A nitrile group-containing polyurethane solid electrolyte membrane, a preparation method thereof, and an electrochemical device

Abstract

This invention discloses a nitrile-containing polyurethane solid electrolyte membrane, its preparation method, and an electrochemical device, belonging to the field of polymer materials technology. Addressing the problem of balancing ionic conductivity and mechanical properties in existing polyurethane solid electrolytes, a novel chain extender, N,N-di(2-hydroxyethyl)-3-aminopropionitrile, is synthesized to covalently anchor the cyano group to the polyurethane backbone, and then composited with hydroxylated boron nitride nanosheets to construct a synergistic transport system. The resulting electrolyte membrane achieves a room-temperature ionic conductivity of 1.2 × 10⁻⁶. ‑4 With an S / cm, electrochemical window ≥4.5V, tensile strength up to 8.5MPa, and thermal decomposition temperature ≥275℃, it eliminates the migration and loss of small molecule plasticizers, and combines high ionic conductivity with excellent mechanical properties. After being assembled into a lithium metal battery, it retains ≥92% capacity after 100 cycles at 0.1C rate, making it suitable for the preparation of high-safety, long-cycle lithium secondary batteries.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a nitrile-containing polyurethane solid electrolyte membrane, its preparation method, and electrochemical devices. Background Technology

[0002] With the rapid development of new energy vehicles and portable electronic devices, the demand for high-energy-density and high-safety lithium-ion batteries is becoming increasingly urgent. Traditional liquid electrolytes pose safety hazards such as flammability, leakage, and volatility, and cannot effectively suppress the growth of lithium dendrites, limiting the practical application of lithium metal batteries. Solid polymer electrolytes, due to their advantages such as light weight, good flexibility, high safety, and good interfacial contact, are considered key materials for next-generation high-energy-density lithium rechargeable batteries.

[0003] Polyurethane, as a block copolymer, possesses a unique microphase separation structure, providing an ideal platform for designing high-performance electrolytes. Polyether-type polyurethanes with polyethylene glycol as the soft segment have attracted widespread attention because they can provide ion transport channels through the soft segment and ensure mechanical strength by forming physical cross-linking points through the hard segment. However, existing polyether polyurethane solid electrolytes still face the following core challenges: First, conventional chain extenders have limited functionality. Second, reliance on small-molecule plasticizers leads to stability issues. Third, the introduction of polar functional groups is limited. Fourth, it is difficult to simultaneously achieve both mechanical properties and ionic conductivity.

[0004] Chinese patent application CN120914330A discloses a DES / polyurethane-based self-healing solid electrolyte, which enhances the polarity of the system and improves ionic conductivity by introducing a deep eutectic solvent (DES). However, since DES is still a physical blend, long-term stability issues exist. Chinese patent application CN121688100A discloses a polyurethane-based composite solid polymer electrolyte film, which improves mechanical properties by blending a polyurethane elastomer with PVDF-HFP, but the improvement in ionic conductivity is limited.

[0005] In summary, existing technologies still have certain limitations and room for improvement in enhancing the performance of polyurethane solid electrolytes. Therefore, developing and constructing all-solid electrolytes that combine high ionic conductivity, excellent mechanical properties, and long-term stability is of great significance. Summary of the Invention

[0006] One of the objectives of this invention is to provide a nitrile-based polyurethane solid electrolyte membrane to solve the problem that it is difficult to balance the ionic conductivity and mechanical properties of polyurethane solid electrolytes in the prior art.

[0007] The second objective of this invention is to provide a method for preparing a nitrile-based polyurethane solid electrolyte membrane, which is used to prepare the aforementioned nitrile-based polyurethane solid electrolyte membrane.

[0008] The third objective of this invention is to provide an application of a nitrile-based polyurethane solid electrolyte membrane in electrochemical devices.

[0009] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a nitrile-based polyurethane solid electrolyte membrane comprises, by weight, the following components: 60-85 parts of nitrile-containing polyether polyurethane polymer, 10-30 parts of lithium salt, and 0.5-5 parts of hydroxylated boron nitride nanosheets.

[0010] By synthesizing a novel nitrile-containing diol chain extender, cyano groups are covalently anchored to the polyurethane backbone, fundamentally eliminating the migration and loss problem of small-molecule plasticizers. Simultaneously, hydroxylated boron nitride nanosheets are introduced, forming a synergistic effect with the cyano groups on the backbone. This significantly improves the lithium salt dissociation degree and ionic conductivity, while also enhancing the mechanical properties and thermal stability of the electrolyte membrane. The aforementioned ratio range ensures that the polymer matrix provides continuous ion transport channels, the lithium salt provides sufficient charge carriers, and the boron nitride nanosheets effectively enhance mechanical properties without hindering ion transport.

[0011] Furthermore, the nitrile-containing polyether polyurethane polymer is synthesized in a two-step process from polyethylene glycol, diisocyanate, and N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender, wherein the molar ratio of polyethylene glycol, diisocyanate, and chain extender is 1:(1.5-3.0):(0.5-2.0). This molar ratio range controls the ratio of hard and soft segments in the polyurethane, enabling the material to possess both good ion transport capability and mechanical strength. If the proportion of diisocyanate is too high, the hard segment content increases, leading to a decrease in ionic conductivity; if the proportion of chain extender is too high, the excessive cyano content will affect the flexibility of the polymer.

[0012] Furthermore, the N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender has the following chemical structure: .

[0013] This chain extender molecule contains a primary hydroxyl group at each end, allowing it to directly participate in the polyurethane chain extension reaction. The cyano group in the middle of the molecule, bridged by an ethylene group, serves as a functional group with a high dielectric constant, effectively promoting lithium salt dissociation. This structure integrates reactivity and functionality into a single molecule, providing a key structural unit for constructing high-performance polyurethane electrolytes.

[0014] Furthermore, the number-average molecular weight of the polyethylene glycol is 200-2000. As a soft segment, the molecular weight of polyethylene glycol directly affects its ion transport capability and crystallinity. If the molecular weight is too low, the soft segment chain length is insufficient, resulting in discontinuous ion transport channels; if the molecular weight is too high, the increased crystallinity will hinder ion transport. Polyethylene glycol with a number-average molecular weight of 200-2000 exhibits low crystallinity while ensuring ion transport.

[0015] Furthermore, the diisocyanate is selected from at least one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). HDI and IPDI are aliphatic diisocyanates, which have excellent resistance to yellowing and low reactivity, making them suitable for preparing stable polyurethane electrolytes; TDI and MDI are aromatic diisocyanates, which have high reactivity and can improve production efficiency.

[0016] Furthermore, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), and lithium tetrafluoroborate (LiBF4). LiTFSI has excellent electrochemical stability and high dissociation degree, and is the most commonly used lithium salt in solid electrolytes; LiPF6 and LiBF4 have good compatibility with cathode materials and can be used in different battery systems.

[0017] Furthermore, the molar ratio of lithium ions in the lithium salt to ether radicals in the nitrile polyether polyurethane polymer is 1:(10-30). This ratio range ensures sufficient dissociation of the lithium salt while avoiding ion aggregation caused by excessive lithium salt. If the lithium ion ratio is too high, ion pairs will form, reducing the free carrier concentration; if the ratio is too low, the number of carriers will be insufficient, and the ionic conductivity will decrease.

[0018] Furthermore, the hydroxylated boron nitride nanosheets are prepared by reflux modification of commercial boron nitride nanosheets with a concentrated sulfuric acid-concentrated nitric acid mixture; the hydroxylated boron nitride nanosheets have a diameter of 50-200 nm, a thickness of 1-5 nm, and a surface hydroxyl content of 3-5 wt%. Hydroxylation modification improves the dispersibility of boron nitride nanosheets in the polymer matrix and avoids agglomeration; the control of the nanosheet diameter and thickness ensures that the nanosheets can be uniformly distributed, forming an effective mechanical reinforcement network and thermal conductivity network.

[0019] Secondly, a method for preparing a nitrile-based polyurethane solid electrolyte membrane includes the following steps: S1. Preparation of nitrile chain extender: Under an inert atmosphere and ice-water bath, acrylonitrile is slowly added dropwise to diethanolamine, and the reaction temperature is controlled at 25-35℃. After the addition is complete, the temperature is raised to 40-70℃ and reacted for 5-24 hours. The N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender is obtained by vacuum distillation and vacuum drying.

[0020] This reaction is a Michael addition reaction, in which the secondary amino group in diethanolamine undergoes an addition reaction with the double bond of acrylonitrile. Ice-water bath cooling and slow dropwise addition of acrylonitrile are used to control the reaction rate and prevent localized overheating that could lead to side reactions. Vacuum distillation and vacuum drying effectively remove unreacted raw materials and low-boiling substances, yielding a high-purity chain extender.

[0021] S2. Synthesis of acrylonitrile-containing polyurethane polymer: Polyethylene glycol is dehydrated under vacuum and reacted with diisocyanate to generate a prepolymer with terminal isocyanate groups. The acrylonitrile-containing chain extender is added to carry out a chain extension reaction to obtain acrylonitrile-containing polyurethane polymer.

[0022] A two-step method for synthesizing polyurethane is employed. First, polyethylene glycol reacts with diisocyanate to generate an NCO-terminated prepolymer, followed by chain extension with a chain extender. This method allows for precise control of the polymer's molecular weight and structure, avoiding the problem of excessively broad molecular weight distribution that can occur with a one-step method.

[0023] S3. Preparation of casting solution: Dissolve the acrylonitrile-containing polyurethane polymer in an organic solvent, add lithium salt and stir until completely dissolved, then add hydroxylated boron nitride nanosheet dispersion, sonicate and stir evenly to obtain casting solution.

[0024] Dissolving the polymer and lithium salt first, then adding the boron nitride nanosheet dispersion, ensures uniform dispersion of the nanosheets. Ultrasonic treatment breaks up nanosheet aggregation and improves dispersibility; controlling the stirring time ensures uniform mixing while avoiding the introduction of excessive air bubbles.

[0025] S4. Film Formation and Drying: The casting solution is cast into a film, which is then dried by programmed temperature rise and vacuum drying to obtain a nitrile-based polyurethane solid electrolyte membrane with a thickness of 20-100 μm.

[0026] Programmed temperature drying can slowly remove the solvent, avoiding membrane surface defects caused by rapid solvent evaporation; vacuum drying can completely remove residual solvent, ensuring the stability of the electrolyte membrane performance. The thickness is controlled between 20-100 μm, balancing ion transport resistance and mechanical strength.

[0027] Furthermore, in step S1, the molar ratio of diethanolamine to acrylonitrile is 1:(1.0-1.3), and the dropping time is 1-3 hours. A slight excess of acrylonitrile ensures complete reaction of the diethanolamine, increasing the yield; controlling the dropping time prevents the reaction from becoming too vigorous and reduces the formation of byproducts.

[0028] Furthermore, in step S1, the reduced pressure distillation conditions are a temperature of 50-70℃ and a pressure of -0.095 to -0.1 MPa, while the vacuum drying conditions are a temperature of 60-80℃ and a time of 12-24 hours. These conditions can effectively remove unreacted acrylonitrile (boiling point 77℃) and moisture, while preventing the decomposition of the chain extender.

[0029] Furthermore, in step S2, the dehydration conditions for polyethylene glycol are: temperature 110-120℃, vacuum degree 0.09-0.098MPa, and time 1-2 hours. Water in polyethylene glycol reacts with isocyanate, consuming NCO groups and affecting the synthesis of the prepolymer. Strict dehydration conditions ensure that the moisture content is ≤0.05%, guaranteeing the smooth progress of the reaction.

[0030] Furthermore, in step S2, the prepolymer reaction temperature is 70-80℃ and the time is 1-2 hours; the chain extension reaction temperature is 50-60℃ and the time is 2-3 hours. A higher prepolymer reaction temperature can accelerate the reaction rate; a lower chain extension reaction temperature can avoid gelation caused by an overly vigorous reaction.

[0031] Furthermore, in step S3, the organic solvent is selected from at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and acetonitrile. DMF and NMP have high boiling points and good solubility, making them suitable for preparing high-concentration polymer solutions; THF and acetonitrile have low boiling points and are easy to remove by drying.

[0032] Furthermore, in step S3, the polymer solution has a mass concentration of 5-15%; the hydroxylated boron nitride nanosheet dispersion has a mass concentration of 1-3%, and the ultrasonic treatment time is 30-60 minutes. This concentration range ensures that the casting solution has a suitable viscosity, facilitating casting into a film; controlling the ultrasonic time can effectively disperse the nanosheets while avoiding structural damage to the nanosheets caused by excessively long ultrasonic treatment times.

[0033] Furthermore, in step S4, the programmed temperature drying conditions are 60-80℃ for 12-24 hours; the vacuum drying conditions are 80-100℃ for 24-48 hours. Programmed temperature drying removes most of the solvent at a lower temperature first, and then dries further at a higher temperature; vacuum drying can completely remove residual solvent at a lower temperature, avoiding the influence of high temperature on polymer properties.

[0034] Thirdly, an electrochemical device includes a positive electrode, a negative electrode, and an electrolyte layer located between the positive and negative electrodes, wherein the electrolyte layer includes the aforementioned nitrile-based polyurethane solid electrolyte membrane; the electrochemical device is a lithium-ion battery or a lithium metal battery.

[0035] The beneficial effects of this invention are: (1) The present invention designs and synthesizes N,N 2(2) Hydroxyethyl) 3 A novel nitrile diol chain extender for aminopropionitrile. This chain extender molecule contains one primary hydroxyl group at each end and can directly replace 1,4-hydroxyl groups. Traditional chain extenders such as butanediol and ethylene glycol undergo chain extension reactions with isocyanates. The introduction of highly polar cyano groups (-CN) at the molecule's midpoint via ethylene bridging provides both high dielectric constant and strong electron-withdrawing ability, significantly promoting lithium salt dissociation. This invention integrates the reactive site and lithium salt dissociation functional groups into the same molecule, eliminating the need for additional functionalization modifications. It can be directly used to construct nitrile-containing polyether polyurethane polymers, providing a key structural unit for preparing high-ionic-conductivity solid electrolytes.

[0036] (2) This invention utilizes N,N 2(2) Hydroxyethyl) 3 The aminopropionitrile chain extender directly anchors cyano groups to the hard segment region of the polyurethane backbone via covalent bonds. This differs from existing technologies that often introduce cyano groups through physical blending with small-molecule nitrile plasticizers or side-chain modification, which can lead to migration and volatilization during long-term cycling, resulting in electrolyte mechanical decay and interface degradation. This invention fundamentally eliminates cyano group migration and loss, significantly improving the long-term structural stability, thermal stability, and electrode interface compatibility of the electrolyte, thereby extending battery cycle life.

[0037] (3) The electrolyte of the present invention is composed of 60–85 parts of acrylonitrile-containing polyether polyurethane polymer, 10–30 parts of lithium salt, and 0.5–5 parts of hydroxylated boron nitride nanosheets, wherein the polymer consists of polyethylene glycol, diisocyanate, and N,N-diisocyanate with a number average molecular weight of 200–2000. 2(2) Hydroxyethyl) 3 Aminopropionitrile was prepared at a molar ratio of 1:(1.5–3.0):(0.5–2.0); hydroxylated boron nitride nanosheets with a diameter of 50–200 nm and a thickness of 1–5 nm played a key role in synergy: the strong polarity of the cyano group can disrupt the regular arrangement of polyethylene glycol soft segments, inhibit crystallization, and construct continuous ion channels; the hydroxylated boron nitride nanosheets provide rigid support and improve thermal stability, and the hydroxyl groups on their surface form hydrogen bonds with the cyano groups, which further promotes lithium salt dissociation and reduces ion transport resistance.

[0038] (4) The N,N prepared by the present invention 2(2) Hydroxyethyl) 3 Aminopropionitrile can directly replace conventional chain extenders. Polyurethane synthesis follows the mature two-step process, requiring no new equipment or complex procedures. High ionic conductivity can be achieved without adding any small molecule plasticizers, completely avoiding the risk of performance degradation caused by plasticizer migration. The process is simple, cost-controllable, and has good stability, making it easy to scale up production. Attached Figure Description

[0039] The invention will now be further described with reference to the accompanying drawings.

[0040] Figure 1 The 1H NMR spectrum of the nitrile diol chain extender synthesized in Example 1 of this invention (… 1 H NMR spectrum; Figure 2 The Fourier transform infrared (FT-IR) spectrum of the acrylonitrile-containing polyurethane polymer synthesized in Example 1 of this invention is shown. Detailed Implementation

[0041] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0042] Example 1 This embodiment provides a nitrile-based polyurethane solid electrolyte membrane, which is prepared through the following steps: S1. Preparation of N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender: 50.0 g (0.475 mol) of diethanolamine was added to a 250 mL three-necked flask. Under nitrogen protection and ice-water bath cooling, 31.5 g (0.594 mol, 1.25 equivalent) of acrylonitrile was slowly added dropwise, controlling the dropping rate to maintain the reaction temperature at 25-35 °C for approximately 2 hours. After the addition was complete, the temperature was raised to 50 °C and the reaction continued for 24 hours. After the reaction was completed, the reaction solution was distilled under reduced pressure at 60 °C and -0.098 MPa for 1 hour to remove unreacted acrylonitrile and low-boiling substances, yielding a pale yellow viscous liquid. This liquid was then dried under vacuum at 70 °C for 12 hours to obtain the N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender.

[0043] The above-mentioned N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender was subjected to 1H NMR spectroscopy at 400 MHz with deuterated chloroform as the solvent. The results are as follows: Figure 1As shown, there are five sets of absorption signals: 3.76 ppm corresponds to a hydrogen atom on the methylene group adjacent to the hydroxyl group, 3.55 ppm corresponds to a hydrogen atom on the methylene group adjacent to the cyano group, 2.83 ppm corresponds to a hydrogen atom on the methylene group bonded to the nitrogen atom, 2.62 ppm corresponds to a hydrogen atom on another methylene group adjacent to the cyano group, and 2.47 ppm corresponds to a hydrogen atom on another methylene group bonded to the nitrogen atom. The integrated area ratio of these five sets of absorption peaks is approximately 2:4:2:4:2, which perfectly matches the chemical environment and number of the 14 hydrogen atoms in the target product N-(2-cyanoethyl)diethanolamine molecule. No signals from the starting material or diaddition byproducts were detected, confirming the successful synthesis of the N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender.

[0044] S2. Preparation of hydroxylated boron nitride nanosheets: 1.0 g of commercial boron nitride nanosheets (100-200 nm in diameter, 2-3 nm in thickness) were added to 100 mL of a mixture of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) and refluxed at 80 °C for 6 hours. After cooling to room temperature, the nanosheets were diluted with deionized water, centrifuged, washed with deionized water until neutral, and vacuum dried at 60 °C for 24 hours to obtain hydroxylated boron nitride nanosheets with a surface hydroxyl content of 4.2 wt%.

[0045] S3. Synthesis of acrylonitrile-containing polyurethane polymer: 12.0 g (0.02 mol) of polyethylene glycol (PEG600) with a number average molecular weight of 600 was placed in a three-necked flask and dehydrated under vacuum at 115 °C and -0.098 MPa for 2 hours until the moisture content was ≤0.05%. The temperature was lowered to 70 °C, and 5.04 g of hexamethylene diisocyanate (HDI, 0.03 mol) was added under nitrogen protection. The mixture was reacted at 75 °C for 1.5 hours to obtain a terminal isocyanate prepolymer. The system was then cooled to 50 °C, and 1.58 g (0.01 mol) of the acrylonitrile-containing diol chain extender prepared above was added. The mixture was kept at this temperature for 2.5 hours to obtain the acrylonitrile-containing polyurethane polymer.

[0046] Infrared spectroscopy analysis of nitrile-containing polyether polyurethane polymers yielded the following results: Figure 2 As shown: ~2250 cm -1 The characteristic absorption peak of cyano group appears at ~3320 cm⁻¹. -1 The peak of NH stretching vibration is at ~1700 cm⁻¹. -1 The appearance of the C=O stretching vibration peak at the point of reaction jointly proves that the nitrile chain extender has successfully participated in the reaction and formed the expected polyurethane structure.

[0047] S4. Preparation of Casting Solution: Dissolve the above-mentioned nitrile-containing polyether polyurethane polymer in N,N-dimethylformamide (DMF) and stir at 60°C until completely dissolved to prepare a polymer solution with a mass concentration of 10%. Add lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to the polymer solution, controlling the molar ratio of ether radicals to lithium ions to be 20:1 (i.e., EO:Li = 20:1), and stir under nitrogen protection for 3 hours until completely dissolved. Disperse 0.2 g of hydroxylated boron nitride nanosheets in 20 mL of DMF and sonicate for 45 minutes to obtain a uniform dispersion. Slowly add this dispersion to the polymer solution and continue stirring for 3 hours to obtain a uniform casting solution.

[0048] S5. Film Formation and Drying: The casting solution is poured onto a clean glass plate and dried at 70°C for 18 hours to remove most of the solvent. Then, it is vacuum dried at 90°C for 36 hours to completely remove the residual solvent, resulting in a nitrile-based polyurethane solid electrolyte membrane with a thickness of about 50 μm.

[0049] Example 2 The difference between this embodiment and Example 1 is that the number average molecular weight of polyethylene glycol is 400, while the other raw materials and preparation process remain the same as in Example 1.

[0050] Example 3 The difference between this embodiment and Example 1 is that the molar ratio of polyethylene glycol, HDI and nitrile chain extender is 1:2:1, while the other raw materials and preparation process remain the same as in Example 1.

[0051] Example 4 The difference between this embodiment and Example 1 is that the diisocyanate used isophorone diisocyanate (IPDI) at a dosage of 6.67 g (0.03 mol), while the other raw materials and preparation process remain the same as in Example 1.

[0052] Example 5 The difference between this embodiment and Example 1 is that EO:Li = 15:1, while the other raw materials and preparation process remain the same as in Example 1.

[0053] Example 6 The difference between this embodiment and Example 1 is that EO:Li = 25:1, while the other raw materials and preparation process remain the same as in Example 1.

[0054] Example 7 The difference between this embodiment and Example 1 is that the amount of hydroxylated boron nitride nanosheets added is 0.1g, while the other raw materials and preparation process remain the same as in Example 1.

[0055] Example 8 The difference between this embodiment and Example 1 is that the amount of hydroxylated boron nitride nanosheets added is 0.4g, while the other raw materials and preparation process remain the same as in Example 1.

[0056] Example 9 The difference between this embodiment and Example 1 is that the amount of acrylonitrile used in the preparation of the chain extender is 27.7g (0.523mol, 1.1 equivalents), the reaction temperature is 60℃, and the reaction time is 18 hours. The other raw materials and preparation process are the same as in Example 1.

[0057] Comparative Example 1 The difference between this comparative example and Example 1 is that a nitrile chain extender is not used; instead, an equimolar amount of 1,4-butanediol (BDO) is used as the chain extender. The other raw materials and preparation process remain the same as in Example 1.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that hydroxylated boron nitride nanosheets are not added, while the other raw materials and preparation process remain the same as in Example 1.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that 10 wt% succinic anionyl nitrile was added as a small molecule plasticizer, and nitrile chain extenders and boron nitride nanosheets were not used. The other raw materials and preparation process remained the same as in Example 1.

[0060] Comparative Example 4 The difference between this comparative example and Example 1 is that unmodified commercial boron nitride nanosheets were used instead of hydroxylated boron nitride nanosheets, while the other raw materials and preparation process remained the same as in Example 1.

[0061] Comparative Example 5 The difference between this comparative example and Example 1 is that the amount of hydroxylated boron nitride nanosheets added is 1.0 g, while the other raw materials and preparation process remain the same as in Example 1.

[0062] Comparative Example 6 The difference between this comparative example and Example 1 is that the number average molecular weight of polyethylene glycol is 2000, while the other raw materials and preparation process remain the same as in Example 1.

[0063] Comparative Example 7 This comparative example is a pure PEO electrolyte membrane, prepared as follows: Polyethylene oxide (PEO) with a number average molecular weight of 600,000 was dissolved in anhydrous acetonitrile, and LiTFSI was added at a ratio of EO:Li = 20:1. After stirring evenly, the mixture was cast into a membrane, dried at 60°C for 18 hours, and then vacuum dried at 80°C for 36 hours to obtain a PEO electrolyte membrane with a thickness of about 50 μm.

[0064] Performance testing After the electrolyte membranes prepared in all examples and comparative examples were stored in a glove box for 24 hours, the following performance tests were performed: 1. Ionic conductivity testing: Electrochemical impedance spectroscopy (EIS) was used. The electrolyte membrane was sandwiched between two stainless steel blocking electrodes. The test frequency range was 1Hz-1MHz, the amplitude was 10mV, and the test temperature was 25℃. The formula for calculating ionic conductivity is: σ=L / (R×S), where L is the membrane thickness, R is the volume resistance, and S is the electrode contact area.

[0065] 2. Electrochemical window testing: Linear sweep voltammetry (LSV) was used with stainless steel as the working electrode, lithium metal as the counter electrode and reference electrode, a scan rate of 1 mV / s, and a voltage range of 0-6 V.

[0066] 3. Mechanical property testing: Using a universal testing machine, tensile rate of 50 mm / min, sample size of 20 mm × 5 mm, tensile strength and elongation at break were tested.

[0067] 4. Thermal stability test: Thermogravimetric analysis (TGA) was used under nitrogen atmosphere, with a heating rate of 10℃ / min and a temperature range of 30-600℃. The thermal decomposition temperature (the temperature at which 5% weight loss occurs) was recorded.

[0068] 5. Lithium-ion transference number test: The constant potential polarization method was used to apply a voltage of 10mV to assemble a lithium-lithium symmetric cell, and the lithium-ion transference number was calculated according to the formula.

[0069] 6. Battery cycle performance test: Using lithium iron phosphate (LFP) as the positive electrode and lithium metal as the negative electrode, CR2032 button batteries were assembled and constant current charge and discharge tests were conducted at 0.1C rate at 25℃, with a voltage range of 2.5-3.8V. The capacity retention rate after 100 cycles was recorded.

[0070] The results are shown in Table 1: Table 1

[0071] Based on the data in Table 1, it can be seen that: Ionic conductivity: The room temperature ionic conductivity of all embodiments is within 10. -5 S / cm or higher, with Example 1 reaching 1.2 × 10⁻⁶. -4 S / cm, far superior to Comparative Example 1 (2.3×10 -6 S / cm) and Comparative Example 7 (1.6×10 -6 S / cm). This is mainly attributed to the high dielectric constant of the cyano group on the main chain promoting lithium salt dissociation, while the cyano group interferes with the crystallization of the PEG soft segment, improving the ion transport channel. Compared with Comparative Example 2 (7.2 × 10⁻⁶), the difference is less than that between the two.-5 Compared to the previous S / cm, the ionic conductivity was further improved after adding hydroxylated boron nitride nanosheets, indicating that the hydroxyl groups on the surface of boron nitride form hydrogen bonds with the cyano groups, which further promotes the dissociation of lithium salt.

[0072] Electrochemical window: The electrochemical windows of all embodiments are above 4.3V, reaching a maximum of 4.5V, which is compatible with mainstream cathode materials such as lithium iron phosphate and lithium manganese oxide. Comparative Example 3, due to the addition of small molecule succinic anionyl nitrile, has an electrochemical window of only 3.9V, indicating that chemically anchored cyano groups have better electrochemical stability than physically blended nitrile plasticizers.

[0073] Mechanical properties: The tensile strength of all examples was above 7.0 MPa, reaching a maximum of 9.3 MPa, significantly higher than that of pure PEO (1.2 MPa) and Comparative Example 3 (3.5 MPa) with added small molecule plasticizer. This is because the introduction of boron nitride nanosheets significantly enhanced the mechanical properties of the polymer matrix, while the physical crosslinking points formed by the polyurethane hard segments also provided good mechanical support. In Comparative Example 5, the excessive amount of boron nitride resulted in a decrease in ionic conductivity, but the tensile strength was further increased to 10.2 MPa, indicating that a balance needs to be struck between the amount of boron nitride added and ionic conductivity and mechanical properties.

[0074] Thermal stability: The thermal decomposition temperatures of all embodiments were above 275°C, significantly higher than those of pure PEO (220°C) and Comparative Example 3 (235°C). Boron nitride nanosheets exhibit excellent thermal stability, and their uniform dispersion within the polymer matrix forms a good thermal conductivity network, thereby increasing the thermal decomposition temperature of the electrolyte membrane.

[0075] Lithium-ion transference number: The lithium-ion transference number of all embodiments was above 0.48, reaching a maximum of 0.54, which was significantly better than the comparative example. This is because the hydroxyl groups on the surfaces of cyano and boron nitride can interact with anions, restricting anion migration and thus increasing the lithium-ion transference number.

[0076] Cycling performance: After 100 cycles at 0.1C, the capacity retention of all assembled batteries in the embodiments was above 89%, far superior to the comparative examples. Comparative Example 3, due to the migration and volatilization of small molecule plasticizers, had a capacity retention of only 52.1% after 100 cycles; Comparative Example 2, due to its poor mechanical properties and inability to effectively suppress lithium dendrite growth, had a capacity retention of 78.5%. In contrast, the electrolyte membrane of this invention exhibits excellent long-term cycling stability due to the chemical anchoring of cyano groups and the reinforcing effect of boron nitride nanosheets.

[0077] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A nitrile group-containing polyurethane solid electrolyte membrane, characterized by, By weight, it includes the following components: 60-85 parts of acrylonitrile-containing polyurethane polymer, 10-30 parts of lithium salt, and 0.5-5 parts of hydroxylated boron nitride nanosheets; The acrylonitrile-containing polyurethane polymer is synthesized in two steps from polyethylene glycol, diisocyanate and N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender, wherein the molar ratio of polyethylene glycol, diisocyanate and chain extender is 1:(1.5-3.0):(0.5-2.0). The hydroxylated boron nitride nanosheets have a diameter of 50-200 nm and a thickness of 1-5 nm.

2. The nitrile group-containing polyurethane solid-state electrolyte membrane according to claim 1, characterized by, The N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender has the following chemical structure: 。 3. The nitrile group-containing polyurethane solid-state electrolyte membrane according to claim 1, characterized by, The number average molecular weight of the polyethylene glycol is 200-2000; the diisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

4. The nitrile group-containing polyurethane solid-state electrolyte membrane according to claim 1, characterized by, The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, and lithium tetrafluoroborate; the molar ratio of lithium ions in the lithium salt to ether radicals in the nitrile polyether polyurethane polymer is 1:(10-30).

5. The nitrile group-containing polyurethane solid-state electrolyte membrane according to claim 1, characterized by, The hydroxylated boron nitride nanosheets were prepared by reflux modification of commercial boron nitride nanosheets with a mixture of concentrated sulfuric acid and concentrated nitric acid, and the surface hydroxyl content was 3-5 wt%.

6. A method for producing a nitrile group-containing polyurethane solid-state electrolyte film according to any one of claims 1 to 5, characterized by, Includes the following steps: S1. Preparation of nitrile chain extender: Under an inert atmosphere and ice-water bath, acrylonitrile was slowly added dropwise to diethanolamine, and the reaction temperature was controlled at 25-35℃. After the addition was completed, the temperature was raised to 40-70℃ and reacted for 5-24 hours. The N,N-bis(2-hydroxyethyl)-3-aminopropionitrile chain extender was obtained by vacuum distillation and vacuum drying. S2. Synthesis of acrylonitrile-containing polyurethane polymer: Polyethylene glycol is dehydrated under vacuum and reacted with diisocyanate to generate a prepolymer with terminal isocyanate groups. The acrylonitrile-containing chain extender is added to carry out a chain extension reaction to obtain acrylonitrile-containing polyurethane polymer. S3. Preparation of casting solution: Dissolve the acrylonitrile-containing polyurethane polymer in an organic solvent, add lithium salt and stir until completely dissolved, then add hydroxylated boron nitride nanosheet dispersion, sonicate and stir evenly to obtain casting solution. S4. Film Formation and Drying: The casting solution is cast into a film, which is then dried by programmed temperature rise and vacuum drying to obtain a nitrile-based polyurethane solid electrolyte membrane with a thickness of 20-100 μm.

7. The method for producing a nitrile group-containing polyurethane solid-state electrolyte film according to claim 6, characterized by, In step S1, the molar ratio of diethanolamine to acrylonitrile is 1:(1.0-1.3), and the dropping time is 1-3 hours; the vacuum distillation conditions are a temperature of 50-70℃ and a pressure of -0.095 to -0.1MPa, and the vacuum drying conditions are a temperature of 60-80℃ and a time of 12-24 hours.

8. The method for preparing a nitrile group-containing polyurethane solid-state electrolyte membrane according to claim 6, characterized by, In step S2, the dehydration conditions for polyethylene glycol are: temperature 110-120℃, vacuum degree 0.09-0.098MPa, and time 1-2 hours; the reaction temperature for the prepolymer is 70-80℃ and time 1-2 hours; and the chain extension reaction temperature is 50-60℃ and time 2-3 hours.

9. The method for preparing a nitrile-containing polyurethane solid electrolyte membrane according to claim 6, characterized in that, In step S3, the organic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, and acetonitrile; the polymer solution has a mass concentration of 5-15%; the hydroxylated boron nitride nanosheet dispersion has a mass concentration of 1-3%; and the ultrasonic treatment time is 30-60 minutes. In step S4, the programmed temperature drying conditions are 60-80℃ for 12-24 hours; the vacuum drying conditions are 80-100℃ for 24-48 hours.

10. An electrochemical device, characterized by, The device comprises a positive electrode, a negative electrode, and an electrolyte layer located between the positive and negative electrodes, wherein the electrolyte layer comprises a nitrile-containing polyurethane solid electrolyte membrane as described in any one of claims 1-5; the electrochemical device is a lithium-ion battery or a lithium metal battery.

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