A quasi-solid-state electrolyte-cathode composite structure, a preparation method thereof and a lithium battery

Abstract

The present disclosure relates to a quasi-solid-state electrolyte-cathode composite structure, a preparation method thereof and a lithium battery. The quasi-solid-state electrolyte-cathode composite structure comprises a quasi-solid-state electrolyte layer and a cathode. The quasi-solid-state electrolyte layer comprises a solid-state electrolyte and an electrolyte solution distributed in the pores of the solid-state electrolyte. The solid-state electrolyte is formed on the surface of the cathode, and at least part of the electrolyte solution contacts the surface of the cathode through the pores of the solid-state electrolyte. The present disclosure can improve the electrochemical performance of the solid-state lithium metal battery and solve the compatibility problem of the solid-state electrolyte and the nickel-rich cathode.

Description

Technical Field

[0001] This disclosure relates to the field of solid-state battery technology, specifically to a quasi-solid-state electrolyte-cathode composite structure, its preparation method, and a lithium battery. Background Technology

[0002] With the rapid development of the portable electronic device and electric vehicle markets, lithium-ion batteries have become a focus of attention in academia and industry. In pursuit of higher energy density, lithium metal is favored due to its high theoretical specific capacity (3860 mAh g⁻¹). -1 The high energy density and low redox potential (-3.040 V relative to the standard hydrogen electrode) make it an ideal alternative to traditional graphite anodes. Solid-state batteries based on lithium metal anodes are highly anticipated due to their high energy density and good safety, and are considered an important direction for the development of next-generation rechargeable batteries. However, the development of solid-state lithium metal batteries still faces a series of challenges, including poor lithium-ion transport performance of solid electrolytes, low ion transport efficiency at the electrolyte-electrode interface, and lithium dendrite growth. Therefore, the preparation of solid electrolytes with excellent electrochemical performance and the improvement of the compatibility between solid electrolytes and lithium metal anodes are the current research focus of solid-state lithium metal batteries.

[0003] However, a significant challenge in applying solid-state electrolytes to lithium-ion batteries is the contact issue at the electrolyte-electrode interface. Because the contact between a solid-state electrolyte and the electrode is a solid-solid contact, compared to the solid-liquid contact of a liquid electrolyte, this change drastically limits the transport efficiency of lithium ions between the electrolyte and the electrode. This hindered lithium-ion transport not only affects the battery's charge-discharge performance but also limits its potential for high energy density and cycle life. To address this issue, researchers have explored in-situ preparation techniques, which involve converting the electrolyte to a solid state through chemical or physical reactions after a good liquid contact has been formed between the electrolyte and the electrode, thereby optimizing the interfacial contact between the electrolyte and the electrode.

[0004] Polyvinylidene fluoride (PVDF) is widely used in battery technology, especially as a binder for positive and negative electrode materials, due to its excellent electrochemical stability, corrosion resistance, and high-temperature resistance. To further optimize the performance of PVDF and reduce its crystallinity to improve flexibility, researchers copolymerized it with hexafluoropropylene (HFP) to prepare a copolymer with improved properties, PVDF-HFP.

[0005] Furthermore, using solid electrolytes instead of liquid electrolytes transforms the solid-liquid contact between the electrolyte and the electrode into a rigid solid-solid contact, severely hindering ion transport at the interface. To further improve battery energy density, using nickel-rich cathodes with high operating voltage and high energy density is the mainstream approach; however, current carbonate electrolytes are prone to chemical reactions with high-voltage nickel-rich cathodes.

[0006] Currently available solid electrolytes still suffer from insufficient electrochemical performance and poor compatibility with high-voltage nickel-rich cathodes. Summary of the Invention

[0007] The purpose of this disclosure is to provide a quasi-solid-state electrolyte-cathode composite structure, its preparation method, and a lithium battery, so as to improve the electrochemical performance of solid-state lithium metal batteries and improve the compatibility between solid electrolytes and nickel-rich cathodes.

[0008] To achieve the above objectives, the first aspect of this disclosure provides a quasi-solid electrolyte-positive electrode composite structure, including a quasi-solid electrolyte layer and a positive electrode; the quasi-solid electrolyte layer includes a solid electrolyte and an electrolyte solution distributed in the pores of the solid electrolyte; the solid electrolyte is formed on the surface of the positive electrode, and at least a portion of the electrolyte solution contacts the surface of the positive electrode through the pores of the solid electrolyte.

[0009] Optionally, the solid electrolyte comprises a polymer and a first lithium salt; preferably, based on the total weight of the solid electrolyte, the polymer content is 30-80% by weight, more preferably 40-60% by weight, with the remainder being the first lithium salt; Optionally, the weight ratio of the polymer to the first lithium salt is 1:0.5~2; preferably 1:0.8~1.2.

[0010] Optionally, the polymer is selected from one or two of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer; optionally, the molecular weight Mn of the polymer is 100,000 to 200,000. Optionally, the first lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonate)imide and lithium bis(fluorosulfonylimide).

[0011] Optionally, based on the total weight of the quasi-solid electrolyte layer, the content of the solid electrolyte is 50-95% by weight, preferably 80-90% by weight, with the remainder being electrolyte. Optionally, in the quasi-solid electrolyte layer, the weight ratio of solid electrolyte to electrolyte is 1~19:1; preferably 4~10:1.

[0012] Optionally, the electrolyte comprises a second lithium salt and a first organic solvent; the second lithium salt comprises LiPF6; preferably, based on the total weight of the electrolyte, the concentration of the second lithium salt is 0.5~3 mol / L, more preferably 1~2 mol / L; Optionally, the first organic solvent is selected from one or more of carbonate organic compounds; optionally, the carbonate organic compounds are selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Optionally, the electrolyte further includes additives selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, and ethylene sulfate; Preferably, the content of the additive is 0.01 to 5% by weight, based on the total weight of the electrolyte.

[0013] Optionally, the positive electrode includes a current collector and an active material layer stacked together, and the quasi-solid electrolyte layer is formed on the surface of the active material layer; The active material layer includes a positive electrode active substance, a conductive agent, and a binder; preferably, based on the total weight of the active material layer, the content of the positive electrode active substance is 80-99% by weight, more preferably 80-95% by weight, the content of the conductive agent is 1-10% by weight, more preferably 3-10% by weight, and the remainder is binder; Optionally, the positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, nickel-cobalt-manganese ternary materials, and nickel-cobalt-aluminum ternary materials; preferably, the nickel content in the positive electrode is 30-80% by weight, more preferably 60-80% by weight. The conductive agent is selected from one or more of acetylene black, graphene, and carbon nanotubes. The adhesive is selected from one or more of PVDF and PVDF-HFP.

[0014] Optionally, the thickness of the quasi-solid electrolyte layer is 30~100μm, preferably 30~50μm; the thickness of the active material layer of the positive electrode is 50~200μm, preferably 90~150μm. Preferably, the thickness ratio of the quasi-solid electrolyte layer to the active material layer is 1:1~5; more preferably, it is 1:1~3.

[0015] A second aspect of this disclosure provides a method for preparing a quasi-solid-state electrolyte-cathode composite structure, comprising the following steps: S1. An electrolyte slurry is applied to the surface of the positive electrode, and the second organic solvent is removed by heating to obtain an intermediate product; the electrolyte slurry comprises a polymer, a first lithium salt, and a second organic solvent. S2. The intermediate product is impregnated with electrolyte to remove the electrolyte from the surface of the impregnated product.

[0016] Optionally, in step S1, the weight ratio of polymer: first lithium salt: second organic solvent in the electrolyte slurry is 1:0.05~2:3~6, preferably 1:0.5~1:4~5; Optionally, the second organic solvent is selected from one or more of N,N-dimethylformamide.

[0017] Optionally, in step S1, the positive electrode includes an active material layer, and the electrolyte slurry is coated on the surface of the active material layer; Optionally, the positive electrode is obtained by uniformly mixing the positive electrode active material, conductive agent, and binder in a third organic solvent, coating it on a current collector, and then removing the solvent. Preferably, the weight ratio of positive electrode active material: conductive agent: binder: third organic solvent is 1:0.01~0.2:0.04~0.2:0.5~4, and more preferably 1:0.05~0.15:0.06~0.15:1~3.5.

[0018] The third aspect of this disclosure provides a quasi-solid-state electrolyte-cathode composite structure prepared according to the method described in the second aspect of this disclosure.

[0019] This disclosure provides a fourth aspect of a lithium battery, which includes the quasi-solid-state electrolyte-cathode composite structure described in the first or third aspect of this disclosure.

[0020] Through the above technical solution, this disclosure provides a quasi-solid-state electrolyte-cathode composite structure, its preparation method, and a lithium battery. In the composite structure provided by this disclosure, the quasi-solid-state electrolyte and the cathode have an "integrated" structure, which can effectively improve interfacial contact and facilitate ion interfacial transport. The quasi-solid-state electrolyte layer has excellent electrochemical performance and good compatibility with high-voltage nickel-rich cathodes. The preparation method provided by this disclosure is simple, and the required equipment is basically the same as that of existing industrialized liquid battery processes, requiring no additional equipment and saving costs.

[0021] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof.

[0023] Figure 1 A photograph of the quasi-solid-state electrolyte-positive electrode composite structure provided in Embodiment 1 of this disclosure; Figure 2 The graph shows the cycle performance of the lithium metal batteries of Example 1 and Comparative Example 1 of this disclosure at 0.3C. Detailed Implementation

[0024] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0026] The first aspect of this disclosure provides a quasi-solid electrolyte-positive electrode composite structure, including a quasi-solid electrolyte layer and a positive electrode; the quasi-solid electrolyte layer includes a solid electrolyte and an electrolyte solution distributed in the pores of the solid electrolyte; the solid electrolyte is formed on the surface of the positive electrode, and at least a portion of the electrolyte solution is in contact with the surface of the positive electrode through the pores of the solid electrolyte.

[0027] This disclosure provides a quasi-solid-state electrolyte-cathode composite structure. In this composite structure, the quasi-solid-state electrolyte and the cathode have an "integrated" structure, which can effectively improve interfacial contact and facilitate ion interfacial transport. The quasi-solid-state electrolyte layer has excellent electrochemical performance and good compatibility with high-voltage nickel-rich cathodes. In this disclosure, "quasi-solid-state electrolyte-cathode composite structure" refers to an electrolyte-cathode composite structure with a solid-like morphology, but the composite structure also contains an electrolyte, making the entire composite structure a near-solid but not completely solid structure.

[0028] In one embodiment, the solid electrolyte comprises a polymer and a first lithium salt; preferably, based on the total weight of the solid electrolyte, the polymer content is 30-80% by weight, more preferably 40-60% by weight, with the remainder being the first lithium salt; the composition of the solid electrolyte is within the content range of this embodiment, especially having the preferred range provided by this embodiment, and the composite structure can have better electrochemical performance in the battery.

[0029] In a preferred embodiment, the weight ratio of the polymer to the first lithium salt is 1:0.5~2; preferably 1:0.8~1.2. When the weight ratio of the polymer to the first lithium salt in the solid electrolyte is within the range of this embodiment, and especially within the preferred range, the composite material exhibits superior performance in battery applications.

[0030] In one specific embodiment, the polymer is selected from one or both of polyvinylidene fluoride (PVDF) and PVDF-HFP copolymer; preferably, PVDF-HFP copolymer, which has better electrochemical stability; optionally, the molecular weight Mn of the polymer is 100,000 to 200,000, preferably 120,000 to 150,000; The first lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonate)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide; wherein the lithium bis(fluorosulfonyl)imide is selected from one or more of lithium bis(trifluoromethanesulfonate)imide and lithium bis(fluorosulfonyl)imide.

[0031] In one embodiment, based on the total weight of the quasi-solid electrolyte layer, the content of the solid electrolyte is 50-90% by weight, preferably 80-90% by weight, with the remainder being electrolyte. When the content of the solid electrolyte in the quasi-solid electrolyte layer of this disclosure is within the optimized range of this embodiment, it can play a better role.

[0032] In one embodiment, the weight ratio of solid electrolyte to electrolyte in the quasi-solid electrolyte layer is 1~19:1; preferably 4~10:1.

[0033] In one embodiment, the electrolyte comprises a second lithium salt and a first organic solvent; the second lithium salt comprises LiPF6; preferably, based on the total weight of the electrolyte, the concentration of the second lithium salt is 0.5~3 mol / L, more preferably 1~2 mol / L; the electrolyte of this disclosure having the composition of this embodiment enables the quasi-solid electrolyte layer to perform a better function.

[0034] In one specific embodiment, the first organic solvent is selected from one or more of carbonate organic compounds; optionally, the carbonate organic compounds are selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the use of carbonate solvents in this disclosure for the quasi-solid electrolyte layer can further improve lithium-ion transport capability.

[0035] In one embodiment, the electrolyte further includes an additive selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, and vinyl sulfate. The addition of additives to the electrolyte in this disclosure is beneficial for the formation of the SEI film.

[0036] In one specific embodiment, based on the total weight of the electrolyte, the content of the additive is 0.01~5% by weight, preferably 0.1~5% by weight.

[0037] In one embodiment, the positive electrode includes a current collector and an active material layer stacked together, and the quasi-solid electrolyte layer is formed on the surface of the active material layer.

[0038] In one embodiment, the active material layer includes a positive electrode active substance, a conductive agent, and a binder; preferably, based on the total weight of the active material layer, the content of the positive electrode active substance is 80-99% by weight, more preferably 80-95% by weight, the content of the conductive agent is 1-10% by weight, more preferably 3-10% by weight, and the remainder is binder.

[0039] In one specific embodiment, the positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, nickel-cobalt-manganese ternary materials, and nickel-cobalt-aluminum ternary materials; preferably, the nickel content in the positive electrode is 30-80% by weight, more preferably 60-80% by weight. The conductive agent is selected from one or more of acetylene black, graphene, and carbon nanotubes. The adhesive is selected from one or more of PVDF and PVDF-HFP; The current collector is aluminum foil.

[0040] The battery components used in this disclosure can all be obtained through ordinary commercial channels or prepared by known methods.

[0041] In one embodiment, the thickness of the quasi-solid electrolyte layer is 30-100 μm, preferably 20-50 μm; the thickness of the active material layer of the positive electrode is 50-200 μm, preferably 90-150 μm; having the layer thickness provided in this embodiment enables the composite structure to have better electrochemical performance in the battery.

[0042] In one specific embodiment, the thickness ratio of the quasi-solid electrolyte layer to the active material layer is 1:1 to 5; preferably 1:1 to 3.

[0043] A second aspect of this disclosure provides a method for preparing a quasi-solid-state electrolyte-cathode composite structure, comprising the following steps: S1. An electrolyte slurry is applied to the surface of the positive electrode, and the second organic solvent is removed by heating to obtain an intermediate product; the electrolyte slurry comprises a polymer, a first lithium salt, and a second organic solvent. S2. The intermediate product is impregnated with electrolyte to remove the electrolyte from the surface of the impregnated product.

[0044] This disclosure achieves a quasi-solid electrolyte-positive electrode integrated structure by applying an electrolyte slurry to the surface of the positive electrode, removing the solvent by heating, and then impregnating the positive electrode with an electrolyte solution to allow the electrolyte solution to enter the pores of the solid electrolyte, thereby obtaining a quasi-solid electrolyte-positive electrode integrated structure. This structure can effectively improve interfacial contact and facilitate ion interfacial transport.

[0045] In one specific embodiment, the electrolyte slurry is obtained by uniformly mixing a polymer, a first lithium salt, and a second organic solvent. The specific process conditions used in the preparation method of the electrolyte slurry are those conventional in the art.

[0046] In one embodiment, in step S1, the mass ratio of polymer: first lithium salt: second organic solvent in the electrolyte slurry is 1:0.05~2:3~6, preferably 1:0.5~1:4~5; the electrolyte slurry with the raw material addition ratio provided in this embodiment is beneficial to forming a quasi-solid electrolyte layer with better effect. Optionally, the second organic solvent is selected from one or more of N,N-dimethylformamide.

[0047] In one specific embodiment, the polymer is selected from one or both of polyvinylidene fluoride (PVDF) and PVDF-HFP copolymer; preferably, PVDF-HFP copolymer, which has better electrochemical stability; optionally, the molecular weight Mn of the polymer is 100,000 to 200,000, preferably 120,000 to 150,000; The first lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonate)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide; wherein the lithium bis(fluorosulfonyl)imide is selected from one or more of lithium bis(trifluoromethanesulfonate)imide and lithium bis(fluorosulfonyl)imide.

[0048] In one specific embodiment, the positive electrode is obtained by uniformly mixing the positive electrode active material, conductive agent, and binder in a third organic solvent, coating the mixture onto a current collector, drying it, and then vacuum drying it.

[0049] In one embodiment, the weight ratio of positive electrode active material: conductive agent: binder: third organic solvent is 1:0.01~0.2:0.04~0.2:0.5~4, preferably 1:0.05~0.15:0.06~0.15:1~3.5.

[0050] In one specific embodiment, the positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, nickel-cobalt-manganese ternary materials, and nickel-cobalt-aluminum ternary materials; preferably, the nickel content in the positive electrode is 30-80% by weight, more preferably 60-80% by weight. The conductive agent is selected from one or more of acetylene black, graphene, and carbon nanotubes. The adhesive is selected from one or more of PVDF and PVDF-HFP; The current collector is aluminum foil; The third organic solvent is selected from one or more of N-methylformamide (NMF).

[0051] In one embodiment, in step S2, the conditions for the impregnation treatment include: a temperature of 20~50℃ and a time of 0.1~0.4h; preferably, a temperature of 25~30℃ and a time of 0.1~0.2h. Optionally, in the impregnation process, the amount of electrolyte used is 2 to 10 g relative to 1 g of solid electrolyte, preferably 2 to 5 g.

[0052] In one specific embodiment, the electrolyte comprises a second lithium salt and a first organic solvent; the second lithium salt comprises LiPF6; preferably, based on the total weight of the electrolyte, the concentration of the second lithium salt is 0.5~3 mol / L, more preferably 1~2 mol / L; the electrolyte in this disclosure having the composition of this embodiment enables the quasi-solid electrolyte layer to perform better, such as FEC.

[0053] In one specific embodiment, the first organic solvent is selected from one or more of carbonate organic compounds; optionally, the carbonate organic compounds are selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate. Optionally, the electrolyte further includes additives selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, and ethylene sulfate.

[0054] In one specific embodiment, based on the total weight of the electrolyte, the content of the additive is 0.01 to 5% by weight, preferably 0.1 to 1% by weight.

[0055] The third aspect of this disclosure provides a quasi-solid-state electrolyte-cathode composite structure prepared according to the method described in the second aspect of this disclosure.

[0056] This disclosure provides a fourth aspect of a lithium battery, which includes the quasi-solid-state electrolyte-cathode composite structure described in the first or third aspect of this disclosure.

[0057] In one specific embodiment, the negative electrode of the lithium battery can be made of one or more of the following: lithium metal sheet, graphite, silicon negative electrode, and hard carbon.

[0058] The present disclosure is further described in detail below through examples. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the present disclosure are commercially available or can be prepared by existing methods.

[0059] Example 1 (1) Preparation of quasi-solid electrolyte slurry: Take 1 g LiTFSI (lithium bis(trifluoromethanesulfonate)imide, first lithium salt), 1 g PVDF-HFP (vinylidene fluoride-hexafluoropropylene copolymer, molecular weight Mn 130000) and 4 g DMF (second organic solvent) and stir at 60℃ for 8 h to make them uniformly mixed to obtain quasi-solid electrolyte slurry. In the electrolyte slurry, the weight ratio of polymer: first lithium salt: second organic solvent is 1:1:4.

[0060] (2) Preparation of positive electrode: 0.8 g NCM811 (nickel-cobalt-manganese ternary positive electrode active material, with a nickel-cobalt-manganese content ratio of 8:1:1 and a nickel element content of 80% by weight), 0.1 g conductive agent SP (acetylene black) and 0.1 g binder PVDF are dissolved in 3 g NMF (third organic solvent, N-methylformamide), wherein the weight ratio of positive electrode active material: conductive agent: binder: third organic solvent is 1:0.125:0.125:3.75. Stir for 12 h to make it uniformly mixed, and then coat it on the surface of carbon-coated aluminum foil. Heat at 100 °C in vacuum for 12 h to evaporate the solvent and obtain the positive electrode. In the active material layer of the obtained positive electrode, based on the total weight of the active material layer, the content of positive electrode active material is 80% by weight, the content of conductive agent is 10% by weight, and the remainder is binder.

[0061] (3) The electrolyte slurry prepared earlier was slowly coated onto the surface of the positive electrode using a scraper. Most of the solvent was evaporated in the air, and then vacuum dried at 80 °C for 12 h to remove the solvent, thus obtaining a positive electrode with a solid electrolyte. After complete drying, it was impregnated with a liquid electrolyte, which included 1 mol / L LiPF6 (second lithium salt), and the first organic solvent included EC (ethylene carbonate) and EMC (ethyl methyl carbonate). The weight ratio of EC to EMC was 3:7, and the content of the additive FEC (fluoroethylene carbonate) in the liquid electrolyte was 5% by weight. The impregnation conditions included a temperature of 60 °C and a time of 12 h. The amount of electrolyte used was 2 g relative to 1 g of solid electrolyte. Then, the surface solvent was wiped off with a lint-free paper, and finally an integrated quasi-solid electrolyte-positive electrode composite structure was obtained. The thickness of the quasi-solid electrolyte layer was 40 μm, the thickness of the active material layer of the positive electrode was 80 μm, and the thickness ratio of the quasi-solid electrolyte layer to the active material layer was 1:2. Based on the total weight of the quasi-solid electrolyte layer, the content of the solid electrolyte is 80% by weight, with the remainder being electrolyte solution.

[0062] A quasi-solid-state electrolyte-cathode composite structure is assembled with a lithium metal anode to form a lithium metal battery.

[0063] Figure 1 The image shows a photograph of the quasi-solid electrolyte-positive electrode composite structure provided in this embodiment. As can be seen from the image, the quasi-solid electrolyte and the positive electrode have good contact, and there are no defects such as cracks or bubbles on the surface.

[0064] Example 2 A lithium metal battery was prepared according to the preparation method in Example 1, except that the composition of the electrolyte slurry was changed. In the electrolyte slurry, the weight ratio of polymer: first lithium salt: second organic solvent was 1:0.05:6.

[0065] Example 3 A lithium metal battery was prepared according to the preparation method in Example 1, except that the composition of the electrolyte slurry was changed. In the electrolyte slurry, the weight ratio of polymer: first lithium salt: second organic solvent was 1:2:4.

[0066] Example 4 A lithium metal battery was prepared according to the preparation method in Example 1, except that the ratio of raw materials added to the positive electrode was changed, wherein the weight ratio of positive electrode active material: conductive agent: binder: third organic solvent was 1:0.01:0.04:3.75.

[0067] Example 5 A lithium metal battery was prepared according to the preparation method in Example 1, except that the thickness ratio of the quasi-solid electrolyte layer to the active material layer was adjusted to 1:4.

[0068] Example 6 This embodiment refers to the method in Embodiment 1, but differs from Embodiment 1 in that: by controlling the immersion time of the electrolyte, the content of the solid electrolyte is 98% by weight, with the remainder being electrolyte, based on the total weight of the quasi-solid electrolyte layer.

[0069] Example 7 This embodiment refers to the method in Embodiment 1, except that the positive electrode active material is replaced with lithium iron phosphate.

[0070] Example 8 This embodiment refers to the method in Embodiment 1, except that the first organic solvent EC in the liquid electrolyte is replaced with DOL (1,3-dioxolane).

[0071] Example 9 A lithium metal battery was prepared according to the preparation method in Example 1, except that the composition of the electrolyte slurry was changed. In the electrolyte slurry, the weight ratio of polymer: first lithium salt: second organic solvent was 1:0.5:6.

[0072] Comparative Example 1 (1) Preparation of positive electrode: 0.8 g NCM811, 0.1 g conductive agent SP and 0.1 g binder PVDF are dissolved in 3 g DMF and stirred for 12 h to make them uniformly mixed. Then they are coated on the surface of carbon-coated aluminum foil and heated in vacuum at 100 °C for 12 h to evaporate the solvent and obtain the positive electrode.

[0073] (2) Battery assembly: First, place the lithium sheet in the positive electrode shell, then add 1M LiPF6EC:EMC = 3:7 5% FEC electrolyte (60 mL), Celgard 2325 separator, positive electrode sheet, gasket, spring sheet and positive electrode shell in sequence, and then use a packaging machine to compact it.

[0074] Comparative Example 2 This comparative example follows the preparation method in Example 1, but differs from Example 1 in that, in step (3), the previously prepared electrolyte slurry is slowly coated onto the positive electrode surface using a scraper, allowing most of the solvent to evaporate in the air. Then, it is vacuum dried at 80 °C for 12 h to remove the solvent. After complete drying, no electrolyte impregnation treatment is performed, i.e., no electrolyte is introduced into the solid electrolyte, thus obtaining the positive electrode structure. This structure is then assembled with a lithium metal negative electrode to form a lithium metal battery.

[0075] Comparative Example 3 In this comparative example, a solid electrolyte was prepared separately and then assembled with the positive and negative electrodes to form a battery, rather than forming a single structure between the solid electrolyte and the positive electrode. Specifically, this includes: PVA (Mw: 89000 g / mol; degree of hydrolysis: >99%) was mixed with water to prepare a 10% PVA aqueous solution. LiTFSI was added to the PVA aqueous solution and stirred to obtain a solution containing PVA (a polymer with crosslinkable functional groups) and LiTFSI (lithium salt). At this time, the molar ratio of the crosslinkable functional group "OH" of PVA to "Li" of lithium salt ([Li] / [OH]) was set to 0.1. The above solution was coated onto an SS foil as a substrate using a rod coating method to form a coating film, which was then frozen at -20°C for 24 hours and thawed at 25°C to obtain a polymer solid electrolyte.

[0076] The polymer solid electrolyte was then impregnated with the electrolyte used in Example 1 to obtain an electrolyte of the same content. The solid electrolyte, which has been impregnated with electrolyte, is assembled with the positive electrode and lithium metal negative electrode obtained in step (2) of Example 1 to form a lithium metal battery.

[0077] The composition and layer thickness of the quasi-solid electrolyte of the lithium metal battery prepared in the above embodiments are listed in Table 1 below.

[0078] Table 1

[0079] Test case This test example is used to illustrate the electrochemical performance of the lithium metal batteries obtained in the examples and comparative examples.

[0080] A constant current charge-discharge test (also known as the chronopotential method) was used: the system was charged and discharged under constant current conditions, and the change in potential over time was recorded. In this disclosure, the assembled battery was subjected to charge-discharge tests, and its electrochemical performance, such as coulombic efficiency, cycle performance, and rate performance, was analyzed to evaluate the electrolyte and battery performance. The instrument used was the Blue Battery Testing System (CT3002A), and the test conditions included a voltage range of 2.5~4.3V and a current of 0.3C. The test results are listed in Table 2 below.

[0081] Table 2

[0082] The data in Table 2 shows that: The battery provided in Comparative Example 1 uses a conventional electrolyte, which has a low initial efficiency and cannot achieve stable cycling for 300 cycles; combined with Figure 2 The cycle performance graphs of the lithium metal batteries in Example 1 and Comparative Example 1 at 0.3C are shown below. Figure 2 As shown in the figure, the lithium metal battery prepared with a quasi-solid-state electrolyte-cathode composite structure provided in Example 1 achieved 300 stable cycles with a capacity retention of approximately 80%. In contrast, the lithium metal battery using an electrolyte in Comparative Example 1 only achieved 150 cycles. This demonstrates that the quasi-solid-state electrolyte provided in this disclosure has good compatibility with the high-nickel cathode and lithium metal.

[0083] Comparative Example 2 does not introduce electrolyte into the solid electrolyte and does not have the composition of a quasi-solid electrolyte; a solid electrolyte is prepared in Comparative Example 3. The batteries in Comparative Examples 2 and 3 have low initial coulombic efficiency and cannot achieve 300 cycles of stability.

[0084] Examples 1-9 employ a quasi-solid-state electrolyte-positive electrode composite structure. The batteries in Examples 1-9 exhibit higher initial efficiency, and most of the batteries in these examples demonstrate good capacity retention after 300 cycles.

[0085] Comparing Example 1 with Examples 2-3 and 9, the electrolyte slurry ratio in Example 1 is within the preferred composition range provided in this disclosure, and the battery prepared in Example 1 has higher initial coulombic efficiency and cycle capacity retention. In Examples 2-3 and 9, the polymer content and polymer:first lithium salt weight ratio in the solid electrolyte prepared in Example 2 are within the preferred range provided in this disclosure, and compared with the batteries in Examples 3 and 9, the battery in Example 2 has higher initial coulombic efficiency and cycle capacity retention. Comparing Example 1 and Example 4, the ratio of raw materials added to the positive electrode in Example 1 (weight ratio of positive electrode active material: conductive agent: binder: third organic solvent) is within the preferred range provided in this disclosure. The battery prepared in Example 1 has a higher initial coulombic efficiency and better cycle capacity retention performance. Comparing Example 1 with Example 5, the thickness ratio of the quasi-solid electrolyte layer to the active material layer in Example 1 is within the preferred range provided in this disclosure. The battery prepared in Example 1 has a higher initial coulombic efficiency and cycle capacity retention. Comparing Example 1 with Example 6, the solid electrolyte content in the quasi-solid electrolyte layer prepared in Example 1 and the weight ratio of solid electrolyte to electrolyte are within the preferred range provided in this disclosure. The battery prepared in Example 1 has higher initial coulombic efficiency and cycle capacity retention. Comparing Example 1 with Example 8, Example 1 uses carbonate organic compounds as the first organic solvent. The battery prepared in Example 1 has higher initial coulombic efficiency and cycle capacity retention.

[0086] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0087] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0088] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A quasi-solid-state electrolyte-positive electrode composite structure, characterized in that, It includes a quasi-solid electrolyte layer and a positive electrode; the quasi-solid electrolyte layer includes a solid electrolyte and an electrolyte solution distributed in the pores of the solid electrolyte; the solid electrolyte is formed on the surface of the positive electrode, and at least a portion of the electrolyte solution is in contact with the surface of the positive electrode through the pores of the solid electrolyte.

2. The composite structure according to claim 1, characterized in that, The solid electrolyte comprises a polymer and a first lithium salt; preferably, based on the total weight of the solid electrolyte, the polymer content is 30-80% by weight, more preferably 40-60% by weight, with the remainder being the first lithium salt; Optionally, the weight ratio of the polymer to the first lithium salt is 1:0.5~2; preferably 1:0.8~1.

2.

3. The composite structure according to claim 2, characterized in that, The polymer is selected from one or two of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer; optionally, the molecular weight Mn of the polymer is 100,000 to 200,000. Optionally, the first lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonate)imide and lithium bis(fluorosulfonylimide).

4. The composite structure according to claim 1, characterized in that, Based on the total weight of the quasi-solid electrolyte layer, the content of the solid electrolyte is 50-95% by weight, preferably 80-90% by weight, with the remainder being electrolyte solution; Optionally, in the quasi-solid electrolyte layer, the weight ratio of solid electrolyte to electrolyte is 1~19:1; preferably 4~10:

1.

5. The composite structure according to claim 4, characterized in that, The electrolyte comprises a second lithium salt and a first organic solvent; the second lithium salt comprises LiPF6; preferably, based on the total weight of the electrolyte, the concentration of the second lithium salt is 0.5~3 mol / L, more preferably 1~2 mol / L; Optionally, the first organic solvent is selected from one or more of carbonate organic compounds; optionally, the carbonate organic compounds are selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Optionally, the electrolyte further includes additives selected from one or more of fluorinated ethylene carbonate, ethylene carbonate, and ethylene sulfate; Preferably, the content of the additive is 0.01 to 5% by weight, based on the total weight of the electrolyte.

6. The composite structure according to claim 1, characterized in that, The positive electrode includes a current collector and an active material layer stacked together, and the quasi-solid electrolyte layer is formed on the surface of the active material layer; The active material layer includes a positive electrode active substance, a conductive agent, and a binder; preferably, based on the total weight of the active material layer, the content of the positive electrode active substance is 80-99% by weight, more preferably 80-95% by weight, the content of the conductive agent is 1-10% by weight, more preferably 3-10% by weight, and the remainder is binder; Optionally, the positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, nickel-cobalt-manganese ternary materials, and nickel-cobalt-aluminum ternary materials; preferably, the nickel content in the positive electrode is 30-80% by weight, more preferably 60-80% by weight. The conductive agent is selected from one or more of acetylene black, graphene, and carbon nanotubes. The adhesive is selected from one or more of PVDF and PVDF-HFP.

7. The composite structure according to claim 6, characterized in that, The thickness of the quasi-solid electrolyte layer is 30~100μm, preferably 30~50μm; the thickness of the active material layer of the positive electrode is 50~200μm, preferably 90~150μm. Preferably, the thickness ratio of the quasi-solid electrolyte layer to the active material layer is 1:1~5; more preferably, it is 1:1~3.

8. A method for preparing a quasi-solid-state electrolyte-cathode composite structure, characterized in that, Includes the following steps: S1. An electrolyte slurry is applied to the surface of the positive electrode, and the second organic solvent is removed by heating to obtain an intermediate product; the electrolyte slurry comprises a polymer, a first lithium salt, and a second organic solvent. S2. The intermediate product is impregnated with electrolyte to remove the electrolyte from the surface of the impregnated product.

9. The method according to claim 8, characterized in that, In step S1, the weight ratio of polymer: first lithium salt: second organic solvent in the electrolyte slurry is 1:0.05~2:3~6, preferably 1:0.5~1:4~5; Optionally, the second organic solvent is selected from one or more of N,N-dimethylformamide.

10. The method according to claim 8, characterized in that, In step S1, the positive electrode includes an active material layer, and the electrolyte slurry is coated on the surface of the active material layer; Optionally, the positive electrode is obtained by uniformly mixing the positive electrode active material, conductive agent, and binder in a third organic solvent, coating it on a current collector, and then removing the solvent. Preferably, the weight ratio of positive electrode active material: conductive agent: binder: third organic solvent is 1:0.01~0.2:0.04~0.2:0.5~4, and more preferably 1:0.05~0.15:0.06~0.15:1~3.

5.

11. The quasi-solid-state electrolyte-positive electrode composite structure prepared by the method according to any one of claims 8 to 10.

12. A lithium battery, characterized in that, Includes the quasi-solid-state electrolyte-positive electrode composite structure as described in any one of claims 1 to 7 and 11.

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