Multi-scale synergistically enhanced self-healing solid polymer electrolyte and preparation method thereof

Abstract

The invention discloses a multi-scale synergistically enhanced self-healing solid polymer electrolyte and a preparation method thereof, and belongs to the technical field of electrolyte materials. The preparation method of the electrolyte comprises the following steps: S1, adding the eight-arm star polymer, the carborane lithium salt, the neutral plastic crystal additive, the ionic liquid monomer and the crown ether functionalized boron alkene two-dimensional filler into a mixed solvent to form electrolyte slurry; s2, uniformly coating a base material with the electrolyte slurry to form a wet film, and drying the wet film; s3, transferring the dried membrane to an environment filled with inert gas, and initiating in-situ polymerization of an ionic liquid monomer by using ultraviolet irradiation to form a polyionic liquid nanofiber network; and S4, placing the membrane under a vacuum condition at a constant temperature of 120 DEG C for 5 hours to obtain the solid polymer electrolyte membrane. The solid polymer electrolyte membrane provided by the invention overcomes the problems of low ionic conductivity, low lithium ion transference number, insufficient mechanical properties, poor interface stability, narrow electrochemical window and the like of the existing solid polymer electrolyte.

Description

Technical Field

[0001] This invention relates to the field of electrolyte materials technology, and in particular to a multi-scale synergistically enhanced self-healing solid polymer electrolyte and its preparation method. Background Technology

[0002] Solid-state electrolytes are key materials for achieving high energy density and high safety in next-generation lithium metal batteries. Among various solid-state electrolytes, solid-state polymer electrolytes (SPEs) have attracted much attention due to their excellent flexibility, ease of processing, and good electrode / electrolyte interface contact. Currently, the most classic solid-state polymer electrolyte system is based on polyethylene oxide (PEO). However, existing PEO-based solid-state electrolytes generally suffer from the following technical bottlenecks: (1) Low ionic conductivity: PEO is semi-crystalline at room temperature (<60℃). The regular segmental crystallization severely restricts the movement of polymer chains, hindering the transport of lithium ions, resulting in its room temperature ionic conductivity usually being lower than 10. -5 S / cm, far from meeting the actual application requirements of batteries (>10). -4 The requirement is S / cm.

[0003] (2) Low lithium-ion transference number: In the PEO system, lithium ions (Li) have a low transference number. + The migration of lithium ions depends on coordination and dissociation with ethylene oxide (EO) units, while the anions of traditional lithium salts (such as lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) also possess considerable migration capabilities, leading to the migration of Li ions. + Number of migrations (t) + (Typical value) is usually below 0.3. Low t + This can cause severe concentration polarization and exacerbate the growth of lithium dendrites.

[0004] (3) Insufficient mechanical properties and poor interface stability: Pure PEO has a low mechanical modulus, which is insufficient to effectively suppress lithium dendrite puncture. To enhance mechanical properties, existing technologies often use the addition of inorganic rigid fillers (such as LLZO, SiO2, etc.) to prepare composite electrolytes. However, these inorganic fillers have poor compatibility with the polymer matrix, are prone to agglomeration, and form an unstable solid electrolyte interphase (SEI) film at the electrode interface, leading to a continuous increase in interfacial resistance and a decrease in battery cycle life.

[0005] (4) Narrow electrochemical window: PEO matrix and commonly used lithium salts such as LiTFSI and LiFSI will undergo oxidative decomposition at voltages above 4.2V, which limits their application in high-voltage cathode materials (such as NMC811, lithium-rich manganese-based materials, etc.).

[0006] In summary, developing a solid polymer electrolyte that can simultaneously achieve high room temperature ionic conductivity, high lithium-ion transference number, excellent mechanical strength, and a wide electrochemical window is a pressing technical challenge in this field. Summary of the Invention

[0007] To address the problems of low ionic conductivity, low lithium-ion transference number, insufficient mechanical properties, poor interface stability, and narrow electrochemical window in current solid polymer electrolytes, this invention provides a self-healing solid polymer electrolyte with multi-scale synergistic enhancement.

[0008] The multi-scale synergistically enhanced self-healing solid polymer electrolyte provided by this invention comprises the following components in weight percentage: Eight-armed star-shaped polymer 50-65%, carborane lithium salt 15-20%, neutral plastic crystal additive 8-15%, polyionic liquid nanofiber network 8-15%, crown ether functionalized boronene two-dimensional filler 2-8%, total 100%.

[0009] The eight-armed star polymer is based on an eight-armed polyethylene oxide (PEO) core, with each arm having a number-average molecular weight (Mn) of approximately 8000 g / mol. Each arm is terminally grafted with a uracil-polyurethane unit, and the middle main chain of each arm is randomly grafted with 2-(2-cyanoethoxy)ethyl units and units containing 15-crown-5 ether groups.

[0010] Preferably, the end of each arm is grafted with 1-(6-hexyl isocyanate)-2-amino-6-methyl-4-(3-oxo-2-butenyl)-pyrimidine-2,4-dione to form a uracil-polyurethane unit.

[0011] Preferably, 10 mol% of 2-(2-cyanoethoxy)ethyl units and 3 mol% of units containing a 15-crown-5 ether group are randomly grafted onto the main chain in the middle of each arm. More preferably, the 2-(2-cyanoethoxy)ethyl unit is -O-CH2CH2-O-CH2CH2-CN, and the unit containing the 15-crown-5 ether group is -O-(CH2)2-15-crown-5. Here, the molar percentage (mol%) refers to (the number of moles of this type of unit after grafting) ÷ (the number of moles of all repeating units in this arm) × 100%. An arm originally contains only ethylene oxide (EO) repeating units, n≈181. Of these, 10% (≈18) of the EO were post-modified to -O-CH2CH2-O-CH2CH2-CN, 3% (≈5-6) of the EO were post-modified to -O-(CH2)2-15-crown-5, and the remaining approximately 87% remained EO. Therefore, 10 mol% and 3 mol% are not ratios between the two types of units, but rather the "molar percentage" of each unit relative to all main chain segments (EO + modified segments) in the entire arm.

[0012] The method for preparing the eight-armed star polymer is as follows: First, an eight-armed PEO is synthesized by ring-opening polymerization (ROP); then, a cyano-containing side group (-O-CH2CH2-O-CH2CH2-CN) and a crown ether-containing side group (-O-(CH2)2-15-crown-5) are selectively introduced onto each arm chain by toluene sulfonation and nucleophilic substitution reaction; finally, a uracil-polyurethane unit is chemically grafted onto the end of each arm by isocyanate to obtain the eight-armed star polymer.

[0013] The star-shaped topology of the eight-armed star polymer fundamentally suppresses the regular arrangement and crystallization of PEO chains (crystallinity Xc < 5%), ensuring that the electrolyte remains amorphous within the range of -20°C to room temperature, providing sufficient free volume for ion transport. The uracil-polyurethane units grafted to the arm ends construct a high-strength, dynamically reversible physical cross-linking network (room temperature shear modulus > 200 MPa) through quadruple hydrogen bonds, endowing the electrolyte with excellent mechanical strength to suppress lithium dendrites, while also enabling "self-healing" upon damage. The -CN group in the -O-CH2CH2-O-CH2CH2-CN side group in the middle of the arm has a strong dipole moment, effectively weakening the Li... + Coordination with the EO chain; the internal size of the 15-crown-5 ether side group and Li + A perfect match, selectively capturing and promoting Li + The "intrachain jump" and the synergistic effect of the two significantly improved Li + The degree of dissociation and migration rate.

[0014] The polyionic liquid nanofiber network is prepared by in-situ free radical polymerization of ionic liquid monomers via photoinitiation. The ionic liquid monomer is 1-allyl-3-(2-methoxyethyl)imidazolium-closed-B 12 H 11 NH, abbreviated as AEMIm-closo-B 12 H 11 NH. Cation: 1-Allyl-3-(2-methoxyethyl)imidazolium + It has a common ionic liquid imidazolium skeleton, with an allyl group at N1 and a 2-methoxyethyl group at N3. Anion: Closed-B 12 H 11 NH - It is a weakly coordinated, superionic, and conductive large cage boron anion. When this ionic liquid monomer is added to an electrolyte slurry, allyl-terminated free radical polymerization can be initiated by photoinitiation (e.g., 365nm ultraviolet light).

[0015] The ionic liquid monomer AEMIm-closo-B 12 H 11 Following NH polymerization, self-assembly forms polyionic liquid (PIL) nanofibers with a diameter of approximately 15 nm. These fibers interweave with each other, constructing a "soft-hard" bicontinuous ion-conducting network within the PEO matrix. (closo-B) 12 H 11 NH - It is a weakly coordinated anion, ensuring a high degree of ionic dissociation. PIL nanofibers themselves are a phase with high ionic conductivity, and the continuous network they form is Li... + It provides a "highway" running through the entire electrolyte membrane, increasing the room temperature conductivity to 1.1-1.3 mS / cm. -1 The imidazolium cationic framework of PIL is immobilized on the polymer chain, and the positively charged framework is effective against Li. + The movement of Li generates electrostatic drive, while simultaneously repelling the movement of anions, further converting Li into Li + Number of migrations (t) + The value was increased to 0.55.

[0016] The neutral plastic crystal additive is 1,3,5-tris(2,2-difluoromethyl-1,3-dioxane-4-yl)benzene, abbreviated as Tri-DFMDB. This molecule is a neutral molecule, does not contain ions, has a melting point of 5°C, and exists as an isotropic plastic crystal phase (rotor phase) in a wide temperature range of -60°C to 120°C, meaning that the molecule can rotate at high speed on the crystal lattice.

[0017] Tri-DFMDB forms an "intercalated" subphase in the PEO matrix, and the rotational motion of its molecules is Li +It provides an additional, low-barrier "bypass" hopping channel, significantly improving the electrolyte's ionic conductivity at low temperatures (still >0.2 mS / cm at -20℃). -1 Furthermore, because it is a neutral molecule, it will not dilute the carrier concentration or reduce the Li₂ concentration. + Number of migrations.

[0018] The preparation method of the crown ether functionalized boronene two-dimensional filler is as follows: at room temperature, hexagonal boron bulk is treated by electrochemical exfoliation, followed by liquid-phase exfoliation with the assistance of ionic liquid to obtain a single-layer or few-layer boronene nanosheet dispersion; the sheet thickness is <2 nm, and the lateral dimension is 200-500 nm. Subsequently, using aromatic diazonium salt chemistry, terephthalaza dicrown ether molecules are covalently coupled to the surface of the boronene nanosheets to obtain the crown ether functionalized boronene two-dimensional filler.

[0019] Crown ether-functionalized borone two-dimensional fillers exhibit in-plane ultrafast lithium conduction, interface stabilization, and dendrite suppression. Borone's sp... 2 The -B atom network itself constitutes a two-dimensional electron ocean, while the surface-modified crown ether side groups can trap Li + And guide it to perform "two-dimensional in-plane hopping" with extremely low energy barriers on the surface of boronene sheets, thus enabling Li + The local diffusion coefficient is improved by 2-3 orders of magnitude. Two-dimensional boronene nanosheets tend to align parallel to the electrode surface near the lithium metal anode, forming a "polarization barrier layer." This layer effectively homogenizes the lithium-ion flow (JLi) and suppresses "hot spot" formation, thus achieving diffusion coefficients >4 mA cm⁻¹. -2 Achieve long-term stable lithium deposition / stripping at high current density, avoiding lithium dendrite growth.

[0020] The lithium carborane salt exhibits weak coordination, preferably lithium dodecafluoro-closed-1-carboborane with the molecular formula LiCB. 11 F 12 Its anion [CB] 11 F 12 ] - It is a large, nearly spherical, highly fluorinated, weakly coordinating anion (pKa≈-10). This anion hardly reacts with Li. + Coordination occurs, causing Li + Existing and migrating in a "quasi-naked" state, thereby greatly improving Li + The effective concentration and transport number of the lithium salt are also high. Furthermore, this lithium salt exhibits extremely high oxidation stability, and its decomposition products can form a stable SEI / CEI interface film rich in LiF and B species on the electrode surface, broadening the stable operating voltage of the electrolyte to above 4.8V.

[0021] This invention also provides a method for preparing the above-mentioned multi-scale synergistically enhanced self-healing solid polymer electrolyte, comprising the following steps: S1. Add the eight-armed star polymer, lithium carborane, neutral plastic crystal additive, ionic liquid monomer, crown ether functionalized boronene two-dimensional filler to a mixed solvent of dimethoxyethane (DME) and hexafluoroisopropanol (HFIP), and sonicate or stir until a uniform and stable electrolyte slurry is formed.

[0022] S2. Coat the electrolyte slurry evenly onto the substrate to form a wet film with a thickness of 30-50 µm, and then dry it.

[0023] S3. Transfer the dried membrane to an environment filled with inert gas and irradiate it with ultraviolet light for 10-30 minutes to induce in-situ polymerization of ionic liquid monomers to form a polyionic liquid nanofiber network.

[0024] S4. The membrane obtained in step S3 is placed at a constant temperature of 120°C under vacuum for 5 hours to obtain a solid polymer electrolyte membrane with a thickness of 25-30 µm.

[0025] Compared with the prior art, the advantages of the present invention are: (1) Achieved extremely high room temperature ionic conductivity: Due to the multi-scale, multi-mode synergistic lithium conduction mechanism, the solid electrolyte of this invention can achieve an ionic conductivity of 1.1-1.3 mS / cm at room temperature (25℃), which is significantly higher than that of traditional PEO-based electrolytes (<10). - 2 The conductivity of the solid electrolyte of this invention is improved by more than two orders of magnitude (mS / cm). Even at a low temperature of -20°C, the conductivity of the solid electrolyte of this invention can still be maintained above 0.25 mS / cm, solving the problem of poor low-temperature performance of solid batteries.

[0026] (2) Extremely high lithium-ion transference number was obtained: This invention uses weakly coordinated [CB] 11 F 12 ] - Anions make Li + It can migrate "freely"; at the same time, the in-situ polymerized positively charged PIL nanofiber framework has a binding effect on anions. Under the synergistic effect of the two, Li + Number of migrations (t) + The value is as high as 0.55, far exceeding that of the traditional system (t). + <0.3). High Li + Migration number can effectively suppress battery polarization, laying the foundation for achieving fast charging and long cycle life.

[0027] (3) Excellent mechanical properties and self-healing ability: The dynamic quadruple hydrogen bond physical cross-linking network formed by the star-shaped PEO backbone and uracil-polyurethane units in the eight-arm star polymer endows the electrolyte membrane with a shear modulus of up to 220 MPa and an elongation at break of 320%, which can effectively block the growth of lithium dendrites. When microcracks are generated in the membrane, the breaking and recombination of dynamic hydrogen bonds can achieve self-healing at room temperature, which improves the service life and safety of the battery.

[0028] (4) Possesses an ultra-wide electrochemical stability window: LiCB carborane salt 11 F 12 Its high oxidation potential, and the dense and stable SEI / CEI film rich in LiF / B species formed synergistically with crown ether functionalized boronene two-dimensional filler at the electrode interface, enable the electrolyte to operate at 0-5.2 V (vs. Li / Li + It remains stable over a wide voltage range and can be perfectly matched with high-voltage cathode materials such as NMC811, giving full play to their high energy density potential.

[0029] (5) Excellent lithium metal interface stability was achieved: The "polarization barrier layer" formed by the self-assembly of crown ether functionalized boronene two-dimensional filler at the negative electrode interface can homogenize the lithium-ion flow and suppress dendrite nucleation and growth from the source. Experimental data show that the assembled Li|Li symmetric battery can achieve a lithium-ion flow rate of 4 mA / cm². 2 It can cycle stably for more than 2000 hours under high current density without short circuit.

[0030] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0031] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0032] Example 1 An eight-armed star-shaped polymer has the following structural parameters: Core: Octahydroxy-POSS, abbreviated as POSS-(OH)8, with a molecular weight of approximately 712 g / mol. POSS-(OH)8 is officially called octa-hydroxyl polyhedral oligomeric silsesquioxane, and is commonly referred to in Chinese as octa-hydroxyl cage-type silsesquioxane or octa-hydroxyl polysilsesquioxane. Its structural characteristic is: Si8O 12The cage-like core, with each Si vertex connected to a -CH2CH2CH2-OH, is widely used as the "core" of star-shaped or cage-like polymers due to its small size (≈1.5 nm) and chemical inertness.

[0033] Each arm: Mn is approximately 8,000 g / mol, which is approximately equal to 181 EO repeating units; the middle of each arm is randomly grafted with a 10% molar percentage of -O-CH2CH2-O-CH2CH2-CN side group; and a 3% molar percentage of -O-(CH2)2-15-crown-5 side group; the end of the arm is grafted with 1-(6-hexyl isocyanate)-2-amino-6-methyl-4-(3-oxo-2-butenyl)-pyrimidine-2,4-dione (abbreviated as UPy-NCO).

[0034] The preparation method of the above-mentioned eight-armed star-shaped polymer is as follows: (1) The eight-arm PEO was synthesized by ring-opening polymerization (ROP) under anhydrous conditions, and the steps are as follows: (a) In a 2 L four-necked flask, add 1.00 g of POSS-(OH)8, 350 mL of anhydrous tetrahydrofuran (THF), and 22.4 mL of a suspension of potassium hydride and THF. The potassium hydride concentration in the suspension is 0.5 M. Stir at room temperature for 0.5 h. Potassium hydride is a strong base / nucleophile that can deprotonate and dehydrogenate -OH to generate -O. - K + (Octapotassium alkoxide), the reaction principle is: R-OH + KH → RO - K + H₂↑. The hydrogen produced during dehydrogenation is discharged via nitrogen diversion or venting. A stir bar, thermometer, inlet pipe (inert nitrogen), and outlet condenser / safety valve are installed at each of the four necks of the four-necked flask to ensure safe H₂ discharge. THF is used as the reaction solvent to provide an anhydrous environment for the subsequent ring-opening polymerization of ethylene oxide. Octappotassium alkoxide is used as an "active initiator" for the subsequent ring-opening polymerization of ethylene oxide.

[0035] (b) Evacuate the four-necked flask to 10°C. -2 Alternatively, high-purity nitrogen (O2 < 1 ppm) is introduced three times, and the mixture is cooled to -20°C. Then, 89 g of high-purity ethylene oxide (EO) is introduced. The EO is slowly injected in four batches, with the temperature controlled at ≤0°C during the injection process. After the injection is completed, the mixture is stirred at a constant temperature of 25°C for 10 h. (c) After reacting for 10 h, 3 mL of methanol was added, the solvent was removed by rotary evaporation, and then the mixture was dried under vacuum at 40 °C for 12 h to obtain an eight-armed PEO with a yield of 97%.

[0036] (2) Toluenesulfonation reaction: 100 g of octagonal PEO was dissolved in 1 L of anhydrous CH2Cl2, and 35.0 g of triethylamine was added under ice bath conditions at 0℃; 56.0 g of p-toluenesulfonyl chloride was dissolved in another part of CH2Cl2, and the p-toluenesulfonyl chloride solution was slowly added dropwise to the solution system containing octagonal PEO and triethylamine under ice bath conditions (0-5 ℃), and the addition was completed in about 1 hour. Then the reaction was stirred at room temperature for 4 hours, and then filtered with a sintered glass funnel. The filtrate was poured into 5 L of anhydrous diethyl ether. The polymer precipitated due to the difference in polarity, and the impurities were still soluble in the diethyl ether / CH2Cl2 mixed phase. After filtration and collection of the precipitate, it was dried under vacuum at 40℃ to obtain PEO containing -OTs active groups, abbreviated as PEO-OTs.

[0037] (3) Grafting crown ether side groups: Dissolve 94 g of PEO-OTs in 500 mL of N-methylpyrrolidone (NMP), then add 29.0 g of 15-crown-5-CH2CH2-OH (crown ether alcohol) and 5.3 g of NaH (NaH is pre-dispersed in white mineral oil or paraffin oil to form a dispersion with a mass concentration of 60%). At 0 °C, NaH reacts with the alcohol hydroxyl group of 15-crown-5-CH2CH2-OH to generate 15-crown-5-CH2CH2-O. - Na + This process generates hydrogen gas, which needs to be vented using nitrogen gas; then the temperature is raised to 50°C and the reaction is stirred for 6 hours to promote the reaction of 15-crown-5-CH2CH2-O. - Attacking PEO-OTs generates PEO-O-CH2CH2-5-crown-15, with the byproduct p-CH3C6H4SO3 produced in the process. - Na + It can be removed by washing with water.

[0038] (4) Grafting of cyanoethoxy side groups: The mixture obtained in the previous step was cooled to 25°C, and 20.5 g of 2-(2-cyanoethoxy)ethanol and 4.4 g of NaH were added. The mixture was stirred at 40°C for 8 h, then 5 L of deionized water was added, and the mixture was dialyzed (MWCO 5 kDa) for 3 days. The mixture was then freeze-dried to obtain PEO-mixed-side. The molecular formula of 2-(2-cyanoethoxy)ethanol is HO-CH2CH2-O-CH2CH2-CN.

[0039] (5) Grafting uracil-polyurethane units (UPy-NCO) onto the arm ends: Under nitrogen protection, 112 g of PEO-mixed-side was dissolved in 600 mL of anhydrous N,N-dimethylformamide (DMF), heated to 40 °C, and 7.33 g of UPy-NCO and 0.10 g of catalyst dibutyltin dilaurate (DBTDL) were added. The mixture was stirred at 40 °C for 12 h. After the reaction, the product was poured into ice-cold ether to precipitate the product. The precipitate was collected by filtration and dried under vacuum at 40 °C for 24 h to obtain a pale yellow solid, i.e., an eight-armed star polymer. The molecular weight Mn was 8.2 × 10⁻⁶. 4 g / mol.

[0040] Example 2 Preparation of crown ether functionalized boronene two-dimensional filler: At room temperature, hexagonal boron bulk was treated by electrochemical exfoliation and liquid-phase exfoliation was carried out with the assistance of ionic liquid to obtain boronene nanosheet dispersion; subsequently, terephthala dicrown ether molecules were covalently coupled to the surface of boronene using aromatic diazonium salt chemistry to obtain crown ether functionalized boronene two-dimensional filler, abbreviated as LC-B filler.

[0041] The specific preparation method is as follows: (1) Electrochemical liquid phase stripping: The apparatus used was a three-electrode H-cell, with a 1.00 g (10×20×1 mm) B metal sheet as the anode; a Pt mesh cathode; and an Ag / AgCl reference electrode.

[0042] Electrolyte: prepared from 60 mL of 1-butyl-3-methylimidazolium dicyandiamide (BMIM-DCA) and 20 mL of anhydrous CH3CN.

[0043] Reaction conditions: The constant potential was set at 10 V, and the reaction was carried out at room temperature for 4 h. During this process, a dark brown colloid was precipitated. Then, the mixture was centrifuged at 6000 rpm for 10 min, and the supernatant was extracted. The precipitate was washed three times with an ethanol / water mixture and then redispersed under vacuum in 200 mL of N,N-dimethylformamide (DMF) to obtain a boronene nanosheet dispersion.

[0044] (2) Aromatic diazonium salt-crown ether coupling modification: (a) 0.50 g of p-aminophenyl-15-crown-5 (molecular formula C) 14 H 21 Add NO5) to 10 mL of 1 M HCl solution, cool to 0℃, then add 0.13 g of NaNO2; maintain the temperature at 0-2℃ and stir for 15 min to obtain a light brown diazonium salt solution.

[0045] (b) Cool the boronene nanosheet dispersion obtained in step (1) to 5°C and add 50 mg of FeCl2·4H2O as a catalyst; then add the diazonium salt solution dropwise to the boronene nanosheet dispersion, under N2 protection throughout the process, stir the reaction at 0-5°C for 4 h, and then stir the reaction at room temperature for 12 h; after the reaction is completed, centrifuge the boronene nanosheets at 10000 rpm, wash them with DMF, acetonitrile, water and diethyl ether in sequence, freeze dry them, and obtain a light gray powder, which is the crown ether functionalized boronene two-dimensional filler, abbreviated as LC-B.

[0046] The specific surface area of ​​LC-B was measured to be 470 m². 2 / g, zeta potential is -38 mV, monolayer ratio is 85%.

[0047] The products prepared in Examples 1 and 2 were used in the following examples.

[0048] Example 3 A multi-scale synergistically enhanced self-healing solid polymer electrolyte is prepared as follows: Take 5.8g of the eight-armed star-shaped polymer prepared in Example 1 and 1.7g of LiCB. 11 F 12 1.0g of Tri-DFMDB, 1.0g of AEMIm-closo-B 12 H 11 NH monomer and 0.5 g of LC-B prepared in Example 2 were dissolved in 20 mL of a DME / HFIP (volume ratio 20:1) mixed solvent and stirred until homogeneous to obtain an electrolyte slurry. The electrolyte slurry was uniformly coated onto a substrate (release film) using a doctor blade coating method to form a wet film with a thickness of 35 µm. The film was dried at 80 °C for 2 h to remove most of the solvent. Then, the dried film was placed in an argon protective atmosphere and irradiated with a 365 nm LED lamp for 15 min to photo-initiate in-situ polymerization of the ionic liquid monomer to form a PIL nanofiber network. Finally, the film was kept at a constant temperature of 120 °C under vacuum for 5 h to promote the equilibrium of the microstructure of each phase within the system, ultimately yielding a solid polymer electrolyte membrane.

[0049] Example 4 Based on Example 3, the amounts of each component were adjusted as follows: 6.5g of the eight-armed star polymer prepared in Example 1, and 2.0g of LiCB. 11 F 12 0.8g of Tri-DFMDB and 0.5g of AEMIm-closo-B 12 H 11 NH monomer, 0.2 g of LC-B prepared in Example 2. Other steps remained unchanged. A solid polymer electrolyte membrane was finally obtained.

[0050] Example 5 Based on Example 3, the amounts of each component were adjusted as follows: 5.0 g of the eight-armed star polymer prepared in Example 1, and 1.5 g of LiCB. 11 F 12 1.5g Tri-DFMDB, 1.5g AEMIm-closo-B 12 H 11 NH monomer, 0.5 g of LC-B prepared in Example 2. Other steps remained unchanged. A solid polymer electrolyte membrane was finally obtained.

[0051] The performance of various electrolyte membranes was tested, and the test methods for each performance aspect are as follows: (1) Ionic conductivity σ: Using a method similar to GB / T 1410-2006, an electrolyte membrane with a thickness of 25-30 µm was sandwiched between SUS316 stainless steel barrier electrodes; after the temperature stabilized for 1 h, it was scanned with an impedance analyzer (1 MHz → 0.1 Hz, 10mV); R_b is the high-frequency intercept, σ = L / (R_b · A).

[0052] (2) Lithium-ion transference number (t) + Using the Bruce-Vincent method (J. Electrochem. Soc. 1991, 138, 8), a Li│SPE│Li symmetric cell (thickness as above) was polarized for 10 mV at 25 °C; I0, I_s, and the impedances R0, R_s, and t before and after polarization were recorded. + = (I_s · (ΔV – I0R0)) / (I0 · (ΔV – I_sR_s)).

[0053] (3) Electrochemical window (LSV): Stainless steel | SPE | Li, scan rate 1 mV s -1 From OCV, the voltage was swept to 6 V. The decomposition potential was determined when the anode current density reached 0.1 mA cm⁻¹. -2 The voltage at that time.

[0054] (4) Shear modulus G′: GB / T 16491-2008 General Rules for Dynamic Mechanical Analysis, parallel plate rheometer, 25℃, 1Hz, 1% strain oscillation.

[0055] (5) Elongation at break: ASTM D638-14 Type V, 25 µm film sample, speed 5 mm min -1 25℃.

[0056] (6) Li│Li symmetrical cycle: CR2032, Li foil 15 µm, commutation every half hour; record ΔV-t. Short circuit judgment: ΔV<10 mV.

[0057] (7) NMC811|Li full cell: positive electrode surface capacity 2 mAh cm -2 , N / P≈3; 50 µm SPE; 30℃, 1 C (≈200 mA g -1 ) Charge and discharge.

[0058] (8) 5C fast charging temperature rise: Charge at 5C constant current to 80% SOC (≈6 min), attach thermocouple to the center of the battery case; record ΔT.

[0059] The solid polymer electrolyte membrane prepared in Example 3 was subjected to performance testing and compared with a typical existing electrolyte (PEO / LiTFSI). The test results are shown in Table 1.

[0060] Table 1. Performance comparison data of the solid polymer electrolyte membrane prepared in Example 3 and the existing electrolyte (PEO / LiTFSI)

[0061] Comparative Example 1 Based on Example 3, 1.7g of LiCB was added. 11 F 12 "The electrolyte membrane was obtained by replacing the lithium salt LiTFSI with an equal amount, while keeping everything else unchanged. The performance test data of this electrolyte membrane and the electrolyte membrane of Example 3 are shown in Table 2."

[0062] Table 2. Performance comparison data of the electrolyte membrane prepared in Example 3 and the electrolyte membrane in Comparative Example 1.

[0063] It can be seen that the performance of the electrolyte membrane in Example 3 is significantly better than that of the electrolyte membrane in Comparative Example 1. This is because the TFSI in the lithium salt LiTFSI used in Comparative Example 1 is superior. - Strong coordination reduces the degree of dissociation, generating EO-Li-TFSI ternary clusters, which begin to oxidize at 4.3 V. SEI / CEI containing S-Ox is easily degraded.

[0064] Comparative Example 2 Based on Example 3, "1.0g of Tri-DFMDB" was removed, meaning no neutral plastic crystal additive was added, while other aspects remained unchanged, resulting in a solid polymer electrolyte membrane. The performance test data of this electrolyte membrane compared to the electrolyte membrane of Example 3 are shown in Table 3.

[0065] Table 3. Performance comparison data of the electrolyte membrane prepared in Example 3 and the electrolyte membrane in Comparative Example 2.

[0066] It can be seen that the electrolyte membrane of Comparative Example 2 shows a large drop in ionic conductivity σ under low temperature conditions (-68%), which verifies that the rotor phase is the main conduction channel in the "cold region".

[0067] Comparative Example 3 Based on Example 3, the phrase "1.0g of AEMIm-closo-B" was removed. 12 H 11 "NH monomer" refers to the removal of the PIL nanofiber network from the electrolyte, and the LED illumination step is omitted in subsequent steps. Everything else remains unchanged to obtain a solid polymer electrolyte membrane. The performance test data of this electrolyte membrane are compared with those of the electrolyte membrane in Example 3, as shown in Table 4.

[0068] Table 4. Performance comparison data of the electrolyte membrane prepared in Example 3 and the electrolyte membrane in Comparative Example 3.

[0069] It can be seen that if the PIL nanofiber network is removed from the electrolyte membrane of this invention, the potential driving force of the cation framework will be lost, t + Both σ and σ decrease significantly, while the interfacial polarization resistance increases threefold.

[0070] Comparative Example 4 Based on Example 3, "0.5g of LC-B prepared in Example 2" was removed, that is, the crown ether functionalized boronene two-dimensional filler was removed from the electrolyte, while other aspects remained unchanged, resulting in a solid polymer electrolyte membrane. The performance test data of this electrolyte membrane compared with those of the electrolyte membrane in Example 3 are shown in Table 5.

[0071] Table 5. Performance comparison data of the electrolyte membrane prepared in Example 3 and the electrolyte membrane in Comparative Example 4.

[0072] Comparative Example 5 5.8 g of the eight-armed star-shaped polymer prepared in Example 1, 1.7 g of LiTFSI, and 5 g of LC-B prepared in Example 2 were dissolved in 20 mL of a DME / HFIP (volume ratio 20:1) mixed solvent and stirred until homogeneous to obtain an electrolyte slurry. The electrolyte slurry was uniformly coated onto a substrate (release film) using a doctor blade coating method to form a wet film with a thickness of 35 µm. The film was dried at 80 °C for 2 h to remove most of the solvent. Then, the dried film was placed under vacuum at 120 °C for 5 h to promote the equilibrium of the microstructure of each phase within the system, resulting in a ternary minimal solid polymer electrolyte membrane. The performance test data of this electrolyte membrane compared with those of the electrolyte membrane in Example 3 are shown in Table 6.

[0073] Table 6. Performance comparison data of the electrolyte membrane prepared in Example 3 and the electrolyte membrane in Comparative Example 5.

[0074] In summary, it can be concluded that in the solid polymer electrolyte of the present invention, if lithium salt LiCB is used... 11 F 12 When replaced with conventional LiTFSI, the electrolyte's ionic conductivity σ and lithium-ion transference number t... + The performance of the electrolyte, including its electrochemical stability window, will significantly degrade, especially its low-temperature conductivity, which drops by nearly an order of magnitude. Removing any of the "soft / hard synergistic channel" elements (Tri-DFMDB, PIL fiber network, or LC-B) will lead to a significant decrease in ionic conductivity σ and interfacial stability. As shown in Table 6, the performance of the ternary simplified electrolyte membrane in Comparative Example 5 is comparable to that of existing electrolytes (PEO / LiTFSI). This fully demonstrates that each component of the solid polymer electrolyte of this invention is indispensable; only when all components form an organic whole can multi-scale synergistic enhancement be achieved, thus overcoming the technical problems of low ionic conductivity, low lithium-ion transference number, insufficient mechanical properties, poor interfacial stability, and narrow electrochemical window in current solid polymer electrolytes.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A self-healing solid polymer electrolyte with multi-scale synergistic enhancement, characterized in that, The components include the following components by mass percentage: Eight-armed star-shaped polymer 50-65%, lithium carborane 15-20%, neutral plastic crystal additive 8-15%, polyionic liquid nanofiber network 8-15%, crown ether functionalized boronene two-dimensional filler 2-8%, total 100%; The eight-armed star polymer is based on an eight-armed polyethylene oxide core, with uracil-polyurethane units grafted to the end of each arm, and 2-(2-cyanoethoxy)ethyl units and units containing 15-crown-5 ether groups randomly grafted onto the main chain in the middle of each arm. The polyionic liquid nanofiber network is prepared by photo-initiated in-situ free radical polymerization of ionic liquid monomers; the ionic liquid monomer is 1-allyl-3-(2-methoxyethyl)imidazolium-closed-B 12 H 11 NH; The neutral plastic crystal additive is 1,3,5-tris(2,2-difluoromethyl-1,3-dioxane-4-yl)benzene.

2. The multi-scale synergistically enhanced self-healing solid polymer electrolyte as described in claim 1, characterized in that, The crown ether functionalized borene two-dimensional filler is a single-layer or few-layer borene nanosheet prepared by electrochemical exfoliation, and the surface of the borene nanosheet is further modified by terephthalazadiazine bis-crown ether molecules.

3. The multi-scale synergistically enhanced self-healing solid polymer electrolyte as described in claim 1, characterized in that, The lithium carborane salt is dodecafluoro-closed-1-carboborane lithium.

4. The multi-scale synergistically enhanced self-healing solid polymer electrolyte as described in claim 1, characterized in that, In the eight-armed star polymer, the end of each arm is grafted with 1-(6-hexyl isocyanate)-2-amino-6-methyl-4-(3-oxo-2-butenyl)-pyrimidine-2,4-dione.

5. The multi-scale synergistically enhanced self-healing solid polymer electrolyte as described in claim 4, characterized in that, The 2-(2-cyanoethoxy)ethyl units randomly grafted onto the main chain in the middle of each arm are -O-CH2CH2-O-CH2CH2-CN.

6. The multi-scale synergistically enhanced self-healing solid polymer electrolyte as described in claim 4, characterized in that, The units containing 15-crown-5 ether groups randomly grafted onto the main chain in the middle of each arm are -O-(CH2)2-15-crown-5.

7. A method for preparing a multi-scale synergistically enhanced self-healing solid polymer electrolyte as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Add the eight-armed star polymer, lithium carborane, neutral plastic crystal additive, ionic liquid monomer and crown ether functionalized boronene two-dimensional filler to a mixed solvent of dimethoxyethane and hexafluoroisopropanol, and sonicate or stir until a uniform and stable electrolyte slurry is formed. S2. The electrolyte slurry is evenly coated onto the substrate to form a wet film, and then dried. S3. Transfer the dried membrane to an environment filled with inert gas and irradiate it with ultraviolet light for 10-30 minutes to initiate an in-situ polymerization reaction of the ionic liquid monomers to form a polyionic liquid nanofiber network. S4. The membrane obtained in step S3 is placed at a constant temperature of 120°C under vacuum for 5 hours to obtain a solid polymer electrolyte membrane with a thickness of 25-30 µm.

8. The method for preparing the multi-scale synergistically enhanced self-healing solid polymer electrolyte as described in claim 7, characterized in that, In step S2, the thickness of the wet film is 30-50 µm.

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