Solid-state electrolyte-coated separator, method of preparation and use

Abstract

The application relates to the technical field of battery separators, and discloses a solid electrolyte-coated separator, a preparation method and application, which comprises a porous base material and a solid electrolyte coating layer arranged on the surface of the porous base material; the solid electrolyte coating layer is obtained by coating slurry 1 and slurry 2 on the surface of the porous base material in sequence and then in-situ polymerization; the slurry 1 comprises inorganic reinforcing fillers, a binder and an initiator in a mass ratio of 9:1:0.5-1.5; the ratio of the average particle size of the inorganic reinforcing fillers to the average pore size of the porous base material is 0.4-1.3; the inorganic reinforcing fillers are of a porous structure; and the slurry 2 comprises lithium salt and polymerization monomers. In the application, the polymer electrolyte not only exists on the surface of the separator but also penetrates into the internal pore network of the separator base material, and forms an organic-inorganic composite integrated separator system together with the inorganic reinforcing fillers, so that the separator system has good interface combination, thermal stability and high ionic conductivity.

Description

Technical Field

[0001] This invention relates to the technical field of battery separators, and in particular to a solid electrolyte coated separator, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and large-scale energy storage due to their high energy density and long cycle life. However, the organic liquid electrolytes used in traditional lithium-ion batteries have inherent defects such as flammability and leakage. Under extreme conditions such as overcharging, impact, or thermal runaway, they may cause fires or even explosions, highlighting increasingly prominent safety hazards. Developing highly safe electrolyte systems has become a key research direction in the lithium battery field.

[0003] Solid-state electrolytes are considered a core technological path to overcome the aforementioned safety bottlenecks and achieve high-energy-density lithium metal anode applications due to their combination of high safety (non-flammability, leak-proofness) and mechanical strength (resistance to lithium dendrite penetration). Among them, polymer-based solid-state electrolytes have attracted particular attention due to their advantages such as being lightweight, flexible, easy to process into films, and having good compatibility with electrode interfaces.

[0004] As a key component of lithium-ion batteries, the separator's performance directly affects the battery's safety and electrochemical performance. Currently, commercial lithium-ion batteries widely use polyolefin porous separators (such as polypropylene, polyethylene, and their composite membranes). While these separators possess good chemical stability, uniform pore structure, and low cost, their inherent defects are also quite prominent: First, polyolefin materials have low surface energy and weak polarity, resulting in poor wettability to liquid precursors and electrolytes, leading to uneven electrolyte filling and prolonged ion transport paths, which is detrimental to fully utilizing the battery's electrochemical performance. Second, polyolefin separators have insufficient thermal dimensional stability, making them prone to shrinkage and deformation at high temperatures, potentially causing internal short circuits or even thermal runaway, seriously threatening battery safety. More importantly, the interfacial compatibility between the polyolefin substrate and the inorganic coating is poor, easily leading to insufficient adhesion between the coating and the substrate, coating peeling, and cracking during the coating and lamination process, severely restricting the overall performance and long-term cycle reliability of the composite separator.

[0005] To address these shortcomings, researchers have attempted to coat the surface of polyolefin separators with inorganic ceramic layers (such as alumina and silicon dioxide) to improve the separator's heat resistance and electrolyte wettability. For example, patent CN121709865A discloses a separator, its preparation method, electrode assembly, and battery. By setting asymmetrical ceramic coatings on the positive and negative sides of the base membrane, the positive side coating has a higher binder content to enhance the bonding strength between the separator and the positive electrode sheet and suppress the risk of internal short circuits caused by positive side shrinkage at high temperatures. The negative side coating has a higher inorganic ceramic particle content to enhance puncture resistance and electrolyte retention. Patent CN121812888A discloses a composite separator and lithium-ion battery. By introducing positive temperature coefficient semiconductor particles into the separator coating, the characteristic of their resistance step increase during abnormal temperature rise is utilized to reduce short-circuit current and interfacial side reaction heat in advance, thereby suppressing the advance of thermal runaway. However, due to the lack of effective chemical bonding or physical anchoring between the polyolefin substrate and the inorganic coating, the interfacial adhesion between the coating and the substrate is weak. During long-term charge-discharge cycles, problems such as coating peeling and structural degradation are still difficult to avoid, ultimately leading to battery performance degradation or even failure. Furthermore, the aforementioned coating modification schemes only form a functional layer on the separator surface and cannot achieve the filling and modification of the internal pores of the separator substrate, limiting their application in solid-state or semi-solid-state battery fields. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a solid electrolyte coated diaphragm, its preparation method, and its application. A filler slurry containing an initiator and a slurry containing polymeric monomers are sequentially coated onto a diaphragm substrate. The porous structure of the filler encapsulates and slowly releases the initiator. In-situ directional polymerization induced by the diaphragm's slow release allows the polymer electrolyte to fill the diaphragm, constructing a continuous ion transport channel. This overcomes the problems of poor wettability and insufficient thermal stability of traditional polyolefin diaphragms, as well as the poor adhesion between the coating and the substrate in existing solid electrolyte coated diaphragms.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a solid electrolyte coated membrane, comprising a porous substrate and a solid electrolyte coating layer disposed on the surface of the porous substrate; the solid electrolyte coating layer is obtained by coating the surface of the porous substrate with slurry 1 and slurry 2 successively, followed by in-situ polymerization; slurry 1 comprises inorganic reinforcing filler, binder and initiator in a mass ratio of 9:1:0.5~1.5; the ratio of the average particle size of the inorganic reinforcing filler to the average pore size of the porous substrate is 0.4~1.3; the inorganic reinforcing filler has a porous structure; slurry 2 comprises lithium salt and polymer monomer.

[0008] Preferably, the ratio of the average particle size of the inorganic reinforcing filler to the average pore size of the porous substrate is 0.8 to 1.1.

[0009] Preferably, the particle size D10 of the inorganic reinforcing filler is less than the average pore size of the porous substrate, and the particle size D90 is greater than the average pore size of the porous substrate.

[0010] Preferably, the specific surface area of ​​the inorganic reinforcing filler is 100~1000 m². 2 / g, more preferably 100~500m 2 / g.

[0011] Preferably, the inorganic reinforcing filler includes one or more of alumina (γ-Al2O3), silica, boehmite, magnesium oxide, zirconium oxide, silicon nitride, and boron nitride.

[0012] Preferably, the solid electrolyte coating layer is obtained by coating a pre-coated diaphragm with slurry 2 and then polymerizing it in situ; the weight gain of the solid electrolyte coated diaphragm relative to the pre-coated diaphragm is 30-60%; the pre-coated diaphragm is obtained by coating a porous substrate with slurry 1 and then drying it; the weight gain of the pre-coated diaphragm relative to the porous substrate is 20-50%.

[0013] Preferably, the average pore size of the porous substrate is ≥100nm.

[0014] Preferably, the porous substrate is made of polyolefin, more preferably one or more of PP and PE.

[0015] Preferably, the concentration of lithium salt in the slurry 2 is 1~3M.

[0016] Preferably, the polymeric monomer includes one or more of 1,3-dioxolane (DOL) and tetrahydrofuran (THF).

[0017] Preferably, the initiator comprises one or more of aluminum trifluoromethanesulfonate (Al(OTf)3), aluminum trichloride (AlCl3), and triethyloxonium tetrafluoroborate (Et3OBF4). When the monomer is 1,3-dioxolane, the initiator is Al(OTf)3 or AlCl3; when the monomer is tetrahydrofuran or a mixture of 1,3-dioxolane and tetrahydrofuran, the initiator is Et3OBF4.

[0018] Preferably, the adhesive is one or more of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), and polymethyl methacrylate (PMMA).

[0019] Preferably, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0020] Secondly, the present invention provides a method for preparing a solid electrolyte coated membrane, comprising the following steps: S1. The porous substrate is subjected to plasma pretreatment; inorganic reinforcing filler, binder and initiator are added to solvent to obtain slurry 1; lithium salt and polymer monomer are mixed to obtain slurry 2; S2. The slurry 1 is coated onto the surface of the pretreated porous substrate by dip coating. After drying, a pre-coated diaphragm is obtained. S3. The slurry 2 is coated onto the surface of the pre-coated diaphragm by dip coating, and then in-situ polymerization is carried out to obtain a solid electrolyte coated diaphragm.

[0021] Preferably, the parameters for plasma pretreatment include: working gas is oxygen (O2), argon (Ar) or air, radio frequency power is 50~100W, gas pressure is 10~50Pa, and time is 1~5min.

[0022] A vacuum plasma treatment instrument was used to pretreat the surface of the polyolefin porous membrane with plasma to enhance interfacial compatibility.

[0023] Preferably, the solid content of the slurry 1 is 15-25%; the solvent is DMF or a mixture of acetone and DMF.

[0024] Preferably, the dipping time in S2 is 5-10 min; the dipping time in S3 is 80-160 s.

[0025] Preferably, the in-situ polymerization is carried out by standing at 20~30℃ for 65~75 hours.

[0026] Preferably, in S2, the weight gain of the pre-coated diaphragm relative to the porous substrate is 20-50%; in S3, the weight gain of the solid electrolyte coated diaphragm relative to the pre-coated diaphragm is 30-60%.

[0027] Thirdly, the present invention provides an application of a solid electrolyte coated separator in a lithium-ion battery.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) By pre-encapsulating the initiator inside the membrane, the monomer solution has already impregnated and filled the pores of the membrane substrate before polymerization. Then, the monomer is polymerized by the initiator in the pores of the substrate. At the same time, the initiator in the mesoporous structure of the filler is continuously released, inducing the monomer to continuously polymerize and fill the pores of the substrate. This achieves the in-situ generation of polymer electrolyte inside the membrane and filling its pore structure. This is fundamentally different from the traditional coating process that only forms a coating on the surface of the membrane and the polymer cannot enter the interior of the membrane. The polymer electrolyte of this invention not only exists on the surface of the membrane, but also penetrates the internal pore network of the membrane substrate, forming a continuous ion transport channel from the inside to the outside, which greatly reduces the ion transport impedance. (2) The porous structure of the filler is used to physically encapsulate the initiator, so that the initiator is uniformly loaded and slowly released inside and on the surface of the membrane. The polymerization reaction is gradually initiated by the initiator loaded inside and on the surface of the membrane. The polymer electrolyte is preferentially formed inside the membrane pores and gradually grows outward, so as to achieve the directional polymerization effect from the inside to the outside. This effectively avoids the problem of the polymerization rate being too fast and the precursor being partially solidified before it fully wets the electrode interface, which is caused by the direct addition of the initiator to the precursor in the traditional method. (3) In the final solid electrolyte coated membrane, the polyolefin substrate provides mechanical support and processability, the inorganic reinforcing filler improves the heat resistance and mechanical strength of the membrane and acts as an initiator reservoir, and the polymer electrolyte generated in situ completely fills the internal pores and outer surface of the membrane. The three constitute an integrated organic-inorganic composite membrane system with good interfacial bonding, thermal stability and high ionic conductivity. Attached Figure Description

[0029] Figure 1 This is a SEM image of the surface of a PE porous membrane substrate.

[0030] Figure 2 This is a cross-sectional SEM image of a PE porous membrane substrate.

[0031] Figure 3 This is a cross-sectional SEM image of the solid electrolyte coated membrane of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] The preparation of the solid electrolyte coated membrane in this invention includes the following steps: S1. Substrate pretreatment and slurry preparation: A vacuum plasma treatment instrument is used to pretreat the surface of a porous substrate to enhance interfacial compatibility. The working gas is oxygen (O2), argon (Ar) or air, the radio frequency power is 50~100W, the gas pressure is 10~50Pa, and the time is 1~5min, to obtain the pretreated porous substrate.

[0034] In an argon glove box with a water and oxygen content of <1 ppm, inorganic reinforcing fillers (one or more of alumina, silica, boehmite, magnesium oxide, zirconium oxide, silicon nitride, and boron nitride), binders (one or more of PVDF, PEO, and PMMA), and initiators (one or more of Al(OTf)3, AlCl3, and Et3OBF4) are mixed with solvent at a mass ratio of 9:1:0.5~1.5. The mixture is then stirred at 500~800 rpm for 8~12 hours to form a stable, non-stratified, and particle-free slurry 1 with a solid content of 15~25%.

[0035] In an argon glove box with a water oxygen content of <1 ppm, lithium salt (one or more of LiTFSI and LiFSI) is mixed evenly with polymer monomer (one or more of 1,3-dioxolane and tetrahydrofuran), and allowed to stand for degassing for 2-3 hours to obtain a clear slurry 2 free of suspended solids, with a lithium salt concentration of 1-3M.

[0036] S2, Slurry 1 coating and drying: Pour slurry 1 into a container, then immerse the pretreated porous substrate completely in slurry 1 for 5-10 minutes. Immersion allows the slurry to fully penetrate the pores of the substrate. After the substrate is evenly loaded inside and out, hang it on a support and air dry at room temperature of 20-30°C for 2-5 hours to slowly evaporate most of the organic solvents and prevent rapid high-temperature drying from causing coating cracking, powder fall-off, and membrane wrinkling. Then place it in a vacuum drying oven for secondary drying at a temperature of 50-60°C and a vacuum degree of <-0.1 MPa for 45-50 hours to completely remove the residual solvent inside, thus obtaining the pre-coated membrane.

[0037] 3. Slurry 2 coating and in-situ polymerization: In an argon glove box with a water and oxygen content of <1 ppm, the pre-coated diaphragm is laid flat in a glass petri dish with a sealed lid. Slurry 2 is added to completely submerge the diaphragm (or only partially submerge it), and it is soaked for 80-160 seconds to ensure that the diaphragm is fully wetted and the internal pores are completely filled. After soaking, it is removed and hung for 40-80 seconds to drain excess slurry from the surface. Then, the diaphragm is laid flat in another glass petri dish with a sealed lid and the inner wall pre-lined with a PTFE film. It is gently shaken for 20-30 seconds to remove air bubbles, and then sealed in the dark. Finally, it is sealed and allowed to stand for 65-75 hours at 20-30℃ for in-situ polymerization to obtain a solid electrolyte-coated diaphragm.

[0038] In a specific embodiment of the present invention, porous silica I has an average particle size of 100 nm, a D10 of 55 nm, a D90 of 168 nm, and a specific surface area of ​​250~350 m². 2 / g.

[0039] In a specific embodiment of the present invention, porous silica II has an average particle size of 200 nm, a D10 of 106 nm, a D90 of 321 nm, and a specific surface area of ​​500-600 m². 2 / g.

[0040] In a specific embodiment of the present invention, the porous zirconia has an average particle size of 150 nm, a D10 of 64 nm, a D90 of 250 nm, and a specific surface area of ​​200-300 m². 2 / g.

[0041] In a specific embodiment of the present invention, the γ-phase alumina (γ-Al2O3) has an average particle size of 50 nm, a D10 of 27 nm, a D90 of 132 nm, and a specific surface area of ​​100~150 m². 2 / g.

[0042] In a specific embodiment of the present invention, the α-phase alumina (α-Al2O3) has an average particle size of 50 nm, a D10 of 30 nm, and a D90 of 124 nm.

[0043] In a specific embodiment of the present invention, the porous substrate is a PE porous membrane substrate with an average pore size of 120 nm and a thickness of 11 μm. Its surface SEM image is shown below. Figure 1 As shown, the cross-sectional SEM is as follows Figure 2 As shown.

[0044] Example 1

[0045] S1. Substrate pretreatment and slurry preparation: The PE porous membrane substrate was placed in a vacuum plasma treatment instrument, and argon (Ar) was used as the working gas. The plasma treatment was carried out for 3 minutes under the conditions of 80 W radio frequency power and 30 Pa pressure to obtain the pretreated porous substrate.

[0046] In an argon glove box with a water and oxygen content of <1 ppm, 90g of inorganic reinforcing filler (porous silica I), 10g of binder (PVDF), 10g of initiator (Al(OTf)3) and 450g of acetone / DMF mixed solvent (acetone to DMF mass ratio of 2:3) were mixed. The mass ratio of inorganic reinforcing filler, binder and initiator was 9:1:1. The mixture was then stirred at 500 rpm for 10h to obtain slurry 1.

[0047] In an argon glove box with a water oxygen content of <1 ppm, 287.09 g of lithium salt (LiTFSI) and polymer monomer (1,3-dioxolane) were mixed evenly and allowed to stand for degassing for 2 hours to obtain slurry 2 with a lithium salt concentration of 1M.

[0048] S2, Slurry 1 coating and drying: Pour slurry 1 into a container, then immerse the pretreated porous substrate completely in slurry 1 for 8 minutes. After that, remove it and hang it on a support, and let it air dry at room temperature of 25°C for 3 hours. Then place it in a vacuum drying oven for secondary drying, set the temperature to 60°C, the vacuum degree to <-0.1 MPa, and dry for 48 hours to obtain a pre-coated diaphragm.

[0049] S3, Slurry 2 coating and in-situ polymerization: In an argon glove box with a water and oxygen content of <1 ppm, the pre-coated diaphragm was laid flat in a glass petri dish with a sealed lid. Slurry 2 was added to submerge the diaphragm, and after soaking for 120 seconds, it was removed and allowed to drain for 60 seconds. The diaphragm was then laid flat in another glass petri dish with a sealed lid and a PTFE film pre-lined on the inner wall. It was gently shaken for 30 seconds to remove air bubbles and then sealed in the dark. Finally, it was allowed to stand in a sealed environment at 25°C for 70 hours for in-situ polymerization to obtain a solid electrolyte-coated diaphragm. The SEM image of the diaphragm cross-section is shown below. Figure 3 As shown.

[0050] Example 2

[0051] Compared with Example 1, this embodiment changes the inorganic reinforcing filler (porous silica I) in step S1 to inorganic reinforcing filler (γ-Al2O3), while the other steps remain unchanged.

[0052] Example 3

[0053] Compared with Example 1, this embodiment changes the inorganic reinforcing filler (porous silica I) in step S1 to inorganic reinforcing filler (porous zirconia), while the other steps remain unchanged.

[0054] Example 4

[0055] Compared with Example 1, this embodiment changes the initiator Al(OTf)3 in step S1 to Et3OBF4, and simultaneously changes the polymerization monomer 1,3-dioxolane to tetrahydrofuran, while keeping the other steps unchanged.

[0056] Example 5

[0057] Compared with Example 1, this embodiment adjusts the mass ratio of inorganic reinforcing filler, binder and initiator in step S1 to 9:1:0.5 (90g of inorganic reinforcing filler (porous silica I), 10g of binder (PVDF), 5g of initiator (Al(OTf)3) and 430g of acetone / DMF mixed solvent (acetone and DMF mass ratio of 2:3) are mixed), and the other steps remain unchanged.

[0058] Example 6

[0059] Compared with Example 1, this embodiment adjusts the mass ratio of inorganic reinforcing filler, binder and initiator in step S1 to 9:1:1.5 (90g of inorganic reinforcing filler (porous silica I), 10g of binder (PVDF), 15g of initiator (Al(OTf)3) and 470g of acetone / DMF mixed solvent (acetone and DMF mass ratio of 2:3) are mixed), and the other steps remain unchanged.

[0060] Comparative Example 1 PE porous membrane substrate only (without any coating).

[0061] Comparative Example 2 Compared with Example 2, this embodiment changes the inorganic reinforcing filler γ-Al2O3 in step S1 to inorganic reinforcing filler α-Al2O3 (non-porous conventional filler), while the other steps remain unchanged.

[0062] Comparative Example 3 Compared with Example 1, this embodiment is modified so that no initiator is added to slurry 1, and an initiator is added to slurry 2 instead, while the other steps remain unchanged.

[0063] In an argon glove box with a water oxygen content of <1 ppm, 90 g of inorganic reinforcing filler (porous silica I), 10 g of binder (PVDF) and 409 g of acetone / DMF mixed solvent (acetone to DMF mass ratio of 2:3) were mixed. The mass ratio of inorganic reinforcing filler to binder was 9:1. The mixture was then stirred at 500 rpm for 10 h to obtain slurry 1.

[0064] In an argon glove box with a water and oxygen content of <1 ppm, 287.09 g of lithium salt (LiTFSI) and polymer monomer (1,3-dioxolane) were mixed evenly to make the lithium salt concentration 1M. 10 g of initiator (Al(OTf)3) was added, and the mixture was allowed to stand for degassing for 2 hours to obtain slurry 2.

[0065] Comparative Example 4 Compared with Example 1, this embodiment is modified so that filler is added to slurry 2 instead of slurry 1, while the other steps remain unchanged.

[0066] In an argon glove box with a water oxygen content of <1 ppm, 10 g of binder (PVDF), 10 g of initiator (Al(OTf)3) and 82 g of acetone / DMF mixed solvent (acetone to DMF mass ratio of 2:3) were mixed. The mass ratio of inorganic reinforcing filler, binder and initiator was 9:1:1. The mixture was then stirred at 500 rpm for 10 h to obtain slurry 1.

[0067] In an argon glove box with a water oxygen content of <1 ppm, 287.09 g of lithium salt (LiTFSI) and polymer monomer (1,3-dioxolane) were mixed evenly to make the lithium salt concentration 1M. 90 g of inorganic reinforcing filler (porous silica I) was added, and the mixture was allowed to stand for degassing for 2 hours to obtain slurry 2.

[0068] Comparative Example 5 Compared with Example 1, this comparative example adjusts the mass ratio of inorganic reinforcing filler, binder, and initiator in step S1 to 10:1:1 (100g of inorganic reinforcing filler (porous silica I), 10g of binder (PVDF), 10g of initiator (Al(OTf)3) and 491g of acetone / DMF mixed solvent (acetone to DMF mass ratio of 2:3) are mixed), while the other steps remain unchanged.

[0069] Comparative Example 6 Compared with Example 1, this comparative example changed the inorganic reinforcing filler (porous silica I) in step S1 to inorganic reinforcing filler (porous silica II), while the other steps remained unchanged.

[0070] The membranes prepared in Examples 1-6 and Comparative Examples 1-6 were subjected to the following performance tests: (1) Diaphragm thickness: The thickness of the coated diaphragm at different locations was measured using a micrometer screw gauge, and the average value was calculated; (2) Ionic conductivity: The bulk resistance was tested using the assembly method of steel sheet / diaphragm / steel sheet and the electrochemical impedance spectroscopy (EIS) mode of VMP3B-10 electrochemical workstation (Bio-Logic Science Instruments). The perturbation voltage amplitude was 5 mV and the frequency was 10 mHz~1 MHz. The relationship between bulk resistance and ionic conductivity is calculated as follows: σ = L / (Rb × A) × 10 -2 Where σ is the ionic conductivity (S / cm), L is the membrane thickness (mm), Rb is the bulk resistance (Ω), and A is the contact area between the membrane and the electrode (m²). 2 ); (3) Heat shrinkage rate: The heat shrinkage rate was tested according to the test method of GB / T-36363-2018. The diaphragm sample was placed in a 150℃ forced-air oven for 0.5h for heat treatment, and the longitudinal (MD) and transverse (TD) heat shrinkage rates were measured respectively. (4) Peel strength test: According to the method in GB / T 2792-2014 Adhesive tape peel strength, the standard tape was pasted on the surface of the diaphragm coating and peeled off by a universal testing machine at 180°. The peel strength was recorded.

[0071] (5) Determination of membrane weight gain: The weight of the porous substrate before coating is recorded as m0, in g; the weight of the pre-coated membrane in step S2 is recorded as m1, in g; the weight of the membrane coated with solid electrolyte in step S3 is recorded as m2, in g. Calculate using the following formula: Pre-coated diaphragm weight gain rate Δ1 (reflecting the loading of slurry 1): Δ1 = (m1 - m0) / m0 × 100%; The weight gain rate Δ2 of the solid electrolyte coated diaphragm (reflecting the loading of slurry 2): Δ2 = (m2 - m1) / m1 × 100%.

[0072] Table 1. Diaphragm thickness and weight gain in Examples 1-6 and Comparative Examples 1-6

[0073] Table 2 Summary of performance test data of the diaphragms in Examples 1-6 and Comparative Examples 1-6

[0074] As can be seen from the data in Tables 1 and 2, the thickness of the pure PE base film without any coating (Comparative Example 1) is 11.0 μm. The increased thickness of the base film in Examples 1-6 indicates that the polymer electrolyte has successfully filled the membrane pores and formed a coating layer on the surface. This is evident from… Figure 2 and Figure 3 This can also be confirmed in the SEM images.

[0075] Meanwhile, the ionic conductivity of Examples 1-6 was significantly better than that of Comparative Examples 1-6. Example 6 exhibited the best conductivity, attributed to the higher initiator ratio, which improved the contact efficiency between monomer and initiator and increased the polymerization rate, resulting in a more complete polymerization reaction and a more complete and continuous polymer electrolyte network. In contrast, the relatively low initiator ratio in Example 5 led to a lower degree of polymerization. Furthermore, Examples 1-3 showed that different types of fillers can cause slight differences in the ionic conductivity of the membrane. This may be due to the influence of filler particle size and specific surface area. Specifically, excessively large filler particle size results in only a small amount filling the pores of the porous substrate (excessively present on the substrate surface), while excessively small filler particle size leads to excessive filling of the pores (easily clogging the substrate channels), both of which are detrimental to the formation of continuous ion transport channels from the inside out by the polymer electrolyte. Additionally, Examples 1 (DOL) and 4 (THF) showed that the ionic conductivity of membranes prepared with different polymer electrolytes also differed. Comparative Example 1 (pure PE membrane) had an ionic conductivity of only 1.2 × 10⁻⁶. -4 S / cm, because it relies solely on electrolyte to wet the pores, lacks continuous polymer ion transport channels.

[0076] In terms of heat shrinkage rate and peel strength, the pure PE base film (Comparative Example 1) exhibited a heat shrinkage rate as high as 18.5% (MD) / 22.0% (TD) at 150°C, while the heat shrinkage rates of Examples 1-6 were significantly reduced. This demonstrates that the organic-inorganic network formed by the inorganic reinforcing filler and the polymer electrolyte effectively suppressed the high-temperature shrinkage of the polyolefin substrate. Moreover, the peel strength of Examples 1-6 was significantly better than that of Comparative Examples 2-6. The peel strength of Comparative Example 1 (pure PE separator) could not be tested because it did not have a coating.

[0077] The membrane performance of Comparative Example 2 (non-porous conventional filler) was significantly lower than that of Example 2 (γ-Al2O3), further demonstrating that the mesoporous structure not only facilitates the encapsulation and slow release of the initiator, but also, combined with its high specific surface area, further enhances the physical anchoring effect between the coating and the substrate, thereby enabling the construction of a continuous ion transport channel from the inside out. Furthermore, fillers without a porous structure cannot form a continuous, dense, rigid interpenetrating network, weakening their ability to restrain thermal shrinkage of the substrate, while fillers with a porous structure help form a uniformly distributed and continuous filler-polymer network, thus effectively suppressing thermal shrinkage of the substrate.

[0078] Comparative Example 3 (initiator added to slurry 2) significantly improved the degree of polymerization and resulted in a thicker membrane, but its ionic conductivity was low. This indicates that the increase in thickness mainly comes from the accumulation of the surface gel layer rather than the effective filling of internal pores. Directly adding the initiator to the monomer leads to an excessively fast polymerization rate. The monomer partially polymerizes before fully wetting the internal pores of the membrane, failing to form a continuous ion transport channel from the inside out. Instead, the dense surface gel layer increases the interfacial resistance. Furthermore, the surface gel layer has limited reinforcing effect on the internal filler network, resulting in a higher membrane shrinkage rate and lower peel strength.

[0079] In Comparative Example 4 (filler added to slurry 2), the substrate pores were initially occupied by slurry 1. After the filler was added to slurry 2, it was essentially unable to penetrate the pores and could only accumulate on the membrane surface. Furthermore, the slurry blended with the monomer had a higher viscosity, which hindered the monomer from penetrating into the substrate pores, leading to an increase in overall impedance and a significant decrease in ionic conductivity. The filler's inability to embed into the substrate pores resulted in a rigid surface layer, leading to higher thermal shrinkage and weak interfacial bonding.

[0080] In Comparative Example 5 (where the filler ratio in slurry 1 was too high), the surface filler accumulation was relatively less than in Comparative Example 4, but it still affected the entry of polymeric monomers into the pores of the substrate. Simultaneously, excessive filler packing and poor dispersibility within the substrate pores also affected monomer polymerization internally, preventing the polymer electrolyte from forming a permeable network. Therefore, the ionic conductivity, thermal shrinkage rate, and peel strength of the diaphragm in Comparative Example 5 were all affected.

[0081] In Comparative Example 6 (where the average particle size of the filler is too large), most of the large-particle fillers cannot embed into the substrate pores. Although in-situ polymerization can still occur within the substrate channels, the interfacial resistance between the coating and the substrate remains high. Furthermore, the lack of secondary filler channels within the substrate to provide additional transport paths increases internal transport resistance, thus reducing ionic conductivity. Moreover, the accumulation of surface fillers results in a lack of rigid support within the substrate. At high temperatures, the intrinsic thermal shrinkage tendency of the polyolefin substrate is not internally constrained, relying solely on the external force of the surface coating. This significantly weakens the constraint effect, leading to an increased thermal shrinkage rate. Similarly, the interfacial adhesion between the coating and the substrate decreases, and the peel strength also decreases significantly.

[0082] In summary, this invention has successfully achieved the filling of the internal pores of the membrane by polymer electrolyte and the firm bonding of the surface coating layer by constructing an integrated technical solution of "plasma activation modification - inorganic filler porous structure encapsulation initiator - initiator slow release induced in situ directional polymerization" on a polyolefin porous membrane substrate.

[0083] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A solid electrolyte coated membrane, characterized in that, The invention includes a porous substrate and a solid electrolyte coating layer disposed on the surface of the porous substrate. The solid electrolyte coating layer is obtained by coating the surface of the porous substrate with slurry 1 and slurry 2 successively, followed by in-situ polymerization. Slurry 1 includes inorganic reinforcing filler, binder and initiator in a mass ratio of 9:1:0.5~1.

5. The ratio of the average particle size of the inorganic reinforcing filler to the average pore size of the porous substrate is 0.4~1.

3. The inorganic reinforcing filler has a porous structure. Slurry 2 includes lithium salt and polymer monomer.

2. The solid electrolyte coated membrane according to claim 1, characterized in that, The inorganic reinforcing filler has a particle size D10 < the average pore size of the porous substrate, and a particle size D90 > the average pore size of the porous substrate; the inorganic reinforcing filler has a specific surface area of ​​100~1000 m². 2 / g.

3. The solid electrolyte coated membrane according to claim 1 or 2, characterized in that, The polymer monomers include one or more of 1,3-dioxolane and tetrahydrofuran; the concentration of lithium salt in the slurry 2 is 1~3M.

4. The solid electrolyte coated membrane according to claim 1 or 2, characterized in that, The inorganic reinforcing filler includes one or more of alumina, silica, boehmite, magnesium oxide, zirconium oxide, silicon nitride, and boron nitride.

5. The solid electrolyte coated membrane according to claim 1, characterized in that, The average pore size of the porous substrate is ≥100nm.

6. The solid electrolyte coated membrane according to claim 1, characterized in that, The initiator includes one or more of aluminum trifluoromethanesulfonate, aluminum trichloride, and triethyloxonium tetrafluoroborate.

7. The solid electrolyte coated membrane according to claim 1, 5, or 6, characterized in that, The adhesive is one or more of polyvinylidene fluoride, polyethylene oxide, and polymethyl methacrylate.

8. A method for preparing a solid electrolyte coated membrane as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. The porous substrate is subjected to plasma pretreatment; inorganic reinforcing filler, binder and initiator are added to solvent to obtain slurry 1; lithium salt and polymer monomer are mixed to obtain slurry 2; S2. The slurry 1 is coated onto the surface of the pretreated porous substrate by dip coating. After drying, a pre-coated diaphragm is obtained. S3. The slurry 2 is coated onto the surface of the pre-coated diaphragm by dip coating, and then in-situ polymerization is carried out to obtain a solid electrolyte coated diaphragm.

9. The method for preparing a solid electrolyte coated membrane according to claim 8, characterized in that, The solid content of the slurry 1 is 15-25%; the in-situ polymerization is carried out by standing at 20-30°C for 65-75 hours.

10. The application of a solid electrolyte coated separator as described in any one of claims 1-7 or a solid electrolyte coated separator prepared by any one of claims 8-9 in a lithium-ion battery.

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