Quasi-solid-state battery electrolyte film, method for producing the same, and quasi-solid-state battery

Abstract

This application relates to the field of new energy technology, and particularly to a quasi-solid-state battery electrolyte membrane, its preparation method, and the quasi-solid-state battery itself. The preparation method includes the following steps: mixing a polymer matrix, a bifunctional reactive liquid crystal monomer, a lithium salt, a mixed solvent, functional additives, and a photoinitiator to obtain a precursor solution, wherein the mixed solvent includes a first solvent and a second solvent; providing a substrate with a thermal conductivity not exceeding 0.3 W / m·K; coating the substrate with the precursor solution to form a wet film; controlling the surface temperature of one side of the wet film to T1 and the surface temperature of the other side to T2; wherein T1-T2 is 25℃~40℃; evaporating the first solvent and retaining at least a portion of the second solvent to form a dry film; photocuring the dry film; removing the substrate to obtain the quasi-solid-state battery electrolyte membrane. The above method can achieve an asymmetric component gradient distribution structure of "polymer enrichment (high stability) on the negative electrode side and liquid crystal enrichment (high conductivity) on the positive electrode side," thereby improving battery cycle performance.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to the electrolyte membrane for quasi-solid-state batteries, its preparation method, and quasi-solid-state batteries. Background Technology

[0002] With the rapid development of new energy electric vehicles and portable electronic devices, lithium-ion batteries are evolving towards higher energy density and higher safety. Solid-state electrolyte technology is considered a core technology for next-generation batteries because it can suppress lithium dendrite growth and eliminate the risk of leakage. Among them, polymer-liquid crystal composite electrolytes utilize the ordered self-assembly characteristics of liquid crystal molecules to construct high-speed ion transport channels, which can significantly improve the room temperature ionic conductivity of polymer electrolytes, making it a research hotspot.

[0003] However, in current polymer-liquid crystal composite electrolytes, liquid crystal monomers are unstable on the lithium metal anode side and are prone to reduction reactions on the anode surface, generating a high-resistivity interface layer. Although the polymer is stable, its high contact impedance with the cathode side limits cycling performance. In summary, traditional polymer-liquid crystal composite electrolytes struggle to simultaneously meet the requirements of high stability on the anode side and high kinetics on the cathode side. While theoretically, gradient component distribution could solve these problems, practical implementation is extremely difficult, especially with the development of ultrathin polymer-liquid crystal composite electrolytes (≤30μm), making precise control of component distribution on ultrathin films challenging. Summary of the Invention

[0004] Therefore, to address the challenge of gradient distribution of liquid crystal and polymer in polymer-liquid crystal composite electrolyte membranes, this application provides a quasi-solid-state battery electrolyte membrane, its preparation method, and a quasi-solid-state battery. During the preparation of the quasi-solid-state battery electrolyte membrane provided in this application, the directional migration of liquid crystal components is driven by asymmetric heat treatment, the difference in evaporation rates between the first and second solvents, and the plasticizing effect of the second solvent, achieving a gradient distribution of liquid crystal and polymer, suitable for thinner films. Simultaneously, this application uses a bifunctional reactive liquid crystal monomer, which can form a high-density cross-linked network through photocuring, physically confining residual second solvent within the network, making it less prone to leakage under high temperature and pressure, and improving the safety of residual solvent.

[0005] The first aspect of this application provides a method for preparing a quasi-solid electrolyte membrane, the technical solution of which is as follows: A method for preparing a quasi-solid-state electrolyte membrane includes the following steps: A precursor solution is obtained by mixing a polymer matrix, a bifunctional reactive liquid crystal monomer, a lithium salt, a mixed solvent, a functional additive, and a photoinitiator. The mixed solvent includes a first solvent and a second solvent, which satisfy the following conditions: (1) under the same conditions, the evaporation rate of the first solvent is greater than that of the second solvent; (2) the second solvent can plasticize the polymer chain segments after photocuring. A substrate is provided, the thermal conductivity of which is not higher than 0.3 W / m·K, and the precursor solution is coated on the substrate to form a wet film; The surface temperature of the wet film on the side away from the substrate is controlled to be T1, and the surface temperature of the substrate on the side away from the wet film is controlled to be T2, where T1 > T2 and T1-T2 is 25°C to 40°C. The first solvent evaporates, and at least a portion of the second solvent is retained to form a dry film. The dry film is photocured, and the substrate is removed to obtain the quasi-solid-state battery electrolyte membrane.

[0006] In one implementation, at least one of the following features is included: (1) The temperature T1 is 55℃~75℃; (2) The T2 is 20℃~45℃.

[0007] In one embodiment, the content of the second solvent is controlled such that the content of the second solvent in the quasi-solid-state battery electrolyte membrane is 3wt%~5wt%.

[0008] In one embodiment, the first solvent accounts for 70% to 95% of the mass of the mixed solvent, and the second solvent accounts for 5% to 30% of the mass of the mixed solvent.

[0009] In one implementation, at least one of the following features is included: (1) The boiling point of the second solvent is ≥200℃; (2) The boiling point of the first solvent is ≤100℃.

[0010] In one implementation, at least one of the following features is included: (1) The second solvent is selected from at least one of propylene carbonate, ethylene carbonate and γ-butyrolactone; (2) The first solvent is selected from at least one of acetonitrile, acetone and ethyl acetate.

[0011] In one embodiment, the bifunctional reactive liquid crystal monomer is selected from bifunctional acrylate liquid crystal monomers.

[0012] In one implementation, at least one of the following features is included: (1) The polymer matrix is ​​selected from at least one of polyethylene oxide, polyethylene glycol diacrylate, polymethyl methacrylate and polyvinylidene fluoride-hexafluoropropylene copolymer; (2) The functional additive is selected from one of lithium difluorophosphate, vinyl sulfate and lithium nitrate; (3) The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium perchlorate; (4) The photoinitiator is selected from at least one of 2-hydroxy-2-methylphenylacetone and benzoin isopropyl ether; (5) In the precursor solution, the polymer matrix is ​​10-30 parts by weight, the bifunctional reactive liquid crystal monomer is 5-15 parts by weight, the lithium salt is 3-10 parts by weight, the mixed solvent is 100-200 parts by weight, the functional additive is 0.1-2 parts by weight, and the photoinitiator is 0.5-2 parts by weight. (6) Control the thickness of the wet film so that the thickness of the quasi-solid electrolyte membrane is 20μm~30μm; (7) The substrate includes a polymer film and a heat-insulating coating on the polymer film.

[0013] The second aspect of this application provides a quasi-solid-state electrolyte membrane, the technical solution of which is as follows: A quasi-solid electrolyte membrane is prepared by the preparation method described above.

[0014] A third aspect of this application provides a quasi-solid-state battery, the technical solution of which is as follows: A quasi-solid-state battery includes a positive electrode, a negative electrode, and a quasi-solid-state battery electrolyte membrane located between the positive electrode and the negative electrode. The quasi-solid-state battery electrolyte membrane is prepared by the preparation method described above, or as described above.

[0015] Compared with traditional solutions, this application has the following advantages: This application prepares a polymer-liquid crystal composite electrolyte membrane using solution casting and in-situ photopolymerization. First, a first solvent and a second solvent with different evaporation rates are added to a precursor solution, and the second solvent with plasticizing effect is selected. Then, the precursor solution is coated on a substrate with a thermal conductivity of no more than 0.3 W / m·K, and the temperature difference between the wet film and the substrate is controlled. While the first solvent evaporates and the polymer crosslinks, the liquid crystal components are driven to migrate in an directional manner. After in-situ photocuring, a gradient distribution of polymer is achieved, realizing an asymmetric component gradient distribution structure of "polymer enrichment (high stability) on the negative electrode side and liquid crystal enrichment (high conductivity) on the positive electrode side", thereby improving the battery cycle performance. Meanwhile, this application leaves at least a portion of the second solvent of the plasticized and photocured polymer segments in the quasi-solid-state battery electrolyte membrane. In traditional processes, solvent residue is considered a defect, which can easily lead to leakage. However, in this application, in order to leave it in place and improve the mobility of the polymer segments to form a component gradient distribution, a bifunctional reactive liquid crystal monomer is used. This monomer can form a high-density cross-linked network through photocuring, physically confining the residual second solvent within the network. This makes it less prone to leakage under high temperature and pressure, thus improving the safety of the residual solvent. Furthermore, the residual second solvent can also improve the conductivity through the mobility of the polymer segments, thus meeting the requirements of high conductivity and high stability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the preparation process of the electrolyte membrane for a quasi-solid-state battery according to one embodiment. Detailed Implementation

[0018] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0020] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings: In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0021] In this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0022] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0023] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0024] In this application, numerical intervals (i.e. numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the above-mentioned numerical intervals are considered continuous, and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints.

[0025] The first aspect of this application provides a method for preparing a quasi-solid electrolyte membrane. Please refer to [link to relevant documentation]. Figure 1 This includes the following steps: S1. A precursor solution is obtained by mixing a polymer matrix, a bifunctional reactive liquid crystal monomer, a lithium salt, a mixed solvent, a functional additive, and a photoinitiator. The mixed solvent includes a first solvent and a second solvent, which satisfy the following conditions: (1) Under the same conditions, the evaporation rate of the first solvent is greater than that of the second solvent; (2) The second solvent can plasticize the polymer chain segments after photocuring.

[0026] First, dissolve the lithium salt in a mixed solvent and stir for 2-4 hours until completely transparent. Add the polymer matrix and stir at 60-70°C for 6-12 hours until completely dissolved. Finally, add the bifunctional reactive liquid crystal monomer, functional additives, and photoinitiator, and stir in the dark for 0.5-1.5 hours to obtain a homogeneous precursor solution.

[0027] Optionally, the polymer matrix is ​​selected from at least one of polyethylene oxide (PEO), polyethylene glycol diacrylate (PEGDA), polymethyl methacrylate (PMMA), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP). Preferably, it is a mixture of PEO and PEGDA. The weight-average molecular weight (MW) of PEO is 100,000 to 1,000,000. The weight-average molecular weight (MW) of PEGDA is 400 to 2,000. The weight-average molecular weight (MW) of PMMA is 100,000 to 200,000. The weight-average molecular weight (MW) of PVDF-HFP is 400,000 to 450,000. The polymer matrix serves to provide an ion transport framework and crosslinking sites.

[0028] Optionally, the bifunctional reactive liquid crystal monomer is selected from bifunctional acrylate liquid crystal monomers. Optionally, the bifunctional acrylate liquid crystal monomer is selected from acrylate liquid crystal monomers containing at least two polymerizable double bonds to ensure the formation of a highly crosslinked three-dimensional crosslinked network after photocuring. This physically confines the residual second solvent within the crosslinked network, restricting the macroscopic flow of solvent molecules and giving it solid-state characteristics rather than a free liquid or gel. The bifunctional acrylate liquid crystal monomer is selected from at least one of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257) and fluorinated biphenyl diacrylate (FBPA).

[0029] Optionally, the content of the second solvent is controlled so that the content of the second solvent in the quasi-solid-state battery electrolyte membrane is 3wt%~5wt%. Optionally, the first solvent accounts for 70%~95% of the mass of the mixed solvent, and the second solvent accounts for 5%~30% of the mass of the mixed solvent. The first solvent mainly plays the role of inducing the volatilization gradient. The second solvent mainly remains in the electrolyte membrane and plays a plasticizing role. The ability of the second solvent to plasticize the photocured polymer segments means that the second solvent can insert between polymer molecular chains, weakening interchain forces (van der Waals forces, hydrogen bonds, dipole interactions), increasing the free volume of the chain segments, thereby lowering the glass transition temperature and increasing the chain segment movement frequency. In this application, the second solvent remains after photocuring and crosslinking, permanently existing in the crosslinking network as an in-situ plasticizer, continuously playing the role of "softening the polymer matrix and promoting Li..." + The role of "migration".

[0030] Optionally, the second solvent has a boiling point ≥200°C. It is used for final residual plasticization. Optionally, the second solvent is selected from at least one of propylene carbonate (PC), ethylene carbonate (EC), and γ-butyrolactone (GBL). Optionally, the first solvent has a boiling point ≤100°C and is used to induce a volatilization gradient. Optionally, the first solvent is selected from at least one of acetonitrile (ACN), acetone, and ethyl acetate (EtOAc).

[0031] Optionally, the functional additive is a high-pressure additive used to suppress high-pressure oxidation of the solvent and stabilize the high-pressure interface or the negative electrode SEI film. The functional additive is selected from at least one of lithium difluorophosphate (LiPO2F2), vinyl sulfate (DTD), and lithium nitrate (LiNO3).

[0032] Optionally, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium perchlorate (LiClO4).

[0033] Optionally, the photoinitiator is selected from at least one of 2-hydroxy-2-methylphenylacetone (1173) and benzoin isopropyl ether (BIE).

[0034] Optionally, in the precursor solution, the polymer matrix is ​​10-30 parts by weight, the bifunctional reactive liquid crystal monomer is 5-15 parts by weight, the lithium salt is 3-10 parts by weight, the mixed solvent is 100-200 parts by weight, the functional additive is 0.1-2 parts by weight, and the photoinitiator is 0.5-2 parts by weight.

[0035] S2. Provide a substrate with a thermal conductivity not higher than 0.3 W / m·K, and coat the precursor solution onto the substrate to form a wet film.

[0036] Optionally, the substrate includes a polymer film and a heat-insulating coating on the polymer film, the heat-insulating coating including at least one of a microporous silica layer, an alumina layer, and an aerogel layer. The precursor solution is coated on the side of the coating away from the polymer film. Optionally, the polymer film is made of at least one of PET and PI.

[0037] Optionally, before coating the precursor solution onto the substrate, a step of plasma liquefaction treatment of the substrate is included. Understandably, the plasma liquefaction treatment is performed on the side of the coating away from the polymer film.

[0038] Optionally, the thickness of the wet film can be controlled to make the thickness of the quasi-solid electrolyte membrane 20μm~30μm.

[0039] S3. Control the surface temperature of the wet film away from the substrate to T1, and the surface temperature of the substrate away from the wet film to T2, where T1 > T2 and T1-T2 is 25°C to 40°C. Volatilize the first solvent and retain at least a portion of the second solvent to form a dry film.

[0040] In this application, under the same conditions, the evaporation rate of the first solvent is greater than that of the second solvent. On the one hand, the difference in evaporation rates between the two solvents can drive the directional migration of liquid crystals. On the other hand, the temperature difference created on both sides of the wet film and substrate, coupled with the low thermal conductivity of the substrate, can suppress interfacial heat conduction on the side of the wet film closer to the substrate, thereby suppressing the evaporation rate of the first solvent on that side, establishing an evaporation rate gradient of the first solvent, and driving liquid crystal molecules to migrate towards the side of the wet film away from the substrate. Furthermore, the plasticizing effect of the second solvent enhances the mobility of polymer chain segments, driving the liquid crystal molecules. In summary, a polymer-liquid crystal composite electrolyte membrane with an asymmetric component gradient distribution structure of "polymer enrichment (high stability) on one side and liquid crystal enrichment (high conductivity) on the other side" is constructed, i.e., a quasi-solid-state electrolyte membrane.

[0041] A single-sided heat source can be placed on the side of the wet film away from the substrate, such that T1 > T2, and T1-T2 is controlled between 25℃ and 40℃. The heat source can be hot air at a temperature of 60~85℃, and the heating time can be 5min~20min.

[0042] Optionally, T1 is 55℃~75℃. Optionally, T2 is 20℃~45℃.

[0043] S4. The dry film is photocured and the substrate is removed to obtain the quasi-solid-state battery electrolyte membrane.

[0044] The photocuring can be ultraviolet (UV) curing with a wavelength of 365 nm and an energy of 100~500 mJ / cm². 2 During photocuring, the polymer matrix, bifunctional reactive liquid crystal monomers, and polymer matrix crosslink to form a high-density crosslinked network, which physically confines the second solvent within the voids of the crosslinked network, restricting its macroscopic flow.

[0045] This application prepares a polymer-liquid crystal composite electrolyte membrane using solution casting and in-situ photopolymerization. First, a first solvent and a second solvent with different evaporation rates are added to a precursor solution, and the second solvent with plasticizing effect is selected. Then, the precursor solution is coated on a substrate with a thermal conductivity of no more than 0.3 W / m·K, and the temperature difference between the wet film and the substrate is controlled. While the first solvent evaporates and the polymer crosslinks, the liquid crystal components are driven to migrate in an directional manner. After in-situ photocuring, a gradient distribution of polymer is achieved, realizing an asymmetric component gradient distribution structure of "polymer enrichment (high stability) on the negative electrode side and liquid crystal enrichment (high conductivity) on the positive electrode side", thereby improving the battery cycle performance. Meanwhile, this application leaves at least a portion of the second solvent of the plasticized and photocured polymer segments in the quasi-solid-state battery electrolyte membrane. In traditional processes, solvent residue is considered a defect, which can easily lead to leakage. However, in this application, in order to leave it in place and improve the mobility of the polymer segments to form a component gradient distribution, a bifunctional reactive liquid crystal monomer is used. This monomer can form a high-density cross-linked network through photocuring, physically confining the residual second solvent within the network. This makes it less prone to leakage under high temperature and pressure, thus improving the safety of the residual solvent. Furthermore, the residual second solvent can also improve the conductivity through the mobility of the polymer segments, thus meeting the requirements of high conductivity and high stability.

[0046] The above preparation method can not only achieve gradient distribution of liquid crystal, but is also easy to operate and suitable for roll-to-roll mass production.

[0047] The second aspect of this application provides a quasi-solid electrolyte membrane, which is prepared by the preparation method described above.

[0048] Optionally, the content of the second solvent in the quasi-solid-state battery electrolyte membrane is 3wt%~5wt%. It can be stored at 60℃ for 7 days with a weight loss rate of less than 1%, and there is no liquid leakage under 0.5MPa pressure.

[0049] Optionally, the quasi-solid-state battery electrolyte membrane has opposing first and second surfaces, with a decreasing liquid crystal concentration gradient along the direction from the first surface to the second surface. The liquid crystal concentration on the first surface is ≥20wt%, representing the liquid crystal enrichment side, used for contacting the positive electrode. The liquid crystal concentration on the second surface is ≤5wt%, representing the polymer enrichment side, used for contacting the negative electrode.

[0050] Optionally, the thickness of the quasi-solid electrolyte membrane is 20 μm to 30 μm.

[0051] The quasi-solid electrolyte membrane provided in this application has a polymer enrichment side that can block direct contact between the liquid crystal and the lithium metal anode, suppressing side reactions and slowing down the growth of SEI membrane impedance; the liquid crystal enrichment side provides ordered ion channels, which is beneficial to reducing the interfacial contact impedance with the cathode and improving battery cycle performance.

[0052] A third aspect of this application provides a quasi-solid-state battery, comprising a positive electrode, a negative electrode, and a quasi-solid-state battery electrolyte membrane located between the positive electrode and the negative electrode. The quasi-solid-state battery electrolyte membrane is prepared by the preparation method described above, or as described above. The polymer-enriched side of the quasi-solid-state battery electrolyte membrane contacts the lithium negative electrode, and the liquid crystal-enriched side contacts the positive electrode.

[0053] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available; the instruments used are all commercially available unless otherwise specified; and the processes involved are conventionally selected by those skilled in the art unless otherwise specified.

[0054] Example 1 Example 1 provides a quasi-solid-state battery electrolyte membrane and its preparation method, the steps of which are as follows: Step S1 (Preparation of precursor solution): Referring to the components and weight percentages in Table 1, in a glove box (water and oxygen content <0.1 ppm), the lithium salt was first dissolved in a mixed solvent (first solvent + second solvent) and stirred for 3 hours until completely transparent. The polymer matrix was then added and stirred at 65°C for 9 hours until completely dissolved. Finally, the bifunctional reactive liquid crystal monomer, functional additives, and photoinitiator were added, and the mixture was stirred in the dark for 1 hour to obtain a homogeneous precursor solution.

[0055] Step S2 (coating): A substrate is provided, comprising a PET film and a microporous silica heat insulation layer on the PET film. The thermal conductivity of the substrate is 0.15 W / m·K. The microporous silica layer is first subjected to plasma liquefaction treatment on the side away from the PET film, and then coated with the above-mentioned precursor solution to obtain a wet film.

[0056] Step S3 (One-way volatilization induction): The substrate with the wet film is placed in the drying tunnel, and hot air is introduced into the side of the wet film away from the substrate. The surface temperature of the wet film away from the substrate is controlled at T1 (see Table 1), and the surface temperature of the substrate away from the wet film is controlled at T2 (see Table 2). After processing for 10 minutes, the first solvent evaporates completely, and a dry film with a thickness of 25 μm ± 2 μm is obtained.

[0057] Step S4 (Cure and Lock): UV curing of substrates with dry films (wavelength 365 nm, energy 300 mJ / cm²) 2The polymer matrix, bifunctional reactive liquid crystal monomers and polymer matrix are cross-linked to form a high-density cross-linked network. The second solvent is physically confined in the voids of the cross-linked network to obtain a quasi-solid-state battery electrolyte membrane with an interface asymmetric structure. The membrane is enriched with liquid crystal on the side away from the substrate and enriched with polymer on the side closer to the substrate. The substrate is peeled off to obtain a quasi-solid-state battery electrolyte membrane with a thickness of 25μm±2μm, which is ready for use.

[0058] Examples 2 to 4 Examples 2 to 4 provide a quasi-solid-state battery electrolyte membrane and its preparation method, which are basically the same as those in Example 1, with the main differences shown in Table 1. The difference lies in the thickness of the microporous silica heat-insulating layer in Examples 2 to 4, resulting in different thermal conductivity of the substrate.

[0059] Examples 5 to 9 Examples 5 to 9 provide a quasi-solid-state battery electrolyte membrane and its preparation method, which are basically the same as those in Example 1. The main differences are shown in Table 2.

[0060] Table 1

[0061] Table 2

[0062] Comparative Example 1 Comparative Example 1 provides a quasi-solid-state battery electrolyte membrane and its preparation method, which are basically the same as those in Example 1. The main differences are shown in Table 3. In Comparative Example 1, the substrate does not contain a microporous silica heat insulation layer, resulting in different thermal conductivity of the substrate and thus different T2 values.

[0063] Comparative Example 2 Comparative Example 2 provides a quasi-solid-state battery electrolyte membrane and its preparation method, which is basically the same as that of Example 1, with the main differences shown in Table 3. In Comparative Example 2, hot air is introduced on both sides of the substrate with the wet membrane, resulting in a different T2 compared to Example 1.

[0064] Comparative Example 3 Comparative Example 3 provides a quasi-solid-state battery electrolyte membrane and its preparation method, which is basically the same as Example 1, except that a second solvent is not added. See Table 3 for details.

[0065] Comparative Example 4 Comparative Example 4 provides a quasi-solid-state battery electrolyte membrane and its preparation method, which is basically the same as Example 1, except that PC is replaced with NMP, as detailed in Table 3.

[0066] Comparative Example 5 Comparative Example 5 provides a quasi-solid-state battery electrolyte membrane and its preparation method, which is basically the same as Example 1, except that RM257 is replaced with 4-(3-acryloyloxypropoxy)benzoic acid-4′-hexyloxyphenyl ester (RM105), which is a monofunctional acrylate liquid crystal monomer, as shown in Table 3.

[0067] Table 3

[0068] Performance testing The performance of the quasi-solid-state battery electrolyte membranes of the above embodiments and comparative examples was tested according to the following methods: Ionic conductivity: Electrochemical impedance spectroscopy (EIS) was used. Specifically, a blocking electrode (stainless steel / electrolyte membrane / stainless steel) was assembled, and the frequency was set to 0.1 Hz to 1 MHz with an amplitude of 10 mV. Electrochemical impedance spectroscopy was performed at a constant temperature of 25 °C. The bulk resistance R was obtained by fitting the Nyquist plot and equivalent circuit. b ;Measure the film thickness d and contact area S;Ionic conductivity = .

[0069] Residual solvent content: Headspace-gas chromatography (HS-GC) was used. Specifically, 5-10 mg of membrane sample was taken, and the headspace vial was equilibrated at 80℃ for 20 min. The second solvent characteristic peak was used as the detection target, and GC-FID / MS was used for quantification. The residual mass fraction (wt%) was extrapolated from the standard curve.

[0070] Liquid crystal concentration measurement: Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to establish an intensity-concentration standard curve using liquid crystal standards of known concentrations. A linear scan was performed along the thickness direction of the electrolyte membrane in the quasi-solid-state battery to extract the integrated intensity I(x) of the liquid crystal characteristic peak at a distance of 2-3 μm from each of the positive and negative electrode surfaces. This integrated intensity was then substituted into the intensity-concentration standard curve to obtain the liquid crystal concentration C(x) at the positive / negative electrode interface. Gradient distribution coefficient = .

[0071] Battery assembly: CR2032 button cells are assembled in a glove box (H2O / O2<0.1ppm). The positive electrode uses a ternary high-nickel system NCM811 lithium nickel cobalt manganese oxide, and the negative electrode uses lithium metal. The polymer enriched side of the quasi-solid-state battery electrolyte membrane contacts the lithium negative electrode, and the liquid crystal enriched side contacts the positive electrode.

[0072] Negative electrode interface impedance: Electrochemical impedance spectroscopy (EIS) was used. Specifically, a symmetrical battery (lithium sheet / electrolyte membrane / lithium sheet) was assembled, and after assembly, it was allowed to stand for 12 hours. The frequency was set to 0.1Hz~1MHz, the amplitude to 10mV, and the electrochemical impedance spectroscopy was performed at a constant temperature of 25℃. The high-frequency impedance R was obtained by fitting the Nyquist plot and equivalent circuit.SEI and intermediate frequency impedance R ct Negative electrode interface impedance = R SEI +R ct .

[0073] High-temperature storage leakage rate: The mass difference method was used, specifically: the electrolyte membrane was stored at a constant temperature of 60℃ for 168 hours, and the initial mass m0 and m were recorded. t High-temperature storage leakage rate = .

[0074] Pressure leak test: The electrolyte membrane is subjected to a vertical pressure of 0.5MPa at 60℃ for 72 h using a custom clamp; after removal, it is placed on filter paper for 10 min. No leakage is indicated by no liquid traces and a weight loss of <1.0wt%.

[0075] Oxidation onset potential: Linear sweep voltammetry (LSV) was used. Specifically, a coin cell (stainless steel / electrolyte membrane / lithium sheet) was assembled and allowed to stand for 12 hours. The scan rate was 0.5 mV / s, and the open-circuit voltage was scanned to 6.0 V (vs. Li / Li). + Record current density > 0.1 mA / cm² 2 The corresponding potential is the oxidation initiation point.

[0076] 100-cycle capacity retention: A battery charge-discharge test system was used, specifically: the assembled coin cell half-cells were charged and discharged at 0.5C at 25℃, with a voltage range of 2.5V~4.35V; the specific capacity Q1 of the first discharge cycle and Q1 of the 100th discharge cycle were recorded. 100 ; Capacity retention rate after 100 cycles = .

[0077] The test results are shown in Tables 4, 5 and 6.

[0078] Table 4

[0079] Table 5

[0080] Table 6

[0081] Results Analysis In Examples 1 to 4, by controlling the thermal conductivity of the substrate and the temperature difference between the wet film and the substrate, and in Examples 5 to 9, by controlling the precursor solution and the film thickness, a gradient distribution of liquid crystal components can be achieved. Furthermore, the residual second solvent has a low leakage rate at high temperatures and no leakage under pressure, resulting in high safety.

[0082] A comparison of Example 1 and Comparative Example 1 shows that the substrate thermal conductivity exceeds 0.3 W / m·K, the gradient distribution coefficient of the liquid crystal on both sides of the electrolyte membrane is small, and the concentration difference is minimal. After assembly into a battery, the negative electrode interface impedance of Comparative Example 1 increased by 50 Ω·cm after 50 cycles. 2 The increase in negative electrode interface impedance is higher than that in Example 1, indicating that the cycle performance of Comparative Example 1 is poor.

[0083] A comparison of Example 1 and Comparative Example 2 shows that the difference between T1 and T2 is 0, indicating a small gradient distribution coefficient of liquid crystals on both sides of the electrolyte membrane and a relatively small concentration difference. After assembly into a battery, the negative electrode interface impedance of Comparative Example 2 increases by 125 Ω·cm after 50 cycles. 2 The increase in negative electrode interface impedance is much higher than that in Example 1, indicating that the cycling performance of Comparative Example 2 is poor. In contrast, the liquid crystal gradient distribution in Example 1 can effectively protect the lithium metal interface and suppress the reduction side reaction of liquid crystal monomers.

[0084] A comparison of Example 1 and Comparative Example 3 shows that the addition of the second solvent can promote the gradient distribution of the liquid crystal and improve the ionic conductivity, while preventing leakage under high temperature and high pressure.

[0085] A comparison of Example 1 and Comparative Example 4 reveals that NMP molecules are highly rigid and have weak interactions with polymer segments, thus failing to effectively lower the glass transition temperature of the system and provide plasticity. During the rapid evaporation of the first solvent stage, the polymer matrix quickly becomes rigid, and the segment mobility drops sharply, resulting in the thermal driving force being unable to overcome the segment frictional resistance. Simultaneously, the high dielectric constant of NMP disrupts the mesocrystalline phase order of the liquid crystal molecules, causing them to lose their directional migration ability. Therefore, the liquid crystal components are frozen in an initial homogeneous state and cannot form a gradient distribution. Furthermore, the oxidation potential of Comparative Example 4 is lower than that of Example 1, demonstrating that PC exhibits greater electrochemical stability than NMP without relying on functional additives.

[0086] A comparison of Example 1 and Comparative Example 5 shows that monofunctional liquid crystals cannot provide sufficient crosslinking density, and the residual solvent encapsulated in the three-dimensional network formed by crosslinking is prone to leakage, resulting in a significant decrease in cycle performance. The bifunctional liquid crystal crosslinking used in Example 1 can physically confine the residual solvent, giving it solid-state characteristics, which distinguishes it from traditional gel electrolytes.

[0087] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a quasi-solid-state battery electrolyte film, characterized by, The method comprises the following steps: mixing a polymer matrix, a bifunctional reactive liquid crystal monomer, a lithium salt, a mixed solvent, a functional additive and a photoinitiator to obtain a precursor solution, wherein the mixed solvent comprises a first solvent and a second solvent, and satisfies the following conditions: (1) the volatilization rate of the first solvent is higher than that of the second solvent under the same conditions; and (2) the second solvent can plasticize the polymer chain segment after photocuring; a substrate with a thermal conductivity of not higher than 0.3 W / m·K is provided, and the precursor solution is coated on the substrate to form a wet film; the temperature of a side surface of the wet film away from the substrate is controlled to be T1, the temperature of a side surface of the substrate away from the wet film is controlled to be T2, T1>T2, and T1-T2 is 25-40 ℃, the first solvent is volatilized, at least part of the second solvent is reserved, and a dry film is formed; the dry film is subjected to photocuring, and the substrate is removed to obtain the quasi-solid-state battery electrolyte film.

2. The method of claim 1, wherein the method is characterized by: At least one of the following features is comprised: (1) T1 is 55-75 ℃; (2) T2 is 20-45 ℃.

3. The method of claim 1, wherein the method is characterized by: The content of the second solvent is controlled so that the content of the second solvent in the quasi-solid-state battery electrolyte film is 3-5 wt%.

4. The method of claim 3, wherein the method is characterized by, The first solvent accounts for 70-95% of the mass of the mixed solvent, and the second solvent accounts for 5-30% of the mass of the mixed solvent.

5. The method of claim 1, wherein the method is characterized by: At least one of the following features is comprised: (1) the boiling point of the second solvent is ≥200 ℃; (2) the boiling point of the first solvent is ≤100 ℃.

6. The method of claim 5, wherein the method further comprises: At least one of the following features is comprised: (1) the second solvent is selected from at least one of propylene carbonate, ethylene carbonate and γ-butyrolactone; (2) the first solvent is selected from at least one of acetonitrile, acetone and ethyl acetate.

7. The method of claim 1, wherein the method is characterized by: The bifunctional reactive liquid crystal monomer is selected from a bifunctional acrylate liquid crystal monomer.

8. The method of claim 1 to 7, wherein At least one of the following features is comprised: (1) the polymer matrix is selected from at least one of polyethylene oxide, polyethylene glycol diacrylate, polymethyl methacrylate and polyvinylidene fluoride-hexafluoropropylene copolymer; (2) the functional additive is selected from one of lithium difluorophosphate, ethylene sulfate and lithium nitrate; (3) the lithium salt is selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bisfluorosulfonylimide and lithium perchlorate; (4) the photoinitiator is selected from at least one of 2-hydroxy-2-methylpropiophenone and benzoin isopropyl ether; (5) in the precursor solution, the weight parts of the polymer matrix are 10-30, the weight parts of the bifunctional reactive liquid crystal monomer are 5-15, the weight parts of the lithium salt are 3-10, the weight parts of the mixed solvent are 100-200, the weight parts of the functional additive are 0.1-2, and the weight parts of the photoinitiator are 0.5-2; (6) the thickness of the wet film is controlled so that the thickness of the quasi-solid-state electrolyte film is 20-30 μm; (7) the substrate comprises a polymer film and a heat insulation coating layer on the polymer film.

9. A quasi-solid-state battery electrolyte film, characterized by, The quasi-solid-state battery electrolyte film is prepared by the preparation method in any one of claims 1-8.

10. A quasi-solid-state battery, characterized by, The battery includes a positive electrode, a negative electrode, and a quasi-solid-state battery electrolyte membrane located between the positive electrode and the negative electrode. The quasi-solid-state battery electrolyte membrane is prepared by the preparation method of any one of claims 1 to 8, or as described in claim 9.

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