Preparation method and application of low-temperature-resistant gel polymer electrolyte

Abstract

The application relates to a preparation method and application of a low-temperature-resistant gel polymer electrolyte, and belongs to the technical field of polymer electrolytes.The application solves the technical problem of providing a preparation method of a low-temperature-resistant gel polymer electrolyte suitable for a lithium metal battery.The method uniformly mixes an ether electrolyte, allyl potassium trifluoroborate, a crosslinking agent such as pentaerythritol tetraacrylate and fluorinated ethylene carbonate to obtain a precursor solution;uniformly mixes azobisisobutyronitrile and the precursor solution to obtain a reaction solution;and then performs a warming reaction to obtain a low-temperature-resistant gel polymer electrolyte.The application significantly improves the frost resistance of the electrolyte by introducing an anion conductor, can realize good low-temperature resistance, and improves the low-temperature cycle performance.The electrolyte has high conductivity, overcomes the defect of low ion conductivity of a conventional polymer electrolyte at low temperature;has high lithium ion transference number, effectively solves the defect of low transference number of a polymer electrolyte Li + +.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying low-temperature resistant gel polymer electrolytes, belonging to the field of polymer electrolyte technology. Background Technology

[0002] With the deepening of the global energy structure transformation, electric vehicles, aerospace, and extreme environment energy storage technologies have experienced rapid development, placing increasingly stringent demands on the performance of high-energy-density energy storage devices under harsh conditions such as low temperatures. Lithium metal batteries, due to their extremely high theoretical energy density, are considered an ideal choice for next-generation energy storage technology. However, lithium metal batteries constructed with traditional liquid electrolytes face severe challenges at low temperatures: the bulk viscosity of the electrolyte increases sharply, leading to a sharp drop in ionic conductivity; simultaneously, the ion desolvation process at the electrode-electrolyte interface is slow, and the charge transfer impedance surges, causing severe kinetic lag. More problematic is that the unstable interfacial processes at low temperatures can easily induce uncontrolled growth of lithium dendrites, which not only accelerates capacity decay but also poses serious safety hazards.

[0003] To overcome the aforementioned problems, gel polymer electrolytes have shown great potential due to their ability to perfectly combine the excellent interfacial wettability of liquid electrolytes with the high safety of solid electrolytes. By anchoring the liquid electrolyte within a polymer backbone, gel polymer electrolytes theoretically combine the excellent interfacial wettability of liquid electrolytes with the high safety and leakage resistance of solid electrolytes, making them a potential solution for achieving high-safety, high-energy-density lithium metal batteries. However, the performance of conventional gel polymer electrolytes (such as systems based on polyethylene oxide (PEO), polyvinylidene fluoride (PVDF)-HFP, etc.) at low temperatures remains unsatisfactory. The core bottleneck lies in the fact that as the temperature decreases, the chain mobility of the polymer matrix significantly declines, and the molecular chains tend to "freeze," making lithium-ion transport extremely difficult, and the ionic conductivity cannot meet the requirements of low-temperature, high-current operation. For example, polyvinylidene fluoride electrolytes, widely used in existing technologies, exhibit reliable mechanical and electrochemical properties at room temperature, but their energy density, power density, and cycle life all decrease significantly at sub-zero temperatures, greatly limiting their applicability in cold climates.

[0004] In existing technologies, researchers have proposed various strategies to improve the low-temperature performance of electrolytes. On the one hand, by designing high-concentration electrolytes (HCE) or locally high-concentration electrolytes (LHCE), special solvation structures are used to lower the desolvation energy barrier of lithium ions and improve the bulk stability of the electrolyte. Recent advances have further demonstrated that introducing multiple lithium salts to form high-entropy electrolytes can alter the solvation structure and customize interface formation. However, these in-situ formed SEI layers typically have uncontrollable composition and poor mechanical properties, resulting in short lifespans for lithium metal batteries (LMBs) at sub-zero temperatures. On the other hand, while methods such as physical blending plasticizers and ceramic fillers can improve ionic conductivity to some extent, they often struggle to simultaneously address multiple key performance indicators, particularly failing to systematically solve the synergistic optimization challenge of "interface compatibility-efficient ion transport-uniform lithium metal deposition."

[0005] Specifically, existing technologies still face two major challenges: first, it is difficult to achieve both high Li-level efficiency and efficient ion transport. + High transport number (>0.5) and high ionic conductivity (>1.5 mS / cm). -1 Secondly, low temperatures exacerbate electrode polarization, causing lithium ions to tend to deposit unevenly on the electrode surface, forming lithium dendrites. The unevenness of ion transport and deposition is amplified at low temperatures, further promoting the growth of lithium dendrites, which poses a serious threat to the safety and lifespan of the battery.

[0006] Chinese invention patent CN113258145A discloses an elastic, low-temperature resistant solid electrolyte and its preparation method. This method utilizes a combination of zwitterions, comonomers, ionic liquids, and zinc salts to improve ionic conductivity and low-temperature performance. However, this method relies on ultraviolet light curing, making the preparation process relatively complex. Furthermore, while the resulting polymer network structure is suitable for flexible zinc-ion batteries, its application in lithium metal batteries remains to be discussed. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a method for preparing a low-temperature resistant gel polymer electrolyte suitable for lithium metal batteries.

[0008] The method for preparing the low-temperature resistant gel polymer electrolyte of the present invention includes the following steps:

[0009] A. Mix the ether electrolyte with potassium allyl trifluoroborate, crosslinking agent and fluoroethylene carbonate to obtain a precursor solution;

[0010] B. Mix azobisisobutyronitrile with the precursor solution to obtain a reaction solution;

[0011] C. Heat the reaction solution described in step B to obtain a low-temperature resistant gel polymer electrolyte;

[0012] The ether electrolyte comprises a lithium salt and an ether solvent; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, or lithium bis(fluorosulfonyl)imide.

[0013] The crosslinking agent is pentaerythritol tetraacrylate, triethylene glycol dimethacrylate, or polyethylene glycol diacrylate.

[0014] This invention discloses a method for preparing a low-temperature resistant gel polymer electrolyte. The method involves a free radical copolymerization reaction initiated by azobisisobutyronitrile (AIBN) using pentaerythritol tetraacrylate as a crosslinking agent, and initiating a reaction containing potassium allyl trifluoroborate. This transforms a liquid electrolyte solution into a gel with a three-dimensional network structure. By covalently anchoring large-volume anions to the backbone, selective promotion of lithium-ion transport (high lithium-ion transference number) is achieved, increasing conductivity. Simultaneously, the addition of ether solvents and fluoroethylene carbonate in the ether-based electrolyte imparts excellent low-temperature resistance to the entire electrolyte.

[0015] In one embodiment of the present invention, the ether electrolyte comprises a lithium salt and an ether solvent. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, or lithium bis(fluorosulfonyl)imide.

[0016] In one embodiment of the invention, the concentration of lithium salt in the ether electrolyte is 0.5–2 M. In a specific embodiment, the concentration of lithium salt in the ether electrolyte is 1 M.

[0017] In one embodiment of the invention, the ether solvent is at least one selected from 1,3-dioxolane and 1,2-dimethoxyethane. In a specific embodiment, the ether solvent is 1,3-dioxolane and 1,2-dimethoxyethane. In a more specific embodiment, the volume ratio of 1,3-dioxolane to 1,2-dimethoxyethane is 1:1.

[0018] In one embodiment of the present invention, in step A, potassium allyl trifluoroborate monomer accounts for 0.8 to 1.2 wt% of the precursor solution; fluoroethylene carbonate accounts for 4 to 6 wt% of the precursor solution; and the molar ratio of potassium allyl trifluoroborate to crosslinking agent is 1 to 1.5:1; in step B, azobisisobutyronitrile accounts for 0.5 to 2 wt% of the precursor solution.

[0019] In a more specific embodiment, in step A, potassium allyl trifluoroborate monomer accounts for 1 to 1.09 wt% of the precursor solution; fluoroethylene carbonate accounts for 5 wt% of the precursor solution; and the molar ratio of potassium allyl trifluoroborate to crosslinking agent is 1.19:1; in step B, azobisisobutyronitrile accounts for 1 wt% of the precursor solution.

[0020] In one embodiment of the present invention, in step C, the heating reaction is carried out at a temperature above 60°C for at least 5 hours; preferably, the heating reaction is carried out at a temperature of 60°C to 70°C.

[0021] The second technical problem solved by the present invention is to provide a low-temperature resistant gel polymer electrolyte.

[0022] The low-temperature resistant gel polymer electrolyte of the present invention is prepared by the above-described method for preparing low-temperature resistant gel polymer electrolyte.

[0023] In one embodiment of the present invention, the low-temperature resistant gel polymer electrolyte has a conductivity of 1.56 mS / cm at 25°C. −1 above.

[0024] The present invention also provides the application of the low-temperature resistant gel polymer electrolyte described herein in lithium metal batteries.

[0025] The low-temperature resistant gel polymer electrolyte of this invention can be used in lithium metal batteries.

[0026] The present invention also provides a lithium metal battery.

[0027] The lithium metal battery of the present invention includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the low-temperature resistant gel polymer electrolyte of the present invention.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The low-temperature resistant gel polymer electrolyte of the present invention significantly improves the antifreeze properties of the electrolyte by introducing anionic conductors, thereby achieving good low-temperature tolerance and improving low-temperature cycling performance.

[0030] 2. The low-temperature resistant gel polymer electrolyte of this invention has high conductivity, with a conductivity of 0.52 mS / cm at -20℃. −1 The above overcomes the drawback of low ionic conductivity at low temperatures in conventional polymer electrolytes.

[0031] 3. The low-temperature resistant gel polymer electrolyte of this invention has a high lithium-ion transference number. The calculated lithium-ion transference number of this low-temperature resistant gel polymer electrolyte is 0.69, effectively solving the problem of lithium-ion transference in polymer electrolytes. + The drawback of low migration count. Attached Figure Description

[0032] Figure 1 These are photographs of the low-temperature resistant gel polymer electrolyte prepared in Example 1 of the present invention before and after the polymerization reaction; wherein, the left side is a photograph of the mixed solution before the polymerization reaction, and the right side is a photograph of the low-temperature resistant gel polymer electrolyte after the polymerization reaction.

[0033] Figure 2 This is a comparison of the Fourier transform infrared (FTIR) spectra of the low-temperature resistant gel polymer electrolyte prepared in Example 1 of this invention with those of PAB, PETEA, and precursor solutions.

[0034] Figure 3 This is a Zeta potential diagram of the low-temperature resistant gel polymer electrolyte and ether electrolyte prepared in Example 1 of the present invention.

[0035] Figure 4 The images show the Raman spectra of the low-temperature resistant gel polymer electrolyte and the ether electrolyte prepared in Example 1 of this invention at room temperature; where a is the Raman spectrum of the ether electrolyte and b is the Raman spectrum of the low-temperature resistant gel polymer electrolyte.

[0036] Figure 5 This is a comparison of the ionic conductivity of the low-temperature resistant gel polymer electrolyte and the ether electrolyte prepared in Example 1 of the present invention at 25°C and -20°C.

[0037] Figure 6 The illustrations show the chronoamperometry curves and AC impedance spectra (before and after polarization) of the low-temperature resistant gel polymer electrolyte and ether electrolyte prepared in Example 1 of this invention at a polarization voltage of 10 mV for a Li||Li symmetric cell; wherein, a is the chronoamperometry curve and AC impedance spectra (before and after polarization) of the ether electrolyte; b is the chronoamperometry curve and AC impedance spectra (before and after polarization) of the low-temperature resistant gel polymer electrolyte; c is the chronoamperometry curve and AC impedance spectra (before and after polarization) of the ether electrolyte at -20℃; and d is the chronoamperometry curve and AC impedance spectra (before and after polarization) of the low-temperature resistant gel polymer electrolyte at -20℃.

[0038] Figure 7 This is a comparison diagram of the impedance of the low-temperature resistant gel polymer electrolyte and the ether electrolyte prepared in Example 1 of the present invention.

[0039] Figure 8 This is a comparison chart of the cycling performance of the low-temperature resistant gel polymer electrolyte and the ether electrolyte of the Li||NCM811 full cell prepared in Example 1 of the present invention at 25°C.

[0040] Figure 9 This is a comparison chart of the cycling performance of the low-temperature resistant gel polymer electrolyte and the ether electrolyte in the Li||LFP battery prepared in Example 1 of the present invention at 25°C.

[0041] Figure 10 This is a comparison of the cycling performance of the low-temperature resistant gel polymer electrolyte and the ether electrolyte in the Li||LFP battery prepared in Example 1 of this invention at -20℃. Detailed Implementation

[0042] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0043] Example 1

[0044] The raw materials used in this embodiment are:

[0045] Potassium allyl trifluoroborate (PAB); Pentaerythritol tetraacrylate (PETEA); Fluorinated ethylene carbonate (FEC); Azobisisobutyronitrile (AIBN); Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); 1,2-Dimethoxyethane (DME); 1,3-Dioxolane (DOL).

[0046] The low-temperature resistant gel polymer electrolyte was prepared according to the following steps:

[0047] Step 1: Add 1 wt% (30 mg) of PAB monomer and 2 wt% (60 mg) of PETEA crosslinking agent (PAB:PETEA molar ratio of 1.19:1) to 2.73 g of ether electrolyte, then add FEC (150 mg) (precursor mass = 30 mg + 60 mg + 2730 mg + 150 mg = 2970 mg, PAB monomer percentage of precursor mass is 30 / 2970 = 1.01 wt%), stir well to obtain precursor solution; wherein, the ether electrolyte is obtained by dissolving LiTFSI in DME / DOL solvent, and the concentration of LiTFSI in the ether electrolyte is 1 M;

[0048] Step 2: Add 1 wt% of AIBN thermal polymerization initiator to the precursor solution, stir until homogeneous, and obtain the reaction solution;

[0049] Step 3: Heat the reaction solution at 70°C for 5 hours to obtain a low-temperature resistant gel polymer electrolyte.

[0050] Performance Characterization

[0051] 1) Appearance

[0052] Photos of the low-temperature resistant gel polymer electrolyte prepared in Example 1 of this invention before and after the polymerization reaction are shown below. Figure 1 The image on the left shows the mixed solution before polymerization, while the image on the right shows the low-temperature resistant gel polymer electrolyte after polymerization.

[0053] Depend on Figure 1As shown, the low-temperature resistant gel polymer electrolyte is prepared by adding PAB and PETEA to an ether electrolyte, then adding FEC, stirring evenly, and finally adding AIBN and polymerizing at 70℃.

[0054] 2) Infrared characterization

[0055] The low-temperature resistant gel polymer electrolyte prepared in Example 1 was characterized by Fourier transform infrared spectroscopy (FTIR), and the results are shown in the figure. Figure 2 .

[0056] Depend on Figure 2 The polymerization of the precursor solution was verified by Fourier transform infrared spectroscopy in the 1600-1650 cm⁻¹ range. −1 Within the range, C=C bending vibrations and tensile vibrations were observed in PAB and PETEA monomers, respectively. No characteristic C=C peaks were observed in the low-temperature resistant gel polymer electrolyte after polymerization, indicating that the low-temperature resistant gel polymer electrolyte was successfully crosslinked and cured.

[0057] 3) Zeta potential

[0058] The low-temperature resistant gel polymer electrolyte prepared in Example 1 was characterized using a nanoparticle size analyzer and a zeta potential analyzer (DLS). The results are shown in [Figure 1]. Figure 3 .

[0059] Depend on Figure 3 The Zeta potentials of the low-temperature resistant gel polymer electrolyte were observed to be -30.65 mV, while those of the ether electrolyte were -16.24 mV. The low-temperature resistant gel polymer electrolyte exhibited a greater negative potential, resulting in a significant repulsive effect on anions, thereby improving the Li... + The number of migrations.

[0060] 4) Raman spectroscopy

[0061] The low-temperature resistant gel polymer electrolyte prepared in Example 1 was characterized using Raman spectroscopy, and the results are shown in the figure. Figure 4 .

[0062] Depend on Figure 4 Raman spectroscopy was used to study TFSI − Coordination states in low-temperature resistant gel polymer electrolytes and ether electrolytes. Quantitative analysis revealed that the low-temperature resistant gel polymer electrolyte contained a significantly higher proportion of aggregates compared to the ether electrolyte. The high content of aggregates indicates that the introduction of polymers can effectively stabilize these aggregates, thereby reducing the coordination of Li+ with solvent molecules. This increased aggregation is associated with the enhanced formation of inorganic-rich SEI / CEI layers, contributing to improved interfacial stability.

[0063] 5) Ionic conductivity

[0064] The stainless steel symmetrical battery assembled with the low-temperature resistant gel polymer electrolyte prepared in Example 1 was tested on the Chenhua tester with an amplitude voltage of 10 mV and a frequency range of 5 MHz to 1 Hz. The results are shown in [Figure 1]. Figure 5 .

[0065] Depend on Figure 5 The comparison of ionic conductivity shows that (a) at 25℃, the low-temperature resistant gel polymer electrolyte achieved 1.56 mS / cm. −1 Its high ionic conductivity is close to that of ether electrolytes (1.79 mS / cm). −1 (a) This indicates that the low-temperature resistant gel polymer electrolyte has excellent ionic conductivity; (b) at -20℃, the low-temperature resistant gel polymer electrolyte achieved a conductivity of 0.52 mS / cm. −1 Its ionic conductivity is higher than that of ether electrolytes (0.33 mS / cm). −1 This indicates that the low-temperature resistant gel polymer electrolyte exhibits excellent ionic conductivity at low temperatures.

[0066] 6) Electrical performance

[0067] Preparation of Li||Li symmetric battery: The Li||Li symmetric battery is assembled in the following order: negative electrode shell - small lithium sheet - electrolyte - PP separator - electrolyte - small lithium sheet - gasket - spring sheet - positive electrode shell.

[0068] Determination of chronoamperometry curves: The Li||Li symmetric cells assembled with the low-temperature resistant gel polymer electrolyte prepared in Example 1 were tested using the CA test program on Eclab software with the program parameters set.

[0069] AC impedance spectroscopy determination: The Li||Li symmetric cell assembled with the low-temperature resistant gel polymer electrolyte prepared in Example 1 was tested using the EIS test program on Eclab software with the program parameters set.

[0070] The results are shown in Figure 6 .

[0071] Depend on Figure 6 The chronoampere curves and AC impedance spectra before and after polarization of the Li||Li symmetric cell (inset) show that (b) the lithium-ion transfer number (t) of the low-temperature resistant gel polymer electrolyte Li + =0.69) is significantly higher than (a) ether electrolyte (t Li +=0.31) higher. (d) At -20℃, the lithium-ion transfer number of the low-temperature resistant gel polymer electrolyte (tLi+=0.65) is significantly higher than that of (c) the ether electrolyte (tLi+=0.23). This significant enhancement is attributed to the anion-rich solvation structure in the low-temperature resistant gel polymer electrolyte regulating the rapid Li+ transfer. + Conduction, multiple Li + The presence of ligands accelerates the Li + Its low-temperature tolerance is demonstrated by its migration and the fact that it can maintain a high ion transference number even at low temperatures.

[0072] Measurement of AC impedance spectroscopy at different temperatures: The Li||Li symmetric cells assembled with the low-temperature resistant gel polymer electrolyte prepared in Example 1 were tested at different temperatures using the EIS test program on Eclab software with the program parameters set.

[0073] The results are shown in Figure 7 .

[0074] Depend on Figure 7 The impedance diagrams show that the impedance of both electrolytes increases as the temperature decreases. However, the low-temperature resistant gel polymer electrolyte exhibits a lower interfacial impedance than the ether electrolyte at all temperatures, indicating that the low-temperature resistant gel polymer electrolyte has better interfacial compatibility and low-temperature resistance.

[0075] 7) Cyclic performance

[0076] Preparation of Li||LFP Battery: 0.2g of polyvinylidene fluoride (PVDF) was first added to 6ml of N-methyl-2-pyrrolidone (NMP), and stirred evenly. Then, 0.2g of conductive carbon black was added, and the mixture was stirred for 12 hours. Then, 1.6g of LiFePO4 powder was added, and the mixture was stirred for another 12 hours to obtain a slurry (PVDF:Super P:LiFePO4 mass ratio of 1:1:8). The slurry was then coated onto aluminum / carbon foil and vacuum dried at 120℃ for 12 hours. Finally, the electrode sheet was cut into 12mm diameter disks to obtain the LiFePO4 positive electrode sheet. The battery was then assembled in the following order: negative electrode shell - large lithium sheet - electrolyte - PP separator - electrolyte - LiFePO4 positive electrode sheet - gasket - spring sheet - positive electrode shell to obtain the Li||LFP battery.

[0077] Preparation of Li||NCM811 Battery: 0.2g of polyvinylidene fluoride (PVDF) was first added to 6ml of N-methyl-2-pyrrolidone (NMP), and stirred evenly. Then, 0.2g of conductive carbon black was added, and the mixture was stirred for 12 hours. Then, 1.6g of NCM811 powder was added, and the mixture was stirred for another 12 hours to obtain a slurry (PVDF:Super P:NCM811 mass ratio of 1:1:8). The slurry was then coated onto aluminum / carbon foil and vacuum dried at 120℃ for 12 hours. Finally, the electrode sheets were cut into 12mm diameter disks to obtain the NCM811 positive electrode sheet. The battery was then assembled in the following order: negative electrode shell - large lithium sheet - electrolyte - PP separator - electrolyte - NCM811 positive electrode sheet - gasket - spring sheet - positive electrode shell to obtain the Li||NCM811 battery.

[0078] Long-cycle testing: The assembled Li||LFP full cells and Li||NCM811 full cells were subjected to a 25℃ long-cycle test on the Xinwei tester, and the Li||LFP full cells were subjected to a -20℃ long-cycle test in a low-temperature chamber.

[0079] The results are shown in Figures 8-10 .in, Figure 8 This is a comparison chart of the cycling performance of Li||NCM811 batteries with low-temperature resistant gel polymer electrolyte and ether electrolyte prepared in Example 1 of the present invention at 25°C. Figure 9 This is a comparison chart of the cycling performance of the low-temperature resistant gel polymer electrolyte and the ether electrolyte in the Li||LFP battery prepared in Example 1 of the present invention at 25°C. Figure 10 This is a comparison of the cycling performance of the low-temperature resistant gel polymer electrolyte and the ether electrolyte in the Li||LFP battery prepared in Example 1 of this invention at -20℃.

[0080] Depend on Figure 8 It can be seen that, after long-cycle testing at room temperature (25°C), the Li||NCM811 battery with low-temperature resistant gel polymer electrolyte can stably cycle for more than 300 cycles with a capacity retention rate of 82.99%. In contrast, the cycling performance of the ether electrolyte-based Li|NCM811 battery deteriorates rapidly, with a capacity retention rate of only 73.50% after 200 cycles.

[0081] Depend on Figure 9 It can be seen that, after long-cycle testing at room temperature (25°C), the Li||LFP battery with low-temperature resistant gel polymer electrolyte can stably cycle for more than 1000 cycles with a capacity retention rate of 80.86%. In contrast, the Li|LFP battery with ether electrolyte has poor cycle performance, with a capacity retention rate of only 72.04% after 900 cycles.

[0082] Depend on Figure 10The results show that, after long-cycle testing at -20°C, the Li||LFP battery with the low-temperature resistant gel polymer electrolyte can stably cycle for over 600 cycles with a capacity retention of 83.45%. Conversely, the Li||LFP battery with the ether-based electrolyte exhibits poorer cycle performance, with a capacity retention of only 74.62% after 600 cycles. This indicates that improving the bulk structure of the low-temperature resistant gel polymer electrolyte is beneficial for enhancing low-temperature tolerance.

[0083] It is evident that the low-temperature resistant gel polymer electrolyte of this invention exhibits rapid Li-ionization in practical lithium metal batteries. + Significant effects on conductivity, high ionic conductivity, high lithium-ion transport number, and low-temperature tolerance.

[0084] Example 2

[0085] The low-temperature resistant gel polymer electrolyte was prepared according to the steps of Example 1, with the only difference being that "2.73 g of ether electrolyte" in step 1 was adjusted to "2.76 g of ether electrolyte" (precursor mass = 30 mg + 60 mg + 2760 mg + 150 mg = 3000 mg, and the percentage of PAB monomer in the precursor mass is 30 / 3000 = 1 wt%); the other steps remained unchanged.

[0086] Example 3

[0087] The low-temperature resistant gel polymer electrolyte was prepared according to the steps of Example 1, except that "2.73 g of ether electrolyte" in step 1 was changed to "2.5 g of ether electrolyte" (precursor mass = 30 mg + 60 mg + 2500 mg + 150 mg = 2740 mg, and the percentage of PAB monomer in the precursor mass is 30 / 2740 = 1.09 wt%); the other steps remained unchanged.

[0088] Example 4

[0089] The low-temperature resistant gel polymer electrolyte was prepared according to the steps of Example 1, except that the step of "heating the reaction solution at 70°C for 5 h" in step 3 was changed to "heating the reaction solution at 65°C for 5 h"; the other steps remained unchanged.

[0090] Example 5

[0091] The low-temperature resistant gel polymer electrolyte was prepared according to the steps of Example 1, except that the step of "heating the reaction solution at 70°C for 5 h" in step 3 was changed to "heating the reaction solution at 75°C for 5 h"; the other steps remained unchanged.

[0092] Determination of low-temperature Li in the gel polymer electrolytes of Examples 2-5 +The ion transport number was determined using the method described in Example 1, and the results are shown in Table 1.

[0093] Table 1

[0094] name Example 2 Example 3 Example 4 Example 5 Ether electrolytes <![CDATA[Ionic conductivity at -20 °C, mS cm −1 > 0.50 0.53 0.52 0.52 0.33

[0095] It is evident that the low-temperature resistant gel polymer electrolyte of this invention can improve the electrolyte's antifreeze properties, achieve good low-temperature tolerance, and improve low-temperature cycling performance.

Claims

1. A method for preparing a cryogenically resistant gel polymer electrolyte, characterized by, The method comprises the following steps: A. mixing ether electrolyte, allyl potassium trifluoroborate, crosslinking agent and fluorinated ethylene carbonate to obtain a precursor solution; B. mixing azobisisobutyronitrile with the precursor solution to obtain a reaction solution; C. heating the reaction solution of step B to obtain a low-temperature-resistant gel polymer electrolyte; The ether electrolyte comprises lithium salt and ether solvent; the lithium salt is lithium bistrifluoromethanesulfonylimide, lithium hexafluorophosphate or lithium bisfluorosulfonylimide; The crosslinking agent is pentaerythritol tetraacrylate, triethylene glycol dimethacrylate or polyethylene glycol diacrylate.

2. The preparation method of the low-temperature-resistant gel polymer electrolyte according to claim 1, characterized in that: The concentration of lithium salt in the ether electrolyte is 0.5-2 M.

3. The preparation method of the low-temperature-resistant gel polymer electrolyte according to claim 2, characterized in that: The concentration of lithium salt in the ether electrolyte is 1 M.

4. The preparation method of the low-temperature-resistant gel polymer electrolyte according to claim 1, characterized in that: The ether solvent is 1,3-dioxolane and 1,2-dimethoxyethane with a volume ratio of 1:

1.

5. The preparation method of the low-temperature-resistant gel polymer electrolyte according to claim 1, characterized in that: In step A, the allyl potassium trifluoroborate monomer accounts for 0.8-1.2 wt% of the precursor solution; the fluorinated ethylene carbonate accounts for 4-6 wt% of the precursor solution; the molar ratio of allyl potassium trifluoroborate to crosslinking agent is 1-1.5:1; in step B, the azobisisobutyronitrile accounts for 0.5-2 wt% of the precursor solution; In step C, the heating reaction is carried out at 60°C or above for at least 5 h.

6. The preparation method of the low-temperature-resistant gel polymer electrolyte according to claim 5, characterized in that: In step A, the allyl potassium trifluoroborate monomer accounts for 1-1.09 wt% of the precursor solution; the fluorinated ethylene carbonate accounts for 5 wt% of the precursor solution; the molar ratio of allyl potassium trifluoroborate to crosslinking agent is 1.19:1; in step B, the azobisisobutyronitrile accounts for 1 wt% of the precursor solution; In step C, the heating reaction is carried out at 60-70°C.

7. The low-temperature-resistant gel polymer electrolyte prepared by the method of any one of claims 1-6.

8. The cryogenically resistant gel polymer electrolyte of claim 7, wherein: The low-temperature-resistant gel polymer electrolyte has an electrical conductivity of 0.52 mS cm at -20°C −1 The above.

9. The low-temperature-resistant gel polymer electrolyte of claim 7 for use in a lithium metal battery.

10. A lithium metal battery comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that: The electrolyte is the low-temperature-resistant gel polymer electrolyte of claim 7.

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