manufactured in the same manner as in Manufacturing Example 1, except that SuperP was used instead of CNF as the second conductive material. <Manufacturing Example 8> All-solid-state battery 100 was manufactured in the same manner as in manufacturing example 2, except that super P was used instead of CNF as the second conductive material. <Manufacturing Example 9> A positive electrode active material / first conductive material mixture was obtained by adding 1.6 parts by mass of super P instead of 0.1 parts by mass of SWCNT as the first conductive material, and an all-solid-state battery 100 was manufactured in the same manner as in Manufacturing Example 1, except that the amount of the second conductive material (CNF) added during the manufacturing of the positive electrode mixture was 1 part by mass.

[0094] The manufacturing conditions for manufacturing examples 1 to 9 are summarized in Table 1 below. All values ​​listed in Table 1 represent parts by mass.

[0095] [Table 1]

[0096] <Examples 1-7 and Comparative Examples 1-9> The all-solid-state batteries manufactured in Manufacturing Examples 1 to 9 were aged in a constant temperature bath maintained at 45°C or 60°C, with a maximum charge voltage of 4.25V and a minimum discharge voltage of 3V, at an initial charge rate of 0.05C and an initial discharge rate of 0.05C (calculated at 1C = 200mAh / g). Hereinafter, Examples 1 to 7 and Comparative Examples 1 to 9 are defined as follows, depending on the temperature of the constant temperature bath used for each manufacturing example and aging. (1) Examples 1-4: All-solid-state batteries manufactured in each of the manufacturing examples 1-4 were subjected to the above aging process in a constant temperature bath maintained at 45°C. (2) Examples 5-7: All-solid-state batteries manufactured in Manufacturing Examples 1-3 were subjected to the above aging process in a constant temperature bath maintained at 60°C. (3) Comparative Examples 1-2: All-solid-state batteries manufactured in Manufacturing Examples 5-6 were subjected to the above aging process in a constant temperature bath maintained at 45°C. (4) Comparative Example 3: The all-solid-state battery manufactured in Manufacturing Example 5 was subjected to the above aging process in a constant temperature bath maintained at 60°C. (5) Comparative Examples 4-6: All-solid-state batteries manufactured in Manufacturing Examples 7-9 were subjected to the above aging process in a constant temperature bath maintained at 45°C. (6) Comparative Examples 7-9: All-solid-state batteries manufactured in Manufacturing Examples 7-9 were subjected to the above aging process in a constant temperature bath maintained at 60°C.

[0097] <Evaluation Example 1: Battery Capacity and Rate Characteristics> For each of Examples 1-7 and Comparative Examples 1-9, the charge / discharge capacity during the initial charge / discharge process was calculated using the initial charge / discharge rates described above. The values ​​obtained by dividing the calculated charge / discharge capacity for each example and comparative example by the charge / discharge capacity (reference value) of Comparative Example 1 are defined as the "initial charge capacity" and "initial discharge capacity" using the following formulas.

number

number

number

[0098] The manufacturing example numbers corresponding to Examples 1-7 and Comparative Examples 1-9, the constant temperature chamber temperature in the battery characteristic evaluation test, and the initial charge / discharge capacity values ​​are shown in Tables 2-1 and 2-2 below. Here, the initial charge / discharge capacity values ​​are relative to Comparative Example 1 and are therefore dimensionless. [Table 2-1] [Table 2-2]

[0099] For each of Examples 1-7 and Comparative Examples 1-9, after aging, the charging current was fixed at 0.1C, and rate tests were performed by changing the discharge rate in the order of 0.1C → 0.2C → 0.33C → 0.5C → 1.0C. Figures 3 and 4 are graphs showing the change in discharge capacity with respect to the discharge rate for Examples 1-7 and Comparative Examples 1-9. The vertical axis in Figure 3 shows the measured value of the discharge capacity, and the vertical axis in Figure 4 shows the discharge capacity normalized for each example, with the discharge capacity at a rate of 0.1C set to 100% (this normalized discharge capacity is called the "rate characteristic"), in order to facilitate comparison of the change in discharge capacity for each example and comparative example.

[0100] <Evaluation Example 2: Scanning Electron Microscope (SEM)> The positive electrode composite material of Example 1 was observed using a scanning electron microscope (SEM). The measurement conditions were as follows: <Measurement conditions> • Equipment used: JSM-IT800 (manufactured by Rigaku Corporation) • Acceleration voltage: 1.0V

[0101] SEM observations revealed, as shown in Figure 1, relatively large positive electrode active material particles, relatively small solid electrolyte particles, relatively small tubular SWCNTs unevenly distributed near the positive electrode active material particles, and relatively large fibrous CNFs distributed throughout the entire positive electrode composite material.

[0102] <Evaluation Example 3: Micro-Raman Spectroscopy> The positive electrode composite material of Example 1 was observed using a Raman microscope. The measurement conditions were as follows: <Measurement conditions> ·Device used: RAMANTouch (manufactured by nano photon) ·Irradiation light wavelength: 532nm • Diffraction grating: 300g / mm Slit width: 50 μm • Objective lens: TU Plan Fluor x20 / NA 0.45 ·Irradiation time: 2s • Total number of times: 20 • Measurement mode: XY Averaging (AreaFlash)

[0103] Raman microscopy observations confirmed the presence of cathode active material particles, solid electrolyte particles, SWCNTs, and CNFs, as shown in Figure 1, similar to the SEM observation results in Evaluation Example 2.

[0104] Next, we measured the Raman spectrum in the region where relatively small fibrous particles were present but relatively large fibrous particles were absent, and the G band (1560 cm⁻¹) was measured. -1 ~1600cm -1 ) Maximum peak intensity I G and D band (1310cm) -1~1350cm -1 ) Maximum peak intensity I D The ratio (G / D ratio) was calculated. Similarly, Raman spectra were measured in areas where relatively large fibrous particles were present and relatively small fibrous particles were absent, and the G / D ratio was calculated. The values ​​normalized to the G band are shown below. Also, the 2D band (2600 cm) -1 ~2800cm -1 ) Maximum peak position and maximum peak intensity I 2D , and I G and I 2D The ratio (G / 2D ratio) is also shown. [Table 3] The G / D ratio was also confirmed to be approximately 1 for Super P used in Comparative Examples 4-9 using the method described above.

[0105] <Discussion of the evaluation results of the examples and comparative examples> The following discussion will examine the evaluation results mentioned above. However, the following discussion is merely a hypothesis at this point in time and does not theoretically restrict the present invention.

[0106] The difference between the above examples and comparative examples is whether or not the first conductive material and the second conductive material are used in combination. The initial charge-discharge capacities of Comparative Examples 1 and 3, which did not use the first conductive material (SWCNT), and Comparative Example 2, which did not use the second conductive material (CNF), were all inferior to those of Examples 1 to 7. Furthermore, the rate characteristics of Comparative Examples 1 to 3 were also inferior to those of Examples 1 to 7 in both the absolute value of the discharge capacity at each rate and the capacity retention rate with repeated rate tests.

[0107] In Comparative Examples 1 and 3, which lacked the first conductive material, the rate characteristics deteriorated drastically. It is presumed that with only CNF added as the second conductive material, the exchange of electrons between the positive electrode active material and the positive electrode current collector was insufficient compared to Examples 1-7, resulting in a significant decrease in the battery's charge / discharge capacity and severe performance degradation due to repeated charge / discharge cycles. On the other hand, in Comparative Example 2, which lacked the second conductive material, the battery's charge / discharge capacity decreased overall. It is presumed that with only the first conductive material distributed near the positive electrode active material, it was difficult to form electron conduction paths from the positive electrode active material located away from the current collector to the positive electrode active material near the current collector, preventing some of the positive electrode active material from participating in the charge / discharge reaction, leading to a decrease in charge / discharge capacity. In Comparative Examples 6 and 9, where Super P was used as the first conductive material, both the initial efficiency and rate characteristics deteriorated significantly. Compared to linear SWCNTs, Super P, which consists of spherical particles, forms conduction paths through point contact between particles. It is presumed that this point contact method of forming conduction paths is prone to deterioration of the conduction network. Furthermore, in high-rate charge-discharge, bottleneck phenomena occur not only in electron transport but also in ion diffusion. It is presumed that while SWCNTs rapidly supply electrons within the electrode, Super P, which forms conduction paths using a point contact method, does not adequately form electron supply paths. In Comparative Examples 4, 5, 7, and 8, where Super P was used as the second conductive material, both the initial efficiency and rate characteristics deteriorated compared to when CNF was used as the second conductive material. This is presumed to be because linear CNF forms an intertwined network, resulting in stable electron conduction paths even with temperature changes, while spherical Super P particles have a large surface area, increasing the reaction area with the solid electrolyte, and thus the adverse effects become even greater with increasing temperature. In particular, when Super P was used as the first or second conductive material, the initial efficiency deteriorated significantly in Comparative Examples 7, 8, and 9, which were aged in a constant temperature bath maintained at 60°C. This is presumed to be because Super P, being spherical particles, has a large surface area, increasing the reaction area with the solid electrolyte, and the adverse effects become even greater as the temperature rises. [Explanation of Symbols]

[0108] 10 Positive electrode active material particles 12 Solid electrolyte particles 14. First conductive material 16. Second conductive material 100 solid state battery 112 Positive electrode current collector 114 Positive electrode composite layer 120 Solid electrolyte layer 132 Negative electrode material layer 134 Negative electrode current collector

Claims

1. A positive electrode composite material for all-solid-state batteries, It comprises a positive electrode active material, a solid electrolyte, a first conductive material, and a second conductive material having lower crystallinity than the first conductive material. The first conductive material is distributed in large quantities near the positive electrode active material. Cathode composite material.

2. The first conductive material includes a linear carbon material, The positive electrode composite material according to claim 1.

3. The second conductive material includes a linear carbon material. The positive electrode composite material according to claim 1.

4. The first conductive material contains carbon nanotubes, The positive electrode composite material according to claim 1.

5. The second conductive material contains carbon nanofibers, The positive electrode composite material according to claim 1.

6. The first conductive material and the second conductive material are both carbon materials. In the Raman spectrum, 1560 cm⁻¹ －１ ~1600cm －１ The maximum peak intensity within the range is I Ｇ , 1310cm －１ ~1350cm －１ The maximum peak intensity within the range is I Ｄ In this case, the G / D ratio of the first conductive material (I Ｇ / I Ｄ ) is greater than the G / D ratio of the second conductive material. The positive electrode composite material according to claim 1.

7. The G / D ratio of the first conductive material is 5 or more and 100 or less when a diffraction grating of 300 gr / mm is used. The positive electrode composite material according to claim 6.

8. The first conductive material is included in the positive electrode composite material in an amount of 0.01% by mass or more and 1% by mass or less, based on the total mass of the positive electrode active material. The positive electrode composite material according to claim 1.

9. The second conductive material is included in the positive electrode composite material in an amount of 0.1% by mass or more and 5% by mass or less, based on the total mass of the positive electrode composite material. The positive electrode composite material according to claim 1.

10. The second conductive material is distributed substantially homogeneously with respect to the positive electrode active material. The positive electrode composite material according to claim 1.

11. The abundance of the first conductive material in the first region near the positive electrode active material is greater than the abundance of the first conductive material in the second region outside the first region. The positive electrode composite material according to claim 1.

12. The abundance of the second conductive material in the second region outside the first region near the positive electrode active material is greater than the abundance of the first conductive material in the second region. The positive electrode composite material according to claim 1.

13. A positive electrode comprising the positive electrode composite material according to any one of claims 1 to 12.

14. A solid-state battery comprising the positive electrode described in claim 13.

15. A method for manufacturing a positive electrode composite material, The steps include: preparing a positive electrode active material / first conductive material mixture by mixing a positive electrode active material and a first conductive material; The steps include mixing the positive electrode active material / first conductive material mixture, a solid electrolyte, and a second conductive material having lower crystallinity than the first conductive material, Methods that include...

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