Secondary battery and electric device

Abstract

This application discloses a secondary battery and an electrical device, belonging to the field of battery technology. The secondary battery includes a positive electrode sheet, which includes a positive current collector and a first positive electrode layer and a second positive electrode layer sequentially disposed on at least one surface of the positive current collector. The first positive electrode layer includes a first positive electrode active material, a first conductive carbon, and a first sulfide electrolyte. The second positive electrode layer includes a second positive electrode active material, a second conductive carbon, and a second sulfide electrolyte. The mass percentage of the first conductive carbon in the first positive electrode layer is M1, and the mass percentage of the first sulfide electrolyte in the first positive electrode layer is N1. The mass percentage of the second conductive carbon in the second positive electrode layer is M2, and the mass percentage of the second sulfide electrolyte in the second positive electrode layer is N2. The battery satisfies the following conditions: M1>M2, N2>N1, exhibiting excellent rate performance and thermal stability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a secondary battery and an electrical device. Background Technology

[0002] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used. Since their development, secondary batteries have been widely used in 3C digital products, electric vehicles, and energy storage power stations.

[0003] The rate performance of a secondary battery refers to the ratio of the current output by the battery to its rated capacity within a specified time, and is usually used to indicate the speed of battery charging and discharging. As the secondary battery market continues to expand, the performance requirements for them are also constantly increasing, especially in fields such as power tools and electric drones, where high rate performance is required. However, the rate performance of existing secondary batteries still needs to be improved.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a secondary battery and power device with excellent rate performance and thermal stability.

[0006] To achieve the above objectives, in a first aspect of this application, this application provides a secondary battery, the secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a first positive electrode layer and a second positive electrode layer sequentially disposed on at least one surface of the positive current collector;

[0007] The first positive electrode layer includes a first positive electrode active material, a first conductive carbon, and a first sulfide electrolyte;

[0008] The second positive electrode layer includes a second positive electrode active material, a second conductive carbon, and a second sulfide electrolyte;

[0009] The mass percentage of the first conductive carbon in the first positive electrode layer is M1, and the mass percentage of the first sulfide electrolyte in the first positive electrode layer is N1.

[0010] The mass percentage of the second conductive carbon in the second positive electrode layer is M2, and the mass percentage of the second sulfide electrolyte in the second positive electrode layer is N2.

[0011] The following conditions must be met: M1>M2, N2>N1.

[0012] As an implementation scheme of this application, at least one of the following (a) to (d) is satisfied:

[0013] (a) 2% ≤ M1 ≤ 5%;

[0014] (b) 4.5% ≤ N1 ≤ 6%;

[0015] (c) 1% ≤ M2 ≤ 2%;

[0016] (d) 12% ≤ N2 ≤ 13%.

[0017] As an embodiment of this application, the first positive electrode layer further includes a first halide electrolyte, wherein the mass ratio of the first sulfide electrolyte to the first halide electrolyte is 5:(4-6); and / or

[0018] The mass ratio of the second sulfide electrolyte to the second conductive carbon is (6-13):1.

[0019] As an embodiment of this application, the mass percentage of the first halide electrolyte in the first positive electrode layer is 4.5% to 6%.

[0020] As an embodiment of this application, the mass percentage of the first positive electrode active material in the first positive electrode layer is 80% to 90%; and / or

[0021] The second positive electrode active material has a mass percentage content of 80% to 90% in the second positive electrode layer.

[0022] As an embodiment of this application, the positive electrode further includes an intermediate layer, which is located between the first positive electrode layer and the second positive electrode layer;

[0023] The intermediate layer includes a third positive electrode active material, a third conductive carbon, an oxide electrolyte, and a second halide electrolyte.

[0024] As an implementation scheme of this application, at least one of the following (Ⅰ) to (Ⅴ) is satisfied:

[0025] (I) The mass ratio of the oxide electrolyte to the second halide electrolyte is 1:(2-12);

[0026] (II) The third conductive carbon in the intermediate layer has a mass percentage content of 0.5% to 2%;

[0027] (III) The oxide electrolyte in the intermediate layer has a mass percentage content of 1% to 5%;

[0028] (IV) The second halide electrolyte has a mass percentage content of 8% to 12% in the intermediate layer;

[0029] (V) The third active material has a mass percentage of 80% to 90% in the intermediate layer.

[0030] As an embodiment of this application, the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material each independently include LiCoO2, Li x1 Ni y1 Co z1 Mn 1-y1-z1 At least one of O2, wherein 0.96 ≤ x1 ≤ 1.1, 0.6 ≤ y1 ≤ 1, 0 ≤ z1 ≤ 0.2; and / or

[0031] The first conductive carbon, the second conductive carbon, and the third conductive carbon each independently include at least one of carbon black, acetylene black, carbon nanotubes, vapor-grown carbon fibers, and graphene.

[0032] As an implementation scheme of this application, at least one of the following (1) to (3) is satisfied:

[0033] (1) The first sulfide electrolyte and the second sulfide electrolyte each independently include Li x2 A y2 B z2 Where A includes at least one of Ge, Sn, and P, B includes S, 3≤x2≤10, 1≤y2≤3, and 0≤z2≤12;

[0034] (2) The first halide electrolyte and the second halide electrolyte each independently include Li x3 DCl6, where D includes at least one of In, Sc, and Zr, and 2≤x3≤3;

[0035] (3) The oxide electrolyte includes Li X4 E y3 G z3 Wherein, E includes at least one of La, Al, Zr, Ti, and Ge, and G includes one of PO and O, 0.3 < X4 ≤ 7, 0.3 ≤ y3 ≤ 3, and 3 ≤ z3 ≤ 12.

[0036] As an embodiment of this application, the thickness of the first positive electrode layer is greater than the thickness of the intermediate layer; and / or

[0037] The thickness of the second positive electrode layer is greater than the thickness of the intermediate layer.

[0038] As an embodiment of this application, the thickness of the first positive electrode layer is 60 μm to 80 μm; and / or

[0039] The thickness of the second positive electrode layer is 60 μm to 80 μm.

[0040] As an embodiment of this application, the thickness of the intermediate layer is 10μm to 20μm.

[0041] In a second aspect, this application provides an electrical device including the aforementioned secondary battery.

[0042] The beneficial effects of this invention are as follows: This application sequentially provides a first positive electrode layer and a second positive electrode layer on at least one surface of the positive electrode current collector. A first conductive carbon and a first sulfide electrolyte are added to the first positive electrode layer, and a second conductive carbon and a second sulfide electrolyte are added to the second positive electrode layer. By controlling M1>M2 and N2>N1, the content of conductive carbon in the first positive electrode layer is greater than that in the second positive electrode layer, and the content of sulfide electrolyte in the first positive electrode layer is less than that in the second positive electrode layer. This allows the first positive electrode layer, which is closer to the positive electrode current collector, to provide more electron pathways, while the second positive electrode layer, which is farther away from the positive electrode current collector, provides more ion pathways, effectively improving the rate performance and thermal stability of the positive electrode sheet. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the positive electrode structure according to an embodiment of the present invention.

[0044] Figure 2 This is a schematic diagram of the positive electrode structure according to another embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0047] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0049] Please see Figure 1 This application provides a secondary battery, which includes a positive electrode sheet. The positive electrode sheet includes a positive current collector 1 and a first positive electrode layer 2 and a second positive electrode layer 3 sequentially disposed on at least one surface of the positive current collector.

[0050] The first positive electrode layer includes a first positive electrode active material, a first conductive carbon, and a first sulfide electrolyte;

[0051] The second positive electrode layer includes a second positive electrode active material, a second conductive carbon, and a second sulfide electrolyte;

[0052] The mass percentage of the first conductive carbon in the first positive electrode layer is M1, and the mass percentage of the first sulfide electrolyte in the first positive electrode layer is N1.

[0053] The mass percentage of the second conductive carbon in the second positive electrode layer is M2, and the mass percentage of the second sulfide electrolyte in the second positive electrode layer is N2.

[0054] The following conditions must be met: M1>M2, N2>N1.

[0055] This application creatively involves sequentially distributing a first positive electrode layer and a second positive electrode layer on at least one surface of a positive electrode current collector. A first conductive carbon layer and a first sulfide electrolyte are added to the first positive electrode layer, and a second conductive carbon layer and a second sulfide electrolyte layer are added to the second positive electrode layer. By controlling M1>M2 and N2>N1, the conductive carbon content in the first positive electrode layer is greater than that in the second positive electrode layer, and the sulfide electrolyte content in the first positive electrode layer is less than that in the second positive electrode layer. This arrangement allows the first positive electrode layer, closer to the positive electrode current collector, to provide more electron pathways, while the second positive electrode layer, farther from the positive electrode current collector, provides more ion pathways, which is beneficial for electron and ion transport and effectively improves the rate performance and thermal stability of the positive electrode sheet.

[0056] In one embodiment, the following condition is satisfied: 2% ≤ M1 ≤ 5%, for example, it can be a range of 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these values. In particular, when the mass percentage of the first conductive carbon in the first positive electrode layer is within this range, it can provide more electron pathways, which is beneficial to electron transport and further improves the rate performance of the positive electrode.

[0057] In one embodiment, the following condition is satisfied: 4.5% ≤ N1 ≤ 6%, for example, it can be a range of 4.5%, 4.6%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, or any two of these values. In particular, when the mass percentage of the first sulfide electrolyte in the first positive electrode layer is within this range, its content is significantly lower than the mass percentage of the second sulfide electrolyte in the second positive electrode layer, providing more ion pathways, which is beneficial for ion transport and improves the rate performance of the positive electrode.

[0058] In one embodiment, the following condition is satisfied: 1% ≤ M2 ≤ 2%, for example, it can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any two of these values. In particular, when the mass percentage of the second conductive carbon in the second positive electrode layer is within this range, its content is lower than the mass percentage of the first conductive carbon in the first positive electrode layer, which can provide more electron pathways, which is beneficial to electron transport. At the same time, it can improve the thermal stability of the positive electrode to a certain extent, and further improve the rate performance of the positive electrode.

[0059] In one implementation, the following condition is satisfied: 12% ≤ N2 ≤ 13%, for example, it can be 12%, 12.1%, 12.2%, 12.3%, 12.4%, 12.5%, 12.6%, 12.7%, 12.8%, 12.9%, 13%, or a range consisting of any two of these values.

[0060] In one embodiment, the first positive electrode layer further includes a first halide electrolyte, wherein the mass ratio of the first sulfide electrolyte to the first halide electrolyte is 5:(4-6), for example, it can be 5:4, 5:4.2, 5:4.5, 5:4.8, 5:5, 5:5.2, 5:5.5, 5:5.8, 5:6 or any two of these values. By adding the first halide electrolyte to the first positive electrode layer, the thermal stability of the positive electrode sheet can be improved. In particular, by controlling the mass ratio of the first sulfide electrolyte to the first halide electrolyte within this range, thermal stability and rate performance can be balanced.

[0061] In one embodiment, the mass ratio of the second sulfide electrolyte to the second conductive carbon is (6-13):1, for example, it can be 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 10:1, 11:1, 12:1, 13:1 or any two of these values. In particular, controlling the mass ratio of the second sulfide electrolyte to the second conductive carbon within this range can effectively balance thermal stability and rate performance.

[0062] In one embodiment, the mass percentage of the first halide electrolyte in the first positive electrode layer is 4.5% to 6%, for example, it can be 4.5%, 4.6%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6% or any two of these values.

[0063] In one embodiment, the mass percentage of the first positive electrode active material in the first positive electrode layer is 80% to 90%, for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or any two of these values.

[0064] In one embodiment, the mass percentage of the second positive electrode active material in the second positive electrode layer is 80% to 90%, for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or any two of these values.

[0065] Please see Figure 2 In one embodiment, the positive electrode further includes an intermediate layer 4, which is located between the first positive electrode layer and the second positive electrode layer;

[0066] The intermediate layer includes a third positive electrode active material, a third conductive carbon, an oxide electrolyte, and a second halide electrolyte.

[0067] This application provides an intermediate layer between the first positive electrode layer and the second positive electrode layer, and adds a third conductive carbon, an oxide electrolyte, and a second halide electrolyte to the intermediate layer, which effectively improves the thermal stability of the positive electrode sheet, thereby reducing the risk of battery thermal runaway caused by a sharp increase in the temperature of the secondary battery and improving the thermal safety of the secondary battery. At the same time, the provision of the intermediate layer can further improve the rate performance.

[0068] In one embodiment, the mass ratio of the oxide electrolyte to the second halide electrolyte is 1:(2 to 12); for example, it can be 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12 or any two of these values.

[0069] In one embodiment, the third conductive carbon has a mass percentage content of 0.5% to 2% in the intermediate layer; for example, it can be 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any two of these values.

[0070] In one embodiment, the oxide electrolyte has a mass percentage of 1% to 5% in the intermediate layer; for example, it can be a range of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these values.

[0071] In one embodiment, the second halide electrolyte has a mass percentage content of 8% to 12% in the intermediate layer; for example, it can be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12% or any two of these values.

[0072] In one embodiment, the third active material has a mass percentage of 80% to 90% in the intermediate layer; for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or a range of any two of these values.

[0073] In one embodiment, the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material each independently include LiCoO2, Li x1 Ni y1 Co z1 Mn 1-y1-z1 At least one of O2, wherein 0.96≤x1≤1.1, 0.6≤y1≤1, and 0≤z1≤0.2.

[0074] In one embodiment, the first conductive carbon, the second conductive carbon, and the third conductive carbon each independently include at least one of carbon black, acetylene black, carbon nanotubes, vapor-grown carbon fibers, and graphene.

[0075] In one embodiment, the first sulfide electrolyte and the second sulfide electrolyte each independently include Li x2 A y2 B z2 Where A includes at least one of Ge, Sn, and P, B includes S, 3≤x2≤10, 1≤y2≤3, and 0≤z2≤12.

[0076] In one embodiment, the first sulfide electrolyte and the second sulfide electrolyte each independently include Li 10 GeP2S 12 Li7P3S 11 Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 At least one of Li3PS4.

[0077] In one embodiment, the first halide electrolyte and the second halide electrolyte each independently include Li x3 DCl6, where D includes at least one of In, Sc, and Zr, and 2≤x3≤3.

[0078] In one embodiment, the first halide electrolyte and the second halide electrolyte each independently include at least one of Li3InCl6, Li3ScCl6, and Li2ZrCl6.

[0079] In one embodiment, the oxide electrolyte comprises Li X4 E y3 G z3 Wherein, E includes at least one of La, Al, Zr, Ti, and Ge, and G includes one of PO and O, and 0.3 < x4 ≤ 7, 0.3 ≤ y3 ≤ 3, and 3 ≤ z3 ≤ 12.

[0080] In one embodiment, the oxide electrolyte comprises Li7La3Zr2O 12 Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li1 .3 Al 0.3 Ge 1.7 (PO4)3, Li 0.33 La 0.55 One or more of TiO3.

[0081] In one embodiment, the thickness of the first positive electrode layer is greater than the thickness of the intermediate layer.

[0082] In one embodiment, the thickness of the second positive electrode layer is greater than the thickness of the intermediate layer.

[0083] This application, by controlling the thickness relationship between the first cathode layer, the second cathode layer, and the intermediate layer, can provide suitable ion and electron transport pathways, with appropriate diffusion distances and paths for ions and electrons, effectively reducing polarization and improving rate performance.

[0084] In one embodiment, the thickness of the first positive electrode layer is 60 μm to 80 μm, for example, it can be 60 μm, 62 μm, 65 μm, 68 μm, 70 μm, 72 μm, 75 μm, 78 μm, 80 μm or any two of these values.

[0085] The thickness of the second positive electrode layer is 60μm to 80μm, for example, it can be 60μm, 62μm, 65μm, 68μm, 70μm, 72μm, 75μm, 78μm, 80μm or any two of these values.

[0086] As an embodiment of this application, the thickness of the intermediate layer is 10μm to 20μm, for example, it can be 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or any two of these values.

[0087] In one embodiment, the first positive electrode layer further includes a first binder, the first binder having a mass percentage content of 0.5% to 2% in the first positive electrode layer; for example, it may be 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any two of these values.

[0088] In one embodiment, the second positive electrode layer further includes a second binder, the second binder having a mass percentage content of 0.5% to 2% in the second positive electrode layer; for example, it can be 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or any two of these values.

[0089] In one embodiment, the intermediate layer further includes a third adhesive, the third adhesive comprising 0.5% to 2% by mass in the intermediate layer; for example, it may be 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any two of these values.

[0090] In one embodiment, the first adhesive, the second adhesive, and the third adhesive each independently include at least one of polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, polyethylene, propylene-α-olefin copolymer, polyvinylidene fluoride, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene block copolymer or its hydrogenated form, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, and ethylene-vinyl acetate copolymer.

[0091] In one embodiment, the type of positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material. In one embodiment, the positive electrode current collector is aluminum.

[0092] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0093] It should be noted that this application can detect the thickness of the first cathode layer, the second cathode layer, and the intermediate layer, as well as the content of each component therein, using the following two methods:

[0094] 1. For cases where the positive electrode sheet can be separated from the battery, the cross-section of the positive electrode is first analyzed using SEM and EDS-mapping. EDS-mapping is used to semi-quantitatively determine the thickness, element types, and element ratios of each layer. Then, powder samples are scraped from both sides of the positive electrode sheet (corresponding to the first and second positive electrode layers, respectively) and analyzed using ICP-OES to quantify the content of all involved elements and calculate the proportions of each component in the first and second positive electrode layers. Finally, the entire positive electrode sheet is analyzed using ICP-OES to quantify the content of all involved elements. The element content in the first and second positive electrode layers is then subtracted to calculate the proportions of each component in the intermediate layer.

[0095] 2. To address the difficulty in separating the positive electrode from the battery, the cross-section of the positive electrode is first analyzed using SEM and EDS-mapping. EDS-mapping is used to semi-quantitatively determine the thickness, element types, and element ratios of each layer. Then, advanced ion beam thinning techniques (CP or FIB) are employed to obtain the surfaces of the first, intermediate, and second positive electrode layers. TOF-SIMS is then used to quantitatively analyze the three surfaces, inferring the composition of each layer.

[0096] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0097] In one embodiment, the secondary battery further includes a negative electrode and a solid electrolyte disposed between the positive electrode and the negative electrode.

[0098] In one embodiment, the negative electrode sheet includes one or more of lithium sheet, indium sheet, and LiIn alloy sheet.

[0099] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0100] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0101] The present application is further illustrated below with specific embodiments:

[0102] Example 1

[0103] A method for preparing a secondary battery includes the following steps:

[0104] (1) Preparation of positive electrode

[0105] LiNi 0.8 Co 0.1 Mn 0.1 O2 (hereinafter referred to as NCM811), Li6PS5Cl, Li3InCl6, vapor-grown carbon fiber (hereinafter referred to as VGCF), and PTFE were weighed in a weight ratio of 87:5:5:2:1 and ball-milled for 1 hour at 200 rpm using a planetary ball mill. The first positive electrode layer was then obtained by roll pressing.

[0106] NCM811, Li6PS5Cl, VGCF and PTFE were weighed in a weight ratio of 85:13:1:1 and ball-milled for 1 hour at 200 rpm using a planetary ball mill. The second cathode layer was then obtained by rolling.

[0107] (2) Assembly of all-solid-state battery: Li6PS5Cl electrolyte powder was added to the mold battery, and then a pressure of 30MPa was applied for pre-pressing. Subsequently, the second positive electrode layer and the first positive electrode layer were added sequentially on one side of the electrolyte. Indium and lithium sheets were added on the other side. Then, a pressure of 400MPa was applied to complete the assembly of the all-solid-state battery. Finally, the assembled all-solid-state battery was subjected to constant current charge-discharge test.

[0108] The thickness, component content, and ratio of Example 1 are shown in Table 1.

[0109] In Table 1, P represents the mass ratio of sulfide electrolyte to first halide electrolyte in the first positive electrode layer; Q represents the mass ratio of sulfide electrolyte to second conductive carbon in the second positive electrode layer.

[0110] Examples 2-18, Comparative Examples 4-7

[0111] The difference between Examples 2-18 and Comparative Examples 4-7 and Example 1 is that Examples 2-18 and Comparative Examples 4-7 change the composition ratio or thickness of the first positive electrode layer and the second positive electrode layer, while everything else remains the same.

[0112] Example 19

[0113] A method for preparing a secondary battery includes the following steps:

[0114] (1) Preparation of positive electrode

[0115] LiNi 0.8 Co 0.1 Mn 0.1 O2 (hereinafter referred to as NCM811), Li6PS5Cl, Li3InCl6, vapor-grown carbon fiber (hereinafter referred to as VGCF), and PTFE were weighed in a weight ratio of 87:5:5:2:1 and ball-milled for 1 hour at 200 rpm using a planetary ball mill. The first positive electrode layer was then obtained by roll pressing.

[0116] NCM811, Li7La3Zr2O 12 Li3InCl6, VGCF and PTFE were weighed in a weight ratio of 85:2:11:1:1, and ball-milled for 1 hour at 200 rpm using a planetary ball mill. The intermediate layer was then obtained by rolling.

[0117] NCM811, Li6PS5Cl, VGCF and PTFE were weighed in a weight ratio of 85:13:1:1 and ball-milled for 1 hour at 200 rpm using a planetary ball mill. The second cathode layer was then obtained by rolling.

[0118] (2) All-solid-state battery assembly: Li6PS5Cl electrolyte powder was added to the mold battery, and then a pressure of 30MPa was applied for pre-pressing. Subsequently, the second positive electrode layer, the intermediate layer, and the first positive electrode layer were added sequentially on one side of the electrolyte. Indium and lithium sheets were added on the other side. Then, a pressure of 400MPa was applied to complete the assembly of the all-solid-state battery. Finally, the assembled all-solid-state battery was subjected to constant current charge-discharge testing.

[0119] The thickness, component content, and ratio of Example 19 are shown in Table 2.

[0120] In Table 2, R represents the mass ratio of the oxide electrolyte to the halide electrolyte in the intermediate layer.

[0121] Examples 20-35

[0122] The difference between Examples 20-35 and Example 19 is that Examples 20-35 change the composition ratio or thickness of the intermediate layer, while everything else remains the same.

[0123] Comparative Example 1

[0124] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain a first intermediate layer, but all other aspects are the same.

[0125] Comparative Example 2

[0126] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not contain a second intermediate layer, but all other aspects are the same.

[0127] Comparative Example 3

[0128] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses a first intermediate layer of the same thickness to replace the second intermediate layer, while everything else is the same.

[0129] Table 1

[0130]

[0131]

[0132]

[0133] Table 2

[0134]

[0135]

[0136] Performance testing

[0137] DSC initial heat release temperature: measured using a Hitachi NEXTADSC series differential scanning calorimeter (DSC).

[0138] 1C capacity / 0.1C capacity: Cut-off voltage 1.9-3.7V, first 3 cycles of 0.1C, then 100 cycles of 0.5C.

[0139] Table 3

[0140]

[0141]

[0142]

[0143] As can be seen from Table 3, the positive electrode sheet described in this invention has excellent rate performance and thermal stability.

[0144] As can be seen from the comparison between Example 1 and Comparative Examples 1 to 3, the first positive electrode layer and the second positive electrode layer sequentially disposed on at least one surface of the positive electrode current collector in this application significantly improve the rate performance and thermal stability.

[0145] As can be seen from the comparison between Example 1 and Comparative Examples 4-7, this application significantly improves the rate performance and thermal stability by controlling M1>M2 and N2>N1.

[0146] Comparing Examples 1-4 with Examples 5-6, it can be seen that by controlling the content of conductive carbon in the first positive electrode layer to be 2%-5% and the content of conductive carbon in the second positive electrode layer to be 1%-3%, the rate performance is further improved.

[0147] Comparing Examples 1, 8, and 9 with Examples 7 and 10, it can be seen that by controlling the content of sulfide electrolyte in the first positive electrode layer to be 4.5% to 6% and the content of sulfide electrolyte in the second positive electrode layer to be 12% to 14%, the rate performance is further improved in this application.

[0148] Comparing Examples 1, 12, and 13 with Examples 11 and 14, it can be seen that as the amount of halide electrolyte in the first positive electrode layer increases, the battery rate performance slightly improves, while the DSC initial exothermic temperature gradually increases, indicating that halide electrolyte is beneficial to improving the safety of the positive electrode.

[0149] Comparing Examples 1, 16, and 17 with Examples 15 and 18, it can be seen that by controlling the thickness of the first positive electrode layer and the second positive electrode layer to be 60 μm to 80 μm, the rate performance is further improved.

[0150] Comparing Example 1 with Examples 19-35, it can be seen that this application further improves the rate performance and thermal stability of the positive electrode by introducing an intermediate layer.

[0151] Comparative examples 19-23 show that as the content of halide electrolyte increases, the rate performance of the positive electrode improves slightly, but the initial exothermic temperature of DSC decreases significantly. The optimal content range of halide electrolyte is 8% to 12%.

[0152] Comparing Examples 21 and 24-27, it can be seen that the optimal content of conductive carbon in the intermediate layer is 0.5% to 2%. Within this content range, a positive electrode sheet with better rate performance and better thermal stability can be obtained.

[0153] Comparative examples 21 and 28-31 show that the optimal amount of oxide electrolyte added to the intermediate layer is 1% to 5%. Within this range, a positive electrode sheet with better rate performance and better thermal stability can be obtained.

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery comprising a positive electrode, characterized in that, The positive electrode includes a positive current collector and a first positive electrode layer and a second positive electrode layer sequentially disposed on at least one surface of the positive current collector; The first positive electrode layer includes a first positive electrode active material, a first conductive carbon, a first sulfide electrolyte, and a first halide electrolyte; The second positive electrode layer includes a second positive electrode active material, a second conductive carbon, and a second sulfide electrolyte; The mass percentage of the first conductive carbon in the first positive electrode layer is M1, and the mass percentage of the first sulfide electrolyte in the first positive electrode layer is N1. The mass percentage of the second conductive carbon in the second positive electrode layer is M2, and the mass percentage of the second sulfide electrolyte in the second positive electrode layer is N2. The following conditions must be met: M1>M2, N2>N1.

2. The secondary battery according to claim 1, characterized in that, Satisfy at least one of the following (a) to (d): (a) 2% ≤ M1 ≤ 5%; (b) 4.5% ≤ N1 ≤ 6%; (c) 1% ≤ M2 ≤ 2%; (d) 12%≤N2≤13%.

3. The secondary battery according to claim 1, characterized in that, The mass ratio of the first sulfide electrolyte to the first halide electrolyte is 5:(4~6); and / or The mass ratio of the second sulfide electrolyte to the second conductive carbon is (6~13):

1.

4. The secondary battery according to claim 3, characterized in that, The mass percentage of the first halide electrolyte in the first positive electrode layer is 4.5% to 6%.

5. The secondary battery according to claim 1, characterized in that, The first positive electrode active material has a mass percentage content of 80%~90% in the first positive electrode layer; and / or The mass percentage of the second positive electrode active material in the second positive electrode layer is 80%~90%.

6. The secondary battery according to claim 1, characterized in that, The positive electrode sheet further includes an intermediate layer, which is located between the first positive electrode layer and the second positive electrode layer; The intermediate layer includes a third positive electrode active material, a third conductive carbon, an oxide electrolyte, and a second halide electrolyte.

7. The secondary battery according to claim 6, characterized in that, Satisfy at least one of the following conditions (Ⅰ) to (Ⅴ): (I) The mass ratio of the oxide electrolyte to the second halide electrolyte is 1:(2~12); (II) The mass percentage of the third conductive carbon in the intermediate layer is 0.5% to 2%; (III) The oxide electrolyte in the intermediate layer has a mass percentage content of 1% to 5%; (IV) The second halide electrolyte has a mass percentage content of 8% to 12% in the intermediate layer; (V) The mass percentage of the third positive electrode active material in the intermediate layer is 80%~90%.

8. The secondary battery according to claim 6, characterized in that, The first, second, and third positive electrode active materials each independently include LiCoO2 and Li x1 Ni y1 Co z1 Mn 1-y1-z1 At least one of O2, wherein 0.96 ≤ x1 ≤ 1.1, 0.6 ≤ y1 ≤ 1, 0 ≤ z1 ≤ 0.2; and / or The first conductive carbon, the second conductive carbon, and the third conductive carbon each independently include at least one of carbon black, acetylene black, carbon nanotubes, vapor-grown carbon fibers, and graphene.

9. The secondary battery according to claim 6, characterized in that, Satisfy at least one of the following (1) to (3): (1) The first sulfide electrolyte and the second sulfide electrolyte each independently include Li x2 A y2 B z2 Where A includes at least one of Ge, Sn, and P, B includes S, 3≤x2≤10, 1≤y2≤3, and 0≤z2≤12; (2) The first halide electrolyte and the second halide electrolyte each independently include Li x3 DCl6, where D includes at least one of In, Sc, and Zr, and 2≤x3≤3; (3) The oxide electrolyte includes Li X4 E y3 G z3 Wherein, E includes at least one of La, Al, Zr, Ti, and Ge, and G includes one of PO and O, and 0.3 < x4 ≤ 7, 0.3 ≤ y3 ≤ 3, and 3 ≤ z3 ≤ 12.

10. The secondary battery according to claim 6, characterized in that, The thickness of the first positive electrode layer is greater than the thickness of the intermediate layer; and / or The thickness of the second positive electrode layer is greater than the thickness of the intermediate layer.

11. The secondary battery according to claim 10, characterized in that, The thickness of the first positive electrode layer is 60 μm to 80 μm; and / or The thickness of the second positive electrode layer is 60μm~80μm.

12. The secondary battery according to claim 9, characterized in that, The thickness of the intermediate layer is 10μm~20μm.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 12.

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