Polyurethane elastomer-deep eutectic composite electrolyte membrane, preparation method and application thereof

Abstract

The present application relates to electrolyte membrane preparation technical field, specifically relates to a kind of polyurethane elastomer-deep eutectic composite electrolyte membrane and preparation method and application.Catalytic condition, by polytetrahydrofuran glycol and toluene-2,4-diisocyanate prepolymerization, then sequentially join dimethylol butyric acid and methyl methacrylic acid tertiary butyl amino ethyl ester are chain-extended, the polyurethane intermediate obtained containing carboxylic acid group and hindered urea bond and the compound containing multiple polymerizable double bond, photo-initiator are mixed into film, sequentially through chain radical polymerization and thermal curing, obtain polyurethane elastomer film;Butanedinitrile, N-methyl acetamide are mixed with bis-trifluoromethanesulfonimide lithium respectively, form deep eutectic electrolyte A and deep eutectic electrolyte B, the equal volume mixture of two obtains composite deep eutectic electrolyte;Polyurethane elastomer film is immersed therein, and the polyurethane elastomer-deep eutectic composite electrolyte membrane prepared overcomes the existing ion conductivity and mechanical property balance problem in prior art.

Description

Technical Field

[0001] This invention relates to the field of electrolyte membrane preparation technology, specifically to a polyurethane elastomer-deep eutectic composite electrolyte membrane, its preparation method, and its application. Background Technology

[0002] Lithium metal, due to its extremely high theoretical specific capacity and ultra-low redox potential, is widely regarded as the most promising anode material for next-generation high-energy-density battery systems. However, lithium metal anodes face multiple challenges in practical applications, including dendrite growth, rapid volume changes, and active electrolyte-side reactions, leading to repeated SEI film rupture and regeneration, increased interfacial impedance, and greater safety risks. Traditional liquid electrolytes, such as carbonates, are volatile and flammable, making it even more difficult to balance safety and reliability under high voltage, wide temperature range, and complex mechanical stress conditions, thus failing to meet the long-term stable operation requirements of high-energy-density lithium metal batteries.

[0003] To alleviate the aforementioned problems, quasi-solid-state or gel-type electrolytes have attracted widespread attention due to their combination of a polymer backbone and a liquid transport phase. These systems provide mechanical support and interfacial stability through a polymer network, while retaining the ion transport capabilities of liquid electrolytes, exhibiting higher safety margins and adaptability in wearable, flexible energy storage, and cryogenic or hyperthermic applications. In recent years, progress has been made in the synergistic regulation of segment polarity, crosslinking density, and solvation structure; simultaneously, the introduction of low-volatility, flame-retardant ionic liquids or deep eutectic electrolytes has expanded the electrochemical stability window and environmental adaptability, achieving substantial progress in improving safety and processing friendliness, and providing a feasible material platform for lithium metal systems.

[0004] However, under the conditions of high current density, large deformation, and wide temperature range for carrying lithium metal, the synergy between mechanical and ion transport remains a key bottleneck restricting performance. Although existing technologies can improve ionic conductivity by increasing the content of liquid electrolyte or plasticizer in the polymer, this weakens the skeletal modulus and puncture resistance. While strengthening crosslinking can improve structural rigidity, it compresses solvation channels, hinders lithium-ion migration, and exacerbates interfacial polarization and contact degradation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a polyurethane elastomer-deep eutectic composite electrolyte membrane, its preparation method, and its applications. This invention uses an isocyanate-terminated prepolymer obtained by the prepolymerization reaction of polytetrahydrofuran diol and toluene-2,4-diisocyanate as the matrix material. Carboxylic acid groups and hindered urea bonds are introduced through a chain extension reaction of dimethylolbutyric acid and tert-butylaminoethyl methacrylate. An interpenetrating polymer network is then constructed through photo-thermal dual curing. This network is then impregnated in a composite deep eutectic electrolyte formed by mixing succinic acid, N-methylacetamide, and lithium bis(trifluoromethanesulfonylimide), respectively, to form a solid-liquid interpenetrating network structure, ultimately yielding the polyurethane elastomer-deep eutectic composite electrolyte membrane. The polyurethane elastomer-deep eutectic composite electrolyte membrane of this invention exhibits excellent mechanical properties, high ionic conductivity, high lithium-ion transference number, a wide electrochemical window, and excellent interfacial stability. This invention overcomes the bottleneck problem of balancing mechanical strength and ionic conductivity in traditional gel electrolytes by introducing hindered urea bonds and carboxylic acid groups into polyurethane segments and forming an interpenetrating network structure using a photo-thermal dual curing process. Simultaneously, by constructing a solid-liquid interpenetrating network structure of a polyurethane elastomer film and a composite deep eutectic electrolyte to synergistically regulate lithium-ion solvation behavior, it solves the problems of interfacial instability and dendrite growth in lithium metal anodes. This fundamentally achieves a comprehensive balance between ion conduction capability, interfacial stability, and safety and reliability, providing a material basis for the long-term stable operation of high-energy-density lithium metal battery systems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a method for preparing a polyurethane elastomer-deep eutectic composite electrolyte membrane, comprising the following steps: S1. Under catalytic conditions, polytetrahydrofuran diol and toluene-2,4-diisocyanate are mixed and subjected to a prepolymerization reaction to obtain an isocyanate-terminated prepolymer. Polytetrahydrofuran diol is a linear polyether diol with a low glass transition temperature, which provides flexible soft segments in the isocyanate-terminated prepolymer, thereby improving the elongation of the polyurethane elastomer film. Toluene-2,4-diisocyanate is an aromatic diisocyanate with high reactivity. The rigid hard segments formed are prone to microphase separation, which can improve the strength and thermal stability of the polyurethane elastomer film.

[0007] S2. Dimethylolbutyric acid (DMO) and tert-butylaminoethyl methacrylate (TBEM) are added sequentially to the prepolymer. A chain extension reaction is carried out in the presence of a catalyst, causing the hydroxyl groups in DMO and TBEM to undergo addition reactions with the terminal isocyanates in the prepolymer, forming urethane bonds. Simultaneously, the tert-butyl-substituted secondary amino groups in TBEM react with the terminal isocyanates in the prepolymer, forming hindered urea bonds. At this point, the carboxylic acid group on DMO and the carbon-carbon double bond on TBEM do not participate in the reaction, yielding a polyurethane intermediate containing carboxylic acid groups and hindered urea bonds. The hindered urea bond structure can achieve network rearrangement through bond breaking and recombination during subsequent heat treatment.

[0008] S3. A polyurethane intermediate, pentaerythritol tetraacrylate containing multiple polymerizable double bonds, and a photoinitiator are mixed. After film formation, under light irradiation, the free radicals generated by the photoinitiator attack the carbon-carbon double bonds in the pentaerythritol tetraacrylate and the carbon-carbon double bonds on the molecular chain of the polyurethane intermediate, initiating a chain-like free radical polymerization reaction to form a first-level crosslinked network. Subsequently, after thermosetting, the hindered urea bonds on the main chain of the polyurethane intermediate undergo reversible cleavage, generating isocyanate and tertiary amine. The generated isocyanate reacts with the carboxylic acid groups on the side chain of the polyurethane intermediate to form urea bonds, forming a second-level crosslinked network between polymer chain segments. At this point, the second-level crosslinked network and the first-level crosslinked network interpenetrate spatially, forming an interpenetrating polymer network. After removing the solvent and water, a polyurethane elastomer film is obtained.

[0009] S4. Succinate and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are mixed to form a deep eutectic electrolyte A. The mass ratio of succinate to LiTFSI is 1.7–2.2:1. Within this range, a transparent and stable deep eutectic electrolyte A can be formed, exhibiting both moderate viscosity and high ionic conductivity. When the mass ratio of succinate to LiTFSI is 2:1, the deep eutectic electrolyte A exhibits optimal non-crystallization, fluidity, and conductivity. Succinate (SN) contains two strongly polar -C≡N groups, has a high dielectric constant (ε≈56), and can promote the dissociation of LiTFSI and provide a suitable electrolyte for Li... + It provides a coordination environment; its linear molecular structure is beneficial for reducing the viscosity of the deep eutectic electrolyte A, thereby promoting ion migration.

[0010] S5. N-methylacetamide and lithium bis(trifluoromethanesulfonyl)imide are mixed to form a deep eutectic electrolyte B. The mass ratio of N-methylacetamide to lithium bis(trifluoromethanesulfonyl)imide is 1.5~2.5:1. Within this range, a deep eutectic electrolyte B with no salt precipitation, low viscosity, and high conductivity can be obtained. When the mass ratio of N-methylacetamide to lithium bis(trifluoromethanesulfonyl)imide is 1.7:1, the deep eutectic electrolyte B exhibits the best overall combination of conductivity and compatibility with the polymer backbone. The amide group (-CONH-) in N-methylacetamide (NMA) possesses both carbonyl oxygen and amino hydrogen, and can react with Li through Lewis acid-base interactions. + It can coordinate with the molecular chain segments of polyurethane elastomer film and form hydrogen bonds, establishing a "molecular bridge" between the solvation layer and the polymer interface.

[0011] The strong polarity of SN synergistically with the hydrogen bond donor capability of NMA weakens Li + -TFSI - Meanwhile, the ion pairs are formed, and the molecules of the composite deep eutectic electrolyte can be constrained by intermolecular hydrogen bond interactions with the polyurethane elastomer film, thereby promoting the redistribution of ions to the solvation shell and constructing a coordination environment rich in anions.

[0012] S6. Mix equal volumes of deep eutectic electrolyte A and deep eutectic electrolyte B to obtain a composite deep eutectic electrolyte.

[0013] S7. The polyurethane elastomer membrane is immersed in the composite deep eutectic electrolyte, allowing the composite deep eutectic electrolyte to penetrate into the interpenetrating polymer network of the polyurethane elastomer membrane and form a solid-liquid interpenetrating network structure with the polar groups (such as urethane groups and amide groups) on the molecular chain segments of the polyurethane elastomer membrane through hydrogen bonds. This stably confines the composite deep eutectic electrolyte in the interpenetrating polymer network, resulting in a polyurethane elastomer-deep eutectic composite electrolyte membrane.

[0014] In this process, the amide hydrogen of NMA forms strong hydrogen bonds with the carbonyl and carboxyl groups in the polyurethane elastomer membrane molecular chain, while the cyano nitrogen of SN forms hydrogen bonds with the NH group of the urea bond in the polyurethane elastomer membrane molecule. This double hydrogen bonding effect stably confines the composite deep eutectic electrolyte within the interpenetrating polymer network, preventing leakage and volatilization. Furthermore, the interpenetrating polymer network provides continuous mechanical support and alleviates local stress concentration during charging and discharging, thereby reducing dendrite growth tendency and improving the uniformity of lithium deposition / stripping, thus extending the battery's cycle life.

[0015] Preferably, the molar ratio of polytetrahydrofuran diol to toluene-2,4-diisocyanate is 1:1.7~2.3, to ensure that the hydroxyl groups react completely during the prepolymerization process while retaining free isocyanate groups at both ends of the prepolymer. The mass fraction of the terminal isocyanate groups accounts for 2.0wt%~4.0wt% of the isocyanate-terminated prepolymer, providing sufficient reaction sites for subsequent chain extension reactions with dimethylolbutyric acid and tert-butylaminoethyl methacrylate, thereby introducing functional groups such as carboxylic acid groups, (meth)acryloyloxy polymerizable double bonds and hindered urea bonds into the polyurethane segments.

[0016] Preferably, the molar ratio of dimethylolbutyric acid to tert-butylaminoethyl methacrylate is 1:1, and the ratio of the sum of the molar amounts of dimethylolbutyric acid and tert-butylaminoethyl methacrylate to the molar amount of isocyanate groups in the prepolymer is 0.95~1.05:1; to ensure that the molar concentrations of hindered urea bonds and carboxylic acid groups are equal after the reaction, providing a balanced functional group basis for the subsequent construction of a second-level crosslinked network through thermosetting treatment.

[0017] Preferably, the conditions for the prepolymerization reaction and the chain extension reaction are the same: under nitrogen protection, the reaction is carried out with stirring at 50℃~60℃ for 3h~5h.

[0018] Preferably, the mass ratio of pentaerythritol tetraacrylate to polyurethane intermediate is 3~7:100.

[0019] Preferably, the mass ratio of the photoinitiator to the total mass of the polyurethane intermediate and pentaerythritol tetraacrylate is 2 to 4:100.

[0020] Preferably, the photoinitiator is (2,4,6-trimethylbenzoyl)diphenylphosphine oxide.

[0021] Preferably, the conditions for the chain free radical polymerization reaction are: irradiation under ultraviolet light with a wavelength of 385 nm for 1 min to 2 min.

[0022] Preferably, the conditions for thermosetting are: heat treatment at 90°C for 5 to 7 hours.

[0023] Preferably, succinic anhydride and N-methylacetamide are dehydrated by 4 Å molecular sieve before preparation in a glove box with a water content of less than 0.1 ppm.

[0024] Preferably, the immersion conditions are: immersion at room temperature for 1 to 4 hours.

[0025] Preferably, the polyurethane elastomer membrane is vacuum dried and stored in a glove box for no less than two weeks before impregnation to remove residual moisture.

[0026] A second objective of this invention is to provide a polyurethane elastomer-deep eutectic composite electrolyte membrane prepared by the above-described method, comprising: an interpenetrating polyurethane polymer network and a composite deep eutectic electrolyte; wherein the interpenetrating polymer network and the composite deep eutectic electrolyte form a stable mechano-electro-synergistic structure through hydrogen bonds.

[0027] A third objective of the present invention is to provide a lithium metal battery comprising a positive electrode, a lithium metal negative electrode, and the aforementioned polyurethane elastomer-deep eutectic composite electrolyte membrane disposed between the positive and negative electrodes.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: 0. This invention provides a method for preparing a polyurethane elastomer-deep eutectic composite electrolyte membrane. Under catalytic conditions, polytetrahydrofuran diol and toluene-2,4-diisocyanate are mixed and subjected to a prepolymerization reaction to obtain an isocyanate-terminated prepolymer. Dimethylolbutyric acid (DMHA) and tert-butylaminoethyl methacrylate (TBEM) are then added sequentially to the prepolymer for chain extension. The hydroxyl groups in DMHA and TBEM react with the terminal isocyanates in the prepolymer to form urethane bonds. Simultaneously, the tert-butyl-substituted secondary amino groups in TBEM react with the terminal isocyanates in the prepolymer to form hindered urea bonds. At this point, the carboxylic acid group on DMHA and the carbon-carbon double bond on TBEM do not participate in the reaction, resulting in a polyurethane containing carboxylic acid groups and hindered urea bonds. Intermediate: A polyurethane intermediate, pentaerythritol tetraacrylate containing multiple polymerizable double bonds, and a photoinitiator are mixed and film-formed. Under light irradiation, the photoinitiator absorbs light energy and decomposes to generate free radicals. These free radicals attack the carbon-carbon double bonds in the compound containing multiple polymerizable double bonds and the carbon-carbon double bonds on the polyurethane intermediate molecular chain, initiating a chain-like free radical polymerization reaction to form a first-level crosslinked network. Subsequently, after thermosetting, the hindered urea bonds on the polyurethane intermediate backbone undergo reversible cleavage, generating isocyanate and tertiary amine. The generated isocyanate reacts with the carboxylic acid groups on the polyurethane intermediate to form urea bonds, forming a second-level crosslinked network between polymer chain segments. At this point, the second-level crosslinked network and the first-level crosslinked network interpenetrate spatially, forming an interpenetrating polymer network. After removing the solvent and water, a polyurethane elastomer film is obtained.

[0029] Succinate and lithium bis(trifluoromethanesulfonyl)imide are mixed to form a deep eutectic electrolyte A; N-methylacetamide and lithium bis(trifluoromethanesulfonyl)imide are mixed to form a deep eutectic electrolyte B; equal volumes of deep eutectic electrolyte A and deep eutectic electrolyte B are mixed to obtain a composite deep eutectic electrolyte; a polyurethane elastomer membrane is impregnated in the composite deep eutectic electrolyte, allowing the composite deep eutectic electrolyte to penetrate into the interpenetrating polymer network of the polyurethane elastomer membrane and form a solid-liquid interpenetrating network structure through hydrogen bonds with the polar groups on the molecular chain segments of the polyurethane elastomer membrane, thereby confining the composite deep eutectic electrolyte within the interpenetrating polymer network, resulting in a polyurethane elastomer-deep eutectic composite electrolyte membrane. The polyurethane elastomer-deep eutectic composite electrolyte membrane prepared by the method of this invention fundamentally achieves a comprehensive balance of ion conduction capability, interfacial stability, and safety reliability, providing a material basis for the long-term stable operation of lithium metal batteries.

[0030] At the microscale, the solid-liquid interpenetrating network structure between the polyurethane elastomer film and the composite deep eutectic electrolyte binds solvent molecules, constructing an anion-rich solvation structure. This is beneficial for increasing the lithium-ion transference number and suppressing concentration polarization, promoting uniform lithium-ion transport and deposition. At the macroscale, the interpenetrating polyurethane cross-linked network forms an elastic framework that internally confines and fixes the composite deep eutectic electrolyte, buffering electrode deformation and maintaining the integrity of the electrode / electrolyte interface, thereby improving interface stability.

[0031] 2. The polyurethane elastomer-deep eutectic composite electrolyte membrane of the present invention has excellent mechanical properties and structural recovery ability, high migration number and stable ion conduction performance, as well as excellent interface stability and dendrite suppression effect, and can be used in flexible energy storage devices, wearable electronic devices and high-safety, high-energy-density lithium metal battery systems.

[0032] Among its key features are excellent mechanical properties and structural recovery capabilities: This invention uses a polyurethane elastomer membrane as a continuous skeleton, providing adjustable viscoelastic support and deformation tolerance under tensile, bending, and volume fluctuation conditions; the polar groups in the polyurethane elastomer membrane and the deep eutectic phase in the composite deep eutectic electrolyte form a stable hydrogen bond network, enhancing the coupling and integrity of the polyurethane elastomer membrane and the composite deep eutectic electrolyte, significantly improving the elongation at break, strain recovery, and cyclic deformation retention of the polyurethane elastomer-deep eutectic composite electrolyte membrane, ensuring that the ion channel remains continuous under large deformation and multiple loading, and providing a foundation for the subsequent realization of a functional modulus window that balances ion conduction and puncture resistance.

[0033] High mobility number and stable ion conductivity: The polyurethane segments in the composite deep eutectic electrolyte and the polyurethane elastomer membrane construct a synergistic hydrogen bonding / solventization microenvironment at the interface, weakening the binding of lithium ions and anions and enriching anion migration channels. The polyurethane elastomer-deep eutectic composite electrolyte membrane of this invention exhibits a mobility number of approximately 8.4 × 10⁻⁶ at room temperature. -4 With an ionic conductivity of S / cm and a lithium-ion transference number of 0.69, it exhibits transport characteristics of low polarization and low impedance growth. Meanwhile, the interpenetrating polymer network effectively suppresses the volatilization and leakage of the composite deep eutectic electrolyte, improving the temporal stability and environmental adaptability of the conduction behavior, and ensuring the structural stability and service life of the polyurethane elastomer-deep eutectic composite electrolyte membrane.

[0034] Excellent interface stability and dendrite suppression: The solid-liquid interpenetrating network structure between the polyurethane elastomer film and the composite deep eutectic electrolyte binds solvent molecules, constructing anion-rich solvation structure. This facilitates the in-situ construction of a stable, dense, and uniform solid electrolyte interface (SEI) on the lithium metal surface, homogenizes the deposition electric field, and reduces side reaction activity, thereby inhibiting the nucleation and penetration of lithium dendrites, reducing short-circuit risk, and extending cycle life and safety window. The continuous adhesion and puncture resistance provided by the interpenetrating polymer network further consolidate the interface integrity, making long-term stability under high current density and high voltage conditions possible. Attached Figure Description

[0035] Figure 1 The graph shows the mechanical property test results of the polyurethane elastomer-deep eutectic composite electrolyte membrane in Example 1.

[0036] Figure 2 The Fourier transform infrared spectrum of the polyurethane elastomer-deep eutectic composite electrolyte membrane in Example 1 is shown.

[0037] Figure 3 The polyurethane intermediate of Example 1 1 H NMR spectrum.

[0038] Figure 4 The figures show the stress-strain curves of the polyurethane elastomer-deep eutectic composite electrolyte membranes of Examples 1 to 3 and Comparative Example 3, with the inset showing the ionic conductivity of the polyurethane elastomer-deep eutectic composite electrolyte membranes of Examples 1 to 3 and Comparative Example 3 at 30°C.

[0039] Figure 5 The stress-strain curves are shown for the polyurethane elastomer-deep eutectic composite electrolyte membrane of Example 1 and the polyurethane-deep eutectic composite electrolyte membrane of Comparative Example 1.

[0040] Figure 6The stress-strain curves are shown for the polyurethane elastomer-deep eutectic composite electrolyte membrane of Example 1 and the polyurethane elastomer electrolyte membrane of Comparative Example 2.

[0041] Figure 7 The graph shows the constant current charge-discharge cycle performance of lithium metal batteries-A1 and-B2, where the left axis represents the discharge specific capacity and the right axis represents the coulombic efficiency.

[0042] Figure 8 The inset shows the current-time curve of the lithium / SCGPE / lithium symmetric cell assembled with the polyurethane elastomer-deep eutectic composite electrolyte membrane in Example 1 under constant potential polarization conditions. The inset shows the AC impedance spectrum of the lithium / SCGPE / lithium symmetric cell before and after polarization.

[0043] Figure 9 The AC impedance spectra of the steel sheet / SCGPE / steel sheet symmetrical cells assembled with the SCGPE gel electrolyte of Example 1 under conditions of 25°C to 70°C.

[0044] Figure 10 The current-voltage curve of the SCGPE gel electrolyte is shown. Detailed Implementation

[0045] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] It should be noted that the technical terms used in this invention are only for describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased commercially or prepared by existing methods. Specifically, SN and NMA were placed in dry containers, 4Å molecular sieves were added, and the containers were left to stand in a glove box (H2O < 0.1ppm) for 48 hours to remove trace amounts of moisture; the photoinitiator, 2,4,6-trimethylbenzoyl)diphenylphosphine oxide, was denoted as TPO.

[0047] The polyurethane elastomer-deep eutectic composite electrolyte membrane of this invention achieves synergistic optimization at both the macroscopic mechanical framework stability and microscopic solvation control levels through a force-electric coupling material design concept, thus balancing the dual requirements of mechanical strength and ion conduction performance. Specifically, the polyurethane elastomer membrane provides continuous and recoverable elastic support, while the composite deep eutectic electrolyte optimizes lithium-ion solvation and migration channels through hydrogen bonding. Together, they reduce polarization and stabilize the electrode / electrolyte interface, thereby achieving a comprehensive and verifiable improvement across multiple indicators, specifically in the following aspects:

[0048] First, in terms of excellent mechanical properties and strong deformation adaptability, the interpenetrating network polyurethane elastomer membrane enables the polyurethane elastomer-deep eutectic composite electrolyte membrane to maintain structural integrity and channel continuity under large strain and repeated loading. The hydrogen bonds between the polar groups (urethane, urea, amide and other groups in the polyurethane elastomer membrane) and the composite deep eutectic electrolyte enhance the coupling and resilience between the polyurethane elastomer membrane and the ion transport phase, as well as significantly improve the elongation at break, strain recovery and deformation retention capabilities, and can maintain low impedance and stable ion transport under conditions such as tension, bending and volume fluctuation.

[0049] Secondly, regarding the stability of the interfacial chemical environment and excellent dendrite suppression performance, the composite deep eutectic electrolyte constructs an anion-rich solvation environment that induces the formation of a dense, uniform, and ion-permeable SEI on the lithium surface. This weakens side reactions on the metal surface, homogenizes the local electric field, suppresses dendrite nucleation and penetration, reduces interfacial impedance growth, and extends cycle life. Compared with traditional strong solvent coordination systems, the polyurethane elastomer-deep eutectic composite electrolyte membrane of this invention exhibits higher stability during long-term cycling and demonstrates lower polarization and a more stable potential plateau in symmetrical lithium batteries and full cells.

[0050] Thirdly, regarding room temperature operating stability, in a full battery using the polyurethane elastomer-deep eutectic composite electrolyte membrane of the present invention as the electrolyte membrane, combined with a lithium iron phosphate (LiFePO4) cathode, an NCM811 high-voltage cathode, and a lithium metal anode, the polyurethane elastomer-deep eutectic composite electrolyte membrane of the present invention can stably support high-capacity and high-efficiency charge-discharge processes at room temperature, effectively suppressing lithium dendrite formation and maintaining low polarization, and exhibiting good cycle stability and rate performance; the polyurethane elastomer membrane's inhibitory effect on the volatilization and leakage of the composite deep eutectic electrolyte further ensures the temporal stability and environmental adaptability of conduction behavior.

[0051] In summary, the polyurethane elastomer-deep eutectic composite electrolyte membrane of the present invention achieves a comprehensive balance in terms of structural design, electrochemical performance, interface stability and safety for application purposes. The polyurethane elastomer membrane ensures channel continuity and puncture resistance, while the composite deep eutectic electrolyte achieves efficient migration and wide window stability. It also exhibits reproducible cycling and rate advantages in actual full cells.

[0052] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will provide a detailed description in conjunction with specific embodiments: Example 1 A method for preparing a polyurethane elastomer-deep eutectic composite electrolyte membrane includes the following steps: S1. Preparation of polyurethane elastomer film: S11. Prepolymer reaction: 0.005 mol of polytetrahydrofuran diol was placed in a three-necked flask equipped with a mechanical stirrer and stirred under vacuum in an oil bath at 120°C for 12 h to remove moisture impurities from the polytetrahydrofuran diol. Subsequently, under a nitrogen atmosphere at 65°C, 50 mL of N,N-dimethylformamide and 0.010 mol of toluene-2,4-diisocyanate were added sequentially to the three-necked flask. After stirring evenly, the catalyst dibutyltin dilaurate was added, and the reaction was stirred at a constant temperature of 65°C for 3 h to obtain an isocyanate-terminated prepolymer, denoted as the prepolymer. The amount of catalyst added was 0.1% of the mass of polytetrahydrofuran diol.

[0053] S12, Chain Extension Reaction: 0.0033 mol of dimethylolbutyric acid was added sequentially to the prepolymer. Under a nitrogen atmosphere, the reaction was carried out at a constant temperature of 65°C for 3 hours. Then, 0.0033 mol of tert-butylaminoethyl methacrylate was added, and the reaction was continued at a constant temperature of 65°C for another 3 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction system, cooled to room temperature, was added dropwise to deionized water while stirring to promote dispersion. After the addition was completed, a pale yellow flocculent precipitate was formed in the system. The mixture containing the precipitate was centrifuged and separated. The precipitate was then collected by filtration and dried in a vacuum oven for 48 hours to remove water, yielding a polyurethane intermediate.

[0054] S13. Introduction of crosslinking agent and photocurable monomer: Pentaerythritol tetraacrylate was added to the polyurethane intermediate and magnetically stirred at room temperature for 2 hours to ensure that the pentaerythritol tetraacrylate was fully dissolved and uniformly dispersed. Then, TPO for subsequent photocuring and crosslinking reaction was added to obtain a mixed system. The amount of pentaerythritol tetraacrylate added was 5 wt% of the mass of the polyurethane intermediate, and the amount of TPO added was 2 wt% of the mass of the polyurethane intermediate.

[0055] S14. Mold forming and first network photocrosslinking: The mixed system is uniformly poured into a PTFE mold and irradiated under ultraviolet light with a wavelength of 385nm for 1 minute. Under the action of TPO, a free radical polymerization reaction is carried out to form the first-level crosslinking network, realizing the initial structural shaping and the construction of the mechanical support skeleton, and obtaining the photocrosslinking pretreated film.

[0056] S15. Thermal curing to construct the interpenetrating structure and post-treatment drying: The photocrosslinked pretreated film is placed in an environment of 90°C for 6 hours for thermal curing treatment, which further drives the polyurethane network in the photocrosslinked pretreated film to break and reconnect bonds, constructing a second-level crosslinking structure. After realizing a complete interpenetrating polymer network, it is dried under vacuum conditions at 60°C for 24 hours to completely remove residual solvent and trace moisture, and obtain a flexible, transparent, and structurally stable polyurethane elastomer film.

[0057] Transfer the polyurethane elastomer membrane to a glove box (H2O < 0.1 ppm) and let it stand for at least two weeks to completely remove any trace amounts of residual moisture before use.

[0058] S2. Preparation of composite deep eutectic electrolyte: S21. Weigh succinate (SN) and LiTFSI in a mass ratio of 2:1. Place SN and LiTFSI together in a dry, sealed container equipped with a magnetic stirrer and stir at room temperature for 6 hours until a transparent and uniform deep eutectic electrolyte A is formed. Weigh N-methylacetamide (NMA) and LiTFSI in a mass ratio of 1.7:1. Place NMA and LiTFSI together in a dry, sealed container equipped with a magnetic stirrer and stir at room temperature for 6 hours until a transparent and uniform deep eutectic electrolyte B is formed. Mix equal volumes of deep eutectic electrolyte A and deep eutectic electrolyte B and stir for 4 hours to ensure uniform mixing to obtain a composite deep eutectic electrolyte.

[0059] S3. Preparation of polyurethane elastomer-deep eutectic composite electrolyte membrane: The polyurethane elastomer membrane was cut into circular sheets with a diameter of 12 mm and immersed in a composite deep eutectic electrolyte for 4 hours at room temperature. Then, it was removed and the residual liquid on the surface was gently wiped off to obtain a polyurethane elastomer-deep eutectic composite electrolyte membrane, namely SCGPE, denoted as A1, which was used for subsequent electrochemical device assembly.

[0060] Based on Example 1, the effects of different impregnation times on the performance of polyurethane elastomer-deep eutectic composite electrolyte membranes were also investigated, as shown in Examples 2-3 and Comparative Example 3.

[0061] Example 2 A method for preparing a polyurethane elastomer-deep eutectic composite electrolyte membrane is the same as that in Example 1, except that the impregnation time in S3 is replaced by 1 hour instead of 4 hours, resulting in a polyurethane elastomer-deep eutectic composite electrolyte membrane, denoted as A2.

[0062] Example 3 A method for preparing a polyurethane elastomer-deep eutectic composite electrolyte membrane is the same as that in Example 1, except that the impregnation time in S3 is replaced by 2 hours instead of 4 hours, resulting in a polyurethane elastomer-deep eutectic composite electrolyte membrane, denoted as A3.

[0063] Comparative Example 1 A method for preparing a polyurethane-deep eutectic composite electrolyte membrane is the same as that in Example 1, except that the photocrosslinking pretreated membrane is not subjected to thermal curing and is directly dried under vacuum at 60°C for 24 hours to obtain a polyurethane elastomer membrane. The obtained polyurethane elastomer membrane relies solely on a single physical crosslinking network for support, ultimately yielding a polyurethane-deep eutectic composite electrolyte membrane, denoted as B1, which is used for subsequent electrochemical device assembly.

[0064] Comparative Example 2 A method for preparing a polyurethane elastomer electrolyte membrane is the same as that in Example 1, except that the composite deep eutectic electrolyte in S3 is replaced with a traditional 1 mol / L LiTFSI electrolyte (the solvent of the LiTFSI electrolyte is a mixture of DME and DOL in equal volumes) to obtain a polyurethane elastomer electrolyte membrane, denoted as B2.

[0065] Comparative Example 3 A method for preparing a polyurethane elastomer-deep eutectic composite electrolyte membrane is the same as that in Example 1, except that the impregnation time in S3 is replaced by 8 hours instead of 4 hours, resulting in a polyurethane elastomer-deep eutectic composite electrolyte membrane, denoted as A4.

[0066] Structural characterization: observe Figure 2 It was found that the polyurethane elastomer-deep eutectic composite electrolyte membrane of Example 1 was effective at 2260 cm⁻¹. -1 The characteristic absorption peak of the isocyanate group (-N=C=O) was not observed at 3300 cm⁻¹, but was observed at 3300 cm⁻¹. -1 The presence of a distinct -NH stretching vibration peak nearby indicates that the isocyanate groups in the polyurethane elastomer-deep eutectic composite electrolyte membrane of Example 1 have been largely reacted, successfully forming a polyurethane-deep eutectic composite electrolyte membrane containing a urethane structure.

[0067] like Figure 3 As shown, the chemical shifts of each characteristic peak in the NMR spectrum correspond perfectly to the hydrogen atom signals marked in the structural illustration, jointly confirming that dimethylolbutyric acid and tert-butylaminoethyl methacrylate have been grafted onto the polyurethane chain segment, successfully constructing the polyurethane intermediate of the target structure.

[0068] ① Tensile property test: The polyurethane elastomer-deep eutectic composite electrolyte membranes of Examples 1 to 3 and Comparative Example 3, the polyurethane-deep eutectic composite electrolyte membrane of Comparative Example 1, and the polyurethane elastomer electrolyte membrane of Comparative Example 2 were cut into dumbbell-shaped specimens (hereinafter referred to as specimens) (referring to GB / T528-2009 standard). The gauge length was 20 mm, the width was 4 mm, and the thickness was measured by micrometer. The specimens were placed at 25℃±2℃ and 50±10% relative humidity for at least 12 hours before testing.

[0069] Using an electronic universal testing machine, the specimen is clamped between fixtures with an initial gauge length L0 of 20 mm and a tensile speed of 100 mm / min. Tensile tests are performed until the specimen breaks, and the maximum tensile load Fmax and the gauge length L at the time of breakage are recorded.

[0070] Depend on Figure 1 The results showed that the polyurethane elastomer-deep eutectic composite electrolyte membrane of Example 1 had a tensile strength of approximately 60 MPa, an elongation at break of over 1500%, and a corresponding toughness of approximately 300 MJ / m. 3 .according to Figure 4 It can be seen that with the extension of impregnation time, the ionic conductivity of the polyurethane elastomer-deep eutectic composite electrolyte membrane significantly increases, while the mechanical properties show a downward trend. The electrolyte membranes in Examples 2 and 3 have high tensile strength but low ionic conductivity, making it difficult to meet the requirements for long-term stable battery cycling; they can only be used as comparative references. The ionic conductivity of the polyurethane elastomer-deep eutectic composite electrolyte membrane in Comparative Example 3 is close to saturation, but its mechanical strength decreases significantly, failing to meet the mechanical strength requirements during battery assembly and use. Considering both ionic conductivity and mechanical properties, Example 1 (A1) achieves a better balance between the two, providing sufficient mechanical strength while also possessing the ionic conduction capability to support normal battery cycling, making it a preferred embodiment of the present invention.

[0071] according to Figure 5 As is known, the mechanical properties of A1 are significantly higher than those of B1, indicating that the present invention effectively improves the mechanical strength and elongation at break of the polyurethane elastomer membrane by introducing an interpenetrating polymer network, thus giving the polyurethane elastomer-deep eutectic composite electrolyte membrane excellent structural stability and flexibility compatibility.

[0072] according to Figure 6 As is known, the mechanical properties of A1 are higher than those of B2, indicating that the hydrogen bonding and other interactions between the polyurethane elastomer membrane and the composite deep eutectic electrolyte can enhance the inter-segment forces, improve the structural integrity and energy dissipation capacity of the interpenetrating polymer network, and thus significantly improve the mechanical strength and toughness of the polyurethane elastomer-deep eutectic composite electrolyte membrane.

[0073] application: In Examples 1 to 3 of this invention, polyurethane elastomer-deep eutectic composite electrolyte membranes were all prepared, and the results were parallel. The performance of the polyurethane elastomer-deep eutectic composite electrolyte membrane of Example 1 and the polyurethane-deep eutectic composite electrolyte membrane of Comparative Example 1 will be studied as follows: Battery assembly method: (1) Lithium iron phosphate powder (LFP), PVDF and Super P were dispersed in N-methyl-2-pyrrolidone in a mass ratio of 8:1:1 to obtain a slurry. The slurry was coated onto a carbon-coated aluminum foil using a scraper. It was first dried at 60°C for 4 hours and then vacuum dried at 80°C for 12 hours to remove residual solvent. Subsequently, it was stamped into a circular electrode with a diameter of 12 mm to obtain a positive electrode sheet, which was stored in an argon-filled glove box (H2O, O2<0.1ppm) for later use.

[0074] (2) Batteries were assembled using the polyurethane elastomer-deep eutectic composite electrolyte membrane of Example 1 and the polyurethane-deep eutectic composite electrolyte membrane of Comparative Example 1, respectively. In a glove box filled with argon (H2O and O2 content are both less than 0.1ppm), the positive electrode, electrolyte membrane and lithium metal negative electrode were stacked in sequence and placed into the CR2025 button battery case.

[0075] (3) After covering with gaskets and springs, seal with a sealing machine to obtain a semi-finished button cell.

[0076] (4) Place the semi-finished button cell in a 60°C environment for 10 hours. After the heat preservation is completed, cool it naturally to room temperature to obtain lithium metal batteries, which are respectively named lithium metal battery-A1 and lithium metal battery-B2.

[0077] ② Battery cycle test: Using the Xinwei multi-channel battery testing system, constant current charge-discharge cycle tests were conducted on lithium metal batteries-A1 and-B2 at 30℃ to test the current rate and voltage window. The test conditions were: 0.5C, LFP loading of 10 mg / cm³. 2 .

[0078] Depend on Figure 7 The results showed that the differences between A1 and B2 were significant, indicating that the polyurethane elastomer film interacted with the composite deep eutectic electrolyte, and that regulating the anion-rich solvation structure helped to improve interfacial stability and electrochemical reversibility.

[0079] ③ Ionic conductivity: Al was assembled in a stainless steel (SS) / / SS symmetric electrode system, and its ionic conductivity, transfer number and electrochemical stability were systematically characterized using an electrochemical workstation (CHI660E).

[0080] The resistance of the polyurethane-deep eutectic composite electrolyte membrane was measured using electrochemical impedance spectroscopy (EIS) within the frequency range of 0.1 Hz to 0.1 MHz under an AC perturbation voltage of 5 mV. The ionic conductivity (δ) was calculated using the following formula:

[0081] .

[0082] Where S represents the effective contact area between the polyurethane-deep eutectic composite electrolyte membrane and SS, R represents the resistance value of the bulk electrolyte, and L is the thickness of GPE.

[0083] Depend on Figure 9 It was found that the AC impedance of the polyurethane-deep eutectic composite electrolyte membrane in Example 1 decreased with increasing temperature. Based on the impedance data at 25°C and combined with the thickness and electrode area of ​​the polyurethane elastomer-deep eutectic composite electrolyte membrane, the ionic conductivity of the polyurethane-deep eutectic composite electrolyte membrane at 25°C was calculated to be approximately 8.4 × 10⁻⁶. -4 S / cm.

[0084] ④ Electrochemical stability window: The electrochemical stability window of the polyurethane elastomer-deep eutectic composite electrolyte membrane was determined by using an asymmetric electrode system SS / / Li and linear scanning voltammetry (LSV) at a scan rate of 10 mV / s within a voltage range of 0 V to 6.0 V.

[0085] Figure 10 The results show that the polyurethane-deep eutectic composite electrolyte membrane exhibits a significant current increase above approximately 4.83V, corresponding to an upper limit of the electrolyte's electrochemical stability window of 4.83V.

[0086] ⑤ Lithium-ion transfer number: The Li content of the electrolyte was measured by the galvanostatic method of a typical Li / / Li symmetric cell. + Transition number (t) Li+ ). t Li+ Calculate using the following equation:

[0087] Where ΔV is the DC polarization voltage (10mV), and I0 and Is represent the initial current and steady-state current of the symmetrical cell before and after polarization, respectively. Meanwhile, R... i0 With R is These represent the interface resistances of the symmetrical cell before and after polarization.

[0088] Depend on Figure 8The results show that under constant potential polarization conditions, the current in the steel sheet / SCGPE / steel sheet symmetrical cell assembled with the polyurethane-deep eutectic composite electrolyte membrane gradually decreases and tends to stabilize over time. Combined with the AC impedance data before and after polarization shown in the inset, the lithium-ion transference number of the polyurethane-deep eutectic composite electrolyte membrane is calculated to be approximately 0.69, indicating that lithium-ion carrier conduction is dominant in the polyurethane-deep eutectic composite electrolyte membrane, which is beneficial for reducing concentration polarization.

[0089] Regarding electrochemical stability, the polyurethane elastomer-deep eutectic composite electrolyte membrane constructed in this invention exhibits a wide electrochemical stability window, with preliminary tests showing a stability of approximately 4.83V (vs. Li / Li). + ),like Figure 10 As shown, it can be adapted to higher voltage cathode materials and reduce side reactions at high potentials; at the same time, the deep eutectic phase has low volatility and potential flame retardant characteristics, and is bound by a polyurethane cross-linking network in this invention, which on the one hand reduces the escape of volatile / flammable components, and on the other hand inhibits the flow and leakage of electrolyte, thereby providing a higher safety margin for high energy density systems.

[0090] This invention significantly improves the tensile strength and toughness of polyurethane elastomer-deep eutectic composite electrolyte membranes by using polyurethane elastomer membranes with an interpenetrating network structure in space. The resulting membranes exhibit a tensile strength of approximately 60 MPa, an elongation at break exceeding 1500%, and a corresponding toughness of approximately 300 MJ / m. 3 This endows the polyurethane elastomer-deep eutectic composite electrolyte membrane with excellent puncture resistance. Furthermore, the introduction of a composite deep eutectic electrolyte composed of succinate, N-methylacetamide, and LiTFSI, along with polar groups (such as urethane and amide groups) on the polyurethane elastomer molecular segments, synergistically regulates the solvation structure of lithium ions through hydrogen bonding and dipole interactions, constructing anion-rich migration pathways. This results in a higher lithium ion transference number and stable ion conduction behavior, making the polyurethane elastomer-deep eutectic composite electrolyte membrane of this invention exhibit excellent mechanical, electrochemical, and environmental adaptability, enabling it to meet the energy storage needs of next-generation high-safety, high-energy-density lithium metal battery systems.

[0091] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A method for preparing a polyurethane elastomer-deep eutectic composite electrolyte membrane, characterized in that, Includes the following steps: Under catalytic conditions, polytetrahydrofuran diol and toluene-2,4-diisocyanate were mixed and subjected to a prepolymerization reaction to obtain an isocyanate-terminated prepolymer; dimethylolbutyric acid and tert-butylaminoethyl methacrylate were added sequentially to the prepolymer to carry out a chain extension reaction to obtain a polyurethane intermediate containing carboxylic acid groups and hindered urea bonds. A polyurethane intermediate, pentaerythritol tetraacrylate containing multiple polymerizable double bonds, and a photoinitiator are mixed and formed into a film. Then, a chain free radical polymerization reaction is carried out under light irradiation to form a first-level crosslinked network. Subsequently, a thermosetting treatment is performed to form a second-level crosslinked network. At this time, the second-level crosslinked network and the first-level crosslinked network interpenetrate each other to form an interpenetrating polymer network. After removing the solvent and water, a polyurethane elastomer film is obtained. Succinate and lithium bis(trifluoromethanesulfonyl)imide are mixed to form a deep eutectic electrolyte A, wherein the mass ratio of succinate to lithium bis(trifluoromethanesulfonyl)imide is 1.7~2.2:1; N-methylacetamide and lithium bis(trifluoromethanesulfonyl)imide are mixed to form a deep eutectic electrolyte B, wherein the mass ratio of N-methylacetamide to lithium bis(trifluoromethanesulfonyl)imide is 1.5~2.5:1; deep eutectic electrolyte A and deep eutectic electrolyte B are mixed in equal volumes to obtain a composite deep eutectic electrolyte; A polyurethane elastomer membrane is immersed in a composite deep eutectic electrolyte, allowing the electrolyte to penetrate into the interpenetrating polymer network of the polyurethane elastomer membrane, thus obtaining a polyurethane elastomer-deep eutectic composite electrolyte membrane.

2. The preparation method according to claim 1, characterized in that, The molar ratio of polytetrahydrofuran diol to toluene-2,4-diisocyanate is 1:1.7~2.

3.

3. The preparation method according to claim 1, characterized in that, The molar ratio of dimethylolbutyric acid to tert-butylaminoethyl methacrylate is 1:1, and the ratio of the sum of the molar amounts of dimethylolbutyric acid and tert-butylaminoethyl methacrylate to the molar amount of isocyanate groups in the prepolymer is 0.95~1.05:

1.

4. The preparation method according to claim 1, characterized in that, The conditions for the prepolymerization reaction and the chain extension reaction are the same: under nitrogen protection, the reaction is carried out with stirring at 50℃~60℃ for 3h~5h.

5. The preparation method according to claim 1, characterized in that, The mass ratio of pentaerythritol tetraacrylate to polyurethane intermediate is 3~7:100; The mass ratio of the photoinitiator to the total mass of the polyurethane intermediate and pentaerythritol tetraacrylate is 2~4:

100.

6. The preparation method according to claim 1, characterized in that, The conditions for the chain radical polymerization reaction are: irradiation under ultraviolet light with a wavelength of 385 nm for 1 min to 2 min.

7. The preparation method according to claim 1, characterized in that, The conditions for thermosetting are: heat treatment at 90℃ for 5 to 7 hours.

8. The preparation method according to claim 1, characterized in that, The immersion conditions are: immersion at room temperature for 1 to 4 hours.

9. A polyurethane elastomer-deep eutectic composite electrolyte membrane prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium metal battery, characterized in that, The polyurethane elastomer-deep eutectic composite electrolyte membrane as described in claim 9 is used to prepare the electrolyte membrane, wherein the polyurethane elastomer-deep eutectic composite electrolyte membrane is disposed between the positive electrode and the lithium metal negative electrode.

Images