An in-situ polymerized crosslinked solid electrolyte and its preparation method

Abstract

This invention provides an in-situ polymerized crosslinked solid electrolyte and its preparation method, belonging to the field of solid electrolyte technology. This invention involves the in-situ polymerization and crosslinking of divinylperfluoroalkane with ester monomers. Utilizing the strong bond energy of the C-F bond, the oxidative decomposition resistance of the resulting in-situ polymer electrolyte is improved, thereby enhancing the electrochemical stability of the lithium-ion battery. Taking advantage of the extremely high chemical inertness of the perfluoroalkane segments, they preferentially accumulate at the interface during the contact between the in-situ polymer electrolyte and the lithium electrode, forming a robust and stable SEI film, improving ionic conductivity, and thus enhancing the capacity retention of the lithium-ion battery. Furthermore, the polymer formed from the divinylperfluoroalkane in the in-situ polymer electrolyte has an amorphous structure, which prevents the crystallization of the ester polymer, enhances the freedom of movement of the perfluoroalkane segments, provides a rapid migration path for lithium ions, further improving ionic conductivity, and thus enhancing the capacity retention of the resulting lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, and in particular to an in-situ polymerized crosslinked solid electrolyte and its preparation method. Background Technology

[0002] With the rapid iteration of new energy vehicles, portable electronic devices, and large-scale energy storage equipment, the market is placing increasingly higher demands on the energy density, safety performance, cycle life, and large-scale manufacturing efficiency of lithium batteries. As the current mainstream rechargeable battery system, lithium batteries consist of a positive electrode, a negative electrode, an electrolyte, and a separator. The electrolyte, acting as a "bridge" for ion transport, directly determines the battery's ionic conductivity, electrochemical stability, interfacial compatibility, and safety performance, making it a key material restricting the upgrade of lithium batteries towards higher energy density and higher safety.

[0003] Electrolytes include liquid electrolytes and solid electrolytes. In-situ solid-state polymeric electrolytes, a branch of solid electrolytes, are prepared by injecting polymeric monomers, lithium salts, and initiators into a membrane on the electrode surface, resulting in in-situ polymerization. This in-situ solid-state polymeric electrolyte achieves integrated contact between the electrode and the electrolyte, solving the leakage and explosion hazards of liquid electrolytes, and avoiding the direct contact between traditional solid electrolytes and electrodes, which leads to numerous microscopic gaps and pores at the interface, resulting in high contact impedance and low ionic conductivity in lithium-ion batteries.

[0004] However, the commonly used monomers in the preparation of in-situ solid polymeric electrolytes are carbonate and acrylate monomers. For example, the in-situ solid electrolyte membrane formed by polymerizing ethylene carbonate and polyethylene glycol dimethacrylate is prone to oxidative decomposition under a wide voltage window (especially above 4.2V), producing small molecule byproducts, consuming electrolyte and lithium salt, resulting in continuous decay of lithium-ion battery ionic conductivity, poor electrochemical stability, and low capacity retention. Furthermore, during the in-situ polymerization process, the wettability of these monomers at the electrode interface differs, easily forming a discontinuous electrolyte coating layer on the electrode surface, creating interfacial voids, leading to insufficient interfacial stability, and consequently, low capacity retention of lithium-ion batteries. After 160 cycles, the capacity retention is only 92%. Summary of the Invention

[0005] The purpose of this invention is to provide an in-situ polymerized crosslinked solid electrolyte and its preparation method. The in-situ polymerized crosslinked solid electrolyte provided by this invention has good interface stability with the lithium electrode and good resistance to oxidation and decomposition. The resulting lithium-ion battery has good electrochemical stability and high capacity retention.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing an in-situ polymerized crosslinked solid electrolyte, comprising: The polymer monomers were mixed with lithium salts and initiators and then subjected to in-situ polymerization and crosslinking on the surface of the lithium electrode to obtain an in-situ polymerized crosslinked solid electrolyte. The polymer monomers are ester monomers and divinyl perfluoroalkane; the ester monomers include ethylene carbonate monomers or acrylate monomers.

[0007] Preferably, the volume ratio of the ester monomer to the divinylperfluoroalkane is (4~9):1.

[0008] Preferably, the carbonate monomers include ethylene carbonate; the acrylate monomers include methyl methacrylate or butyl acrylate; and the divinyl perfluoroalkane includes 1,6-divinyl perfluorohexane or 1,4-divinyl perfluorobutane.

[0009] Preferably, the concentration of lithium salt in the in-situ polymerization and crosslinking system is 1~2 mol / L.

[0010] Preferably, the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, or lithium difluorooxalate borate.

[0011] Preferably, the mass of the initiator is 0.5 to 2% of the mass of the polymer monomer.

[0012] Preferably, the initiator includes azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, diethylhexyl peroxide, potassium persulfate, or ammonium persulfate.

[0013] Preferably, the in-situ polymerization and crosslinking temperature is 60~70℃, and the in-situ polymerization and crosslinking time is 10~12h.

[0014] Preferably, a separator is laid on the surface of the lithium electrode, and then the polymer monomer is mixed with lithium salt and initiator and injected between the lithium electrode and the separator for in-situ polymerization and crosslinking.

[0015] The present invention also provides an in-situ polymerized crosslinked solid electrolyte prepared by the preparation method described in the above technical solution.

[0016] This invention provides a method for preparing an in-situ polymerized crosslinked solid electrolyte, comprising mixing a polymer monomer with a lithium salt and an initiator and then placing the mixture on a lithium electrode for in-situ polymerization and crosslinking to obtain an in-situ polymerized crosslinked solid electrolyte; wherein the polymer monomer is an ester monomer and a divinyl perfluoroalkane; wherein the ester monomer includes ethylene carbonate monomers or acrylate monomers. This invention involves in-situ polymerization and crosslinking of divinylperfluoroalkane with ester monomers. Utilizing the strong bond energy of the CF bond (485~498 kJ / mol), the resulting in-situ polymer electrolyte exhibits improved resistance to oxidative decomposition under high voltage (greater than 4.2V), thereby enhancing the electrochemical stability of the lithium-ion battery. Furthermore, the extremely high chemical inertness of the perfluoroalkane segments allows them to preferentially accumulate at the interface during contact between the in-situ polymer electrolyte and the lithium electrode, forming a robust and stable SEI film rich in LiF. This effectively prevents lithium dendrite penetration, improves interfacial stability with the lithium electrode, increases ionic conductivity, and thus enhances the capacity retention of the resulting lithium-ion battery. Moreover, the amorphous structure of the polymer formed from the divinylperfluoroalkane in the in-situ polymer electrolyte prevents ester polymer crystallization, strengthens the freedom of movement of the perfluoroalkane segments, and provides a rapid migration path for lithium ions, further improving ionic conductivity and ultimately enhancing the capacity retention of the resulting lithium-ion battery. The results of the examples show that the lithium-ion battery prepared by the in-situ polymerized crosslinked solid electrolyte provided by the present invention has a discharge specific capacity of 147 mAh / g at a charge-discharge rate of 0.5C; and a capacity retention rate of 99% after 140 cycles. Attached Figure Description

[0017] Figure 1 The infrared spectra of the in-situ polymerized crosslinked solid electrolyte (CCP), ethylene ethylene carbonate polymer (PVEC), ethylene ethylene carbonate (VEC), and 1,6-divinylperfluorohexane (DFDDF) prepared in Example 1 of this invention are shown. Figure 2 Impedance diagrams of lithium-ion batteries assembled from in-situ solid electrolytes obtained in Examples 1-3 and Comparative Examples 1-2 of this invention. Figure 3 The bar chart shows the ionic conductivity of lithium-ion batteries assembled from in-situ solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-2 of this invention. Figure 4 Electrochemical window diagrams of lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 and Comparative Example 1 of the present invention. Figure 5 The leakage current diagrams of the lithium-ion batteries assembled with in-situ solid electrolytes in Example 1 and Comparative Example 1 of the present invention under different high voltage constant voltage conditions are shown. Figure 6 This is a SEM image of the lithium metal surface in Example 1 after 100 cycles of the present invention. Figure 7 The image shows the SEM image of the lithium metal surface in Comparative Example 1 after 100 cycles of the present invention. Figure 8 The energy spectrum of the lithium metal surface in Example 1 after 100 cycles of the present invention; Figure 9 The energy spectrum of the lithium metal surface in Comparative Example 1 after 100 cycles of testing according to the present invention is shown. Figure 10 The cycling performance diagrams are for lithium-ion batteries assembled from in-situ polymerized crosslinked solid electrolytes in Examples 1 and 1-2 of this invention. Figure 11 This is a specific capacity test diagram of a lithium-ion battery assembled from an in-situ polymerized crosslinked solid electrolyte according to Example 1 of the present invention at different rates. Figure 12 The specific capacity test graphs of the lithium-ion battery assembled with the in-situ polymerized crosslinked solid electrolyte of Comparative Example 1 of the present invention at different rates are shown. Figure 13 The graphs show the constant current charge-discharge cycle test results of symmetrical batteries assembled from in-situ polymerized crosslinked solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention. Figure 14 The graphs show the constant current charge-discharge cycle test results of symmetrical batteries assembled from in-situ polymerized crosslinked solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention. Figure 15 The critical current density test diagram is shown for the symmetrical battery assembled from the in-situ polymerized crosslinked solid electrolyte prepared in Comparative Example 1 of this invention. Figure 16 This is a critical current density test diagram of a symmetrical battery assembled from an in-situ polymerized crosslinked solid electrolyte prepared in Example 1 of the present invention. Figure 17 The graph shows the cycle performance of the Li|NCM811 battery assembled from the in-situ polymerized crosslinked solid electrolyte of Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0018] This invention provides a method for preparing an in-situ polymerized crosslinked solid electrolyte, comprising: The polymer monomers were mixed with lithium salts and initiators and then subjected to in-situ polymerization and crosslinking on the surface of the lithium electrode to obtain an in-situ polymerized crosslinked solid electrolyte. The polymer monomers are ester monomers and divinyl perfluoroalkane; the ester monomers include ethylene carbonate monomers or acrylate monomers.

[0019] In this invention, the polymer monomers are ester monomers and divinylperfluoroalkane. In this invention, the polymer monomers include ethylene carbonate monomers or acrylate monomers. This invention ensures high bulk ionic conductivity by limiting the types of polymer monomers and utilizing the flexible ionic solvation sites provided by the polymer monomers. As one embodiment of this invention, the ethylene carbonate monomer may include ethylene ethylene carbonate. As one embodiment of this invention, the acrylate monomer may include methyl methacrylate or butyl acrylate.

[0020] In this invention, the CF bond in the divinylperfluoroalkane has a strong bond energy (485~498 kJ / mol), which can improve the antioxidant decomposition performance of the in-situ polymer electrolyte under high voltage (greater than 4.2V), thereby improving the electrochemical stability of the lithium-ion battery. Utilizing the extremely high chemical inertness of the perfluoroalkane segments, during the contact between the in-situ polymer electrolyte and the lithium electrode, it preferentially accumulates at the interface, forming a robust and stable SEI film rich in LiF, improving the interfacial stability with the lithium electrode. The polymer formed by the divinylperfluoroalkane has an amorphous structure, which can prevent ester polymer crystallization, enhance the freedom of movement of the perfluoroalkane segments, provide a rapid migration path for lithium ions, further improve ionic conductivity, and thus improve the capacity retention of the prepared lithium-ion battery. As one embodiment of this invention, the divinylperfluoroalkane may include 1,6-divinylperfluorohexane or 4-divinylperfluorobutane.

[0021] In one embodiment of the present invention, the volume ratio of the ester monomer to the divinylperfluoroalkane can be (4~9):1. In specific embodiments of the present invention, the volume ratio of the ester monomer to the divinylperfluoroalkane can be 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1. The present invention ensures that the polymer formed from the divinylperfluoroalkane can be fully crosslinked with the ester monomer polymer by limiting the volume ratio of the ester monomer to the divinylperfluoroalkane, thereby regulating the antioxidant properties of the ester monomer polymer and forming a robust and stable SEI film rich in LiF when in contact with the electrode.

[0022] In one embodiment of the present invention, the lithium salt may include lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, or lithium difluorooxalate borate. The present invention provides migratory lithium ions by limiting the type of lithium salt, ensuring smooth ion conduction and electrochemical reactions in the battery.

[0023] In one embodiment of the present invention, the concentration of lithium salt in the in-situ polymerization and crosslinking system can be 1~2 mol / L. In specific embodiments of the present invention, the concentration of lithium salt in the in-situ polymerization and crosslinking system can be 1 mol / L, 1.5 mol / L, or 2 mol / L. The present invention controls the ionic conductivity of the electrolyte and avoids the agglomeration of inorganic fillers by limiting the concentration of lithium salt in the mixture.

[0024] In one embodiment of the present invention, the initiator may include azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, diethylhexyl percarbonate, potassium persulfate, or ammonium persulfate. The present invention ensures that the polymer monomers are fully initiated to form a polymer by limiting the type of initiator. In one embodiment of the present invention, the mass of the initiator can be 0.5% to 2% of the mass of the polymer monomers. In embodiments of the present invention, the mass of the initiator may specifically be 0.5%, 1%, 1.5%, or 2% of the mass of the polymer monomers. The present invention controls the degree of polymerization of the polymer monomers by limiting the content of the initiator, thereby balancing the mechanical properties and ionic conductivity of the electrolyte.

[0025] In one embodiment of the present invention, the mixing of the polymer monomer with the lithium salt and the initiator can be performed by first mixing the polymer monomer with the lithium salt, and then adding the initiator for a second mixing. In another embodiment, the first mixing can be carried out under stirring, with a stirring rate of 500-600 r / min and a stirring time of 6-12 h. In specific embodiments of the present invention, the stirring time can be 6 h, 8 h, 10 h, or 12 h. In another embodiment, the second mixing can be carried out under stirring, with a stirring rate of 500-600 r / min and a stirring time of 4-6 h.

[0026] In one embodiment of the present invention, a separator can be first deposited on the surface of the lithium electrode, and then the polymer monomer, lithium salt, and initiator are mixed and injected between the lithium electrode and the separator for in-situ polymerization and crosslinking. In another embodiment, the separator may include a polypropylene (PP) separator, a polyethylene (PE) separator, a double-layered polypropylene and polyethylene separator, or a glass fiber separator. In another embodiment, the injection volume can be 40-60 μL. The present invention does not impose any particular limitation on the injection method; any injection method well known in the art can be used.

[0027] In this invention, during the in-situ polymerization and crosslinking process, the carbon-carbon double bonds in the ester monomers and divinylperfluoroalkane undergo polymerization, and the carbon-carbon double bonds in the ester monomers and divinylperfluoroalkane open, resulting in crosslinking. As one embodiment of this invention, the temperature for in-situ polymerization and crosslinking can be 60-70°C, and the time for in-situ polymerization and crosslinking can be 10-12 hours. This invention controls the progress of the in-situ polymerization and crosslinking reaction by limiting the temperature and time of in-situ polymerization and crosslinking, ensuring that the in-situ polymerized and crosslinked solid electrolyte forms a uniform and dense interface layer on the electrode surface.

[0028] This invention also provides an in-situ polymerized crosslinked solid electrolyte prepared by the preparation method described in the above technical solution. The in-situ polymerized crosslinked solid electrolyte provided by this invention is a moderately crosslinked network constructed by introducing perfluorinated segments as the main polymer monomer. The perfluorinated segments possess extremely high antioxidant capacity and extremely high chemical inertness. The introduction of these segments significantly improves the electrochemical stability of the entire polymer backbone. During the contact between the electrolyte and lithium metal, the fluorine-rich segments preferentially accumulate at the interface, forming a robust and stable SEI film rich in LiF. This film effectively prevents lithium dendrite penetration, thereby achieving excellent interface stability and inhibiting lithium dendrite growth.

[0029] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] Example 1 Ethylene carbonate and 1,6-divinylperfluorohexane were mixed, and lithium bis(trifluoromethanesulfonyl)imide was added and stirred at 600 rpm for 10 h. Then, azobisisobutyronitrile was added and stirred at 600 rpm for 4 h. The mixture was then injected into a PP membrane and allowed to stand at 60 °C for 12 h to obtain an in-situ polymerized crosslinked solid electrolyte. The volume ratio of ethylene carbonate to 1,6-divinylperfluorohexane was 9:1. The concentration of lithium bis(trifluoromethanesulfonyl)imide in the in-situ polymerization and crosslinking system was 1 mol / L. The mass of azobisisobutyronitrile was 1% of the total mass of ethylene carbonate and 1,6-divinylperfluorohexane.

[0031] Example 2 The difference between this embodiment and Example 1 is that the volume ratio of ethylene carbonate to 1,6-divinylperfluorohexane is 5.6:1; the rest is the same as in Example 1.

[0032] Example 3 The difference between this embodiment and Example 1 is that the volume ratio of ethylene carbonate to 1,6-divinylperfluorohexane is 4:1; the rest is the same as in Example 1.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that the addition of 1,6-divinylperfluorohexane is omitted, while the rest is the same as in Example 1.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that 1,6-divinylperfluorohexane is replaced with allylpentafluorobenzene, while the rest is the same as in Example 1.

[0035] The structures of the in-situ polymerized crosslinked solid electrolyte (CCP), ethylene ethylene carbonate polymer (PVEC), ethylene ethylene carbonate (VEC), and 1,6-divinylperfluorohexane (DFDDF) prepared in Example 1 were characterized using Fourier transform infrared spectroscopy. The results are as follows: Figure 1 As shown in the figure. It can be seen from the figure that at 1782 cm... -1 The signal is the stretching vibration of C=O; for VEC and DFDDF at 1648 cm -1 The signal that appears is the stretching vibration of CF. This signal can also appear in CCP, indicating that DFDDF participates in the polymerization reaction (due to the overlap between the CF peak and the COC peak, and the fact that the COC signal intensity is significantly stronger than that of CF (VEC dosage is significantly greater than DFDDF), a weaker peak splitting phenomenon occurs).

[0036] Using steel sheets as positive and negative electrodes, lithium-ion batteries were assembled with in-situ solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-2, respectively, and denoted as CCP-10VOL%, CCP-15VOL%, CCP-20VOL%, PVEC, and Comparative Example 2. The impedance of the assembled lithium-ion batteries at 35°C was tested using Donghua testing instruments, and the results are as follows: Figure 2 As shown in the figure, the impedance values ​​of the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 and Comparative Examples 1-2 are 5.25Ω, 5.72Ω, 7.94Ω, 13.14Ω, and 5.89Ω, respectively. Therefore, the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 of this invention have low impedance values.

[0037] Based on the impedance values ​​obtained above, the ionic conductivity of the in-situ solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-2 assembled into lithium-ion batteries was calculated, as follows: Figure 3As shown in the figure, the ionic conductivity of the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 and Comparative Examples 1-2 are 2.1 mS / cm, 1.76 mS / cm, 1.26 mS / cm, 0.69 mS / cm, and 1.7 mS / cm, respectively. Therefore, the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 of this invention have high ionic conductivity.

[0038] The electrochemical windows of the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 and Comparative Example 1 were tested using Donghua testing instruments. The results are as follows: Figure 4 As shown in the figure, the electrochemical windows of the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 and Comparative Example 1 are 5V, 5V, 5.1V, and 4.6V, respectively. Therefore, the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1-3 of this invention have a higher electrochemical window.

[0039] The leakage current of the lithium-ion batteries assembled with in-situ solid electrolytes in Example 1 and Comparative Example 1 under different high-voltage constant-voltage conditions was tested using a Blue Electric testing instrument. In this test and subsequent tests, the lithium-ion battery assembled with in-situ solid electrolytes in Example 1 was named CCP. The results are as follows: Figure 5 As shown in the figure, the lithium-ion batteries assembled with in-situ solid electrolytes in Examples 1 and Comparative Example 1 exhibit leakage currents below 0.01 mA at 4.6V, while the lithium-ion battery assembled with the in-situ solid electrolyte in Comparative Example 1 exhibits leakage currents exceeding 0.01 mA at 4.5V. This demonstrates that the in-situ solid electrolyte-electrode interface in the lithium-ion batteries assembled with in-situ solid electrolytes in the embodiments of the present invention exhibits good stability.

[0040] The morphology of the lithium metal surfaces of Example 1 and Comparative Example 1 after 100 cycles of cyclic testing was characterized using scanning electron microscopy. The results are as follows: Figures 6-7 As shown in the figure. From the figure, we can see that: Figure 6 Example 1: The surface morphology of the in-situ polymerized crosslinked solid electrolyte is smooth, with no pores or protrusions, indicating that lithium can be uniformly deposited on its surface; Figure 7 Comparative Example 1 shows that the surface morphology of the in-situ polymerized crosslinked solid electrolyte has obvious pores and protrusions.

[0041] The primary lithium metal of Example 1 and Comparative Example 1 was analyzed using X-ray photoelectron spectroscopy, and the results are as follows: Figures 8-9 As shown in the figure. From the figure, we can see that: Figure 8 In Example 1, the in-situ polymerized crosslinked solid electrolyte exhibited higher peak areas and greater content of CF and Li-F; while Figure 9In Comparative Example 1, the CF and Li-F peak areas in the in-situ polymerized crosslinked solid electrolyte are smaller and the content is lower. This indicates that the in-situ polymerized crosslinked solid electrolyte of Example 1 of the present invention can form a stable solid electrolyte interface (SEI) film with lithium fluoride (LiF) as the main inorganic component. This interface film has both good ionic conductivity and mechanical strength, greatly reducing charge transfer resistance, thereby accelerating the interfacial reaction kinetics.

[0042] Using LFP as the positive electrode, lithium-ion batteries were assembled with in-situ polymerized crosslinked solid electrolytes from Examples 1 and 1-2. The cycle performance of the lithium-ion batteries was tested using a Newway battery tester. The results are as follows: Figure 10 As shown in the figure, the lithium-ion battery assembled with the in-situ polymerized crosslinked solid electrolyte in Example 1 has a specific capacity of 150 mAh / g at a charge / discharge rate of 0.5C, and retains 97.3% of its capacity after 200 cycles. In contrast, the lithium-ion batteries assembled with the in-situ polymerized crosslinked solid electrolytes in Comparative Examples 1 and 2 have specific capacities of 144.2 mAh / g and 148.8 mAh / g, respectively, at a charge / discharge rate of 0.5C. Furthermore, Comparative Example 1 retains 96.6% of its capacity after 200 cycles, and Comparative Example 2 retains 97.1% of its capacity after 30 cycles.

[0043] Using LFP as the positive electrode, lithium-ion batteries were assembled with in-situ polymerized crosslinked solid electrolytes from Example 1 and Comparative Example 1. Using NCM811 as the positive electrode, lithium-ion batteries were also assembled with in-situ polymerized crosslinked solid electrolytes from Example 1 and Comparative Example 1. The specific capacity of these two sets of lithium-ion batteries at different rate tests was measured using a Newway testing instrument. The results are shown below. Figures 11-12 As shown in the figure. From the figure, we can see that: Figure 11 In the tests conducted at 0.2C, 0.5C, 1C, 2C, and 5C, the specific capacities of the lithium-ion batteries assembled with the in-situ polymerized crosslinked solid electrolyte of Example 1 were 154 mAh / g, 143 mAh / g, 134 mAh / g, 123 mAh / g, and 106 mAh / g, respectively; while the specific capacities of the lithium-ion batteries assembled with the in-situ polymerized crosslinked solid electrolyte of Comparative Example 1 were 142 mAh / g, 134 mAh / g, 125 mAh / g, 112 mAh / g, and 95 mAh / g, respectively. Therefore, it is evident that the lithium-ion batteries assembled with the in-situ polymerized crosslinked solid electrolyte of Example 1 exhibit higher specific capacities and better interface stability at different rates compared to Comparative Example 1. Figure 12In the tests conducted at 0.2C, 0.5C, 1C, 2C, and 5C, the specific capacities of the lithium-ion batteries assembled with the in-situ polymerized crosslinked solid electrolyte of Example 1 were 195 mAh / g, 187 mAh / g, 177 mAh / g, 168 mAh / g, 152 mAh / g, and 134 mAh / g, respectively. In contrast, the specific capacities of the lithium-ion batteries assembled with the in-situ polymerized crosslinked solid electrolyte of Comparative Example 1 were 178 mAh / g, 170 mAh / g, 159 mAh / g, 147 mAh / g, 125 mAh / g, and 97 mAh / g, respectively. Therefore, it is evident that the lithium-ion batteries assembled with the in-situ polymerized crosslinked solid electrolyte of Example 1 exhibit higher specific capacities and better interface stability at different rates compared to Comparative Example 1.

[0044] A symmetrical battery assembled in the order of lithium electrode | electrolyte | lithium electrode, wherein the lithium and electrolyte are in-situ polymerized crosslinked solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention, with a current density and depth of charge / discharge of 0.2 mA / cm². -2 0.2mAh cm -2 Under these conditions, a constant current charge-discharge cycle test was performed, and the results are as follows: Figures 13-14 As shown in the figure. From the figure, we can see that: Figure 13 In Comparative Example 1, the symmetric battery prepared by in-situ polymerized crosslinked solid electrolyte experienced a voltage drop after nearly 600 hours, which can be attributed to the uneven Li dendrite deposition piercing the electrolyte layer and causing a short circuit. Therefore, the in-situ polymerized crosslinked solid electrolyte of this invention exhibits better interfacial stability and results in a longer lifespan for the prepared symmetric battery. Figure 14 In the middle, for Figure 13 The magnified images from 500 to 700 hours further demonstrate that the symmetric cell prepared by the in-situ polymerized crosslinked solid electrolyte of Comparative Example 1 experienced a voltage drop at nearly 600 hours.

[0045] A symmetrical battery was assembled in the order of lithium electrode | electrolyte | lithium electrode, wherein the lithium and electrolyte were in-situ polymerized crosslinked solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention. The critical current density of the assembled symmetrical battery was tested by continuously linearly increasing the current density, while the voltage response of the battery was monitored. The results are as follows: Figures 15-16 As shown in the figure. From the figure, we can see that: Figure 15 In Comparative Example 1, the symmetric battery prepared by in-situ polymerized crosslinked solid electrolyte achieved a current density exceeding 2.2 mA / cm². -2 Subsequently, the voltage curve drops sharply, indicating that the battery has failed due to a short circuit caused by the rapid growth of lithium dendrites. The current density at this point can be considered the critical current density of the electrolyte. Figure 16In Example 1, the symmetric cell prepared by in-situ polymerization and crosslinking of solid electrolyte maintained a stable voltage response curve throughout the entire linear current density scan; at the final 4 mA cm⁻¹... -2 No failure behavior occurred even at high current densities, indicating that the in-situ polymerized crosslinked solid electrolyte of Example 1 can effectively suppress the nucleation and growth of lithium dendrites at high current densities, thereby providing the battery with a wider safe operating window and higher fast charging potential.

[0046] Li|NCM811 batteries were assembled using the in-situ polymerized crosslinked solid electrolytes prepared in Example 1 and Comparative Example 1 of this invention, respectively. Charge-discharge cycle tests were conducted at a 1C rate, and the results are as follows: Figure 17 As shown in the figure, the Li|NCM811 battery assembled with the in-situ polymerized crosslinked solid electrolyte prepared in Example 1 had an initial capacity of 188 mAh / g, a specific capacity of 165 mAh / g after 250 cycles, a capacity retention rate of 90%, and an average coulombic efficiency consistently above 99.8%. In contrast, the Li|NCM811 battery assembled with the in-situ polymerized crosslinked solid electrolyte prepared in Comparative Example 1 had an initial capacity of only 15 mAh / g, and a capacity of only 118 mAh / g after 110 cycles, with a capacity retention rate of only 74.6%.

[0047] In summary, the in-situ polymerized crosslinked solid electrolyte provided by this invention has good interface stability with the lithium electrode, and the resulting lithium-ion battery has good electrochemical stability and low capacity retention.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an in-situ polymerized crosslinked solid electrolyte, comprising: The polymer monomers were mixed with lithium salts and initiators and then subjected to in-situ polymerization and crosslinking on the surface of the lithium electrode to obtain an in-situ polymerized crosslinked solid electrolyte. The polymer monomers are ester monomers and divinyl perfluoroalkane; the ester monomers include ethylene carbonate monomers or acrylate monomers.

2. The preparation method according to claim 1, characterized in that, The volume ratio of the ester monomer to the divinylperfluoroalkane is (4~9):

1.

3. The preparation method according to claim 1 or 2, characterized in that, The carbonate monomers include ethylene carbonate; the acrylate monomers include methyl methacrylate or butyl acrylate; the divinyl perfluoroalkane includes 1,6-divinyl perfluorohexane or 1,4-divinyl perfluorobutane.

4. The preparation method according to claim 1 or 2, characterized in that, The concentration of lithium salt in the in-situ polymerization and crosslinking system is 1~2 mol / L.

5. The preparation method according to claim 1, characterized in that, The lithium salts include lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, or lithium difluorooxalate borate.

6. The preparation method according to claim 1, characterized in that, The mass of the initiator is 0.5 to 2% of the mass of the polymer monomer.

7. The preparation method according to claim 1 or 6, characterized in that, The initiator includes azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, diethylhexyl peroxide, potassium persulfate, or ammonium persulfate.

8. The preparation method according to claim 1, characterized in that, The in-situ polymerization and crosslinking are performed at a temperature of 60-70°C for 10-12 hours.

9. The preparation method according to claim 1, characterized in that, A separator is laid on the surface of the lithium electrode, and then the polymer monomer is mixed with lithium salt and initiator and injected between the lithium electrode and the separator for in-situ polymerization and crosslinking.

10. The in-situ polymerized crosslinked solid electrolyte prepared by the preparation method according to any one of claims 1 to 9.

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