An all-solid-state secondary battery and a method for manufacturing the same

Abstract

The application belongs to the technical field of batteries, and particularly relates to a full-solid-state secondary battery and a preparation method thereof. The full-solid-state secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte film, the electrolyte film is arranged between the positive electrode sheet and the negative electrode sheet, a gradient coating I is formed between the electrolyte film and the positive electrode sheet, and the concentration of a polymer electrolyte A and a polymer electrolyte B in the gradient coating I changes in a gradient manner; a gradient coating II is formed between the electrolyte film and the negative electrode sheet, and the concentration of the polymer electrolyte A and a polymer electrolyte C in the gradient coating II changes in a gradient manner. The gradient change coating between the electrolyte film and the positive and negative electrode sheets can effectively improve the interface contact of sulfide and lithium metal electrodes, thereby being beneficial to ion conduction in the charging and discharging process; the gradient change coating can construct a continuous ion transmission layer, eliminate the contact interface in the film, and effectively inhibit the interface reaction and dendrite growth.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an all-solid-state secondary battery and its preparation method. Background Technology

[0002] Sulfide solid electrolytes are promising electrolyte materials for all-solid-state rechargeable batteries due to their high ionic conductivity and good flexibility. However, the application of sulfide solid electrolytes in all-solid-state lithium batteries still faces many challenges. Among them, the compatibility between the electrolyte and the positive and negative electrodes is a hot research topic. The conventional approach is to coat the sulfide surface with a polymer electrolyte layer to improve the interfacial compatibility between the sulfide and the positive and negative electrodes. However, a single interfacial layer is basically unable to meet the expected requirements. For example, PEO (polyethylene oxide) is not resistant to high voltage, but has good compatibility with the negative electrode; PPC (polypropylene carbonate) has poor stability between the positive and negative electrodes, but has high ionic conductivity; PMMA (polymethyl methacrylate) is resistant to high voltage, but has low ionic conductivity, and often significantly reduces battery performance. Summary of the Invention

[0003] This invention aims to solve the above problems and provides an all-solid-state secondary battery and its preparation method. It adopts a concentration gradient coating method to improve the electrolyte membrane and the positive / negative electrode interface, while suppressing interfacial side reactions and lithium dendrite growth.

[0004] According to the technical solution of the present invention, the all-solid-state secondary battery includes a positive electrode, a negative electrode, and an electrolyte membrane, wherein the electrolyte membrane is disposed between the positive electrode and the negative electrode.

[0005] A gradient coating I is formed between the electrolyte membrane and the positive electrode plate. The gradient coating I contains polymer electrolyte A and polymer electrolyte B. The concentration of polymer electrolyte A in the gradient coating I gradually decreases from the electrolyte membrane to the positive electrode plate, and the concentration of polymer electrolyte B in the gradient coating I gradually decreases from the positive electrode plate to the electrolyte membrane.

[0006] A gradient coating II is formed between the electrolyte membrane and the negative electrode plate. The gradient coating II contains polymer electrolyte A and polymer electrolyte C. The concentration of polymer electrolyte A in the gradient coating II gradually decreases from the electrolyte membrane to the negative electrode plate, and the concentration of polymer electrolyte C in the gradient coating II gradually decreases from the negative electrode plate to the electrolyte membrane.

[0007] The polymer electrolyte A and polymer electrolyte B, and the polymer electrolyte A and polymer electrolyte C are different polymer electrolytes.

[0008] Specifically, the gradient coating I and gradient coating II also contain lithium salts; the type of lithium salt is the same in gradient coating I or gradient coating II, and the mass of the lithium salt is 5%-20% of the total mass of the polymer electrolyte in each gradient coating (gradient coating I or gradient coating II).

[0009] Furthermore, the thickness of both gradient coating I and gradient coating II is 4µm to 20µm.

[0010] Furthermore, the electrolyte membrane is a sulfide electrolyte membrane (SSE), and its material is selected from Li. 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 , Li6PS5Cl, Li6PS5Br, Li6PS5I, Li6PS5ClBr, Li 10 SnP2S 12 , Li7GePS8, 70Li2S-30P2S5, Li2S-SiS2, 80Li2S-20P2S5, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 One or more of them.

[0011] Furthermore, at least one of the following conditions must be met:

[0012] Polymer electrolyte A is selected from one or more of poly(propylene carbonate) (PPC), poly(trimethylene carbonate) (PTMC), and poly(β-propiolactone);

[0013] Polymer electrolyte B is selected from one or more of polymethyl methacrylate (PMMA), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), poly(acrylonitrile) (PAN), polyacrylamide (PAM), polyamine (such as polyethyleneimine), and poly(vinylidene fluoride) (PVDF);

[0014] The polymer electrolyte C is selected from one or more of polyethylene oxide (PEO), polycaprolactone (PCL), and poly(ethylene carbonate) (PVEC).

[0015] A second aspect of the present invention provides a method for preparing the above-described all-solid-state secondary battery, comprising the following steps:

[0016] S1: Polymer electrolyte A, polymer electrolyte B and polymer electrolyte C are dissolved in solvents respectively, and lithium salts are added to obtain coating solution A, coating solution B and coating solution C respectively;

[0017] Polymer electrolyte A and polymer electrolyte B, and polymer electrolyte A and polymer electrolyte C are different polymer electrolytes;

[0018] S2: Coating solution A is coated onto the surface of the electrolyte membrane, coating solution B is coated onto the surface of the positive electrode, and coating solution C is coated onto the surface of the negative electrode, and then pre-baked.

[0019] S3: Assemble the electrolyte membrane, positive electrode, and negative electrode after step S2 according to the cell structure, and dry them to obtain a bare cell;

[0020] S4: The bare cell is tab-welded, and after welding, it is placed in the casing. After formation and capacity testing, the all-solid-state secondary battery is obtained.

[0021] Furthermore, in the coating solution A, the mass fraction of polymer electrolyte A is 10%-60%;

[0022] In the coating solution B, the mass fraction of polymer electrolyte B is 10%-60%;

[0023] In the coating solution C, the mass fraction of polymer electrolyte C is 10%-60%.

[0024] Furthermore, at least one of the following conditions must be met:

[0025] The solvent is selected from one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), heptane, and tetrahydrofuran; the solvents of different coating solutions (coating solution A, coating solution B, and coating solution C) may be the same or different;

[0026] The lithium salt is selected from one or more of LiFSI, LiTFSI, LiClO4, and LiPF6.

[0027] Furthermore, in the coating solutions A, B, and C, the mass of lithium salt is 5%-20% of the mass of polymer electrolyte A, polymer electrolyte B, and polymer electrolyte C, respectively.

[0028] Furthermore, in step S2, the coating thickness of coating solution A, coating solution B and coating solution C are all 20um-100um (drying thickness is 2um-10um).

[0029] Furthermore, in step S2, the pre-baking temperature is 30℃-50℃, and the pre-baking time is 1h-3h.

[0030] Furthermore, in step S3, the drying temperature is 70℃-90℃, and the drying time is 20h-40h.

[0031] The technical solution of the present invention has the following advantages compared with the prior art:

[0032] 1. Forming a gradient coating between the electrolyte membrane and the positive and negative electrodes can effectively improve the interfacial contact between the sulfide and lithium metal electrodes, thereby facilitating ion conduction during charging and discharging and improving cycle life.

[0033] 2. Gradient-change coatings can construct a continuous ion transport layer, eliminate intrafilm contact interfaces, effectively suppress interfacial reactions and dendrite growth, and extend cycle life. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0035] The present invention provides an all-solid-state secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte membrane, wherein the electrolyte membrane is disposed between the positive electrode and the negative electrode.

[0036] A gradient coating I is formed between the electrolyte membrane and the positive electrode. The gradient coating I contains polymer electrolyte A, polymer electrolyte B, and lithium salt. Polymer electrolyte A and polymer electrolyte B are different polymer electrolytes. The concentration of polymer electrolyte A in the gradient coating I gradually decreases from the electrolyte membrane to the positive electrode; the concentration of polymer electrolyte B in the gradient coating I gradually decreases from the positive electrode to the electrolyte membrane.

[0037] A gradient coating II is formed between the electrolyte membrane and the negative electrode. The gradient coating I contains polymer electrolyte A and polymer electrolyte C. Polymer electrolyte A and polymer electrolyte C are different polymer electrolytes. The concentration of polymer electrolyte A in the gradient coating II gradually decreases from the electrolyte membrane to the negative electrode. The concentration of polymer electrolyte C in the gradient coating II gradually decreases from the negative electrode to the electrolyte membrane.

[0038] In some preferred embodiments, in gradient coating I, the mass of lithium salt is 5%-20% of the total mass of polymer electrolyte A and polymer electrolyte B;

[0039] In gradient coating II, the mass of lithium salt is 5%-20% of the total mass of polymer electrolyte A and polymer electrolyte C.

[0040] In some preferred embodiments, the electrolyte membrane is a sulfide electrolyte membrane (SSE), and its material is selected from Li. 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12, Li6PS5Cl, Li6PS5Br, Li6PS5I, Li6PS5ClBr, Li 10 SnP2S 12 , Li7GePS8, 70Li2S-30P2S5, Li2S-SiS2, 80Li2S-20P2S5, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 One or more of the following;

[0041] The lithium salt is selected from one or more of LiFSI, LiTFSI, LiClO4 and LiPF6.

[0042] In some preferred embodiments,

[0043] Polymer electrolyte A is a polymer electrolyte with high ionic conductivity to provide good interfacial ion transport capability, and can be selected from one or more of PPC, PTMC, and poly(β-propiolactone);

[0044] Polymer electrolyte B is a high-voltage resistant polymer electrolyte to provide better high-voltage interface stability, and can be selected from one or more of PMMA, PVDF-HFP, PAN, PAM, polyamine (such as polyethyleneimine), and PVDF;

[0045] Polymer electrolyte C is a polymer electrolyte with good mechanical stability to meet the requirements of the negative electrode and withstand the effects of negative electrode volume changes. It can be selected from one or more of PEO, PCL, and PVEC.

[0046] The aforementioned all-solid-state secondary battery can be prepared by the following method:

[0047] S1: Three different polymer electrolytes (polymer electrolyte A, polymer electrolyte B and polymer electrolyte C) are dissolved in solvent with lithium salt to obtain three coating solutions (coating solution A, coating solution B and coating solution C);

[0048] S2: Coating solution A is coated on the surface of the electrolyte membrane, coating solution B is coated on the surface of the positive electrode, and coating solution C is coated on the surface of the negative electrode. The coating thickness is controlled to be 20um-100um, and the coating is pre-baked at 30℃-50℃ for 1h-3h respectively.

[0049] S3: Assemble the electrolyte membrane, positive electrode, and negative electrode after step S2 according to the cell structure, and dry them at 70℃-90℃ for 20h-40h to obtain an all-solid-state secondary battery.

[0050] Specifically, in step S2, the concentration of the coating solution is increased by pre-baking (removing some solvent) to prevent the coating solution from flowing down during the subsequent assembly process (step S3). During the assembly process, the two coatings are bonded together (coating solution B on the surface of the positive electrode is bonded to coating solution A on one side of the electrolyte membrane, and after drying, coating I is formed; coating solution C on the surface of the negative electrode is bonded to coating solution A on the other side of the electrolyte membrane, and after drying, coating II is formed). Since the coating solutions themselves have not yet completely solidified, the two bonded components will form a gradient concentration change through thermodynamic means (concentration difference / Brownian motion), thereby forming a gradient coating. That is, in gradient coating I, the concentration of polymer electrolyte A in gradient coating I gradually decreases from the electrolyte membrane to the positive electrode, and the concentration of polymer electrolyte B in gradient coating I gradually decreases from the positive electrode to the electrolyte membrane; in gradient coating II, the concentration of polymer electrolyte A gradually decreases from the electrolyte membrane to the negative electrode; and the concentration of polymer electrolyte C gradually decreases from the negative electrode to the electrolyte membrane.

[0051] In some preferred embodiments, the solvent is selected from one or more of NMP, DMF, heptane and tetrahydrofuran; the mass fraction of the polymer electrolyte in each coating solution is 10%-60%.

[0052] Example 1

[0053] This embodiment provides an all-solid-state secondary battery, the preparation method of which is as follows:

[0054] 1. Preparation of positive and negative electrodes and sulfide electrolyte membranes

[0055] The binder polyvinylidene fluoride (PVDF) was dissolved in the solvent N-methylpyrrolidone (NMP) and stirred thoroughly. Then, the positive electrode active material lithium nickel cobalt manganese oxide and the conductive agent SuperP were added, with a weight ratio of positive electrode active material:PVDF:SuperP = 95:2:3. Finally, vacuum was applied to remove air bubbles. The resulting positive electrode slurry was uniformly coated onto an aluminum foil current collector and dried at 100°C. After drying, the positive electrode sheet was obtained.

[0056] Styrene-butadiene rubber (SBR) binder is dissolved in water to obtain an SBR aqueous solution. Then, artificial graphite, Super P and thickener sodium carboxymethyl cellulose (CMC) are added to the SBR aqueous solution in a weight ratio of artificial graphite:Super P:CMC2200:SBR = 96:1:1:2. After stirring evenly, the solution is coated on a copper foil current collector and then dried at 110°C to obtain a negative electrode sheet.

[0057] Sulfide powder is pressed to obtain a sulfide electrolyte membrane (SSE).

[0058] 2. Preparation of positive and negative electrode sheets and gradient coating of sulfide electrolyte membrane

[0059] Prepare coating solutions: Prepare sulfide electrolyte membrane (SSE) coating solution A with a mass ratio of PPC:LITFSI:NMP = 40:4:56; prepare negative electrode coating solution C with a mass ratio of PEO:LITFSI:NMP = 40:4:56; and prepare positive electrode coating solution B with a mass ratio of PMMA:LITFSI:NMP = 40:4:56.

[0060] Coating preparation: Different coating solutions were coated on the positive and negative electrode surfaces and the sulfide electrolyte membrane respectively using a doctor blade, with the thickness controlled at 50 μm;

[0061] Gradient coating preparation: Positive / negative electrodes and sulfide electrolyte membranes containing different polymer coatings were placed in an oven and pre-baked at 40°C for 2 hours. Then, the pre-baked positive / negative electrodes and sulfide electrolyte membranes were stacked and placed in an 80°C oven for 24 hours to dry, thus forming a gradient concentration change coating and obtaining the interface layer of Cathode|B|B…A|A|SSE|A|A…C|C|Anode.

[0062] 3. Battery assembly and testing

[0063] A cell is formed by stacking dried positive electrode sheets with polymer coatings, sulfide electrolyte membranes, and negative electrode membranes, and then performing processes such as formation, degassing, settling, and capacity testing to obtain an all-solid-state secondary battery.

[0064] Example 2

[0065] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 is that the coating thickness of each coating is controlled at 20 μm in the coating preparation step.

[0066] Example 3

[0067] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 is that the coating thickness of each coating is controlled at 100 μm in the coating preparation step.

[0068] Example 4

[0069] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 lies in the polymer content of each coating solution during the coating solution preparation step. Specifically:

[0070] Coating solution A: mass ratio of PPC:LITFSI:NMP = 10:1:89;

[0071] Coating solution C: The mass ratio of PEO:LITFSI:NMP is 10:1:89;

[0072] Coating solution B: mass ratio of PMMA:LITFSI:NMP = 10:1:89.

[0073] Example 5

[0074] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 lies in the polymer content of each coating solution during the coating solution preparation step. Specifically:

[0075] Coating solution A: mass ratio of PPC:LITFSI:NMP = 60:6:34;

[0076] Coating solution C: mass ratio of PEO:LITFSI:NMP = 60:6:34;

[0077] Coating solution B: mass ratio of PMMA:LITFSI:NMP = 60:6:34.

[0078] Example 6

[0079] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 is that in the gradient coating preparation step, the oven temperature is controlled at 30°C and the time is 1 hour for pre-baking.

[0080] Example 7

[0081] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 is that in the gradient coating preparation step, the oven temperature is controlled at 50°C and the time is 3 hours for pre-baking.

[0082] Example 8

[0083] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 is that in the gradient coating preparation step, the oven temperature is controlled at 30°C and the time is 3 hours for pre-baking.

[0084] Example 9

[0085] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 is that in the gradient coating preparation step, the oven temperature is controlled at 50°C and the time is 1 hour for pre-baking.

[0086] Example 10

[0087] This embodiment provides an all-solid-state secondary battery. The difference between its preparation method and that of Embodiment 1 lies in the type of polymer used in each coating solution during the preparation of the coating solution. Specifically:

[0088] Coating solution A: mass ratio of PTMC:LITFSI:NMP = 40:4:56;

[0089] Coating solution C: mass ratio of PVEC:LITFSI:NMP = 40:4:56;

[0090] Coating solution B: mass ratio of PVDF-HFP:LITFSI:NMP = 40:4:56.

[0091] Comparative Example 1

[0092] This comparative example provides an all-solid-state secondary battery, the preparation method of which differs from that of Example 1 in that it does not include step 2, the preparation of positive and negative electrode sheets and sulfide electrolyte membrane gradient coating, and directly assembles the battery for testing.

[0093] Comparative Example 2

[0094] This comparative example provides an all-solid-state secondary battery. The difference between its preparation method and that of Example 1 is that in the coating preparation step, only a sulfide film coating is prepared, without positive / negative electrode film coatings.

[0095] Comparative Example 3

[0096] This comparative example provides an all-solid-state secondary battery. The difference between its preparation method and that of Example 1 lies in the polymer content in each coating solution during the coating solution preparation step. Specifically:

[0097] Coating solution A: mass ratio of PPC:LITFSI:NMP = 5:0.5:94.5;

[0098] Coating solution C: mass ratio of PEO:LITFSI:NMP = 5:0.5:94.5;

[0099] Coating solution B: mass ratio of PMMA:LITFSI:NMP = 5:0.5:94.5.

[0100] Comparative Example 4

[0101] This comparative example provides an all-solid-state secondary battery. The difference between its preparation method and that of Example 1 lies in the polymer content in each coating solution during the coating solution preparation step. Specifically:

[0102] Coating solution A: mass ratio of PPC:LITFSI:NMP = 70:7:23;

[0103] Coating solution C: mass ratio of PEO:LITFSI:NMP = 70:7:23;

[0104] Coating solution B: mass ratio of PMMA:LITFSI:NMP = 70:7:23.

[0105] Comparative Example 5

[0106] This comparative example provides an all-solid-state secondary battery. The difference between its preparation method and that of Example 1 is that the coating thickness of each coating is controlled at 10 μm in the coating preparation step.

[0107] Comparative Example 6

[0108] This comparative example provides an all-solid-state secondary battery. The difference between its preparation method and that of Example 1 is that the coating thickness of each coating is controlled at 150 μm in the coating preparation step.

[0109] Comparative Example 7

[0110] This comparative example provides an all-solid-state secondary battery. The difference between its preparation method and that of Example 1 is that in the gradient coating preparation step, there is no pre-baking process; instead, the stacked cells are dried at 80°C for 24 hours.

[0111] Comparative Example 8

[0112] This comparative example provides an all-solid-state secondary battery. The difference between its preparation method and that of Example 1 is that in the gradient coating preparation step, the oven temperature is controlled at 80°C and the time is 2 hours for pre-baking.

[0113] Results analysis:

[0114] 1. The all-solid-state secondary battery in the embodiments was characterized as follows:

[0115] a. CP (Argon Ion Cutting) + SEM + EDS

[0116] The experimentally prepared sulfide all-solid-state battery with gradient coating was disassembled in a glove box, and the positive electrode / sulfide / negative electrode were cut into pieces. The cross-sections were subjected to CP treatment and electron microscopy. A clear interface layer was found on the surface of the positive electrode, negative electrode and sulfide film, and the structure of the two polymer layers intertwined could be seen. EDS analysis revealed that certain elements were distributed in a gradient on the interface layer, such as nitrogen in poly(acrylonitrile) (PAN), fluorine in poly(vinylidene fluoride) and silicon in polysilane.

[0117] b. XPS etching depth analysis

[0118] The experimentally prepared sulfide all-solid-state battery with a gradient coating was disassembled in a glove box. The disassembled positive / negative electrode sheets were cleaned with DMC, dried, and then subjected to XPS analysis. XPS analysis revealed varying intensities of structures such as C=O and CO as the etching depth increased. This variation was attributed to the different intensities of C=O and CO resulting from the gradient changes in different polymers. Other polymers also contained corresponding unique structures such as CN, NH, CO, SI-O, and SI-C bonds.

[0119] 2. The all-solid-state secondary batteries in Examples 1-10 and Comparative Examples 1-8 were subjected to room temperature cycling and high temperature cycling tests. The results are shown in Table 1. The specific test methods are as follows:

[0120] 25℃ Cyclic Test: The charge and discharge cycle test is carried out at a temperature of 25℃, a cycle current of 0.5C, and a voltage range of 2.5V-4.25V until the discharge capacity is lower than 80% of the initial capacity. The number of cycles at this point is recorded.

[0121] 45℃ Cyclic Test: The charge and discharge cycle test is carried out at a temperature of 45℃, a cycle current of 1C, and a voltage range of 2.5V-4.25V until the discharge capacity is lower than 80% of the initial capacity. The number of cycles at this point is recorded.

[0122] Table 1

[0123]

[0124]

[0125] The results show that the all-solid-state secondary battery of the present invention has better cycle performance.

[0126] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A solid-state secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte membrane, wherein the electrolyte membrane is disposed between the positive electrode and the negative electrode, characterized in that, A gradient coating I is formed between the electrolyte membrane and the positive electrode plate. The gradient coating I contains polymer electrolyte A and polymer electrolyte B. The concentration of polymer electrolyte A in the gradient coating I gradually decreases from the electrolyte membrane to the positive electrode plate, and the concentration of polymer electrolyte B in the gradient coating I gradually decreases from the positive electrode plate to the electrolyte membrane. A gradient coating II is formed between the electrolyte membrane and the negative electrode plate. The gradient coating II contains polymer electrolyte A and polymer electrolyte C. The concentration of polymer electrolyte A in the gradient coating II gradually decreases from the electrolyte membrane to the negative electrode plate, and the concentration of polymer electrolyte C in the gradient coating II gradually decreases from the negative electrode plate to the electrolyte membrane. The polymer electrolyte A and polymer electrolyte B, and polymer electrolyte A and polymer electrolyte C are different polymer electrolytes; The electrolyte membrane is a sulfide electrolyte membrane; Polymer electrolyte A is selected from one or more of poly(propylene carbonate), poly(trimethylene carbonate), and poly(β-propiolactone); Polymer electrolyte B is selected from one or more of polymethyl methacrylate, vinylidene fluoride-hexafluoropropylene copolymer, poly(acrylonitrile), polyacrylamide, polyamine and poly(vinylidene fluoride); The polymer electrolyte C is selected from one or more of polyethylene oxide, polycaprolactone, poly(ethylene carbonate), and polysilane; The method for preparing the all-solid-state secondary battery includes the following steps: S1: Polymer electrolyte A, polymer electrolyte B and polymer electrolyte C are dissolved in solvents respectively, and lithium salts are added to obtain coating solution A, coating solution B and coating solution C respectively; The polymer electrolyte A and polymer electrolyte B, and polymer electrolyte A and polymer electrolyte C are different polymer electrolytes; S2: Coating solution A is coated onto the surface of the electrolyte membrane, coating solution B is coated onto the surface of the positive electrode, and coating solution C is coated onto the surface of the negative electrode, and then pre-baked. S3: Assemble the electrolyte membrane, positive electrode, and negative electrode after step S2 according to the cell structure, and dry them to obtain a bare cell; S4: The bare cell is tab welded, and after welding, it is placed in the casing. After formation and capacity testing, the all-solid-state secondary battery is obtained.

2. The all-solid-state secondary battery as described in claim 1, characterized in that, The electrolyte membrane is made of Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 , Li6PS5Cl, Li6PS5Br, Li6PS5I, Li6PS5ClBr, Li 10 SnP2S 12 , Li7GePS8, 70Li2S-30P2S5, Li2S-SiS2, 80Li2S-20P2S5, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 One or more of them.

3. The method for preparing an all-solid-state secondary battery as described in claim 1 or 2, characterized in that, Includes the following steps, S1: Polymer electrolyte A, polymer electrolyte B and polymer electrolyte C are dissolved in solvents respectively, and lithium salts are added to obtain coating solution A, coating solution B and coating solution C respectively; The polymer electrolyte A and polymer electrolyte B, and polymer electrolyte A and polymer electrolyte C are different polymer electrolytes; S2: Coating solution A is coated onto the surface of the electrolyte membrane, coating solution B is coated onto the surface of the positive electrode, and coating solution C is coated onto the surface of the negative electrode, and then pre-baked. S3: Assemble the electrolyte membrane, positive electrode, and negative electrode after step S2 according to the cell structure, and dry them to obtain a bare cell; S4: The bare cell is tab welded, and after welding, it is placed in the casing. After formation and capacity testing, the all-solid-state secondary battery is obtained.

4. The preparation method according to claim 3, characterized in that, In the coating solution A, the mass fraction of polymer electrolyte A is 10%-60%; In the coating solution B, the mass fraction of polymer electrolyte B is 10%-60%; In the coating solution C, the mass fraction of polymer electrolyte C is 10%-60%.

5. The preparation method according to claim 3, characterized in that, At least one of the following conditions must be met: The solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, heptane, and tetrahydrofuran; The lithium salt is selected from one or more of LiFSI, LiTFSI, LiClO4, and LiPF6.

6. The preparation method according to claim 3 or 5, characterized in that, In the coating solutions A, B, and C, the mass of lithium salt is 5%-20% of the mass of polymer electrolyte A, polymer electrolyte B, and polymer electrolyte C, respectively.

7. The preparation method according to claim 3, characterized in that, In step S2, the coating thickness of coating solution A, coating solution B and coating solution C are all 20um-100um.

8. The preparation method according to claim 3, characterized in that, In step S2, the pre-baking temperature is 30℃-50℃, and the pre-baking time is 1h-3h.

9. The preparation method according to claim 3, characterized in that, In step S3, the drying temperature is 70℃-90℃ and the drying time is 20h-40h.

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