A composite electrolyte membrane for solid-state batteries and a preparation method thereof

Abstract

The present invention relates to the field of solid-state battery electrolyte membranes and discloses a composite electrolyte membrane for solid-state batteries and its preparation method. A PET support with a multi-level pore structure is first prepared through SIPS coupled with supercritical drying. The composite electrolyte is then filled into the pores of the PET support through a gradient filling process using vacuum infusion-spin coating. Finally, a transition layer of Al2O3 and graphene is sputtered to strengthen the lithium metal interface. Through simultaneous optimization of material screening, process innovation, and structural design, the present invention achieves a PET base membrane with both high penetration rate and tensile strength. Furthermore, through step-by-step filling and interfacial cross-linking techniques, the interfacial compatibility problem between a rigid inorganic electrolyte and a flexible polymer matrix is ​​addressed, significantly improving the ionic conductivity of the electrolyte membrane, reducing interfacial resistance, and enhancing the rate capability and cycle performance of solid-state batteries.

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 considered the core of the next generation of energy storage technology due to their high safety and theoretical energy density, but their electrolyte / electrode interface compatibility and ion transfer efficiency are still difficulties in industrialization. At present, inorganic solid electrolytes (such as lithium lanthanum zirconium oxide (LLZO), lithium aluminum titanium phosphate (LATP), and sulfide systems) have received great attention, but they are brittle and easily break when the thickness is less than 100μm, and cannot suppress the penetration of lithium dendrites; the interface impedance is high, and the rigid interface is difficult to adapt to the volume change during the charge and discharge process. In addition, polymer electrolytes (such as polyethylene oxide (PEO) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)) have also been widely studied, but they have insufficient mechanical strength, and the room temperature tensile strength is generally less than 10MPa. Lithium dendrites can easily penetrate and cause short circuits; the room temperature ionic conductivity is low, and the σ of pure PEO-based electrolytes is <1×10 -4 S / cm, and needs to be heated to above 60°C for practical use.

[0003] In order to balance mechanical strength and ion transmission performance, the industry currently generally adopts a composite structure of "porous support + electrolyte filling". However, the existing technology generally has problems such as insufficient pore structure of the support, single pore size, and low pore penetration rate, making it difficult to balance electrolyte wettability and mechanical strength. For example, patent CN113571764B discloses a composite solid electrolyte membrane and its preparation method. First, SNE with high ionic conductivity is infiltrated and filled into porous silica (SiO2) ceramic particles with high porosity, and then the particles are compounded with a polymer electrolyte to obtain the result. However, porous SiO2 ceramics are brittle materials, which causes the electrolyte membrane to crack after bending, and the cost is more than 10 times that of a polymer membrane. Summary of the Invention

[0004] The present invention aims to overcome the above-mentioned 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 simultaneous optimization of material screening, process innovation and structural design, the "traitorous increase and decrease" contradiction between porosity and mechanical strength in the traditional phase separation method is broken through. Through solvent system optimization and supercritical drying technology, a PET base membrane with high permeability (≥89%) and tensile strength (≥45MPa) is obtained; at the same time, step-by-step filling and interface cross-linking technology are developed to solve the interface compatibility problem between rigid inorganic electrolytes and flexible polymer matrices.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a composite electrolyte membrane for a solid-state battery, comprising the following steps:

[0007] (1) PET and a nucleating agent are added to a mixed solvent of hexafluoroisopropanol (HFIP) and water and dispersed uniformly to obtain a film-forming liquid, which is then cast into a film and solidified;

[0008] (2) drying the cast film with supercritical CO2 to obtain a main film;

[0009] (3) Spraying a PET chloroform solution with a template agent on the surface of the main membrane, and evaporating the solvent to obtain a PET support with multi-level pores;

[0010] (4) dispersing the composite electrolyte and lithium salt in an ionic liquid to obtain an electrolyte slurry;

[0011] (5) Vacuum-infusing the electrolyte slurry into the PET support and curing it;

[0012] (6) adding acrylic acid monomer to the electrolyte slurry to obtain a composite slurry, spin-coating the composite slurry on the surface of the PET support, and UV curing the composite slurry;

[0013] (7) Sputter Al2O3 and graphene onto the surface of the PET support.

[0014] The present invention adopts hexafluoroisopropanol (HFIP) as the main solvent and water as the phase separation inducer in step (1), and prepares a cast membrane with a double continuous pore structure based on solvent-induced phase separation (SIPS) under the accelerating action of a nucleating agent, and then combines CO2 supercritical drying to eliminate the pore collapse caused by capillary force, which can break the "one increases while the other decreases" contradiction between porosity and mechanical strength in the traditional phase separation method, and obtain a PET main membrane with both high permeability (≥89%) and tensile strength (≥45MPa); then, through step (3), a PET chloroform solution with a template agent added is sprayed on the surface of the main membrane, and the solvent evaporation can form a nano-microporous layer with a pore size of less than 20nm on the surface of the main membrane, further improving the porosity, and obtaining a PET support with a multi-level pore structure, which can significantly improve the ion transmission efficiency of the electrolyte membrane. The present invention then uses a gradient filling process, first performing a primary vacuum infusion process, followed by a secondary spin coating process, to fill the composite electrolyte into the pores of the PET support. The vacuum-spin coating gradient composite can eliminate interface defects, achieve complete penetration of nanoscale pores, and reduce interface impedance. At the same time, ultraviolet light curing can stimulate the grafting of acrylic monomers on the PET surface, bonding the composite electrolyte to the PET pore walls through an acrylic cross-linking layer. Through step-by-step filling and interfacial cross-linking technology, the interface compatibility problem between the rigid inorganic electrolyte and the flexible polymer matrix is ​​solved. Finally, the present invention sputters Al2O3 and graphene transition layers on the surface of the PET support. The graphene sheets are arranged perpendicular to the electrodes, inhibiting the lateral growth of lithium dendrites. The synergistic effect of the sputtering filter layer and the densified filling can significantly improve the cycle life of the battery.

[0015] Preferably, the intrinsic viscosity of the PET 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; and the obtained film-forming solution has a mass concentration of HFIP of 70-80%, a mass concentration of water of 5-15%, a mass concentration of the nucleating agent of 0.1-1%, and the balance being PET;

[0016] The casting temperature during film formation was 25±0.5°C, and the resulting wet film thickness ranged from 250 to 350μm. The wet film solidified in a methanol coagulation bath, where the temperature was cooled from room temperature to below 5°C at a rate of 1-5°C / min. Using methanol as the coagulation bath medium rapidly displaced HFIP, inducing pore penetration. Simultaneously, a linear cooling rate of 1-5°C / min was used to prolong the separation time of the bicontinuous phase and ensure high porosity.

[0017] Preferably, the conditions for CO2 supercritical drying in step (2) are: 15-25 MPa, 35-45°C, 3-5 h.

[0018] Preferably, in the PET chloroform solution to which the template is added in step (3), the mass concentration of PET is 3-7%, the mass concentration of the template is 1-2%, and the template is P123; the spraying thickness is 1-5 μm.

[0019] Preferably, the composite electrolyte in step (4) comprises polyethylene oxide (PEO) and lithium lanthanum zirconium oxide (LLZO), the lithium salt is lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and / or lithium bis(oxalatoborate) (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; and the mass fraction of the ionic liquid in the electrolyte slurry is 70-80%.

[0020] Preferably, the vacuum pressure during vacuum infusion in step (5) is ≤-0.08 MPa, and the vacuum is circulated and released 2 to 3 times; the curing conditions are: thermal curing at 75 to 85°C for 1 to 3 hours.

[0021] Preferably, the acrylic monomer in step (6) is hydroxyethyl methacrylate (HEMA), and the mass concentration of the acrylic monomer in the composite slurry 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 thickness is 4-6 μm; the UV intensity during UV curing is 5-15 mW / cm 2 , UV curing time 5~15min.

[0022] Preferably, the mass ratio of sputtered Al2O3 to graphene in step (7) is 1-3:1, and the sputtered thickness is 30-80 nm.

[0023] The present invention also provides a composite electrolyte membrane for solid-state batteries prepared by the above-mentioned preparation method, comprising a PET support and a composite electrolyte filled in the gaps of the PET support; the PET support comprises a main membrane and a nanoporous layer on the surface of the main membrane, the main membrane is provided with through main pores with a pore size of 50 to 200 nm, and the nanoporous layer is provided with micropores with a pore size of less than 20 nm.

[0024] Preferably, the porosity of the PET support is ≥80%.

[0025] Therefore, the present invention has the following beneficial effects:

[0026] (1) Through the "dual engine" strategy of SIPS coupled with supercritical drying, the traditional contradictory relationship between porosity and strength is broken through, and a PET main membrane with both high penetration rate and tensile strength is obtained. A nanoporous layer is then set on it to obtain a PET support with a multi-level pore structure;

[0027] (2) The composite electrolyte is filled with a gradient filling process of vacuum-spin coating, which can eliminate interface defects and achieve complete penetration of nano-scale pores; combining the high-porosity PET support and the composite electrolyte gradient filling process can significantly improve the ion transfer efficiency of the electrolyte membrane, reduce the electrode-electrolyte contact resistance, and improve the rate performance of the whole battery;

[0028] (3) Through the combination of in-situ polymerization and transition layer design, the ion transmission and dendrite suppression capabilities can be improved simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 1 is a SEM image of the PET support prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments.

[0031] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0032] Overall embodiment:

[0033] A method for preparing a composite electrolyte membrane for a solid-state battery, comprising the following steps:

[0034] (1) PET and a nucleating agent are added to a mixed solvent of HFIP and water and dispersed evenly to obtain a film-forming liquid, which is then cast into a film and solidified;

[0035] (2) drying the cast film with supercritical CO2 to obtain a main film;

[0036] (3) Spraying a PET chloroform solution with a template agent on the surface of the main membrane, and evaporating the solvent to obtain a PET support with multi-level pores;

[0037] (4) dispersing the composite electrolyte and lithium salt in an ionic liquid to obtain an electrolyte slurry;

[0038] (5) Vacuum-infusing the electrolyte slurry into the PET support and curing it;

[0039] (6) adding acrylic acid monomer to the electrolyte slurry to obtain a composite slurry, spin-coating the composite slurry on the surface of the PET support, and UV curing the composite slurry;

[0040] (7) Sputter Al2O3 and graphene onto the surface of the PET support.

[0041] 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 liquid, 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.

[0042] As a specific embodiment, the casting temperature during the film casting in step (1) is 25±0.5°C, and the thickness of the wet film obtained by casting is 250~350μm; the wet film is solidified in a coagulation bath, the coagulation bath medium is methanol, and the temperature in the coagulation bath is cooled from room temperature to below 5°C at a rate of 1~5°C / min.

[0043] As a specific embodiment, the conditions for CO2 supercritical drying in step (2) are: 15~25MPa, 35~45℃, 3~5h.

[0044] As a specific embodiment, in the PET chloroform solution to which the template agent is added 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.

[0045] As a specific embodiment, the composite electrolyte described in step (4) includes PEO and LLZO, 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; and the mass fraction of the ionic liquid in the electrolyte slurry is 70~80%.

[0046] As a specific implementation method, the vacuum pressure during vacuum infusion in step (5) is ≤-0.08 MPa, and the vacuum is circulated and released 2 to 3 times; the curing conditions are: thermal curing at 75 to 85°C for 1 to 3 hours.

[0047] As a specific embodiment, the acrylic monomer described in step (6) is hydroxyethyl methacrylate, and the mass concentration of the acrylic monomer in the composite slurry 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 thickness is 4-6 μm; the UV intensity during UV curing is 5-15 mW / cm 2 , UV curing time 5~15min.

[0048] As a specific embodiment, the mass ratio of sputtered Al2O3 to graphene in step (7) is 1~3:1, and the sputtering thickness is 30~80nm.

[0049] As a specific embodiment, the composite electrolyte membrane for solid-state batteries prepared by the above-mentioned preparation method includes a PET support and a composite electrolyte filled in the gaps of the PET support; the PET support includes a main membrane and a nanoporous layer on the surface of the main membrane, the main membrane is provided with through main pores with a pore size of 50~200nm, and the nanoporous layer is provided with micropores with a pore size of less than 20nm.

[0050] As a specific embodiment, the porosity of the PET support is ≥80%.

[0051] Example 1:

[0052] A method for preparing a composite electrolyte membrane for a solid-state battery, comprising the following steps:

[0053] (1) PET (intrinsic viscosity 0.9 dL / g, glass transition temperature Tg = 75°C) and nano-SiO2 as a nucleating agent were added to a mixed solvent of HFIP and water and dispersed uniformly to obtain a film-forming solution. The obtained film-forming solution had a mass concentration of HFIP of 75%, a mass concentration of water of 10%, a mass concentration of the nucleating agent of 0.5%, and the balance of PET.

[0054] (2) The film-forming liquid was cast into a film and phase separated in a coagulation bath; the casting temperature was 25°C, the wet film thickness was 300 μm, the coagulation bath medium was methanol, and the temperature was linearly decreased from 25°C to 5°C at a rate of 3°C / min; after phase separation, the film thickness shrank to 80 μm;

[0055] (3) The cast film is subjected to CO2 supercritical drying to obtain the main film; supercritical drying conditions: 20 MPa, 40 ° C, 4 h;

[0056] (4) Spraying a PET chloroform solution with template P123 added on the surface of the main membrane, the concentration of PET is 5wt%, and the concentration of P123 is 1.5wt%. After evaporating the solvent at 60°C, a nanoporous layer with a thickness of 3μm and a pore size of <20nm is formed on the surface of the main membrane, and a PET support with multi-level pores is obtained, as shown in the SEM image. Figure 1 As shown in;

[0057] (5) Dispersing the composite electrolyte and LiTFSI 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%;

[0058] (6) The electrolyte slurry was vacuum-infused into the PET support and thermally cured at 80°C for 2 h. The pressure of the vacuum infiltration device was -0.1 MPa, and the vacuum was evacuated and released three times.

[0059] (7) Add hydroxyethyl methacrylate to the electrolyte slurry to obtain a composite slurry, wherein the mass concentration of hydroxyethyl methacrylate in the composite slurry is 30%; the composite slurry is then spin-coated on the surface of the PET support, with the spin-coating parameters of 2000 rpm×30s and a film thickness of 5 μm; and UV curing is performed with an UV light intensity of 10 mW / cm 2 , UV curing time 10min;

[0060] (8) Al2O3 and graphene (mass ratio 2:1) were magnetron sputtered onto the surface of a PET support with a sputtering thickness of 50 nm, an Ar gas pressure of 1.5 Pa, and a power of 150 W to obtain the composite electrolyte membrane.

[0061] Example 2:

[0062] A method for preparing a composite electrolyte membrane for a solid-state battery, comprising the following steps:

[0063] (1) PET (intrinsic viscosity 0.9 dL / g, glass transition temperature Tg = 75°C) and nano-SiO2 as a nucleating agent were added to a mixed solvent of HFIP and water and dispersed uniformly to obtain a film-forming solution. The obtained film-forming solution had a mass concentration of HFIP of 70%, a mass concentration of water of 15%, a mass concentration of the nucleating agent of 0.5%, and the balance of PET.

[0064] (2) The film-forming liquid was cast into a film and phase-separated in a coagulation bath; the casting temperature was 25°C, the wet film thickness was 100 μm, the coagulation bath medium was methanol, and the temperature was linearly decreased from 25°C to 5°C at a rate of 5°C / min; after phase separation, the film thickness shrank to 50 μm;

[0065] (3) The cast film is subjected to CO2 supercritical drying to obtain the main film; supercritical drying conditions: 20 MPa, 40 ° C, 4 h;

[0066] (4) Spraying a PET chloroform solution with a template agent P123 on the surface of the main membrane, wherein the concentration of PET is 5 wt% and the concentration of P123 is 1.5 wt%. After evaporating the solvent at 60 °C, a nanoporous layer with a thickness of 2 μm and a pore size of <20 nm is formed on the surface of the main membrane, thereby obtaining a PET support with multi-level pores.

[0067] (5) Dispersing the composite electrolyte and LiTFSI 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%;

[0068] (6) The electrolyte slurry was vacuum-infused into the PET support and thermally cured at 80°C for 2 h. The pressure of the vacuum infiltration device was -0.1 MPa, and the vacuum was evacuated and released three times.

[0069] (7) Add hydroxyethyl methacrylate to the electrolyte slurry to obtain a composite slurry. The mass concentration of hydroxyethyl methacrylate in the composite slurry is 20%. The composite slurry is then spin-coated on the surface of the PET support. The spin-coating parameters are: 2000 rpm×30s, and the film thickness is 5μm. The composite slurry is then UV-cured with an UV light intensity of 10mW / cm 2 , UV curing time 5min;

[0070] (8) Al2O3 and graphene (mass ratio 2:1) were magnetron sputtered onto the surface of a PET support with a sputtering thickness of 50 nm, an Ar gas pressure of 1.5 Pa, and a power of 150 W to obtain the composite electrolyte membrane.

[0071] Example 3:

[0072] A method for preparing a composite electrolyte membrane for a solid-state battery, comprising the following steps:

[0073] (1) PET (intrinsic viscosity 0.9 dL / g, glass transition temperature Tg = 75°C) and nano-SiO2 as a nucleating agent were added to a mixed solvent of HFIP and water and dispersed uniformly to obtain a film-forming solution. The obtained film-forming solution had a mass concentration of HFIP of 80%, a mass concentration of water of 5%, a mass concentration of the nucleating agent of 0.5%, and the balance of PET.

[0074] (2) The film-forming liquid was cast into a film and phase separated in a coagulation bath; the casting temperature was 25°C, the wet film thickness was 300 μm, the coagulation bath medium was methanol, and the temperature was linearly decreased from 25°C to 5°C at a rate of 3°C / min; after phase separation, the film thickness shrank to 80 μm;

[0075] (3) The cast film is subjected to CO2 supercritical drying to obtain the main film; supercritical drying conditions: 20 MPa, 40 ° C, 4 h;

[0076] (4) Spraying a PET chloroform solution with a template agent P123 on the surface of the main membrane, wherein the concentration of PET is 5 wt% and the concentration of P123 is 1.5 wt%. After evaporating the solvent at 60 °C, a nanoporous layer with a thickness of 4 μm and a pore size of <20 nm is formed on the surface of the main membrane, thereby obtaining a PET support with multi-level pores.

[0077] (5) The composite electrolyte and LiTFSI and LiBOB (the mass of LiBOB is 5% 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%;

[0078] (6) The electrolyte slurry was vacuum-infused into the PET support and thermally cured at 80°C for 2 h. The pressure of the vacuum infiltration device was -0.1 MPa, and the vacuum was evacuated and released three times.

[0079] (7) Adding hydroxyethyl methacrylate to the electrolyte slurry to obtain a composite slurry, wherein the mass concentration of hydroxyethyl methacrylate in the composite slurry is 40%; the composite slurry is then spin-coated on the surface of the PET support, with the spin-coating parameters of 2000 rpm×30s and a film thickness of 5 μm; and UV curing is performed with an UV light intensity of 10 mW / cm 2 , UV curing time 10min;

[0080] (8) Al2O3 and graphene (mass ratio 2:1) were magnetron sputtered onto the surface of a PET support with a sputtering thickness of 50 nm, an Ar gas pressure of 1.5 Pa, and a power of 150 W to obtain the composite electrolyte membrane.

[0081] Comparative Example 1 (without supercritical drying):

[0082] 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 in Example 1.

[0083] Comparative Example 2 (no nanoporous layer):

[0084] The difference between Comparative Example 2 and Example 1 is that in step (4), the PET chloroform solution with template P123 added is not sprayed on the surface of the main film, and the remaining steps are the same as in Example 1.

[0085] Comparative Example 3 (without vacuum perfusion):

[0086] The difference between Comparative Example 3 and Example 1 is that in step (6), the electrolyte slurry is not vacuum-infused, but directly spin-coated on the surface of the PET support. The remaining steps are the same as those in Example 1.

[0087] Comparative Example 4 (no secondary spin coating):

[0088] The difference between Comparative Example 4 and Example 1 is that the electrolyte slurry is not spin-coated after vacuum infusion in step (7), and the remaining steps are the same as those in Example 1.

[0089] Comparative Example 5 (no sputtering of Al2O3 and graphene transition layer):

[0090] 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.

[0091] Comparative Example 6 (crosslinking without acrylic acid monomer):

[0092] The difference between Comparative Example 6 and Example 1 is that in step (6), hydroxyethyl methacrylate is not added to the electrolyte slurry, and the electrolyte slurry is directly spin-coated. The rest is the same as in Example 1.

[0093] 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.

[0094] Table 1: Composite electrolyte membrane performance test results

[0095]

[0096] The composite electrolyte membranes prepared in the above examples and comparative examples were assembled into solid-state batteries, and their initial discharge capacity retention and cycle performance were tested. The results are shown in Table 2. In the solid-state battery, the positive electrode was LiFePO4 (LFP), and the negative electrode was a lithium metal sheet (50 μm thick).

[0097] The first discharge capacity retention rate is tested by discharging the battery at a constant current of 0.2C to the cutoff voltage at 25°C, recording the actual discharge capacity. The ratio of the actual discharge capacity to the rated capacity is the first discharge capacity retention rate. The cycling performance is tested by charging and discharging the battery at a fixed rate of 0.2C at 25°C, and calculating the capacity retention rate after 200 cycles (i.e., the ratio of the 200th cycle capacity to the initial capacity).

[0098] Table 2: Solid-state battery performance test results

[0099]

[0100] As can be seen from the results of Tables 1 and 2, the PET supports obtained by the method of the present invention in Examples 1 to 3 have high porosity, penetration rate and tensile strength, and the resulting composite electrolyte membrane has high ionic conductivity and low interface resistance. However, in Comparative Example 1, the cast film obtained by the SIPS process is not subjected to supercritical drying, resulting in a decrease in the porosity and penetration rate of the PET support, thereby decreasing the ionic conductivity of the composite electrolyte membrane, and ultimately causing the rate performance and cycle performance of the solid-state battery to decrease. In Comparative Example 2, a nanoporous layer is not provided on the surface of the PET support, and the addition of the template agent P123 is lacking, resulting in a disordered pore size distribution and a decrease in penetration rate of the PET support, and an increase in the interface resistance of the composite electrolyte membrane, thereby decreasing the rate performance and cycle performance of the solid-state battery. In Comparative Examples 3 and 4, gradient filling is not performed, and only vacuum infusion or spin coating is performed. The LLZO distribution of the composite electrolyte membrane is uneven and the interface bonding force is 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 reduced interfacial stability of the composite electrolyte membrane, which in turn reduced the cycling performance of the solid-state battery. In Comparative Example 6, the PET surface and the composite electrolyte were not cross-linked using an acrylate monomer. This caused the membrane layer to crack, resulting in reduced mechanical properties of the composite electrolyte membrane, reduced cycling performance of the solid-state battery, and a lower assembly yield.

[0101] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a composite electrolyte membrane for a solid-state battery, characterized in that the steps include: (1) PET and a nucleating agent are added to a mixed solvent of HFIP and water and dispersed evenly to obtain a film-forming liquid, which is then cast into a film and solidified; (2) drying the cast film with supercritical CO2 to obtain a main film; (3) Spraying a PET chloroform solution with a template agent on the surface of the main membrane, and evaporating the solvent to obtain a PET support with multi-level pores; (4) dispersing a composite electrolyte and a lithium salt in an ionic liquid to obtain an electrolyte slurry; the composite electrolyte comprises polyethylene oxide and lithium lanthanum zirconium oxide; (5) Vacuum-infusing the electrolyte slurry into the PET support and curing it; (6) adding acrylic acid monomer to the electrolyte slurry to obtain a composite slurry, spin-coating the composite slurry on the surface of the PET support, and UV curing the composite slurry; (7) Sputter Al2O3 and graphene onto the surface of the PET support.

2. The method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1, wherein: 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; the obtained film-forming solution has a mass concentration of HFIP of 70-80%, a mass concentration of water of 5-15%, a mass concentration of the nucleating agent of 0.1-1%, and the balance being PET; The casting temperature during film casting is 25±0.5°C, and the thickness of the wet film obtained by casting is 250~350μm; the wet film is solidified in a coagulation bath, the coagulation bath medium is methanol, and the temperature in the coagulation bath is cooled from room temperature to below 5°C at a rate of 1~5°C / min.

3. The method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1, wherein: The conditions for CO2 supercritical drying in step (2) are: 15~25MPa, 35~45℃, 3~5h.

4. The method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1, wherein: In the PET chloroform solution to which the template agent is added 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 method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1, wherein: The lithium salt described in step (4) is lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(oxalatoborate); 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 lithium salt is 35-45:45-55:10; and the mass fraction of the ionic liquid in the electrolyte slurry is 70-80%.

6. The method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1, wherein: The vacuum pressure during vacuum infusion in step (5) is ≤-0.08 MPa, and the vacuum is circulated and released 2 to 3 times; the curing conditions are: thermal curing at 75 to 85°C for 1 to 3 hours.

7. The method for preparing a composite electrolyte membrane for a solid-state battery according to claim 1 or 6, wherein: The acrylic monomer described in step (6) is hydroxyethyl methacrylate, and the mass concentration of the acrylic monomer in the composite slurry 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 thickness is 4-6 μm; the UV intensity during UV curing is 5-15 mW / cm 2 , UV curing time 5~15min.

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

9. A composite electrolyte membrane for solid-state batteries prepared by the preparation method according to any one of claims 1 to 8, characterized in that: It includes a PET support and a composite electrolyte filled in the gaps of the PET support; the PET support includes a main membrane and a nano-microporous layer on the surface of the main membrane, the main membrane is provided with through main pores with a pore size of 50-200nm, and the nano-microporous layer is provided with micropores with a pore size of less than 20nm.

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

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