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

Abstract

The application discloses a kind of self-healing solid-state polymer electrolyte of multiscale synergistic enhancement and preparation method thereof, belong to electrolyte material technical field.The preparation method of electrolyte: S1, eight-arm star polymer, lithium carborane salt, neutral plastic crystal additive, ionic liquid monomer, crown ether functionalized boronene two-dimensional filler are added into mixed solvent to form electrolyte slurry;S2, electrolyte slurry is uniformly coated on substrate to form wet film, and is dried;S3, the film of drying is transferred to the environment filled with inert gas, and in-situ polymerization of ionic liquid monomer is initiated using ultraviolet irradiation to form polyionic liquid nanofiber network;S4, the film is placed at 120 DEG C under vacuum condition for 5 h, and solid-state polymer electrolyte film is obtained.The solid-state polymer electrolyte film of the application overcomes the problems of low ionic conductivity, low lithium ion transference number, insufficient mechanical properties, poor interface stability, narrow electrochemical window and other problems existing in existing solid-state polymer electrolyte.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolyte materials, and particularly relates to a self-healing solid-state polymer electrolyte with multi-scale synergistic reinforcement and a preparation method thereof. BACKGROUND

[0002] Solid-state electrolyte is a key material for realizing next-generation lithium metal batteries with high energy density and high safety. Among various solid-state electrolytes, solid-state polymer electrolyte (SPE) is attracting much attention due to its excellent flexibility, easy processing and good electrode / electrolyte interface contact. At present, the most classic solid-state polymer electrolyte system is the electrolyte based on polyethylene oxide (PEO). However, the existing PEO-based solid-state electrolyte generally has the following technical bottlenecks:

[0003] (1) Low ionic conductivity: PEO is in a semi-crystalline state at room temperature (<60℃), and the regular chain segment crystallization seriously hinders the movement of the polymer chain, which hinders the transmission of lithium ions, resulting in that the room temperature ionic conductivity of PEO is usually less than 10 -5 S / cm, which cannot meet the demand of battery practical application (>10 -4 S / cm).

[0004] (2) Low lithium ion transference number: In the PEO system, the transference of lithium ions (Li + +) depends on the coordination and dissociation with ethylene oxide (EO) units, and the anion of the traditional lithium salt (such as lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) also has considerable transference ability, resulting in that the transference number (t + ) of Li + + is usually less than 0.3. The low t + will cause serious concentration polarization and aggravate the growth of lithium dendrites.

[0005] (3) Insufficient mechanical property and poor interface stability: the mechanical modulus of pure PEO is low, which is not enough to effectively inhibit the penetration of lithium dendrites. In order to enhance the mechanical property, the existing technology often adopts the method of adding inorganic rigid fillers (such as LLZO, SiO2, etc.) to prepare a composite electrolyte. However, these inorganic fillers have poor compatibility with the polymer matrix, are easy to agglomerate, and form an unstable solid-state electrolyte interface film (SEI) at the electrode interface, resulting in continuous increase of the interface resistance and attenuation of the battery cycle life.

[0006] (4) Narrow electrochemical window: the PEO matrix and the commonly used lithium salts such as LiTFSI and LiFSI will be oxidized and decomposed at a voltage higher than 4.2V, which limits its application on high-voltage positive electrode materials (such as NMC811, lithium-rich manganese-based, etc.).

[0007] In summary, developing a solid-state polymer electrolyte that can simultaneously achieve high room temperature ionic conductivity, high lithium ion transference number, excellent mechanical strength and wide electrochemical window is a technical problem that needs to be solved in the field at present. SUMMARY

[0008] In order to solve the problems of low ionic conductivity, low lithium ion transference number, insufficient mechanical properties, poor interface stability and narrow electrochemical window of the current solid-state polymer electrolyte, the present application provides a multi-scale synergistically reinforced self-healing solid-state polymer electrolyte.

[0009] The multi-scale synergistically reinforced self-healing solid-state polymer electrolyte provided by the present application comprises the following components in mass percentage:

[0010] 8-arm star polymer 50 - 65%, carborane lithium salt 15 - 20%, neutral plastic crystal additive 8 - 15%, poly ionic liquid nanofiber network 8 - 15%, crown ether functionalized boronene two-dimensional filler 2 - 8%, total 100%.

[0011] Among them, the eight-arm star polymer takes eight-arm polyethylene oxide (PEO) as the core, and the number average molecular weight (Mn) of each arm is about 8000 g / mol. The end of each arm is grafted with a uracil-based polyurethane unit, and the middle main chain of each arm is randomly grafted with 2-(2-cyanoethoxy) ethyl units and 15-crown-5 ether group-containing units.

[0012] Preferably, the end of each arm is grafted with 1-(6-isocyanate hexyl)-2-amino-6-methyl-4-(3-oxo-2-butenyl)-pyrimidine-2,4-dione to form a uracil-based polyurethane unit.

[0013] Preferably, 10 mol% of 2-(2-cyanoethoxy)ethyl units and 3 mol% of 15-crown-5 ether group-containing units are randomly grafted on the middle part of each arm. Further preferably, the 2-(2-cyanoethoxy)ethyl units are -O-CH2CH2-O-CH2CH2-CN, and the 15-crown-5 ether group-containing units are -O-(CH2)2-15-crown-5. The mol% here refers to (the number of moles of this kind of unit after grafting) ÷ (the number of moles of all the repeating units of this arm) × 100%. An arm originally has only ethylene oxide (EO) repeating units n≈181. Of which 10% (≈18) EO is post-modified into -O-CH2CH2-O-CH2CH2-CN, and 3% (≈5-6) EO is post-modified into -O-(CH2)2-15-crown-5, and the rest is still EO, about 87%. Therefore, 10 mol% and 3 mol% are not the ratio between the two kinds of units, but the "molar percentage" of each in all the main chain links (EO + modified links) of the entire arm.

[0014] The preparation method of the eight-arm star polymer: first, an eight-arm 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 on each arm chain through toluenesulfonation and nucleophilic substitution reaction; finally, a uracil-based polyurethane unit is grafted on each arm end through isocyanate chemistry to obtain an eight-arm star polymer.

[0015] The star topology of the eight-arm star polymer fundamentally inhibits the regular arrangement and crystallization of PEO chains (crystallinity Xc<5%), ensuring that the electrolyte remains amorphous at -20°C to room temperature, providing sufficient free volume for ion transport. The uracil-based polyurethane unit grafted at the end of the arm constructs a high-strength dynamic reversible physical crosslinking network (room temperature shear modulus >200 MPa), which gives the electrolyte excellent mechanical strength to inhibit lithium dendrites, while enabling "self-healing" when damaged. The -CN in the -O-CH2CH2-O-CH2CH2-CN side group in the middle of the arm has a strong dipole moment, which can effectively weaken the coordination of Li + with the EO chain; the inner cavity size of the 15-crown-5 ether side group is perfectly matched with Li + , which can selectively capture and promote the "in-chain hopping" of Li + , and the two work together to significantly improve the dissociation degree and migration rate of Li + .

[0016] The polyionic liquid nanofiber network is made of ionic liquid monomers by in-situ radical polymerization initiated by light. The ionic liquid monomer is 1-allyl-3-(2-methoxyethyl)imidazolium-closo-B 12 H 11 NH, abbreviated as AEMIm-closo-B 12 H 11 NH. Cation: 1-allyl-3-(2-methoxyethyl)imidazolium + is a common ionic liquid imidazolium skeleton, with an allyl group on N1 and a 2-methoxyethyl group on N3. Anion: closo-B 12 H 11 NH - is a weakly coordinated, super-ionic conductive large-cage boron anion. When this ionic liquid monomer is added to an electrolyte slurry, radical polymerization of the allyl end can be initiated by light (e.g., 365 nm UV light).

[0017] The ionic liquid monomer AEMIm-closo-B 12 H 11 NH is polymerized to form polyionic liquid (PIL) nanofibers with a diameter of about 15 nm, which interpenetrate and construct a "soft-hard" bicontinuous ion-conductive network in the PEO matrix. 12 H 11 NH - is a weakly coordinated anion that ensures high ion dissociation. The PIL nanofibers themselves are high-ionic-conductivity phases, and the continuous network they form provides a "highway" for Li + throughout the entire electrolyte film, increasing the room-temperature conductivity to 1.1-1.3 mS / cm -1 . The imidazolium cation skeleton of the PIL is fixed on the polymer chain, and the positively charged skeleton electrostatically drives the movement of Li + while repelling the movement of anions, further increasing the Li + transference number (t + ) to 0.55.

[0018] The neutral plastic crystal additive is 1,3,5-tris(2,2-difluoromethyl-1,3-dioxolan-4-yl)benzene, abbreviated as Tri-DFMDB. This molecule is a neutral molecule that does not contain ions, and has a melting point of 5°C, existing in an isotropic plastic crystal phase (rotator phase) at a wide temperature range of -60°C to 120°C, i.e., the molecules can rotate at high speed on the crystal lattice.

[0019] Tri-DFMDB forms a "crystal-embedded" sub-phase in the PEO matrix, and the rotational motion of the molecules drives the movement of Li +Additional, low-barrier "bypass" hopping channels are provided, significantly boosting the ionic conductivity of the electrolyte at low temperatures (>0.2 mS / cm at -20℃ -1 ). Moreover, as it is a neutral molecule, it does not dilute the carrier concentration or reduce the Li + transport number.

[0020] The preparation method of the crown ether functionalized boronene two-dimensional filler is: at room temperature, a hexagonal boron bulk is treated by an electrochemical exfoliation method, and liquid phase exfoliation is carried out under the assistance of an ionic liquid to obtain a single-layer or few-layer boronene nanosheet dispersion liquid; the sheet thickness is less than 2 nm, and the lateral size is 200-500 nm. Subsequently, aromatic diazonium salt chemistry is used to covalently couple p-phenylenediamine bis-crown ether molecules to the surface of the boronene nanosheet to obtain the crown ether functionalized boronene two-dimensional filler.

[0021] The crown ether functionalized boronene two-dimensional filler has in-plane ultrafast lithium guiding effect, interface stability and dendrite inhibition effect. The sp 2 -B atom network of boronene itself constitutes a two-dimensional electron sea, and the surface modified crown ether side group can capture Li + and guide it to perform a very low energy barrier "two-dimensional in-plane hopping" (surf-hopping) on the surface of the boronene sheet layer, so that the Li + diffusion coefficient is increased by 2-3 orders of magnitude. The two-dimensional boronene nanosheet tends to arrange parallel to the electrode surface at the interface close to the lithium metal negative electrode to form a "polarization barrier layer". The layer can effectively homogenize the lithium ion flow (JLi), inhibit the formation of "hot spots", and thus realize long-term stable lithium deposition / exfoliation at a large current density of >4 mA cm -2 , and avoid lithium dendrite growth.

[0022] The carborane lithium salt has weak coordination, and is preferably dodecafluoro-closed-1-carbocarborane lithium, and the molecular formula is LiCB 11 F 12 . The anion [CB 11 F 12 ] - is a large-volume, nearly spherical, highly fluorinated weakly coordinated anion (pKa≈-10). The anion almost does not coordinate with Li + , so that Li + exists and migrates in a "quasi-bare" state, thereby greatly increasing the effective concentration and transport number of Li + . At the same time, the lithium salt has extremely high oxidation stability, and the decomposition products can form a stable SEI / CEI interface film rich in LiF and B species on the electrode surface, widening the stable working voltage of the electrolyte to more than 4.8 V.

[0023] The application also provides a preparation method of the self-healing solid-state polymer electrolyte with multi-scale synergistic enhancement, comprising the following steps:

[0024] S1, adding an eight-arm star polymer, a lithium carborane salt, a neutral plastic crystal additive, an ionic liquid monomer, and a crown ether functionalized boronene two-dimensional filler into a mixed solvent of dimethoxyethane (DME) and hexafluoroisopropanol (HFIP), and ultrasonicating or stirring until a uniform and stable electrolyte slurry is formed.

[0025] S2, uniformly coating the electrolyte slurry on a substrate to form a wet film with a thickness of 30-50 µm, and then drying.

[0026] S3, transferring the dried film to an inert gas-filled environment, and irradiating with ultraviolet light for 10-30 min to initiate in-situ polymerization of the ionic liquid monomer to form a polyionic liquid nanofiber network.

[0027] S4, placing the film obtained in step S3 in a vacuum at 120℃ for 5h to obtain a solid-state polymer electrolyte film with a thickness of 25-30 µm.

[0028] Compared with the prior art, the application has the following advantages:

[0029] (1) Achieving extremely high room temperature ionic conductivity: due to the multi-scale and multi-mode synergistic lithium ion conduction mechanism, the solid-state electrolyte of the application has an ionic conductivity of 1.1-1.3 mS / cm at room temperature (25℃), which is more than two orders of magnitude higher than that of traditional PEO-based electrolytes (<10 - 2 mS / cm). Even at a low temperature of -20℃, the conductivity of the solid-state electrolyte of the application can still remain above 0.25 mS / cm, solving the pain point of poor low-temperature performance of solid-state batteries.

[0030] (2) Achieving extremely high lithium ion transference number: the application uses a weakly coordinated [CB 11 F 12 ] - anion, which allows Li + to migrate "freely"; at the same time, the in-situ polymerized positively charged PIL nanofiber skeleton has a binding effect on the anion. Under the synergistic action of the two, the Li + transference number (t + ) is as high as 0.55, which is much higher than that of traditional systems (t + <0.3). High Li + transference number can effectively suppress battery polarization, laying a foundation for achieving fast charging and long cycle life.

[0031] (3) Excellent mechanical properties and self-healing ability: the dynamic quadruple hydrogen bonds formed by the star-shaped PEO backbone and the uracil-based polyurethane units in the eight-arm star-shaped polymer form a physical cross-linking network, which gives the electrolyte membrane a shear modulus of up to 220 MPa and a breaking elongation of 320%, effectively preventing the growth of lithium dendrites. When the membrane produces microcracks, the breaking and recombination of dynamic hydrogen bonds can achieve self-healing at room temperature, improving the service life and safety of the battery.

[0032] (4) Ultra-wide electrochemical stability window: the carbon borane lithium salt LiCB 11 F 12 Its high oxidation potential and the dense and stable SEI / CEI film rich in LiF / B species formed by its coordination with crown ether functionalized boronene two-dimensional fillers at the electrode interface make the electrolyte stable in a wide voltage range of 0-5.2 V (vs. Li / Li + ) and can perfectly match high-voltage positive electrode materials such as NMC811, fully realizing the potential of high energy density.

[0033] (5) Achieving excellent lithium metal interface stability: the "polarization barrier layer" formed by the self-assembly of crown ether functionalized boronene two-dimensional fillers at the negative electrode interface can homogenize the lithium ion flow and inhibit the nucleation and growth of dendrites from the source. Experimental data show that the assembled Li|Li symmetrical battery can be stably cycled for more than 2000 hours at a large current density of 4 mA / cm 2 .

[0034] Other advantages, objects, and features of the present application will be apparent from the following description, and will be understood by persons skilled in the art. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present application are described below, and it should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application, and are not intended to limit the present application.

[0036] Example 1

[0037] An eight-arm star-shaped polymer has the following structural parameters:

[0038] Core: octahydroxy-POSS, abbreviated as POSS-(OH)8, Mw is about 712 g / mol. The full name of POSS-(OH)8 in English is octa-hydroxyl polyhedral oligomeric silsesquioxane, and it is commonly called octahydroxyl cage-type silsesquioxane or octahydroxyl polyhedral silsesquioxane in Chinese. Its structural characteristics are: Si8O 12Si8O12 / 8, each Si vertex is connected with one -CH2CH2CH2-OH, due to its small size (≈1.5 nm) and chemical inertness, it is widely used as the "core" of star-shaped or cage-shaped polymers.

[0039] Each arm: Mn is about 8 000 g / mol, which is about equal to 181 EO repeat units; 10% of the molar percentage of -O-CH2CH2-O-CH2CH2-CN side groups are randomly grafted in the middle of each arm; and 3% of the molar percentage of -O-(CH2)2-15-crown-5 side groups are randomly grafted; the arm terminal is grafted with 1-(6-isocyanatohexyl)-2-amino-6-methyl-4-(3-oxo-2-butenyl)-pyrimidine-2,4-dione (abbreviated as UPy-NCO).

[0040] The preparation method of the above eight-arm star polymer is as follows:

[0041] (1) Synthesis of eight-arm PEO by ring-opening polymerization (ROP) in anhydrous environment, the steps are as follows:

[0042] (a) In a 2 L four-necked flask, 1.00 g of POSS-(OH)8, 350 mL of anhydrous tetrahydrofuran (THF), and 22.4 mL of a suspension of potassium hydride in THF are added, the concentration of potassium hydride in the suspension is 0.5 M, and the suspension is stirred at room temperature for 0.5 h. Potassium hydride is a strong base / nucleophile, which can deprotonate -OH to generate -O - K + (eight potassium alkoxide), and the reaction principle is: R-OH + KH → R-O - K + H2↑. The hydrogen generated by deprotonation is discharged by nitrogen flow or evacuation. The four ports of the four-necked flask are respectively equipped with a stirring rod, a thermometer, an inlet tube (inert nitrogen), and an outlet gas condenser / safety valve, so as to safely discharge H2. THF is used as a reaction solvent to provide an anhydrous environment for subsequent ring-opening polymerization of ethylene oxide. Eight potassium alkoxide is used as an "active initiator" for subsequent ring-opening polymerization of ethylene oxide.

[0043] (b) The four-necked flask is evacuated to 10 -2 Pa or three times of high-purity nitrogen (O2<1 ppm) is introduced, and then cooled to -20℃, then 89 g of high-purity ethylene oxide EO is introduced, which is slowly injected in four batches, and the temperature is controlled to be ≤0℃ during the injection process; after the injection is completed, the temperature is kept at 25℃, and the reaction is stirred for 10 h;

[0044] (c) After 10 h of reaction, 3 mL of methanol is added, and the solvent is removed by rotary evaporation, and then vacuum drying at 40℃ for 12 h to obtain eight-arm PEO, with a yield of 97 %.

[0045] (2) Toluene sulfonylation: 100 g of the eight-arm PEO was dissolved in 1 L of anhydrous CH2Cl2, and 35.0 g of triethylamine was added at 0 °C in an ice bath. 56.0 g of p-toluenesulfonyl chloride was dissolved in another portion of CH2Cl2, and the p-toluenesulfonyl chloride solution was slowly added to the solution system containing the eight-arm PEO and triethylamine under ice bath conditions (0-5 °C). The addition was completed in about 1 h, and then the reaction was stirred at room temperature for 4 h. Then, it was filtered with a sand funnel, and 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 dissolved in the CH2Cl2 / diethyl ether mixed phase. The precipitate was collected by filtration and dried at 40 °C under vacuum to obtain PEO containing -OTs active groups, referred to as PEO-OTs.

[0046] (3) Grafting crown ether side groups: 94 g of PEO-OTs was dissolved in 500 mL of N-methylpyrrolidone (NMP), and then 29.0 g of 15-crown-5-CH2CH2-OH (crown ether alcohol) and 5.3 g of NaH (previously dispersed in white mineral oil or paraffin oil to form a dispersion with a mass concentration of 60 %) were added. NaH reacted with the alcohol hydroxyl group of 15-crown-5-CH2CH2-OH at 0 °C to form 15-crown-5-CH2CH2-O - Na + During this process, hydrogen gas was generated and needed to be discharged by nitrogen gas. Then, the temperature was increased to 50 °C, and the reaction was stirred for 6 h to promote the attack of 15-crown-5-CH2CH2-O - on PEO-OTs to form PEO-O-CH2CH2-5-crown-15. The byproduct p-CH3C6H4SO3 - Na + was removed by water washing.

[0047] (4) Grafting cyanoethoxy side groups: the mixed solution 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 reaction was stirred at 40 °C for 8 h, and then poured into 5 L of deionized water. Dialysis (MWCO 5 kDa) was performed for 3 d, and freeze-drying was performed to obtain PEO-mixed-side. The molecular formula of 2-(2-cyanoethoxy)ethanol is HO-CH2CH2-O-CH2CH2-CN.

[0048] (5) Arm end grafting of a ureido-polyurethane unit (UPy-NCO): 112 g of PEO-mixed-side was dissolved in 600 mL of anhydrous N,N-dimethylformamide (DMF) under nitrogen protection, and the temperature was raised to 40°C. 7.33 g of UPy-NCO and 0.10 g of a catalyst dibutyltin dilaurate (DBTDL) were added, and the reaction was stirred at 40°C for 12 h. After the reaction was completed, the reaction product was poured into ice ether to precipitate the precipitate, which was collected by filtration and dried at 40°C under vacuum for 24 h to obtain a light yellow solid, which was an eight-arm star polymer. The molecular weight Mn was 8.2×10 4 g / mol.

[0049] Example 2

[0050] Preparation of crown ether functionalized boronene two-dimensional filler: Hexagonal boron bulk was treated by electrochemical exfoliation at room temperature, and boronene nanosheet dispersion was obtained by liquid phase exfoliation assisted by ionic liquid; then, p-phenylenediamine bis-crown ether molecules were covalently coupled to the surface of boronene by aromatic diazonium salt chemistry to obtain crown ether functionalized boronene two-dimensional filler, abbreviated as LC-B filler.

[0051] The specific preparation method is as follows:

[0052] (1) Electrochemical liquid phase exfoliation:

[0053] Device used: three-electrode H-Cell, anode B metal sheet 1.00 g (10×20×1 mm); Pt mesh cathode; Ag / AgCl reference electrode.

[0054] Electrolyte: prepared from 60 mL of 1-butyl-3-methylimidazolium dicyanamide (BMIM-DCA) and 20 mL of anhydrous CH3CN.

[0055] Reaction conditions: set the constant potential to 10 V, and react at room temperature for 4 h, during which black-brown colloid is precipitated; then centrifuge at 6000 rpm for 10 min, and extract the supernatant; the precipitate is washed with an ethanol / water mixture for 3 times, and is re-dispersed in 200 mL of N,N-dimethylformamide (DMF) under vacuum to obtain boronene nanosheet dispersion.

[0056] (2) Aromatic diazonium salt-crown ether coupling modification:

[0057] (a) 0.50 g of p-aminophenyl-15-crown-5 (molecular formula C 14 H 21 NO5) was added to 10 mL of 1 M HCl solution, cooled to 0°C, and then 0.13 g of NaNO2 was added. The temperature was kept at 0-2°C, and the reaction was stirred for 15 min to obtain a light brown diazonium salt solution.

[0058] (b) The boronene nanosheet dispersion obtained in step (1) was cooled to 5℃, and 50 mg of FeCl2·4H2O was added as a catalyst; then the diazonium salt solution was added dropwise into the boronene nanosheet dispersion under N2protection, and stirred at 0-5℃ for 4 h, and then stirred at room temperature for 12 h; after the reaction was completed, the boronene nanosheet was separated by centrifugation at 10000 rpm, and was washed with DMF, acetonitrile, water and diethyl ether in sequence, and was freeze-dried to obtain a light gray powder, which was a crown ether functionalized boronene two-dimensional filler, abbreviated as LC-B.

[0059] The specific surface area of LC-B was measured to be 470 m 2 / g, the zeta potential was -38 mV, and the monolayer rate was 85 %.

[0060] The products prepared in Examples 1 and 2 were used in the following examples.

[0061] Example 3

[0062] A multiscale synergistically reinforced self-healing solid-state polymer electrolyte was prepared by the following method:

[0063] 5.8 g of the eight-arm star polymer prepared in Example 1, 1.7 g of LiCB 11 F 12 , 1.0 g of Tri-DFMDB, 1.0 g 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 to obtain an electrolyte slurry. The electrolyte slurry was uniformly coated on a substrate (release film) by a doctor blade coating method to form a wet film with a thickness of 35 µm, and was dried at 80℃ 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 induce in-situ polymerization of the PIL monomer to form a PIL nanofiber network. Finally, the film was placed in a vacuum at 120℃ for 5 h to promote the microstructure of each phase in the system to reach equilibrium, and finally a solid-state polymer electrolyte film was obtained.

[0064] Example 4

[0065] On the basis of Example 3, the amounts of the components were adjusted as follows: 6.5 g of the eight-arm star polymer prepared in Example 1, 2.0 g of LiCB 11 F 12 , 0.8 g of Tri-DFMDB, 0.5 g of AEMIm-closo-B 12 H 11NH monomer, 0.2 g LC-B prepared in Example 2. Other steps remain unchanged. Finally, a solid-state polymer electrolyte film is obtained.

[0066] Example 5

[0067] On the basis of Example 3, the amount of each component is adjusted to: 5.0 g of the eight-arm star polymer prepared in Example 1, 1.5 g of LiCB 11 F 12 , 1.5 g of Tri-DFMDB, 1.5 g of AEMIm-closo-B 12 H 11 NH monomer, 0.5 g LC-B prepared in Example 2. Other steps remain unchanged. Finally, a solid-state polymer electrolyte film is obtained.

[0068] The performance of various electrolyte films is tested, and the test methods of various performances are as follows:

[0069] (1) Ionic conductivity σ: using a method similar to GB / T 1410-2006, the electrolyte film with a thickness of 25-30 µm is sandwiched between SUS316 stainless steel blocking electrodes; after 1 h of temperature stabilization, it is scanned with an impedance analyzer (1 MHz → 0.1 Hz, 10 mV); R_b is the high-frequency intercept, and σ = L / (R_b · A).

[0070] (2) Lithium ion transference number (t + ): using the Bruce-Vincent method (J. Electrochem. Soc. 1991, 138, 8), Li│SPE│Li symmetric battery (thickness as above) is polarized by 10 mV at 25℃; record I0, I_s and impedance R0, R_s before and after polarization, t + = (I_s · (ΔV – I0R0)) / (I0· (ΔV – I_sR_s)).

[0071] (3) Electrochemical window (LSV): stainless steel│SPE│Li, scan rate 1 mV s -1 , from OCV to 6 V. The decomposition potential is taken as the voltage when the anode current density reaches 0.1 mA cm -2 .

[0072] (4) Shear modulus G′: using GB / T 16491-2008 General Principles for Dynamic Mechanical Analysis, parallel plate rheometer, 25℃, 1 Hz, 1% strain oscillation.

[0073] (5) Elongation at break: ASTM D638-14 Type V, 25 pm film, 5 mm min -1 at 25 °C.

[0074] (6) Li | Li symmetric cycling: CR2032, Li foil 15 pm, every half hour reversal; record AV-t. Short circuit criterion: AV<10 mV.

[0075] (7) NMC811 | Li full cell: positive electrode face capacity 2 mAh cm -2 , N / P ~ 3; 50 pm SPE; 30 °C, 1 C (~ 200 mA g -1 ) charge-discharge.

[0076] (8) 5 C fast charging temperature rise: 5 C constant current charging to 80 % SOC (~ 6 min), thermocouple attached to the center position outside the battery shell; record AT.

[0077] The solid-state polymer electrolyte film prepared in Example 3 was subjected to performance testing, and was compared with a typical existing electrolyte (PEO / LiTFSI). The test results are shown in Table 1.

[0078] Table 1, performance comparison data of the solid-state polymer electrolyte film prepared in Example 3 and the existing electrolyte (PEO / LiTFSI)

[0079]

[0080] Comparative Example 1

[0081] On the basis of Example 3, “1.7 g of LiCB 11 F 12 ” was replaced with an equal amount of lithium salt LiTFSI, and the others remained unchanged, to obtain a solid-state polymer electrolyte film. The performance test data of the electrolyte film and the electrolyte film of Example 3 were compared as shown in Table 2.

[0082] Table 2, performance comparison data of the electrolyte film prepared in Example 3 and the electrolyte film of Comparative Example 1

[0083]

[0084] It can be seen that the performance of the electrolyte film of Example 3 is significantly better than that of Comparative Example 1 electrolyte film. This is because the TFSI - strong coordination in the lithium salt LiTFSI used in Comparative Example 1 reduces the degree of dissociation, produces EO-Li-TFSI ternary clusters, and starts to oxidize at 4.3 V, and the SEI / CEI contains S-Ox which is easy to crack.

[0085] Comparative Example 2

[0086] On the basis of Example 3, delete "1.0 g of Tri-DFMDB", that is, do not add neutral plastic crystal additives, and other remain unchanged, to obtain a solid-state polymer electrolyte film. The performance test data of the electrolyte film and the electrolyte film of Example 3 are compared as shown in Table 3.

[0087] Table 3, performance comparison data of the electrolyte film prepared in Example 3 and the electrolyte film of Comparative Example 2

[0088]

[0089] It can be seen that the ion conductivity σ of the electrolyte film of Comparative Example 2 drops greatly (-68%) under low temperature conditions, verifying that the rotor phase is the main conduction channel in the "cold region".

[0090] Comparative Example 3

[0091] On the basis of Example 3, delete "1.0 g of AEMIm-closo-B 12 H 11 NH monomer", that is, remove the PIL nanofiber network in the electrolyte, and omit the LED light irradiation step in the subsequent steps. Other remain unchanged, to obtain a solid-state polymer electrolyte film. The performance test data of the electrolyte film and the electrolyte film of Example 3 are compared as shown in Table 4.

[0092] Table 4, performance comparison data of the electrolyte film prepared in Example 3 and the electrolyte film of Comparative Example 3

[0093]

[0094] It can be seen that if the PIL nanofiber network is removed from the electrolyte film of the application, the potential driving of the cation skeleton will be lost, t + σ are significantly decreased, and the interfacial polarization resistance is increased by 3 times.

[0095] Comparative Example 4

[0096] On the basis of Example 3, delete "0.5 g of LC-B prepared in Example 2", that is, remove the crown ether functionalized boronene two-dimensional filler in the electrolyte, and other remain unchanged, to obtain a solid-state polymer electrolyte film. The performance test data of the electrolyte film and the electrolyte film of Example 3 are compared as shown in Table 5.

[0097] Table 5, performance comparison data of the electrolyte film prepared in Example 3 and the electrolyte film of Comparative Example 4

[0098]

[0099] Comparative Example 5

[0100] Take 5.8g of the eight-arm star polymer prepared in Example 1, 1.7g of LiTFSI, 5g of LC-B prepared in Example 2, and dissolve them in 20mL of DME / HFIP (volume ratio 20:1) mixed solvent, stir uniformly to obtain an electrolyte slurry. The electrolyte slurry is uniformly coated on the substrate (release film) by using a doctor blade coating method, and a wet film with a thickness of 35 µm is formed. After drying at 80℃ for 2h, most of the solvent is removed; then the dried film is placed in a constant temperature oven at 120℃ under vacuum for 5h to promote the microstructure of each phase in the system to reach equilibrium, and a ternary minimalist solid-state polymer electrolyte film is obtained. The performance test data of the electrolyte film and the electrolyte film of Example 3 are compared as shown in Table 6.

[0101] Table 6, performance comparison data of the electrolyte film prepared in Example 3 and the electrolyte film of Comparative Example 5

[0102]

[0103] From the above, it can be concluded that in the solid-state polymer electrolyte of the present application, if the lithium salt LiCB 11 F 12 is replaced by the conventional LiTFSI, the ionic conductivity σ, lithium ion transference number t + and electrochemical stability window of the electrolyte will be significantly attenuated, especially the low-temperature conductivity performance will drop nearly an order of magnitude. If any one of the "soft / hard synergistic channel" elements (Tri-DFMDB, PIL fiber network or LC-B) is removed, the ionic conductivity σ and the interface stability will be significantly reduced. As can be seen from Table 6, the performance of the ternary minimalist electrolyte film of Comparative Example 5 is comparable to that of the existing electrolyte (PEO / LiTFSI). This fully proves that each component of the solid-state polymer electrolyte of the present application is indispensable, and each component forms an organic whole to achieve multi-scale synergistic enhancement, so as to overcome the technical problems of the existing solid-state polymer electrolyte, such as low ionic conductivity, low lithium ion transference number, insufficient mechanical properties, poor interface stability, narrow electrochemical window, etc.

[0104] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, and any simple modification, equivalent change and modification of the above embodiments based on the technical essence of the present application are still within the scope of the technical solution of the present application.

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 of each arm; the eight-armed polyethylene oxide is obtained by ring-opening polymerization of ethylene oxide with an octahydroxy-POSS core under an anhydrous environment; 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 boronene two-dimensional filler is a monolayer or few-layer boronene nanosheet prepared by electrochemical exfoliation, and the surface of the boronene nanosheet is further modified by terephthala dicrown 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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