Modified solid electrolytes, their preparation methods, and solid-state batteries

Abstract

This application provides a modified solid-state electrolyte, its preparation method, and a solid-state battery. The modified solid-state electrolyte provided in this application includes a garnet-type solid-state electrolyte sheet and a modified layer in situ modified on the surface of the garnet-type solid-state electrolyte sheet. The material of the modified layer is selected from at least one of alumina, zinc oxide, nickel oxide, and cobalt oxide. The modified solid-state electrolyte provided in this application not only ensures close contact between the modified layer and the garnet-type solid-state electrolyte sheet, effectively preventing the modified layer from detaching during cycling, but also allows molten lithium liquid to spread and wet the surface of the modified layer uniformly, significantly reducing interfacial contact resistance. Simultaneously, it can suppress element diffusion and oxidation side reactions on the positive electrode side, promote lithium-ion cross-interface migration, suppress lithium dendrite formation during cycling, maintain a uniform interfacial lithium-ion flux during cycling, and thus improve the electrochemical performance and long-cycle stability of the solid-state battery.

Description

Technical Field

[0001] This application relates to the field of solid electrolyte technology, and more specifically, to a modified solid electrolyte, its preparation method, and a solid battery. Background Technology

[0002] With the booming development of hybrid electric vehicles, plug-in hybrid electric vehicles, and electric vehicles, lithium-ion batteries with high-energy-density electrode materials have been widely used. However, the use of high-nickel cathodes increases safety risks because the higher the nickel ratio, the worse the thermal stability of the cathode material, and the closer the lithium-ion battery is to its theoretical capacity limit. Furthermore, the use of liquid electrolytes has also long been criticized for safety issues.

[0003] Solid-state batteries based on solid-state electrolytes are considered one of the most promising next-generation battery systems. Solid-state electrolytes can replace flammable liquid organic electrolytes, significantly reducing safety risks. Among the many solid-state electrolytes, oxide-based garnet-type solid-state electrolytes stand out due to their high ionic conductivity (10⁻⁶ Ω·cm at room temperature). -4 ~10 -3 S cm -1 Wide electrochemical window (>5 V vsLi) + The lithium-garnet solid-state electrolyte (Li₂SSE) has attracted much attention due to its chemical stability with lithium metal. However, the interface problem between the lithium-garnet solid-state electrolyte and the electrode remains a core obstacle to its commercialization. On the negative electrode side, the surface of the lithium-garnet solid-state electrolyte exhibits lithium-phobic properties due to residual alkaline impurities, resulting in a relatively high contact resistance at the lithium-garnet interface. On the positive electrode side, under high-voltage charge-discharge conditions, the positive electrode active material and the lithium-garnet solid-state electrolyte are prone to oxidation side reactions, forming a space charge layer with high interfacial impedance. This hinders the cross-interface migration of lithium ions, leading to capacity decay and a decrease in rate performance in solid-state batteries.

[0004] Therefore, there is an urgent need to find an efficient, low-cost and scalable interface modification strategy to construct a robust and lithium-friendly interface layer, enhance the interface contact on the negative electrode side while isolating element diffusion on the positive electrode side, and achieve excellent electrochemical performance of solid-state batteries. Summary of the Invention

[0005] The main objective of this application is to provide a modified solid electrolyte, its preparation method, and a solid-state battery, in order to solve the problems that the garnet-type solid electrolyte exhibits lithium-phobic properties on its surface, resulting in a large number of micropores at the solid-solid interface between the negative electrode lithium and the solid electrolyte, leading to a significant increase in interfacial contact resistance; and that the garnet-type solid electrolyte is prone to oxidation side reactions with the active material on the positive electrode side, forming a high interfacial impedance space charge layer, which hinders the cross-interface migration of lithium ions, leading to capacity decay and reduced rate performance of the solid-state battery.

[0006] To achieve the above objectives, according to one aspect of this application, a modified solid electrolyte is provided, the modified solid electrolyte sheet comprising a garnet-type solid electrolyte sheet and a modified layer in situ modified on the surface of the garnet-type solid electrolyte sheet, wherein the material of the modified layer is selected from at least one of alumina, zinc oxide, nickel oxide and cobalt oxide.

[0007] Furthermore, the thickness of the modified layer is 0.6~1.8μm.

[0008] Furthermore, the thickness of the garnet-type solid electrolyte sheet is 0.3~1.2 mm.

[0009] Furthermore, the modified layer is made of aluminum oxide.

[0010] Furthermore, the chemical formula of the garnet-type solid electrolyte sheet is Li. 7-x La3Zr 2-x M x O 12 M is selected from at least one of Ta, Nb, Ga, Al, W, and Ba, and 0 ≤ x ≤ 2.

[0011] To achieve the above objectives, according to another aspect of this application, a method for preparing a modified solid electrolyte is provided. The method includes: step S1, providing a garnet-type solid electrolyte sheet, coating the surface of the garnet-type solid electrolyte sheet with an aqueous solution of a metal salt, and allowing it to stand to induce a protonation reaction on the surface of the garnet-type solid electrolyte sheet, thereby forming a metal hydroxide in situ on the surface of the garnet-type solid electrolyte sheet to obtain a modified solid electrolyte precursor; step S2, subjecting the modified solid electrolyte precursor to vacuum sintering to obtain the modified solid electrolyte; wherein the metal salt in the aqueous solution of the metal salt is selected from at least one of aluminum nitrate, zinc nitrate, nickel nitrate, and cobalt nitrate.

[0012] Further, in step S1, the molar concentration of the metal salt in the aqueous solution is 0.8~1.2 mol / L, based on the molar amount of the metal element.

[0013] Further, in step S2, the temperature of the vacuum sintering treatment is 350~450℃, and the time of the vacuum sintering treatment is 3~6h.

[0014] Further, in step S1, the ratio of the coating amount of the metal salt aqueous solution to the surface area of ​​the garnet-type solid electrolyte sheet is 0.1 mL: (130~155) mm. 2 .

[0015] Furthermore, the settling temperature is 15~35℃, and the settling time is 2~5 minutes.

[0016] Furthermore, the coating methods include drop coating and / or spin coating.

[0017] Furthermore, step S1 also includes washing and drying processes after settling.

[0018] Furthermore, the washing solution used in the washing process is anhydrous ethanol, and the washing process is repeated 3 to 5 times.

[0019] Furthermore, the drying temperature is 60~80℃, and the drying time is 3~10min.

[0020] According to another aspect of this application, a solid-state battery is provided, comprising a positive electrode, a negative electrode, and a solid electrolyte, wherein the solid electrolyte is a modified solid electrolyte provided in the first aspect or a modified solid electrolyte obtained according to the preparation method provided in the second aspect above.

[0021] Furthermore, the solid electrolyte includes any one of all-solid-state lithium metal batteries, all-solid-state lithium-sulfur batteries, or semi-solid-state lithium-ion batteries.

[0022] Furthermore, the negative electrode is lithium metal. The preparation method of the solid-state battery includes: step S1, melting lithium metal into lithium liquid, uniformly wetting and spreading the lithium liquid on the surface of one side of the modified solid electrolyte, cooling to form a lithium layer adhering to the surface of the modified solid electrolyte, and obtaining a solid electrolyte containing a negative electrode; step S2, wetting the side of the solid electrolyte containing the negative electrode away from the lithium layer with electrolyte, and then attaching it to the positive electrode to obtain a solid-state battery.

[0023] By applying the technical solution of this application, the modified solid electrolyte provided by this application modifies the surface of the garnet-type solid electrolyte sheet in situ with a modification layer. The modification layer is in close contact with the garnet-type solid electrolyte sheet, effectively preventing the modification layer from falling off during cycling. The material of the modification layer is selected from at least one of alumina, zinc oxide, nickel oxide, and cobalt oxide. The modification layer can improve the lithiophilicity of the solid electrolyte, allowing the molten lithium liquid to spread and wet the surface of the modification layer evenly, eliminating a large number of micropores between the solid electrolyte and the negative electrode, and significantly reducing the interfacial contact resistance. At the same time, the modification layer can also suppress element diffusion and oxidation side reactions on the positive electrode side, promote lithium ion cross-interface migration, suppress the generation of lithium dendrites during cycling, and maintain a uniform interfacial lithium ion flux during cycling, thereby improving the electrochemical performance and long-cycle stability of the solid battery.

[0024] Furthermore, the modified layer of the modified solid electrolyte provided in this application can isolate the surface of the garnet-type solid electrolyte sheet from contact with air, solving the problem that the garnet-type solid electrolyte is highly sensitive to humidity and air, and that LiOH and Li2CO3 impurities will form on the surface of the garnet-type solid electrolyte. This reduces the requirements for storage and transportation conditions, and the inert interface layer maintains chemical stability during long-term cycling, reducing the environmental control costs of battery assembly. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0026] Figure 1 The XRD patterns of the solid electrolytes provided in Examples 1-4 and Comparative Examples 1, 4, and 6 of this application are shown.

[0027] Figure 2 SEM images of the solid electrolytes provided in Examples 1-4 and Comparative Examples 1 and 6 are shown.

[0028] Figure 3 Cross-sectional SEM images of solid electrolytes containing a negative electrode prepared using the solid electrolytes provided in Example 1 and Comparative Example 1 are shown.

[0029] Figure 4 Electrochemical interfacial impedance test diagrams for Examples 1-4, Example 14, and Comparative Example 6;

[0030] Figure 5 The graphs show the cycle performance and coulombic efficiency of Example 1 and Comparative Example 6. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0032] As analyzed in the background section of this application, on the negative electrode side, the garnet-type solid electrolyte exhibits lithium-phobic properties due to residual lithium impurities on its surface, resulting in numerous micropores at the solid-solid interface between the negative electrode lithium and the solid electrolyte, significantly increasing the interfacial contact resistance. On the positive electrode side, the solid electrolyte readily undergoes oxidation side reactions with the active materials in the positive electrode, forming a high interfacial impedance space charge layer that hinders lithium-ion cross-boundary migration, leading to capacity decay and reduced rate performance in solid-state batteries. To address these issues, this application provides a modified solid electrolyte, its preparation method, and a solid-state battery.

[0033] In a first typical embodiment of this application, a modified solid electrolyte is provided, comprising a garnet-type solid electrolyte sheet and a modified layer in situ modified on the surface of the garnet-type solid electrolyte sheet, wherein the material of the modified layer is selected from at least one of alumina, zinc oxide, nickel oxide, silicon oxide and iron oxide.

[0034] It should be noted that in the modified solid electrolyte provided in this application, the modified layer is applied in situ to the entire surface of the garnet-type solid electrolyte sheet.

[0035] The modified solid electrolyte provided in this application involves in-situ modification of the surface of a garnet-type solid electrolyte sheet with a modified layer. The modified layer is in close contact with the garnet-type solid electrolyte sheet, effectively preventing the modified layer from falling off during cycling. The material of the modified layer is selected from at least one of lithium-philic alumina, zinc oxide, nickel oxide, and cobalt oxide, which can promote the uniform spreading and wetting of molten lithium liquid on the surface of the modified layer, eliminate a large number of micropores between the solid electrolyte and the negative electrode, and achieve a significant reduction in interfacial contact resistance. At the same time, the modified layer can also be used to suppress element diffusion and oxidation side reactions on the positive electrode side, promote lithium ion migration across the interface, suppress the generation of lithium dendrites during cycling, and maintain a uniform interfacial lithium ion flux, thereby improving the electrochemical performance and long-cycle stability of the solid battery.

[0036] Furthermore, the modified layer of the modified solid electrolyte provided in this application can isolate the surface of the garnet-type solid electrolyte sheet from contact with air, solving the problem that the garnet-type solid electrolyte is highly sensitive to humidity and air, and that LiOH and Li2CO3 impurities will form on the surface of the garnet-type solid electrolyte. This reduces the requirements for storage and transportation conditions, and the inert interface layer maintains chemical stability during long-term cycling, reducing the environmental control costs of battery assembly.

[0037] In some embodiments of this application, the thickness of the modified layer is 0.6~1.8 μm, which is more conducive to improving the air stability of the modified solid electrolyte and the uniform spreading and wetting of molten lithium liquid on the surface of the modified layer, while also taking into account excellent electrochemical performance. If the thickness of the modified layer is too low, it is impossible to form a uniform modified layer that covers the entire interface, affecting the interface layer and the air stability of the modified solid electrolyte. If the thickness of the modified layer is too high, it will lead to a significant increase in interface impedance, hindering lithium ion transport. Specifically, the thickness of the modified layer is 0.6 μm, 0.9 μm, 1.2 μm, 1.5 μm, 1.8 μm, or any range of two values.

[0038] In some embodiments of this application, the thickness of the garnet-type solid electrolyte sheet is 0.3~1.2 mm to facilitate superior ion transport performance. Specifically, the thickness of the garnet-type solid electrolyte sheet is 0.3 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, or any combination of two values.

[0039] In some embodiments of this application, the modified layer is made of alumina. During electrochemical cycling via Li... + Repeated insertion and extraction transform the LiAlO2 interface phase in situ into a LiAlO2 interface phase with higher ionic conductivity, exhibiting excellent self-healing effects. The LiAlO2 interface phase also possesses good electrochemical stability and flexibility, providing additional assurance for the long lifespan of solid-state batteries.

[0040] In some embodiments of this application, the specific type of material for the garnet-type solid electrolyte sheet is not limited, such as LATP, LLTO and other oxide-based solid electrolytes, to facilitate compatibility with various solid-state battery systems such as high-nickel ternary and lithium-sulfur.

[0041] In some embodiments of this application, the chemical formula of the material of the garnet-type solid electrolyte sheet is Li. 7- x La3Zr 2-x M x O 12 M is selected from one or more of Ta, Nb, Ga, Al, W, and Ba, and 0≤x≤2, in order to further improve the ionic conductivity and cycle stability of the garnet-type solid electrolyte sheet.

[0042] In some specific embodiments, the material of the garnet-type solid electrolyte sheet includes, but is not limited to, Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 wait.

[0043] In some specific embodiments, the garnet-type solid electrolyte sheet is formed by pressing garnet-type solid electrolyte particles with a particle size D50 of 0.5~15μm, which is more conducive to increasing the compaction density of the garnet-type solid electrolyte sheet and further improving the lithium-ion transport capability. Specifically, the particle size D50 of the garnet-type solid electrolyte particles is 0.5μm, 0.6μm, 0.8μm, 1.0μm, 1.5μm, 2μm, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, or any range of two values.

[0044] In a second typical embodiment of this application, a method for preparing a modified solid electrolyte is provided. The method includes: step S1, providing a garnet-type solid electrolyte sheet, coating the surface of the garnet-type solid electrolyte sheet with an aqueous solution of a metal salt, and allowing it to stand to induce a protonation reaction on the surface of the garnet-type solid electrolyte sheet, thereby forming a metal hydroxide in situ on the surface of the garnet-type solid electrolyte sheet to obtain a modified solid electrolyte precursor; step S2, subjecting the modified solid electrolyte precursor to vacuum sintering to obtain a modified solid electrolyte; wherein the metal salt in the aqueous solution of the metal salt is selected from one or more of aluminum nitrate, zinc nitrate, nickel nitrate, and cobalt nitrate.

[0045] The method for preparing the modified solid electrolyte provided in this application involves allowing a metal salt aqueous solution to stand and induce a protonation reaction on the surface of a garnet-type solid electrolyte sheet, thereby increasing the H+ content in the metal salt aqueous solution. + Li in the lattice of the garnet-based solid electrolyte sheet surface + Proton exchange occurs, and H2O dissociates to release OH-. - OH - The metal hydroxide precipitate is formed in situ with the metal cation. Subsequently, through sintering, the metal hydroxide precipitate is dehydrated in situ and transformed into a metal oxide modified layer that is in close contact with the surface of the garnet-type solid electrolyte. This significantly improves the lithium affinity. Moreover, the process does not require other additives or vacuum deposition equipment. The method is simple and easy to implement, the raw materials are inexpensive and readily available, and it is easy to achieve large-scale production, which can effectively reduce the preparation cost.

[0046] Furthermore, this application generates a modified layer of metal oxide material in situ on the surface of the garnet-type solid electrolyte sheet. This modified layer is stable and inert, which, on the one hand, isolates air and water vapor, preventing the garnet-type solid electrolyte sheet from reacting with water vapor, oxygen, and carbon dioxide in the air to form LiOH and Li2CO3 impurities, thereby improving the air stability of the modified solid electrolyte, reducing storage and transportation requirements, and decreasing environmental control costs for battery assembly; on the other hand, the modified layer has high ionic conductivity, allowing Li... + The modified solid-state electrolyte sheet allows for rapid electron flow while simultaneously blocking electron injection into the electrolyte, inhibiting lithium dendrite growth and penetration, and ensuring a uniform distribution of lithium ion flux. This suppresses lithium dendrite nucleation at the source, significantly improving cycle life and safety. Furthermore, the inert modified layer inhibits oxidation and element diffusion on the positive electrode side during high-voltage cycling, enhancing the cycle stability of the solid-state battery. The preparation method of the modified solid-state electrolyte sheet provided in this application is compatible with various garnet-type solid-state electrolytes and metal salts, enabling its widespread application in various solid-state battery systems and demonstrating excellent process versatility and industrial expansion potential.

[0047] In some embodiments of this application, in step S1, the molar concentration of the metal salt in the aqueous solution is 0.8~1.2 mol / L, based on the molar amount of the metal element. If the molar concentration of the metal salt in the aqueous solution is too high, the resulting modified layer will be too thick, leading to a significant increase in interfacial resistance and hindering lithium-ion transport. If the molar concentration of the metal salt in the aqueous solution is too low, the density of the in-situ generated modified layer will be too low, which is not conducive to reducing interfacial resistance and improving ion transport performance. Specifically, the molar concentration of the metal salt in the aqueous solution, based on the molar amount of the metal element, is 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, or any combination of two values ​​within a range.

[0048] In some embodiments of this application, in step S1, the ratio of the coating amount of the aqueous metal salt to the surface area of ​​the garnet-type solid electrolyte sheet is 0.1 mL: (130~155) mm. 2 A suitable amount of aqueous solution of metal salt is more conducive to forming a uniform, dense, and moderately thick modified layer. Specifically, the ratio of the amount of aqueous solution of metal salt to the surface area of ​​the garnet-type solid electrolyte sheet is 0.1 mL: 130 mm². 2 0.1mL:135mm 2 0.1mL:140mm 2 0.1mL:145mm 2 0.1mL:150mm 2 0.1mL:155mm 2 Or a range of values ​​consisting of any two numerical values.

[0049] In some embodiments of this application, the coating method for coating the surface of the garnet-type solid electrolyte sheet with the aqueous solution of the metal salt in step S1 above includes, but is not limited to, drop coating and / or spin coating, with drop coating being preferred.

[0050] In some embodiments of this application, the settling temperature is 15~35℃, and the settling time is 2~5 min. The above settling can be carried out at room temperature, requiring no complex equipment or process control, which is more conducive to reducing the preparation cost of the modified solid electrolyte. If the settling time is too long, the resulting modified layer will be too thick, leading to increased interfacial impedance and hindering lithium-ion transport. If the settling time is too short, the proton-induced reaction will not proceed sufficiently, resulting in insufficient in-situ generation of metal hydroxide, leading to low density, uneven thickness, and insufficient ion transport performance of the modified layer. Specifically, the settling temperature is 15℃, 18℃, 20℃, 22℃, 25℃, 28℃, 30℃, 32℃, 35℃, or any two of these values, and the settling time is 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 5 min, or any two of these values.

[0051] In some embodiments of this application, step S1 above further includes washing and drying after standing (inducing protonation reaction) to remove soluble substances and impurities generated by the induced reaction, so as to avoid introducing impurity elements during subsequent vacuum sintering and affecting the electrochemical performance of the modified solid electrolyte sheet.

[0052] In some specific embodiments, anhydrous ethanol is used as the washing solution to remove soluble substances while avoiding the introduction of new impurities. The number of washing cycles is not limited, but is preferably 3 to 5 times.

[0053] In some specific embodiments, the drying temperature is 60~80℃, and the drying time is 3~10min, to facilitate the removal of impurities for subsequent vacuum sintering and to avoid the introduction of impurities by residual washing liquid during the vacuum sintering process. Specifically, the drying temperature is 60℃, 65℃, 70℃, 75℃, 80℃ or any two of these values, and the drying time is 3min, 3.5min, 4min, 4.5min, 5min, 8min, 10min or any two of these values.

[0054] In some embodiments of this application, in step S2 above, the vacuum sintering temperature is 350~450℃, and the vacuum sintering time is 3~6h, so as to improve the efficiency of vacuum sintering while ensuring the structural stability of the modified solid electrolyte. Specifically, the vacuum sintering temperature is 350℃, 380℃, 400℃, 420℃, 450℃, or any two of these values; the vacuum sintering time is 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any two of these values.

[0055] In a third typical embodiment of this application, a solid-state battery is also provided, which includes a positive electrode, a negative electrode and a solid electrolyte. The solid electrolyte is a modified solid electrolyte provided in the first typical embodiment of this application or a modified solid electrolyte obtained according to the preparation method provided in the second typical embodiment described above.

[0056] The solid-state battery provided in this application uses a modified solid-state electrolyte with an in-situ modified layer on the surface of a garnet-type solid-state electrolyte sheet. This not only ensures a strong bond between the modified layer and the garnet-type solid-state electrolyte sheet, effectively preventing the modified layer from falling off during cycling, but also utilizes at least one of aluminum oxide, zinc oxide, nickel oxide, and cobalt oxide as the material for the modified layer. This improves the lithium affinity of the solid-state electrolyte, enabling the molten lithium liquid to spread and wet the surface of the modified layer uniformly. This eliminates a large number of micropores between the solid-state electrolyte and the negative electrode, reducing the interfacial contact resistance. Simultaneously, the modified layer can isolate element diffusion and oxidation side reactions on the positive electrode side, promote lithium-ion cross-interface migration, suppress lithium dendrite formation during cycling, maintain a uniform interfacial lithium-ion flux during cycling, and thus improve the electrochemical performance and long-cycle stability of the solid-state battery.

[0057] In this application, the specific type of solid-state battery is not limited, including but not limited to any one of all-solid-state lithium metal batteries, all-solid-state lithium sulfur batteries, or semi-solid-state lithium-ion batteries.

[0058] In some embodiments of this application, when the negative electrode is lithium metal, the method for preparing a solid-state battery includes: step S1, melting lithium metal into a lithium liquid, uniformly wetting and spreading the lithium liquid on the surface of one side of the modified garnet solid electrolyte, cooling the lithium liquid to form a lithium layer adhering to the surface of the modified solid electrolyte, and obtaining a solid electrolyte containing a negative electrode; step S2, wetting the side of the solid electrolyte containing the negative electrode away from the lithium layer with an electrolyte, and then attaching it to the positive electrode to obtain a solid-state battery.

[0059] In some specific embodiments, the positive electrode includes a current collector and a positive electrode material layer attached to the surface of the current collector. The positive electrode material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes, but is not limited to, any one of layered transition metal oxides, olivine phosphates, and spinel-type lithium manganese oxide, preferably LiCoO2 or LiNi. x Co y Mn z O2(x+y+z=1,0.5≤x<0.9,0.1≤y≤0.2,0 <z≤0.3)、LiNi x Co y Al zO2 (where x+y+z=1, 0.8≤x≤0.9, 0.05≤y≤0.15, 0.02≤z≤0.05), LiFePO4, LiMn2O4; conductive agents and binders are commonly used substances in this field and will not be described in detail here.

[0060] In some embodiments, the positive electrode active material is LiNi. 0.928 Co 0.072 In O2, the positive electrode is prepared according to the following steps: LiNi 0.928 Co 0.072 O2 and acetylene black were added to an N-methyl-2-pyrrolidone solution containing polyvinylidene fluoride (PVDF), mixed thoroughly by centrifugation, coated onto carbon-coated aluminum foil, and vacuum-dried overnight at 110°C. The resulting product was then cut into 8mm diameter discs. The mass fraction of PVDF in the N-methyl-2-pyrrolidone solution was 6 wt%. LiNi... 0.928 Co 0.072 The weight ratio of O2, acetylene black, and polyvinylidene fluoride is 8:1:1.

[0061] In some embodiments, the negative electrode is lithium metal, and the solid electrolyte containing the negative electrode is prepared according to the following steps: a commercial lithium sheet is placed in a nickel crucible and heated to 350°C on a heating table in an argon glove box to melt it. The oxide film on the surface of the lithium liquid is carefully scraped off with tweezers and a stainless steel spoon. The modified solid electrolyte is then held in the lithium liquid with tweezers and scraped so that one side is completely wetted and covered by molten lithium. After cooling, the edge is polished so that lithium is retained only on one side, thus obtaining a solid electrolyte containing the negative electrode.

[0062] In some embodiments, the solid-state battery is assembled according to the following steps: 7µL of lithium salt electrolyte (1.0 M LiPF6, solvent is ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) is added to the side of the solid electrolyte containing the negative electrode away from the lithium layer to ensure good contact between the solid electrolyte and the positive electrode, and then it is attached to the positive electrode; then nickel foam is placed on the outside of both the negative and positive electrodes to act as a buffer and prevent the solid electrolyte from breaking during the battery encapsulation process; finally, it is installed in a CR2032 coin cell and held at a pressure of 500 psi for 10 seconds on a battery sealing machine to obtain the solid-state battery.

[0063] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0064] Example 1

[0065] This embodiment provides a modified solid electrolyte, which is prepared according to the following steps:

[0066] (1) Prepare a 1 mol / L Al(NO3)3 aqueous solution, and uniformly drop about 0.1 mL onto the surface of a garnet-type solid electrolyte sheet at room temperature. Let it stand for 2 min, wash it three times with anhydrous ethanol, and dry it at 60℃ for 3 min to obtain the modified solid electrolyte precursor.

[0067] (2) Subsequently, the modified solid electrolyte precursor was vacuum sintered at 400℃ for 4 h in a tube furnace and then naturally cooled to obtain the modified solid electrolyte; wherein, the material of the garnet-type solid electrolyte sheet was Li 6.4 La3Zr 1.4 Ta 0.6 O 12 It is circular, with a diameter of 13mm and a thickness of 1mm.

[0068] Example 2

[0069] The difference between this embodiment and Example 1 is that a 1 mol / L Zn(NO3)2 aqueous solution is used instead of an Al(NO3)3 aqueous solution.

[0070] Example 3

[0071] The difference between this embodiment and Example 1 is that a 1 mol / L Ni(NO3)2 aqueous solution is used instead of an Al(NO3)3 aqueous solution.

[0072] Example 4

[0073] The difference between this embodiment and Example 1 is that a 1 mol / L Co(NO3)2 aqueous solution is used instead of an Al(NO3)3 aqueous solution.

[0074] Example 5

[0075] The difference between this embodiment and Embodiment 1 is that the diameter of the garnet-type solid electrolytic sheet is 14 mm.

[0076] Example 6

[0077] The difference between this embodiment and Embodiment 1 is that the settling time is 5 minutes.

[0078] Example 7

[0079] The difference between this embodiment and Example 1 is that the concentration of the Al(NO3)3 aqueous solution is 0.8 mol / L.

[0080] Example 8

[0081] The difference between this embodiment and Example 1 is that the concentration of the Al(NO3)3 aqueous solution is 1.2 mol / L.

[0082] Example 9

[0083] The difference between this embodiment and Embodiment 1 is that the settling time is 1 minute.

[0084] Example 10

[0085] The difference between this embodiment and Embodiment 1 is that the settling time is 8 minutes.

[0086] Example 11

[0087] The difference between this embodiment and Embodiment 1 is that the diameter of the garnet-type solid electrolytic sheet is 20 mm.

[0088] Example 12

[0089] The difference between this embodiment and Embodiment 1 is that the diameter of the garnet-type solid electrolyte sheet is 10 mm.

[0090] Example 13

[0091] The difference between this embodiment and Example 1 is that the concentration of the Al(NO3)3 aqueous solution is 0.5 mol / L.

[0092] Example 14

[0093] The difference between this embodiment and Example 1 is that the concentration of the Al(NO3)3 aqueous solution is 1.5 mol / L.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is that a 1 mol / L Fe(NO3)3 aqueous solution is used instead of an Al(NO3)3 aqueous solution.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that a 1 mol / L Pb(NO3)2 aqueous solution is used instead of an Al(NO3)3 aqueous solution.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that a 1 mol / L Ti(NO3)4 aqueous solution is used instead of an Al(NO3)3 aqueous solution.

[0100] Comparative Example 4

[0101] The difference between this comparative example and Example 1 is that step (2) was not performed, and the modified solid electrolyte precursor was used as the modified solid electrolyte.

[0102] Comparative Example 5

[0103] The difference between this comparative example and Example 1 is that deionized water is used instead of the Al(NO3)3 aqueous solution.

[0104] Comparative Example 6

[0105] The solid electrolyte provided in this comparative example is the garnet-type solid electrolyte sheet from Example 1.

[0106] Experimental Example 1

[0107] The XRD tests were performed on Examples 1-4 and Comparative Examples 1, 4, and 6, and the spectra are shown below. Figure 1 As shown, from Figure 1 As can be seen, Examples 1, 2, 3, and 4 respectively show the characteristic peaks of the corresponding metal oxides, indicating that the metal salt aqueous solution induced a protonation reaction on the surface of the garnet-type solid electrolyte sheet, and the H in the aqueous solution... + With Li in solid electrolyte + An exchange reaction occurred to produce OH. – The ions, together with the metal cations, form hydroxide precipitates, which are dehydrated and decomposed in subsequent vacuum sintering, forming a thin and dense metal oxide modified layer in situ.

[0108] In Comparative Example 1, the characteristic peaks of Fe₂O₃ were not obvious and the intensity was weak. The diffraction peaks were diffuse and not sharp, indicating that the reaction was incomplete and the modification effect was not ideal. Comparative Example 4 showed Al(OH)₃ precipitation on the surface of the solid electrolyte after Al(NO₃)₃ solution treatment, confirming the occurrence and effect of the protonation reaction. Comparative Example 6 showed the reaction between the unmodified garnet-type solid electrolyte and the cubic garnet phase Li₅La₃Nb₂O₃. 12 (PDF 45-0109) Good overlap indicates that a garnet-type solid electrolyte (LLZO) with a pure cubic phase has been successfully synthesized, which has higher lithium-ion conductivity compared with the tetragonal garnet phase.

[0109] Experimental Example 2

[0110] The solid electrolytes provided in Examples 1-4 and Comparative Examples 1 and 6 were subjected to morphological observation using scanning electron microscopy. The results are as follows: Figure 2 As shown. From Figure 2 As can be seen, Examples 1, 2, 3, and 4 exhibit relatively dense modified morphologies, with the corresponding metal oxides successfully nucleating and growing on the surface of the solid electrolyte, uniformly covering the entire surface of the garnet-type solid electrolyte sheet. In Comparative Example 1, the distribution of Fe2O3 is not uniform enough, the reaction for metal oxide formation is incomplete, and the modification effect is limited. Comparative Example 6 shows the surface morphology of the unmodified garnet-type solid electrolyte, exhibiting a particle size distribution of 5–20 μm. Its grain growth is relatively complete, and the structure is relatively dense, but the inherent porosity still affects its electrochemical performance.

[0111] Experimental Example 3

[0112] The solid electrolytes provided in Example 1 and Comparative Example 6 were respectively prepared into solid electrolyte sheets containing lithium anodes. The specific steps included: placing a commercial lithium sheet in a nickel crucible and heating it to 350°C on a heating stage in an argon glove box; carefully scraping off the oxide film on the surface of the lithium liquid with tweezers and a stainless steel spoon; then holding the modified solid electrolyte in the lithium liquid with tweezers and scraping it so that one side is completely wetted and covered by molten lithium; after cooling, grinding the edges so that lithium is only retained on one side, thus obtaining a solid electrolyte containing anode.

[0113] The cross-sectional morphology of the above-mentioned solid electrolytes containing negative electrodes was observed using scanning electron microscopy, and the results are as follows: Figure 3 As shown. Figure 3 Cross-sectional SEM images of solid electrolytes containing negative electrodes prepared from the solid electrolyte sheets provided in Example 1 and Comparative Example 6, from... Figure 3 In the middle, the top part is a garnet-type solid electrolyte sheet, and the bottom part is a lithium metal anode. Figure 3 The interfacial contact between the garnet-type solid electrolyte sheet and the molten lithium metal anode is shown. In Comparative Example 6, the interface between the unmodified garnet-type solid electrolyte sheet and the lithium metal anode shows some isolated pores. This is because the unmodified LLZO surface has poor lithiophilicity and porosity defects, preventing the molten lithium from fully wetting it, reducing the contact area, and resulting in uneven interfacial lithium-ion flux and charge distribution, leading to high interfacial resistance and premature lithium dendrite growth during electrochemical cycling. Example 1 presents a compact, pore-free interfacial contact. The lithiophilic Al2O3 modified layer fully wets the molten lithium metal, and the electron-blocking, ion-conducting interfacial layer significantly reduces the interfacial resistance, maintaining a uniform interfacial lithium-ion flux during subsequent electrochemical cycles. This accelerates lithium-ion transport while suppressing dendrite growth, achieving long-term stable electrochemical performance of the solid-state battery.

[0114] Test Example 4

[0115] (1) The uniformity and average thickness of the modified layers of the solid electrolytes provided in the above embodiments and comparative examples were observed by scanning electron microscopy, and the results are shown in Table 1 below. The average thickness of the modified layer was obtained by taking the average value of the thickness at 10 different locations in the modified layer of the solid electrolyte by scanning electron microscopy.

[0116] (2) The solid electrolytes provided in the above examples and comparative examples were assembled into all-solid-state batteries, and the electrochemical interface impedance was tested. The results are shown in Table 1 below.

[0117] Among them, (2.1) all-solid-state batteries include a positive electrode, a negative electrode and a solid electrolyte.

[0118] (a) The positive electrode is prepared according to the following steps: LiNi0.928 Co 0.072 O2 and acetylene black were added to an N-methyl-2-pyrrolidone solution containing polyvinylidene fluoride (PVDF), mixed thoroughly by centrifugation, coated onto carbon-coated aluminum foil, and vacuum-dried overnight at 110°C. The resulting product was then cut into 8mm diameter discs. The mass fraction of PVDF in the N-methyl-2-pyrrolidone solution was 6 wt%. LiNi... 0.928 Co 0.072 The weight ratio of O2, acetylene black, and polyvinylidene fluoride is 8:1:1.

[0119] (b) The negative electrode is a lithium sheet, and the solid electrolyte containing the negative electrode is prepared according to the following steps: a commercial lithium sheet is placed in a nickel crucible and heated to 350°C on a heating table in an argon glove box. The oxide film on the surface of the lithium liquid is carefully scraped off with tweezers and a stainless steel spoon. The modified solid electrolyte is then held in the lithium liquid with tweezers and scraped so that one side is completely wetted and covered by molten lithium. After cooling, the edge is polished so that lithium is only retained on one side, thus obtaining a solid electrolyte containing the negative electrode.

[0120] (c) The solid-state battery is assembled according to the following steps: 7µL of lithium salt electrolyte (1.0 M LiPF6, solvent is ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1) is dropped onto the side of the solid electrolyte containing the negative electrode away from the lithium layer to ensure good contact between the solid electrolyte and the positive electrode, and then attached to the positive electrode; then nickel foam is placed on the outside of both the negative and positive electrodes to act as a buffer to prevent the solid electrolyte from breaking during the battery encapsulation process. Finally, it is installed in a CR2032 coin cell and held at a pressure of 500 psi for 10 seconds on a battery sealing machine to obtain the solid-state battery.

[0121] (2.2) Electrochemical interface impedance test: The test was conducted using an electrochemical workstation (WonATech ZIVE SP2) in the frequency range of 1Hz to 7MHz, with an AC amplitude of 50mV applied to the solid-state battery.

[0122] Table 1

[0123]

[0124] Note: (1) Uniform thickness of the modified layer means that the difference between the thickness of each part of the modified layer and the average thickness of the modified layer is ≤ 10% of the average thickness of the modified layer. Non-uniform thickness of the modified layer means that the difference between the thickness of each part of the modified layer and the average thickness of the modified layer is ≥ 20% of the average thickness of the modified layer. Slightly poor thickness uniformity of the modified layer means that the difference between the thickness of each part of the modified layer and the average thickness of the modified layer is greater than 10% of the average thickness of the modified layer and less than 20% of the thickness of the modified layer.

[0125] (2) The above “—” indicates that the thickness of the modified layer is uneven and an accurate value cannot be given.

[0126] A comparison of Examples 1-8 with Comparative Examples 1-3 shows that when the modified layer is made of iron oxide, lead oxide, and titanium oxide, its interfacial impedance increases significantly, which hinders the cross-interface migration of lithium ions and reduces the electrochemical performance of solid-state batteries.

[0127] The comparison between Examples 1-8 and Comparative Example 4 shows that when the modified layer material is not sintered into an oxide, its impurity content is too high, which will lead to a significant increase in interfacial impedance, hindering the cross-interface migration of lithium ions and reducing the electrochemical performance of solid-state batteries.

[0128] A comparison of Examples 1-8 with Comparative Examples 5-6 shows that the garnet-type solid-state electrolytic cell without a modification layer has a high interfacial impedance, which hinders the cross-interface migration of lithium ions and reduces the electrochemical performance of the solid-state battery.

[0129] A comparison of Examples 1-8 and Examples 9-10 shows that if the aqueous solution of metal salt is left to stand on the surface of the garnet-type solid electrolyte sheet for too short a time, the aqueous solution of metal salt cannot fully induce the protonation reaction on the garnet-type solid electrolyte sheet, which is not conducive to the formation of a uniform and dense modified layer and will lead to an increase in interfacial impedance. If the aqueous solution of metal salt is left to stand on the surface of the garnet-type solid electrolyte sheet for too long, the thickness of the modified layer will increase and the interfacial impedance will also increase.

[0130] A comparison of Examples 1-8 with Examples 11-12 shows that both excessively high and insufficient coating amounts of the aqueous solution of metal salts on the surface of the garnet-type solid electrolytic sheet per unit area are detrimental to the formation of a uniform, dense, and appropriately thick modified layer.

[0131] A comparison of Examples 1-8 with Examples 13-14 shows that both excessively high and excessively low molar concentrations of metal salts in aqueous solutions are not conducive to the formation of a uniform, dense, and appropriately thick modified layer.

[0132] Figure 4 The electrochemical interfacial impedance test results are for Examples 1-4, Example 14, and Comparative Example 6. Figure 4 In the Nyquist plot, the low-frequency straight line (ion blocking behavior) and the capacitive behavior of the two semicircles are shown. The high-frequency semicircle represents the sum of the bulk resistance of the solid electrolyte and the grain boundary resistance, while the mid-frequency semicircle represents the interfacial impedance between the solid electrolyte and the lithium anode. By fitting an appropriate equivalent circuit and dividing the diameter of the mid-frequency semicircle by the surface area of ​​the solid electrolyte (2×π×0.7²), the interfacial impedance of each sample is obtained, in Ω cm. -2 Comparative Example 6, unmodified LLZO, showed 113.1 Ω·cm. -2The low interfacial impedance is due to the insufficient lithiophilicity of the LLZO surface and its tendency to react with water and air to form lithiophore-free impurity interfacial phases. Examples 1, 2, 3, and 4 all showed optimized interfacial impedance, confirming the interfacial modification effect of lithiophilic metal oxides. Molten lithium fully wetted the modified surface, forming a tightly contacted anodic interface. Among them, Example 1 showed the best modification effect of alumina, with the interfacial impedance reduced to 21.8 Ω cm. -2 In Comparative Example 1, due to the incomplete formation and uneven nucleation of iron oxide in the garnet-type solid electrolyte, the lithium affinity was poor, and lithium metal could not be well wetted, resulting in excessive interfacial impedance. Examples 11-12 explored the optimal concentration of the metal salt solution, showing that both excessively thin and excessively thick modified layers weakened the modification effect, further proving that 1 mol / L was a suitable concentration in the examples. The results of Comparative Example 5 were similar to those of Comparative Example 6, confirming that the negative impact of deionized water on the solid electrolyte was limited and was restored during the subsequent vacuum sintering process.

[0133] Experimental Example 5

[0134] The solid-state battery clips prepared in Example 1 and Comparative Example 1 were tested using a Blue Electricity testing system (CT3002A). The solid-state batteries were held in the battery clips and connected to the Blue Electricity testing system. After standing for 1 hour, a current density of 0.1 C (1 C = 200 mAh g⁻¹) was applied. -1 The battery was charged to 4.3 V, allowed to stand for 1 minute, then discharged at 0.1 C to 2.7 V, allowed to stand for 1 minute, and the coulombic efficiency and cycle stability were tested. The results are as follows: Figure 5 As shown. Figure 5 The graphs show the cycle performance and coulombic efficiency of Example 1 and Comparative Example 6; from Figure 5 It can be seen that Comparative Example 6 exhibits rapid capacity decay after more than 50 cycles, which may be due to poor interfacial contact and rapid penetration of lithium dendrites caused by electron injection along grain boundaries. In contrast, the modified solid electrolyte of Example 1 shows a capacity of 182.7 mAh g⁻¹. -1 The initial discharge specific capacity and good interfacial stability allow it to retain 71.8% of its capacity after 150 cycles, with an average coulombic efficiency of 98.2%. The relatively stable capacity change indicates the high reversibility of the interface. The inert Al2O3 modified layer increases the compatibility between the solid electrolyte and the high-voltage cathode, maintaining stability during high-voltage cycling.

[0135] As can be seen from the above description, the embodiments of this application achieve the following technical effects: The modified solid electrolyte provided by this application has a modified layer in situ modified on the surface of the garnet-type solid electrolyte sheet, which makes the bond between the modified layer and the garnet-type solid electrolyte sheet strong and effectively prevents the modified layer from falling off during cycling; the material of the modified layer is selected from at least one of alumina, zinc oxide, nickel oxide and cobalt oxide, which can improve the lithium affinity of the solid electrolyte, realize the uniform spreading and wetting of molten lithium liquid on the surface of the modified layer, eliminate a large number of micropores between the solid electrolyte and the negative electrode, and reduce the interfacial contact resistance; at the same time, the modified layer can also isolate the element diffusion and oxidation side reaction on the positive electrode side, promote the cross-interface migration of lithium ions, suppress the generation of lithium dendrites during cycling, maintain a uniform interfacial lithium ion flux during cycling, and thus improve the electrochemical performance and long-cycle stability of the solid battery.

[0136] Furthermore, the modified solid electrolyte provided in this application solves the problem of the high sensitivity of garnet-type solid electrolytes to humidity and air, and the formation of LiOH and Li2CO3 impurities on the garnet surface by in-situ modifying the surface of the garnet-type solid electrolyte sheet with a modified layer. This solves the inherent defect of poor air stability of garnet-type solid electrolytes, reduces the requirements for storage and transportation conditions, and ensures that the interface layer maintains chemical stability during long-term cycling, thereby reducing the environmental control costs of battery assembly.

[0137] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A modified solid electrolyte, characterized in that, The modified solid electrolyte includes a garnet-type solid electrolyte sheet and a modified layer in situ modified on the surface of the garnet-type solid electrolyte sheet. The material of the modified layer is selected from at least one of alumina, zinc oxide, nickel oxide and cobalt oxide.

2. The modified solid electrolyte according to claim 1, characterized in that, The thickness of the modified layer is 0.6~1.8μm; And / or, the thickness of the garnet-type solid electrolyte sheet is 0.3~1.2 mm.

3. The modified solid electrolyte according to claim 1, characterized in that, The modified layer is made of aluminum oxide.

4. The modified solid electrolyte according to any one of claims 1 to 3, characterized in that, The chemical formula of the material of the garnet-type solid electrolyte sheet is Li. 7-x La3Zr 2-x M x O 12 M is selected from at least one of Ta, Nb, Ga, Al, W, and Ba, and 0 ≤ x ≤ 2.

5. A method for preparing a modified solid electrolyte, characterized in that, The preparation method includes: Step S1: Provide a garnet-type solid electrolyte sheet, coat the surface of the garnet-type solid electrolyte sheet with an aqueous solution of a metal salt, allow it to stand to allow the aqueous solution of the metal salt to spread and wet the surface of the garnet-type solid electrolyte sheet and induce a protonation reaction, and form a metal hydroxide in situ on the surface of the garnet-type solid electrolyte sheet to obtain a modified solid electrolyte precursor. Step S2: The modified solid electrolyte precursor is subjected to vacuum sintering to obtain the modified solid electrolyte. The metal salt in the aqueous solution of the metal salt is selected from at least one of aluminum nitrate, zinc nitrate, nickel nitrate, and cobalt nitrate.

6. The preparation method according to claim 5, characterized in that, In step S1, the molar concentration of the metal salt in the aqueous solution is 0.8~1.2 mol / L, based on the molar amount of the metal element. And / or, in step S2, the temperature of the vacuum sintering treatment is 350~450℃, and the time of the vacuum sintering treatment is 3~6h.

7. The preparation method according to claim 5, characterized in that, In step S1, the ratio of the coating amount of the aqueous solution of the metal salt to the surface area of ​​the garnet-type solid electrolytic sheet is 0.1 mL: (130~155) mm. 2 ; And / or, the settling temperature is 15~35℃, and the settling time is 2~5min; And / or, the coating method includes drop coating and / or spin coating.

8. The preparation method according to claim 5, characterized in that, Step S1 also includes washing and drying after settling. Preferably, the washing solution used in the washing process is anhydrous ethanol, and the number of washing processes is 3 to 5. Preferably, the drying temperature is 60~80℃ and the drying time is 3~10min.

9. A solid-state battery, characterized in that, The solid-state battery includes a positive electrode, a negative electrode, and a solid electrolyte, wherein the solid electrolyte is a modified solid electrolyte according to any one of claims 1 to 4 or a modified solid electrolyte obtained by the preparation method according to any one of claims 5 to 8; And / or, the solid-state battery includes any one of an all-solid-state lithium metal battery, an all-solid-state lithium-sulfur battery, or a semi-solid-state lithium-ion battery.

10. The solid-state battery according to claim 9, characterized in that, The negative electrode is lithium metal, and the method for preparing the solid-state battery includes: Step S1: Melt the lithium metal into a lithium liquid, and spread the lithium liquid evenly on the surface of the modified solid electrolyte. Cool to form a lithium layer that adheres to the surface of the modified solid electrolyte, and obtain a solid electrolyte containing a negative electrode. Step S2: Wet the side of the solid electrolyte containing the negative electrode away from the lithium layer with electrolyte, and then attach it to the positive electrode to obtain the solid battery.

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