Composite electrolyte membrane for solid-state battery and preparation method of composite electrolyte membrane

Abstract

The invention relates to the field of solid-state battery electrolyte membranes, and discloses a composite electrolyte membrane for a solid-state battery and a preparation method thereof.The preparation method comprises the steps that firstly, a PET supporting body of a hierarchical pore structure is prepared through SIPS coupling supercritical drying, then pores of the PET supporting body are filled with composite electrolyte through a vacuum infusion-spin coating gradient filling technology, and the composite electrolyte membrane is prepared. And finally, the lithium metal interface is strengthened by sputtering Al2O3 and a graphene transition layer. Through synchronous optimization of material screening, process innovation and structural design, the PET base film with high penetration rate and tensile strength is obtained; meanwhile, through a step-by-step filling and interface cross-linking technology, the interface compatibility problem of the rigid inorganic electrolyte and the flexible polymer matrix is solved, the ionic conductivity of the electrolyte membrane is remarkably improved, the interface resistance is reduced, and the rate performance and the cycle performance of the solid-state battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state battery electrolyte membranes, and in particular to a composite electrolyte membrane for solid-state batteries and a preparation method thereof. Background Art

[0002] Solid-state batteries are regarded as the core of the next-generation energy storage technology due to their high safety and theoretical energy density. However, the compatibility between the electrolyte / electrode interface and the ion transport efficiency are still difficult points in industrialization. At present, inorganic solid electrolytes (such as lithium lanthanum zirconium oxide (LLZO), lithium aluminum titanium phosphate (LATP), sulfide systems) have received great attention, but they have problems such as high brittleness, easy to break when the thickness is less than 100 μm, and inability to inhibit lithium dendrite penetration; high interfacial impedance, and the rigid interface is difficult to adapt to the volume change during charge and discharge. In addition, polymer electrolytes (such as polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)) have also been studied more, but they have problems such as insufficient mechanical strength, the room temperature tensile strength is generally lower than 10 MPa, and lithium dendrites are easy to penetrate and cause short circuits; low room temperature ionic conductivity, and the σ of pure PEO-based electrolytes < 1×10 -4 S / cm, and it needs to be heated to above 60 °C for practical use.

[0003] To balance the mechanical strength and ion transport performance, the industry generally adopts a composite structure of "porous support + electrolyte filling" at present. However, the existing technologies generally have problems such as insufficient pore structure of the support, single pore diameter, and low pore channel penetration rate of the support, making it difficult to balance the electrolyte wettability and mechanical strength. For example, a composite solid electrolyte membrane and a preparation method thereof disclosed in Patent CN113571764B are obtained by first infiltrating and filling SNE with high ionic conductivity into porous silica (SiO2) ceramic particles with high porosity, and then compounding it with a polymer electrolyte. However, the porous SiO2 ceramic is a brittle material, resulting in cracking of the electrolyte membrane after bending, and the cost is more than 10 times that of the polymer membrane. Summary of the Invention

[0004] The present invention aims to overcome the above problems existing in the composite structure electrolyte membrane in the prior art, and provides a composite electrolyte membrane for solid-state batteries and a preparation method thereof. Through synchronous optimization of material selection, process innovation, and structural design, the contradiction of "one increases while the other decreases" between porosity and mechanical strength in the traditional phase separation method is broken through. Through solvent system optimization and supercritical drying technology, a PET-based membrane with both high penetration rate (≥89%) and tensile strength (≥45 MPa) is obtained; at the same time, a step-by-step filling and interfacial cross-linking technology is developed to solve the interfacial compatibility problem between the rigid inorganic electrolyte and the flexible polymer matrix.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a composite electrolyte membrane for a solid-state battery, the steps including: (1) Dispersing PET and a nucleating agent evenly in a mixed solvent of hexafluoroisopropanol (HFIP) and water to obtain a film-forming solution, casting the film-forming solution into a film and solidifying it; (2) Performing CO2 supercritical drying on the cast film to obtain a main body film; (3) Spraying a PET chloroform solution added with a templating agent on the surface of the main body film, and obtaining a PET support with a hierarchical pore structure after evaporating the solvent; (4) Dispensing a composite electrolyte and a lithium salt in an ionic liquid to obtain an electrolyte slurry; (5) Vacuum-injecting the electrolyte slurry into the PET support and curing it; (6) Adding an acrylic monomer to the electrolyte slurry to obtain a composite slurry, spin-coating the composite slurry on the surface of the PET support, and performing ultraviolet curing; (7) Sputtering Al2O3 and graphene on the surface of the PET support.

[0006] In step (1) of the present invention, hexafluoroisopropanol (HFIP) is used as the main solvent and water is used as a phase separation inducing agent. Under the accelerating action of the nucleating agent, a cast film with a bicontinuous pore structure is prepared based on solvent-induced phase separation (SIPS). Then, combined with CO2 supercritical drying, the pore collapse caused by capillary force is eliminated, and the contradiction of "one increases while the other decreases" between porosity and mechanical strength in the traditional phase separation method can be broken through, and a PET main body film with both a high through rate (≥89%) and a tensile strength (≥45 MPa) can be obtained. Then, in step (3), a PET chloroform solution added with a templating agent is sprayed on the surface of the main body film, and a nano-microporous layer with a pore diameter <20 nm can be formed on the surface of the main body film after the solvent evaporates, further improving the porosity, and obtaining a PET support with a hierarchical pore structure, which can significantly improve the ion transport efficiency of the electrolyte membrane. Then, the present invention adopts a gradient filling process, first performing primary vacuum injection, and then performing secondary spin-coating, filling the composite electrolyte in the pores of the PET support. The vacuum-spin-coating gradient composite can eliminate interface defects, achieve complete penetration of nano-scale pores, and reduce the interface impedance; at the same time, ultraviolet curing can stimulate the grafting of the PET surface and the acrylic monomer, bonding the composite electrolyte and the PET pore wall through an acrylic cross-linking layer. Through the step-by-step filling and interface cross-linking technology, the interface compatibility problem between the rigid inorganic electrolyte and the flexible polymer matrix is solved. Finally, in the present invention, an Al2O3 and graphene transition layer is sputtered on the surface of the PET support, and the graphene sheets are arranged perpendicular to the electrode, inhibiting the lateral growth of lithium dendrites. Through the synergy of the sputtering filter layer and the densification filling, the cycle life of the battery can be significantly improved.

[0007] Preferably, in step (1), the intrinsic viscosity of the PET is 0.8 to 1.0 dL / g, and the glass transition temperature is 70 to 80 °C; the nucleating agent is nano-SiO2; in the obtained film-forming solution, the mass concentration of HFIP is 70 to 80%, the mass concentration of water is 5 to 15%, the mass concentration of the nucleating agent is 0.1 to 1%, and the balance is PET; The casting temperature during casting film formation is 25 ± 0.5 °C, and the thickness of the wet film obtained by casting is 250 to 350 μm; the wet film is solidified in a coagulation bath, the coagulation bath medium is methanol, and the temperature in the coagulation bath is lowered from room temperature to below 5 °C at a rate of 1 to 5 °C / min. Using methanol as the medium of the coagulation bath can quickly displace HFIP and induce pore penetration; at the same time, linear cooling is carried out at a rate of 1 to 5 °C / min to extend the double continuous phase separation time and ensure the porosity.

[0008] Preferably, the conditions for CO2 supercritical drying in step (2) are: 15 to 25 MPa, 35 to 45 °C, 3 to 5 h.

[0009] Preferably, in the PET chloroform solution added with a template agent in step (3), the mass concentration of PET is 3 to 7%, the mass concentration of the template agent is 1 to 2%, and the template agent is P123; the spraying thickness is 1 to 5 μm.

[0010] Preferably, in step (4), the composite electrolyte includes polyethylene oxide (PEO) and lithium lanthanum zirconium oxide (LLZO), and the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and / or lithium bis(oxalato)borate (LiBOB); the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; in the electrolyte slurry, the mass ratio of PEO, LLZO and the lithium salt is 35 to 45:45 to 55:10; the mass fraction of the ionic liquid in the electrolyte slurry is 70 to 80%.

[0011] Preferably, in step (5), the vacuum pressure during vacuum perfusion is ≤ -0.08 MPa, and the cycle of pumping and releasing is carried out 2 to 3 times; the curing conditions are: thermal curing at 75 to 85 °C for 1 to 3 h.

[0012] Preferably, in step (6), the acrylic monomer is 2-hydroxyethyl methacrylate (HEMA), and in the composite slurry, the mass concentration of the acrylic monomer is 20 to 40%; the spin coating speed in step (6) is 1500 to 2500 rpm, the spin coating time is 25 to 35 s, and the film-forming thickness is 4 to 6 μm; the ultraviolet light intensity during ultraviolet curing is 5 to 15 mW / cm 2 , and the ultraviolet curing time is 5 to 15 min.

[0013] Preferably, in step (7), the mass ratio of sputtered Al2O3 to graphene is 1 to 3:1, and the sputtering thickness is 30 to 80 nm.

[0014] The present invention also provides a composite electrolyte membrane for a solid-state battery prepared by the above preparation method, comprising a PET support and a composite electrolyte filled in the voids of the PET support; the PET support includes a main body film and a nano-microporous layer on the surface of the main body film, and through holes with a pore diameter of 50 to 200 nm are provided in the main body film, and micropores with a pore diameter < 20 nm are provided in the nano-microporous layer.

[0015] Preferably, the porosity of the PET support is ≥ 80%.

[0016] Therefore, the present invention has the following beneficial effects: (1) By the "dual-engine" strategy of SIPS coupling supercritical drying, the traditional contradictory relationship between porosity and strength is broken through, a PET main body film with both high through-rate and tensile strength is obtained, and a nano-microporous layer is provided thereon to obtain a PET support with a multi-level pore structure; (2) The composite electrolyte is filled by a vacuum- spin coating composite gradient filling process, which can eliminate interface defects and achieve complete penetration of nano-scale pores; combined with a high-porosity PET support and a composite electrolyte gradient filling process, the ion transport efficiency of the electrolyte membrane can be significantly improved, the electrode-electrolyte contact resistance can be reduced, and the rate performance of the whole battery can be improved; (3) Through the "rigid-flexible combination" of in-situ polymerization and transition layer design, the ion transport and dendrite inhibition capabilities can be improved simultaneously. Description of the Drawings

[0017] Figure 1 is the SEM image of the PET support prepared in Example 1 of the present invention. Detailed Embodiments

[0018] The following further describes the present invention in conjunction with specific embodiments.

[0019] In the present invention, unless otherwise specified, all devices and raw materials can be purchased from the market or are commonly used in this industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in this field.

[0020] General Embodiment: A preparation method of a composite electrolyte membrane for a solid-state battery, the steps include: (1) Dispersing PET and a nucleating agent evenly in a mixed solvent of HFIP and water to obtain a film-forming solution, casting the film-forming solution into a film and solidifying it; (2) Subjecting the cast film to CO2 supercritical drying to obtain a main body film; (3) Spray a PET chloroform solution added with a templating agent on the surface of the main body film, and obtain a PET support with hierarchical pores after evaporating the solvent; (4) Disperse the composite electrolyte and lithium salt in an ionic liquid to obtain an electrolyte slurry; (5) Vacuum infuse the electrolyte slurry into the PET support and cure it; (6) Add acrylic monomers to the electrolyte slurry to obtain a composite slurry, spin-coat it on the surface of the PET support, and cure it by ultraviolet light; (7) Sputter Al2O3 and graphene on the surface of the PET support.

[0021] As a specific embodiment, the intrinsic viscosity of the PET described in step (1) is 0.8 - 1.0 dL / g, and the glass transition temperature is 70 - 80 °C; the nucleating agent is nano-SiO2; in the obtained film-forming solution, the mass concentration of HFIP is 70 - 80%, the mass concentration of water is 5 - 15%, the mass concentration of the nucleating agent is 0.1 - 1%, and the balance is PET.

[0022] As a specific embodiment, the casting temperature during casting and film formation in step (1) is 25 ± 0.5 °C, and the thickness of the obtained wet film is 250 - 350 μm; the wet film is solidified in a coagulation bath, the coagulation bath medium is methanol, and the temperature in the coagulation bath is decreased from room temperature to below 5 °C at a rate of 1 - 5 °C / min.

[0023] As a specific embodiment, the conditions for CO2 supercritical drying in step (2) are: 15 - 25 MPa, 35 - 45 °C, 3 - 5 h.

[0024] As a specific embodiment, in the PET chloroform solution added with a templating agent in step (3), the mass concentration of PET is 3 - 7%, the mass concentration of the templating agent is 1 - 2%, and the templating agent is P123; the spraying thickness is 1 - 5 μm.

[0025] As a specific embodiment, the composite electrolyte described in step (4) includes PEO and LLZO, and the lithium salt is LiTFSI and / or LiBOB; the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; in the electrolyte slurry, the mass ratio of PEO, LLZO and lithium salt is 35 - 45:45 - 55:10; the mass fraction of the ionic liquid in the electrolyte slurry is 70 - 80%.

[0026] As a specific embodiment, during vacuum infusion in step (5), the vacuum pressure ≤ -0.08 MPa, and the cycle of pumping and releasing is 2 - 3 times; the curing conditions: heat curing at 75 - 85 °C for 1 - 3 h.

[0027] As a specific embodiment, the acrylic monomer described in step (6) is hydroxyethyl methacrylate. In the composite slurry, the mass concentration of the acrylic monomer is 20-40%; in step (6), the spin coating speed is 1500-2500 rpm, the spin coating time is 25-35 s, and the film forming thickness is 4-6 μm; the ultraviolet light intensity during ultraviolet curing is 5-15 mW / cm 2 , and the ultraviolet curing time is 5-15 min.

[0028] As a specific embodiment, the mass ratio of sputtered Al2O3 to graphene in step (7) is 1-3:1, and the sputtering thickness is 30-80 nm.

[0029] As a specific embodiment, the composite electrolyte membrane for a solid-state battery prepared by the above preparation method includes a PET support and a composite electrolyte filled in the voids of the PET support; the PET support includes a main body membrane and a nano-porous layer on the surface of the main body membrane. The main body membrane is provided with through holes with a pore diameter of 50-200 nm, and the nano-porous layer is provided with pores with a pore diameter <20 nm.

[0030] As a specific embodiment, the porosity of the PET support is ≥80%.

[0031] Example 1: A preparation method of a composite electrolyte membrane for a solid-state battery, the steps are as follows: (1) Disperse PET (intrinsic viscosity 0.9 dL / g, glass transition temperature Tg = 75 °C) and nucleating agent nano-SiO2 in a mixed solvent of HFIP and water to obtain a film-forming solution. In the obtained film-forming solution, the mass concentration of HFIP is 75%, the mass concentration of water is 10%, the mass concentration of the nucleating agent is 0.5%, and the balance is PET; (2) Cast the film-forming solution into a film and perform phase separation in a coagulation bath; the casting temperature is 25 °C, the wet film thickness is 300 μm, the coagulation bath medium is methanol, and it is linearly cooled from 25 °C to 5 °C at a rate of 3 °C / min; after phase separation, the film thickness shrinks to 80 μm; (3) Perform CO2 supercritical drying on the cast film to obtain the main body membrane; supercritical drying conditions: 20 MPa, 40 °C, 4 h; (4) Spray a PET chloroform solution added with template agent P123 on the surface of the main body membrane. The concentration of PET is 5 wt%, and the concentration of P123 is 1.5 wt%; after evaporating the solvent at 60 °C, a nano-porous layer with a thickness of 3 μm and a pore diameter <20 nm is formed on the surface of the main body membrane to obtain a PET support with hierarchical pores, and its SEM image is as shown in Figure 1 shown; (5) The composite electrolyte and LiTFSI are dispersed in the ionic liquid [EMIM][TFSI] to obtain an electrolyte slurry; the composite electrolyte includes PEO (molecular weight 600k) and LLZO nanowires (diameter 30nm, aspect ratio > 50); the mass ratio of PEO, LLZO nanowires and LiTFSI is 4:5:1, and the mass fraction of the ionic liquid in the electrolyte slurry is 75%; (6) The electrolyte slurry is vacuum-injected into the PET support and thermally cured at 80 °C for 2 h; the pressure of the vacuum infiltration device is -0.1 MPa, and the cycle of pumping and releasing is carried out 3 times; (7) Hydroxyethyl methacrylate is added to the electrolyte slurry to obtain a composite slurry. In the composite slurry, the mass concentration of hydroxyethyl methacrylate is 30%; then the composite slurry is spin-coated on the surface of the PET support, and the spin-coating parameters are: 2000 rpm × 30 s, and the film-forming thickness is 5 μm; and ultraviolet curing is carried out, and the ultraviolet light intensity is 10 mW / cm 2 , and the ultraviolet curing time is 10 min; (8) Al2O3 and graphene (mass ratio 2:1) are magnetron sputtered on the surface of the PET support, the sputtering thickness is 50 nm, the Ar gas pressure during sputtering is 1.5 Pa, and the power is 150 W to obtain the composite electrolyte membrane.

[0032] Example 2: A preparation method of a composite electrolyte membrane for a solid-state battery, the steps are as follows: (1) PET (intrinsic viscosity 0.9 dL / g, glass transition temperature Tg = 75 °C) and the nucleating agent nano-SiO2 are added to the mixed solvent of HFIP and water and dispersed evenly to obtain a film-forming solution. In the obtained film-forming solution, the mass concentration of HFIP is 70%, the mass concentration of water is 15%, the mass concentration of the nucleating agent is 0.5%, and the balance is PET; (2) The film-forming solution is cast into a film and undergoes phase separation in a coagulation bath; the casting temperature is 25 °C, the wet film thickness is 100 μm, the coagulation bath medium is methanol, and it is linearly cooled from 25 °C to 5 °C at a rate of 5 °C / min; after phase separation, the film thickness shrinks to 50 μm; (3) The cast film is subjected to CO2 supercritical drying to obtain a main body film; the supercritical drying conditions are: 20 MPa, 40 °C, 4 h; (4) A PET chloroform solution added with the template agent P123 is sprayed on the surface of the main body film, the concentration of PET is 5 wt%, and the concentration of P123 is 1.5 wt%; after evaporating the solvent at 60 °C, a nano-porous layer with a thickness of 2 μm and a pore diameter < 20 nm is formed on the surface of the main body film to obtain a PET support with hierarchical pores; (5) The composite electrolyte and LiTFSI are dispersed in the ionic liquid [EMIM][TFSI] to obtain an electrolyte slurry; the composite electrolyte includes PEO (molecular weight 600k) and LLZO nanowires (diameter 30nm, aspect ratio >50); the mass ratio of PEO, LLZO nanowires and LiTFSI is 4:5:1, and the mass fraction of the ionic liquid in the electrolyte slurry is 75%; (6) The electrolyte slurry is vacuum infused into a PET support and thermally cured at 80°C for 2h; the pressure of the vacuum infiltration device is -0.1MPa, and the cycle of pumping and releasing is carried out 3 times; (7) Hydroxyethyl methacrylate is added to the electrolyte slurry to obtain a composite slurry. In the composite slurry, the mass concentration of hydroxyethyl methacrylate is 20%; then the composite slurry is spin-coated on the surface of the PET support, and the spin-coating parameters are: 2000 rpm × 30s, and the film-forming thickness is 5μm; and ultraviolet curing is carried out, and the ultraviolet light intensity is 10mW / cm 2 , and the ultraviolet curing time is 5min; (8) Al2O3 and graphene (mass ratio 2:1) are magnetron sputtered on the surface of the PET support, the sputtering thickness is 50nm, the Ar gas pressure during sputtering is 1.5Pa, and the power is 150W to obtain the composite electrolyte membrane.

[0033] Example 3: A method for preparing a composite electrolyte membrane for a solid-state battery, the steps are as follows: (1) PET (intrinsic viscosity 0.9 dL / g, glass transition temperature Tg = 75°C) and the nucleating agent nano-SiO2 are added to a mixed solvent of HFIP and water and dispersed evenly to obtain a film-forming solution. In the obtained film-forming solution, the mass concentration of HFIP is 80%, the mass concentration of water is 5%, the mass concentration of the nucleating agent is 0.5%, and the balance is PET; (2) The film-forming solution is cast into a film and phase separation is carried out in a coagulation bath; the casting temperature is 25°C, the wet film thickness is 300μm, the coagulation bath medium is methanol, and the temperature is linearly decreased from 25°C to 5°C at a rate of 3°C / min; after phase separation, the film thickness shrinks to 80μm; (3) The cast film is subjected to CO2 supercritical drying to obtain a main body film; the supercritical drying conditions are: 20 MPa, 40°C, 4h; (4) A PET chloroform solution added with the template agent P123 is sprayed on the surface of the main body film. The concentration of PET is 5wt%, and the concentration of P123 is 1.5wt%; after evaporating the solvent at 60°C, a nano-porous layer with a thickness of 4μm and a pore diameter <20nm is formed on the surface of the main body film to obtain a PET support with hierarchical pores; (5) The composite electrolyte, LiTFSI, and LiBOB (the mass of LiBOB is 5% of that of LiTFSI) are dispersed in the ionic liquid [EMIM][TFSI] to obtain an electrolyte slurry; the composite electrolyte includes PEO (molecular weight 600k) and LLZO nanowires (diameter 30nm, aspect ratio > 50); the mass ratio of PEO and LLZO nanowires to the total mass of LiTFSI and LiBOB is 4:5:1, and the mass fraction of the ionic liquid in the electrolyte slurry is 75%; (6) The electrolyte slurry is vacuum-injected into a PET support and thermally cured at 80 °C for 2 h; the pressure of the vacuum infiltration device is -0.1 MPa, and the cycle of pumping and releasing is carried out 3 times; (7) Hydroxyethyl methacrylate is added to the electrolyte slurry to obtain a composite slurry. In the composite slurry, the mass concentration of hydroxyethyl methacrylate is 40%; then the composite slurry is spin-coated on the surface of the PET support. Spin-coating parameters: 2000 rpm × 30 s, film-forming thickness 5 μm; and ultraviolet curing is carried out, ultraviolet light intensity 10 mW / cm 2 , ultraviolet curing time 10 min; (8) Al2O3 and graphene (mass ratio 2:1) are magnetron sputtered on the surface of the PET support, the sputtering thickness is 50 nm, the Ar gas pressure during sputtering is 1.5 Pa, and the power is 150 W to obtain the composite electrolyte membrane.

[0034] Comparative Example 1 (without supercritical drying): The difference between Comparative Example 1 and Example 1 is that in step (3), the cast film is dried at 40 °C for 4 h without CO2 supercritical drying, and the remaining steps are the same as those in Example 1.

[0035] Comparative Example 2 (without setting the nano-porous layer): The difference between Comparative Example 2 and Example 1 is that in step (4), the PET chloroform solution added with the template agent P123 is not sprayed on the surface of the main film, and the remaining steps are the same as those in Example 1.

[0036] Comparative Example 3 (without vacuum injection): The difference between Comparative Example 3 and Example 1 is that in step (6), the electrolyte slurry is not vacuum-injected, and the electrolyte slurry is directly spin-coated on the surface of the PET support, and the remaining steps are the same as those in Example 1.

[0037] Comparative Example 4 (without secondary spin-coating): The difference between Comparative Example 4 and Example 1 is that in step (7), after vacuum injection, the electrolyte slurry is not spin-coated, and the remaining steps are the same as those in Example 1.

[0038] Comparative Example 5 (without sputtering the Al2O3 and graphene transition layer): The difference between Comparative Example 5 and Example 1 is that in step (8), Al2O3 and graphene are not sputtered on the surface of the PET support, and the rest are the same as in Example 1.

[0039] Comparative Example 6 (without cross-linking through acrylic monomers): The difference between Comparative Example 6 and Example 1 is that in step (6), 2-hydroxyethyl methacrylate is not added to the electrolyte slurry, and the electrolyte slurry is directly spin-coated, and the rest are the same as in Example 1.

[0040] The properties of the PET supports and composite electrolyte membranes obtained in the above examples and comparative examples were tested, and the results are shown in Table 1.

[0041] Table 1: Test Results of Composite Electrolyte Membrane Properties

[0042] The composite electrolyte membranes prepared in the above examples and comparative examples were assembled into solid-state batteries, and their initial discharge capacity retention rate and cycling performance were tested, and the results are shown in Table 2. In the solid-state battery, the positive electrode is LiFePO4 (LFP); the negative electrode is a lithium metal sheet (thickness 50 μm).

[0043] Among them, the test method for the initial discharge capacity retention rate is: at 25 °C, a constant current discharge is carried out at a current of 0.2C until the cut-off voltage, and the actual discharge capacity is recorded. The ratio of the actual discharge capacity to the rated capacity is the initial discharge capacity retention rate. The test method for the cycling performance is: at 25 °C, charge and discharge cycles are carried out at a fixed rate of 0.2C, and the capacity retention rate after 200 cycles is calculated (i.e., the ratio of the capacity of the 200th cycle to the initial capacity).

[0044] Table 2: Test Results of Solid-State Battery Properties

[0045] As can be seen from the results of Table 1 and Table 2, the PET supports prepared by the method of the present invention in Examples 1 to 3 have both high porosity, through-hole rate and tensile strength, and the obtained composite electrolyte membrane has high ionic conductivity and low interfacial resistance. In Comparative Example 1, the cast film prepared by the SIPS process was not subjected to supercritical drying, resulting in a decrease in the porosity and through-hole rate of the PET support, thereby reducing the ionic conductivity of the composite electrolyte membrane and ultimately leading to a decrease in the rate performance and cycling performance of the solid-state battery. In Comparative Example 2, a nano-porous layer was not provided on the surface of the PET support, and the addition of the template agent P123 was lacking, resulting in a disordered pore size distribution and a decrease in the through-hole rate of the PET support, and an increase in the interfacial resistance of the composite electrolyte membrane, thereby reducing the rate performance and cycling performance of the solid-state battery. In Comparative Examples 3 and 4, gradient filling was not carried out, and only vacuum perfusion or spin coating was carried out, and the distribution of LLZO in the composite electrolyte membrane was uneven and the interfacial bonding force was poor, resulting in a decrease in the conductivity and cycle life of the solid-state battery. In Comparative Example 5, the Al2O3 and graphene transition layer was not sputtered, resulting in a decrease in the interfacial stability of the composite electrolyte membrane, thereby reducing the cycling performance of the solid-state battery. In Comparative Example 6, the PET surface and the composite electrolyte were not crosslinked by acrylate monomers, and the film layer was prone to cracking, resulting in a decrease in the mechanical properties of the composite electrolyte membrane, a decrease in the cycling performance of the solid-state battery, and a reduction in the assembly yield.

[0046] The above-described embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent shall be subject to the appended claims.

Claims

1. A method for preparing a composite electrolyte membrane for a solid-state battery, characterized in that the steps Comprising: (1) Adding PET and a nucleating agent into a mixed solvent of HFIP and water, dispersing them evenly to obtain a film-forming solution, casting the solution into a film and solidifying it; (2) Performing CO2 supercritical drying on the cast film to obtain a main body film; (3) Spraying a PET chloroform solution added with a template agent on the surface of the main body film, and obtaining a PET support with hierarchical pores after evaporating the solvent; (4) Dispersing a composite electrolyte and a lithium salt in an ionic liquid to obtain an electrolyte slurry; (5) Vacuum-injecting the electrolyte slurry into the PET support and curing it; (6) Adding an acrylic monomer to the electrolyte slurry to obtain a composite slurry, spin-coating the composite slurry on the surface of the PET support, and curing it by ultraviolet light; (7) Sputtering Al2O3 and graphene on the surface of the PET support.

2. The preparation method of the composite electrolyte membrane for a solid-state battery according to claim 1, characterized in that, In step (1), the intrinsic viscosity of the PET is 0.8 - 1.0 dL / g, and the glass transition temperature is 70 - 80 °C; the nucleating agent is nano-SiO2; in the obtained film-forming solution, the mass concentration of HFIP is 70 - 80%, the mass concentration of water is 5 - 15%, the mass concentration of the nucleating agent is 0.1 - 1%, and the balance is PET; The casting temperature during film casting is 25 ± 0.5 °C, and the thickness of the wet film obtained by casting is 250 - 350 μm; the wet film is solidified in a coagulation bath, the medium of the coagulation bath is methanol, and the temperature is decreased from room temperature to below 5 °C at a rate of 1 - 5 °C / min in the coagulation bath.

3. The preparation method of the composite electrolyte membrane for a solid-state battery according to claim 1, characterized in that, The conditions for CO2 supercritical drying in step (2) are: 15 - 25 MPa, 35 - 45 °C, 3 - 5 h.

4. The preparation method of the composite electrolyte membrane for a solid-state battery according to claim 1, characterized in that, In the PET chloroform solution added with a template agent in step (3), the mass concentration of PET is 3 - 7%, the mass concentration of the template agent is 1 - 2%, and the template agent is P123; the spraying thickness is 1 - 5 μm.

5. The preparation method of the composite electrolyte membrane for a solid-state battery according to claim 1, characterized in that, In step (4), the composite electrolyte includes polyethylene oxide and lithium lanthanum zirconium oxide, and the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(oxalato)borate; the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; in the electrolyte slurry, the mass ratio of polyethylene oxide, lithium lanthanum zirconium oxide and the lithium salt is 35 - 45:45 - 55:10; the mass fraction of the ionic liquid in the electrolyte slurry is 70 - 80%.

6. The preparation method of the composite electrolyte membrane for a solid-state battery according to claim 1, wherein In step (5), the vacuum pressure during vacuum injection is ≤ -0.08 MPa, and the cycle of pumping and releasing is 2 - 3 times; the curing conditions are: thermal curing at 75 - 85 °C for 1 - 3 h.

7. The method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1 or 6, characterized in that, The acrylic monomer described in step (6) is hydroxyethyl methacrylate. In the composite slurry, the mass concentration of the acrylic monomer is 20-40%; the spin coating speed in step (6) is 1500-2500 rpm, the spin coating time is 25-35 s, and the film forming thickness is 4-6 μm; the ultraviolet light intensity during ultraviolet curing is 5-15 mW / cm 2 , and the ultraviolet curing time is 5-15 min.

8. The method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1, wherein In step (7), the mass ratio of sputtered Al2O3 to graphene is 1 - 3:1, and the sputtering thickness is 30 - 80 nm.

9. A composite electrolyte membrane for a solid-state battery prepared by the preparation method according to any one of claims 1 to 8, characterized in that, Comprising a PET support and a composite electrolyte filled in the voids of the PET support; the PET support includes a main body film and a nano-microporous layer on the surface of the main body film, and through main pores with a pore diameter of 50 - 200 nm are provided in the main body film, and micropores with a pore diameter < 20 nm are provided in the nano-microporous layer.

10. The composite electrolyte membrane for a solid-state battery according to claim 9, characterized in that, The porosity of the PET support is ≥ 80%.

Images