Coated positive electrode active material and battery using the same

Abstract

The coated positive electrode active material (100) of the present disclosure includes particulate positive electrode active material (101) and a solid electrolyte (102) that coats the surface of the positive electrode active material (101). The solid electrolyte (102) forms a coating layer, and the coating layer is formed to fill the concave portions on the surface of the positive electrode active material with the solid electrolyte (102), and the convex portions on the surface of the positive electrode active material (101) are exposed on the surface of the coated positive electrode active material (100). When the unevenness degree of the particle group of the positive electrode active material (101) is defined as ζ1 and the unevenness degree of the particle group of the coated positive electrode active material 100 is defined as ζ2, the unevenness change degree R defined by the following formula (2) is 1.1 or more. R = ζ2 / ζ1 ··· (2).

Description

Technical Field

[0001] The present disclosure relates to a coated positive electrode active material and a battery using the same. Background Art

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

[0003] Patent Document 2 discloses a positive electrode material and a secondary battery. The positive electrode material includes a positive electrode active material and a halide solid electrolyte. The halide solid electrolyte includes yttrium, chlorine, and bromine.

[0004] Prior Art Documents

[0005] Patent Document 1: International Publication No. 2018 / 038037

[0006] Patent Document 2: International Publication No. 2019 / 135322 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In the prior art, further improvement in the charge and discharge efficiency of a battery has been desired.

[0009] Means for Solving the Problems

[0010] A coated positive electrode active material according to one aspect of the present disclosure includes a particulate positive electrode active material and a solid electrolyte coating the surface of the positive electrode active material.

[0011] The solid electrolyte forms a coating layer.

[0012] The coating layer is formed so as to fill recesses on the surface of the positive electrode active material with the solid electrolyte.

[0013] Protrusions on the surface of the positive electrode active material are exposed on the surface of the coated positive electrode active material.

[0014] The unevenness degree ζ of a particle group is defined by the following formula (1).

[0015]

[0016] In formula (1), n is an integer of 3 or more representing the number of measured particles, Lpi represents the total perimeter of the contour of the cross-sectional image of each particle, Lei represents the total perimeter of an equivalent smooth ellipse having the same aspect ratio and area as the aspect ratio and area of the cross-sectional image of each particle, and the aspect ratio represents the ratio of the minor axis of the cross-sectional image to the major axis of the cross-sectional image.

[0017] When the concavity and convexity of the particle group of the positive electrode active material is defined as ζ 1 and the concavity and convexity of the particle group of the coated positive electrode active material is defined as ζ 2 the degree of change in concavity and convexity R defined by the following formula (2) is 1.1 or more,

[0018] R = ζ 2 / ζ 1 ···(2)

[0019] The solid electrolyte has a composition represented by the following formula (3),

[0020] Li α M β Cl γ ···(3)

[0021] In the formula (3), α, β, and γ are values greater than 0, and M contains at least one selected from metal elements and metalloid elements other than Li.

[0022] Effects of the Invention

[0023] According to the present disclosure, the charge and discharge efficiency of the battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a cross-sectional view showing a schematic structure of the coated positive electrode active material in Embodiment 1.

[0025] Figure 2 is a cross-sectional view showing a schematic structure of the positive electrode material in Embodiment 1.

[0026] Figure 3 is a cross-sectional view showing a schematic structure of the battery in Embodiment 2.

[0027] Figure 4A is a binarized image of a cross-sectional image obtained by observing the coated positive electrode active material of Example 1a with a scanning electron microscope.

[0028] Figure 4B is a binarized image of a cross-sectional image obtained by observing the coated positive electrode active material of Comparative Example 1a with a scanning electron microscope. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0030] The following descriptions are general or specific examples. The numerical values, compositions, shapes, film thicknesses, electrical properties, structures of secondary batteries, electrode materials, etc. shown below are only examples, and their purpose does not limit the present invention. In addition, constituent elements not described in the independent claims representing the highest concept are arbitrary constituent elements.

[0031] (Insights that form the basis of this disclosure)

[0032] In Patent Document 1, the positive electrode active material is coated with a sulfide solid electrolyte. The sulfide solid electrolyte is a material with high ion conductivity, but has problems in oxidation resistance.

[0033] In Patent Document 2, a bromine-containing halide solid electrolyte is used. The present inventors have conducted intensive research and found that if a bromine-containing halide solid electrolyte is included in the positive electrode material, the halide solid electrolyte undergoes oxidative decomposition during the battery charging process, and the battery charging and discharging efficiency is reduced.

[0034] Specifically, in a material containing bromine as an anion constituting a solid electrolyte, when using a positive electrode active material having an average relative Li potential of 3.7V or more, the solid electrolyte decomposes by an oxidation reaction during charging, and the oxidative decomposition product sometimes acts as a resistance layer. Here, the oxidation reaction refers to a conventional charging reaction of removing lithium and electrons from the positive electrode active material in the positive electrode material, and also refers to a side reaction of removing electrons from a solid electrolyte containing anions in contact with the positive electrode active material. It is believed that with this oxidation reaction, an oxidative decomposition layer lacking lithium ion conductivity is formed between the positive electrode active material and the solid electrolyte, and the oxidative decomposition layer acts as a large interface resistance.

[0035] Bromine has a smaller electronegativity and a larger ionic radius than chlorine. Therefore, it is believed that the interaction between the cationic component constituting the halide solid electrolyte and bromine is weak, and bromine is easily oxidized. Therefore, it is believed that a battery using a solid electrolyte in which the anion constituting the solid electrolyte is composed of chlorine shows excellent oxidation resistance and can improve the charge and discharge efficiency of the battery.

[0036] In order to suppress the oxidative decomposition of the solid electrolyte and suppress the generation of the high resistance layer between the positive electrode active material and the solid electrolyte, it is necessary to select a solid electrolyte with excellent oxidation resistance. In addition, in order to improve the charge and discharge efficiency of the battery, it is necessary to reduce the interface resistance between the positive electrode active material and the solid electrolyte. However, in a battery using a positive electrode active material coated with a solid electrolyte, it is difficult to simultaneously satisfy the requirements of suppressing the generation of the high resistance layer and improving the charge and discharge efficiency of the battery.

[0037] Based on the above insights, the present inventors came up with the idea of forming a coating layer using a solid electrolyte whose anions constituting the solid electrolyte are chlorine. As a result, it was found that the oxidation reaction of the solid electrolyte can be suppressed, and the charge-discharge efficiency of the battery can be further improved.

[0038] The present inventors further conducted in-depth research and found that a structure in which the concave portions of the uneven portions on the surface of the positive electrode active material are filled with the solid electrolyte and the convex portions of the uneven portions on the surface of the positive electrode active material are exposed on the surface of the coated positive electrode active material is effective for reducing the interfacial resistance. That is, the present inventors found that by realizing a coated positive electrode active material having a smooth surface, the interfacial resistance between the positive electrode active material and the solid electrolyte can be reduced, and the charge-discharge efficiency of the battery can be further improved.

[0039] (Summary of a technical solution related to the present disclosure)

[0040] A coated positive electrode active material includes particulate positive electrode active material and a solid electrolyte that coats the surface of the positive electrode active material.

[0041] The solid electrolyte forms a coating layer.

[0042] The coating layer is formed by filling the concave portions of the surface of the positive electrode active material with the solid electrolyte.

[0043] The convex portions of the surface of the positive electrode active material are exposed on the surface of the coated positive electrode active material.

[0044] The unevenness degree ζ of the particle group is defined by the following formula (1).

[0045]

[0046] In the formula (1), n is an integer of 3 or more representing the number of measured particles, Lpi represents the total perimeter of the contour of the cross-sectional image of each particle, Lei represents the total perimeter of an equivalent smooth ellipse having the same aspect ratio and area as the aspect ratio and area of the cross-sectional image of each particle, and the aspect ratio represents the ratio of the minor axis of the cross-sectional image to the major axis of the cross-sectional image.

[0047] When the unevenness degree of the particle group of the positive electrode active material is defined as ζ 1 , and the unevenness degree of the particle group of the coated positive electrode active material is defined as ζ 2 , the unevenness change degree R defined by the following formula (2) is 1.1 or more.

[0048] R = ζ 2 / ζ 1 ···(2)

[0049] The solid electrolyte has a composition represented by the following formula (3),

[0050] Li α M β Cl γ ···(3)

[0051] In the formula (3), α, β, and γ are values greater than 0, and M includes at least one selected from metal elements other than Li and metalloid elements.

[0052] According to the first aspect of the technology, the charge and discharge efficiency of the battery can be improved.

[0053] The second aspect of the present disclosure can be set as follows, for example: in the coated positive electrode active material according to the first aspect of the technology, the ratio of the mass of the solid electrolyte to the mass of the positive electrode active material is in the range of 3 / 100 or more and 1 / 10 or less. According to the second aspect of the technology, the interfacial resistance between the positive electrode active material and the solid electrolyte can be reduced. Thereby, the charge and discharge efficiency of the battery can be improved.

[0054] The third aspect of the present disclosure can be set as follows, for example: in the coated positive electrode active material according to the first aspect of the technology, the ratio of the mass of the solid electrolyte to the mass of the positive electrode active material is in the range of 1 / 20 or more and 7 / 100 or less. According to the third aspect of the technology, the charge and discharge efficiency of the battery can be further improved.

[0055] The fourth aspect of the present disclosure can be set as follows, for example: in the coated positive electrode active material according to any one of the first to third aspects of the technology, in the cross-sectional image of the coated positive electrode active material, when the total perimeter of the contour of the positive electrode active material is defined as L and the total length of the contact portion between the positive electrode active material and the coating layer is defined as C, the coating rate represented by the ratio of the total length C to the total perimeter L, i.e., C / L, is in the range of 0.3 or more and 0.95 or less. According to the fourth aspect of the technology, the interfacial resistance between the positive electrode active material and the solid electrolyte can be reduced. Thereby, the charge and discharge efficiency of the battery can be improved.

[0056] The fifth aspect of the present disclosure can be set as follows, for example: in the coated positive electrode active material according to any one of the first to fourth aspects of the technology, the average film thickness of the coating layer is in the range of 1 nm or more and 300 nm or less. According to the fifth aspect of the technology, the interfacial resistance between the positive electrode active material and the solid electrolyte can be reduced. Thereby, the charge and discharge efficiency of the battery can be improved.

[0057] The sixth technical solution of the present disclosure can be set as follows, for example: in the coated positive electrode active material involved in any one of the first to fourth technical solutions, the average film thickness of the coating layer is in the range of 2 nm or more and 200 nm or less. According to the sixth technical solution, the interfacial resistance between the positive electrode active material and the solid electrolyte can be reduced. Thereby, the charge-discharge efficiency of the battery can be improved.

[0058] The seventh technical solution of the present disclosure can be set as follows, for example: in the coated positive electrode active material involved in any one of the first to sixth technical solutions, M contains yttrium. According to the seventh technical solution, the ionic conductivity of the solid electrolyte can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0059] The eighth technical solution of the present disclosure can be set as follows, for example: in the coated positive electrode active material involved in any one of the first to seventh technical solutions, α, β, and γ respectively satisfy 2.5 ≤ α ≤ 3, 1 ≤ β ≤ 1.1, and γ = 6. According to the eighth technical solution, the ionic conductivity of the solid electrolyte can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0060] The ninth technical solution of the present disclosure can be set as follows, for example: in the coated positive electrode active material involved in any one of the first to eighth technical solutions, the positive electrode active material contains lithium nickel cobalt manganese oxide. According to the ninth technical solution, the energy density of the battery can be further improved.

[0061] The tenth technical solution of the present disclosure can be set as follows, for example: in the coated positive electrode active material involved in any one of the first to ninth technical solutions, the positive electrode active material has a surface layer containing a lithium metal oxide. According to the tenth technical solution, the charge-discharge efficiency of the battery can be further improved.

[0062] The eleventh technical solution of the present disclosure can be set as follows, for example: in the coated positive electrode active material involved in the tenth technical solution, the lithium metal oxide contains lithium niobate. According to the eleventh technical solution, the charge-discharge efficiency of the battery can be further improved.

[0063] The positive electrode material according to the twelfth technical solution of the present disclosure includes:

[0064] the coated positive electrode active material involved in any one of the first to eleventh technical solutions; and

[0065] a positive electrode solid electrolyte.

[0066] By using the coated positive electrode active material of the present disclosure for the positive electrode material, a battery with excellent charge-discharge efficiency can be obtained.

[0067] The 13th technical solution of the present disclosure can be set as follows, for example: in the positive electrode material involved in the 12th technical solution, the positive electrode solid electrolyte includes a halide solid electrolyte. The halide solid electrolyte exhibits excellent ion conductivity.

[0068] The 14th technical solution of the present disclosure can be set as follows, for example: in the positive electrode material involved in the 12th or 13th technical solution, the positive electrode solid electrolyte includes a sulfide solid electrolyte. The sulfide solid electrolyte exhibits excellent ion conductivity.

[0069] The battery according to the 15th technical solution of the present disclosure includes:

[0070] a positive electrode including the positive electrode material involved in any one of the 12th to 14th technical solutions;

[0071] a negative electrode; and

[0072] an electrolyte layer disposed between the positive electrode and the negative electrode.

[0073] According to the 15th technical solution, by using the positive electrode material of the present disclosure for the positive electrode, a battery with excellent charge and discharge efficiency can be obtained.

[0074] The 16th technical solution of the present disclosure can be set as follows, for example: in the battery involved in the 15th technical solution, the electrolyte layer includes at least one selected from a solid electrolyte having the same composition as the solid electrolyte contained in the coating layer and a solid electrolyte having the same composition as the positive electrode solid electrolyte. According to the 16th technical solution, the charge and discharge characteristics of the battery can be further improved.

[0075] The 17th technical solution of the present disclosure can be set as follows, for example: in the battery involved in the 15th technical solution, the electrolyte layer includes a halide solid electrolyte having a composition different from the composition of the solid electrolyte contained in the coating layer and / or the composition of the positive electrode solid electrolyte. According to the 17th technical solution, the charge and discharge characteristics of the battery can be further improved.

[0076] The 18th technical solution of the present disclosure can be set as follows, for example: in the battery involved in any one of the 15th to 17th technical solutions, the electrolyte layer includes a sulfide solid electrolyte. According to the 18th technical solution, the charge and discharge characteristics of the battery can be further improved.

[0077] The manufacturing method according to the 19th technical solution of the present disclosure is a method for manufacturing the coated positive electrode active material involved in any one of the 1st to 11th technical solutions,

[0078] including treating the positive electrode active material and the solid electrolyte by using a dry particle compounding method,

[0079] The treatment by the dry particle compounding method includes imparting at least one type of mechanical energy selected from impact, compression, and shear to the positive electrode active material and the solid electrolyte.

[0080] According to the 19th aspect, a desired coated positive electrode active material can be manufactured.

[0081] The 20th aspect of the present disclosure can be set as follows, for example: in the manufacturing method according to the 19th aspect, the ratio of the average particle diameter Da of the positive electrode active material to the average particle diameter Dc of the solid electrolyte, that is, Da / Dc, is 2 or more. According to the 20th aspect, the interfacial resistance between the positive electrode active material and the coating layer can be reduced, and the charge-discharge efficiency of the battery can be further improved.

[0082] The 21st aspect of the present disclosure can be set as follows, for example: in the manufacturing method according to the 19th aspect, the ratio of the average particle diameter Da of the positive electrode active material to the average particle diameter Dc of the solid electrolyte, that is, Da / Dc, is 5 or more. According to the 21st aspect, the interfacial resistance between the positive electrode active material and the coating layer can be further reduced, and the charge-discharge efficiency of the battery can be further improved.

[0083] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0084] (Embodiment 1)

[0085] (Coated Positive Electrode Active Material)

[0086] Figure 1 It is a cross-sectional view showing a schematic structure of the coated positive electrode active material 100 in Embodiment 1.

[0087] The coated positive electrode active material 100 in Embodiment 1 includes particulate positive electrode active material 101 and a solid electrolyte 102 that coats the surface of the positive electrode active material 101. The solid electrolyte 102 forms a coating layer. The coating layer is formed in such a manner that the concave portions on the surface of the positive electrode active material 101 are filled with the solid electrolyte 102. The convex portions on the surface of the positive electrode active material 101 are exposed on the surface of the coated positive electrode active material 100.

[0088] Here, the concavity-convexity ζ of the particle group is defined by the following formula (1).

[0089]

[0090] In formula (1), n is an integer of 3 or more that represents the number of measured particles. There is no particular limitation on the upper limit value of n, and for example, it is 50. Lpi represents the total perimeter of the contour of the cross-sectional image of each particle. Lei represents the total perimeter of an equivalent smooth ellipse having the same aspect ratio and area as the aspect ratio and area of the cross-sectional image of each particle. The aspect ratio represents the ratio of the minor axis of the cross-sectional image to the major axis of the cross-sectional image. Lpi and Lei can be calculated from the binary image of the cross-sectional SEM image obtained by observing the cross-section of the particles with a scanning electron microscope (SEM: Scanning Electron Microscope).

[0091] The concavity-convexity ζ represents the degree of concavity and convexity of the contour of the positive electrode active material 101 and the degree of concavity and convexity of the contour of the positive electrode active material 100 covered. The concavity-convexity ζ satisfies 0 ≤ ζ ≤ 1. The closer the shape of the particle is to a smooth ellipse (circle), the closer the concavity-convexity ζ is to 1. The greater the degree of concavity and convexity of the particle, the closer the concavity-convexity ζ is to 0.

[0092] In this specification, the concavity-convexity of the particle group of the positive electrode active material 101 is defined as ζ 1 . The concavity-convexity of the particle group of the positive electrode active material 100 covered is defined as ζ 2 . The concavity-convexity ζ of the positive electrode active material 101 1 can be calculated from the binary image of the cross-sectional SEM image of the particles of the positive electrode active material 101 with the coating layer removed, based on the total perimeter Lp of the particles of the positive electrode active material 101 and the total perimeter Le of the equivalent smooth ellipse. The equivalent smooth ellipse is an ellipse having the same aspect ratio and cross-sectional area as the aspect ratio and cross-sectional area of the particles of the positive electrode active material 101. The concavity-convexity ζ of the positive electrode active material 100 covered 2 can be calculated from the binary image of the cross-sectional SEM image of the particles of the positive electrode active material 100 covered including the coating layer, based on the total perimeter Lp' of the particles of the positive electrode active material 100 covered including the coating layer and the total perimeter Le' of the equivalent smooth ellipse. The equivalent smooth ellipse is an ellipse having the same aspect ratio and cross-sectional area as the aspect ratio and cross-sectional area of the particles of the positive electrode active material 100 covered.

[0093] In addition, when the coating layer does not contact the surface of the positive electrode active material 101 and the coating layer floats (peels off) from the positive electrode active material 101, the floating part is removed from the coating layer, and each total perimeter is calculated. That is, the floating part is not regarded as the coating layer and is not treated as the coating layer. The same applies when determining the equivalent smooth ellipse. This explanation also applies to the calculation of the coating rate described later.

[0094] In the positive electrode active material 100 covered in this embodiment, the concavity-convexity change degree R defined by the following formula (2) is 1.1 or more.

[0095] R = ζ 2 / ζ 1 ···(2)

[0096] That is, the unevenness change degree R of the coated positive electrode active material 100 is determined by the unevenness degree ζ of the coated positive electrode active material 100 2 relative to the unevenness degree ζ of the positive electrode active material 101 1 ratio (ζ 2 / ζ 1 ). The upper limit value of the unevenness change degree R is the value when the contour of the coated positive electrode active material 100 is a true circle (perfect circle). That is, when the unevenness degree ζ 2 = 1 of the coated positive electrode active material 100, the unevenness change degree R takes the upper limit value. The upper limit value of the unevenness change degree R is 1 / ζ 1 . For example, if the lower limit of the unevenness degree (average value) of the positive electrode active material 101 is 0.5, the upper limit value of the unevenness change degree R is 2.0.

[0097] By covering the concave portions of the uneven portions on the surface of the positive electrode active material 101 with the solid electrolyte 102, a smooth coated positive electrode active material 100 can be achieved, and the interfacial resistance between the positive electrode active material 101 and the solid electrolyte 102 can be reduced. It can be said that the unevenness change degree R directly represents the filling situation of the concave portions by the solid electrolyte 102. In addition, by exposing at least one convex portion of the uneven portions on the surface of the positive electrode active material 101 on the surface (the outermost surface) of the coated positive electrode active material 100, the electron conductivity between adjacent coated positive electrode active materials 100 can be ensured. That is, by the contact between convex portions, the electron conductivity between the particles of the coated positive electrode active material 100 is sufficiently ensured. From this perspective, it is preferable that a plurality of convex portions are exposed on the surface (the outermost surface) of the coated positive electrode active material 100. In this case, the probability of contact between convex portions is increased. In addition, it is not necessary to expose the entire convex portion. Even if only a part of the convex portion is exposed, the above effects can be obtained.

[0098] According to the above technical configuration, the charge and discharge efficiency of the battery can be improved.

[0099] In the coated positive electrode active material 100, the ratio of the mass of the solid electrolyte 102 to the mass of the positive electrode active material 101 can be in the range of 3 / 100 or more and 1 / 10 or less. If the ratio of the mass of the solid electrolyte 102 is 3 / 100 or more, since the proportion of the solid electrolyte 102 covering the surface of the positive electrode active material 101 becomes sufficiently high, the recesses can be sufficiently filled with the solid electrolyte 102. When the ratio of the mass of the solid electrolyte 102 is 1 / 10 or less, it is difficult for the solid electrolyte 102 covering the surface of the positive electrode active material 101 to hinder the electron transfer between the positive electrode active materials 101. In this case, a battery using the coated positive electrode active material 100 as a positive electrode material can achieve excellent charge-discharge efficiency.

[0100] According to the above technical configuration, the interfacial resistance between the positive electrode active material 101 and the solid electrolyte 102 can be reduced. Thereby, the charge-discharge efficiency of the battery can be improved.

[0101] In the coated positive electrode active material 100, the ratio of the mass of the solid electrolyte 102 to the mass of the positive electrode active material 101 can be in the range of 1 / 20 or more and 7 / 100 or less.

[0102] According to the above technical configuration, the charge-discharge efficiency of the battery can be further improved.

[0103] In the cross-sectional image of the coated positive electrode active material 100, the total perimeter of the contour of the positive electrode active material 101 is defined as L, and the total length of the contact portion between the positive electrode active material 101 and the coating layer is defined as C. At this time, the coating rate represented by the ratio of the total length C to the total perimeter L, that is, C / L, can be in the range of 0.3 or more and 0.95 or less. When the coating rate is 0.3 or more, the recesses are sufficiently filled with the solid electrolyte 102. When the coating rate is 0.95 or less, it is difficult for the solid electrolyte 102 covering the surface of the positive electrode active material 101 to hinder the electron transfer between the positive electrode active materials 101. In this case, a battery using the coated positive electrode active material 100 as a positive electrode material can achieve excellent charge-discharge efficiency.

[0104] According to the above technical configuration, the interfacial resistance between the positive electrode active material 101 and the solid electrolyte 102 can be reduced. Thereby, the charge-discharge efficiency of the battery can be improved.

[0105] The coating rate can be in the range of 0.7 or more and 0.92 or less.

[0106] According to the above technical configuration, the charge-discharge efficiency of the battery can be further improved.

[0107] The coverage rate can be calculated based on the binary image of the cross-sectional SEM image of the coated positive electrode active material 100. In the plane of the same field of view of the cross-sectional SEM image of the coated positive electrode active material 100, the total perimeter L of the contour of the positive electrode active material 101 and the total length C of the contact portion between the positive electrode active material 101 and the coating layer can be obtained through image processing. The ratio C / L is defined as the coverage rate of the coating layer of the coated positive electrode active material 100. Furthermore, when the coating layer does not contact the surface of the positive electrode active material 101 and the coating layer floats from the positive electrode active material 101, this part is removed from the contact portion, and the total length C is calculated. That is, this part is not regarded as the contact portion.

[0108] The average film thickness of the coating layer can be, for example, in the range of 1 nm or more and 300 nm or less. When the average thickness of the coating layer is 1 nm or more, the recesses can be sufficiently filled with the solid electrolyte 102. When the average thickness of the coating layer is 300 nm or less, the solid electrolyte 102 coating the surface of the positive electrode active material 101 hardly hinders the electron transfer between the positive electrode active materials 101. The average thickness of the coating layer can be obtained as follows: The thicknesses of the coating layer at any 16 points are measured based on the cross-sectional SEM image of the coated positive electrode active material 100 obtained by a scanning electron microscope, and the average value is calculated from these measured values. The average film thickness of the coating layer can also be in the range of 2 nm or more and 200 nm or less.

[0109] Based on the above technical configuration, the interfacial resistance between the positive electrode active material 101 and the solid electrolyte 102 can be reduced. Thereby, the charge and discharge efficiency of the battery can be improved.

[0110] (Solid electrolyte 102 constituting the coating layer)

[0111] As the solid electrolyte 102 constituting the coating layer, a material having lithium ion conductivity, low electron conductivity, and oxidation resistance can be used.

[0112] As the solid electrolyte 102, an ion-crystalline halide solid electrolyte material can be used. The halide solid electrolyte material may not contain sulfur.

[0113] A material in which the anion constituting the solid electrolyte 102 is chlorine can be used. In other words, a material in which the anion constituting the solid electrolyte 102 is only chloride ions can be used.

[0114] More specifically, the solid electrolyte 102 has a composition represented by the following formula (3). In formula (3), α, β, and γ are values greater than 0, and M includes at least one selected from metal elements other than Li and semi-metal elements (metalloid elements).

[0115] Li α Mβ Cl γ ···(3)

[0116] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0117] "Metal elements" include all elements contained in Groups 1 to 12 of the periodic table except hydrogen, and all elements contained in Groups 13 to 16 except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. That is, "metal elements" are a group of elements that can become cations when forming inorganic compounds with halogen compounds.

[0118] If the solid electrolyte 102 contains at least one element selected from metal elements other than Li and metalloid elements, the solid electrolyte 102 has a higher ionic conductivity than a solid electrolyte 102 such as LiI composed only of Li and halogen elements. Therefore, when the solid electrolyte 102 containing at least one element selected from metal elements other than Li and metalloid elements is used in a battery, the charge-discharge efficiency of the battery can be improved.

[0119] In formula (3), M may contain yttrium. That is, the solid electrolyte 102 may contain Y as a metal element.

[0120] According to the above technical configuration, the ionic conductivity of the solid electrolyte 102 can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0121] The solid electrolyte 102 containing Y may also be a compound represented by the composition formula Li a Me b Y c Cl 6 Here, a + mb + 3c = 6 and c > 0 are satisfied. Me is at least one element selected from metal elements and metalloid elements other than Li and Y. m is the valence of Me.

[0122] As Me, at least one element selected from Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, Gd, Sm, Tb, and Nb can be used.

[0123] According to the above technical configuration, the ionic conductivity of the solid electrolyte 102 can be further improved.

[0124] In formula (3), 2.5 ≤ α ≤ 3, 1 ≤ β ≤ 1.1, and γ = 6 can be satisfied.

[0125] Based on the above technical configuration, the ionic conductivity of the solid electrolyte 102 can be further improved. Thereby, the charge and discharge efficiency of the battery can be further improved.

[0126] The solid electrolyte 102 may have a composition represented by the following formula (A1). In the formula (A1), 0 < d < 2 is satisfied.

[0127] Li 6-3d Y d Cl 6 ···(A1)

[0128] Based on the above technical configuration, the ionic conductivity of the solid electrolyte 102 can be further improved. Thereby, the charge and discharge efficiency of the battery can be further improved.

[0129] The solid electrolyte 102 may have a composition represented by the following formula (A2).

[0130] Li 3 YCl 6 ···(A2)

[0131] Based on the above technical configuration, the ionic conductivity of the solid electrolyte 102 can be further improved. Thereby, the charge and discharge efficiency of the battery can be further improved.

[0132] The solid electrolyte 102 may have a composition represented by the following formula (A3). In the formula (A3), 0 < δ ≤ 0.15 is satisfied.

[0133] Li 3-3δ Y 1+δ Cl 6 ···(A3)

[0134] Based on the above technical configuration, the ionic conductivity of the solid electrolyte 102 can be further improved. Thereby, the charge and discharge efficiency of the battery can be further improved.

[0135] The "solid electrolyte" in the present disclosure is not limited to a substance that strictly satisfies the above compositional formula, and also includes a substance containing extremely trace impurities in addition to the constituent elements represented by the compositional formula. For example, in the coating material, the impurities contained in addition to the constituent elements represented by the compositional formula may be 10 mol% or less.

[0136] (Method for manufacturing the solid electrolyte 102)

[0137] The solid electrolyte 102 (the first solid electrolyte) in Embodiment 1 can be manufactured by the following method.

[0138] Prepare raw material powder of halides having a mixing ratio of the target composition. For example, when preparing Li 3 YCl6 In the case of, LiCl and YCl 3 are prepared in a molar ratio of 3:1. At this time, by selecting the types of raw material powders, "M" and "Me" in the above compositional formula can be determined. In addition, by adjusting the raw materials, mixing ratio, and synthesis process, the above values of "α", "β", "γ", "d", and "δ" can be adjusted.

[0139] After thoroughly mixing the raw material powders, the mechanical chemical grinding method is used to mix, crush, and react the raw material powders with each other. Alternatively, after thoroughly mixing the raw material powders, the mixed powder can be fired in a vacuum or an inert atmosphere. The firing conditions can be, for example, firing for 1 hour or more within the range of 100°C or higher and 650°C or lower. Thus, the solid electrolyte 102 having the above composition is obtained.

[0140] In addition, the composition (crystal structure) of the crystal phase in the coating material can be determined by adjusting the reaction method and reaction conditions between the raw material powders.

[0141] (Positive electrode active material 101)

[0142] The positive electrode active material 101 is, for example, a material having the property of occluding and releasing metal ions (such as lithium ions). As the positive electrode active material 101, lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides can be cited. As the lithium-containing transition metal oxide, Li(Ni,Co,Al)O 2 , Li(Ni,Co,Mn)O 2 and LiCoO 2 etc. can be cited. One or a mixture of two or more selected from them can be used as the positive electrode active material 101.

[0143] When using a lithium-containing transition metal oxide as the positive electrode active material 101, the manufacturing cost of the positive electrode can be reduced and the average discharge voltage can be increased.

[0144] The positive electrode active material 101 may contain lithium nickel cobalt manganese oxide. The positive electrode active material 101 may contain Li(NiCoMn)O 2 . As the positive electrode active material 101, lithium nickel cobalt manganese oxide can be used alone. According to the above technical composition, the energy density of the battery can be further improved.

[0145] There is no particular limitation on the shape of the particles of the positive electrode active material 101. The shape of the particles of the positive electrode active material 101 can be spherical, ellipsoidal, scaly, or fibrous.

[0146] In Embodiment 1, the positive electrode active material 101 may have a surface layer containing a lithium metal oxide. The lithium metal oxide constituting the surface layer has a composition different from that of the lithium-containing transition metal oxide constituting the main body portion (the portion excluding the surface layer) of the positive electrode active material 101. As the lithium metal oxide, LiNbO 3 (lithium niobate), etc. can be used. By the positive electrode active material 101 having a surface layer containing LiNbO 3 , side reactions between the positive electrode active material 101 and the coating layer during charging can be suppressed. Therefore, according to this technical configuration, the coated positive electrode active material 100 in Embodiment 1 can effectively suppress the formation of a high-resistance layer on the surface of the positive electrode active material 101. As a result, the charge-discharge efficiency of the battery can be further improved.

[0147] When the positive electrode active material 101 has the above surface layer, the surface layer is also regarded as a part of the positive electrode active material 101.

[0148] (Manufacturing method of the coated positive electrode active material 100)

[0149] The manufacturing method of the coated positive electrode active material 100 in Embodiment 1, for example, includes treating the positive electrode active material 101 and the solid electrolyte 102 constituting the coating layer by a dry particle compounding method. The treatment by the dry particle compounding method includes imparting at least one of mechanical energies selected from impact, compression, and shear to the positive electrode active material 101 and the solid electrolyte 102. The positive electrode active material 101 and the solid electrolyte 102 are mixed in an appropriate ratio.

[0150] By the above method, the desired coated positive electrode active material 100 can be manufactured.

[0151] The device that can be used in the manufacturing method of the coated positive electrode active material 100 is not particularly limited, and it can be a device that can impart mechanical energies such as impact, compression, and shear to the mixture. As the device that can impart mechanical energy, ball mills, "MECHANOFUSION" (manufactured by Hosokawa Micron Corporation), "NOBILTA" (manufactured by Hosokawa Micron Corporation), etc. compression-shear type processing devices (particle compounding devices) can be cited. Among them, "MECHANOFUSION" and "NOBILTA" are preferred, and "NOBILTA" is more preferred.

[0152] "MECHANOFUSION" is a particle compounding device that uses a dry mechanical compounding technology that applies strong mechanical energy to multiple different raw material particles. In MECHANOFUSION, particle compounding is caused by applying mechanical energies such as compression, shear, and friction to the powder raw materials input between a rotating container and a pressing head.

[0153] “NOBILTA” is a particle compounding device that uses a dry mechanical compounding technique to develop particle compounding technology for compounding with nanoparticles as raw materials. NOBILTA manufactures composite particles by applying mechanical energy of impact, compression, and shear to multiple raw material powders.

[0154] In “NOBILTA”, a rotor configured to have a predetermined gap with the inner wall of a horizontal cylindrical mixing container rotates at high speed, and the raw material powder is repeatedly subjected to a process of being forced through the gap multiple times. Thereby, forces of impact, compression, and shear can act on the mixture to produce composite particles of the positive electrode active material 101 and the solid electrolyte 102. Conditions such as the rotation speed of the rotor, the processing time, and the loading amount can be appropriately adjusted.

[0155] In the manufacture of the coated positive electrode active material 100, a powder of the solid electrolyte 102 is used. The ratio Da / Dc of the average particle diameter Da of the positive electrode active material 101 to the average particle diameter Dc of the solid electrolyte 102 can be 2 or more. In this case, the concave portions of the uneven portions on the surface of the positive electrode active material 101 are densely filled with the solid electrolyte 102. As a result, the interfacial resistance between the positive electrode active material 101 and the coating layer is reduced, and the charge and discharge efficiency of the battery can be further improved.

[0156] The ratio Da / Dc can be 5 or more. In this case, the concave portions of the uneven portions on the surface of the positive electrode active material 101 are more densely filled with the solid electrolyte 102. As a result, the interfacial resistance between the positive electrode active material 101 and the coating layer is further reduced, and the charge and discharge efficiency of the battery can be further improved.

[0157] The average particle diameters of the positive electrode active material 101 and the coating material can be measured using, for example, SEM images. Specifically, using SEM images, the average value of the equivalent circle diameters of 50 randomly selected particles of the positive electrode active material 101 and 50 randomly selected particles of the solid electrolyte 102 is calculated, and thereby the average particle diameters of the positive electrode active material 101 and the solid electrolyte 102 are obtained. The “equivalent circle diameter” refers to the diameter of a circle having an area equal to the area of the image of a specific particle.

[0158] (Positive electrode material 1000)

[0159] Figure 2 It is a cross-sectional view showing the general structure of the positive electrode material 1000 in Embodiment 1.

[0160] The positive electrode material 1000 in Embodiment 1 includes the coated positive electrode active material 100 and the positive electrode solid electrolyte 202 in the above Embodiment 1. By using the coated positive electrode active material 100 of Embodiment 1 for the positive electrode material, a battery with excellent charge-discharge efficiency can be obtained.

[0161] The positive electrode solid electrolyte 202 includes, for example, a solid electrolyte with high ionic conductivity.

[0162] The positive electrode solid electrolyte 202 may have the same composition as the solid electrolyte 102 constituting the coating layer. As the positive electrode solid electrolyte 202, for example, Li 3 YCl 6 etc. can be used.

[0163] The positive electrode solid electrolyte 202 may include a halide solid electrolyte. As the halide solid electrolyte, for example, Li 3 (Ca,Y,Gd)X 6 、Li 2 MgX 4 、Li 2 FeX 4 、Li(Al,Ga,In)X 4 、Li 3 (Al,Ga,In)X 6 、LiI, etc. Here, in these solid electrolytes, the element X is at least one selected from Cl, Br, and I. In addition, in the present disclosure, when expressing an element in a formula as “(Al,Ga,In)”, this notation means at least one element selected from the group of elements in the parentheses. That is, “(Al,Ga,In)” is synonymous with “at least one selected from Al, Ga, and In”. The same applies to other elements. The halide solid electrolyte exhibits excellent ionic conductivity.

[0164] The positive electrode solid electrolyte 202 may be a halide solid electrolyte. For example, the halide solid electrolyte includes lithium, yttrium, chlorine, and bromine. The halide solid electrolyte may be Li 3 YBr 2 Cl 4 .

[0165] The positive electrode solid electrolyte 202 may include a sulfide solid electrolyte. As the sulfide solid electrolyte, for example, Li 2 S-P 2 S 5 、Li 2 S-SiS 2 、Li 2 S-B 2 S 3 、Li 2 S-GeS2 , Li 3.25 , Ge 0.25 , P 0.75 , S 4 , Li 10 , GeP 2 , S 12 etc. LiX, Li can also be added thereto 2 , O, MO q , Li p , MO q etc. Here, the element X in "LiX" is one or more elements selected from F, Cl, Br, and I. "MO q " and "Li p , MO q " The element M in is one or more elements selected from P, Si, Ge, B, Al, Ga, In, Fe, and Zn. "MO q " and "Li p , MO q " The p and q in are independent natural numbers respectively.

[0166] The positive electrode solid electrolyte 202 can be a sulfide solid electrolyte. For example, the sulfide solid electrolyte can contain lithium sulfide and phosphorus sulfide. For example, the sulfide solid electrolyte can be Li 2 S-P 2 S 5 . The sulfide solid electrolyte exhibits excellent ionic conductivity.

[0167] As the positive electrode solid electrolyte 202, a mixture of one or more selected from the above solid electrolytes can be used.

[0168] There is no particular limitation on the shape of the positive electrode solid electrolyte 202. The shape of the positive electrode solid electrolyte 202 can be needle-like, spherical, ellipsoidal, etc. The shape of the positive electrode solid electrolyte 202 can also be particles.

[0169] When the shape of the positive electrode solid electrolyte 202 is particle-like (e.g., spherical), the median particle size of the positive electrode solid electrolyte 202 can be 100 μm or less. When the median particle size of the positive electrode solid electrolyte 202 is 100 μm or less, the coated positive electrode active material 100 and the positive electrode solid electrolyte 202 can form a good dispersion state in the positive electrode material 1000. Therefore, the charge-discharge characteristics of the battery using the positive electrode material 1000 are improved.

[0170] The median particle size of the positive electrode solid electrolyte 202 can be 10 μm or less. According to this technical configuration, in the positive electrode material 1000, the coated positive electrode active material 100 and the positive electrode solid electrolyte 202 can form a better dispersion state.

[0171] The median particle size of the positive electrode solid electrolyte 202 can be smaller than the median particle size of the coated positive electrode active material 100. According to this technical configuration, in the positive electrode material 1000, the coated positive electrode active material 100 and the positive electrode solid electrolyte 202 can form a better dispersion state.

[0172] The median particle size of the coated positive electrode active material 100 can be 0.1 μm or more and 100 μm or less.

[0173] If the median particle size of the coated positive electrode active material 100 is 0.1 μm or more, in the positive electrode material 1000, the coated positive electrode active material 100 and the positive electrode solid electrolyte 202 can form a good dispersion state. As a result, the charge-discharge characteristics of the battery using the positive electrode material 1000 are improved. In addition, if the median particle size of the coated positive electrode active material 100 is 100 μm or less, the lithium diffusion rate in the coated positive electrode active material 100 is increased. Therefore, the battery using the positive electrode material 1000 can operate at a high output.

[0174] The median particle size of the coated positive electrode active material 100 can also be larger than the median particle size of the positive electrode solid electrolyte 202. Thereby, the coated positive electrode active material 100 and the positive electrode solid electrolyte 202 can form a good dispersion state.

[0175] In the positive electrode material 1000, the positive electrode solid electrolyte 202 and the coating layer of the coated positive electrode active material 100 can be in contact with each other.

[0176] In addition, the positive electrode material 1000 in Embodiment 1 may include a plurality of positive electrode solid electrolytes 202 and a plurality of coated positive electrode active materials 100.

[0177] In addition, in the positive electrode material 1000 of Embodiment 1, the content of the positive electrode solid electrolyte 202 and the content of the coated positive electrode active material 100 may be the same or different from each other.

[0178] (Embodiment 2)

[0179] Hereinafter, Embodiment 2 will be described. The description of the parts overlapping with Embodiment 1 above will be appropriately omitted.

[0180] Figure 3 It is a cross-sectional view showing a schematic structure of the battery in Embodiment 2.

[0181] The battery 300 in Embodiment 2 includes a positive electrode 301 containing the positive electrode material 1000 described in Embodiment 1 above, an electrolyte layer 302, and a negative electrode 303. By using the positive electrode material 1000 in the positive electrode 301, a battery 300 with excellent charge-discharge efficiency can be obtained.

[0182] The positive electrode 301 contains a material having the property of occluding and releasing metal ions (e.g., lithium ions). The positive electrode 301 includes a coated positive electrode active material 100 and a positive electrode solid electrolyte 202.

[0183] When the volume ratio of the positive electrode active material 101 contained in the positive electrode 301 to the total of the solid electrolyte 102 and the positive electrode solid electrolyte 202 is set to "v1:100 - v1", 30 ≤ v1 ≤ 95 can be satisfied. Here, v1 represents the volume fraction of the positive electrode active material 101 when the total volume of the positive electrode active material 101, the solid electrolyte 102, and the positive electrode solid electrolyte 202 contained in the positive electrode 301 is set to 100. When 30 ≤ v1 is satisfied, it is easy to ensure a sufficient energy density of the battery 300. When v1 ≤ 95 is satisfied, the operation of the battery 300 at high output becomes easier.

[0184] The thickness of the positive electrode 301 can be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 301 is 10 μm or more, a sufficient energy density of the battery 300 can be ensured. When the thickness of the positive electrode 301 is 500 μm or less, the operation of the battery 300 at high output can be achieved.

[0185] The electrolyte layer 302 is disposed between the positive electrode 301 and the negative electrode 303.

[0186] The electrolyte layer 302 is a layer containing an electrolyte material. This electrolyte material can contain, for example, a solid electrolyte (the second solid electrolyte). That is, the electrolyte layer 302 can be a solid electrolyte layer.

[0187] As the solid electrolyte contained in the electrolyte layer 302, at least one selected from halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes can be used.

[0188] The electrolyte layer 302 can contain at least one selected from a solid electrolyte having the same composition as the solid electrolyte 102 contained in the coating layer covering the positive electrode active material 100 and a solid electrolyte having the same composition as the positive electrode solid electrolyte 202.

[0189] When the electrolyte layer 302 contains a halide solid electrolyte, the halide solid electrolyte can have the same composition as the halide solid electrolyte contained in the solid electrolyte 102, or can have the same composition as the halide solid electrolyte contained in the positive electrode solid electrolyte 202. When the composition of the halide solid electrolyte contained in the solid electrolyte 102 is different from the composition of the halide solid electrolyte contained in the positive electrode solid electrolyte 202, the electrolyte layer 302 can contain these halide solid electrolytes having different compositions from each other.

[0190] Based on the above technical configuration, the charge and discharge characteristics of the battery 300 can be further improved.

[0191] The electrolyte layer 302 may include a halide solid electrolyte having a composition different from that of the solid electrolyte 102 contained in the coating layer and / or the positive electrode solid electrolyte 202.

[0192] Based on the above technical configuration, the charge and discharge characteristics of the battery 300 can be further improved.

[0193] The electrolyte layer 302 may include a sulfide solid electrolyte. The sulfide solid electrolyte contained in the electrolyte layer 302 may have the same composition as the sulfide solid electrolyte contained in the positive electrode solid electrolyte 202.

[0194] Based on the above technical configuration, the charge and discharge characteristics of the battery can be further improved.

[0195] If the electrolyte layer 302 includes a sulfide solid electrolyte with excellent reduction stability, the negative electrode 303 can use a low-potential negative electrode material such as graphite or metallic lithium. Thereby, the energy density of the battery 300 can be increased.

[0196] The electrolyte layer 302 may include an oxide solid electrolyte. As the oxide solid electrolyte contained in the electrolyte layer 302, for example, NASICON-type solid electrolyte materials represented by LiTi 2 (PO 4 ) 3 and its element substitution bodies, perovskite-type solid electrolyte materials of the (LaLi)TiO 3 system, LISICON-type solid electrolyte materials represented by Li 14 ZnGe 4 O 16 、Li 4 SiO 4 、LiGeO 4 and their element substitution bodies, garnet-type solid electrolyte materials represented by Li 7 La 3 Zr 2 O 12 and its element substitution bodies, Li 3 PO 4 and its N substitution bodies, LiBO 2 、Li 3 BO 3 and other Li-B-O compounds with Li 2 SO 4 、Li 2 CO 3Glass formed by equalizing, glass ceramics, etc.

[0197] The solid electrolyte contained in the electrolyte layer 302 may include a polymer solid electrolyte. As the polymer solid electrolyte contained in the electrolyte layer 302, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may also have an ethylene oxide (oxirane) structure. The polymer compound having an ethylene oxide structure can contain a relatively large amount of lithium salt. Therefore, the ionic conductivity can be further improved. As the lithium salt, LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiSO 3 CF 3 , LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ), LiC(SO 2 CF 3 ) 3 etc. The lithium salt can be used alone as one kind, or two or more kinds can be used in combination.

[0198] The electrolyte layer 302 may include a complex hydride solid electrolyte. As the complex hydride solid electrolyte contained in the electrolyte layer 302, for example, LiBH 4 -LiI, LiBH 4 -P 2 S 5 etc.

[0199] In addition, the electrolyte layer 302 may contain the above solid electrolyte as a main component. That is, the electrolyte layer 302 can contain, for example, a solid electrolyte in a mass ratio of 50% or more (i.e., 50 mass% or more) with respect to the entire electrolyte layer 302.

[0200] According to the above technical configuration, the output characteristics of the battery 300 can be further improved.

[0201] In addition, the electrolyte layer 302 can contain, for example, a solid electrolyte in a mass ratio of 70% or more (i.e., 70 mass% or more) with respect to the entire electrolyte layer 302.

[0202] According to the above technical configuration, the output characteristics of the battery 300 can be further improved.

[0203] In addition, the electrolyte layer 302 may contain a solid electrolyte as a main component, and also contains inevitable impurities, starting materials used in synthesizing the solid electrolyte, by-products, decomposition products, etc.

[0204] In addition, for example, except for the inevitably mixed impurities, the electrolyte layer 302 may contain a solid electrolyte in a mass ratio of 100% (i.e., 100 mass%) with respect to the entire electrolyte layer 302.

[0205] According to the above technical configuration, the output characteristics of the battery 300 can be further improved.

[0206] As described above, the electrolyte layer 302 may be composed only of a solid electrolyte.

[0207] In addition, the electrolyte layer 302 may contain two or more of the materials listed as solid electrolyte materials. For example, the electrolyte layer 302 may include a halide solid electrolyte and a sulfide solid electrolyte.

[0208] The thickness of the electrolyte layer 302 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 302 is 1 μm or more, the possibility of short - circuit between the positive electrode 301 and the negative electrode 303 becomes low. In addition, when the thickness of the electrolyte layer 302 is 300 μm or less, high - output operation becomes easy. That is, if the thickness of the electrolyte layer 302 is appropriately adjusted, sufficient safety of the battery 300 can be ensured, and the battery 300 can operate at high output.

[0209] The negative electrode 303 contains a material having the property of occluding and releasing metal ions (such as lithium ions). The negative electrode 303 contains a negative electrode active material 203 (such as negative electrode active material particles).

[0210] The negative electrode active material 203 can use a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound, etc. The metal material can be a single metal. Or, the metal material can be an alloy. Examples of the metal material include lithium metal or a lithium alloy. Examples of the carbon material include natural graphite, coke, graphitized intermediate carbon, carbon fiber, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, silicon, tin, a silicon compound, or a tin compound can be preferably used. A mixture of one or two or more of these materials can be used as the negative electrode active material 203.

[0211] The negative electrode 303 may include a negative electrode solid electrolyte 205. According to the above technical structure, the lithium ion conductivity inside the negative electrode 303 can be improved, enabling operation at high output. As the negative electrode solid electrolyte 205, materials listed as examples of the solid electrolyte of the electrolyte layer 302 can be used.

[0212] The median particle size of the particles of the negative electrode active material 203 can be larger than the median particle size of the negative electrode solid electrolyte 205. Thus, a good dispersion state of the negative electrode active material 203 and the negative electrode solid electrolyte 205 can be formed.

[0213] Regarding the volume ratio "v2:100 - v2" of the negative electrode active material 203 and the negative electrode solid electrolyte 205 contained in the negative electrode 303, 30 ≤ v2 ≤ 95 can be satisfied. When 30 ≤ v2 is satisfied, it is easy to ensure sufficient energy density of the battery 300. When v2 ≤ 95 is satisfied, the operation of the battery 300 at high output becomes easier.

[0214] The thickness of the negative electrode 303 can be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 303 is 10 μm or more, it is easy to ensure sufficient energy density of the battery 300. When the thickness of the negative electrode 303 is 500 μm or less, the operation of the battery 300 at high output becomes easier.

[0215] In at least one of the positive electrode 301, the electrolyte layer 302, and the negative electrode 303, a binder may be contained to improve the adhesion between particles. The binder is used to improve the adhesion of the materials constituting the electrode. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, methyl polyacrylate, ethyl polyacrylate, hexyl polyacrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropropylene, styrene-butadiene rubber, carboxymethyl cellulose, etc. In addition, as the binder, a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, hexadiene can be used. In addition, two or more selected from them can also be mixed and used as the binder.

[0216] In order to improve the electronic conductivity, at least one of the positive electrode 301 and the negative electrode 303 may contain a conductive additive. As the conductive additive, for example, graphite-based materials such as natural graphite or artificial graphite, carbon black-based materials such as acetylene black or Ketjen black, conductive fiber-based materials such as carbon fiber or metal fiber, carbon fluoride, metal powder-based materials such as aluminum, conductive whisker-based materials such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, conductive polymer compounds such as polyaniline, polypyrrole or polythiophene, etc. can be used. In the case of using a carbon conductive additive, cost reduction can be achieved.

[0217] In addition, the battery 300 in Embodiment 2 can be configured as a battery in various shapes such as coin type, cylindrical type, square type, sheet type, button type, flat type, laminated type, etc.

[0218] The battery 300 in Embodiment 2 can also be manufactured, for example, by separately preparing the positive electrode material, the material for forming the electrolyte layer, and the material for forming the negative electrode in Embodiment 1, and using a known method to fabricate a laminate in which the positive electrode, the electrolyte layer, and the negative electrode are sequentially arranged.

[0219] Examples

[0220] Hereinafter, the present disclosure will be described in more detail using examples.

[0221] (Example 1a)

[0222] [Production of Solid Electrolyte]

[0223] In a glove box with an argon atmosphere where the dew point is -60°C or lower and the oxygen value is 5 ppm or lower, the raw material powders LiCl and YCl 3 were weighed at a molar ratio of LiCl:YCl 3 = 3:1. These raw material powders were mixed in an agate mortar to obtain a mixture. Then, the mixture was heat-treated at 500°C for 12 hours in an inert atmosphere to obtain a fired product represented by the composition formula Li 3 YCl 6 (hereinafter referred to as LYC). By pulverizing the fired product with an agate mortar, a powder of LYC with an average particle size of 5 μm was obtained. The powder of LYC was mixed with an appropriate amount of solvent, and using a planetary ball mill device (manufactured by Fritsch, model P-7), it was ground at 200 rpm for 20 minutes, then the solvent was removed and dried. Thus, a powder of LYC with an average particle size of 0.5 μm as the solid electrolyte was obtained. The particle size of the solid electrolyte is the median particle size, which is obtained by calculating the average value of the equivalent circle diameters of 50 randomly selected particles inside the particles of the solid electrolyte observed at a magnification of 5000 times using a scanning electron microscope (manufactured by Keyence, 3D true surface view microscope, VE-8800).

[0224] [Positive electrode active material]

[0225] As the positive electrode active material, Li(NiCoMn)O with an average particle size of 5 μm was used 2 (hereinafter referred to as NCM).

[0226] [Production of coated positive electrode active material]

[0227] A particle composite device (NOBILTA, NOB-MINI, manufactured by Hosokawa Micron Corporation) was used to coat the positive electrode active material with a solid electrolyte. 50 g of NCM and 2.5 g of LYC powder were placed in the container of NOB-MINI, and NCM and LYC were subjected to a composite treatment at a rotational speed of 6000 rpm, an operating time of 15 minutes, and a power value of 640 W to produce a coated positive electrode active material.

[0228] (Example 1b)

[0229] A coated positive electrode active material was produced in the same manner as in Example 1a, except that the mixing amount of LYC was set to 5 g.

[0230] (Comparative Example 1a)

[0231] A coated positive electrode active material was produced in the same manner as in Example 1a, except that the mixing amount of LYC was set to 1.25 g.

[0232] (Comparative Example 1b)

[0233] A coated positive electrode active material was produced in the same manner as in Example 1a, except that LYC with an average particle size of 5 μm was used instead of LYC with an average particle size of 0.5 μm.

[0234] [Measurement of coating rate and average film thickness of coating layer]

[0235] The unevenness change degree, coating rate, and average film thickness of the coating layer of the coated positive electrode active materials of Example 1a, Example 1b, Comparative Example 1a, and Comparative Example 1b were measured. In the measurement, 3 randomly selected coated positive electrode active materials were used. A cross-sectional SEM image of the coated positive electrode active material was obtained using a scanning electron microscope (SU-70, manufactured by HITACHI). Avoiding parts where materials such as positive electrode active materials and solid electrolytes agglomerated, particles of the coated positive electrode active material were selected in an average field of view where a uniform coated positive electrode active material was observed. The unevenness change degree, coating rate, and average film thickness of the coating layer were calculated based on the cross-sectional SEM image of the coated positive electrode active material. The results are shown in Table 1. The "coating weight ratio" is the weight ratio of the positive electrode active material to the solid electrolyte of the coating layer.

[0236] Figure 4A and Figure 4B are respectively the binary images of the cross-sectional SEM images of the coated positive electrode active materials of Example 1a and Comparative Example 1b.

[0237] Table 1

[0238] Particle size of LYC (μm) Coating weight ratio Degree of unevenness change Coating rate Average film thickness (nm) Example 1a 0.5 100∶5 1.12 0.75 130 Example 1b 0.5 100∶10 1.20 0.92 203 Comparative Example 1a 0.5 100∶2.5 1.05 0.25 22 Comparative Example 1b 5 100∶5 1.03 0.41 64

[0239] As can be seen from Table 1, the coated positive electrode active materials of Example 1a and Example 1b have an unevenness change degree of 1.1 or more. The unevenness change degrees of the coated positive electrode active materials of Example 1a and Example 1b are 1.12 and 1.20 respectively. The coated positive electrode active materials of Example 1a and Example 1b have a coating rate of 0.7 or more and 0.95 or less. The coating rates of the coated positive electrode active materials of Example 1a and Example 1b are 0.75 and 0.92 respectively. The coating layers of the coated positive electrode active materials of Example 1a and Example 1b have an average film thickness of 100 nm or more and 300 nm or less. The average film thicknesses of the coating layers of the coated positive electrode active materials of Example 1a and Example 1b are 130 nm and 203 nm respectively.

[0240] From Figure 4A it can be seen that in the coated positive electrode active material of Example 1a, the coating layer is formed in such a way that the concave portions of the uneven portions on the surface of the light gray positive electrode active material are filled with the black solid electrolyte. A part of the convex portions of the uneven portions on the surface of the light gray positive electrode active material is exposed on the surface of the coated positive electrode active material.

[0241] By densely forming the coating layer in such a way as to fill the concave portions of the uneven portions on the surface of the positive electrode active material, the interfacial resistance when lithium ions move between the surface of the positive electrode active material and the coating layer is reduced. In addition, by exposing a part of the convex portions of the uneven portions on the surface of the positive electrode active material, the electron conductivity between adjacent positive electrode active materials can be ensured. Thereby, the charge and discharge efficiency of the battery can be improved.

[0242] On the other hand, from Figure 4B it can be seen that in the coated positive electrode active material of Comparative Example 1b, the coating layer is formed in such a way that the concave portions of the light gray positive electrode active material become voids. There are portions where the concave portions of the uneven portions on the surface of the light gray positive electrode active material are not sufficiently filled with the black solid electrolyte.

[0243] [Fabrication of Battery]

[0244] (Example 2a, Example 2b, Comparative Examples 2a to 2c)

[0245] Using the coated positive electrode active materials of the above Example 1a, Example 1b, Comparative Example 1a and Comparative Example 1b, the following steps were carried out.

[0246] In a glove box with an argon atmosphere having a dew point of -60°C or less and an oxygen value of 5 ppm or less, the coated positive electrode active material and Li as the positive electrode solid electrolyte of any one of Example 1a, Example 1b, Comparative Example 1a and Comparative Example 1b were weighed. 2 SP 2 S 5 The volume ratio of the positive electrode active material to the solid electrolyte forming the coating layer and the positive electrode solid electrolyte was 60:40. These were mixed in an agate mortar to prepare positive electrode materials of Example 2a, Example 2b, Comparative Example 2a and Comparative Example 2b.

[0247] 80 mg of Li was added to the insulating outer cylinder. 2 SP 2 S 5 , and it is press-formed at a pressure of 80MPa to obtain an electrolyte layer. Next, 14 mg of the positive electrode material of any one of Example 1a, Example 1b, Comparative Example 1a and Comparative Example 1b is added in terms of the positive electrode active material equivalent, and is press-formed at a pressure of 720MPa to obtain a positive electrode layer. Next, metal In (thickness 200μm), metal Li (thickness 300μm), and metal In (thickness 200μm) are stacked in sequence on the electrolyte layer on the counter electrode side. It is press-formed at a pressure of 80MPa to obtain a negative electrode layer. Next, stainless steel collectors are arranged above and below the stack comprising the positive electrode layer, the electrolyte layer, and the negative electrode layer, and a collector lead is attached to the collector. Finally, the insulating outer cylinder is sealed by using an insulating hoop to isolate the inside of the insulating outer cylinder from the external gas atmosphere, thereby making a battery. Furthermore, the inner diameter of the insulating outer cylinder used in this embodiment is 9.5mm, and the projected area of ​​the electrode is 0.71cm 2 .

[0248] (Comparative Example 2c)

[0249] A battery was prepared in the same manner as in Example 2a except that a positive electrode active material having no coating layer was used as the positive electrode material.

[0250] Using the batteries of Example 2a, Example 2b, Comparative Example 2a, Comparative Example 2b, and Comparative Example 2c, battery evaluation was performed under the following conditions.

[0251] The batteries of the examples and comparative examples were placed in a constant temperature chamber at 85°C.

[0252] The battery was charged at a constant current of 140 μA at a rate of 0.05C (20-hour rate) relative to the theoretical capacity of the battery. +When the voltage of the reference voltmeter reaches 4.3 V, the charging ends. Then, the battery is charged at a constant voltage of 3.68 V, and the charging ends when the current value at a rate of 0.01C becomes 28 μA or less. After charging, the interfacial resistance value between the coated positive electrode active material and the positive electrode solid electrolyte is obtained by impedance measurement using the AC impedance method. The impedance measurement conditions are a voltage amplitude of 5 mV, a measurement frequency of 1 MHz to 0.1 Hz, and 85°C. The results are shown in Table 2. Then, the battery is left standing in an open circuit state for 3 days. Then, the battery is discharged with a current value of 140 μA at a rate of 0.05C, and the discharge ends when the voltage reaches 1.88 V (equivalent to 2.5 V with the reference voltmeter). + When the voltage of the reference voltmeter reaches 2.5 V, the discharge ends.

[0253] Through the above, the discharge capacities and capacity efficiencies of the batteries in the above-mentioned examples and comparative examples are obtained. The results are shown in Table 2 below. The capacity efficiency is the ratio of the discharge capacity to the charge capacity. The capacity efficiency has the same meaning as the charge-discharge efficiency.

[0254] As can be seen from Table 2, the batteries of Examples 2a and 2b show higher discharge capacities and capacity efficiencies than the batteries of Comparative Examples 2a to 2c. The batteries of Examples 2a and 2b show lower interfacial resistances than the batteries of Comparative Examples 2a to 2c.

[0255] Table 2

[0256] Discharge capacity (mAh / g) Capacity efficiency (%) Interface resistance (Ω) Example 2a 198 93.7 11 Example 2b 195 91.6 8.3 Comparative Example 2a 185 86.5 27 Comparative Example 2b 178 87.8 60 Comparative Example 2c 185 88.8 64

[0257] (Example 3)

[0258] Except for using Li 3 YCl 6 as the positive electrode solid electrolyte for the positive electrode material, a battery is fabricated according to the same procedure as in Example 2a.

[0259] (Comparative Example 3a)

[0260] Except for using Li 3 YCl 6 as the positive electrode solid electrolyte for the positive electrode material, a battery is fabricated according to the same procedure as in Comparative Example 2b.

[0261] (Comparative Example 3b)

[0262] Except for using Li 3 YCl 6 as the positive electrode solid electrolyte for the positive electrode material, a battery is fabricated according to the same procedure as in Comparative Example 2c.

[0263] Using the batteries of Example 3, Comparative Example 3a, and Comparative Example 3b above, battery evaluation is carried out under the same conditions as in Example 2a. The results are shown in Table 3 below.

[0264] As shown in Table 3, in the case where a halide solid electrolyte is used for the positive electrode solid electrolyte, the battery of Example 3 also shows a higher discharge capacity and capacity efficiency than the batteries of Comparative Example 3a and Comparative Example 3b. In addition, the battery of Example 3 shows a lower interfacial resistance than the batteries of Comparative Example 3a and Comparative Example 3b.

[0265] Table 3

[0266] Discharge capacity (mAh / g) Capacity efficiency (%) Interface resistance (Ω) Example 3 205 96.9 12 Comparative Example 3a 191 95.1 55 Comparative Example 3b 183 95.2 35

[0267] (Example 4)

[0268] NCM using lithium niobate film with an average film thickness of 6 nm is used, and Li 3 YBr 2 Cl 4 is used. A conductive additive (VGCF-H, manufactured by Showa Denko K.K.) is added to the positive electrode material in an amount of 2% by weight based on the positive electrode active material, and the battery is fabricated in the same manner as in Example 2a except for this.

[0269] (Comparative Example 4)

[0270] NCM using lithium niobate film with an average film thickness of 6 nm is used, and Li 3 YBr 2 Cl 4 is used. A conductive additive (VGCF-H) is added to the positive electrode material in an amount of 2% by weight based on the positive electrode active material, and the battery is fabricated in the same manner as in Comparative Example 2b except for this.

[0271] Using the batteries of Example 4 and Comparative Example 4 described above, battery evaluation was carried out under the same conditions as in Example 2a. The results are shown in Table 4 below.

[0272] As shown in Table 4, in the case where a halide solid electrolyte having a composition different from that of the solid electrolyte of the coating layer is used for the positive electrode solid electrolyte, the battery of Example 4 also shows a higher discharge capacity and capacity efficiency than the battery of Comparative Example 4. The battery of Example 4 shows a lower interfacial resistance than the battery of Comparative Example 4.

[0273] Table 4

[0274] Discharge capacity (mAh / g) Capacity efficiency (%) Interface resistance (Ω) Example 4 208 94.3 1.1 Comparative Example 4 203 90.1 8.2

[0275] Industrial Applicability

[0276] The technology of the present disclosure can be used, for example, in all-solid-state lithium-ion secondary batteries.

[0277] Description of Reference Numerals

[0278] 100 Coated positive electrode active material

[0279] 101 Positive electrode active material

[0280] 102 Solid electrolyte (coating layer)

[0281] 202 Positive electrode solid electrolyte

[0282] 203 Negative electrode active material

[0283] 205 Negative electrode solid electrolyte

[0284] 300 Battery

[0285] 301 Positive electrode

[0286] 302 Electrolyte layer

[0287] 303 Negative electrode

[0288] 1000 Positive electrode material

Claims

1. A coated positive electrode active material includes particulate positive electrode active material and a solid electrolyte coating the surface of the positive electrode active material. The solid electrolyte forms a coating layer. The coating layer is formed so as to fill recesses on the surface of the positive electrode active material with the solid electrolyte. Protrusions on the surface of the positive electrode active material are exposed on the surface of the coated positive electrode active material. The unevenness ζ of a particle group is defined by the following formula (1). In the formula (1), n is an integer of 3 or more representing the number of particles measured, Lpi represents the total perimeter of the contour of the cross-sectional image of each particle, Lei represents the total perimeter of an equivalent smooth ellipse having the same aspect ratio and area as the aspect ratio and area of the cross-sectional image of each particle, and the aspect ratio represents the ratio of the minor axis of the cross-sectional image to the major axis of the cross-sectional image. The concavity and convexity of the particle group of the positive electrode active material is defined as ζ 1 The concavity and convexity of the particle group coated with the positive electrode active material is defined as ζ 2 When the concavo-convex variation R defined by the following formula (2) is 1.1 or more, R = ζ 2 / ζ 1 ···(2) The solid electrolyte has a composition represented by the following formula (3). Li α M β Cl γ ···(3) In the formula (3), α, β, and γ are values greater than 0, and M contains at least one selected from metal elements other than Li and metalloid elements.

2. The coated positive electrode active material according to claim 1. The ratio of the mass of the solid electrolyte to the mass of the positive electrode active material is in the range of 3 / 100 or more and 1 / 10 or less.

3. The coated positive electrode active material according to claim 1. The ratio of the mass of the solid electrolyte to the mass of the positive electrode active material is in the range of 1 / 20 or more and 7 / 100 or less.

4. The coated positive electrode active material according to any one of claims 1 to 3. In the cross-sectional image of the coated positive electrode active material, when the total perimeter of the contour of the positive electrode active material is defined as L and the total length of the contact portion between the positive electrode active material and the coating layer is defined as C. The coating rate represented by the ratio C / L of the total length C to the total perimeter L is in the range of 0.3 or more and 0.95 or less.

5. The coated positive electrode active material according to any one of claims 1 to 3. The average film thickness of the coating layer is in the range of 1 nm or more and 300 nm or less.

6. The coated positive electrode active material according to any one of claims 1 to 3. The average film thickness of the coating layer is in the range of 2 nm or more and 200 nm or less.

7. The coated positive electrode active material according to any one of claims 1 to 3. The M contains yttrium.

8. The coated positive electrode active material according to any one of claims 1 to 3. α, β, and γ respectively satisfy 2.5 ≤ α ≤ 3, 1 ≤ β ≤ 1.1, and γ = 6.

9. The coated positive electrode active material according to any one of claims 1 to 3. The positive electrode active material contains lithium nickel cobalt manganate.

10. The coated positive electrode active material according to any one of claims 1 to 3. The positive electrode active material has a surface layer containing a lithium metal oxide.

11. The coated positive electrode active material according to claim 10. The lithium metal oxide contains lithium niobate.

12. A positive electrode material comprising the coated positive electrode active material according to any one of claims 1 to 11 and a positive electrode solid electrolyte.

13. The positive electrode material according to claim 12, wherein the positive electrode solid electrolyte comprises a halide solid electrolyte.

14. The positive electrode material according to claim 12 or 13, wherein the positive electrode solid electrolyte comprises a sulfide solid electrolyte.

15. A battery comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode comprises the positive electrode material according to any one of claims 12 to 14.

16. The battery according to claim 15, wherein the electrolyte layer comprises at least one selected from a solid electrolyte having the same composition as the solid electrolyte contained in the coating layer and a solid electrolyte having the same composition as the positive electrode solid electrolyte.

17. The battery according to claim 15, wherein the electrolyte layer comprises a halide solid electrolyte having a composition different from the composition of the solid electrolyte contained in the coating layer and / or the composition of the positive electrode solid electrolyte.

18. The battery according to any one of claims 15 to 17, wherein the electrolyte layer comprises a sulfide solid electrolyte.

19. A method for manufacturing a coated positive electrode active material, which is a method for manufacturing the coated positive electrode active material according to any one of claims 1 to 11, comprising treating the positive electrode active material and the solid electrolyte by a dry particle compounding method, wherein the treatment by the dry particle compounding method comprises imparting at least one type of mechanical energy selected from impact, compression, and shear to the positive electrode active material and the solid electrolyte.

20. The method for manufacturing a coated positive electrode active material according to claim 19, wherein the ratio of the average particle diameter Da of the positive electrode active material to the average particle diameter Dc of the solid electrolyte, i.e., Da / Dc, is 2 or more.

21. The method for manufacturing a coated positive electrode active material according to claim 19, wherein the ratio of the average particle diameter Da of the positive electrode active material to the average particle diameter Dc of the solid electrolyte, i.e., Da / Dc, is 5 or more.

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