Positive electrode composite active material, lithium ion secondary battery, composite active material, method for manufacturing positive electrode composite active material, and method for manufacturing lithium ion secondary battery

Abstract

To provide a positive electrode composite active material, a lithium ion secondary battery, a manufacturing method of a positive electrode composite active material, a manufacturing method of a lithium ion secondary battery, and a composite active material that can suppress the generation of gas due to oxidative decomposition of a non-aqueous electrolytic solution more than before.SOLUTION: A positive electrode composite active material includes a positive electrode active material and an oxide-based solid electrolyte, and the positive electrode active material is coated with an oxide-based solid electrolyte, and the oxide-based solid electrolyte is represented by Li1+p+q+rAlpGaq(Ti,Ge)2-p-qSirP3-rO12(0<p≤1, 0≤q<1, and 0≤r≤1), and the oxide-based solid electrolyte is layered and has a coating thickness of 5 nm or more and 50 nm or less. In the oxide-based solid electrolyte, an amorphous portion and a crystalline portion are mixed, and the amorphous portion is configured to be in contact with the positive electrode active material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode composite active material, a lithium ion secondary battery, and a composite active material. More specifically, the present invention relates to a positive electrode composite active material, a lithium ion secondary battery, and a composite active material that suppress gas generation during operation at high potential. [Background technology]

[0002] Research and development of lithium-ion secondary batteries is actively being conducted for a wide range of applications, including portable devices, hybrid vehicles, electric vehicles, and home energy storage. Lithium-ion secondary batteries used in these fields are required to have high safety, long-term cycle stability, and high energy density.

[0003] In recent years, lithium-ion secondary batteries using lithium titanate (LTO) as the negative electrode active material have been proposed from the viewpoints of high safety and long-term cycle stability. The operating potential of lithium titanate is higher than that of graphite, a common negative electrode active material, making lithium deposition less likely to occur and improving safety, but this is disadvantageous from the viewpoint of energy density. On the other hand, with regard to the positive electrode active material, a material that operates at a high potential of 4.5 V or more relative to the deposition potential of Li has been proposed (for example, Patent Document 1).

[0004] The reduction in energy density caused by the high operating potential of lithium titanate is expected to be improved by combining it with a positive electrode active material that operates at a high potential, as shown in Patent Document 1. On the other hand, in conventional lithium-ion secondary batteries that use graphite as the negative electrode active material, gas is generated by oxidative decomposition of the liquid non-aqueous electrolyte on the surface of the positive electrode active material, but the problem of gas generation becomes more pronounced in secondary batteries that have a higher operating potential of the positive electrode active material than conventional secondary batteries.

[0005] Furthermore, in conventional lithium ion secondary batteries, an additive is added to the non-aqueous electrolyte to form a coating on the surface of the positive electrode, thereby suppressing gas generation. However, although the same principle can be applied to the formation of a coating on the positive electrode surface for a high-potential positive electrode active material, the coating needs to have higher oxidation resistance, and therefore the effect is thought to be insufficient. Another related document is Patent Document 2. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-185148 [Patent Document 2] International Publication No. 2020 / 049843 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the above-mentioned conventional techniques still have room for improvement in terms of suppressing gas generation when a high-potential positive electrode active material is used.

[0008] Therefore, an object of the present invention is to provide a positive electrode composite active material, a lithium ion secondary battery, a composite active material, a method for manufacturing a positive electrode composite active material, and a method for manufacturing a lithium ion secondary battery, which can suppress gas generation due to oxidative decomposition of a non-aqueous electrolyte more than conventional methods. [Means for solving the problem]

[0009] In view of the above-mentioned problems, the present inventors have investigated means for suppressing the gas generation. That is, recent research has shown that even solid electrolytes exhibit conductivity similar to that of liquid electrolytes. Because solid electrolytes are structurally stable, their crystalline structure is not easily destroyed even at high potentials, and gas generation is also difficult. Therefore, as in Patent Document 2, it is believed that by covering the surface of the positive electrode active material with a solid electrolyte and not directly exposing the surface of the positive electrode active material to the non-aqueous electrolyte, it is possible to suppress the generation of gas due to decomposition of the non-aqueous electrolyte by the positive electrode active material. When attempting to trial-produce a positive electrode composite active material following Patent Document 2, it was found that when the thickness of the solid electrolyte increases, although the amount of gas generation can be suppressed, the resistance of the positive electrode composite active material increases significantly due to the presence of the solid electrolyte. On the other hand, when the thickness of the solid electrolyte is decreased, although the increase in resistance of the positive electrode composite active material due to the presence of the solid electrolyte becomes smaller, the gas generation suppression effect also tends to become smaller. Therefore, when examining by changing the thickness of the solid electrolyte, it was discovered that by satisfying (1) covering the positive electrode active material in layers with the solid electrolyte, (2) being within a certain thickness range, and (3) having a mixture of a crystalline part with a maintained crystal structure and an amorphous part with a disrupted crystal structure, where the amorphous part is in contact with the positive electrode active material, it is possible to suppress both the decrease in conductivity due to the solid electrolyte and gas generation.

[0010] One aspect of the present invention derived from the above findings is a positive electrode composite active material that constitutes a part of the positive electrode of a lithium-ion secondary battery using a non-aqueous electrolyte, having a positive electrode active material and an oxide-based solid electrolyte, wherein the positive electrode active material is coated with the oxide-based solid electrolyte, and the oxide-based solid electrolyte is 1+p+q+r Al p Ga q (Ti,Ge) 2-p-q Si r P 3-r O 12 (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1), and the oxide-based solid electrolyte is layered with a coating thickness of 5 nm or more and less than or equal to 50 nm. The oxide-based solid electrolyte has a mixture of an amorphous part and a crystalline part, and the amorphous part is in contact with the positive electrode active material.

[0011] The "amorphous part" referred to here is an amorphous part where the crystal structure is not maintained. For example, it refers to a part where regularly arranged lattice fringes cannot be seen when observed under a transmission electron microscope at a magnification of 500,000 times. The "crystalline part" referred to here is a part where the crystal structure is maintained. For example, it refers to a part where regularly arranged lattice fringes can be seen when observed under a transmission electron microscope at a magnification of 500,000 times.

[0012] According to this aspect, since the oxide-based solid electrolyte is coated in layers on the surface of the positive electrode active material, even when used as the positive electrode active material of a lithium-ion secondary battery using a non-aqueous electrolyte solution as the non-aqueous electrolyte, the non-aqueous electrolyte solution is not exposed to the positive electrode active material, and generation of gas due to oxidative decomposition of the non-aqueous electrolyte solution by the positive electrode active material can be suppressed. According to this aspect, as the oxide-based solid electrolyte, Li 1+p+q+r Al p Ga q (Ti,Ge) 2-p-q Si r P 3-r O 12 (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1) (hereinafter, also simply referred to as LATP) is used, and the oxide-based solid electrolyte has a coating thickness of 5 nm or more and 50 nm or less. Therefore, the resistance is small and resistance loss due to the oxide-based solid electrolyte can be suppressed. According to this aspect, the oxide-based solid electrolyte is layered, and an amorphous part and a crystalline part are mixed in the layer, and the amorphous part is in contact with the positive electrode active material. Therefore, both lithium ion conductivity and gas generation suppression effect can be exhibited.

[0013] Here, based on the above-described findings, LATP was coated on the surface of the positive electrode active material operating at a high potential under various conditions and further examined. As a result, it was discovered that when the integrated intensity ratio of the peak of the 4-fold coordination is 5% or less at the peak corresponding to Al (aluminum) when LATP is measured by solid NMR, gas generation due to oxidative decomposition of the non-aqueous electrolyte can be dramatically suppressed.

[0014] A preferable aspect derived from the above findings is that the integrated intensity ratio of the peak of the 4-fold coordination to the total peak area at the Al peak measured by solid NMR of the oxide-based solid electrolyte is 1% or more and 5% or less.

[0015] Also, it was discovered that when LATP was measured by solid-state NMR, gas generation could be dramatically suppressed when the peak top of the peak corresponding to P (phosphorus) was present at 0 to -20 ppm and the integrated intensity ratio of the peak was 50% or more with respect to the total peak area.

[0016] A preferred aspect derived from the above discovery is that the oxide-based solid electrolyte has an integrated intensity ratio of the peak at 0 to -20 ppm with respect to the total peak area in the P peak measured by solid-state NMR of 50% or more.

[0017] A preferred aspect is that the oxide-based solid electrolyte has an average particle size of 10 nm or less, and the cathode active material has a median diameter of 5 μm or more.

[0018] According to this aspect, since the particle size of the oxide-based solid electrolyte is extremely small compared to the particle size of the cathode active material, the oxide-based solid electrolyte forms a continuous layer that densely covers the surface shape of the cathode active material. Therefore, it is difficult for the non-aqueous electrolyte to directly contact the cathode active material, and the gas generation suppression effect is high.

[0019] A preferred aspect is that the cathode active material is a lithium ion conductive active material having an operating potential of 4.5 V (vs. Li / Li + ).

[0020] According to this aspect, even when a cathode active material having a high operating potential of 4.5 V is used, the generation of gas due to the decomposition of the non-aqueous electrolyte can be suppressed.

[0021] A preferred aspect is that the cathode active material is a substituted lithium manganese compound represented by the following formula (la). Li 1+x M y Mn 2-x-y O4···(1) In the formula (1), x and y each satisfy 0 ≤ x ≤ 0.2 and 0 < y ≤ 0.8, and M is at least one selected from the group consisting of Al, Mg, Zn, Ni, Co, Fe, Ti, Cu, and Cr.

[0022] According to this aspect, since a substituted lithium manganese compound is used as the positive electrode active material, it is more stable and has a wider potential window than conventional positive electrode active materials such as lithium cobalt oxide.

[0023] One aspect of the present invention is a method for producing the above-mentioned cathode composite active material, which includes an electrolyte dispersion forming step of dispersing an oxide-based solid electrolyte in a dispersion solvent to form an electrolyte dispersion, a ground material forming step of grinding the electrolyte dispersion into the cathode active material to form a ground material, and a removal step of removing the dispersion solvent from the ground material.

[0024] According to this aspect, the surface of the positive electrode active material is easily coated with the oxide-based solid electrolyte.

[0025] In a preferred aspect, the removal step involves heat treatment at 300° C. or higher to remove the dispersion solvent.

[0026] In a preferred aspect, the method includes a pulverization step of pulverizing the oxide-based solid electrolyte to an average particle size of 10 nm or less, prior to the electrolyte dispersion formation step.

[0027] When the oxide-based solid electrolyte is coated on the surface of a positive electrode active material, the oxide-based solid electrolyte must be pulverized to a BET specific surface area equivalent diameter of 100 nm or less. Methods for pulverizing oxide-based solid electrolytes include wet pulverization and dry pulverization, with wet pulverization having the advantage of being able to pulverize to smaller particle sizes than dry pulverization. On the other hand, in the case of wet pulverization, it is necessary to disperse the oxide-based solid electrolyte in a volatile solvent, pulverize it into a powder, and then volatilize the volatile solvent to extract the oxide-based solid electrolyte as a powder. Furthermore, if the volatile solvent is heated to accelerate the volatilization, the particles of the oxide-based solid electrolyte will aggregate, which will cause a problem of variations when the oxide-based solid electrolyte is coated on the surface of the positive electrode active material in a subsequent step.

[0028] Therefore, in a preferred aspect, in the electrolyte dispersion forming step, the oxide-based solid electrolyte is dispersed in the dispersion solvent while being pulverized to an average particle size of 10 nm or less.

[0029] According to this aspect, the oxide-based solid electrolyte is pulverized and dispersed in the dispersion solution simultaneously in the electrolyte dispersion formation step, so that aggregation of the oxide-based solid electrolyte is unlikely to occur in the milled product formation step, and variation in the coating of the oxide-based solid electrolyte on the surface of the positive electrode active material is unlikely to occur.

[0030] One aspect of the present invention is a lithium ion secondary battery having a positive electrode containing the above-described positive electrode composite active material, a negative electrode, and a non-aqueous electrolyte.

[0031] According to this aspect, even when a non-aqueous electrolyte is used, generation of gas in the non-aqueous electrolyte can be suppressed.

[0032] In a preferred aspect, the negative electrode has a negative electrode active material including lithium titanate.

[0033] One aspect of the present invention is a method for manufacturing a lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, the method including a positive electrode coating step of coating a positive electrode current collector with a positive electrode mixture containing the above-described positive electrode composite active material.

[0034] According to this aspect, it is easy to manufacture a lithium ion secondary battery.

[0035] One aspect of the present invention is a cathode composite active material that constitutes a part of a cathode of a lithium ion secondary battery, the cathode composite active material having a cathode active material and an oxide-based solid electrolyte, the cathode active material being coated with the oxide-based solid electrolyte, and the oxide-based solid electrolyte being a Li 1+p+q+r Al p Ga q (Ti,Ge) 2-p-q Si r P 3-r O 12It is represented by (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1), and the oxide-based solid electrolyte is a positive electrode composite active material in which the peak intensity ratio of the four-coordinated peak in the Al peak measured by solid NMR is 1% or more and 5% or less.

[0036] According to this aspect, the generation of gas due to the oxidative decomposition of the non-aqueous electrolyte can be suppressed more effectively than before.

[0037] One aspect of the present invention is a composite active material that constitutes a part of an electrode of a lithium-ion secondary battery using a non-aqueous electrolyte, which has an active material and an oxide-based solid electrolyte, the active material is coated with the oxide-based solid electrolyte, and the oxide-based solid electrolyte is Li 1+p+q+r Al p Ga q (Ti, Ge) 2-p-q Si r P 3-r O 12 It is represented by (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1), the oxide-based solid electrolyte is layered with a coating thickness of 5 nm or more and 50 nm or less, the oxide-based solid electrolyte has an amorphous part and a crystalline part mixed, and the amorphous part is in contact with the active material.

[0038] According to this aspect, even when used as an active material of a lithium-ion secondary battery using a non-aqueous electrolyte solution as the non-aqueous electrolyte, the non-aqueous electrolyte solution is not exposed to the active material, and the generation of gas due to the oxidative decomposition of the non-aqueous electrolyte solution by the positive electrode active material can be suppressed. According to this aspect, the resistance is small and the resistance loss due to the oxide-based solid electrolyte can be suppressed. According to this aspect, both lithium ion conductivity and gas generation suppression effect can be exhibited.

Advantages of the Invention

[0039] According to the present invention, even when a positive electrode active material that operates at a high potential is used, the generation of gas due to the oxidative decomposition of the non-aqueous electrolyte can be suppressed more effectively than before.

Brief Description of the Drawings

[0040] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium ion secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing the P peak measured by solid-state NMR in Experimental Example 8. [Figure 3] FIG. 10 is a diagram showing the P peak measured by solid-state NMR in Experimental Example 9. [Figure 4] FIG. 10 is a diagram showing the P peak measured by solid-state NMR in Experimental Example 10. [Figure 5] 10 is a transmission electron microscope image of the vicinity of the interface between LNMO and LATP in Experimental Example 12. [Figure 6] This is a transmission electron microscope image of an enlarged region A in FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0041] A lithium ion secondary battery 1 according to one embodiment of the present invention will be described below, but the present invention is not limited to this. As shown in FIG. 1, the lithium ion secondary battery 1 includes a positive electrode 2, a negative electrode 3, a non-aqueous electrolyte 5, and a separator 6, and an external load 7 is connected to the positive electrode 2 and the negative electrode 3. The positive electrode 2 is formed by laminating a positive electrode composite active material layer 11 containing a positive electrode composite active material 20 on a positive electrode current collector 10 . The negative electrode 3 is formed by laminating a negative electrode active material layer 13 containing a negative electrode active material 21 on a negative electrode current collector 12 .

[0042] The positive electrode composite active material 20 is a coated positive electrode active material in which the surface of a positive electrode active material 30 is coated with an oxide-based solid electrolyte 31 (hereinafter also simply referred to as solid electrolyte 31).

[0043] Generally, lithium ion secondary batteries use non-aqueous electrolytes, which are fluid non-aqueous electrolytes 5 (nonaqueous electrolyte solutions) in which lithium salts are dissolved in a non-aqueous solvent. On the other hand, there are solid electrolytes in a solid state that combine the functions of both a non-aqueous solvent and a lithium salt. Solid electrolytes have higher oxidation resistance than liquid non-aqueous electrolytes, so oxidative decomposition at high potentials is suppressed. However, because lithium ion conductivity is lower in the solid state than in the liquid state, replacing the entire electrolyte with a solid electrolyte significantly reduces battery performance.

[0044] Therefore, in the positive electrode composite active material 20 of this embodiment, gas generation can be suppressed even if the non-aqueous electrolyte is the conventional one by coating only the surface of the high-potential positive electrode active material 30 with the solid electrolyte 31. That is, the lithium ion secondary battery 1 exhibits the gas generation suppression effect even when the liquid non-aqueous electrolyte 5 is used as the non-aqueous electrolyte.

[0045] The method for coating the solid electrolyte 31 is not particularly limited, but a method that allows for uniform coating, such as spray coating or mechanical coating, is preferred. Spray coating is preferred because the solid electrolyte 31 is dispersed in a solvent, which provides adhesiveness and ductility, allowing for uniform coating. Furthermore, when volatilizing the solvent by heat treatment, the heat treatment temperature is adjusted, and preferably the particle size of the solid electrolyte 31 and the mixing ratio with the positive electrode active material 30 are controlled. This allows the solid electrolyte 31 to coat the positive electrode active material 30 without substantially increasing the resistance of the positive electrode active material 30 and without degrading battery performance.

[0046] The solid electrolyte 31 contains aluminum as an element, and is an oxide-based solid electrolyte in consideration of chemical stability. The oxide-based solid electrolyte used for the solid electrolyte 31 may be an antifluorite type, a NASICON type, a perovskite type, a garnet type, or the like, depending on the crystal structure, but is not particularly limited. The oxide-based solid electrolyte used for the solid electrolyte 31 is, for example, solid electrolyte Li 1+p+q+r Al p Gaq (Ti, Ge) 2-p-q Si r P 3-r O 12 (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1) (hereinafter also referred to as LATP) can be used, particularly Li 1+p Al p Ti 2-p P3O 12 (0 ≤ p ≤ 1) is preferred. Since the solid electrolyte 31 is in a solid state, a certain amount of significant energy is required to coat the solid positive electrode active material 30. Therefore, the method of coating the positive electrode active material 30 with the solid electrolyte 31 preferably uses a mechanical coating method using a mechanochemical method that can apply shear force and compressive force. By coating the positive electrode active material 30 with the solid electrolyte 31, the contact between the liquid non-aqueous electrolyte 5 and the positive electrode active material 30 can be reduced, and gas generation can be suppressed, similar to the conventional non-aqueous electrolyte. Furthermore, similar to spray coating, the heat treatment temperature is adjusted, and preferably, the particle size of the solid electrolyte 31 and the mixing ratio with the positive electrode active material 30 are controlled. By doing so, the solid electrolyte 31 can be coated on the positive electrode active material 30 without substantially increasing the resistance of the positive electrode active material 30 and without degrading the battery performance.

[0047] Regardless of the coating method, in the positive electrode composite active material 20, the area of contact with the non-aqueous electrolyte 5 serving as the electrolyte solution is reduced due to the uniform coating of the positive electrode active material 30 with the solid electrolyte 31, and gas generation is suppressed. Also, even when a part of the non-aqueous electrolyte 5 serving as the electrolyte solution and the additive decompose, the decomposition products fill the gaps in the coating of the solid electrolyte 31 to form a good film, making it possible to further suppress the decomposition of the electrolyte solution.

[0048] The evaluation of the solid electrolyte 31 in the positive electrode composite active material 20 can be evaluated by solid NMR measurement. <00ness="1">The evaluation of the solid electrolyte 31 in the positive electrode composite active material 20 can be, for example 27 evaluated by the spectrum of Al-NMR and 31 the spectrum of P-NMR. In order to exhibit good battery characteristics, the positive electrode composite active material 20 needs to be coated with the positive electrode active material 30 without the decomposition of the solid electrolyte 31.

[0049] Here, the solid electrolyte Li 1+p+q+r Al p Ga q (Ti,Ge) 2-p-q Si r P 3-r O 12 (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1), aluminum is usually 6 - coordinated with respect to oxygen, but when it decomposes to form AlPO4, it becomes 4 - coordinated.

[0050] When pulverization is performed to promote crystal structure destruction, the amount of 4 - coordinated aluminum increases. When it is micronized to about 1 / 30 of the particle size and the particle surface decomposes, more than 20% of the original volume decomposes, and it is considered that the 4 - coordination of Al becomes more than 20% of the whole. On the other hand, by pulverizing so as to suppress crystal structure destruction, it becomes possible to suppress the generation of 4 - coordinated Al.

[0051] When the coordination number of aluminum changes, the peak position of the solid 27 Al - NMR spectrum changes, so it becomes possible to evaluate the degree of decomposition of the solid electrolyte 31. The ratio of 4 - coordination in the total peak intensity of the aluminum spectrum is 1% or more and 5% or less, more preferably 2% or more and 5% or less. In such a case, gas generation can be suppressed. That is, the solid electrolyte 31 is solid 27 In the Al - NMR spectrum, the area of the maximum peak (the peak attributed to 4 - coordination) in the range of 30 ppm to 50 ppm with respect to the total peak area is preferably 0.01 or more and 0.05 or less, and more preferably 0.02 or more and 0.05 or less. The solid electrolyte 31 is solid 27In the Al-NMR spectrum, it is preferable that the ratio of the area of the maximum peak in the range of -30 ppm to 5 ppm (the area of the peak attributed to six coordination) to the area of the maximum peak in the range of 30 ppm to 50 ppm (the area of the peak attributed to four coordination) is 85 or more and 95 or less.

[0052] Also, for the solid electrolyte Li 1+p+q+r Al p Ga q (Ti, Ge) 2-p-q Si r P 3-r O 12 (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1), phosphorus usually only takes a single bonded state, and only peaks with peak tops at a chemical shift of -20 to -30 ppm are observed. On the other hand, when micronized, the bonding state due to micronization, particularly the atoms bonded to oxygen bonded to phosphorus, changes, and peaks with peak tops at -20 to 0 ppm are mixed or only such peaks are observed. When the ratio of the integrated intensity of the peaks at -20 to 0 ppm in the total peak intensity of the phosphorus spectrum is 50% or more and 1 hundred% or less, more preferably 70% or more and 1 hundred% or less, gas generation can be effectively suppressed.

[0053] <Spray coating method> Spray coating means that the base material is wetted by the mist of the spray liquid containing the coating agent sprayed from the spray nozzle, and at the same time, the solid components contained in the spray liquid adhere to the surface of the base material, dry and solidify, and a coating layer is formed on the surface of the base material. [[ID=二十九]] In the present invention, the positive electrode active material 30 corresponds to the base material, and the coating agent corresponds to the solid electrolyte 31. The apparatus to be used is not particularly limited, but for example, a fluidized bed coating apparatus, a centrifugal rolling type coating apparatus, or a rolling fluidized bed coating apparatus can be preferably used.

[0054] The solvent used in the spray coating process is not particularly limited, and water or an organic solvent can be used. Examples of the organic solvent include alcohols such as ethanol. Mixing a polymer material, such as polyethylene glycol or polyvinyl alcohol, into the solvent can prevent the solid electrolyte 31 from aggregating, enabling the solid electrolyte 31 to be uniformly coated on the surface of the positive electrode active material 30. When the solid electrolyte 31 is dispersed in a solvent and spray-coated in the form of a slurry, the concentration of the solid electrolyte 31 in the slurry is, for example, 10 to 25% by mass.

[0055] The treatment temperature for spray coating is preferably 5 to 100°C, more preferably 8 to 80°C, and even more preferably 10 to 50°C. The treatment time depends on the size of the apparatus, but is preferably 5 to 90 minutes, more preferably 10 to 60 minutes. The treatment atmosphere is not particularly limited, and may be an inert gas atmosphere or an air atmosphere.

[0056] <Mechanical coating method> The mechanical coating method refers to a means of applying at least one type of energy from shear force, compression force, collision force, and centrifugal force to the base material and / or coating agent (preferably, shear force and compression force can be applied, and more preferably, shear force, compression force, and collision force can be applied), while mechanically contacting the base material and coating agent, thereby mixing the base material and coating agent and applying the coating agent to the surface of the base material. In the positive electrode composite active material 20, the positive electrode active material 30 corresponds to the base material, and the coating material corresponds to the solid electrolyte 31. The device to be used is not particularly limited, but for example, a grinding mill such as Nobilta manufactured by Hosokawa Micron Corporation or a planetary ball mill (for example, manufactured by Fritsch) can be suitably used. Among these, the grinding mill is preferred from the viewpoints that it is easy to operate, does not require separation of the balls after treatment as in a ball mill, coating proceeds preferentially over particle aggregation, and surface smoothness can be easily obtained.

[0057] In the method for producing the cathode composite active material 20 of this embodiment, a cylindrical container with a bottom and a rotor with tip blades are provided, and the rotor is rotated with a predetermined clearance between the tip blades and the inner periphery of the container. In this way, it is preferable to apply compressive force and shear force to the mixture containing the cathode active material 30 and the solid electrolyte 31, thereby performing mechanical coating.

[0058] The treatment by the mechanical coating method may be a dry method or a wet method. In the case of a wet method, the solvent used is not particularly limited, and water or an organic solvent can be used. As the organic solvent, for example, an alcohol such as ethanol can be used. In the case of a wet method, the timing of adding the solvent is not particularly limited, but the solid electrolyte 31 may be dispersed in a solvent and used in the mechanical coating method in the form of a slurry. The concentration of the solid electrolyte 31 in the slurry is, for example, 10 to 30 wt %, preferably 15 to 30 wt %, and more preferably 15 to 25 wt %.

[0059] The treatment temperature for mechanical coating is preferably 5 to 100°C, more preferably 8 to 80°C, and even more preferably 10 to 50°C. The treatment time for the mechanical coating is preferably 5 to 90 minutes, more preferably 10 to 60 minutes. The atmosphere in which the mechanical coating is carried out is not particularly limited, and may be an inert gas atmosphere or an air atmosphere.

[0060] Although it is possible to use the sample as it is after spray coating or mechanical coating, it is preferable to perform a heat treatment. This improves the adhesion between the positive electrode active material 30 and the solid electrolyte 31, preventing the solid electrolyte 31 from peeling off from the positive electrode active material 30 even after repeated charge and discharge, improving the long-term reliability of the battery.

[0061] <Cathode active material> The positive electrode active material 30 of this embodiment has an average potential of lithium deintercalation and intercalation of Li + / Li, i.e., with respect to the deposition potential of Li (vs. Li+ It is preferably a lithium ion conductive active material that is 4.5V or more and 5.0V or less (also shown as / Li). The positive electrode active material 30 preferably has an operating potential of 4.5V or more and 5.0V or less based on lithium metal alone. The potential of the lithium ion insertion / desorption reaction (hereinafter also referred to as voltage) (vs. Li + / Li) can be obtained, for example, by measuring the charge-discharge characteristics of a half-cell with an operating electrode using the positive electrode active material 30 and a lithium metal as a counter electrode, and reading the voltage values at the start and end of the plateau. When there are two or more plateaus, it is sufficient if the plateau with the lowest voltage value is 4.5V (vs. Li + / Li) or more, and it is sufficient if the plateau with the highest voltage value is 5.0V (vs. Li + / Li) or less.

[0062] The positive electrode active material 30 is not particularly limited as long as the insertion / desorption reaction of lithium ions proceeds at 4.5V or more and 5.0V or less with respect to the deposition potential of Li, but a substituted lithium manganese compound represented by the following formula (1) is preferable. Li 1+x M y Mn 2-x-y O4 ···(1) In the above formula (1), x and y each satisfy 0≦x≦0.2 and 0<y≦0.8, and M is at least one selected from the group consisting of Al, Mg, Zn, Ni, Co, Fe, Ti, Cu, and Cr.

[0063] Among the above formula (1), a Ni-substituted lithium manganese compound (LNMO) in which M is Ni is preferable, and particularly preferably x = 0, y = 0.5, and M = Ni, that is, LiNi 0.5 Mn 1.5 O4 is particularly preferable because of its high stability effect on the charge-discharge cycle.

[0064] The particle size of the positive electrode active material 30 is not particularly limited, but if the particle size is too small, the difference with the particle size of the solid electrolyte 31 described below becomes small, making coating difficult. Therefore, the median diameter d50 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. The median diameter d50 of the positive electrode active material 30 is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 50 μm or less, and particularly preferably 30 μm or less. Taking into consideration the thickness range when processing into an electrode, the median diameter d50 of the positive electrode active material 30 is preferably 10 μm or more, and more preferably 20 μm or more.

[0065] <Solid electrolyte 31> In order to uniformly coat the surface of the positive electrode active material 30, the particle size of the solid electrolyte 31 in this embodiment is preferably micronized to a BET specific surface area equivalent diameter (dBET) of 10 nm or less, more preferably 8 nm or less, and even more preferably 6 nm or less. Furthermore, the particle size of the solid electrolyte 31 is preferably such that the average particle size calculated using small-angle X-ray scattering is 10 nm or less. As a method for microparticulation treatment, known means such as a ball mill, a bead mill, etc. can be used. The BET specific surface area equivalent diameter (dBET) is a particle size calculated by determining the nitrogen adsorption BET specific surface area by the single-point nitrogen adsorption method according to the method specified in JIS Z8830 (2013), and then using the formula dBET = 6 / (density × BET specific surface area).

[0066] The ratio of the median diameter d50 of the positive electrode active material 30 to the BET specific surface area equivalent diameter dBET of the solid electrolyte 31 is preferably 10000:1 to 50:1, more preferably 5000:1 to 100:1, still more preferably 2000:1 to 500:1, and particularly preferably 1000:1 to 100:1. The difference between the median diameter d50 of the positive electrode active material 30 and the BET specific surface area equivalent diameter (dBET) of the solid electrolyte 31 is preferably as large as possible. If the difference is small, aggregation of the solid electrolytes 31 themselves or the formation of aggregates between the positive electrode active material 30 and the solid electrolyte 31 may become dominant over the coating of the solid electrolyte 31 on the positive electrode active material 30, and the desired effect may not be achieved.

[0067] The ratio of the solid electrolyte 31 (solid content when used as a slurry) to 100 parts by mass of the positive electrode active material 30 is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 4 parts by mass or less. The ratio is preferably 1 part by mass or more and 5 parts by mass or less (i.e., the mass ratio of the positive electrode active material 30 to the solid electrolyte 31 is 100:1 to 20:1), and also preferably 2 parts by mass or more and 4 parts by mass or less (i.e., the mass ratio of the positive electrode active material 30 to the solid electrolyte 31 is 50:1 to 25:1).

[0068] To coat the surface of the positive electrode active material 30 with an oxide-based solid electrolyte by a mechanical coating method after a pulverization process (nanoparticle formation process) for microparticulating the solid electrolyte 31, which will be described later, it is necessary to prepare the solid electrolyte 31 in a state where it is dispersed in a dispersion solvent (alcohol solution). Ethanol is preferred as the alcohol from the viewpoints of volatility and safety, but a mixture of multiple alcohol solutions may also be used.

[0069] As shown in FIG. 1, the solid electrolyte 31 has an amorphous portion 40 and a crystalline portion 41. The amorphous portion 40 is an amorphous portion that does not substantially have a crystalline structure, and is a portion in which no lattice fringes of crystals are observed when observed with a transmission electron microscope (TEM). In other words, the amorphous portion 40 is a portion in which crystal destruction occurs during manufacturing and which does not have a crystalline structure. The crystalline portion 41 is a portion having a crystalline structure, and when observed with a TEM, the lattice fringes of regularly arranged crystals are clearly visible. In other words, the crystalline portion 41 is a portion where no crystal destruction occurred during manufacturing and where the crystalline structure is maintained. In a cross section passing through the positive electrode active material 30 and the solid electrolyte 31, the solid electrolyte 31 covering one particle of the positive electrode active material 30 has an amorphous portion 40 having a larger area than the crystalline portion 41, and the proportion of the area occupied by the crystalline portion 41 of the solid electrolyte 31 is preferably 5% or more and 30% or less.

[0070] <Lithium-ion secondary battery 1> As shown in FIG. 1, a lithium ion secondary battery 1 is composed of a positive electrode 2, a negative electrode 3, and a non-aqueous electrolyte 5. The positive electrode 2 is produced by applying a positive electrode mixture containing a positive electrode composite active material 20 (coated positive electrode active material), a conductive additive, a binder, and the like, to a positive electrode current collector 10. The positive electrode composite active material 20 is suitably used as the active material for the positive electrode 2 of the lithium ion secondary battery 1. The negative electrode 3 is produced by applying a negative electrode mixture containing a negative electrode active material 21, a conductive additive, a binder, and the like, to a negative electrode current collector 12. The positive electrode 2 can be formed by applying a positive electrode mixture to the positive electrode current collector 10 and then drying it at about 100 to 200°C. The negative electrode 3 can be formed by applying the negative electrode mixture to the negative electrode current collector 12 and then drying it at about 100 to 200°C.

[0071] The configuration of the lithium ion secondary battery 1 using the positive electrode composite active material 20, the materials used other than the positive electrode composite active material 20, and the manufacturing equipment and conditions for the lithium ion secondary battery 1 may be conventionally known and are not particularly limited.

[0072] <Negative electrode active material 21> As described above, lithium titanate is preferably used as the negative electrode active material 21, from the viewpoint of preventing lithium deposition and improving safety. Among lithium titanates, lithium titanate with a spinel structure is particularly preferred, since the active material undergoes small expansion and contraction during the lithium ion insertion and desorption reactions. Lithium titanate may contain trace amounts of elements other than lithium and titanium, such as Nb.

[0073] <Conductive additive> The conductive additive is not particularly limited, but is preferably a carbon material, such as natural graphite, artificial graphite, vapor-grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. These carbon materials may be used alone or in combination of two or more. The amount of the conductive additive contained in the positive electrode 2 is preferably 1 part by weight to 30 parts by weight, more preferably 2 parts by weight to 15 parts by weight, per 100 parts by weight of the positive electrode composite active material 20 . Within the above range, the conductivity of the positive electrode 2 can be ensured. In addition, the adhesiveness to the binder is maintained, and sufficient adhesiveness to the positive electrode current collector 10 can be obtained. The amount of the conductive additive contained in the negative electrode 3 is preferably 1 part by weight to 30 parts by weight, more preferably 2 parts by weight to 15 parts by weight, per 100 parts by weight of the negative electrode active material 21.

[0074] <Binder> The binder is not particularly limited, but for both the positive electrode 2 and the negative electrode 3, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof can be used. For ease of fabrication of the positive electrode 2 and the negative electrode 3, the binder is preferably dissolved or dispersed in a non-aqueous solvent or water. The non-aqueous solvent is not particularly limited, but examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, tetrahydrofuran, etc. A dispersant and a thickener may be added to these. The amount of binder contained in the positive electrode 2 is preferably 1 part by weight to 30 parts by weight, more preferably 2 parts by weight to 15 parts by weight, per 100 parts by weight of the positive electrode composite active material 20 . Within the above range, the adhesiveness between the positive electrode composite active material 20 and the conductive additive is maintained, and sufficient adhesiveness with the positive electrode current collector 10 can be obtained. The amount of binder contained in the negative electrode 3 is preferably 1 part by weight to 30 parts by weight, more preferably 2 parts by weight to 15 parts by weight, per 100 parts by weight of the negative electrode active material 21.

[0075] <Current collectors 10, 12> Both the positive electrode current collector 10 and the negative electrode current collector 12 are preferably made of aluminum or an aluminum alloy. Since aluminum or an aluminum alloy is stable in a positive electrode reaction atmosphere and a negative electrode reaction atmosphere, it is not particularly limited, but high purity aluminum represented by JIS standards 1030, 1050, 1085, 1N90, 1N99, etc. is preferred. The thickness of the current collectors 10 and 12 is not particularly limited, but is preferably 10 μm or more and 100 μm or less. Within this range, it is easy to balance the ease of handling during battery fabrication, cost, and the resulting battery characteristics. The current collectors 10 and 12 may also be made of metals other than aluminum (copper, SUS, nickel, titanium, and alloys thereof) coated with a metal that does not react with the potentials of the positive electrode 2 and the negative electrode 3.

[0076] <Non-aqueous electrolyte 5> The non-aqueous electrolyte 5 is not particularly limited, but may be a non-aqueous electrolytic solution in which a solute is dissolved in a non-aqueous solvent, or a gel electrolyte in which a polymer is impregnated with a non-aqueous electrolytic solution in which a solute is dissolved in a non-aqueous solvent.

[0077] The non-aqueous solvent preferably contains a cyclic aprotic solvent and / or a chain aprotic solvent. Examples of the cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones, and cyclic ethers. Examples of the chain aprotic solvent include chain carbonates, chain carboxylic acid esters, chain ethers, and acetonitrile, which are solvents commonly used as solvents for non-aqueous electrolytes. More specifically, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, sulfolane, dioxolane, and methyl propionate can be used. These solvents may be used alone or in combination of two or more. However, it is preferable to use a mixture of two or more solvents because of the ease of dissolving the solute and the high lithium ion conductivity described below.

[0078] When two or more types are mixed, a mixture of one or more types of chain carbonates exemplified by dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, and methyl propyl carbonate with one or more types of cyclic compounds exemplified by ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone is preferred, as this provides high stability at high temperatures and high lithium conductivity at low temperatures, and a mixture of one or more types of chain carbonates exemplified by dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate with one or more types of cyclic carbonates exemplified by ethylene carbonate, propylene carbonate, and butylene carbonate is particularly preferred.

[0079] The solute used in the non-aqueous electrolyte 5 is not particularly limited, but examples thereof include LiClO4, LiBF4, LiPF6, LiAsF6, LiCF3SO3, LiBOB (Lithium Bis(Oxalato)Borate), and LiN(SO2CF3)2, which are preferred because they are easily soluble in the solvent. The concentration of the solute contained in the non-aqueous electrolyte 5 is preferably 0.5 mol / L or more and 2.0 mol / L or less. If the solute concentration is less than 0.5 mol / L, the desired lithium ion conductivity may not be achieved, whereas if the solute concentration is more than 2.0 mol / L, the solute may not dissolve any further.

[0080] The amount of non-aqueous electrolyte 5 is not particularly limited, but is preferably 0.1 mL to 10 mL per 1 Ah of battery capacity. This amount ensures the conduction of lithium ions involved in the electrode reaction, and the desired battery performance is achieved.

[0081] When the non-aqueous electrolyte 5 has fluidity, it may be contained in the positive electrode 2, the negative electrode 3, and the separator 6 in advance, or may be added after wrapping or laminating an assembly in which the separator 6 is disposed between the positive electrode 2 side and the negative electrode 3 side.

[0082] In addition to the above-described configuration, the lithium ion secondary battery 1 usually further includes a separator 6 and an exterior material.

[0083] (Separator 6) The separator 6 may be disposed between the positive electrode 2 and the negative electrode 3 and may have any structure as long as it is insulating and can contain the non-aqueous electrolyte 5. Examples of the separator 6 include woven fabrics, nonwoven fabrics, and microporous membranes made of nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, polyethylene terephthalate, and composites of two or more of these materials. The separator 6 is preferably a nonwoven fabric made of nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, polyethylene terephthalate, or a composite of two or more of these materials, as these have excellent stability in cycle characteristics.

[0084] The separator 6 may contain various plasticizers, antioxidants, and flame retardants, and may be coated with metal oxides or the like. The thickness of the separator 6 is not particularly limited, but is preferably 10 μm or more and 100 μm or less. Within this range, short-circuiting between the positive electrode 2 and the negative electrode 3 can be prevented while suppressing an increase in the resistance of the battery. From the viewpoints of economy and ease of handling, a thickness of 15 μm or more and 50 μm or less is even more preferable.

[0085] The porosity of the separator 6 is preferably 30% or more and 90% or less. If it is 30% or more, the diffusibility of lithium ions is less likely to decrease, making it easier to maintain cycle characteristics, while if it is 90% or less, the risk of short circuits caused by electrode irregularities penetrating the separator 6 can be effectively reduced. The porosity of the separator 6 is more preferably 35% or more and 85% or less from the viewpoint of a balance between ensuring lithium ion diffusibility and preventing short circuits, and is particularly preferably 40% or more and 80% or less because this provides an especially excellent balance.

[0086] (exterior materials) The exterior packaging material is a member that encapsulates a laminate formed by alternately stacking or winding a positive electrode 2, a negative electrode 3, and a separator 6, as well as terminals that electrically connect the laminate. Examples of exterior packaging materials that can be used include composite films in which a thermoplastic resin layer for heat sealing is provided on a metal foil, and metal layers formed by vapor deposition or sputtering. Metal cans that are rectangular, oval, cylindrical, coin-shaped, button-shaped, or sheet-shaped are also suitable.

[0087] Next, a method for manufacturing the lithium ion secondary battery 1 of this embodiment will be described.

[0088] The lithium ion secondary battery 1 of this embodiment is mainly composed of a positive electrode formation process for forming a positive electrode 2, a negative electrode formation process for forming a negative electrode 3, and a secondary battery assembly process for assembling the positive electrode 2, the negative electrode 3, and the non-aqueous electrolyte 5. The negative electrode formation process and the secondary battery assembly process are the same as conventional processes, and therefore will not be described here.

[0089] In the positive electrode forming step, first, the solid electrolyte 31 is pulverized by a pulverizing device such as a ball mill so that the average particle size is 10 nm or less (pulverizing step, nanoparticle forming step).

[0090] Subsequently, the solid electrolyte 31 that has been pulverized into fine particles in the pulverization step is dispersed in a dispersion solvent to form an electrolyte dispersion (electrolyte dispersion formation step).

[0091] The dispersion solvent used in this case is preferably one or more alcohol solutions as described above, and more preferably ethanol. The electrolyte dispersion thus formed is a transparent sol having fluidity. The crystalline structure of the solid electrolyte 31 in the electrolyte dispersion is partially destroyed by the pulverization process, making the solid electrolyte 31 amorphous.

[0092] Next, the electrolyte dispersion is ground into the positive electrode active material 30 by a grinding device such as a grinding mill to form a ground product (ground product forming step).

[0093] Subsequently, the ground product is subjected to a heat treatment to remove the dispersion solvent from the ground product, thereby forming positive electrode composite active material 20 (removal step).

[0094] The heat treatment temperature at this time is preferably 300°C or higher, and more preferably 350°C or higher. If the heat treatment temperature is below 300° C., the adhesion between the positive electrode active material 30 and the solid electrolyte 31 will be insufficient, which may cause the solid electrolyte 31 to peel off during charging and discharging of the battery, leading to a decrease in the long-term reliability of the battery. On the one hand, if the heat treatment temperature is too high, the crystal structure of the solid electrolyte 31 changes, the Li ion conductivity decreases, and the charge and discharge of the battery may not be carried out normally. Therefore, the heat treatment temperature is preferably 600 °C or lower, more preferably 500 °C or lower. The heat treatment time is preferably 30 minutes or longer, more preferably 1 hour or longer, and the upper limit is not particularly limited, but for example, it is 3 hours or shorter.

[0095] The positive electrode composite active material 20 obtained by the above process is mixed with a conductive assistant and a binder to prepare a positive electrode mixture, which is then applied to the positive electrode current collector 10 (positive electrode coating process).

[0096] Subsequently, the positive electrode current collector 10 coated with the positive electrode mixture is dried to form the positive electrode 2 (positive electrode drying process).

[0097] The positive electrode 2 formed by the above-described process is assembled together with the negative electrode 3 formed by the negative electrode forming process and the non-aqueous electrolyte 5 in the same manner as in the prior art to complete the lithium ion secondary battery 1.

[0098] According to the positive electrode composite active material 20 of the present embodiment, since the solid electrolyte 31 is coated in a layer on the surface of the positive electrode active material 30, the generation of gas caused by the oxidative decomposition of the non-aqueous electrolyte 5 can be suppressed. According to the positive electrode composite active material 20 of the present embodiment, as the solid electrolyte 31, Li 1+p+q+r Al p Ga q (Ti, Ge) 2-p-q Si r P 3-r O 12 (0 < p ≤ 1, 0 ≤ q < 1, 0 ≤ r ≤ 1) is used, and the solid electrolyte 31 has a coating thickness of 5 nm or more and 50 nm or less. Therefore, the resistance is small and the resistance loss due to the solid electrolyte 31 can be suppressed. According to the positive electrode composite active material 20 of the present embodiment, the solid electrolyte 31 is layered, the amorphous part 40 and the crystalline part 41 are mixed, and the amorphous part 40 is in contact with the positive electrode active material 30. Therefore, both the lithium ion conductivity and the gas generation suppression effect can be exhibited.

[0099] In the positive electrode composite active material 20 of this embodiment, the solid electrolyte 31 has an integrated intensity ratio of the tetracoordination peak to the total peak area of ​​the Al peak measured by solid-state NMR of 1% to 5%, which further suppresses gas generation due to oxidative decomposition of the nonaqueous electrolyte 5.

[0100] In the above-described embodiment, the solid electrolyte 31 is pulverized to an average particle size of 10 nm or less prior to the electrolyte dispersion formation step, but the present invention is not limited to this. In the electrolyte dispersion formation step, the solid electrolyte 31 may be dispersed in the dispersion solvent while being pulverized to an average particle size of 10 nm or less. In this way, the solid electrolyte 31 is pulverized and dispersed in the dispersion solvent simultaneously in the electrolyte dispersion formation step, which simplifies the positive electrode formation step, and also makes it less likely for the solid electrolyte 31 to aggregate in the milled product formation step, thereby reducing variations in the coverage of the solid electrolyte 31 on the surface of the positive electrode active material 30. In this case, the electrolyte dispersion preferably has a solid content concentration of the solid electrolyte 31 in the dispersion solvent of 2% or more and 7% or less.

[0101] In the above-mentioned application example, the positive electrode active material 30 is covered with the solid electrolyte 31 to form the positive electrode composite active material 20, but the negative electrode active material 21 may be covered with the solid electrolyte 31 to form the negative electrode composite active material. In this case, the negative electrode active material 21 may be lithium titanate (e.g., Li4Ti5O 12 ) and other titanium oxides are preferred.

[0102] In the above-described embodiments, each component can be freely substituted or added between the respective embodiments as long as it falls within the technical scope of the present invention. [Example]

[0103] The present invention will be explained in more detail below by way of experimental examples. The present invention is not limited by the following experimental examples, and it is of course possible to carry out the present invention by making appropriate modifications within the scope that is compatible with the above-mentioned and below-mentioned purposes, and all of these modifications are included in the technical scope of the present invention.

[0104] The batteries obtained in the following experimental examples were evaluated by the following methods.

[0105] (gas generation amount) The amount of gas generated from the lithium ion secondary battery before and after the cycle performance evaluation in each experiment was evaluated using the Archimedes method, that is, the buoyancy of the lithium ion secondary battery. The evaluation was performed as follows.

[0106] First, the weight of the lithium-ion secondary battery was measured using an electronic balance. Next, the weight in water was measured using a hydrometer (manufactured by Alpha Mirage, product number: MDS-3000). The buoyancy was calculated by taking the difference between these weights. This buoyancy was calculated based on the density of water (1.0 g / cm 3 The volume of the lithium ion secondary battery was calculated by dividing the volume by the measured value (%). The volume after aging was compared with the volume after the cycle characteristic evaluation described below to calculate the amount of gas generated. A battery with a gas generation amount of less than 20 ml was judged to be good.

[0107] (Evaluation of cycle characteristics of lithium-ion secondary batteries) The lithium-ion secondary battery fabricated in the experimental example was connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko Corporation) and cycled. In a 60°C environment, constant-current charging was performed at a current value equivalent to 1.0 C until the battery voltage reached a cut-off voltage of 3.4 V, at which point charging was stopped. Subsequently, constant-current discharging was performed at a current value equivalent to 1.0 C, and discharging was stopped when the battery voltage reached 2.5 V. This constituted one cycle, and charging and discharging were repeated. The stability of the cycle characteristics was evaluated as the discharge capacity retention rate (%), where the discharge capacity at the 500th cycle was taken as 100. A discharge capacity retention rate of 80% or more at the 500th cycle was considered good, and a rate of less than 80% was considered poor.

[0108] Synthesis Example 1 (Preparation of solid electrolyte) As a solid electrolyte, Li 1.3 Al 0.3 Ti 1.7(PO4)3 (hereinafter referred to as LATP) was prepared. The starting materials, Li2CO3, AlPO4, TiO2, NH4H2PO4, and the solvent ethanol, were mixed in predetermined amounts and processed in a planetary ball mill at 150 G for 1 hour using 3 mm diameter zirconia balls. After the processing, the zirconia balls were removed from the mixture using a sieve, and the mixture was dried at 120 °C to remove the ethanol. The mixture was then processed at 800 °C for 2 hours to obtain LATP powder.

[0109] The obtained LATP powder was mixed with a predetermined amount of ethanol as a solvent and treated in a planetary ball mill using zirconia balls with a diameter of 0.5 mm for 1 to 3 hours. The zirconia balls were removed from the treated mixture using a sieve, and the mixture was dried at 120°C to remove the ethanol. This resulted in LATP fine powder with a dBET of 3 to 25 nm. Next, the LATP fine powder was mixed with ethanol to obtain a slurry (electrolyte dispersion) in which the LATP fine powder and solid electrolyte were dispersed in 16.4 wt% ethanol.

[0110] (Experimental Example 1) (i) Preparation of the positive electrode The positive electrode active material was a spinel-type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4, hereafter also referred to as LNMO) was used.

[0111] 40 g of LNMO was placed in a grinding mill (manufactured by Hosokawa Micron Corporation, product name: Nobilta) and rotated at 2600 rpm with a clearance of 0.6 mm and a rotor load power of 1.5 kW. While the mill was being rotated, 6.1 g of an ethanol-dispersed slurry of LATP fine powder, which had been milled for 3 hours in Synthesis Example 1, was added in two portions. The rotor rotation speed was then maintained between 2600 rpm and 3000 rpm, and the mixture was treated at room temperature in an air atmosphere for 10 minutes to obtain LNMO with a surface coated with LATP. The resulting surface-coated LNMO was then heat-treated at 350°C for 1 hour to obtain a positive electrode composite active material.

[0112] A mixture containing the obtained cathode composite active material (surface-coated LNMO), acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder at solid concentrations of 90 parts by weight, 6 parts by weight, and 4 parts by weight, respectively, was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The binder was prepared as an N-methyl-2-pyrrolidone (NMP) solution with a solid concentration of 5% by weight, and NMP was further added to adjust the viscosity to facilitate coating, as described below.

[0113] The slurry was applied to a 20 μm thick aluminum foil and then dried in an oven at 120° C. This operation was performed on both sides of the aluminum foil, and then the foil was further dried in a vacuum at 170° C. to prepare a positive electrode.

[0114] (ii) Preparation of the negative electrode The negative electrode active material was spinel-type lithium titanate (Li4Ti5O 12 (hereinafter, also referred to as LTO) was used. A mixture containing 100 parts by weight of the LTO, acetylene black as a conductive additive, and 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder, respectively, in terms of solid content, was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The binder was prepared as an NMP solution with a solid content of 5% by weight, and further NMP was added to adjust the viscosity to facilitate coating, as described below.

[0115] The slurry was applied to a 20 μm thick aluminum foil and then dried in an oven at 120° C. This operation was performed on both sides of the aluminum foil, and then the foil was further dried in a vacuum at 170° C. to prepare a negative electrode.

[0116] (iii) Fabrication of lithium-ion secondary batteries A battery was fabricated using the positive and negative electrodes fabricated in (i) and (ii) above and a 20 μm polypropylene separator according to the following procedure. First, the positive and negative electrodes were dried under reduced pressure at 80°C for 12 hours. Next, 15 positive electrodes and 16 negative electrodes were stacked in the order of negative electrode / separator / positive electrode. The outermost layers were both separators. Next, aluminum tabs were vibration-welded to both ends of the positive and negative electrodes.

[0117] Two sheets of aluminum laminate film were prepared as exterior materials, and a depression to become a battery portion and a depression to become a gas collection portion were formed by pressing, after which the electrode laminate was placed inside. The outer periphery, leaving a space for injecting the non-aqueous electrolyte, was heat-sealed at 180°C for 7 seconds, and a non-aqueous electrolyte prepared by dissolving LiPF6 at a ratio of 1 mol / L in a solvent made by mixing ethylene carbonate, propylene carbonate, and ethyl methyl carbonate in a volume ratio of ethylene carbonate / propylene carbonate / ethyl methyl carbonate = 15 / 15 / 70 was poured into the unsealed portion, and the unsealed portion was then heat-sealed at 180°C for 7 seconds while the pressure was reduced. The resulting battery was charged at a constant current equivalent to 0.2 C until the battery voltage reached a cut-off voltage of 3.4 V, at which point charging was stopped. After leaving the battery at rest for 24 hours in a 60°C environment, it was discharged at a constant current equivalent to 0.2 C, and discharge was stopped when the battery voltage reached 2.5 V. After discharging was stopped, the gas trapped in the gas collection section was removed and the battery was resealed. A lithium-ion secondary battery for evaluation was produced using the above procedures.

[0118] (Experimental Example 2) A lithium ion secondary battery for evaluation was produced in the same manner as in Experimental Example 1, except that in the production of the positive electrode, the surface-coated LNMO was produced by spray coating using a tumbling fluidizer.

[0119] (Experimental Example 3) In the preparation of the positive electrode, the particle size of LATP is the same, 27 A lithium ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 1, except that a material having a tetrahedral Al spectrum ratio of 5% or more in Al-NMR was used.

[0120] (Experimental Example 4) In the preparation of the positive electrode, the particle diameter of LATP is about 10 nm, 27 A lithium ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 1, except that the Al-NMR spectrum ratio of 4-coordinated Al was 5% or more.

[0121] (Experimental Example 5) In the preparation of the positive electrode, the particle diameter of LATP is about 20 nm, 27 A lithium ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 1, except that the Al-NMR spectrum ratio of 4-coordinated Al was 5% or more.

[0122] (Experimental Example 6) In the preparation of the positive electrode, the particle diameter of LATP is about 20 nm, 27 A lithium ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 2, except that a material having a tetrahedral Al spectrum ratio of 5% or more in Al-NMR was used.

[0123] (Experimental Example 7) A lithium ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 1, except that LNMO without surface coating was used.

[0124] The evaluation results of Experimental Examples 1 to 7 are shown in Table 1.

[0125] [Table 1]

[0126] The lithium ion secondary batteries of Experimental Examples 1 and 2 showed significantly less gas generation and higher capacity retention rates than those of conventional batteries in cycle performance evaluations. That is, in Experimental Examples 1 and 2, the gas generation rate was 10 ml or less, and the capacity retention rate was 90% or more.

[0127] On the other hand, in Experimental Example 3, which had a particle size equivalent to those of Experimental Examples 1 and 2 but a tetracoordination ratio greater than 5%, the amount of gas generated was smaller and the capacity retention rate could be maintained as compared to Experimental Example 7, which was not coated with a solid electrolyte. However, the amount of gas generated was larger and the capacity retention rate was lower than those of Experimental Examples 1 and 2. Furthermore, Experimental Examples 4 and 5, which had larger particle diameters than Experimental Examples 1 and 2, generated less gas and were able to maintain a higher capacity retention rate than Experimental Example 7, which was not coated with a solid electrolyte. However, compared to Experimental Examples 1 and 2, they generated more gas and had a lower capacity retention rate.

[0128] Furthermore, even when the coating method was changed in Experimental Example 6, when the tetracoordination intensity ratio was large, the amount of gas generated was smaller and the capacity retention rate could be maintained compared to Experimental Example 7, where no solid electrolyte was coated, but the amount of gas generated was larger and the cycle characteristics were poorer than those of Experimental Examples 1 and 2. This suggests that the tetracoordination intensity ratio of Al contributes to the amount of gas generated and the cycle characteristics. As mentioned above, the hexacoordinated peak is dominant for LATP, but when LATP decomposes to form AlPO4, the crystal structure is destroyed, and a tetracoordinated peak appears. The intensity ratio of the tetracoordinated peak is thought to be related to the amount of AlPO4 produced, and the above results suggest that the gas generation amount and cycle characteristics can be improved by forming AlPO4 while keeping the amount of AlPO4 produced below a certain level.

[0129] (Experimental Example 8) In the preparation of the positive electrode, spinel-type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 The procedure was the same as in Experimental Example 1, except that LNMO was used.

[0130] That is, 40 g of LNMO was placed in a grinding mill (manufactured by Hosokawa Micron Corporation, product name: Nobilta), and while rotating at 2600 rpm with a clearance of 0.6 mm and a rotor load power of 1.5 kW, 6.1 g of an ethanol-dispersed slurry of LATP fine powder that had been milled for 1 hour in Synthesis Example 1 was added in two portions to prepare a positive electrode. The particle size of the crushed LATP was 6 nm. 31 The peak intensity ratio between 0 and -20 ppm in P-NMR measurement was 80%. NMR measurement was performed using a VNMRS600 manufactured by VARIAN. The NMR measurement results are shown in Figure 2.

[0131] (Experimental Example 9) A lithium-ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 8, except that in the fabrication of the positive electrode, the LATP was ground for 3 hours, the particle size of LATP was 3 nm, and the integrated ratio of the peak present at 0 to -20 ppm in 31P-NMR was 100% to fabricate the surface-coated LNMO. The NMR measurement results are shown in Figure 3.

[0132] (Experimental Example 10) A lithium-ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 8, except that in the fabrication of the positive electrode, the grinding time was 30 minutes, the particle size of LATP was 9 nm, and the integral ratio of the peak present at 0 to -20 ppm in 31P-NMR was 47%. The NMR measurement results are shown in Figure 4.

[0133] (Experimental Example 11) A lithium ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 8, except that LNMO without surface coating was used.

[0134] The evaluation results of Experimental Examples 8 to 11 are shown in Table 2.

[0135] [Table 2]

[0136] 31 In the lithium ion secondary batteries of Experimental Examples 8 and 9, in which the integrated intensity ratio of the peak between 0 and -20 ppm in the P peak was 50% or more of the total peak area, the amount of gas generated in the cycle characteristic evaluation was significantly smaller than that of Experimental Example 11, in which the solid electrolyte was not coated, and the capacity retention rate was also high. This is thought to be because the bonding state of phosphorus changes when the solid electrolyte is made into fine particles, leading to an effect of suppressing gas generation and improving cycle characteristics.

[0137] On the other hand, the particle size was 12 nm, which was larger than that of Experimental Examples 8 and 9. 31 Experimental Example 10, in which the peak ratio present at -20 to 0 ppm in P-NMR was 47%, generated less gas and maintained a higher capacity retention rate than Experimental Example 11, which was not coated with a solid electrolyte. However, the amount of gas generated was greater and the capacity retention rate was lower than in Experimental Examples 8 and 9. This is thought to be because the LATP particles were not sufficiently pulverized, and the bonding state of the phosphorus did not have a structure that suppressed gas generation.

[0138] (Experimental Example 12) In the preparation of the positive electrode, the surface-coated LNMO was heat-treated at 400°C for 1 hour to obtain a positive electrode composite active material.

[0139] The positive electrode composite active material of Experimental Example 12 was observed with a transmission electron microscope (TEM). As shown in Figure 5, the positive electrode composite active material was a positive electrode active material coated with a layer of solid electrolyte, and the thickness of the solid electrolyte was approximately 40 nm. The positive electrode composite active material of Experimental Example 12 had a mixture of amorphous portions where no crystal arrangement was observed and crystalline portions where a regular crystal arrangement was observed, as shown in Figure 6. In the positive electrode composite active material of Experimental Example 12, the amorphous portions were in contact with the positive electrode active material, LNMO. These results are thought to be due to the occurrence of areas where the crystalline structure of LATP was maintained, areas where the crystalline structure of LATP could not be maintained and became amorphous, or areas where the LATP locally decomposed into aluminum phosphate (AlPO3).

[0140] (Experimental Example 13) (iv) Preparation of the positive electrode A positive electrode was prepared in the same manner as in Experimental Example 1(i), except that LNMO without surface coating was used.

[0141] (v) Preparation of coated negative electrode active material First, in the preparation of the solid electrolyte in Synthesis Example 1, a planetary ball mill treatment was carried out for 3 to 6 hours, and the other procedures were the same as in the preparation of the solid electrolyte in Synthesis Example 1, to obtain a slurry (electrolyte dispersion). As the negative electrode active material, spinel-type lithium titanate (Li4Ti5O 12 Using a grinding mill (hereinafter referred to as LTO), 40 g of LTO was placed in a grinding mill (Hosokawa Micron Corporation, Nobilta). While rotating with a clearance of 0.6 mm, a rotor load power of 1.5 kW, and 2600 rpm, 6.1 g of the resulting transparent sol-state slurry was added in two batches. The rotor rotation speed was then maintained between 2600 and 3000 rpm, and the mixture was treated at room temperature for 10 minutes in an air atmosphere to obtain LTO coated with LATP. The resulting surface-coated LTO was then heat-treated at 350°C for 1 hour to obtain a coated negative electrode active material.

[0142] (vi) Preparation of negative electrode A mixture containing the obtained surface-coated LTO, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder at solid concentrations of 90 parts by weight, 5 parts by weight, and 5 parts by weight, respectively, was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a negative electrode mixture. The binder was prepared as an N-methyl-2-pyrrolidone (NMP) solution with a solid concentration of 5% by weight, and NMP was further added to adjust the viscosity to facilitate coating, as described below.

[0143] The negative electrode mixture was applied to a 20 μm thick aluminum foil and then dried in an oven at 120° C. This operation was performed on both sides of the aluminum foil, and then the foil was further dried in a vacuum at 170° C. to prepare a negative electrode.

[0144] (vii) Fabrication of lithium-ion secondary batteries A lithium ion secondary battery for evaluation was fabricated in the same manner as in Experimental Example 1(iii) using the positive electrode and negative electrode fabricated in (iv) and (vi) above.

[0145] (Experimental Example 14) A coated negative electrode active material was produced in the same manner as in Experimental Example 13, except that the amount of LATP coated in a transparent sol state was 9.1 g. This was designated Experimental Example 14.

[0146] (Experimental Example 15) A negative electrode active material was produced in the same manner as in Example 1, except that LTO without surface coating was used.

[0147] The evaluation results of Experimental Examples 13 to 15 are shown in Table 3.

[0148] [Table 3]

[0149] The lithium ion secondary batteries of Examples 13 and 14 showed a smaller amount of gas generated and a higher capacity retention rate in the cycle performance evaluation compared to Experimental Example 15 which was not coated with LATP.

[0150] These results demonstrate that coating the negative electrode active material with a solid electrolyte can also suppress gas generation and improve cycle characteristics.

[0151] From the above results, it became clear that a lithium-ion secondary battery using a positive electrode composite active material in which the surface of a positive electrode active material that operates at a high potential is coated with a solid electrolyte containing at least aluminum generates little gas even when charged and discharged at a high potential, and also has good cycle characteristics. It was also found that the amount of gas generated can be reduced and cycle characteristics can be improved by suppressing the peak intensity ratio of the tetracoordination of Al in the positive electrode composite active material to 5% or less. Furthermore, it was revealed that lithium-ion secondary batteries using a positive electrode active material in which the surface of the positive electrode active material, which operates at a high potential, is coated with a solid electrolyte containing at least phosphorus, generate little gas even when charged and discharged at a high potential, and also have good cycle characteristics. The positive electrode composite active material has a layered oxide-based solid electrolyte with a coating thickness of 5 nm to 50 nm, and is composed of a mixture of amorphous and crystalline parts. The amorphous parts are in contact with the positive electrode active material, suggesting that gas generation can be suppressed by the LATP or AlPO3 corresponding to the amorphous parts, and that lithium insertion and desorption can be performed quickly by the LATP corresponding to the crystalline parts. It was also revealed that coating the negative electrode active material with a solid electrolyte can suppress gas generation and improve cycle characteristics. [Industrial Applicability]

[0152] The composite active material of the present invention is suitably used as an active material for an electrode of a lithium ion secondary battery. [Explanation of symbols]

[0153] 1. Lithium-ion secondary battery 2 Positive electrode 3 negative electrode 5. Non-aqueous electrolyte 10 Positive electrode current collector 21 Negative electrode active material 30 Cathode active material 31 Oxide solid electrolyte 40 amorphous part 41 Crystalline part

Claims

1. A positive electrode composite active material constituting a part of a positive electrode of a lithium ion secondary battery using a non-aqueous electrolyte, A positive electrode active material and an oxide-based solid electrolyte are included. the positive electrode active material is coated with the oxide-based solid electrolyte, The oxide-based solid electrolyte is Li １＋ｐ＋ｑ＋ｒ Al ｐ Ga ｑ (Ti, Ge) ２－ｐ－ｑ Si ｒ P ３－ｒ O １２ (0<p≦1, 0≦q<1, 0≦r≦1), the oxide-based solid electrolyte is layered and has a coating thickness of 5 nm or more and 50 nm or less; the oxide-based solid electrolyte has a mixture of an amorphous portion and a crystalline portion, and the amorphous portion is in contact with the positive electrode active material; The oxide-based solid electrolyte has an integrated intensity ratio of a tetracoordination peak to a total peak area of ​​an Al peak measured by solid-state NMR of 1% to 5%.

2. A positive electrode composite active material constituting a part of a positive electrode of a lithium ion secondary battery using a non-aqueous electrolyte, comprising: A positive electrode active material and an oxide-based solid electrolyte are included. the positive electrode active material is coated with the oxide-based solid electrolyte, The oxide-based solid electrolyte is represented by Li 1+p+q+r Al p Ga q (Ti, Ge) 2-p-q Si r P 3-r O 12 (0<p≦1, 0≦q<1, 0≦r≦1), the oxide-based solid electrolyte is layered and has a coating thickness of 5 nm or more and 50 nm or less; the oxide-based solid electrolyte has a mixture of an amorphous portion and a crystalline portion, and the amorphous portion is in contact with the positive electrode active material; The oxide-based solid electrolyte has a positive electrode composite active material in which the integrated intensity ratio of the peak at −20 to 0 ppm to the total peak area of ​​the P peak measured by solid-state NMR is 50% or more.

3. The oxide-based solid electrolyte has an average particle size of 10 nm or less, The positive electrode composite active material according to claim 1 or 2, wherein the positive electrode active material has a median diameter of 5 μm or more.

4. A positive electrode composite active material constituting a part of a positive electrode of a lithium ion secondary battery using a non-aqueous electrolyte, comprising: A positive electrode active material and an oxide-based solid electrolyte are included, the positive electrode active material is coated with the oxide-based solid electrolyte, The oxide-based solid electrolyte is represented by Li 1+p+q+r Al p Ga q (Ti, Ge) 2-p-q Si r P 3-r O 12 (0<p≦1, 0≦q<1, 0≦r≦1), the oxide-based solid electrolyte is layered and has a coating thickness of 5 nm or more and 50 nm or less; the oxide-based solid electrolyte has a mixture of an amorphous portion and a crystalline portion, and the amorphous portion is in contact with the positive electrode active material; The positive electrode active material has an operating potential of 4.5 V (vs. Li / Li ＋ ) or more of a lithium ion conductive active material.

5. The positive electrode composite active material according to any one of claims 1 to 4, wherein the positive electrode active material is a substituted lithium manganese compound represented by the following formula (1): Li １＋ｘ M ｙ Mn ２－ｘ－ｙ O ４ ・・・(1) In the formula (1), x and y satisfy the conditions 0≦x≦0.2 and 0<y≦0.8, respectively, and M is at least one element selected from the group consisting of Al, Mg, Zn, Ni, Co, Fe, Ti, Cu, and Cr.

6. A positive electrode composite active material constituting a part of a positive electrode of a lithium ion secondary battery using a non-aqueous electrolyte, comprising: A positive electrode active material and an oxide-based solid electrolyte are included, the positive electrode active material is coated with the oxide-based solid electrolyte, The oxide-based solid electrolyte is represented by Li 1+p+q+r Al p Ga q (Ti, Ge) 2-p-q Si r P 3-r O 12 (0<p≦1, 0≦q<1, 0≦r≦1), the oxide-based solid electrolyte is layered and has a coating thickness of 5 nm or more and 50 nm or less; a method for producing a cathode composite active material, the method comprising the steps of: an electrolyte dispersion forming step of dispersing an oxide-based solid electrolyte in a dispersion solvent to form an electrolyte dispersion; a grinding step of grinding the electrolyte dispersion into the positive electrode active material to form a grinding material; The method for producing a positive electrode composite active material includes a removal step of removing the dispersion solvent from the ground product.

7. The method for producing a cathode composite active material according to claim 6 , wherein the dispersing solvent is removed by heat treatment at 300° C. or higher in the removing step.

8. 8. The method for producing a positive electrode composite active material according to claim 6, further comprising, prior to the electrolyte dispersion forming step, a pulverizing step of pulverizing the oxide-based solid electrolyte to an average particle size of 10 nm or less.

9. 8. The method for producing a cathode composite active material according to claim 6, wherein in the electrolyte dispersion forming step, the oxide-based solid electrolyte is dispersed in the dispersion solvent while being pulverized to an average particle size of 10 nm or less.

10. A lithium ion secondary battery comprising a positive electrode containing the positive electrode composite active material according to any one of claims 1 to 5, a negative electrode, and a non-aqueous electrolyte.

11. 11. The lithium ion secondary battery according to claim 10, wherein the negative electrode has a negative electrode active material comprising lithium titanate.

12. A method for manufacturing a lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, comprising: A method for producing a lithium ion secondary battery, comprising a positive electrode coating step of coating a positive electrode current collector with a positive electrode mixture containing the positive electrode composite active material according to any one of claims 1 to 5.

13. A positive electrode composite active material that constitutes a part of a positive electrode of a lithium ion secondary battery, A positive electrode active material and an oxide-based solid electrolyte are included, the positive electrode active material is coated with the oxide-based solid electrolyte, The oxide-based solid electrolyte is Li １＋ｐ＋ｑ＋ｒ Al ｐ Ga ｑ (Ti, Ge) ２－ｐ－ｑ Si ｒ P ３－ｒ O １２ (0<p≦1, 0≦q<1, 0≦r≦1), The oxide-based solid electrolyte has a peak intensity ratio of 4-coordination in Al peaks measured by solid-state NMR of 1% or more and 5% or less.

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