Gradient-designed polymer-based lithium solid-state electrolyte, preparation method thereof and lithium metal solid-state battery

Abstract

The invention discloses a polymer-based lithium solid electrolyte with gradient design, a preparation method thereof and a lithium metal solid battery, effective dispersion of a silanized quaternary ammonium salt cationic active agent and a fast ion conductor is realized by bonding the silanized quaternary ammonium salt cationic active agent and the fast ion conductor, and the fast ion conductor-rich layer-modified interface layer-polymer-rich layer is constructed in a gradient manner, so that the polymer-based lithium solid electrolyte with gradient design is obtained. And the flux distribution of lithium ions is regulated and controlled, the uniform deposition of the lithium ions is guided, so that the growth of lithium dendrites is inhibited, and the lithium metal solid-state battery prepared based on the design has excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal batteries, and in particular to a gradient-designed polymer-based lithium solid-state electrolyte, a preparation method thereof, and a lithium metal solid-state battery. Background Art

[0002] As the global energy mix shifts toward cleaner, lower-carbon energy sources, high-energy-density energy storage technologies have become a research hotspot. Lithium metal batteries, with their high theoretical specific capacity (3860 mAh / g) and low redox potential (-3.04 V vs. SHE), are considered a key solution for next-generation power batteries. However, practical applications of lithium metal anodes face a significant challenge: the uncontrolled growth of lithium dendrites. These dendrites can not only pierce the separator and cause short circuits, leading to thermal runaway or even explosion, but also accelerate the loss of active lithium, significantly reducing battery cycle life and safety. Although researchers have mitigated the dendrite problem through strategies such as optimizing electrode structure, manipulating electrolyte composition (such as introducing fluorinated solvents or additives), and designing three-dimensional current collectors, the inherent limitations of liquid electrolytes (such as low mechanical strength and high volatility) remain a major challenge in fundamentally addressing the dendrite growth problem. Solid-state electrolytes, with their high mechanical strength and non-flammability, are an ideal choice for suppressing lithium dendrites. Inorganic solid electrolytes have attracted widespread attention due to their high ionic conductivity and mechanical strength. However, their inherent high rigidity inevitably reduces interfacial contact and increases interfacial impedance, severely hindering the practical application of inorganic SSEs. In recent years, polymer / inorganic composite solid electrolytes have attracted increasing attention due to their simple preparation, high flexibility, and wide application scenarios. However, conventional polymer solid electrolytes suffer from insufficient ionic conductivity and low lithium ion transference numbers, resulting in limited dendrite suppression. The fundamental reason is the uneven lithium ion transport pathways within the polymer matrix, which prevents uniform lithium deposition. Currently proposed modification methods mainly include artificial solid electrolyte interface (SEI) construction, filler modification, and interface design. While filler modification can improve the performance of polymer electrolytes, problems such as filler agglomeration and uneven dispersion have limited their further development. Interface design, which optimizes the interfacial properties between the electrolyte and the electrode, is considered an ideal modification method. Therefore, how to improve the ion transport uniformity and dendrite suppression ability of composite solid electrolytes through interface design has become a key breakthrough in current research. Summary of the Invention

[0003] In order to solve the problem of uneven lithium deposition in existing composite solid electrolytes, the present invention aims to provide a gradient-designed polymer-based lithium solid electrolyte, its preparation method, and a lithium metal solid-state battery. By bonding a silanized quaternary ammonium salt cationic active agent with a fast ion conductor, effective dispersion of the two is achieved. At the same time, a gradient structure of fast ion conductor-rich layer-modified interface layer-polymer-rich layer is constructed to achieve regulation of lithium ion flux distribution, guide the uniform deposition of lithium ions, and thus inhibit the growth of lithium dendrites. The lithium metal solid-state battery prepared based on this design has excellent electrochemical properties.

[0004] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: A method for preparing a gradient-designed polymer-based lithium solid electrolyte comprises the following steps: (1) Under an inert atmosphere, a quaternary ammonium salt surfactant was dispersed in DMF, and then 3-aminopropyltriethoxysilane was added and refluxed at 65-75°C to obtain a bifunctional surfactant; (2) Pre-treating the fast ion conductor by immersing it in hydrogen peroxide at 75-85°C, ultrasonically dispersing the pre-treated fast ion conductor in anhydrous ethanol containing a bifunctional surfactant, and stirring the reaction at 55-65°C to obtain a bifunctional surfactant-modified fast ion conductor; (3) The fast ion conductor modified by the bifunctional surfactant, the olefin polymer and the lithium salt are dispersed in a polar solvent, which is referred to as liquid A; the olefin polymer and the lithium salt are dispersed in a polar solvent, which is referred to as liquid B; and the substrate is coated on a polytetrafluoroethylene plate by a step-by-step spin coating method, wherein the first layer is coated with liquid A, which is dried to form a film, and the second layer is coated with a mixture of liquid A and liquid B, which is dried to form a film, and the third layer is coated with liquid B, which is dried to form a film to obtain a polymer-based lithium solid electrolyte.

[0005] Preferably, in step (1), the quaternary ammonium salt surfactant is selected from one or more of cetyltrimethylammonium chloride (CTAC), dodecyltrimethylammonium chloride (DTAC), octadecyltrimethylammonium chloride (OTAC), and cetyltrimethylammonium bromide (CTAB). Taking CTAC as an example, the following reaction occurs: CTAC + NH2(CH2)3Si(OC2H5)3 → [CTA]⁺[⁻OOC(CH2)3Si(OC2H5)3] + HCl Silanization of quaternary ammonium surfactants can adjust the hydrophilicity and hydrophobicity of the surfactant surface. The silane group can form a chemical bond with the surface of the fast ion conductor and adsorb on the surface of the fast ion conductor. Its long-chain organic group can form a steric hindrance on the particle surface, thereby improving dispersion stability and preventing particle agglomeration.

[0006] Preferably, in step (1), the mass volume ratio of the quaternary ammonium salt surfactant to DMF is 0.5-1 g:1 ml; the mass volume ratio of the quaternary ammonium salt surfactant to 3-aminopropyltriethoxysilane is 2-5 g:1 ml.

[0007] Preferably, in step (2), the fast ion conductor is selected from one or more of LLZO, LLTO, LLZTO, LATP, and NASICON. After soaking, the surface carbonate of the fast ion conductor is removed to expose the -OH group and achieve hydroxylation. In the subsequent stirring reaction process, -Si(OC2H5)3 is hydrolyzed to -Si(OH)3 and condensed with the -OH group on the surface of the fast ion conductor to form a unique Si-OT (T is Zr, Ta, Al, Ti) chemical bond. The hydrophobic tail of the surfactant can extend outward, reducing the hydrophilicity of the surface of the fast ion conductor. The steric hindrance effect is used to improve the dispersibility of the fast ion conductor in the solvent, effectively preventing the agglomeration of the fast ion conductor and the surfactant.

[0008] Preferably, in step (2), the mass ratio of the fast ion conductor to the bifunctional surfactant is 1:0.05-0.2; and the concentration of the bifunctional surfactant in the anhydrous ethanol containing the bifunctional surfactant is 0.5-2 wt%.

[0009] Preferably, in step (3), the mass ratio of the bifunctional surfactant-modified fast ion conductor, the vinyl polymer and the lithium salt in the liquid A is 70:20:10; and the mass ratio of the vinyl polymer and the lithium salt in the liquid B is 90:10.

[0010] Preferably, in step (3), the vinyl polymer is selected from one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-trifluoroethylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer; The lithium salt is selected from one or more of LiCl, LiF, LiBr, LiI, Li2SO4, LiNO3, LiPF6, LiTFSI, LiFSI, and LiDFOB.

[0011] The polar solvent is selected from one or more of tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, and 2,2,2-trifluoro-N,N-dimethylacetamide.

[0012] Preferably, in step (3), the coating thickness of liquid A, the mixture of liquid A and liquid B, and liquid B is 100 μm, wherein the volume ratio of liquid A to liquid B in the mixture of liquid A and liquid B is 1:1.

[0013] Taking LLZO as an example, the polymer electrolyte with a gradient structure design of the present invention can be recorded as: LLZO-rich layer → modified interface layer → polymer-rich layer (close to lithium metal). A gradual transition method is adopted. The LLZO-rich layer provides a rapid lithium ion transmission path, and the modified interface layer bridges the ceramic / polymer through Si-O-Zr covalent bonds, effectively reducing the interface impedance between different components. The highly flexible polymer-rich layer adapts to the volume change of the lithium negative electrode. This design can reduce the transmission resistance of ions between different layers, effectively reduce interface polarization, achieve high-speed ion transmission, and effectively improve interface compatibility. At the same time, it effectively reduces stress concentration at the interface and improves the mechanical stability and chemical stability of the interface. Therefore, the gradient structure design realizes the regulation of lithium ion flux distribution and guides the uniform deposition of lithium ions, thereby achieving the effect of suppressing lithium dendrites.

[0014] The present invention also provides a gradient-designed polymer-based lithium solid electrolyte prepared by the above preparation method.

[0015] The present invention also provides a lithium metal solid-state battery, comprising a positive electrode sheet, a gradient-designed polymer-based lithium solid-state electrolyte, and a lithium metal negative electrode.

[0016] In the present invention, the active material of the positive electrode sheet can be a conventional commercial lithium battery positive electrode material, and the lithium metal negative electrode can be lithium metal, lithium copper composite strip or other alloyed lithium metal negative electrode, and there are no special requirements.

[0017] Beneficial technical effects of the present invention: 1. The present invention forms a unique Si-OT (T is Zr, Ta, Al, Ti) chemical bond by condensing the silanized quaternary ammonium salt surfactant with the -OH group on the surface of the fast ion conductor. The hydrophobic tail of the surfactant can extend outward, reducing the hydrophilicity of the LLZO surface. The steric hindrance effect is utilized to improve the dispersibility of the fast ion conductor in the organic solvent, effectively preventing the agglomeration of the fast ion conductor and the surfactant.

[0018] 2. The present invention designs a fast ion conductor-rich layer-modified interface layer-polymer-rich layer. The fast ion conductor-rich layer can provide a high-speed ion channel, the modified interface layer can achieve stress buffering and bonding of hydrogen bonds between the fast ion conductor (through Si-OT) and the polymer to form a covalent bond network bridge, and the polymer-rich layer can achieve close electrode contact. Through this design, the lithium ion flux distribution can be regulated and uniform deposition can be guided, thereby achieving the effect of inhibiting the growth of lithium dendrites.

[0019] 3. The polymer-based lithium solid-state battery of the present invention is equipped with a gradient-designed polymer-based lithium solid-state electrolyte, which has high ionic conductivity (2.71 mS / cm), a wide electrochemical window, and a high ion transference number (0.59). The lithium-lithium symmetric battery can be stably cycled for 1500 h, and the full battery can be stably cycled for 1500 cycles at a rate of 1 C at room temperature with a capacity retention rate of >80%. The soft-pack battery assembled with the modified composite solid-state electrolyte can achieve more than 200 stable cycles, which has industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Graph showing room temperature ionic conductivity of button cells assembled according to Example 1 of the present invention and Comparative Example 1.

[0021] Figure 2 Graph showing room temperature electrochemical window test results of button cells assembled according to Example 1 of the present invention and Comparative Example 1.

[0022] Figure 3 Graphs showing the ion migration of lithium metal symmetrical batteries assembled according to Example 1 of the present invention and Comparative Example 1.

[0023] Figure 4 This is a room temperature stability test chart of the lithium metal symmetrical battery assembled according to Example 1 of the present invention and Comparative Example 1.

[0024] Figure 5 The room temperature electrochemical performance of the button cell assembled in Example 1 of the present invention at 2°C.

[0025] Figure 6 The room temperature electrochemical performance of the lithium metal soft pack battery assembled in Example 1 of the present invention at 0.2°C. DETAILED DESCRIPTION

[0026] Example 1

[0027] (1) Synthesis of bifunctional surfactant: Dissolve 10 g of hexadecyltrimethylammonium chloride (CTAC) in 15 mL of DMF, stir under nitrogen, add 3 mL of 3-aminopropyltriethoxysilane, and reflux at 70 °C for 12 h. After cooling, centrifuge, wash three times with ethanol and deionized water, respectively, and vacuum dry to obtain silanized Si-CTAC. The reaction equation is as follows: CTAC + NH2(CH2)3Si(OC2H5)3 → [CTA]⁺[⁻OOC(CH2)3Si(OC2H5)3] + HCl (2) Atomic bonding on the LLZO surface: LLZO powder was immersed in 30% H2O2 and treated at 80 °C for 2 hours to remove surface carbonates, expose -OH groups, and achieve hydroxylation. 1g of LLZO was dispersed in 10g of anhydrous ethanol containing 1wt% Si-CTAC and ultrasonically treated for 1h, then stirred at 60 °C for 12h to hydrolyze -Si(OC2H5)3 to -Si(OH)3 and condense with -OH on the LLZO surface. The powder was collected by centrifugation and vacuum dried to obtain CTAC-Si-LLZO, forming Si-O-Zr chemical bonds. (3) Gradient structure design: Prepare the following: Solution A: CTAC-Si-LLZO / PVDF / LiTFSI (mass ratio 70:20:10) dissolved in 10 mL THF solution; Solution B: PVDF / LiTFSI (mass ratio 90:10) dissolved in 10 mL THF solution. Layers were applied to a polytetrafluoroethylene plate using a stepwise spin coating method: First layer: Apply solution A (100 μm) and dry at 60 °C for 2 h to form a film; Second layer: Apply a mixture of A:B = 1:1 (volume ratio) (100 μm) and dry at 60 °C for 2 h to form a film; Third layer: Apply solution B (100 μm) and dry at 60 °C for 12 h to remove residual solvent, resulting in a polymer electrolyte with a gradient structure design: LLZO-rich layer → modified interface layer → polymer-rich layer.

[0028] (4) Preparation of positive electrode: lithium nickel cobalt manganese (LiNi 0.8 Co 0.1 Mn 0.1 O2) was used as the active material, mixed with a conductive agent (acetylene black) and a binder [polyvinylidene fluoride (PVDF)] in a mass ratio of 80:10:10, coated on a carbon-coated aluminum foil, and dried in a vacuum drying oven at 80 °C for 24 h to remove the solvent.

[0029] (5) Selection of negative electrode: 450μm metal lithium sheet is used as the negative electrode.

[0030] (6) Assembly of lithium solid-state batteries: Assemble symmetrical batteries in the order of negative electrode shell, gasket (304 stainless steel, diameter × thickness: 15.6 mm × 0.5 mm), gradient structure polymer-based solid electrolyte, gasket (15.6 mm × 0.5 mm), and positive electrode shell, and test the ionic conductivity of the solid electrolyte. Assemble batteries in the order of negative electrode shell, lithium sheet (15.6 mm × 0.45 mm), gradient structure polymer-based solid electrolyte, lithium sheet (15.6 mm × 0.45 mm), and positive electrode shell, and test the ion migration number and lithium stability of the solid electrolyte. Assemble batteries in the order of negative electrode shell, lithium sheet (15.6 mm × 0.45 mm), gradient structure polymer-based solid electrolyte, positive electrode sheet, and positive electrode shell, and test the room temperature impedance and charge and discharge performance.

[0031] (7) Assembly of lithium soft-pack batteries: Cut the positive electrode sheet into 43×56 mm, the negative electrode sheet into 45×58 mm, and the polymer-based solid electrolyte with a gradient structure design into 50×65 mm. Stack and seal the sheets in an inert atmosphere in the order of positive electrode, solid electrolyte, and negative electrode, and place them in a cabinet for soft-pack battery cycle performance testing.

[0032] After testing, the polymer-based solid electrolyte with a gradient structure design has a high ionic conductivity of 2.71 mS / cm. The high ion migration number of the assembled lithium metal symmetric battery reaches 0.59. The assembled Li||Li symmetric battery can be stably cycled for 1500 hours. The assembled lithium metal solid-state battery can be stably cycled for 1500 cycles at a rate of 1C at room temperature, with a capacity retention rate of >80%. The assembled soft-pack battery can achieve more than 200 cycles, which is of great industrial application value.

[0033] Example 2

[0034] The same method as Example 1 differs only in that 10 g of dodecyltrimethylammonium chloride (DTAC) was dissolved in 15 mL of DMF and stirred under nitrogen. 3 mL of 3-aminopropyltriethoxysilane was added and the mixture was refluxed at 70°C for 12 h. After cooling, the mixture was centrifuged, washed three times with ethanol and deionized water, and dried under vacuum to obtain silanized Si-DTAC. The reaction equation is as follows: DTAC + NH2(CH2)3Si(OC2H5)3 → [DTA]⁺[⁻OOC(CH2)3Si(OC2H5)3] + HCl.

[0035] Example 3

[0036] The same method as Example 1 differs only in that 10 g of hexadecyltrimethylammonium bromide (CTAB) was dissolved in 15 mL of DMF and stirred under nitrogen. 3 mL of 3-aminopropyltriethoxysilane was added and the mixture was refluxed at 70°C for 12 h. After cooling, the mixture was centrifuged, washed three times with ethanol and three times with deionized water, and dried under vacuum to obtain silanized Si-CTAB. The reaction equation is as follows: CTAB + NH2(CH2)3Si(OC2H5)3 → [CTA]⁺[⁻OOC(CH2)3Si(OC2H5)3] + HBr.

[0037] Comparative Example 1 The same as Example 1, except that step (1) is omitted and silanization of the quaternary ammonium salt surfactant is not performed. The specific steps are: (1) Preparation of 1 wt% CTAC anhydrous ethanol solution: 0.1 g CTAC powder was dissolved in 9.9 g anhydrous ethanol and ultrasonically stirred for 2 h to obtain a 1 wt% CTAC anhydrous ethanol solution; (2) Soak the LLZO powder in 30% H2O2 and treat it at 80 °C for 2 hours to remove the surface carbonate, expose the -OH group, and achieve hydroxylation. Disperse 1g of LLZO in anhydrous ethanol containing 1wt% CTAC and ultrasonicate for 1 hour. Stir at 60 °C for 12 hours, collect the powder by centrifugation, and dry it in vacuum. The subsequent steps are the same as in Example 1.

[0038] Comparative Example 2 The same as Example 1, except that step (1) is omitted, quaternary ammonium salt surfactant is not introduced, and 3-aminopropyltriethoxysilane is used alone. The specific steps are: (1) Soak LLZO powder in 30% H2O2 and treat at 80 °C for 2 hours to remove surface carbonates, expose -OH groups, and achieve hydroxylation. Disperse 1g of LLZO in a mixture of anhydrous ethanol and 3-aminopropyltriethoxysilane, ultrasonicate for 1 hour, stir at 60 °C for 12 hours, collect the powder by centrifugation, and dry in vacuum. The subsequent steps are the same as in Example 1.

[0039] Comparative Example 3 Same as Example 1, except that an imidazoline cationic surfactant is used. The specific steps are as follows: (1) Dissolve 10 g of ethyl 3-methyl-2-thioimidazoline-1-carboxylate in 15 mL of DMF, stir under nitrogen, add 3 mL of 3-aminopropyltriethoxysilane, and reflux at 70 °C for 12 h. Cool and centrifuge, wash three times with ethanol and deionized water, and dry in vacuum. The subsequent steps are the same as in Example 1.

[0040] Comparative Example 4 The same as Example 1, except that an amine cationic surfactant is used, the specific steps are as follows: (1) Dissolve 10 g of 4-(N,N-dimethylamino)pyridine (DMAP) in 15 mL of DMF, stir under nitrogen, add 3 mL of 3-aminopropyltriethoxysilane, and reflux at 70 °C for 12 h. Cool and centrifuge, wash three times with ethanol and deionized water, and dry in vacuum. The subsequent steps are the same as in Example 1.

[0041] Comparative Example 5 The same as Example 1, except that in step (3), only liquid A (300 μm) was coated on the polytetrafluoroethylene plate and dried at 60°C for 12 h to remove the residual solvent, thereby obtaining a composite solid electrolyte for assembling a battery.

[0042] Comparative Example 6 The same as Example 1, except that a two-layer structure design is adopted in step (3): the first layer: coating liquid A (150 μm), drying at 60 ° C for 2 h to form a film; the second layer: coating liquid B (150 μm) and drying at 60 ° C for 12 h to remove the residual solvent, thereby obtaining a composite solid electrolyte for assembling a battery.

[0043] Comparative Example 7 The same as Example 1, except that in step (3), only the A:B = 1:1 mixture (300 μm) is coated on a polytetrafluoroethylene plate and dried at 60 °C for 12 h to remove the residual solvent, thereby obtaining a composite solid electrolyte for assembling a battery.

[0044] Table 1 Performance test results of various embodiments and comparative examples Group Room temperature ionic conductivity (mS / cm) Ion mobility <![CDATA[Electrochemical window (Vs. Li + / Li) (V)]]> Full cell impedance at room temperature (Ω) <![CDATA[Symmetric battery at 0.1 mA / cm 2 Stable cycling duration]]> Capacity retention rate after 1500 cycles at 1C at room temperature (%) Stable cycle times of soft pack battery at room temperature 0.2C Example 1 2.71 0.59 4.8 34 1500 81.34 206 Example 2 1.64 0.55 4.5 61 1150 73.41 137 Example 3 1.96 0.56 4.7 45 1370 78.63 184 Comparative Example 1 0.981 0.32 4.3 91 628 31.24 51 Comparative Example 2 0.175 0.1 3.6 317 83 0 3 Comparative Example 3 0.177 0.21 4.2 248 417 13.49 27 Comparative Example 4 0.556 0.17 4.1 283 267 7.91 12 Comparative Example 5 0.981 0.35 4.4 175 891 45.18 84 Comparative Example 6 1.385 0.41 4.5 124 1087 58.42 97 Comparative Example 7 1.171 0.39 4.4 147 911 51.71 90 As shown in Table 1, when a monofunctional quaternary ammonium salt cationic surfactant (unsilanized) was used in Comparative Example 1, the ion migration number was 0.32, the electrochemical window was 4.3 V, and the full-cell impedance at room temperature was 91 Ω. The Li||Li symmetric button cell cycled for 628 h, and the solid-state lithium metal button cell with the assembled NCM811 cathode had a capacity retention of 31.24% after 1500 cycles at room temperature and 2°C. This indicates that the unsilanized quaternary ammonium salt cationic surface activity prevents effective dispersion of the fast ion conductor and surfactant, resulting in increased interfacial impedance and poor electrochemical performance.

[0045] Comparative Example 2 shows that the silane additive alone cannot be effectively adsorbed into the fast ion conductor, with an ion transfer number of 0.1 and an electrochemical window of only 3.6 V. The full-cell impedance at room temperature reaches 317 Ω, and the Li||Li button-type symmetrical battery can only cycle for 83 h, indicating that the silanized additive cannot interact with the fast ion conductor to form a bond, and the interfacial impedance is huge.

[0046] Comparative Examples 3 and 4 show that the non-quaternary ammonium salt cationic surfactant additive cannot undergo condensation reaction with the silanized additive to form silicon-oxygen bonds, and exhibits very poor electrochemical performance.

[0047] Comparative Examples 5, 6, and 7 show that the polymer electrolytes using single-layer and double-layer structures cannot achieve high-speed lithium ion transmission due to the interface impedance between the components, and have poor interface compatibility.

[0048] In Example 1, effective dispersion of the two was achieved by bonding the bifunctional surfactant to the fast ion conductor. The gradient structure design of the fast ion conductor-rich layer → modified interface layer → polymer-rich layer effectively reduced the interfacial impedance between different interface layers, achieving high room temperature ionic conductivity (2.71 mS / cm) and high ion transference number (t Li + =0.59), a wide electrochemical window (4.8 V), and low interfacial impedance (34 Ω). A symmetrical Li||Li coin-shaped cell achieved stable cycling for 1500 h. A solid-state lithium metal coin-shaped cell with an NCM811 cathode exhibited a capacity retention of 81.34% after 1500 cycles at room temperature and 2°C. Furthermore, a soft-pack cell assembled using a gradient-structured composite solid electrolyte achieved stable cycling for 200 cycles at 0.2°C. Examples 2 and 3 demonstrate that the use of different quaternary ammonium surfactants exhibits excellent ionic conductivity and electrochemical performance, demonstrating the innovative nature of this design.

Claims

1. A method for preparing a gradient-designed polymer-based lithium solid electrolyte, characterized in that: The steps include: (1) Under an inert atmosphere, a quaternary ammonium salt surfactant was dispersed in DMF, and then 3-aminopropyltriethoxysilane was added and refluxed at 65-75°C to obtain a bifunctional surfactant; (2) Pre-treating the fast ion conductor by immersing it in hydrogen peroxide at 75-85°C, ultrasonically dispersing the pre-treated fast ion conductor in anhydrous ethanol containing a bifunctional surfactant, and stirring the reaction at 55-65°C to obtain a bifunctional surfactant-modified fast ion conductor; (3) The fast ion conductor modified by the bifunctional surfactant, the olefin polymer and the lithium salt are dispersed in a polar solvent, which is referred to as liquid A; the olefin polymer and the lithium salt are dispersed in a polar solvent, which is referred to as liquid B; and the substrate is coated on a polytetrafluoroethylene plate by a step-by-step spin coating method, wherein the first layer is coated with liquid A, which is dried to form a film, and the second layer is coated with a mixture of liquid A and liquid B, which is dried to form a film, and the third layer is coated with liquid B, which is dried to form a film to obtain a polymer-based lithium solid electrolyte.

2. The preparation method according to claim 1, characterized in that In step (1), the quaternary ammonium salt surfactant is selected from one or more of hexadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, and hexadecyltrimethylammonium bromide.

3. The preparation method according to claim 1, characterized in that In step (1), the mass volume ratio of the quaternary ammonium salt surfactant to DMF is 0.5-1 g:1 ml; the mass volume ratio of the quaternary ammonium salt surfactant to 3-aminopropyltriethoxysilane is 2-5 g:1 ml.

4. The preparation method according to claim 1, characterized in that In step (2), the fast ion conductor is selected from one or more of LLZO, LLTO, LLZTO, LATP, and NASICON.

5. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of the fast ion conductor to the bifunctional surfactant is 1:0.05-0.2; and the concentration of the bifunctional surfactant in the anhydrous ethanol containing the bifunctional surfactant is 0.5-2 wt%.

6. The preparation method according to claim 1, characterized in that In step (3), the mass ratio of the fast ion conductor modified with the bifunctional surfactant, the olefin polymer and the lithium salt in the liquid A is 70:20:10; the mass ratio of the olefin polymer and the lithium salt in the liquid B is 90:

10.

7. The preparation method according to claim 1, characterized in that In step (3), the vinyl polymer is selected from one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-trifluoroethylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer; The lithium salt is selected from one or more of LiCl, LiF, LiBr, LiI, Li2SO4, LiNO3, LiPF6, LiTFSI, LiFSI, and LiDFOB; The polar solvent is selected from one or more of tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, and 2,2,2-trifluoro-N,N-dimethylacetamide.

8. The preparation method according to claim 1, characterized in that In step (3), the coating thickness of liquid A, the mixture of liquid A and liquid B, and liquid B is 100 μm, wherein the volume ratio of liquid A to liquid B in the mixture of liquid A and liquid B is 1:

1.

9. A gradient-designed polymer-based lithium solid electrolyte prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium metal solid-state battery, characterized in that: The invention comprises a positive electrode sheet, a polymer-based lithium solid electrolyte with a gradient design as claimed in claim 9, and a lithium metal negative electrode.

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