Cationic polymer electrolyte as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, discloses a cationic polymer electrolyte as well as a preparation method and application thereof, and aims to solve the problems of low ionic conductivity, low lithium transfer number and lithium dendrite growth of a PEO-based electrolyte. The preparation method comprises the following steps: (1) carrying out acid catalytic polymerization on dibenzo-18-crown-6 and 1-methyl-4-piperidone to obtain a polymer precursor p-PCEP; (2) the polymer precursor p-PCEP is subjected to a Menshukin reaction, and quaternized p-PCEP is obtained; (3) dissolving the quaternized p-PCEP in DMF (Dimethyl Formamide), pouring to form a film, and exchanging I <-> through TFSI <-> to obtain PCEP; and (4) dissolving PEO, LiTFSI and PCEP in DMF, and preparing the cationic polymer electrolyte by a solvent casting method. The cationic piperidine and the crown ether group are added into the PCEP, so that the synergistic regulation of cations and anions is promoted, rapid Li < + > transportation is realized, and meanwhile, the growth of lithium dendrites is inhibited, so that the electrochemical performance of the all-solid-state lithium metal battery is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a cationic polymer electrolyte. Background Art

[0002] Lithium metal electrodes have a very high theoretical capacity (3862 mAh g -1 ) and low electrochemical potential (-3.04V compared to the standard hydrogen electrode), are considered to be the "holy grail" of the next generation of lithium-ion battery anodes, showing great potential in the field of energy storage technology. However, in practical applications, the uncontrolled growth of lithium dendrites and the fire hazards associated with organic liquid electrolytes have greatly hindered their development. Solid-state electrolytes provide a promising alternative solution. Among them, polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) have attracted widespread attention due to their good flexibility, good interfacial compatibility with lithium metal, and scalability for commercial applications. However, PEO-based solid polymer electrolytes still face the problem of low ionic conductivity (10 at 60°C) -7 Up to 10 -6 S cm -1 )、Li + Transfer number (t Li+ ) and uncontrollable lithium dendrite growth.

[0003] Ideal solid polymer electrolytes (SPEs) should be able to promote the + ) while inhibiting the formation of lithium dendrites at the lithium / electrolyte interface. Nowadays, the Li+ / -carbon ratio in SPEs can be improved by using cross-linked polymers, increasing the operating temperature, adding plasticizers, ionic liquids, and embedding inorganic fillers. + conductivity, but these approaches often require a trade-off between ionic conductivity and other key performance parameters. In addition, lithium dendrites penetrating SPEs can lead to reduced Coulombic efficiency of the battery, poor cycling performance, and potential short-circuit risks, which remains a major challenge in the practical application of solid-state batteries. Solid electrolytes with a shear modulus exceeding twice that of metallic lithium (about 3.4 GPa) can serve as effective mechanical barriers to inhibit dendrite growth, but the increased rigidity may impair the interfacial contact with the lithium anode. For example (Han, F., Yue, J., Zhu, X., & Wang, C. Suppressing Li dendrite formation in Li 2 SP 2 S 5 solid electrolyte by LiI incorporation. Adv. Energy Mater. 8, 1703644 (2018)). LiI incorporation is used to inhibit Li2 SP 2 S 5 Lithium dendrites are formed in the solid electrolyte, but the capacity retention rate (%) of the LFP battery designed with this design (60°C, 0.1C, after 100 cycles) is only 79.9%. Regulating steric hindrance of porous organic polymers in composite solid-state electrolytes to induce the formation of LiF-Rich SEI in Li-ion batteries. Angew. Chem. Int. Ed. 62, e202308738 (2023). This method focuses on regulating the steric hindrance of porous organic polymers in composite solid-state electrolytes to induce the formation of LiF-Rich SEI, and the ionic conductivity (S cm -1 ) is 1.5×10 -4 , and the obtained product Li / Li symmetric battery polarization voltage (V) (60℃, 0.2mA cm -2 , after 400 hours of cycling) is only about 0.24 (rapidly drops to close to 0V after 36 hours of cycling). Therefore, improving ionic conductivity, increasing the number of lithium ion migration, inhibiting lithium dendrite growth, and solving the problem of polysulfide shuttling in lithium-sulfur batteries are important technical challenges faced in the development of solid-state lithium metal batteries. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a cationic polymer electrolyte and a preparation method and application thereof.

[0005] To achieve the above object, the technical solution of the present invention is implemented as follows:

[0006] A method for preparing a cationic polymer electrolyte, comprising the following steps:

[0007] (1) dibenzo-18-crown-6, 1-methyl-4-piperidone, an acid catalyst and a solvent A are mixed, stirred at room temperature, and then added to a precipitant B for precipitation to obtain a polymer precursor p-PCEP;

[0008] (2) adding the polymer precursor p-PCEP and methyl iodide to a polar aprotic solvent, reacting at room temperature, adding to a precipitant C for precipitation, washing and drying to obtain quaternized p-PCEP;

[0009] (3) dissolving the quaternized p-PCEP in DMF to prepare a solution, and casting the solution into a membrane; soaking the membrane in a lithium bis(trifluoromethanesulfonyl)imide solution to obtain PCEP;

[0010] (4) Polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide and PCEP were dissolved in DMF and a cationic polymer electrolyte was prepared by a solvent casting method, which was recorded as CPE-x-PCEP.

[0011] In the above step (1), the molar ratio of dibenzo-18-crown-6 to 1-methyl-4-piperidone is 1:(1-2); 1.1-2.2 mol of dibenzo-18-crown-6 is added per liter of acid catalyst; and the stirring time at room temperature is 18-24 hours.

[0012] In the above step (1), the acid catalyst is trifluoromethanesulfonic acid and trifluoroacetic acid; the solvent A is dichloromethane or dimethyl sulfoxide; and the precipitant B is ethanol or methanol.

[0013] In the above step (2), 1-2 g of polymer precursor p-PCEP is added to each mL of methyl iodide; the volume ratio of methyl iodide to polar aprotic solvent is 1:(10-20).

[0014] In the above step (2), the polar aprotic solvent is dimethyl sulfoxide or dimethylformamide; the precipitant C is diethyl ether or dimethyl ether; and the reaction time at room temperature is 24-48 hours.

[0015] In the above step (3), the content of quaternized p-PCEP in the solution is 10-20 wt %.

[0016] The soaking temperature in the above step (3) is room temperature and the soaking time is 48-96 hours.

[0017] In the above step (4), the mass ratio of polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide and PCEP is 4:3:(1-4).

[0018] The cationic polymer electrolyte is prepared by the above preparation method.

[0019] The ionic conductivity of the cationic polymer electrolyte is 4.2×10 -4 S / cm; Li + The transfer number is 0.7.

[0020] Application of the above cationic polymer electrolyte in all-solid-state lithium metal batteries.

[0021] The beneficial effects produced by the present invention are:

[0022] (1) The present invention proposes a new type of cationic polymer electrolyte material. By introducing polycrown ether piperidine (PCEP) into the polymer electrolyte, the ionic conductivity of the electrolyte is significantly improved, which is beneficial to improving the charge and discharge efficiency of the battery. On the one hand, the addition of PCEP reduces the crystallinity of polyethylene oxide (PEO), increasing the amorphous phase of PEO; on the other hand, the crown ether group has a great influence on the Li+ exhibits a strong coordination tendency and provides efficient Li + diffusion channel, which reduces the energy barrier between adjacent hopping sites, thus making the ionic conductivity reach 4.2×10 -4 S / cm, higher than 1.5×10 -4 S / cm.

[0023] (2) The polymer electrolyte material proposed in the present invention can increase the lithium transfer number (t Li+ The functionalized PCEP molecules containing piperidine and crown ether groups enhance the Li+ / LiTFSI system through the synergistic effects of “cation-assisted” and “anion-immobilized”. + The crown ether group can coordinate with lithium ions and provide efficient Li + Diffusion channel; the piperidine cation group hinders the movement of free bis(trifluoromethanesulfonyl)imide anion (TFSI-) through electrostatic interaction, thus increasing the lithium ion migration number (t Li+ ), t Li+ It can reach 0.7.

[0024] (3) The polymer electrolyte material of the present invention can significantly inhibit the formation of dendrites. Anion immobilization reduces the + The concentration gradient at the lithium / SPE interface prevents the formation of a large electric field, thereby inhibiting the growth of lithium dendrites. A higher concentration can reduce the concentration polarization of the battery during charge and discharge, and improve the cycle stability and rate performance of the battery.

[0025] (4) The electrolyte of the present invention improves the overall performance of the battery. The application of the cationic polymer electrolyte of the present invention to an all-solid-state lithium metal battery (paired with a sulfur cathode (C / S composite material) electrode) improves the electrochemical performance of the battery, including rate capability and cycle stability, which makes the all-solid-state lithium metal battery have a broader application prospect in the field of energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 Schematic diagram of the synthesis of CPE-2-PCEP and a flow chart for preparing all-solid-state batteries using lithium iron phosphate (LFP) or C / S positive electrode.

[0028] Figure 2(a) Fourier transform infrared spectra and (b) X-ray diffraction patterns of PEO, PCEP, SPE and CPE-x-PCEP.

[0029] Figure 3 are scanning electron microscope images; wherein, (a) is a surface SEM image of CPE-2-PCEP prepared in Example 2, wherein the inset is a cross-sectional scanning electron microscope image; and (b) is a scanning electron microscope image of SPE prepared in Comparative Example 1.

[0030] Figure 4 The electrochemical properties of cationic polymer-based electrolytes; (a) is the electrochemical impedance spectrum of CPE-2-PCEP at different temperatures; (b) is the electrochemical impedance spectrum of SPE.

[0031] Figure 5 This is the DC polarization curve of CPE-2-PCEP at 10 mV, where the inset is the Nyquist diagram before and after polarization.

[0032] Figure 6 are the ionic conductivity and lithium ion transference number of different solid electrolytes (SPEs) at 60°C.

[0033] Figure 7 The lithium ion migration energy barriers of polyethylene oxide (a) and PCEP (b) coordinated with two lithium ions are shown in turn; (c) is the density functional theory (DFT) calculation of the cationic group and crown ether group with bis(trifluoromethanesulfonyl)imide anion (TFSI - ) binding energy; (d) is a schematic diagram of the “anion fixation” and “cation-assisted” strategies.

[0034] Figure 8 Electrochemical performance of Li / SPE (or CPE-2-PCEP) / Li battery; (a and b) at 0.2 mA cm -2 Scanning electron microscopy (SEM) images of lithium metal in Li / CPE-2-PCEP / Li and Li / SPE / Li batteries after 20 cycles of lithium plating and stripping at a current density of 0.2 mA cm -2 Initial, intermediate, and steady-state stages of lithium deposition at different current densities. Li in CPE-2-PCEP and SPE + distribution and electric potential (d).

[0035] Fig. 9 The electrochemical performance of Li-S button cells based on CPE-2-PCEP and SPE electrolytes; (a) is the rate performance; (b) is the cycle performance.

[0036] Fig.10Li containing piperidine groups, crown ether groups and polyethylene oxide (PEO) molecules 2 S 6 Optimized adsorption model (a) and the adsorption of crown ether groups, piperidine groups and polyethylene oxide molecules on Li 2 S X Binding energies of (x = 1, 2, 4, 6 and 8) (b). DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] The preparation method of the cationic polymer electrolyte of this embodiment is as follows: Figure 1 As shown, the specific steps are as follows:

[0040] (1) Dibenzo-18-crown-6 (3.6041 g), 1-methyl-4-piperidone (1.1316 g), trifluoromethanesulfonic acid (TFMSA, 8.0 mL), trifluoroacetic acid (TFA, 1.0 mL), and dichloromethane (DCM, 30 mL) were mixed and stirred at room temperature (RT) for 24 h. The reaction mixture was poured into ethanol to precipitate the polymer. The obtained polymer was washed with deionized water and dried at 60°C overnight to obtain p-PCEP.

[0041] (2) p-PCEP (2.0 g), methyl iodide (2.0 mL) and dimethyl sulfoxide (DMSO, 20 mL) were mixed in a flask and reacted at room temperature for 24 h. The reaction mixture was then poured into ether to precipitate the product, which was then washed and dried to obtain quaternized p-PCEP.

[0042] (3) The quaternized p-PCEP was dissolved in dimethylformamide (DMF) to obtain a 10 wt% solution. The solution was filtered, poured onto a glass plate, and heated at 60°C for 12 h to form a film. The film was peeled off and immersed in a 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solution at room temperature for 48 h. - Exchange I - Finally, the membrane was washed with deionized water and dried at 60 °C for 12 h to obtain poly(crown ether piperidine), i.e., PCEP.

[0043] (4) The cationic polymer electrolyte was prepared by solvent casting. Polyethylene oxide (PEO, MW: 1 million, 0.4 g), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.3262 g) and PCEP (0.1131 g) were dissolved in dimethylformamide (DMF) respectively, and the mixture was stirred for at least 24 h to ensure homogeneity. The obtained uniform solution was poured into a polytetrafluoroethylene (PTFE) mold to form a dry cationic polymer electrolyte, which was recorded as CPE-1-PCEP. The polymer electrolyte was then stored in a glove box for future use.

[0044] Example 2

[0045] The preparation method of the cationic polymer electrolyte of this embodiment comprises the following steps:

[0046] (1) Dibenzo-18-crown-6 (3.6041 g), 1-methyl-4-piperidone (1.1316 g), trifluoromethanesulfonic acid (TFMSA, 8.0 mL), trifluoroacetic acid (TFA, 1.0 mL), and dichloromethane (DCM, 30 mL) were mixed and stirred at room temperature (RT) for 24 h. The reaction mixture was poured into ethanol to precipitate the polymer. The obtained polymer was washed with deionized water and dried at 60°C overnight to obtain p-PCEP.

[0047] (2) p-PCEP (2.0 g), methyl iodide (2.0 mL) and dimethyl sulfoxide (DMSO, 20 mL) were mixed in a flask and reacted at room temperature for 24 h. The reaction mixture was then poured into ether to precipitate the product, which was then washed and dried to obtain quaternized p-PCEP.

[0048] (3) The quaternized p-PCEP was dissolved in dimethylformamide (DMF) to obtain a 10 wt% solution. The solution was filtered, poured onto a glass plate, and heated at 60°C for 12 h to form a film. The film was peeled off and immersed in a 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solution at room temperature for 48 h. - Exchange I - Finally, the membrane was washed with deionized water and dried at 60 °C for 12 h to obtain poly(crown ether piperidine), i.e., PCEP.

[0049] (4) Cationic polymer electrolytes were prepared by solvent casting. Polyethylene oxide (PEO, MW: 1 million, 0.4 g), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.3262 g) and PCEP (0.2263 g) were dissolved in dimethylformamide (DMF) respectively, and the mixture was stirred for at least 24 h to ensure homogeneity. The obtained uniform solution was poured into a polytetrafluoroethylene (PTFE) mold to form a dry cationic polymer electrolyte, recorded as CPE-2-PCEP. The polymer electrolyte was then stored in a glove box for future use. Figure 3 It can be seen in a that the surface of CPE-2-PCEP is dense and smooth, with a thickness of 120 μm.

[0050] Example 3

[0051] The preparation method of the cationic polymer electrolyte of this embodiment comprises the following steps:

[0052] (1) Dibenzo-18-crown-6 (3.6041 g), 1-methyl-4-piperidone (1.1316 g), trifluoromethanesulfonic acid (TFMSA, 8.0 mL), trifluoroacetic acid (TFA, 1.0 mL), and dichloromethane (DCM, 30 mL) were mixed and stirred at room temperature (RT) for 24 h. The reaction mixture was poured into ethanol to precipitate the polymer. The obtained polymer was washed with deionized water and dried at 60°C overnight to obtain p-PCEP.

[0053] (2) p-PCEP (2.0 g), methyl iodide (2.0 mL) and dimethyl sulfoxide (DMSO, 20 mL) were mixed in a flask and reacted at room temperature for 24 h. The reaction mixture was then poured into ether to precipitate the product, which was then washed and dried to obtain quaternized p-PCEP.

[0054] (3) The quaternized p-PCEP was dissolved in dimethylformamide (DMF) to obtain a 10 wt% solution. The solution was filtered, poured onto a glass plate, and heated at 60°C for 12 h to form a film. The film was peeled off and immersed in a 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solution at room temperature for 48 h. - Exchange I - Finally, the membrane was washed with deionized water and dried at 60 °C for 12 h to obtain poly(crown ether piperidine), i.e., PCEP.

[0055] (4) The cationic polymer electrolyte was prepared by solvent casting. Polyethylene oxide (PEO, MW: 1 million, 0.4 g), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.3262 g) and PCEP (0.3394 g) were dissolved in dimethylformamide (DMF) respectively, and the mixture was stirred for at least 24 h to ensure homogeneity. The obtained uniform solution was poured into a polytetrafluoroethylene (PTFE) mold to form a dry cationic polymer electrolyte, which was recorded as CPE-3-PCEP. The polymer electrolyte was then stored in a glove box for future use.

[0056] Example 4

[0057] The preparation method of the cationic polymer electrolyte of this embodiment comprises the following steps:

[0058] (1) Dibenzo-18-crown-6 (3.6041 g), 1-methyl-4-piperidone (2.2632 g), trifluoromethanesulfonic acid (TFMSA, 5.0 mL), trifluoroacetic acid (TFA, 1.0 mL), and dimethyl sulfoxide (DCM, 30 mL) were mixed and stirred at room temperature (RT) for 18 h. The reaction mixture was poured into methanol to precipitate the polymer. The obtained polymer was washed with deionized water and dried at 60°C overnight to obtain p-PCEP.

[0059] (2) p-PCEP (4.0 g), methyl iodide (2.0 mL) and dimethyl sulfoxide (DMSO, 30 mL) were mixed in a flask and reacted at room temperature for 48 h. The reaction mixture was then poured into ether to precipitate the product, which was then washed and dried to obtain quaternized p-PCEP.

[0060] (3) The quaternized p-PCEP was dissolved in dimethylformamide (DMF) to obtain a 15 wt% solution. The solution was filtered, poured onto a glass plate, and heated at 60°C for 12 h to form a film. The film was peeled off and immersed in a 0.5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solution at room temperature for 72 h. - Exchange I - Finally, the membrane was washed with deionized water and dried at 60 °C for 12 h to obtain poly(crown ether piperidine), i.e., PCEP.

[0061] (4) The cationic polymer electrolyte was prepared by solvent casting. Polyethylene oxide (PEO, MW: 1 million, 0.4 g), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.3262 g) and PCEP (0.2263 g) were dissolved in dimethylformamide (DMF) respectively, and the mixture was stirred for at least 24 h to ensure homogeneity. The obtained uniform solution was poured into a polytetrafluoroethylene (PTFE) mold to form a dry cationic polymer electrolyte, which was recorded as CPE-4-PCEP. The polymer electrolyte was then stored in a glove box for future use.

[0062] Example 5

[0063] The preparation method of the cationic polymer electrolyte of this embodiment comprises the following steps:

[0064] (1) Dibenzo-18-crown-6 (3.6041 g), 1-methyl-4-piperidone (1.6973 g), trifluoromethanesulfonic acid (TFMSA, 4.0 mL), trifluoroacetic acid (TFA, 0.5 mL), and dichloromethane (DCM, 30 mL) were mixed and stirred at room temperature (RT) for 20 h. The reaction mixture was poured into ethanol to precipitate the polymer. The obtained polymer was washed with deionized water and dried at 60°C overnight to obtain p-PCEP.

[0065] (2) p-PCEP (3.0 g), methyl iodide (2.0 mL) and dimethyl sulfoxide (DMSO, 40 mL) were mixed in a flask and reacted at room temperature for 32 h. The reaction mixture was then poured into ether to precipitate the product, which was then washed and dried to obtain quaternized p-PCEP.

[0066] (3) The quaternized p-PCEP was dissolved in dimethylformamide (DMF) to obtain a 20 wt% solution. After filtering the solution, it was poured onto a glass plate and heated at 60°C for 12 h to form a film. The film was peeled off and immersed in a 0.5 M lithium bistrifluoromethanesulfonyl imide (LiTFSI) solution at room temperature for 96 h to exchange I- with TFSI-. Finally, the membrane was washed with deionized water and dried at 60°C for 12 h to obtain poly(crown ether piperidine), i.e., PCEP.

[0067] (4) The cationic polymer electrolyte was prepared by solvent casting. Polyethylene oxide (PEO, MW: 1 million, 0.4 g), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.3262 g) and PCEP (0.2263 g) were dissolved in dimethylformamide (DMF) respectively, and the mixture was stirred for at least 24 h to ensure homogeneity. The obtained uniform solution was poured into a polytetrafluoroethylene (PTFE) mold to form a dry cationic polymer electrolyte, which was recorded as CPE-5-PCEP. The polymer electrolyte was then stored in a glove box for future use.

[0068] Comparative Example 1

[0069] The preparation method of the polymer electrolyte of this comparative example comprises the following steps:

[0070] Polyethylene oxide (PEO, MW: 1 million, 0.4 g) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.3262 g) were dissolved in dimethylformamide (DMF) and the mixture was stirred for at least 24 h to ensure homogeneity. The resulting homogeneous solution was poured into a polytetrafluoroethylene (PTFE) mold to form a dry polymer electrolyte, referred to as SPE. Due to the crystallization of PEO, SPE has a porous surface, as shown in the SEM image. Figure 3 b. The polymer electrolyte was then stored in a glove box for future use.

[0071] Implementation effect example

[0072] The chemical structures of CPE-x-PCEP and SPE were studied by Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). In the infrared spectrum of CPE-2-PCEP, 842, 961 and 1099 cm -1 The absorption peak at corresponds to the characteristic functional group of PEO ( Figure 2 a). XRD spectra of PEO, SPE and CPE-x-PCEP (x=1,2,3) are shown in Figure 2 As shown in b. For PEO powder, two obvious peaks were observed at 19.1° and 23.2°, corresponding to the (120) and (112) planes of crystalline PEO, respectively. After the introduction of LiTFSI in the PEO matrix, the intensity of these peaks weakened. In addition, there is an obvious LiTFSI crystallization peak, indicating the coexistence of crystalline PEO and LiTFSI in SPE, which is the main reason for the low ionic conductivity of SPE. CPE-x-PCEP produces a broad peak at around 20°, which is a characteristic of amorphous PEO, while there is no observable peak in crystalline LiTFSI. This shows that PCEP promotes the amorphization of PEO and enhances the dissolution of LiTFSI, thereby improving Li + Conductivity.

[0073] In order to further study the change of ionic conductivity of CPE-x-PCEP and SPE over time, CPE-2-PCEP was assembled with stainless steel into stainless steel (SS) | CPE-2-PCEP | SS button cells. The assembly process of the battery is as follows: the CPE-2-PCEP electrolyte membrane is cut into a suitable size and placed between two stainless steel sheets to ensure that the electrolyte membrane is in full contact with the stainless steel sheets without wrinkles or bubbles. Then, a diaphragm is placed on both sides of the electrolyte membrane. The diaphragm should cover the electrolyte membrane to isolate the positive and negative electrodes and prevent short circuits. Finally, the assembled structure is placed in a button cell shell and encapsulated by a tablet press and other equipment to ensure that the battery is well sealed and the components are tightly combined.

[0074] The ionic conductivity of the SS|SPE|SS (SS: stainless steel) button cell can be calculated by formula (1):

[0075]

[0076] Where T is the thickness of the electrolyte, A is the surface area of ​​the electrolyte, and R is the resistance. The impedance spectrum is measured from 1 MHz to 10 MHz as a function of temperature. The measurement temperature is between 70°C and 20°C with an interval of 10°C.

[0077] The EIS curves of CPE-2-PCEP and SPE are shown in Figure 4 a and Figure 4 As shown in b, it can be seen that the impedance (EIS) of CPE-2-PCEP decreases with increasing temperature, which is due to the increase in the amorphous region of PEO; and its impedance is significantly smaller than that of SPE. Figure 6 The ionic conductivity and lithium ion transfer number of different solid electrolytes (SPEs) at 60°C are shown. It can be seen that the ionic conductivity of the polymer increases with the addition of PCEP, which is due to the decrease in the crystallinity of PEO. Among these electrolytes, CPE-2-PCEP has the highest ionic conductivity, reaching 4.2×10 -4 S / cm, is SPE (1.5×10 -4 S / cm).

[0078] Ionic conductivity does not guarantee effective Li + Transmission, at the same time, Li + The transfer number is crucial to the performance of the electrolyte. Li+The Bruce-Vincent method was used to determine the polarization of symmetric Li||Li cells with different polymer electrolytes at 60°C. For the symmetric lithium button cells, two lithium metal electrodes with a diameter of 12.7 mm were assembled with a solid polymer electrolyte (SPE or CPE-x-PCEP) film in between and cycled at 60°C using a LAND-CT2001A battery tester.

[0079] Transfer number: measured by chronoamperometry at a constant step potential of 10 mV using an electrochemical workstation ( Figure 5 Each electrolyte was sandwiched between two lithium metal electrodes in a button cell, and the cells were subjected to impedance spectroscopy at frequencies ranging from 1 MHz to 10 MHz before and after DC polarization. The lithium ion transfer number (t Li+ ) is calculated by formula (2):

[0080]

[0081] Among them I 0 and I s are the initial current value and the steady-state current value, ΔV is the potential applied in the chronoamperometry, and R 0 and R s are the interfacial resistance of DTP-SPE membrane before and after DC polarization obtained by EIS analysis. Li+ is 0.70, much higher than 0.29, 0.55 and 0.59 of SPE, CPE-1-PCEP and CPE-3-PCEP ( Figure 6 ).

[0082] Lithium ion diffusion path: Based on density functional theory (DFT) calculations, the lithium ion (Li + ) binding energy. All calculations were performed using the ORCA (version 6.0) program, with conformational optimization performed at the B3LYP-D3 and def2-TZVP basis set levels, and energy calculations performed at the def2-TZVPP basis set with higher accuracy. The binding energy calculation formula is as follows (3):

[0083] E bind =E (A-Li) -E A -E Li (3)

[0084] E (A-Li) 、E (A) 、E (Li) Respectively represent and Li + The energy of the combined macromolecules, the energy of the individual macromolecules, and Li +The energy of Li in the PEO matrix is ​​calculated. + The migration barrier is about 0.9 eV ( Figure 7 a) In addition, the migration barrier of lithium ions along the crown ether coordinated with lithium ions in the PCEP molecule was calculated. Figure 7 As shown in (b), the lithium ion migration barrier of PCEP coordinated with two lithium atoms (about 0.3 eV) is significantly lower than that of PEO (about 0.9 eV), indicating that the crown ether group can coordinate with lithium ions and provide efficient Li + Diffusion channels. DFT was used to calculate the diffusion paths of piperidine and crown ether groups in PCEP with TFSI. - The binding energy between Figure 7 c). Piperidine-TFSI - The binding energy (-1.22 eV) is significantly higher than that of crown ether-TFSI - The binding energy of the piperidine group is -0.71 eV, indicating that the piperidine group is important in fixing TFSI. - plays a leading role in improving t Li+ In summary, the functionalized PCEP molecules containing piperidine and crown ether groups enhance the Li+ / LiTFSI system through the synergistic effects of “cation-assisted” and “anion-immobilized”. + Conduction Figure 7 d). Specifically, the crown ether group is Li + exhibits a strong coordination tendency and provides efficient Li + The piperidine group of the piperidine cation hinders the free bis(trifluoromethanesulfonyl)imide anion (TFSI) through electrostatic interaction. - ) movement, thus increasing the lithium ion migration number. The present invention achieves a high lithium ion migration number (t Li+ ), and has an ionic conductivity comparable to existing polyethylene oxide (PEO)-based polymers, which is a significant advantage.

[0085] The above-mentioned lithium symmetric battery (assembled as described above) was assembled and the assembled battery was charged at a current density of 0.2 mA cm -2 , and the cycling performance tests were carried out at 60 °C. To investigate the enhanced stability of lithium symmetric batteries using CPE-2-PCEP, the -2 Scanning electron microscope (SEM) images of the lithium metal anode were obtained after 20 cycles of lithium plating and stripping at a current density of 1.5 Å. Figure 8a and 8b show that lithium dendrites appeared on the lithium metal surface paired with SPE, while no lithium dendrites were observed when CPE-2-PCEP was used, indicating that the use of CPE-2-PCEP can effectively inhibit dendrite formation and thus improve the life of lithium / lithium symmetric batteries. Finite element method (FEM) simulation was used to study the inhibitory effect of CPE-2-PCEP on lithium dendrite growth. The simulation results show that during the lithium deposition process, CPE-2-PCEP allows both lithium ions and anions to maintain extremely small concentration gradients. In the absence of interference from free anions, lithium ions can quickly and uniformly penetrate the polymer electrolyte membrane, thereby achieving uniform deposition on the lithium metal surface. This uniformity avoids the formation of large electric fields and is conducive to dendrite-free lithium deposition. In contrast, in solid polymer electrolytes (SPEs), lithium ion migration is hindered due to the reverse movement of anions and lithium ions, resulting in a higher lithium ion concentration gradient ( Figure 8 c). Anion consumption near the lithium metal anode generates space charge, which in turn forms a large electric field ( Figure 8 d). This electric field will induce uneven lithium deposition and promote the growth of lithium dendrites. Therefore, the expansion of lithium dendrites will produce new preferential deposition sites, eventually leading to battery short circuit.

[0086] Application Examples

[0087] CPE-2-PCEP and SPE were applied to Li-S button cells. The specific battery preparation process is as follows:

[0088] (1) Positive electrode material (Ketjen black / sulfur (C / S) composite material): Ketjen black and sulfur powder were mixed in a mass ratio of 2:8. The mixture was sealed in an autoclave under an argon atmosphere and heated at 155°C for 12 h to prepare a C / S positive electrode. C / S was mixed with carbon black, polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a mass ratio of 70:10:11:9 using a doctor blade coating technique to obtain a slurry, which was then coated on a carbon-coated aluminum foil substrate to prepare an electrode. After drying overnight at 50°C under vacuum conditions, the electrode was cut into discs with a diameter of 12.7 mm. The surface loading of the C / S electrode was 1.0 mg cm -2 .

[0089] (2) In an argon-filled glove box (UNIlab plus, M.BRAUN, oxygen content p (O 2 )<0.01ppm, water content p(H 2 O) <0.01ppm), a CR2032 button cell was assembled with lithium foil as the negative electrode and a solid polymer electrolyte (SPE or CPE-2-PCEP) with a diameter of 18 mm as the separator and electrolyte.

[0090] Before the electrochemical tests, all button cells were aged at an open circuit potential of 60 °C for 12.0 h to ensure good interfacial contact. The specific capacity was calculated based on the mass of sulfur (S). The rate performance of the lithium-sulfur button cells of CPE-2-PCEP and SPE is shown in Fig. 9 a, at current densities of 0.1C, 0.2C and 0.5C (1C = 1675 mAh g -1 ), the specific capacities of the button cells containing CPE-2-PCEP were 1034.0, 841.3, and 692.7 mAh g -1 When the current density returned to 0.1C, the CPE-2-PCEP-based button cell maintained 865.8 mAh g -1 The SPE button cell has a high capacity and excellent rate performance at current densities of 0.1C, 0.2C and 0.5C, with a discharge capacity of 800.3, 393.9 and 136.0 mAh g -1 When the current density returned to 0.1C, the discharge capacity remained at 246.0 mAh g -1 The initial discharge capacity of the lithium-sulfur button cell using CPE-2-PCEP is 968.0 mAh g -1 , which is significantly higher than the 831.7 mAh g of button cells using SPE. -1 The initial Coulombic efficiency of the CPE-2-PCEP button cell was close to 98%, and remained stable throughout the entire cycle. In contrast, the SPE-based button cell showed irregular fluctuations in Coulombic efficiency due to the lithium polysulfide (LiPSs) shuttle effect. After 80 cycles, the capacity retention rate of the CPE-2-PCEP button cell was 80.7% (671.8 mAh g -1 ), far exceeding the 30.6% capacity retention rate of the SPE-based button cell ( Fig. 9 b). The enhanced cycling performance of the lithium-sulfur button cell using CPE-2-PCEP indicates that the introduction of PCEP into PEO / LiTFSI can effectively prevent the shuttling of dissolved lithium polysulfides. To further understand the mechanism, density functional theory (DFT) calculations were performed to compare the adsorption behaviors of PCEP and PEO toward various lithium polysulfide species. Fig.10 a shows a representative lithium polysulfide (Li 2 The optimized adsorption model of Sx, x = 1, 2, 4, 6 and 8). The corresponding binding energy is as follows Fig.10 As shown in b, the crown ether group has the lowest binding energy with all LiPS species, which is due to their +The above results show that compared with PEO, piperidinium cationic groups exhibit lower binding energy with all lithium polysulfide species, indicating that they can electrostatically adsorb lithium polysulfide anions and reduce lithium polysulfide shuttling. This interaction helps to stabilize the cycling performance of lithium-sulfur batteries.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a cationic polymer electrolyte, characterized in that: Here are the steps: (1) dibenzo-18-crown-6, 1-methyl-4-piperidone, an acid catalyst and solvent A are mixed, stirred at room temperature, and then added to a precipitant B for precipitation to obtain a polymer precursor p-PCEP; (2) adding the polymer precursor p-PCEP and methyl iodide to a polar aprotic solvent, reacting at room temperature, adding to a precipitant C for precipitation, washing and drying to obtain quaternized p-PCEP; (3) dissolving the quaternized p-PCEP in DMF to prepare a solution and casting it into a membrane; immersing the membrane in a lithium bis(trifluoromethanesulfonyl)imide solution to obtain PCEP; (4) Polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide and PCEP were dissolved in DMF and a cationic polymer electrolyte was prepared by a solvent casting method.

2. The method for preparing a cationic polymer electrolyte according to claim 1, characterized in that: In the step (1), the molar ratio of dibenzo-18-crown-6 to 1-methyl-4-piperidone is 1: (1-2); 1.1-2.2 mol of dibenzo-18-crown-6 is added per liter of acid catalyst; and the stirring time at room temperature is 18-24 h.

3. The method for preparing a cationic polymer electrolyte according to claim 2, characterized in that: In the step (1), the acid catalyst is trifluoromethanesulfonic acid and trifluoroacetic acid; the solvent A is dichloromethane or dimethyl sulfoxide; and the precipitant B is ethanol or methanol.

4. The method for preparing a cationic polymer electrolyte according to claim 3, characterized in that: In the step (2), 1-2 g of polymer precursor p-PCEP is added to each mL of methyl iodide; the volume ratio of methyl iodide to polar aprotic solvent is 1:(10-20).

5. The method for preparing a cationic polymer electrolyte according to claim 4, characterized in that: In the step (2), the polar aprotic solvent is dimethyl sulfoxide or dimethylformamide; the precipitant C is diethyl ether or dimethyl ether; and the reaction time at room temperature is 24-48 hours.

6. The method for preparing a cationic polymer electrolyte according to claim 5, characterized in that: In the step (3), the content of quaternized p-PCEP in the solution is 10-20 wt %; the immersion temperature is room temperature, and the immersion time is 48-96 h.

7. The method for preparing a cationic polymer electrolyte according to claim 6, characterized in that: In the step (4), the mass ratio of polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide and PCEP is 4:3:(1-4).

8. A cationic polymer electrolyte prepared by the preparation method according to any one of claims 1 to 7.

9. The cationic polymer electrolyte according to claim 8, characterized in that The cationic polymer electrolyte has an ionic conductivity of 4.2×10 -4 S / cm; Li + The transfer number is 0.

7.

10. Use of the cationic polymer electrolyte according to claim 8 in an all-solid-state lithium metal battery.

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