Composite positive electrode, solid-state lithium ion secondary battery, and electric device

Abstract

The application discloses a composite positive electrode, a solid-state lithium ion secondary battery and an electric device. The composite positive electrode comprises a current collector, a positive active material layer and a halide solid-state electrolyte layer; the positive active material layer is located between the current collector and the halide solid-state electrolyte layer; and the halide solid-state electrolyte layer comprises a halide solid-state electrolyte A. The composite positive electrode is used for a sulfide full solid-state battery, can completely isolate direct contact of a high-voltage positive electrode material and a sulfide solid-state electrolyte, inhibit formation of a space charge layer, and further improve cycle stability of the battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of solid-state lithium ion batteries, and particularly relates to a composite positive electrode, a solid-state lithium ion secondary battery and an electric device. BACKGROUND

[0002] Solid-state batteries have been widely studied by enterprises and colleges and universities due to excellent safety performance and high energy density. In the solid-state battery, a solid-state electrolyte is used to replace the volatile and flammable liquid electrolyte and separator in the traditional lithium ion battery. Compared with the liquid electrolyte, the solid-state electrolyte has the advantages of not volatilizing, not flammable, no corrosion, high mechanical strength, etc., avoids the dangers such as electrolyte leakage and electrode short circuit in the traditional lithium ion battery, and reduces the sensitivity of the battery pack to temperature. Due to the high mechanical strength of the solid-state electrolyte, the growth of lithium dendrites can be effectively blocked, and the solid-state battery has extremely high safety in use.

[0003] At present, the solid-state electrolyte mainly includes sulfide, halide, oxide and polymer solid-state electrolyte. The ionic conductivity of oxide and polymer solid-state electrolyte is low, about 10 -6 -10 -4 S / cm; the ionic conductivity of halide solid-state electrolyte is about 10 -3 S / cm; the sulfide solid-state electrolyte has excellent ionic conductivity, about 10 -3 -10 -2 S / cm, and the ionic conductivity of some sulfide solid-state electrolyte is even higher than that of commercial liquid electrolyte. The sulfide solid-state electrolyte is suitable for high-energy density energy storage devices, and thus becomes one of the most promising technical routes for developing all-solid-state lithium ion batteries.

[0004] However, in the all-solid-state battery, when the transition metal oxide is used as the positive electrode and the sulfide is used as the solid-state electrolyte, since the potential of lithium ion in the oxide is higher than that in the sulfide, the lithium ion is driven by the electric field force to migrate from the sulfide solid-state electrolyte to the oxide solid-state electrolyte positive electrode, until the potential balance at both ends of the interface. When the balance is reached, a low lithium ion concentration region, i.e. a space charge layer, is formed at the interface between the sulfide solid-state electrolyte and the oxide positive electrode material, which causes the impedance of the positive electrode / sulfide electrolyte layer interface to increase sharply.

[0005] Therefore, it is urgent to develop a solid-state battery with more excellent electrochemical performance to solve the above problems. SUMMARY

[0006] The purpose of the present application is to provide a composite positive electrode, a solid-state lithium ion secondary battery and an electric device to overcome the problem that the interface stability between the sulfide solid-state electrolyte and the high-voltage positive electrode is poor, and the space charge is easily generated at the interface, thereby causing the interface resistance to increase continuously.

[0007] The application provides a composite positive electrode, comprising a current collector, a positive active material layer and a halide solid electrolyte layer;

[0008] The positive active material layer is located between the current collector and the halide solid electrolyte layer.

[0009] The halide solid electrolyte layer comprises a halide solid electrolyte A.

[0010] In the composite positive electrode, the particle size D 50 of the halide solid electrolyte A can be 1-15 μm, and specifically can be 1 μm, 10 μm or 15 μm. The particle size of the halide solid electrolyte A affects the grain boundary of the electrolyte layer formed. When the particle size D 50 of the halide solid electrolyte A is 1-15 μm, the electrolyte layer formed has fewer grain boundaries, and thus has smaller grain boundary resistance, which is more conducive to lithium ion transmission.

[0011] In the composite positive electrode, the thickness of the halide solid electrolyte layer can be 5-30 μm, and specifically can be 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, and preferably can be 10-20 μm.

[0012] In the application, the halide solid electrolyte layer cannot be too thin. If it is too thin, the composite positive electrode cannot effectively isolate the positive active material layer in the composite positive electrode from the sulfide solid electrolyte layer in the solid-state secondary battery when the composite positive electrode is used as the positive electrode of the solid-state secondary battery. Also, the halide solid electrolyte layer cannot be too thick. If it is too thick, it is not conducive to lithium ion transmission.

[0013] In the composite positive electrode, the positive active material layer comprises a positive active material, a halide solid electrolyte B, a conductive agent and a binder.

[0014] In the composite positive electrode, the positive active material layer comprises the following components in mass parts:

[0015]

[0016] In the composite positive electrode, the particle size D 50 of the halide solid electrolyte B can be 0.5-5 μm.

[0017] In the composite positive electrode, the thickness of the positive active material layer is 100-500 μm. If the positive active material layer is too thin, the active material loading is small, and the capacity is low. If the positive active material layer is too thick, the active layer impedance is large. Specifically, the thickness can be 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 100-200 μm, 100-300 μm, 100-400 μm, 400-500 μm, 200-300 μm or 200-400 μm.

[0018] The positive electrode active material comprises at least one of lithium iron phosphate, lithium cobaltate, lithium manganate, nickel cobalt manganese ternary material and nickel cobalt aluminum ternary material;

[0019] The conductive agent comprises one or more of Super P, acetylene black, ketjen black, carbon black, carbon nanotube, graphene and vapor grown carbon fiber;

[0020] The binder comprises one or more of PTFE, SBS, SEBS, PVDF, PTFE, PAALi, SBR, NBR, butylene rubber, styrene rubber and polyurethane.

[0021] In the composite positive electrode, the molecular formula of the halide solid-state electrolyte A and the halide solid-state electrolyte B is Li3MX6, wherein M comprises at least one of In, Y, Sc, Er, Mg, Zr and Al, and X comprises at least one of Cl, F, Br and I; the molecular formula of the halide solid-state electrolyte A and the halide solid-state electrolyte B is the same or different.

[0022] The halide solid-state electrolyte A and the halide solid-state electrolyte B specifically comprise at least one of Li3YCl6, Li3ErCl6, Li3YBr6, Li3InBr6 and Li3InCl6.

[0023] The application also provides a preparation method of the composite positive electrode, comprising the following steps:

[0024] 1) The positive electrode active material, the binder, the conductive agent and the organic solvent A are prepared into a slurry a according to a certain proportion, which is coated on the surface of the current collector, and after drying and rolling, the positive electrode active material layer is formed;

[0025] 2) The halide solid-state electrolyte, the binder and the organic solvent B are prepared into a slurry b according to a certain proportion, which is coated on the surface of the positive electrode active material layer, and after drying and rolling, the composite positive electrode is formed.

[0026] In the application, the preparation method of the composite positive electrode is used to coat the halide solid-state electrolyte slurry on the surface of the positive electrode active material layer, and after drying, the halide electrolyte layer is formed on the surface of the positive electrode active material layer. On one hand, the electrolyte layer can isolate the direct contact between the high-voltage positive electrode material and the sulfide solid-state electrolyte, and inhibit the formation of the space charge layer; on the other hand, the halide electrolyte layer has high ion conductivity, which is beneficial to the transmission of lithium ions; in addition, in-situ wet coating can effectively improve the interface contact between the positive electrode and the halide electrolyte, and the good flexibility of the halide also improves the interface contact between the halide electrolyte and the sulfide electrolyte.

[0027] In the preparation method, the organic solvent A comprises at least one of N-methylpyrrolidone, dimethyl carbonate, ethyl acetate, anhydrous ethanol, acetone, diethyl carbonate, and methyl propionate.

[0028] In the preparation method, the positive active material accounts for 70-95% in the slurry a; the binder accounts for 2-27%; and the conductive agent accounts for 3-28%.

[0029] In the preparation method, the solid content of the slurry a can be 40-60%.

[0030] In the preparation method, the organic solvent B comprises at least one of a polar solvent and a non-polar solvent.

[0031] The polar solvent comprises at least one of N-methylpyrrolidone, dimethyl carbonate, ethyl acetate, anhydrous ethanol, acetone, diethyl carbonate, and methyl propionate; and the non-polar solvent comprises at least one of toluene, p-xylene, cyclohexane, and isopropyl alcohol.

[0032] The application further provides a solid-state lithium ion secondary battery comprising the composite positive electrode, a solid-state electrolyte layer, and a negative electrode.

[0033] In the solid-state lithium ion secondary battery, the solid-state electrolyte layer is made of a sulfide solid-state electrolyte.

[0034] The negative electrode comprises at least one of metallic lithium, metallic indium, lithium-indium alloy, silicon-carbon, silicon, graphite, and lithium titanate.

[0035] In the application, the sulfide solid-state electrolyte is at least one of xLi2S·(100–x)P2S5(20≤x≤80) glass, Li-P-S glass ceramic, lithium fast ion conductor type, Li6PS5X(X=Cl, Br and I) argyrodite, Li 11-c M 2-c P 1+c S 12 (M=Ge, Sn and Si); and preferably at least one of lithium fast ion conductor type, Li6PS5X(X=Cl, Br and I) argyrodite, Li 11 -cM 2-c P 1+c S 12 (M=Ge, Sn and Si).

[0036] In the solid-state lithium ion secondary battery, the solid-state electrolyte layer has a density of 85-95%.

[0037] The particle size D 50 of the sulfide solid-state electrolyte is 1-10 μm.

[0038] In the present application, the negative electrode can be any conventional negative electrode in the art, and specifically can include at least one of metal lithium, metal indium, lithium-indium alloy, silicon-carbon, silicon, graphite, and lithium titanate.

[0039] In the present application, the positive electrode active material layer in the solid-state lithium ion secondary battery is generally prepared by coating a slurry obtained by mixing a positive electrode active material, a solid-state electrolyte, a conductive agent, and a binder. The solid-state electrolyte affects lithium ion transmission, and when a halide solid-state electrolyte B is used, the positive electrode active material does not need to be coated.

[0040] The present application further provides an electrical equipment comprising the above-mentioned solid-state lithium ion secondary battery.

[0041] Compared with the prior art, the present application has the following advantages:

[0042] The composite positive electrode of the present application is used in a sulfide full-solid-state battery, which can completely isolate the direct contact between the high-voltage positive electrode material and the sulfide solid-state electrolyte, inhibit the formation of a space charge layer, and further improve the cycle stability of the battery. The halide solid-state electrolyte with high oxidation potential is used as the positive electrode coating material. On the one hand, the halide solid-state electrolyte has high ionic conductivity, which is beneficial to the transmission of lithium ions in the electrochemical process. On the other hand, the formed slurry b can fill the voids of the positive electrode active material layer, promoting the transmission of lithium ions in the positive electrode active material layer. The preparation of the composite positive electrode avoids the coating process of the positive electrode active material in the use of the sulfide full-solid-state battery, simplifying the positive electrode preparation process. In addition, in-situ wet coating can effectively improve the interface contact between the positive electrode and the halide electrolyte, and the good flexibility of the halide also improves the interface contact between the halide electrolyte and the sulfide electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 Figure 1 is a structural schematic diagram of a solid-state lithium ion secondary battery according to an embodiment of the present application.

[0044] In the figure, the various marks are as follows:

[0045] 1. Composite positive electrode sheet, 2. Solid-state electrolyte layer, 3. Lithium-indium negative electrode. DETAILED DESCRIPTION

[0046] In the following examples, the experimental methods used are conventional methods unless otherwise specified.

[0047] In the following examples, the materials, reagents, etc. used are commercially available unless otherwise specified.

[0048] The application aims at the problem that the interface stability of sulfide solid electrolyte and high-voltage cathode is poor, space charge is easily generated at the interface, and the interface resistance is continuously increased, and provides a composite cathode, which comprises a current collector, a cathode active material layer and a halide solid electrolyte layer which are sequentially stacked.

[0049] The halide solid electrolyte layer comprises halide solid electrolyte A.

[0050] In a specific embodiment, because the particle size of halide solid electrolyte A will affect the grain boundary of the formed electrolyte layer, when the particle size D of the halide solid electrolyte A is 1-15 μm, preferably 1 μm, 10 μm or 15 μm, the electrolyte layer has less grain boundary, and thus has smaller grain boundary resistance, which is more conducive to lithium ion transmission. 50 When the particle size D of the halide solid electrolyte A is 1-15 μm, preferably 1 μm, 10 μm or 15 μm, the electrolyte layer has less grain boundary, and thus has smaller grain boundary resistance, which is more conducive to lithium ion transmission.

[0051] In a specific embodiment, when the composite cathode is used as the cathode of a solid-state secondary battery, the halide solid electrolyte layer cannot be too thin, and too thin cannot effectively isolate the cathode active material layer in the composite cathode from the sulfide solid electrolyte layer in the solid-state secondary battery; and the halide solid electrolyte layer cannot be too thick, and too thick will be not conducive to lithium ion transmission, therefore, the thickness of the halide solid electrolyte layer can be 5-30 μm, more preferably the thickness of the halide solid electrolyte layer is 10-20 μm, and in a specific embodiment, the thickness of the halide solid electrolyte layer can be 10 μm, 15 μm, 20 μm or 30 μm, which is conducive to lithium ion transmission.

[0052] In a specific embodiment, the cathode active material layer comprises the following components by mass: cathode active material 25-85 parts; halide solid electrolyte B 2-20 parts; conductive agent 1 part; and binder 0.25-2 parts.

[0053] Preferably, the particle size D of the halide solid electrolyte B is 0.5-5 μm. 50 Preferably, the particle size D of the halide solid electrolyte B is 0.5-5 μm.

[0054] The thickness of the cathode active material layer is 100-500 μm.

[0055] Preferably, the halide solid electrolyte A and the halide solid electrolyte B can be at least one selected from Li3YCl6, Li3ErCl6, Li3YBr6, Li3InBr6 and Li3InCl6.

[0056] In a specific embodiment, because the positive active material layer is too thin, the active material load is small, and the capacity is low; the positive active material layer is too thick, the impedance of the active layer is large, the thickness of the positive active material layer can be 100-500 μm, specifically 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 100-200 μm, 100-300 μm, 100-400 μm, 400-500, 200-300 μm, or 200-400 μm.

[0057] Preferably, the positive active material is selected from at least one of lithium iron phosphate, lithium cobaltate, lithium manganate, nickel-cobalt-manganese ternary material, and nickel-cobalt-aluminum ternary material.

[0058] The conductive agent is selected from one or more of Super P, acetylene black, Ketjen black, carbon black, carbon nanotubes, graphene, and vapor-grown carbon fibers.

[0059] The binder is selected from one or more of PTFE, SBS, SEBS, PVDF, PTFE, PAA Li, SBR, NBR, butylene rubber, styrene rubber, and polyurethane.

[0060] Preferably, the molecular formula of the halide solid-state electrolyte A and the halide solid-state electrolyte B is Li3MX6, wherein M is selected from at least one of In, Y, Sc, Er, Mg, Zr, and Al, and X is selected from at least one of Cl, F, Br, and I; the molecular formula of the halide solid-state electrolyte A and the halide solid-state electrolyte B is the same or different.

[0061] The application also provides a preparation method of the composite positive electrode, comprising the following steps:

[0062] 1) The positive active material, the binder, the conductive agent, and the organic solvent A are prepared into a slurry a in a certain proportion, and are coated on the surface of the current collector, and after drying and rolling, the positive active material layer is formed.

[0063] 2) The halide solid-state electrolyte, the binder, and the organic solvent B are prepared into a slurry b in a certain proportion, and are coated on the surface of the positive active material layer, and after drying and rolling, the composite positive electrode is formed.

[0064] In the present application, the preparation method of the solid-state battery composite positive electrode, which coats halide solid-state electrolyte slurry on the surface of the positive active material layer, and forms a halide electrolyte layer on the surface of the positive active material layer after drying, which can isolate the high-voltage positive material from direct contact with the sulfide solid-state electrolyte, inhibit the formation of space charge layer; on the other hand, the halide electrolyte layer has high ionic conductivity, which is conducive to the transmission of lithium ions; in addition, in-situ wet coating can effectively improve the interface contact between the positive electrode and the halide electrolyte, and the good flexibility of the halide also improves the interface contact between the halide electrolyte and the sulfide electrolyte.

[0065] Preferably, the organic solvent A is at least one of N-methyl pyrrolidone, dimethyl carbonate, ethyl acetate, anhydrous ethanol, acetone, diethyl carbonate, methyl propionate.

[0066] Preferably, the positive active material in the slurry a accounts for 70% to 95%; the binder accounts for 2% to 27%; and the conductive agent accounts for 3% to 28%.

[0067] Preferably, the solid content of the slurry a is 40% to 60%.

[0068] Preferably, the organic solvent B is at least one of a polar solvent and a non-polar solvent.

[0069] The polar solvent is at least one of N-methyl pyrrolidone, dimethyl carbonate, ethyl acetate, anhydrous ethanol, acetone, diethyl carbonate, and methyl propionate; and the non-polar solvent is at least one of toluene, p-xylene, cyclohexane, and isopropyl alcohol.

[0070] The present application further provides a solid-state lithium ion secondary battery, which comprises the above composite positive electrode, a solid-state electrolyte layer, and a negative electrode.

[0071] Preferably, the solid-state electrolyte layer comprises a sulfide solid-state electrolyte.

[0072] The negative electrode is selected from at least one of metal lithium, metal indium, lithium-indium alloy, silicon-carbon, silicon, graphite, and lithium titanate.

[0073] In the present application, the sulfide solid-state electrolyte is at least one of xLi2S·(100–x)P2S5(20≤x≤80) glass, Li-P-S glass ceramic, lithium fast ion conductor type, Li6PS5X(X=Cl, Br and I) argyrodite, Li 11-c M 2-c P 1+c S 12 (M=Ge, Sn and Si); and the sulfide solid-state electrolyte is preferably lithium fast ion conductor type, Li6PS5X(X=Cl, Br and I) argyrodite, Li11-c M 2-c P 1+c S 12 at least one of (M = Ge, Sn and Si).

[0074] Preferably, the density of the solid electrolyte layer is 85% to 95%;

[0075] The particle size D of the sulfide solid electrolyte is 1 to 10 μm. 50

[0076] In the present application, the negative electrode can be any conventional negative electrode in the art, and the negative electrode can specifically be selected from at least one of metal lithium, metal indium, lithium-indium alloy, silicon-carbon, silicon, graphite and lithium titanate.

[0077] In the present application, the positive electrode active material layer in the solid-state lithium ion secondary battery is usually prepared by coating a slurry obtained by mixing a positive electrode active material, a solid electrolyte, a conductive agent and a binder. The solid electrolyte affects lithium ion transmission, and when a halide solid electrolyte B is used, the positive electrode active material does not need to be coated.

[0078] Example 1

[0079] The present embodiment provides a preparation method of a solid-state lithium ion secondary battery, comprising the following steps:

[0080] S1. Preparation process of the composite positive electrode:

[0081] S11. The positive electrode active material NCM622, the binder PVDF, the conductive agent vapor-grown carbon fiber and the electrolyte Li3InCl6 are weighed and mixed according to the mass ratio of 85:0.5:1.5:13, then N-methyl pyrrolidone (NMP) solution is added to form a slurry with a solid content of 45%, which is coated on the surface of the current collector aluminum foil (thickness of 10 μm), dried at 80°C under vacuum and rolled to form a positive electrode active material layer, and the thickness of the positive electrode active material layer after rolling is 300 μm, wherein the D of the electrolyte Li3InCl6 is 3 μm; 50

[0082] S12. The halide solid electrolyte Li3InCl6 and the binder NBR are weighed and mixed according to the mass ratio of 98.5:1.5, then dimethylbenzene is added to form a slurry with a solid content of 60%, which is coated on the surface of the positive electrode active material layer, dried and rolled to form a composite positive electrode, and the thickness of the composite positive electrode (thickness excluding the current collector) after rolling is 315 μm (i.e. the thickness of the halide electrolyte layer is 15 μm), wherein the D of the halide solid electrolyte Li3InCl6 is 10 μm. 50

[0083] S2. Preparation of a solid-state lithium ion secondary battery:​​​

[0084] S21. Preparation of the composite positive electrode sheet: The composite positive electrode prepared in S1 above is cut into a sheet, and a composite positive electrode sheet with a diameter of 10 mm is formed by cutting;

[0085] S22. Preparation of the solid-state electrolyte layer: 70 mg of sulfide solid-state electrolyte Li6PS5Cl with a particle size D50 of 5 μm is weighed, and a solid-state electrolyte sheet with a density of 85% and a diameter of 10 mm is formed under a pressure of 8 MPa;

[0086] S23. Assembly of the solid-state battery: The lithium-indium negative electrode 3 is matched, and the composite positive electrode sheet 1, the solid-state electrolyte sheet (i.e., the solid-state electrolyte layer) 2, and the lithium-indium negative electrode 3 are sequentially assembled in the solid-state battery test mold, and a pressure of 2 MPa is applied to form a full solid-state battery, and a structural schematic diagram thereof is shown in Figure 1 .

[0087] Example 2

[0088] The difference between this embodiment and Example 1 is that the thickness of the halide solid-state electrolyte layer is 20 μm.

[0089] Example 3

[0090] The difference between this embodiment and Example 1 is that the thickness of the halide solid-state electrolyte layer is 10 μm.

[0091] Example 4

[0092] The difference between this embodiment and Example 1 is that the thickness of the halide solid-state electrolyte layer is 5 μm.

[0093] Example 5

[0094] The difference between this embodiment and Example 1 is that the thickness of the halide solid-state electrolyte layer is 30 μm.

[0095] Example 6

[0096] The difference between this embodiment and Example 1 is that the thickness of the halide solid-state electrolyte layer is 4.5 μm.

[0097] Example 7

[0098] The difference between this embodiment and Example 1 is that the thickness of the halide solid-state electrolyte layer is 35 μm.

[0099] Example 8

[0100] The difference between this embodiment and Example 1 is that the particle size D 50 of the halide solid-state electrolyte Li3InCl6 in step S12 is 15 μm.

[0101] Example 9

[0102] The difference between this example and Example 1 is that the particle size D50 of the halide solid electrolyte Li3InCl6 in step S12 is 1 μm. 50

[0103] Example 10

[0104] The difference between this example and Example 1 is that the particle size D50 of the halide solid electrolyte Li3InCl6 in step S12 is 0.5 μm. 50

[0105] Example 11

[0106] The difference between this example and Example 1 is that the particle size D50 of the halide solid electrolyte Li3InCl6 in step S12 is 20 μm. 50

[0107] Example 12

[0108] The difference between this example and Example 1 is that LATP is used instead of the electrolyte Li3InCl6 in step S11.

[0109] Example 13

[0110] The difference between this example and Example 1 is that Li3InBr6 is used instead of the electrolyte Li3InCl6 in step S11.

[0111] Example 14

[0112] The difference between this example and Example 1 is that Li3ErCl6 is used instead of the electrolyte Li3InCl6 in step S11.

[0113] Example 15

[0114] The difference between this example and Example 1 is that the particle size D50 of the electrolyte Li3InCl6 in step S11 is 0.5 μm.

[0115] Example 16

[0116] The difference between this example and Example 1 is that the particle size D50 of the electrolyte Li3InCl6 in step S11 is 5 μm.

[0117] Example 17

[0118] The difference between this example and Example 1 is that the particle size D50 of the electrolyte Li3InCl6 in step S11 is 0.1 μm.

[0119] Example 18

[0120] ​​​The difference between this example and Example 1 is that the particle size D50 of the electrolyte Li3InCl6 in step S11 is 10 μm.

[0121] Example 19

[0122] The difference between this example and Example 1 is that the thickness of the positive electrode active material layer in step S11 is 100 μm.

[0123] Example 20

[0124] The difference between this example and Example 1 is that the thickness of the positive electrode active material layer in step S11 is 500 μm.

[0125] Example 21

[0126] The difference between this example and Example 1 is that the thickness of the positive electrode active material layer in step S11 is 50 μm.

[0127] Example 22

[0128] The difference between this example and Example 1 is that the thickness of the positive electrode active material layer in step S11 is 700 μm.

[0129] Comparative Example 1

[0130] The difference between this example and Example 1 is that the halide solid electrolyte layer is not included in the composite positive electrode.

[0131] Performance test

[0132] The tests of the solid-state lithium ion secondary batteries described in Examples 1-22 and Comparative Example 1 were all carried out using a new Wei test cabinet to perform long cycle tests of rate charging and discharging, the battery test rate was 0.1C (1C = 180 mA / g), the test voltage range was 1.9-3.7V, and the cycle was 100 cycles. The test results are shown in Table 1.

[0133] From the results in Table 1, it can be seen that:

[0134] 1. The effect of the thickness of the halide electrolyte layer on the performance of the solid-state lithium ion secondary battery

[0135] First, through the solid-state lithium ion secondary batteries prepared by the halide electrolyte layer thicknesses of 4.5 μm in Examples 1-5 and 35 μm in Example 7, the first charge specific capacity, the first discharge specific capacity, the first efficiency, and the capacity retention rate after 100 cycles of Examples 1-5 are better than those of Examples 6-7, so the optimized thickness range of the halide solid electrolyte layer is 5-30 μm.

[0136] Secondly, by comparing the data effects in Example 1-3 and Example 4-5, a more preferred thickness range of 10-20 μm of the halide solid electrolyte layer is obtained.

[0137] Finally, by comparing the data in Example 1-7 and Comparative Example 1, it can be seen that the solid-state lithium ion secondary battery prepared by using the composite positive electrode with the halide solid electrolyte layer has better first charge specific capacity, first discharge specific capacity, first efficiency and capacity retention rate after 100 cycles than the comparative example, which shows that the composite positive electrode of the application is beneficial to the capacity development of the solid-state lithium ion secondary battery and the improvement of the cycle performance.

[0138] 2, the particle size D of the halide solid electrolyte A in S12 50 Influence on the performance of the solid-state lithium ion secondary battery

[0139] The D of Li3InCl6 in Example 1, 8 and 9 of the application 50 The D of Li3InCl6 in Example 10 and 11 of the application is 10 μm, 15 μm and 1 μm respectively 50 The performance of the solid-state lithium ion secondary battery obtained by each of the above-mentioned D of Li3InCl6 in Example 1, 8 and 9 of the application is better, so the preferred particle size D of the halide solid electrolyte A in the application is 1-15 μm. 50 Furthermore, by comparing the data in Example 1, 8-11 and Comparative Example, it can be seen that the solid-state lithium ion secondary battery prepared by using the composite positive electrode with the halide solid electrolyte layer has better first charge specific capacity, first discharge specific capacity, first efficiency and capacity retention rate after 100 cycles than the comparative example, which shows that the application is beneficial to the capacity development of the solid-state lithium ion secondary battery and the improvement of the cycle stability of the battery.

[0140] 3, the influence of different halide solid electrolyte B selected in step S11 on the performance of the solid-state lithium ion secondary battery

[0141] By comparing Example 1, Example 12-14 and Comparative Example, it can be seen that the effects of different electrolytes selected in the application are better than those of the comparative example, which shows that the application is beneficial to the capacity development of the solid-state lithium ion secondary battery and the improvement of the cycle stability of the battery.

[0142] 4, the particle size D of the halide solid electrolyte B in step S11 50 Influence on the performance of the solid-state lithium ion secondary battery

[0143] The particle size D of the halide solid electrolyte B Li3InCl6 selected in Example 1 of the application 50The particle size D of the preferred halide solid-state electrolyte B of the present application is 3 μm, and the performance data of the solid-state lithium ion secondary batteries prepared in Examples 15-16 are all better than those of Examples 17-18, thus the particle size D of the preferred halide solid-state electrolyte B of the present application is preferably 3 μm 50 The particle size D of the preferred halide solid-state electrolyte B of the present application is 0.5-5 μm. However, the effects of Examples 1, 15-18 of the present application are all obviously better than those of the comparative examples, thus the particle size D of the preferred halide solid-state electrolyte B of the present application is preferably 0.5-5 μm.

[0144] 5. Effect of the thickness of the positive active material layer in step S11 on the performance of the solid-state lithium ion secondary battery

[0145] From the comparison of the data in Example 1 (300 μm) of the present application, Example 19 (100 μm), Example 20 (500 μm) and Examples 21-22 (50, 700 μm), it can be seen that the preferred thickness of the positive active material layer of the present application is 100-500 μm; from the comparison of Examples 1, 19-22 of the present application with the comparative examples, the effects of Examples 1, 19-22 of the present application are all obviously better than those of the comparative examples, thus the thickness of the positive active material layer of the present application is preferably 100-500 μm, and the solid-state lithium ion secondary battery prepared by using the positive active material layer with the thickness of 100-500 μm is beneficial to the capacity development of the solid-state lithium ion secondary battery and the improvement of the cycle performance.

[0146] Table 1. Performance test results of the solid-state lithium ion secondary battery

[0147]

[0148]

Claims

1. A composite positive electrode, characterized by comprising: The composite cathode includes a current collector, a cathode active material layer, and a halide solid electrolyte layer; The cathode active material layer is located between the current collector and the halide solid electrolyte layer; The halide solid electrolyte layer includes a halide solid electrolyte A; The cathode active material layer includes a cathode active material, a halide solid electrolyte B, a conductive agent, and a binder; The molecular formula of the halide solid electrolyte A and the halide solid electrolyte B is Li3MX6, wherein M includes at least one of In, Y, Sc, Er, Mg, Zr, and Al, and X includes at least one of Cl, F, Br, and I; the molecular formula of the halide solid electrolyte A and the halide solid electrolyte B is the same or different; The particle size D of the halide solid-state electrolyte A 50 is 1 to 15 μm; The particle size D of the halide solid-state electrolyte B is 0.5 to 5 μm. 50 is 0.5 to 5 μm.

2. The composite cathode according to claim 1, wherein The thickness of the halide solid electrolyte layer is 5-30 μm.

3. The composite cathode of claim 1, wherein The thickness of the halide solid electrolyte layer is 10-20 μm.

4. The composite cathode of claim 1, wherein The thickness of the cathode active material layer is 100-500 μm.

5. The composite cathode of claim 1, wherein The cathode active material includes at least one of lithium iron phosphate, lithium cobaltate, lithium manganate, nickel-cobalt-manganese ternary material, and nickel-cobalt-aluminum ternary material; The conductive agent includes one or more of Super P, acetylene black, Ketjen black, carbon nanotube, graphene, and vapor-phase growth carbon fiber; The binder includes one or more of PTFE, SBS, SEBS, PVDF, PTFE, PAA Li, SBR, NBR, butylene rubber, styrene rubber, and polyurethane.

6. A solid-state lithium-ion secondary battery, characterized by comprising: The solid-state lithium ion secondary battery includes the composite cathode of any one of claims 1-5, a sulfide solid electrolyte layer, and an anode.

7. The solid-state lithium-ion secondary battery according to claim 6, wherein The anode includes at least one of metallic lithium, metallic indium, lithium-indium alloy, silicon-carbon, silicon, graphite, and lithium titanate.

8. An electrical device, characterized by The solid-state lithium ion secondary battery includes the composite cathode of any one of claims 1-5, a sulfide solid electrolyte layer, and an anode.

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