A polycationic anchor dianion solid-state polymer electrolyte and a preparation method and application thereof

Abstract

This invention relates to the field of lithium secondary batteries and solid-state electrolytes, and particularly to a polycation-anchored dianion solid polymer electrolyte, its preparation method, and its applications. The polycation-anchored dianion solid polymer electrolyte provided by this invention differs from existing technologies: this invention does not rely on additional liquid components to improve conductivity, but rather constructs a "single lithium salt + dianion + polycation framework" system by introducing the polymerizable ionic liquid monomer VEIMTFSI into the VEC-based polymerization network. In this system, the imidazolium cation is covalently anchored to the polymer ionic framework, which on the one hand improves polymerization integrity and reduces the residual liquid VEC content, and on the other hand inhibits anion migration and increases the lithium-ion transference number. Simultaneously, the dianion structure can induce the formation of an organic outer layer / inorganic inner layer gradient interface film on the lithium anode and cathode surfaces, thereby simultaneously improving interface stability, lithium-ion transport capacity, and high-voltage adaptability.

Description

Technical Field

[0001] This invention relates to the field of lithium secondary battery and solid electrolyte technology, and in particular to a polycation-anion-anion solid polymer electrolyte, its preparation method and application. Background Technology

[0002] The lithium metal anode has a capacity of 3860 mAh·g -1 The theoretical specific capacity and -3.04 V (vs. Li) + The electrochemical potential of lithium metal (Li₂ / Li₃) is crucial for constructing high-energy-density secondary batteries. However, in traditional liquid electrolytes, continuous side reactions and dendrite growth easily occur on the lithium metal surface, leading to a continuous increase in interfacial impedance, a decrease in coulombic efficiency, and even internal short circuits and safety risks. To address these issues, solid-state lithium metal batteries have attracted widespread attention due to their high safety and good interfacial flexibility. Among them, solid polymer electrolytes, which combine flexibility, processability, and easy adhesion to electrodes, represent an important development direction.

[0003] Among existing solid polymer electrolytes, polycarbonate electrolytes, due to their abundant carbonyl and carbonate oxygen sites, can provide coordination and migration channels for lithium ions, thus showing good application potential. Polymer electrolyte systems formed by the polymerization of vinylvinyl carbonate (VEC) can, to some extent, balance interfacial compatibility and room-temperature ion transport. However, existing technologies still generally suffer from the following problems: First, the polymerization efficiency of VEC copolymerization with conventional vinyl monomers is limited, often leaving a large amount of unpolymerized liquid components in the system, making it difficult to distinguish between actual conductivity and the contribution of the true polymer backbone; Second, the anion transference number in the system is high, while the lithium ion transference number is low, easily leading to concentration polarization during cycling; Third, the interfacial film formed after the electrolyte contacts the lithium anode and high-voltage cathode is usually dominated by organic components, with limited mechanical strength and ion transport capacity, which is detrimental to long-life cycling and high-voltage stable operation; Fourth, existing modification strategies often rely on inorganic fillers, additional solvents, or complex multi-component additives. While these can improve performance to some extent, they also bring problems such as complex formulations, unclear structure-performance relationships, and reduced process repeatability.

[0004] To address these issues, existing VEC-based polycarbonate solid polymer electrolyte systems, as well as electrolyte systems modified by introducing inorganic fillers, fluorinated functional monomers, or single-ion conductors, are typically designed to improve room-temperature ionic conductivity or interfacial stability. However, they generally still suffer from problems such as insufficient VEC polymerization, a high proportion of residual liquid monomers, difficulty in effectively suppressing anion migration, and the inability of the interfacial film to simultaneously achieve both density and rapid lithium-ion transport.

[0005] Therefore, developing a VEC-based solid polymer electrolyte that combines high polymerization integrity, high lithium-ion transference number, wide electrochemical stability window, and stable electrode / electrolyte interface is of great significance for promoting the practical application of solid-state lithium metal batteries. Summary of the Invention

[0006] In view of this, the present invention provides a polycation-anchored dianion solid polymer electrolyte, its preparation method and application. The polycation-anchored dianion solid polymer electrolyte (denoted as PVIM) provided by the present invention improves the overall polymerization integrity, interface stability, lithium-ion transport capability and high voltage adaptability.

[0007] This invention provides a polycation-anchored dianionic solid polymer electrolyte, prepared from the following raw materials: VEC, 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide (VEIMTFSI), lithium source, crosslinking agent, and thermal initiator; wherein the lithium source is lithium difluorooxalate borate (LiDFOB); LiDFOB is the sole source of lithium salt, and VEIMTFSI is both a comonomer and provides TFSI. - It forms a polycation-anchored bi-anion environment.

[0008] Preferably, the mass ratio of VEC to VEIMTFSI is 100:24~26; the mass ratio of VEC to lithium source is 100:20~22; the mass ratio of VEC to crosslinking agent is 100:3~5; and the mass ratio of the total mass of VEC and VEIMTFSI to the mass of thermal initiator is 100:2.5~3.5.

[0009] Preferably, the crosslinking agent is an acrylamide crosslinking agent; the acrylamide crosslinking agent is N,N′-methylenebisacrylamide (MBA).

[0010] This invention also provides a method for preparing the polycationically anchored bi-anion solid polymer electrolyte described above, comprising the following steps: (1) Under inert atmosphere conditions, VEC, LiDFOB, crosslinking agent, VEIMTFSI and thermal initiator are mixed (referred to as the first mixture) to obtain electrolyte precursor solution (referred to as VIM); (2) The electrolyte precursor solution is introduced into the diaphragm or the electrode / diaphragm interface, and the electrolyte precursor solution is infiltrated into the porous support framework and the electrode surface and then thermally polymerized in situ to obtain the polycation-anion-anion solid polymer electrolyte.

[0011] Preferably, the first mixing is a stirring mixture; the first mixing time is 5.5~6.5 h; the first mixing is carried out in an argon glove box with both water and oxygen content below 0.1 ppm.

[0012] Preferably, the amount of electrolyte precursor solution added to introduce the diaphragm or electrode / diaphragm interface is 28~32μL per side; the introduction of the diaphragm or electrode / diaphragm interface is carried out in an argon glove box with both water and oxygen content below 0.1 ppm.

[0013] Preferably, the immersion temperature is 28~32 ℃, the immersion time is 5.5~6.5 h, the immersion is carried out under static conditions, and the immersion is carried out in an argon glove box with both water and oxygen content below 0.1 ppm.

[0014] Preferably, the in-situ thermal polymerization is carried out at a temperature of 60-80 °C and a holding time of 9-11 h; the in-situ thermal polymerization is carried out in an argon glove box with both water and oxygen content below 0.1 ppm.

[0015] The present invention also provides the application of the polycation-anion-anion solid polymer electrolyte described in the above-described scheme or the polycation-anion-anion solid polymer electrolyte prepared by the above-described scheme in solid lithium metal batteries.

[0016] The present invention also provides a solid lithium metal battery, including an electrolyte; the electrolyte includes the polycation-anchored dianionite solid polymer electrolyte described in the above-described scheme or the polycation-anchored dianionite solid polymer electrolyte obtained by the preparation method described in the above-described scheme.

[0017] This invention provides a polycation-anchored dianionic solid polymer electrolyte. The polycation-anchored dianionic solid polymer electrolyte provided by this invention uses VEC as the main component, VEIMTFSI (a polymerizable ionic liquid monomer) as the functional comonomer, and LiDFOB as the lithium salt. This invention differs from existing technologies in its structural design, interface regulation mechanism, and electrochemical performance. The working mechanism is as follows: Figure 1 As shown: This invention does not rely on additional liquid components to improve conductivity, but rather constructs a "single lithium salt + two anions (DFOB)" structure by introducing the polymerizable ionic liquid monomer VEIMTFSI into the VEC-based polymerization network. - / TFSI - A system consisting of an imidazolium cation (VEIM) and a polycationic backbone. In this system, the imidazolium cation (VEIM)... +By covalently anchoring itself to the polymer ionic framework, it improves the overall polymerization integrity and reduces the residual liquid VEC content. On the other hand, it can inhibit anion migration and increase the lithium ion transference number. At the same time, the dual anion structure can induce the formation of an organic outer layer / inorganic inner layer gradient interface film on the lithium anode and cathode surfaces, thereby simultaneously improving interface stability, lithium ion transport capacity and high voltage adaptability.

[0018] This invention also provides a method for preparing the polycationically anchored bi-anion solid polymer electrolyte described in the above-mentioned scheme. This invention utilizes an in-situ thermal polymerization method, employing VEC and VEIMTFSI, and introducing a crosslinking agent to construct a solid electrolyte system with high polymerization degree, high lithium-ion transference number, wide electrochemical stability window, and stable gradient anode / cathode electrolyte interface (SEI / CEI) without introducing additional solvents. Benefiting from VEIM... + The fixation and cross-linking network on the polymer chain improves the lithium-ion transference number, VEC polymerization degree, and electrochemical performance, solving the problems of incomplete polymerization, excessive residual liquid components, low lithium-ion transference number, severe interfacial side reactions, and insufficient high-voltage adaptability in existing VEC-based solid polymer electrolytes.

[0019] This invention also provides the application of the polycation-anion-anion solid polymer electrolyte described in the above-described scheme or the polycation-anion-anion solid polymer electrolyte prepared by the above-described scheme in solid-state lithium metal batteries. The polycation-anion-anion solid polymer electrolyte provided by this invention can be used in solid-state lithium metal batteries, such as lithium metal symmetric batteries, lithium iron phosphate full batteries, or high-nickel ternary full batteries, and can achieve excellent long-cycle stability, rate performance, and safety.

[0020] Overall, the present invention achieves the following beneficial effects: (1) This invention introduces VEIMTFSI into the VEC-based system, thereby enabling VEIM... + Covalent anchoring in the polymer ionic framework significantly improves the polymerization integrity of the system and reduces the content of residual liquid VEC. Vacuum heating and NMR quantitative analysis showed that the residual VEC in the system was 15.0%–16.0% of the initial VEC mass, significantly reducing the dominant role of residual liquid species in electrochemical behavior.

[0021] (2) This invention constructs a single lithium salt dual-anion environment, which significantly improves ion transport performance while maintaining a relatively simple formulation system. The results of the examples show that the polycation-anchored dual-anion solid polymer electrolyte achieves an ionic conductivity of 0.41 mS·cm at 25 °C. -1 The lithium-ion transference number reached 0.54, which was significantly better than the control system without VEIMTFSI.

[0022] (3) The polycationically anchored bi-anion solid polymer electrolyte provided by this invention has a wide electrochemical stability window. Example results show that, with an oxidation initiation current threshold of 10 μA, its oxidation decomposition potential reaches 5.1 V (vs. Li). + / Li), which can be adapted to higher voltage cathode systems.

[0023] (4) In this invention, the polymer ionic framework formed by VEIMTFSI polymerization can restrict anion migration and promote the enrichment and decomposition of anions on both the lithium anode and cathode sides through the regulation of the interfacial electrostatic environment, thereby forming gradient SEI / CEI films rich in LiF, Li3N, and boron-containing inorganic components, respectively. This invention forms an organic outer layer / inorganic inner layer gradient SEI on the lithium anode surface and a thin and dense gradient CEI on the cathode surface through the synergistic effect of the polymer ionic framework and the dual anions; the inorganic inner layer is rich in LiF, Li3N, and boron-containing components, and has both high mechanical strength and fast lithium-ion transport capability, thereby helping to suppress lithium dendrite growth and continuous side reactions.

[0024] (5) The present invention exhibits excellent cycle stability in lithium metal batteries. Example results show that the Li||Li symmetric battery achieves excellent cycle stability at 0.1 mA·cm⁻¹. -2 0.1 mAh·cm -2 Under the given conditions, it can be stably cycled for 4000 h; the Li||LFP full cell retains 80.0% capacity after 800 cycles at 25 ℃ and 1 C; the Li||NCM811 full cell retains 81.9% capacity after 300 cycles at 25 ℃ and 0.5 C, indicating that the present invention has both good long-cycle performance and practical application potential. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of this invention, the accompanying drawings used in the embodiments of this invention or in the prior art are briefly described below. For those skilled in the art, other drawings can be derived from the following drawings without creative effort, and all such drawings are within the protection scope of this invention.

[0026] Figure 1 The diagram shows the working mechanism and process flow of polycationically anchored dianionic solid polymer electrolyte; (a) is the working mechanism diagram of polycationically anchored dianionic solid polymer electrolyte, and (b) is the process flow diagram for preparing polycationically anchored dianionic solid polymer electrolyte. Figure 2Raman spectra, surface morphology diagrams, thermogravimetric curves, and nuclear magnetic resonance (NMR) spectra of VEC, VEIMTFSI, VIM, and polycationically anchored dianionic solid polymer electrolytes; wherein, (a) is the Raman spectrum of VIM and polycationically anchored dianionic solid polymer electrolyte in Example 1, (b) is the surface morphology diagram of polycationically anchored dianionic solid polymer electrolyte in Example 1, (c) is the thermogravimetric curve of polycationically anchored dianionic solid polymer electrolyte in Example 1 and solid polymer electrolyte in Comparative Example 1, (d) is the NMR spectrum of VEC and VEIMTFSI in Example 1, (e) is the NMR spectrum of VIM and polycationically anchored dianionic solid polymer electrolyte in Example 1, and (f) is the NMR spectrum of polycationically anchored dianionic solid polymer electrolyte in Example 1. Figure 3 The solvation structure analysis and schematic diagram of polycationically anchored dianionic solid polymer electrolytes and solid polymer electrolytes, along with molecular dynamics / theoretical calculation diagrams; where (a) is DFOB. - Raman spectroscopy diagrams of the solvated structures of the polycationically anchored dianionic solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1 are shown below. (b) is a schematic diagram of the solvated structure of the polycationically anchored dianionic solid polymer electrolyte of Example 1 at room temperature. (c) is a schematic diagram of the solvated structure of the solid polymer electrolyte of Comparative Example 1 at room temperature (where purple spheres represent Li, red spheres represent O, gray spheres represent C, white spheres represent H, blue spheres represent N, blue-green spheres represent F, pink spheres represent B, and yellow spheres represent S). (d) is a radial distribution function and coordination number diagram of the polycationically anchored dianionic solid polymer electrolyte of Example 1. (e) is a radial distribution function and coordination number diagram of the solid polymer electrolyte of Comparative Example 1 (where Li-VEC-O represents the interaction between lithium ions and oxygen atoms in VEC molecules, and Li-DFOB-O represents the interaction between lithium ions and DFOB molecules). - The interaction between oxygen atoms in the anion, Li-DFOB-F represents the interaction between lithium ions and DFOB. - The interaction between fluorine atoms in the anion, Li-TFSI-O represents the interaction between lithium ions and TFSI. - The interaction between oxygen atoms in the anion, Li-TFSI-N represents the interaction between lithium ions and TFSI. - The interaction between nitrogen atoms in the anion, Li-TFSI-F represents the interaction between lithium ions and TFSI. - Interactions between fluorine atoms in the anions; (f) represents the Li in the polycationically anchored dianionic solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1. + Mean square displacement-time curve; Figure 4The figures show the thermal analysis and electrochemical performance characterization results of the polycationically anchored dianionic solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1; wherein, (a) is the differential scanning calorimetry (DSC) of the polycationically anchored dianionic solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1, (b) is the Arrhenius plot of the polycationically anchored dianionic solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1, and (c) is the combined DC polarization and AC impedance test results of the polycationically anchored dianionic solid polymer electrolyte of Example 1 (the inset shows the polarization). (d) Nyquist plots of the polycation-anion-anion solid polymer electrolyte of Example 1 and Comparative Example 1 solid polymer electrolyte; (e) Tafel test results of the polycation-anion-anion solid polymer electrolyte of Example 1 and Comparative Example 1 solid polymer electrolyte; (f) Critical current density of the Li||Li symmetric cell of the polycation-anion-anion solid polymer electrolyte of Example 1 and Comparative Example 1 solid polymer electrolyte (current density of 0.05 mA·cm⁻¹ for the first 5 cycles). -2 and at 0.1 mA·cm -2 The step size is increased until the test ends. Figure 5 The figures show the battery cycling and negative electrode interface test results of the polycation-anion-anion-anion solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1; wherein, (a) is the constant current cycling (0.1 mA·cm) of the symmetric Li||Li battery of Example 1 polycation-anion-anion-anion solid polymer electrolyte and Comparative Example 1 solid polymer electrolyte at 25°C. -2 0.1 mAh·cm -2 (b) are scanning electron microscope images of the lithium anode surface of the Li||Li battery using the polycation-anion-anion solid polymer electrolyte of Example 1 after 60 hours of operation; Figure 6 The diagram shows the analytical results of the lithium anode of the battery in Example 1 (polycation-anchored dual-anion solid polymer electrolyte) or Comparative Example 1 (solid polymer electrolyte), and the schematic diagram of the VEIMTFSI-mediated mechanism; wherein, (a) shows the VEC and VEIM in the polycation-anchored dual-anion solid polymer electrolyte of Example 1. +(a) is the molecular energy level diagram of MBA, (b) is the full X-ray photoelectron spectrum of the SEI formed on the lithium anode after 30 cycles of the polycationically anchored dianionic solid polymer electrolyte of Example 1, (c) is the scanning electron microscope image of the lithium anode surface after working for 60 hours using the Li||Li symmetric battery of Comparative Example 1, (d) is the peak fitting diagram of fluorine (F 1s) in the polycationically anchored dianionic solid polymer electrolyte of Example 1, (e) is the peak fitting diagram of nitrogen (N 1s) in the polycationically anchored dianionic solid polymer electrolyte of Example 1, and (f) is the schematic diagram of the VEIMTFSI-mediated mechanism. Figure 7 The following are electrochemical performance graphs of the Li||LFP full cells assembled with polycation-anion-anion solid polymer electrolyte of Example 1 or solid polymer electrolyte of Comparative Example 1: (a) is the battery cycle performance graph of the Li||LFP full cell assembled with polycation-anion-anion solid polymer electrolyte of Example 1 or solid polymer electrolyte of Comparative Example 1 at 25 °C and 1 C; (b) is the capacity-voltage curve of the Li||LFP full cell assembled with polycation-anion-anion solid polymer electrolyte of Example 1; (c) is the cycle performance graph of the Li||LFP full cell assembled with polycation-anion-anion solid polymer electrolyte of Example 1 or solid polymer electrolyte of Comparative Example 1 at 25 °C and 2 C; and (d) is the rate performance test graph of the Li||LFP full cell assembled with polycation-anion-anion solid polymer electrolyte of Example 1 or solid polymer electrolyte of Comparative Example 1 at 25 °C. Figure 8 The performance comparison chart of the Li||LFP full cell assembled with the polycation-anion-anion solid polymer electrolyte of Example 1 and the reported VEC-based electrolyte full cell (all using LFP cathode). Figure 9 The diagram shows the cycle performance of the Li||NCM811 full cell and the test results of the pouch cell. Among them, (a) is the cycle performance of the Li||NCM811 full cell assembled with polycation-anion-anion solid polymer electrolyte of Example 1 under the conditions of 25℃ and 0.5 C; (b) is the cycle performance of the Li||NCM811 pouch cell assembled with polycation-anion-anion solid polymer electrolyte of Example 1 under the conditions of 25℃ and 0.2 C; and (c) is the safety test diagram of the Li||NCM811 pouch cell assembled with polycation-anion-anion solid polymer electrolyte of Example 1 under partial cutting and half cutting. Figure 10The figures show the characterization of the LFP cathode CEI and the LFP surface adsorption energy analysis of the Li||LFP full cell in Example 1 and Comparative Example 1 in Test Example 6; wherein, (a) is the peak fitting diagram of carbon (C 1s) of the LFP cathode CEI of the Li||LFP full cell in Test Example 6, (b) is the peak fitting diagram of fluorine (F 1s) of the LFP cathode CEI of the Li||LFP full cell in Test Example 6, (c) is the peak fitting diagram of boron (B 1s) of the LFP cathode CEI of the Li||LFP full cell in Test Example 6, and (d) is the peak fitting diagram of nitrogen (N) of the LFP cathode CEI of the Li||LFP full cell in Test Example 6. (e) is a transmission electron microscope (TEM) image of the LFP cathode CEI in the Li||LFP full cell of Test Example 6; (f) is a TEM image of the LFP cathode CEI in the Li||LFP full cell assembled with solid polymer electrolyte in Comparative Example 1; and (g) is a TEM image of VEC and VEIM. + TFSI - and DFOB - Adsorption energy analysis diagram of LFP; Figure 11 The XPS spectra of the lithium anode in the Li||Li symmetric battery with solid polymer electrolyte in Comparative Example 1 are shown; where (a) is the XPS F 1s spectrum and (b) is the XPS N 1s spectrum. Detailed Implementation

[0027] This invention provides a polycation-anchored dianionic solid polymer electrolyte, prepared from the following raw materials: VEC, VEIMTFSI, lithium source, crosslinking agent, and thermal initiator; the lithium source is LiDFOB; LiDFOB is the sole source of lithium salt, and VEIMTFSI serves as both a comonomer and a source of TFSI. - It forms a polycation-anchored bi-anion environment.

[0028] In this invention, the mass ratio of VEC to VEIMTFSI is preferably 100:24~26, more preferably 100:25.

[0029] In this invention, the mass ratio of VEC to lithium source is preferably 100:20~22, more preferably 100:21.

[0030] In this invention, the crosslinking agent is preferably an acrylamide-based crosslinking agent; the acrylamide-based crosslinking agent is preferably MBA.

[0031] In this invention, the mass ratio of VEC to crosslinking agent is preferably 100:3~5, more preferably 100:4.

[0032] In this invention, the thermal initiator is preferably an azo initiator; the azo initiator is preferably azobisisobutyronitrile (AIBN).

[0033] In this invention, the ratio of the total mass of VEC and VEIMTFSI to the mass of the thermal initiator is preferably 100:2.5 to 3.5, more preferably 100:3.

[0034] The polycationically anchored bi-anionally solid polymer electrolyte provided by this invention uses LiDFOB as the sole source of lithium salt, and VEIMTFSI serves both as a comonomer and as a source of TFSI for the system. - Anions, thereby forming DFOB in polycation-anchored dianionic solid polymer electrolytes. - / TFSI - A dual anion environment.

[0035] This invention also provides a method for preparing the polycationically anchored bi-anion solid polymer electrolyte described above, comprising the following steps: (1) Under inert atmosphere conditions, VEC, LiDFOB, crosslinking agent, VEIMTFSI and thermal initiator are mixed for the first time to obtain electrolyte precursor solution; (2) The electrolyte precursor solution is introduced into the diaphragm or the electrode / diaphragm interface, and the electrolyte precursor solution is infiltrated into the porous support framework and the electrode surface and then thermally polymerized in situ to obtain the polycation-anion-anion solid polymer electrolyte.

[0036] The process flow for preparing polycationically anchored bi-anion solid polymer electrolytes according to this invention is as follows: Figure 1 As shown. In this invention, under an inert atmosphere, VEC, LiDFOB, a crosslinking agent, VEIMTFSI, and a thermal initiator are first mixed to obtain an electrolyte precursor solution.

[0037] In this invention, the inert atmosphere is preferably argon.

[0038] In this invention, the first mixing is preferably stirred; the first mixing time is preferably 5.5~6.5h, more preferably 6h; the first mixing is preferably carried out in an argon glove box with both water and oxygen content below 0.1 ppm. This invention obtains a homogeneous, transparent or semi-transparent electrolyte precursor solution through the first mixing.

[0039] After obtaining the electrolyte precursor solution, the present invention introduces the electrolyte precursor solution into the diaphragm or the electrode / diaphragm interface, and then performs in-situ thermal polymerization after the electrolyte precursor solution wets the porous support framework and the electrode surface to obtain the polycation-anion-anion solid polymer electrolyte.

[0040] In this invention, the amount of electrolyte precursor solution added to introduce the diaphragm or electrode / diaphragm interface is preferably 28~32μL per side, more preferably 30 μL; the introduction of the diaphragm or electrode / diaphragm interface is preferably carried out in an argon glove box with both water and oxygen content below 0.1ppm.

[0041] In this invention, the wetting temperature is preferably 28-32 °C, more preferably 30 °C, and the wetting time is preferably 5.5-6.5 h, more preferably 6 h; the wetting is preferably carried out under static conditions; the wetting is preferably carried out in an argon glove box with both water and oxygen content below 0.1 ppm. This invention, through wetting, ensures that the electrolyte precursor solution fully wets the porous support framework and electrode surface. The invention uses a relatively low static temperature to ensure sufficient wetting of the electrolyte precursor solution.

[0042] In this invention, the in-situ thermal polymerization temperature is preferably 60-80 °C, more preferably 70 °C, and the holding time is preferably 9-11 h, more preferably 10 h; the in-situ thermal polymerization is preferably carried out in an argon glove box with both water and oxygen content below 0.1 ppm. The preparation method provided by this invention is carried out entirely in an argon glove box with both water and oxygen content below 0.1 ppm.

[0043] The present invention also provides the application of the polycation-anion-anion solid polymer electrolyte described in the above-described scheme or the polycation-anion-anion solid polymer electrolyte prepared by the above-described scheme in solid lithium metal batteries.

[0044] In this invention, the method of application preferably includes the following steps: assembling a solid lithium metal battery using a polycation-anion-anion-anionized solid polymer electrolyte.

[0045] In this invention, the solid-state lithium metal battery is preferably a lithium metal symmetric battery (Li||Li symmetric battery), a lithium metal full battery, a lithium iron phosphate full battery, or a high-nickel ternary full battery.

[0046] The present invention also provides a solid lithium metal battery, including an electrolyte; the electrolyte includes the polycation-anchored dianionite solid polymer electrolyte described in the above-described scheme or the polycation-anchored dianionite solid polymer electrolyte obtained by the preparation method described in the above-described scheme.

[0047] In this invention, the solid-state lithium metal battery preferably further includes a separator; the separator is preferably a ceramic-coated polyethylene separator; the ceramic-coated polyethylene separator is preferably an Al2O3-coated PE separator.

[0048] In this invention, the solid-state lithium metal battery preferably further includes a positive electrode; the positive electrode is preferably iron phosphate or LiNi. 0.8 Co0.1 Mn 0.1 O2 positive electrode.

[0049] In this invention, when the solid-state lithium metal battery is a lithium iron phosphate full battery, the positive electrode slurry is prepared from an active material, a conductive agent, and a binder; the active material preferably includes lithium iron phosphate (LFP); the conductive agent preferably includes conductive carbon black (Super P); the binder preferably includes polyvinylidene fluoride (PVDF); the mass ratio of the active material to the conductive agent is preferably 78~82:8~12, more preferably 80:10; the mass ratio of the active material to the binder is preferably 78~82:8~12, more preferably 80:10.

[0050] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments.

[0051] Example 1: 1) Preparation of electrolyte precursor solution: All reagents (VEC, VEIMTFSI, LiDFOB, MBA, and AIBN) were stored and used in an argon-filled glove box, where the water and oxygen content were controlled below 0.1 ppm. 1 g of VEC, 0.21 g of LiDFOB, 0.04 g of MBA, 0.25 g of VEIMTFSI, and 3 wt% of AIBN (based on the total mass of the monomers (VEC and VEIMTFSI)) were weighed and placed in a sealed container and magnetically stirred for 6 h to obtain a homogeneous electrolyte precursor solution.

[0052] 2) Preparation of polycationically anchored bi-anionally solid polymer electrolyte: A ceramic-coated polyethylene membrane (Al2O3-coated PE membrane) was used as the mechanical support framework. 30 μL of the prepared electrolyte precursor solution was added to each side of the membrane, for a total of 60 μL. A button cell was then assembled and allowed to stand at 30 °C for 6 h to allow the precursor solution to fully wet the membrane and electrode surfaces. The temperature was then raised to 70 °C and maintained for 10 h to allow in-situ thermal polymerization, yielding a polycation-anion-anionic solid polymer electrolyte.

[0053] Comparative Example 1: The preparation method of this comparative example is the same as that of Example 1, except that VEIMTFSI is not added in step (1) to obtain a solid polymer electrolyte (denoted as PVEC).

[0054] Test Example 1: The structure and polymerization integrity of the polycationically anchored bi-anionally solid polymer electrolyte of Example 1 were characterized as follows: 1) Raman characterization was performed on VIM and polycationically anchored bi-anionally solid polymer electrolyte in Example 1, and the results are as follows: Figure 2 As shown in (a) of the diagram. According to Figure 2 As can be seen in (a) of the electrolyte precursor solution, the electrolyte is located at 1650 cm⁻¹ -1 The C=C characteristic peaks in the vicinity disappeared after in-situ thermal polymerization, indicating that the double bonds were effectively consumed.

[0055] 2) The surface morphology of the polycationically anchored bi-anionally solid polymer electrolyte prepared in Example 1 was observed, and the results are as follows: Figure 2 As shown in (b) of the diagram. According to Figure 2 As can be seen from (b) in the figure, the surface of the polycation-anion-anion solid polymer electrolyte is uniform and dense, with no obvious pores.

[0056] 3) Thermogravimetric analysis was performed on the polycationically anchored bi-anion solid polymer electrolyte prepared in Example 1 and the solid polymer electrolyte prepared in Comparative Example 1. The results are as follows: Figure 2 As shown in (c) of the diagram. According to... Figure 2 As can be seen from (c), the mass loss of the system in Example 1 during the heating process was about 24%, which was lower than that of the control system in Comparative Example 1 that did not contain VEIMTFSI (about 39%).

[0057] 4) Using tetramethylsilane (TMS) as an internal standard, the VEC, VEIMTFSI, VIM, and polycationically anchored bianionic solid polymer electrolyte (in dimethyl sulfoxide-d6 solvent) from Example 1 were tested. 1 1H NMR quantitative characterization, results are as follows Figure 2 As shown in (d)~(f). According to Figure 2 As can be seen from (d) to (f), by comparing its integral with the residual monomer C=C signal, the residual liquid component of Example 1 is about 16% (TGA weight loss is not equivalent to residual VEC, and may also include other volatilization or decomposition contributions), which is consistent with the above results. This indicates that the electrochemical performance of the polycationically anchored bi-anionic solid polymer electrolyte of Example 1 does not mainly originate from unreacted liquid monomers.

[0058] Test Example 2: The ion solvation and migration mechanisms of the polycation-anion-anion-anion solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1 were investigated using Raman analysis, molecular dynamics simulations, and density functional calculations. The results are as follows: Figure 3 As shown.

[0059] according to Figure 3 As can be seen, Raman spectroscopy reveals the solvation structures in PVIM and PVEC; 741 cm⁻¹ -1721cm -1 and 711 cm -1 The bands at these locations belong to aggregates (AGG), contact ion pairs (CIP), and solvent-separated ion pairs (SSIP), respectively; in PVECs, undissociated ion pairs dominate, resulting in a single major solvation motif; 1-vinyl-3-ethylimidazolium cation (VEIM) + The framework electrostatically confines anions, promoting partial dissociation of LiDFOB and inducing the formation of solvated structures consisting of aggregates / contact ion pairs / solvent separation ion pairs. Simultaneously, the polycation-anion-anion-anionic solid polymer electrolyte contains Li... + Both the mean square displacement and diffusion coefficient of Li are higher than those of Comparative Example 1. + The binding energy between the polymer chain segments decreased to 3.20 eV, indicating that the system of the present invention has faster microscopic ion migration kinetics.

[0060] Test Example 3: The residual VEC quantification, AC impedance spectroscopy, thermal analysis, ion transport, and electrochemical performance tests of the polycationically anchored bi-anionally solid polymer electrolyte of Example 1 were performed as follows: 1) Quantitative analysis of residual VEC: The polycationically anchored bianionic solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1 were treated at 80 °C and a vacuum of 133 Pa for 12 h. The results showed that the residual VEC mass was approximately 15% of the initial VEC mass.

[0061] 2) The AC impedance of the polycation-anion-anion-supported solid polymer electrolyte of Example 1 was tested using a stainless steel symmetrical battery. The results showed that the ionic conductivity of the polycation-anion-supported solid polymer electrolyte of Example 1 at 25 °C was 0.41 mS·cm. -1 .

[0062] 3) Differential scanning calorimetry analysis was performed on the polycationically anchored bi-anionally solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1. The results are as follows: Figure 4 As shown in (a) of the diagram. According to Figure 4 As can be seen from (a) in the figure, the glass transition temperature of Example 1 is -74.9 ℃; the Arrhenius fitting results are as follows: Figure 4 As shown in (b) in the figure, according to Figure 4 As can be seen from (b) in the figure, the ion transport activation energy of Example 1 is 0.22 eV.

[0063] 4) Using a Li||Li symmetric cell, the DC polarization and AC impedance of the polycation-anion-anion-anion-supported solid polymer electrolyte of Example 1 were jointly tested. The results are as follows: Figure 4As shown in (c) of the diagram. According to... Figure 4 As can be seen from (c) in Example 1, the lithium-ion transference number is 0.54.

[0064] 5) Linear sweep voltammetry, Tafel analysis, and critical current density testing were performed on the polycationically anchored bi-anionally solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1. The scan rate was 1 mV / s to evaluate oxidation stability (oxidation current exceeding 10 μA). The results are as follows: Figure 4 As shown in (d)~(f). According to Figure 4 As can be seen from (d) in the figure, when the oxidation current reaches 10 μA, the oxidation decomposition potential of the polycationically anchored bi-anionally solid polymer electrolyte of Example 1 is approximately 5.1 V (vs. Li). + / Li); according to Figure 4 As can be seen from (e), the Tafel test shows that the polycationically anchored bi-anionally solid polymer electrolyte of Example 1 has an exchange current density of 0.109 mA·cm⁻¹. -2 ;according to Figure 4 As can be seen from (f) in the figure, the critical current density test shows that the critical current density of the polycationically anchored bi-anionally solid polymer electrolyte in Example 1 is 1.3 mA·cm⁻¹. -2 .

[0065] Test Example 4: The lithium-symmetric battery cycling and negative electrode interface analysis of the polycation-anion-anion-anionic solid polymer electrolyte of Example 1 are as follows: 1) The polycation-anion-anion-anion solid polymer electrolyte of Example 1 and the solid polymer electrolyte of Comparative Example 1 were used in Li||Li symmetric cells, respectively, at 25 °C and 0.1 mA·cm⁻¹. -2 0.1 mAh·cm -2 Under these conditions, constant current cycling was performed, and the results are as follows: Figure 5 As shown in (a) of the diagram. According to Figure 5 As can be seen from (a), the battery can cycle stably for 4000 h with a low polarization voltage; when the current density and areal capacity are increased to 0.2 mA·cm⁻¹ -2 and 0.2 mAh·cm -2 Even at this time, the battery can still cycle stably for more than 3000 hours.

[0066] 2) After the above cycles, the surface of the lithium anode of the battery using the polycation-anion-anion-anionic solid polymer electrolyte of Example 1 or the solid polymer electrolyte of Comparative Example 1 was observed by scanning electron microscopy. The results are as follows: Figure 5 (b) and Figure 6 As shown in (c) of the diagram. According to... Figure 5 (b) and Figure 6 As can be seen from (c) in Example 1, the lithium anode of the battery with polycation-anion-anion-anionic solid polymer electrolyte has a smooth, dense, and continuous surface; while the lithium anode of the battery with solid polymer electrolyte in Comparative Example 1 has obvious grooves and wrinkles on its surface.

[0067] 3) Using XPS combined with Ar + Gas-puff ion beam depth profiling was used to analyze the SEI composition on the surface of the lithium anode of the battery using the polycation-anion-anion-modified solid polymer electrolyte of Example 1, and the VEIMTFSI-mediated mechanism was analyzed. The results are as follows: Figure 6 As shown in (a)~(b) and (d)~(f). According to Figure 6 As shown in (a)~(b) and (d)~(f), the system of this invention forms an organic outer layer / inorganic inner layer gradient SEI on the surface of the lithium anode. The outer layer contains components such as CF and BF, gradually transforming into an inorganic enriched layer dominated by LiF towards the inner layer, accompanied by the presence of nitrogen-containing components related to the decomposition of Li3N and imidazolium. This gradient SEI is beneficial for improving the interfacial mechanical stability and promoting lithium-ion cross-interfacial transport.

[0068] Test Example 5: The full-cell performance of the polycation-anion-anion-anion solid polymer electrolyte of Example 1 was verified as follows: 1) A positive electrode slurry was prepared using LFP, Super P, and PVDF, with a mass ratio of LFP to Super P of 8:1 and a mass ratio of LFP to PVDF of 8:1. The slurry was coated onto aluminum foil and vacuum dried at 80 °C for 12 h to obtain an active material surface loading of 2 mg·cm³. -2 The LFP positive electrode was used. The LFP positive electrode, along with a lithium negative electrode and the polycation-anion-anion-supported solid polymer electrolyte from Example 1, were assembled into a Li||LFP full cell for testing. The results are as follows: Figure 7 and Figure 8As shown (where Ref.[1] is J. Chen, C. He, X. Peng, et al., Nat. Commun. 16 (2025) 8494, Ref.[2] is L. Wang, SZYi, QQ Liu, et al., Energy Storage Mater. 63 (2023) 102961, Ref.[3] is L. Tang, B. Chen, Z. Zhang, et al., Nat. Commun. 14 (2023) 2301, Ref.[4] is Y. Li, P. Ding, L. Cai, et al., Adv. Energy Mater. 15 (2025) 2501056, Ref.[5] is B. Kim, SH Yang, JH Seo, YC Kang, Adv. Funct. Mater. 34 (2024) 2310957). According to Figure 7 and Figure 8 It can be seen that, under the conditions of 25 ℃ and 1 C, the initial discharge specific capacity is 126.9 mAh g. -1 After 800 cycles, the capacity retention rate was 80.0%, and the average coulombic efficiency was 99.99%. Under 25 °C and 2 C conditions, the capacity retention rate remained at 80.0% after 600 cycles. Rate testing showed that the battery could provide 163.7, 159.1, 146.0, 130.0, 106.9, and 67.9 mAh g⁻¹ at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 5 C, respectively. -1 The reversible capacity; Example 1 shows higher performance compared to previously reported VEC-based electrolytes.

[0069] 2) The polycation-anion-anion-anion solid polymer electrolyte from Example 1 was further used in Li||NCM811 full cells for testing, and the results are as follows: Figure 9 As shown in (a) of the diagram. According to Figure 9 As can be seen from (a) above, under the conditions of 25 °C and 0.5 C, its initial discharge specific capacity is 165.6 mAh g. -1 After 300 cycles, the capacity retention rate was 81.9%.

[0070] 3) The polycation-anion-anion-anion solid polymer electrolyte from Example 1 was further assembled into a Li||NCM811 pouch cell, and the results are as follows: Figure 9 As shown in (b) to (c) of the diagram. According to... Figure 9As can be seen from (b) to (c), under the conditions of 25 ℃ and 0.2 C, the discharge specific capacity can be increased from 158.1 mAh g⁻¹. -1 Maintained at 152.7 mAh g -1 The coulombic efficiency remained above 99.0%; after partial cutting and half-cutting tests, the soft-pack battery could still maintain stable power supply, indicating that the polycation-anion-anion solid polymer electrolyte of Example 1 has good application safety.

[0071] Test Example 6: X-ray photoelectron spectroscopy and transmission electron microscopy were used to analyze the CEI depth of the LFP cathode in the Li||LFP full cell of Test Example 5, and the cathode interface film was verified. Furthermore, following the method used for the Li||LFP full cell in Test Example 5, a Li||LFP full cell with a solid polymer electrolyte in Comparative Example 1 was assembled, and the above tests were performed. The results are as follows: Figure 10 As shown.

[0072] according to Figure 10 It can be seen that the LFP cathode surface of Example 1 forms a dense CEI film with a thickness of 2 nm, which differs in morphology from Comparative Example 1. The outer layer contains organic / fluorine-containing components such as CF and BF, and gradually transforms into an inorganic enrichment layer containing more LiF, Li3N, and boron-containing inorganic substances towards the inner layer. Combined with theoretical calculations, it can be known that VEIM... + The strong interaction between the lithium anode and the LFP surface facilitates the enrichment and synergistic decomposition of anions near the interface. These results demonstrate that the present invention can not only stabilize the lithium anode interface but also simultaneously stabilize the high-voltage cathode interface.

[0073] Test Example 7: The solid polymer electrolyte prepared in Comparative Example 1 was characterized and tested as follows: 1) Ion transport and electrochemical performance analysis: The solid polymer electrolyte of Comparative Example 1 was characterized using the same electrochemical testing methods as in Example 1, and the results are as follows: Figure 4 As shown in the figure. Characterization results indicate that its ionic conductivity at 25 °C is 0.12 mS·cm. -1 The lithium-ion transference number is 0.30; according to Figure 4 It can be seen that its glass transition temperature is -69.2 ℃, its ion migration activation energy is 0.30 eV, and its oxidative decomposition potential is approximately 4.4 V (vs. Li). + / Li), with an exchange current density of 0.0357 mA·cm. -2 The critical current density is 0.7 mA·cm. -2Compared to Example 1, Comparative Example 1 lacks a polycationic framework and a bi-anionic environment, resulting in significantly poorer ion transport capabilities, interfacial kinetics, and high-voltage stability.

[0074] 2) Cycling and Interface Analysis of Lithium-ion Symmetric Batteries: The solid polymer electrolyte of Comparative Example 1 was used in a Li||Li symmetric cell at 25 °C and 0.1 mA·cm⁻¹. -2 0.1mAh·cm -2 Cycling was performed under these conditions. Test results showed that the battery experienced a short circuit after 2060 hours, and the voltage fluctuations during cycling increased significantly. Scanning electron microscopy (SEM) images of the lithium anode surface after cycling are shown below. Figure 6 As shown in (c), according to Figure 6 As can be seen in (c), the negative electrode surface exhibits obvious grooves, wrinkles, and rough deposits. The XPS depth profile results for Comparative Example 1 are as follows... Figure 11 As shown. According to Figure 11 The results show that its SEI tends to form a single inorganic film layer dominated by LiF, lacking the gradient characteristics of organic outer layer / inorganic inner layer in Example 1, thus resulting in poor interface compatibility and long-term stability.

[0075] 3) Full battery performance analysis: The solid polymer electrolyte of Comparative Example 1 was used in a Li||LFP full cell, and the test was conducted using the same method as in Test Example 5. The results are as follows: Figure 7 As shown. According to Figure 7 It can be seen that, under the conditions of 25 ℃ and 1 C, the initial discharge specific capacity is 103.7 mAh·g. -1 After 600 cycles, the concentration decreased to 62.2 mAh·g. -1 The capacity retention rate was 60%; however, after 300 cycles at 25 °C and 2 °C, the capacity retention rate was less than 50.0%. These results indicate that using only a single anion VEC-based polymer electrolyte cannot simultaneously meet the requirements of high-rate, high-voltage, and long-cycle applications.

[0076] The embodiments of the present invention have been described above; however, these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the above embodiments of the present invention without inventive effort are within the protection scope of the present invention.

Claims

1. A polycationically anchored bi-anionally charged solid polymer electrolyte, characterized in that, It is prepared from the following raw materials: Vinylvinylene carbonate, 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, lithium source, crosslinking agent and thermal initiator; The lithium source is lithium difluorooxalate borate; LiDFOB is the sole source of lithium salts, while VEIMTFSI serves as both a comonomer and a source of TFSI. - It forms a polycation-anchored bi-anion environment.

2. The polycationically anchored bi-anionally solid polymer electrolyte according to claim 1, characterized in that, The mass ratio of the vinylidene carbonate to 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide is 100:24~26; The mass ratio of the vinylidene carbonate to the lithium source is 100:20~22; The mass ratio of the vinylidene carbonate to the crosslinking agent is 100:3~5; The ratio of the total mass of the vinylidene carbonate and 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide to the mass of the thermal initiator is 100:2.5~3.

5.

3. The polycationically anchored bi-anionally solid polymer electrolyte according to claim 1, characterized in that, The crosslinking agent is an acrylamide-based crosslinking agent; The acrylamide crosslinking agent is N,N′-methylenebisacrylamide.

4. The method for preparing the polycationically anchored bi-anionally solid polymer electrolyte according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Under an inert atmosphere, vinylidene carbonate, lithium difluorooxalate borate, crosslinking agent, 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide and thermal initiator are mixed to obtain an electrolyte precursor solution. (2) The electrolyte precursor solution is introduced into the diaphragm or the electrode / diaphragm interface, and the electrolyte precursor solution is infiltrated into the porous support framework and the electrode surface and then thermally polymerized in situ to obtain the polycation-anion-anion solid polymer electrolyte.

5. The preparation method according to claim 4, characterized in that, The first mixing is a stirring mixture; The first mixing time is 5.5~6.5 h; The first mixing was carried out in an argon glove box with both water and oxygen content below 0.1 ppm.

6. The preparation method according to claim 4, characterized in that, The amount of electrolyte precursor solution introduced into the diaphragm or electrode / diaphragm interface is 28~32μL per side; The introduction of the diaphragm or electrode / diaphragm interface is carried out in an argon glove box with both water and oxygen content below 0.1 ppm.

7. The preparation method according to claim 4, characterized in that, The immersion temperature is 28~32 ℃, and the immersion time is 5.5~6.5 h; The impregnation was carried out under static conditions; The immersion was carried out in an argon glove box with both water and oxygen content below 0.1 ppm.

8. The preparation method according to claim 4, characterized in that, The in-situ thermal polymerization temperature is 60~80 ℃, and the holding time is 9~11 h; The in-situ thermal polymerization was carried out in an argon glove box with both water and oxygen contents below 0.1 ppm.

9. The application of a polycation-anion-anion-anionic solid polymer electrolyte in solid-state lithium metal batteries, characterized in that, The polycationically anchored bianionic solid polymer electrolyte is the polycationically anchored bianionic solid polymer electrolyte according to any one of claims 1 to 3 or the polycationically anchored bianionic solid polymer electrolyte obtained by the preparation method according to any one of claims 4 to 8.

10. A solid-state lithium metal battery, characterized in that, The electrolyte includes the polycation-anion-anion solid polymer electrolyte according to any one of claims 1 to 3 or the polycation-anion-anion solid polymer electrolyte obtained by the preparation method according to any one of claims 4 to 8.

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