Cathode Materials and Batteries

Abstract

This positive electrode substance 1000 is provided with a positive electrode active material 110 and a coating layer 111 which contains a first solid electrolyte and which covers at least part of the surface of the positive electrode active material 110. The first solid electrolyte is represented by the following composition formula: Formula (1) ... Liα1M1β1X1γ1. In composition formula (1), α1, β1 and γ1 are independently positive real numbers, M1 contains calcium, yttrium and at least one rare earth element other than yttrium, and X1 includes at least one item selected from the group consisting of F, Cl, Br and I.

Description

[Technical Field]

[0001] The present disclosure relates to positive electrode materials for batteries and batteries. [Background technology]

[0002] Patent Document 1 discloses a battery using a halide as a solid electrolyte. Non-Patent Document 1 discloses a battery using a sulfide as a solid electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 025582 [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of Power Sources 159(2006), p193-199 Summary of the Invention

[0005] The present disclosure provides a positive electrode material that can improve the charge / discharge efficiency of a battery.

[0006] In one embodiment of the present disclosure, the positive electrode material is a positive electrode active material; a coating layer including a first solid electrolyte and coating at least a portion of the surface of the positive electrode active material; Equipped with The first solid electrolyte is represented by the following composition formula (1): Li α1 M1 β1 X1 γ1 ...Equation (1) where: In the composition formula (1), α1, β1, and γ1 are each independently a positive real number; M1 includes calcium, yttrium, and at least one rare earth element other than yttrium; X1 includes at least one selected from the group consisting of F, Cl, Br, and I.

[0007] According to the present disclosure, the charge and discharge efficiency of a battery can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery according to the second embodiment. [Figure 3] FIG. 3 is a schematic diagram of a pressure forming die used to evaluate the ionic conductivity of a solid electrolyte. [Figure 4] FIG. 4 is a graph showing a Cole-Cole plot obtained by measuring the impedance of the second solid electrolyte according to Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Findings that formed the basis of this disclosure) Patent Document 1 mentions that good charge / discharge characteristics can be obtained by using an all-solid-state secondary battery containing a solid electrolyte made of a halide containing Cl or Br.

[0010] On the other hand, as a result of extensive research, the present inventors have found that the ionic conductivity of a solid electrolyte in contact with a positive electrode active material contributes to the charge-discharge efficiency of a battery. For example, if the ionic conductivity of a solid electrolyte in contact with a positive electrode active material is low, the charge-discharge efficiency of the battery is also low. To solve this problem, it is necessary to bring a solid electrolyte with higher ionic conductivity into contact with the positive electrode active material.

[0011] Non-Patent Document 1 mentions that an all-solid-state secondary battery containing a sulfide solid electrolyte can provide good charge-discharge characteristics.

[0012] Meanwhile, the inventors have found, through extensive research, that when a sulfide solid electrolyte is in contact with a positive electrode active material, the sulfide solid electrolyte undergoes oxidative decomposition during charging. Oxidative decomposition of the solid electrolyte reduces the charge / discharge efficiency of the battery. To solve this problem, it is necessary to bring a solid electrolyte that is oxidation-stable, i.e., that is resistant to oxidation, into contact with the positive electrode active material.

[0013] The inventors of the present invention have proposed a method for coating the surface of a positive electrode active material with a solid electrolyte having oxidation stability, which may enable the positive electrode active material to be in contact with the solid electrolyte. In particular, since halide solid electrolytes have higher oxidation stability than sulfide solid electrolytes, the coating layer of the halide solid electrolyte can also suppress the oxidative decomposition of other solid electrolytes.

[0014] Based on the above findings, the present inventors have arrived at the positive electrode material of the present disclosure, which is capable of improving the charge / discharge efficiency of a battery.

[0015] (Summary of one aspect of the present disclosure) The positive electrode material according to the first aspect of the present disclosure is a positive electrode active material; a coating layer including a first solid electrolyte and coating at least a portion of the surface of the positive electrode active material; Equipped with The first solid electrolyte is represented by the following composition formula (1): Li α1 M1 β1 X1 γ1 ...Equation (1) where: In the composition formula (1), α1, β1, and γ1 are each independently a positive real number; M1 includes calcium, yttrium, and at least one rare earth element other than yttrium; X1 includes at least one selected from the group consisting of F, Cl, Br, and I.

[0016] According to the above configuration, the charge-discharge efficiency of the battery can be improved.

[0017] In the second aspect of the present disclosure, for example, in the positive electrode material according to the first aspect, the first solid electrolyte may be represented by the following compositional formula (2). Li 6-2a-3d Ca a (Y 1-b Gd b ) d Br 6-c Cl c ··· Formula (2) Here, the compositional formula (2) satisfies 0 < a, 0 < b < 1, 0 < c < 6, and 0 < d < 1.5. The positive electrode material containing the first solid electrolyte represented by the compositional formula (2) can further improve the charge-discharge efficiency of the battery.

[0018] In the third aspect of the present disclosure, for example, in the positive electrode material according to the second aspect, the compositional formula (2) may satisfy 0.01 ≤ a ≤ 0.3. According to such a configuration, the charge-discharge efficiency of the battery can be further improved.

[0019] In the fourth aspect of the present disclosure, for example, in the positive electrode material according to the third aspect, the compositional formula (2) may satisfy a ≤ 0.2. According to such a configuration, the charge-discharge efficiency of the battery can be further improved.

[0020] In the fifth aspect of the present disclosure, for example, in the positive electrode material according to any one of the second to fourth aspects, the compositional formula (2) may satisfy 0.1 ≤ b ≤ 0.9. According to such a configuration, the charge-discharge efficiency of the battery can be improved.

[0021] In the sixth aspect of the present disclosure, for example, in the positive electrode material according to any one of the second to fourth aspects, the compositional formula (2) may satisfy 0.8 ≤ b < 1. According to such a configuration, the charge-discharge efficiency of the battery can be improved.

[0022] In the seventh aspect of the present disclosure, for example, in the positive electrode material according to any one of the second to sixth aspects, the composition formula (2) may satisfy 1.0≦c≦1.2. This configuration can further improve the charge / discharge efficiency of the battery.

[0023] In an eighth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to seventh aspects, the positive electrode active material may contain Ni, Co, and Mn, which can further improve the energy density and charge / discharge efficiency of the battery.

[0024] In a ninth aspect of the present disclosure, for example, the cathode material according to any one of the first to eighth aspects may further include a second solid electrolyte, which can ensure sufficient ionic conductivity in the cathode material.

[0025] In a tenth aspect of the present disclosure, for example, in the positive electrode material according to the ninth aspect, the second solid electrolyte may be represented by the following composition formula (3): Li α2 M2 β2 X2 γ2 ...Equation (3) Here, in the composition formula (3), α2, β2, and γ2 may each independently be a positive real number, M2 may contain at least one element selected from the group consisting of metal elements and semimetal elements other than Li, and X2 may contain at least one element selected from the group consisting of F, Cl, Br, and I. A positive electrode material containing the second solid electrolyte represented by the composition formula (3) can improve the output characteristics of a battery.

[0026] In an eleventh aspect of the present disclosure, for example, in the positive electrode material according to the tenth aspect, M2 may contain yttrium. This configuration can improve the charge / discharge characteristics of the battery.

[0027] In a twelfth aspect of the present disclosure, for example, in the positive electrode material according to the tenth or eleventh aspect, the composition formula (3) may satisfy 2.5≦α2≦3, 1≦β2≦1.1, and γ2=6. This configuration can further improve the charge / discharge characteristics of the battery.

[0028] In a thirteenth aspect of the present disclosure, for example, in the positive electrode material according to any one of the tenth to twelfth aspects, X2 may include at least one selected from the group consisting of Cl and Br. This configuration can further improve the charge / discharge characteristics of the battery.

[0029] In a fourteenth aspect of the present disclosure, for example, in the cathode material according to any one of the tenth to thirteenth aspects, the second solid electrolyte may contain LiYBrCl. This configuration can further improve the charge / discharge characteristics of the battery.

[0030] In a fifteenth aspect of the present disclosure, for example, in the positive electrode material related to the tenth aspect, the second solid electrolyte may include a sulfide solid electrolyte. With this configuration, the charge / discharge characteristics of the battery can be further improved.

[0031] A battery according to a sixteenth aspect of the present disclosure comprises: a positive electrode comprising the positive electrode material according to any one of the tenth to fifteenth aspects; a negative electrode; an electrolyte layer provided between the positive electrode and the negative electrode; Equipped with.

[0032] According to the above configuration, the charge / discharge efficiency of the battery can be improved.

[0033] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0034] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 1000 according to the first embodiment.

[0035] The positive electrode material 1000 in the first embodiment includes a coated active material 130. The coated active material 130 includes a positive electrode active material 110 and a coating layer 111. The positive electrode active material 110 has a particulate shape, for example. The coating layer 111 coats at least a portion of the surface of the positive electrode active material 110.

[0036] The coating layer 111 is a layer containing a first solid electrolyte. The coating layer 111 is provided on the surface of the positive electrode active material 110. The coating layer 111 may contain only the first solid electrolyte. "Containing only the first solid electrolyte" means that, with the exception of inevitable impurities, no materials other than the first solid electrolyte are intentionally added. For example, the raw materials of the first solid electrolyte and by-products generated when producing the first solid electrolyte are included in the inevitable impurities.

[0037] The positive electrode material 1000 further includes a second solid electrolyte 100. The second solid electrolyte 100 is, for example, in the form of particles. The second solid electrolyte 100 ensures sufficient ionic conductivity in the positive electrode material 1000.

[0038] The positive electrode active material 110 is separated from the second solid electrolyte 100 by the coating layer 111. The positive electrode active material 110 does not need to be in direct contact with the second solid electrolyte 100. This is because the coating layer 111 has ion conductivity.

[0039] The coating layer 111 may uniformly coat the positive electrode active material 110. The coating layer 111 prevents direct contact between the positive electrode active material 110 and the second solid electrolyte 100, and suppresses side reactions of the second solid electrolyte 100. As a result, the charge / discharge efficiency of the battery can be improved, and an increase in the reaction overvoltage of the battery can be suppressed.

[0040] The coating layer 111 may cover only a portion of the surface of the positive electrode active material 110. The particles of the positive electrode active material 110 come into direct contact with each other through the portion not covered by the coating layer 111, thereby improving the electronic conductivity between the particles of the positive electrode active material 110. As a result, the battery can operate at high power output.

[0041] The coating of the positive electrode active material 110 with the coating layer 111 suppresses the formation of an oxide film due to oxidative decomposition of other solid electrolytes (for example, the second solid electrolyte 100) during charging of the battery, thereby improving the charge / discharge efficiency of the battery.

[0042] The thickness of the coating layer 111 may be, for example, not less than 1 nm and not more than 500 nm.

[0043] When the thickness of the coating layer 111 is 1 nm or more, contact between the positive electrode active material 110 and the second solid electrolyte 100 is suppressed, and side reactions of the second solid electrolyte 100 can be suppressed, thereby improving the charge / discharge efficiency of the battery.

[0044] Furthermore, by making the thickness of the coating layer 111 500 nm or less, it is possible to sufficiently reduce the internal resistance of the battery due to the thickness of the coating layer 111. As a result, it is possible to improve the energy density of the battery.

[0045] The method for measuring the thickness of the coating layer 111 is not particularly limited. For example, the thickness of the first solid electrolyte can be determined by direct observation using a transmission electron microscope or the like. Alternatively, the thickness of the coating layer 111 can be determined from changes in the spectrum derived from the active material by measuring XPS while scraping the coating layer 111 by Ar sputtering.

[0046] The positive electrode active material 110, the coating layer 111, and the second solid electrolyte 100 will now be described in more detail.

[0047] (Coating layer 111) The first solid electrolyte contained in the coating layer 111 is a halide solid electrolyte.

[0048] Halide solid electrolytes have high ionic conductivity and excellent high-potential stability. Furthermore, because they have low electronic conductivity and high oxidation resistance, they are less susceptible to oxidative decomposition upon contact with the positive electrode active material. Therefore, the use of halide solid electrolytes can further improve the charge / discharge efficiency of batteries and further suppress an increase in the battery's reaction overvoltage.

[0049] The halide solid electrolyte is represented by, for example, the following composition formula (1).

[0050] Li α1 M1 β1 X1 γ1 ...Equation (1)

[0051] In composition formula (1), α1, β1, and γ1 are each independently a positive real number. M1 includes calcium, yttrium, and at least one rare earth element other than yttrium. X1 includes at least one element selected from the group consisting of F, Cl, Br, and I.

[0052] The halide solid electrolyte represented by composition formula (1) has a higher ionic conductivity than halide solid electrolytes such as LiI, which are composed of Li and halogen elements. Therefore, when the halide solid electrolyte represented by composition formula (1) is used in a battery, the output characteristics of the battery can be improved.

[0053] In composition formula (1), the at least one rare earth element other than yttrium contained in M1 is at least one selected from the group consisting of Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Since the chemical properties of rare earth elements are similar to each other, any of them can be used as a constituent element of the halide solid electrolyte of this embodiment. In composition formula (1), M1 may include at least one selected from the group consisting of gadolinium and samarium. In composition formula (1), M1 may include only one selected from the group consisting of gadolinium and samarium.

[0054] In compositional formula (1), M1 may contain calcium, yttrium, and one rare earth element other than yttrium. That is, M1 may contain only one rare earth element other than yttrium.

[0055] The first solid electrolyte may be represented by the following compositional formula (2).

[0056] Li 6-2a-3d Ca a (Y 1-b Gd b ) d Br 6-c Cl c ··· Formula (2)

[0057] Compositional formula (2) satisfies 0 < a, 0 < b < 1, 0 < c < 6, and 0 < d < 1.5.

[0058] According to the above configuration, the ionic conductivity of the first solid electrolyte can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0059] Compositional formula (2) may satisfy 0.01 ≤ a ≤ 0.3.

[0060] According to the above configuration, the ionic conductivity of the first solid electrolyte can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0061] Compositional formula (2) may satisfy a ≤ 0.2.

[0062] According to the above configuration, the ionic conductivity of the first solid electrolyte can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0063] Compositional formula (2) may satisfy 0.1 ≤ b ≤ 0.9.

[0064] According to the above configuration, the ionic conductivity of the first solid electrolyte can be further improved, thereby further improving the charge / discharge efficiency of the battery.

[0065] The composition formula (2) may satisfy 0.8≦b<1.

[0066] According to the above configuration, the ionic conductivity of the first solid electrolyte can be further improved, thereby further improving the charge / discharge efficiency of the battery.

[0067] The composition formula (2) may satisfy 1.0≦c≦1.2.

[0068] According to the above configuration, the ionic conductivity of the first solid electrolyte can be further improved, thereby further improving the charge / discharge efficiency of the battery.

[0069] The first solid electrolyte and the halide solid electrolyte do not necessarily need to contain sulfur.

[0070] (Second solid electrolyte) The second solid electrolyte 100 includes a material having high ionic conductivity. As the second solid electrolyte 100, a compound represented by the following composition formula (3) can be used.

[0071] Li α2 M2 β2 X2 γ2 ...Equation (3)

[0072] In the composition formula (3), α2, β2, and γ2 are each independently a positive real number. M2 includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li. X2 includes at least one element selected from the group consisting of F, Cl, Br, and I.

[0073] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0074] "Metal elements" include all elements in groups 1 to 12 of the periodic table except hydrogen, and all elements in groups 13 to 16 except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming inorganic compounds with halogen compounds.

[0075] The above configuration can further improve the ionic conductivity of the second solid electrolyte 100, thereby further improving the charge / discharge characteristics of the battery.

[0076] In composition formula (3), M2 may contain yttrium, that is, the second solid electrolyte 100 may contain Y as a metal element.

[0077] The above configuration can further improve the ionic conductivity of the second solid electrolyte 100, thereby further improving the charge / discharge characteristics of the battery.

[0078] The composition formula (3) may satisfy 2.5≦α2≦3, 1≦β2≦1.1, and γ2=6.

[0079] The above configuration can further improve the ionic conductivity of the second solid electrolyte 100, thereby further improving the charge / discharge characteristics of the battery.

[0080] In the composition formula (3), X2 may contain at least one selected from the group consisting of Cl and Br. X2 may contain Cl and Br.

[0081] The above configuration can further improve the ionic conductivity of the second solid electrolyte 100, thereby further improving the charge / discharge characteristics of the battery.

[0082] The second solid electrolyte 100 may be a compound represented by the following composition formula (A1).

[0083] Li6-3d Y d X6 ··· Formula (A1)

[0084] In the compositional formula (A1), X contains at least one selected from the group consisting of F, Cl, Br, and I. In the compositional formula (A1), the mathematical formula: 0 < d < 2, is satisfied.

[0085] According to the above configuration, the ionic conductivity of the second solid electrolyte 100 can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0086] The second solid electrolyte 100 may be a compound represented by the following compositional formula (A2).

[0087] Li3YX6 ··· Formula (A2)

[0088] In the compositional formula (A2), X contains at least one selected from the group consisting of F, Cl, Br, and I.

[0089] According to the above configuration, the ionic conductivity of the second solid electrolyte 100 can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0090] The second solid electrolyte 100 may be a compound represented by the following compositional formula (A3).

[0091] Li 3-3δ+a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A3)

[0092] In the compositional formula (A3), Me is at least one element selected from the group consisting of Mg, Ca, Sr, Ba, and Zn.

[0093] The compositional formula (A3) satisfies -1 < δ < 2, 0 < a < 3, 0 < (3 - 3δ + a), 0 < (1 + δ - a), 0 ≤ x < 6, 0 < y ≤ 6, and (x + y) < 6.

[0094] According to the above configuration, the ionic conductivity of the second solid electrolyte 100 can be further improved. Thereby, the charge and discharge efficiency of the battery can be further improved.

[0095] The second solid electrolyte 100 may be a compound represented by the following compositional formula (A4).

[0096] Li 3-3δ Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A4)

[0097] In the compositional formula (A4), Me is at least one element selected from the group consisting of Al, Sc, Ga, and Bi.

[0098] The compositional formula (A4) satisfies -1 < δ < 1, 0 < a < 2, 0 < (1 + δ - a), 0 ≤ x < 6, 0 < y ≤ 6, and (x + y) < 6.

[0099] According to the above configuration, the ionic conductivity of the second solid electrolyte 100 can be further improved. Thereby, the charge and discharge efficiency of the battery can be further improved.

[0100] The second solid electrolyte 100 may be a compound represented by the following compositional formula (A5).

[0101] Li 3-3δ-a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A5)

[0102] In the compositional formula (A5), Me is at least one element selected from the group consisting of Zr, Hf, and Ti.

[0103] The compositional formula (A5) satisfies -1 < δ < 1, 0 < a < 1.5, 0 < (3 - 3δ - a), 0 < (1 + δ - a), 0 ≤ x < 6, 0 < y ≤ 6, and (x + y) < 6.

[0104] According to the above configuration, the ionic conductivity of the second solid electrolyte 100 can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0105] The second solid electrolyte 100 may be a compound represented by the following compositional formula (A6).

[0106] Li 3-3δ-2a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A6)

[0107] In the compositional formula (A6), Me is at least one element selected from the group consisting of Ta and Nb.

[0108] The compositional formula (A6) satisfies the following seven mathematical formulas: -1 < δ < 1, 0 < a < 1.2, 0 < (3 - 3δ - 2a), 0 < (1 + δ - a), 0 ≤ x < 6, 0 < y ≤ 6, and (x + y) < 6.

[0109] According to the above configuration, the ionic conductivity of the second solid electrolyte 100 can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0110] Note that the second solid electrolyte 100 may not contain sulfur.

[0111] Examples of the second solid electrolyte 100 that can be used include Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, and Li3(Al,Ga,In)X6, where X includes I and at least one element selected from the group consisting of Cl and Br.

[0112] In the present disclosure, the notation "(A, B, C)" in a chemical formula means "at least one selected from the group consisting of A, B, and C." For example, "(Al, Ga, In)" is synonymous with "at least one selected from the group consisting of Al, Ga, and In."

[0113] A typical composition of Li3YX6 is, for example, Li3YBr2Cl4. The second solid electrolyte 100 may contain Li3YBr2Cl4.

[0114] The above configuration can further improve the ionic conductivity of the second solid electrolyte 100, thereby further improving the charge / discharge characteristics of the battery.

[0115] The second solid electrolyte 100 may include a sulfide solid electrolyte. Examples of sulfide solid electrolytes include Li2S—P2S5, Li2S—SiS2, Li2S—B2S3, Li2S—GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These can be used in addition to LiX, Li2O, MO q , Li p MO q The element X in "LiX" is at least one element selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q "The element M is at least one element selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q" p and q in this expression are independent natural numbers.

[0116] In the first embodiment, the second solid electrolyte 100 may be a sulfide solid electrolyte. For example, the sulfide solid electrolyte may contain lithium sulfide and phosphorus sulfide. The sulfide solid electrolyte may be Li2S-P2S5.

[0117] Li2S-P2S5 has high ionic conductivity and is stable against oxidation and reduction, so the use of Li2S-P2S5 can further improve the charge-discharge efficiency of batteries.

[0118] The second solid electrolyte 100 may be a mixture of two or more selected from the group consisting of halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes. For example, the second solid electrolyte 100 may be a mixture of a halide solid electrolyte and a sulfide solid electrolyte.

[0119] (Cathode active material) The positive electrode active material 110 includes a material capable of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material 110 that can be used include lithium-containing transition metal oxides (e.g., Li(NiCoAl)O2, Li(NiCoMn)O2, LiCoO2, etc.), transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using a lithium-containing transition metal oxide as the positive electrode active material 110 can reduce manufacturing costs and increase the average discharge voltage.

[0120] In the first embodiment, the positive electrode active material 110 may contain Ni, Co, and Mn. The positive electrode active material 110 may be lithium nickel cobalt manganese oxide (i.e., NMC). For example, the positive electrode active material 110 may be Li(NiCoMn)O.

[0121] According to the above configuration, the energy density and charge / discharge efficiency of the battery can be further increased.

[0122] The shape of second solid electrolyte 100 in embodiment 1 is not particularly limited and may be, for example, needle-like, spherical, oval-spherical, etc. For example, second solid electrolyte 100 may be in the form of particles.

[0123] For example, when the second solid electrolyte 100 in the first embodiment is particulate (e.g., spherical), the median diameter may be 100 μm or less. When the median diameter is 100 μm or less, the coated active material 130 and the second solid electrolyte 100 can be well dispersed in the positive electrode material 1000. This improves the charge / discharge characteristics of the battery. In the first embodiment, the median diameter of the second solid electrolyte 100 may be 10 μm or less.

[0124] According to the above configuration, in the positive electrode material 1000, the coated active material 130 and the second solid electrolyte 100 can be well dispersed.

[0125] In the first embodiment, the median diameter of the second solid electrolyte 100 may be smaller than the median diameter of the coated active material 130 .

[0126] According to the above configuration, the second solid electrolyte 100 and the coated active material 130 can be dispersed in the positive electrode material 1000 in a more favorable manner.

[0127] The median diameter of the coated active material 130 may be 0.1 μm or more and 100 μm or less.

[0128] When the median diameter of the coated active material 130 is 0.1 μm or more, the coated active material 130 and the second solid electrolyte 100 can be well dispersed in the positive electrode material 1000. As a result, the charge / discharge characteristics of the battery are improved.

[0129] When the median diameter of the coated active material 130 is 100 μm or less, a sufficient diffusion rate of lithium is ensured within the coated active material 130. This allows the battery to operate at high power output.

[0130] The median diameter of the coated active material 130 may be larger than the median diameter of the second solid electrolyte 100. This allows the coated active material 130 and the second solid electrolyte 100 to form a well-dispersed state.

[0131] Here, the median diameter means the particle size when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measuring device or an image analyzer.

[0132] On the surface of the positive electrode active material 110, a Li-Nb-O compound such as LiNbO3, a Li-BO compound such as LiBO2 or Li3BO3, a Li-Al-O compound such as LiAlO2, a Li-Si-O compound such as Li4SiO4, Li2SO4, Li4Ti5O 12 Li-Ti-O compounds such as LiZrO, Li-Zr-O compounds such as LiZrO, Li-Mo-O compounds such as LiMoO, Li-VO compounds such as LiVO, Li-WO compounds such as LiWO, or Li-PO compounds such as LiPO.

[0133] According to the above configuration, oxidation of the first solid electrolyte in the positive electrode can be suppressed.

[0134] In the positive electrode material 1000 of the first embodiment, the second solid electrolyte 100 and the coated active material 130 may be in contact with each other, as shown in Fig. 1. In this case, the coating layer 111 and the positive electrode active material 110 are in contact with each other.

[0135] The positive electrode material 1000 in the first embodiment may include a plurality of particles of the second solid electrolyte 100 and a plurality of particles of the coated active material 130.

[0136] In the positive electrode material 1000 of the first embodiment, the content of the second solid electrolyte 100 and the content of the coated active material 130 may be the same as or different from each other.

[0137] <Method for producing the first solid electrolyte and the second solid electrolyte> The first solid electrolyte contained in the coating layer 111 and the second solid electrolyte 100 can be produced, for example, by the following method.

[0138] Raw material powders are prepared and mixed to achieve the desired composition. Examples of raw material powders include oxides, hydroxides, halides, and oxyhalides. For example, to produce Li3YCl6, LiCl and YCl3 are prepared in a molar ratio of 3:1.

[0139] In this case, by selecting the type of raw material powder, it is possible to determine "M1" and "X1" in the composition formula representing the first solid electrolyte. In addition, by adjusting the raw materials, the compounding ratio, and the synthesis process, it is possible to adjust the values ​​"α1," "β1," "γ1," "a," "b," "c," and "d" in the composition formula representing the first solid electrolyte. In addition, by selecting the type of raw material powder, it is possible to determine "M2," "Me," "X2," and "X" in the composition formula representing the second solid electrolyte. In addition, by adjusting the raw materials, the compounding ratio, and the synthesis process, it is possible to adjust the values ​​"α2," "β2," "γ2," "d," "δ," "a," "x," and "y" in the composition formula representing the second solid electrolyte.

[0140] After the raw material powders are thoroughly mixed, they are mixed, pulverized, and reacted with each other using a mechanochemical milling method, or alternatively, the raw material powders may be thoroughly mixed and then sintered in a vacuum.

[0141] As a result, the first solid electrolyte and the second solid electrolyte 100 are obtained.

[0142] The constitution of the crystalline phase in the solid electrolyte (ie, the crystalline structure) can be determined by adjusting the reaction method and reaction conditions of the raw material powders.

[0143] <Method of manufacturing coated active material> The coated active material 130 can be produced, for example, by the following method.

[0144] A powder of the positive electrode active material 110 and a powder of the first solid electrolyte are mixed in an appropriate ratio to obtain a mixture. The mixture is then milled to impart mechanical energy to the mixture. A mixing device such as a ball mill can be used for the milling process. The milling process may be performed in a dry and inert atmosphere to prevent oxidation of the materials.

[0145] The coated active material 130 may be manufactured by a dry particle compounding method. The treatment by the dry particle compounding method includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the positive electrode active material 110 and the first solid electrolyte. The positive electrode active material 110 and the first solid electrolyte are mixed in an appropriate ratio.

[0146] The apparatus used in the method for producing the coated active material 130 is not particularly limited, and may be an apparatus capable of applying mechanical energy such as impact, compression, and shear to the mixture of the positive electrode active material 110 and the first solid electrolyte. Examples of apparatus capable of applying mechanical energy include a ball mill and a compression shear processing apparatus (particle composite apparatus) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) or "Nobilta" (manufactured by Hosokawa Micron Corporation).

[0147] "Mechanofusion" is a particle compounding device that uses dry mechanical compounding technology by applying strong mechanical energy to particles of multiple different materials. In mechanofusion, powder raw materials are fed between a rotating container and a press head, and mechanical energy such as compression, shear, and friction is applied to them, causing the particles to compound.

[0148] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced form of particle compounding technology, to compound nanoparticles as raw materials. Nobilta produces composite particles by applying mechanical energy of impact, compression, and shear to multiple raw material powders.

[0149] In the Nobilta, a rotor positioned at a predetermined gap between itself and the inner wall of a horizontal cylindrical mixing vessel rotates at high speed, forcing the raw material powder through the gap, a process that is repeated multiple times. This applies impact, compression, and shear forces to the mixture, producing composite particles of the positive electrode active material 110 and the first solid electrolyte. Conditions such as the rotor rotation speed, processing time, and feed amount can be adjusted as needed.

[0150] <Method of manufacturing positive electrode material> The positive electrode material 1000 is obtained by mixing the coated active material 130 and the second solid electrolyte 100. The method for mixing the coated active material 130 and the second solid electrolyte 100 is not particularly limited. For example, the coated active material 130 and the second solid electrolyte 100 may be mixed using a tool such as a mortar, or may be mixed using a mixing device such as a ball mill. The mixing ratio of the coated active material 130 and the second solid electrolyte 100 is not particularly limited.

[0151] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0152] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the second embodiment.

[0153] The battery 2000 in the second embodiment includes a positive electrode 201 , an electrolyte layer 202 , and a negative electrode 203 .

[0154] The positive electrode 201 includes the positive electrode material 1000 in the first embodiment.

[0155] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0156] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be improved.

[0157] The volume ratio "v1:100-v1" of the positive electrode active material 110 to the second solid electrolyte 100 contained in the positive electrode 201 may satisfy 30≦v1≦95. When 30≦v1 is satisfied, it is easy to ensure a sufficient energy density of the battery 2000. When v1≦95 is satisfied, it is easier for the battery 2000 to operate at high output.

[0158] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 is 10 μm or more, the energy density of the battery 2000 is sufficiently ensured. When the thickness of the positive electrode 201 is 500 μm or less, high-power operation is possible.

[0159] The electrolyte layer 202 is a layer containing an electrolyte. The electrolyte is, for example, a solid electrolyte. The solid electrolyte contained in the electrolyte layer 202 is called a third solid electrolyte. That is, the electrolyte layer 202 may include a third solid electrolyte layer.

[0160] The third solid electrolyte may be a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte.

[0161] When the third solid electrolyte is a halide solid electrolyte, the halide solid electrolyte may be the same as the first solid electrolyte and / or the second solid electrolyte in Embodiment 1. That is, electrolyte layer 202 may contain a halide solid electrolyte having the same composition as the first solid electrolyte and / or the second solid electrolyte.

[0162] According to the above configuration, the output density and charge / discharge characteristics of the battery 2000 can be further improved.

[0163] The third solid electrolyte may be a halide solid electrolyte having a composition different from that of the first and second solid electrolytes, i.e., the electrolyte layer 202 may contain a halide solid electrolyte having a composition different from that of the first and second solid electrolytes.

[0164] According to the above configuration, the charge and discharge characteristics of the battery can be further improved.

[0165] When the third solid electrolyte is a sulfide solid electrolyte, examples of the sulfide solid electrolyte include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These can be used in addition to LiX, Li2O, MO q , Li p MO q The element X in "LiX" is at least one element selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q "The element M is at least one element selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q " p and q in this expression are independent natural numbers.

[0166] The third solid electrolyte may be the same sulfide solid electrolyte as the second solid electrolyte in embodiment 1. That is, electrolyte layer 202 may include a sulfide solid electrolyte having the same composition as the second solid electrolyte in embodiment 1.

[0167] According to the above configuration, since the electrolyte layer 202 contains a sulfide solid electrolyte having excellent reduction stability, it is possible to use a low-potential negative electrode material such as graphite or metallic lithium, thereby improving the energy density of the battery 2000. Furthermore, according to the configuration in which the electrolyte layer 202 contains the same sulfide solid electrolyte as the second solid electrolyte, it is possible to improve the charge / discharge efficiency of the battery 2000.

[0168] When the third solid electrolyte is an oxide solid electrolyte, examples of the oxide solid electrolyte include NASICON-type solid electrolytes represented by LiTi2(PO4)3 and its element substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element-substituted LISICON-type solid electrolytes, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those substituted with LiN and its element, LiN and its H-substituted compounds, LiPO and its N-substituted compounds, and glasses or glass ceramics containing Li-BO compounds such as LiBO and LiBO, to which materials such as LiSO and LiCO are added, can be used.

[0169] When the third solid electrolyte is a polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used as the polymer solid electrolyte. The polymer compound may have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain a large amount of lithium salt, thereby further increasing ionic conductivity. As the lithium salt, LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc. can be used. As the lithium salt, one type of lithium salt selected from these may be used alone, or a mixture of two or more types of lithium salts selected from these may be used.

[0170] When the third solid electrolyte is a complex hydride solid electrolyte, for example, LiBH4-LiI, LiBH4-P2S5, or the like can be used as the complex hydride solid electrolyte.

[0171] The electrolyte layer 202 may contain the third solid electrolyte as a main component, i.e., the electrolyte layer 202 may contain, for example, 50% or more (i.e., 50 mass % or more) of the third solid electrolyte in terms of mass ratio relative to the entire electrolyte layer 202.

[0172] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be further improved.

[0173] The electrolyte layer 202 may contain the third solid electrolyte in a mass ratio relative to the entire electrolyte layer 202 of 70% or more (ie, 70 mass % or more).

[0174] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be further improved.

[0175] The electrolyte layer 202 contains the third solid electrolyte as a main component, and may further contain unavoidable impurities, or starting materials, by-products, decomposition products, etc. used in synthesizing the third solid electrolyte.

[0176] The electrolyte layer 202 may contain, for example, 100% (ie, 100 mass %) of the third solid electrolyte in terms of mass ratio to the entire electrolyte layer 202, excluding unavoidable impurities.

[0177] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be further improved.

[0178] As described above, the electrolyte layer 202 may be composed of only the third solid electrolyte.

[0179] The electrolyte layer 202 may contain two or more of the materials listed as the third solid electrolyte. For example, the electrolyte layer 202 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0180] The thickness of the electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the positive electrode 201 and the negative electrode 203 can be more reliably separated. When the thickness of the electrolyte layer 202 is 300 μm or less, high-power operation can be achieved.

[0181] The negative electrode 203 includes a material having the property of absorbing and releasing metal ions (for example, lithium ions). The negative electrode 203 includes, for example, a negative electrode active material.

[0182] The negative electrode active material may be a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, or the like. The metal material may be a simple metal. Alternatively, the metal material may be an alloy. Examples of the metal material include lithium metal and lithium alloys. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), a silicon compound, or a tin compound may be used.

[0183] The negative electrode 203 may contain a solid electrolyte. As the solid electrolyte, any of the solid electrolytes exemplified as materials constituting the electrolyte layer 202 may be used. With the above configuration, lithium ion conductivity inside the negative electrode 203 is increased, enabling high-power operation.

[0184] The median diameter of the particles of the negative electrode active material may be 0.1 μm or more and 100 μm or less. When the median diameter of the particles of the negative electrode active material is 0.1 μm or more, the negative electrode active material and the solid electrolyte can be well dispersed in the negative electrode. This improves the charge / discharge characteristics of the battery 2000. Furthermore, when the median diameter of the negative electrode active material is 100 μm or less, lithium diffusion within the negative electrode active material is accelerated. This allows the battery 2000 to operate at high power.

[0185] The median diameter of the particles of the negative electrode active material may be larger than the median diameter of the solid electrolyte contained in the negative electrode 203. This allows the particles of the negative electrode active material and the particles of the solid electrolyte to be well dispersed.

[0186] The volume ratio "v2:100-v2" of the negative electrode active material to the solid electrolyte contained in the negative electrode 203 may satisfy 30≦v2≦95. When 30≦v2, a sufficient energy density of the battery 2000 can be ensured. When v2≦95, high-power operation can be achieved.

[0187] The thickness of the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 203 is 10 μm or more, a sufficient energy density of the battery 2000 can be ensured. Furthermore, when the thickness of the negative electrode 203 is 500 μm or less, high-power operation can be achieved.

[0188] At least one of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder to improve adhesion between particles. The binder is used to improve the binding properties of the materials constituting the electrodes. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. The binder may be a copolymer of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Alternatively, a mixture of two or more materials selected from these may be used as the binder.

[0189] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives that can be used include graphites (natural graphite or artificial graphite), carbon blacks (acetylene black, ketjen black, etc.), conductive fibers (carbon fiber or metal fiber, etc.), metal powders (carbon fluoride, aluminum, etc.), conductive whiskers (zinc oxide, potassium titanate, etc.), conductive metal oxides (titanium oxide, etc.), and conductive polymer compounds (polyaniline, polypyrrole, polythiophene, etc.). Using a carbon conductive additive can reduce costs.

[0190] The battery in the second embodiment can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type. [Example]

[0191] Hereinafter, the present disclosure will be described in detail using examples and comparative examples.

[0192] Example 1 [Preparation of second solid electrolyte] In an argon glove box with a dew point of -60°C or less, raw material powders of LiCl, LiBr, and YCl3 were weighed out so that the molar ratio of LiCl:LiBr:YCl3 was 1:2:1. The resulting mixture was then milled for 25 hours at 600 rpm using a planetary ball mill (Fritsch, Model P-5). This resulted in a powder of the second solid electrolyte according to Example 1, represented by the formula Li3Y1Br2Cl4 (hereinafter referred to as LYBC). The composition of the second solid electrolyte according to Example 1 is shown in Table 1.

[0193] (Evaluation of ionic conductivity) FIG. 3 is a schematic diagram of a pressure forming die 300 used to evaluate the ionic conductivity of the solid electrolyte.

[0194] The pressure molding die 300 had a frame 301, a lower punch 302, and an upper punch 303. The frame 301 was made of electronically insulating polycarbonate, while the lower punch 302 and upper punch 303 were made of electronically conductive stainless steel.

[0195] Using a pressure molding die 300 shown in FIG. 3, the ionic conductivity of the second solid electrolyte of Example 1 was evaluated by the following method.

[0196] In a dry atmosphere having a dew point of −30° C. or less, powder 304 of the second solid electrolyte according to Example 1 was filled into a pressing die 300. Inside the pressing die 300, a pressure of 300 MPa was applied to powder 304 of the second solid electrolyte according to Example 1 using upper punch 303 and lower punch 302.

[0197] While pressure was still applied, the upper punch 303 and the lower punch 302 were connected to a potentiostat (Princeton Applied Research, VersaSTAT4) equipped with a frequency response analyzer. The upper punch 303 was connected to a working electrode and a potential measurement terminal. The lower punch 302 was connected to a counter electrode and a reference electrode. The impedance of the second solid electrolyte was measured at room temperature by electrochemical impedance measurement.

[0198] FIG. 4 is a graph showing a Cole-Cole plot obtained by measuring the impedance of the second solid electrolyte according to Example 1.

[0199] 4, the real value of the impedance at the measurement point where the absolute value of the phase of the complex impedance is smallest was considered to be the resistance value for ion conduction of the second solid electrolyte according to Example 1. The real value is indicated by the arrow R SE Using the resistance value, the ionic conductivity was calculated based on the following formula (C1).

[0200] σ=(R SE ×S / t) -1 ...Formula (C1)

[0201] In formula (C1), σ represents ionic conductivity. S represents the contact area between the second solid electrolyte and the upper punch portion 303 (equivalent to the cross-sectional area of ​​the hollow portion of the frame mold 301 in FIG. 3). R SE represents the resistance value of the second solid electrolyte in the impedance measurement, and t represents the thickness of the second solid electrolyte (i.e., the thickness of the layer formed from the second solid electrolyte powder 304 in FIG. 3).

[0202] The ionic conductivity of the second solid electrolyte (i.e., LYBC) according to Example 1 measured at 22°C was 1.41 × 10 -3 S / cm.

[0203] [Preparation of the first solid electrolyte] In an argon glove box with a dew point of -60°C or less, the raw material powders LiCl, LiBr, YCl3, GdCl3, and CaBr2 were weighed out so that the molar ratio was LiCl:LiBr:YCl3:GdCl3:CaBr2 = 1:1.8:0.9:0.1:0.1. These were ground and mixed in a mortar. The resulting mixture was then milled for 12 hours at 600 rpm using a planetary ball mill (Fritsch, P-7 model). This resulted in the formation of Li 2.8 Ca 0.1 Y 0.9 Gd 0.1 A powder of the first solid electrolyte according to Example 1, represented by the formula Br2Cl4, was obtained. The composition of the first solid electrolyte according to Example 1 and the values ​​corresponding to a, b, c, and d in formula (2) are shown in Table 1.

[0204] The contents of Li, Ca, Y, and Gd per unit mass of the entire first solid electrolyte according to Example 1 were measured by ICP atomic emission spectroscopy, and the contents of Li, Ca, Y, and Gd were converted into molar ratios. The ratio of Li:Ca:Y:Gd was 2.8:0.1:0.9:0.1. The device used to measure the composition was an ICP atomic emission spectroscopy analyzer ("iCAP 7400" manufactured by Thermo Fisher Scientific).

[0205] (Evaluation of ionic conductivity) The ionic conductivity of the first solid electrolyte was measured using the same method as that of the second solid electrolyte. The ionic conductivity of the first solid electrolyte according to Example 1 measured at 22°C was 2.10 × 10 -3 S / cm.

[0206] [Preparation of coated active material] Li(NiCoMn)O2 (hereafter referred to as NCM) was used as the positive electrode active material. 2.8 Ca 0.1 Y 0.9 Gd 0.1 A coating layer made of Br2Cl4 was formed. The coating layer was formed by compressive shear treatment using a particle composite device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, the positive electrode active material and the first solid electrolyte were weighed out to a mass ratio of 95.72:4.28, and treated under conditions of a blade clearance of 2 mm and a treatment time of 50 minutes, thereby forming a coating layer made of the first solid electrolyte on the surface of the positive electrode active material particles. In this manner, the coated active material of Example 1 was obtained.

[0207] [Preparation of cathode material] In an argon glove box, the positive electrode active material of the coated active material of Example 1, the first solid electrolyte of Example 1, and the second solid electrolyte of Example 1 were weighed out so that the volume ratio of the positive electrode active material:first solid electrolyte+second solid electrolyte was 73:27. These were mixed in an agate mortar to produce the positive electrode material of Example 1.

[0208] Example 2 Weigh out LiCl, LiBr, YCl3, GdCl3, and CaBr2 as raw material powders. 2.8 Ca 0.1 Y 0.6 Gd 0.4 A first solid electrolyte according to Example 2 was prepared, represented by the composition formula Br2Cl4. The composition of the first solid electrolyte according to Example 2 and the values ​​corresponding to a, b, c, and d in composition formula (1) are shown in Table 1. The cathode material of Example 2 was obtained in the same manner as in Example 1, except that the first solid electrolyte represented by the composition formula above was used as the coating layer. The ionic conductivity of the first solid electrolyte according to Example 2 was measured using the same method as in measuring the ionic conductivity of the second solid electrolyte according to Example 1. The ionic conductivity of the first solid electrolyte according to Example 2, measured at 22°C, was 2.51 × 10 -3 S / cm.

[0209] Example 3 Weigh out LiCl, LiBr, YCl3, GdCl3, and CaBr2 as raw material powders. 2.8 Ca 0.1 Y 0.1 Gd 0.9 A first solid electrolyte according to Example 3 was prepared, represented by the composition formula Br2Cl4. The composition of the first solid electrolyte according to Example 3 and the values ​​corresponding to a, b, c, and d in composition formula (1) are shown in Table 1. The cathode material of Example 3 was obtained in the same manner as in Example 1, except that the first solid electrolyte represented by the composition formula above was used as the coating layer. The ionic conductivity of the first solid electrolyte according to Example 3 was measured using the same method as in measuring the ionic conductivity of the second solid electrolyte according to Example 1. The ionic conductivity of the first solid electrolyte according to Example 3, measured at 22°C, was 2.24 × 10 -3 S / cm.

[0210] Example 4 [Preparation of sulfide solid electrolyte] In an argon glove box with a dew point of -60°C or less, raw material powders of Li2S and P2S5 were weighed out to a molar ratio of Li2S:P2S5 = 75:25. These were ground and mixed in a mortar to obtain a mixture. The mixture was then milled for 10 hours at 510 rpm using a planetary ball mill (Fritsch, Model P-7). This yielded a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated in an inert atmosphere at 270°C for 2 hours. This yielded a glass-ceramic solid electrolyte, Li2S-P2S5 (hereinafter referred to as LPS), as the second solid electrolyte according to Example 4.

[0211] (Evaluation of ionic conductivity) The ionic conductivity of the second solid electrolyte according to Example 4 was measured by the same method as that of the second solid electrolyte according to Example 1. The ionic conductivity of the second solid electrolyte according to Example 4 measured at 22°C was 0.60 × 10 -3 S / cm.

[0212] [Preparation of cathode material] In an argon glove box, the positive electrode active material of the coated active material of Example 2, the first solid electrolyte of Example 2, and the second solid electrolyte of Example 4 were weighed out so that the volume ratio of positive electrode active material:first solid electrolyte+second solid electrolyte=50:50 was obtained. These were mixed in an agate mortar to produce the positive electrode material of Example 4.

[0213] Comparative Example 1 A positive electrode material of Comparative Example 1 was obtained in the same manner as in Example 1, except that no coating layer was formed and NCM without a coating layer was used as the positive electrode active material.

[0214] Comparative Example 2 A positive electrode material of Comparative Example 2 was obtained in the same manner as in Example 4, except that no coating layer was formed and NCM without a coating layer was used as the positive electrode active material.

[0215] [Battery construction] The following steps were carried out using the positive electrode materials of Examples 1 to 4 and Comparative Examples 1 and 2, LYBC, and glass ceramic LPS.

[0216] First, 60 mg of LPS, 20 mg of LYBC, and the positive electrode material were layered in this order in an insulating outer cylinder. The mass of the positive electrode material was weighed so that the mass of the positive electrode active material was 14 mg. This was then press-molded at a pressure of 720 MPa to obtain a positive electrode and a solid electrolyte layer.

[0217] Next, metallic Li (200 μm thick) was laminated on the side of the solid electrolyte layer opposite to the side in contact with the positive electrode, and the resulting laminate was press-molded at a pressure of 80 MPa to produce a laminate consisting of the positive electrode, the solid electrolyte layer, and the negative electrode.

[0218] Next, stainless steel current collectors were placed on the top and bottom of the laminate, and current collecting leads were attached to each current collector.

[0219] Finally, the insulating outer cylinder was sealed using an insulating ferrule to isolate the inside of the outer cylinder from the outside atmosphere, thereby completing the battery.

[0220] In this manner, the batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were fabricated.

[0221] [Charging test] Using the batteries of Examples 1 to 4 and Comparative Examples 1 and 2 described above, charging tests were carried out under the following conditions.

[0222] The battery was placed in a thermostatic chamber at 25°C.

[0223] The battery was charged at a constant current of 140 μA, which corresponds to a 0.05 C rate (20-hour rate) relative to the theoretical capacity of the battery, until the voltage reached 4.3 V. After a 20-minute rest period, the battery was discharged at a constant current of 140 μA, which corresponds to a 0.05 C rate (20-hour rate), until the voltage reached 2.5 V, and then rested for 20 minutes.

[0224] The ratio of the discharge capacity to the charge capacity obtained above was calculated as the charge-discharge efficiency. The results are shown in Table 1.

[0225] [Table 1]

[0226] ≪Consideration≫ The results of Examples 1 to 3 and Comparative Example 1 shown in Table 1 confirmed the following: When a halide solid electrolyte was used as the second solid electrolyte, the charge / discharge efficiency of the battery was improved by using a positive electrode material in which the surface of the positive electrode active material was coated with a halide solid electrolyte having a higher conductivity than the second solid electrolyte. This is thought to be because the insertion / desorption of Li between the active material and the electrolyte is rate-determined by the ionic conductivity of the electrolyte, and improving the conductivity of the electrolyte in contact with the active material reduced the resistance to insertion / desorption of Li.

[0227] The results of Example 4 and Comparative Example 2 shown in Table 1 confirmed the following: When a sulfide solid electrolyte was used as the second solid electrolyte, the charge / discharge efficiency of the battery was improved by using a positive electrode material in which the surface of the positive electrode active material was coated with a halide solid electrolyte. This is thought to be the result of the halide solid electrolyte having high ionic conductivity and high oxidation resistance suppressing oxidation of the sulfide solid electrolyte. [Industrial Applicability]

[0228] The battery of the present disclosure can be used, for example, as an all-solid-state lithium secondary battery. [Explanation of symbols]

[0229] 1000 cathode materials 100 Second solid electrolyte 110 Cathode active material 111 Covering layer 130 Coated active material 2000 batteries 201 Positive electrode 202 Electrolyte layer 203 Negative electrode 300 pressure forming die 301 Frame type 302 Punch bottom 303 Punch top 304 Secondary solid electrolyte powder

Claims

1. a positive electrode active material; a coating layer including a first solid electrolyte and coating at least a portion of a surface of the positive electrode active material; Equipped with The first solid electrolyte is represented by the following composition formula (2): Li 6-2a-3d Ca a (Y 1-b Gd b ) d Br 6-c Cl c ...Formula (2) where: The composition formula (2) is 0<a, 0.8≦b<1, 0<c<6, and 0<d<1.5 fulfill, Positive electrode material.

2. The composition formula (2) satisfies 0.01≦a≦0.

3. The positive electrode material according to claim 1 .

3. The composition formula (2) satisfies a≦0.

2. The positive electrode material according to claim 2 .

4. The composition formula (2) satisfies 0.8≦b≦0.

9. The positive electrode material according to any one of claims 1 to 3.

5. The composition formula (2) satisfies 1.0≦c≦1.2, The positive electrode material according to any one of claims 1 to 4.

6. The positive electrode active material contains Ni, Co, and Mn. The positive electrode material according to any one of claims 1 to 5.

7. Further comprising a second solid electrolyte. The positive electrode material according to any one of claims 1 to 6.

8. The second solid electrolyte is represented by the following composition formula (3): Li α2 M2 β2 X2 γ2 ...Form (3) where: In the composition formula (3), α2, β2, and γ2 are each independently a positive real number; M2 contains at least one element selected from the group consisting of metal elements and metalloid elements other than Li, 8. The positive electrode material of claim 7, wherein X2 comprises at least one selected from the group consisting of F, Cl, Br, and I.

9. M2 includes yttrium; The positive electrode material according to claim 8.

10. The composition formula (3) satisfies 2.5≦α2≦3, 1≦β2≦1.1, and γ2=6. The positive electrode material according to claim 8 or 9.

11. X2 includes at least one selected from the group consisting of Cl and Br; The positive electrode material according to any one of claims 8 to 10.

12. The second solid electrolyte is Li 3 YBr 2 Cl 4 Including, The positive electrode material according to any one of claims 8 to 11.

13. The second solid electrolyte includes a sulfide solid electrolyte. The positive electrode material according to claim 7.

14. A positive electrode active material; a coating layer including a first solid electrolyte and coating at least a portion of a surface of the positive electrode active material; Equipped with The first solid electrolyte is represented by the following composition formula (2): Li 6-2a-3d Ca a (Y 1-b Gd b ) d Br 6-c Cl c ...Formula (2) where: The composition formula (2) is 0<a, 0<b<1, 1.0≦c≦1.2, and 0<d<1.5 fulfill, Positive electrode material.

15. A positive electrode comprising the positive electrode material according to any one of claims 8 to 14; a negative electrode; an electrolyte layer provided between the positive electrode and the negative electrode; A battery.

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