A eutectic-derived solid electrolyte, its preparation method, and a lithium-ion battery

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a eutectic-derived solid electrolyte, its preparation method, and a lithium-ion battery. The electrolyte is formed by mixing a eutectic bis(fluorosulfonyl)imide alkali metal salt with a metal oxide to form a heterojunction. The heterojunction interface exhibits Lewis acid-base interactions, including ternary bis(fluorosulfonyl)imide alkali metal salt-metal oxide electrolytes and binary bis(fluorosulfonyl)imide alkali metal salt-metal oxide electrolytes. The electrolyte is a solid powder at room temperature, with a low melting point, a low glass transition temperature, and a room temperature ionic conductivity of 0.07~0.1 mS·cm. ‑1 It exhibits an electrochemical stability window of -0.2 to 5.9 V and strong compatibility with the electrode interface. When used in solid-state lithium-ion batteries, the electrolyte demonstrates excellent cycle stability, high coulombic efficiency, and combines flame retardancy with environmental friendliness, showing great potential for application in energy storage.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a eutectic-derived solid electrolyte, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid growth in energy storage demand, solid-state lithium-ion batteries, which offer higher energy density and superior safety compared to traditional lithium-ion batteries using liquid electrolytes, have attracted widespread attention. Solid-state electrolytes, which provide excellent ionic conductivity and suppress dendrite formation, greatly contribute to the superior performance of solid-state batteries. Based on their chemical composition, solid-state electrolytes can be classified into four categories: oxides, sulfides, halides, and polymers.

[0003] Oxide-based solid electrolytes possess a wide electrochemical stability window (up to 4.5V), but their preparation requires high-temperature calcination and often faces the problem of poor electrode-electrolyte interface contact. Sulfide solid electrolytes exhibit excellent ionic conductivity and good ductility; however, their electrochemical instability under high-voltage cathode materials and poor moisture resistance (generating toxic H₂S gas) limit their practical applications. Halide solid electrolytes, while possessing high oxidation resistance, still face significant challenges due to their incompatibility with lithium metal anodes. Finally, polymer solid electrolytes demonstrate significant deformation capabilities, which is beneficial for achieving tight interfacial contact and simplifying assembly processes; however, their low room-temperature ionic conductivity and insufficient thermal stability restrict their development.

[0004] Currently, no single solid-state electrolyte can simultaneously meet all the stringent requirements of practical solid-state lithium batteries, especially in balancing electrochemical performance, interface compatibility, manufacturing feasibility, environmental sustainability, and intrinsic safety. Therefore, constructing multilayer solid-state electrolytes has become a widely adopted strategy to fully leverage the complementary advantages of different material systems. For example, combining oxides with polymer solid-state electrolytes not only improves the ionic conductivity of the polymer matrix but also alleviates the inherent interfacial contact problems of rigid oxides. Furthermore, employing a bilayer structure comprising an antioxidant layer (facing the positive electrode) and a reduction-resistant layer (facing the lithium metal anode) can effectively extend the overall electrochemical stability window. However, the assembly process of multilayer solid-state electrolytes inevitably reduces the battery's energy density and increases additional manufacturing complexity. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a eutectic-derived solid electrolyte, its preparation method, and a lithium-ion battery. This invention forms T-AMFSI-MO through eutectic derivatization. x (Tripartite bis(fluorosulfonyl)imide alkali metal salt-metal oxide) or D-AMFSI-MO x(Bibasic bis(fluorosulfonyl)imide alkali metal salt-metal oxide), MO x The strong interaction with FSI⁻ weakens the binding energy between Li⁺ and FSI⁻ and catalyzes the decoupling of Li⁺. This interaction simultaneously induces local structural perturbations and topological disorder, generating numerous defect microregions and forming permeation channels that promote rapid ion transport, thereby improving overall ionic conductivity. Secondly, the electrolyte's extremely low glass transition temperature endows it with excellent deformation capabilities at mild temperatures. This deformation property optimizes the contact between the electrolyte and electrodes, expands the electrochemical active area, and reduces interfacial impedance. This solves the problem of reduced battery energy density and increased manufacturing complexity in existing multilayer solid-state electrolyte assembly processes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a eutectic-derived solid electrolyte, wherein the eutectic-derived solid electrolyte is formed by mixing a eutectic bis(fluorosulfonyl)imide alkali metal salt with a metal oxide to form a heterojunction, the heterojunction interface having Lewis acid-base interactions, the eutectic bis(fluorosulfonyl)imide alkali metal salt being formed by eutectic melting of at least two bis(fluorosulfonyl)imide alkali metal salts; the amount of metal oxide used is 5 wt.% to 10 wt.% of the mass of the eutectic bis(fluorosulfonyl)imide alkali metal salt.

[0007] In a preferred embodiment of the present invention, the metal oxide is MO. x , M is Al, Ti, Ce, Li, Zr, La, Sn, Y or Si.

[0008] A second objective of this invention is to provide a method for preparing the above-mentioned eutectic-derived solid electrolyte, comprising the following steps: Using at least two bisfluorosulfonylimide alkali metal salts as raw materials, a eutectic melting process is carried out to obtain a bisfluorosulfonylimide alkali metal liquid; a metal oxide is added to the liquid and heated at 100℃~130℃ to form a heterojunction structure, thereby obtaining a eutectic derived solid electrolyte.

[0009] In a preferred embodiment of the present invention, the eutectic bisfluorosulfonyl imide alkali metal salt is at least two of lithium bisfluorosulfonyl imide, potassium bisfluorosulfonyl imide, cesium bisfluorosulfonyl imide, sodium bisfluorosulfonyl imide, and rubidium bisfluorosulfonyl imide.

[0010] In a preferred embodiment of the present invention, when there are two eutectic bis(fluorosulfonyl)imide alkali metal salts, the molar ratio of any two salts is 31~69:31~69.

[0011] In a preferred embodiment of the present invention, when the eutectic alkali metal salt of bisfluorosulfonylimide is any three of lithium bisfluorosulfonylimide, potassium bisfluorosulfonylimide, cesium bisfluorosulfonylimide, and sodium bisfluorosulfonylimide, the molar ratio of any three salts is 25~40:25~40:25~40.

[0012] In a preferred embodiment of the present invention, the heating time is 1h to 3h.

[0013] A third objective of this invention is to provide a lithium-ion battery comprising a positive electrode, a lithium negative electrode, a glass fiber separator, and an electrolyte, wherein the electrolyte is the aforementioned eutectic-derived solid electrolyte.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a eutectic-derived solid electrolyte, obtained by heating and mixing a eutectic bis(fluorosulfonyl)imide alkali metal salt and a metal oxide; significant Lewis acid-base interactions exist between the eutectic bis(fluorosulfonyl)imide alkali metal salt and the metal oxide at the heterogeneous interface, thereby obtaining a homogeneous eutectic-derived solid electrolyte. Firstly, the T-AMFSI-MO formed by eutectic derivatization in this invention... x or D-AMFSI-MO x Because of the metal oxide MO x The strong interaction with FSI⁻ anions effectively weakens the binding energy between Li⁺ and FSI⁻ and catalyzes the decoupling of Li⁺. This interaction simultaneously induces local structural perturbations and topological disorder, generating numerous defect microregions and forming permeation channels that promote rapid ion transport, ultimately significantly improving the overall ionic conductivity. Secondly, the electrolyte exhibits an extremely low glass transition temperature, thus possessing excellent deformation capability at mild temperatures. This deformation characteristic optimizes the contact between the electrolyte and the electrode, thereby effectively expanding the electrochemical active area and significantly reducing the interfacial impedance caused by porosity. This structure addresses the problems of reduced battery energy density and increased manufacturing complexity in the assembly of existing multilayer solid-state electrolytes.

[0015] 2. The eutectic-derived solid electrolyte provided by this invention exhibits high ionic conductivity and excellent ion transport performance. Specifically, LiKCsFSI-5%Al2O3 achieves a room-temperature ionic conductivity of 0.1 mS·cm. -1 At 30℃, it rises to 0.14 mS·cm -1 The LiKCsFSI-MO exhibits significantly higher ionic conductivity than pure LiKFSI at 30°C, meeting the ion transport requirements of solid-state lithium-ion batteries. Furthermore, the solid electrolyte possesses a wide electrochemical stability window, making it suitable for high-voltage cathode materials. xThe electrolyte has an electrochemical stability window of -0.1V to 5.7V (relative to Li). + LiKFSI-10%Li2O also reaches -0.2~5.9V, which is much wider than traditional sulfide, oxide, halide and PEO-based electrolytes. It is perfectly compatible with high voltage cathode materials such as 4.8V high voltage lithium manganese oxide and 4.5V lithium cobalt oxide, breaking through the voltage compatibility limitations of traditional electrolytes.

[0016] 3. This invention provides a method for preparing eutectic-derived solid electrolytes, which is simple to operate, operates under mild conditions, has good process repeatability, and is applicable to the entire series of T-AMFSI-MOs. x Electrolyte preparation; simultaneously, depending on cost requirements, low-cost D-AMFSI-MO can be prepared by removing high-valent CsFSI using the same eutectic derivatization process. x The electrolyte significantly reduces raw material costs while slightly sacrificing some ionic conductivity, enabling flexible adaptation between high-performance and low-cost versions to meet the needs of different application scenarios.

[0017] 4. This invention provides a lithium-ion battery in which the eutectic-derived electrolyte is heated to a molten state and injected into the separator during battery assembly, forming a tight interfacial contact with the electrodes. This significantly increases the microscopic contact area and completely solves the problem of poor interfacial contact in traditional inorganic solid electrolytes. No additional external stacking pressure is required during battery assembly and use, simplifying the battery manufacturing process. Furthermore, the electrolyte of this invention exhibits good interfacial compatibility with lithium anodes and various cathode materials, and the charge transfer resistance and interfacial impedance remain stable during charging and discharging, with no significant side reactions. When LiKCsFSI-5%Al2O3 was matched with LFP, the capacity retention rate reached 98.7% after 200 cycles at 30℃ and 1C, with an average coulombic efficiency of 99.7%. When matched with LRMO, the capacity retention rate was 81.1% after 80 cycles at 0.4C, and the coulombic efficiency exceeded 99% after the initial cycle. The low-cost LiKFSI-10%Li2O matched with LFP and LCO showed a capacity retention rate of over 98.5% after 60-70 cycles, with an average coulombic efficiency of nearly 100%, which is far superior to LiKCsFSI and LiKFSI-based electrolytes without added metal oxides. Attached Figure Description

[0018] Figure 1 The present invention is LiKFSI-MO x A schematic diagram illustrating the function of electrolytes. Figure 1 Figure a shows the crystal structures of LiFSI, KFSI, and CsFSI; Figure b is a schematic diagram of the eutectic derivatization process; and Figure c shows the crystal structure of MO. x A schematic diagram of the interaction between ions and FSI⁻ ions.

[0019] Figure 2These are physical images of the solid electrolytes of Examples 1 to 6 of the present invention. Figure 2 Figure a is a physical picture of Example 1, Figure b is a physical picture of Example 3, Figure c is a physical picture of Example 5, Figure d is a physical picture of Example 2, Figure e is a physical picture of Example 4, and Figure f is a physical picture of Example 6.

[0020] Figure 3 These are thermal analysis diagrams of the solid electrolytes in Examples 1 to 6 of the present invention. Figure 3 Figure a is the thermal analysis diagram of Example 1, Figure b is the thermal analysis diagram of Example 3, Figure c is the thermal analysis diagram of Example 5, Figure d is the thermal analysis diagram of Example 2, Figure e is the thermal analysis diagram of Example 4, and Figure f is the thermal analysis diagram of Example 6.

[0021] Figure 4 The diagram shows the ionic conductivity of the solid electrolytes in Examples 1 to 6 and Comparative Example 1 of this invention.

[0022] Figure 5 The images show the XRD patterns of the solid electrolytes of Examples 1 to 6 and Comparative Example 1 of this invention.

[0023] Figure 6 This is a linear sweep voltammetry curve of the solid electrolyte in Example 1 of the present invention.

[0024] Figure 7 This is a comparison diagram of the electrochemical windows of the solid electrolyte in Example 1 of the present invention.

[0025] Figure 8 The figures show the electrochemical performance of the Li / LiKCsFSI-5%Al2O3 / LFP battery and the Li / LiKCsFSI-5%Al2O3 / LRMO battery of this invention. Figure 8 Figure a shows the rate performance of the LFP-based battery, Figure b shows the cycle performance of the LFP-based battery, Figure c shows the constant current charge-discharge curve of the LFP-based battery, Figure d shows the cycle performance of the LRMO-based battery, Figure e shows the constant current charge-discharge curve of the LRMO-based battery, Figure f shows the off-site relaxation time distribution analysis of the LFP-based battery, and Figure g shows the off-site relaxation time distribution analysis of the LRMO-based battery.

[0026] Figure 9 This is a constant current charge-discharge curve of the Li / LiKCsFSI / LFP battery of the present invention.

[0027] Figure 10 The above are linear sweep voltammetry curves of the solid electrolytes in Examples 2 to 6 of this invention. Figure 10Figure a shows the LiKCsFSI-10%Al2O3, Figure b shows the LiKCsFSI-5%TiO2, Figure c shows the LiKCsFSI-10%TiO2, Figure d shows the LiKCsFSI-5%CeO2, and Figure e shows the LiKCsFSI-10%CeO2.

[0028] Figure 11 The diagram shows the cycle performance of different Li / SE / LFP full cells of this invention.

[0029] Figure 12 This is a physical image of the solid electrolyte of Embodiment 7 of the present invention.

[0030] Figure 13 This is a thermal analysis diagram of the solid electrolyte in Example 7 of the present invention.

[0031] Figure 14 The figures show the electrochemical performance of the Li / LiKFSI-10%Li2O / LFP battery and the Li / LiKFSI-10%Li2O / LCO battery of this invention. Figure 14 Figure a shows the ionic conductivity of LiKFSI-10%Li2O and LiKFSI; Figure b shows the XRD patterns of LiKFSI-10%Li2O, LiKFSI, and Li2O; Figure c shows the linear sweep voltammetry of LiKFSI-10%Li2O; Figure d shows the electrochemical window comparison of LiKFSI-10%Li2O; Figure e shows the rate performance of the LFP-based battery; Figure f shows the rate performance of the LCO-based battery; Figure g shows the cycle performance of the LFP-based battery; Figure h shows the constant current charge-discharge curve of the LFP-based battery; Figure i shows the cycle performance of the LCO-based battery; and Figure j shows the constant current charge-discharge curve of the LCO-based battery.

[0032] Figure 15 The figures show the electrochemical performance of the Li / LiKFSI / LFP and Li / LiKFSI / LCO batteries of this invention. Figure 15 Figure a shows the constant current charge-discharge curve of the LFP-based battery, and Figure b shows the constant current charge-discharge curve of the LCO-based battery. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0035] Existing multilayer assembled electrolytes inevitably reduce energy density and increase processing difficulty. Therefore, it is crucial to develop monolayer solid electrolytes with high ionic conductivity, enhanced mechanical compatibility, and a wide electrochemical window.

[0036] Based on this, firstly, the present invention provides a eutectic-derived solid electrolyte, which is formed by mixing a eutectic bis(fluorosulfonyl)imide alkali metal salt with a metal oxide to form a heterojunction. The heterojunction interface has Lewis acid-base interactions. The eutectic bis(fluorosulfonyl)imide alkali metal salt is formed by eutectic melting of at least two bis(fluorosulfonyl)imide alkali metal salts. The amount of metal oxide used is 5 wt.% to 10 wt.% of the mass of the eutectic bis(fluorosulfonyl)imide alkali metal salt.

[0037] The metal oxide is MO. x M is Al, Ti, Ce, Li, Zr, La, Sn, Y, or Si. The metal oxide is preferably Al2O3, TiO2, CeO2, Li2O, ZrO2, La2O3, SnO2, Y2O3, or SiO2, and more preferably Al2O3, TiO2, CeO2, or Li2O.

[0038] It should be noted that this invention utilizes the eutectic derivatization method to improve electrochemical performance, optimize interfacial contact, and expand the electrochemical window, with the aim of preparing a series of high-quality solid electrolytes.

[0039] In a preferred embodiment of the present invention, the solid electrolyte is LiKCsFSI-MO. x Electrolytes, their interactions are as follows Figure 1 As shown. Specifically, as Figure 1 a and 1b, amorphous LiKCsFSI can be synthesized by heating crystalline lithium, potassium, and cesium bis(fluorosulfonyl)imides (LiFSI, KFSI, and CsFSI). Compared with crystalline materials, amorphous materials have a larger free volume and weaker ion interactions, resulting in higher ionic conductivity. To further promote ion transport in LiKCsFSI materials, metal oxides (MO) are introduced. x ).like Figure 1 c, MO x It interacts strongly with FSI⁻ anions, thereby effectively weakening Li +The binding energy with FSI⁻ releases Li⁺ from the lithium salt. This interaction simultaneously induces local structural perturbations and topological disorder, generating numerous defect microregions and forming permeation channels that promote rapid ion transport. Therefore, the prepared LiKCsFSI-MO x The material exhibits significantly improved ionic conductivity. Furthermore, LiKCsFSI-MO x The electrolyte has an extremely low glass transition temperature, thus exhibiting excellent deformation capability at mild temperatures, thereby optimizing the contact between the electrolyte and the electrode. In addition to the above advantages, LiKCsFSI-MO prepared via eutectic derivatization... x The electrolyte also possesses an extremely wide electrochemical window, flame retardancy, and environmental friendliness, indicating its potential for practical applications. It should be noted that the remaining T-AMFSI-MO... x Electrolyte Mechanism of Action and LiKCsFSI-MO x Electrolytes are similar.

[0040] Secondly, this invention provides a method for preparing the above-mentioned eutectic-derived solid electrolyte, comprising the following steps: Using at least two bisfluorosulfonylimide alkali metal salts as raw materials, a eutectic melting process is carried out to obtain a bisfluorosulfonylimide alkali metal liquid; a metal oxide is added to the liquid and heated at 100℃~130℃ to form a heterojunction structure, thereby obtaining a eutectic derived solid electrolyte.

[0041] The alkali metal salt of bisfluorosulfonylimide is at least two of lithium bisfluorosulfonylimide (LiFSI), potassium bisfluorosulfonylimide (KFSI), cesium bisfluorosulfonylimide (CsFSI), sodium bisfluorosulfonylimide (NaFSI), and rubidium bisfluorosulfonylimide (RbFSI).

[0042] In a preferred embodiment, when the eutectic alkali metal salt of bisfluorosulfonylimide is any three of lithium bisfluorosulfonylimide, potassium bisfluorosulfonylimide, cesium bisfluorosulfonylimide, and sodium bisfluorosulfonylimide, the molar ratio of any three salts is 25~40:25~40:25~40. In a more preferred embodiment, when the salt is LiFSI, NaFSI, and KFSI, the molar ratio of LiFSI, NaFSI, and KFSI is 3:4:3. When the salt is LiFSI, NaFSI, and CsFSI, the molar ratio of LiFSI, NaFSI, and CsFSI is 3:4:3. When the salt is LiFSI, KFSI, and CsFSI, the molar ratio of LiFSI, KFSI, and CsFSI is 30:35:30. When the salts are NaFSI, KFSI, and CsFSI, the molar ratio of NaFSI, KFSI, and CsFSI is 40:25:35. It should be noted that RbFSI is not used as one of the three salts in the preferred scheme due to its higher cost.

[0043] When the alkali metal salt of bisfluorosulfonylimide is any three of lithium bisfluorosulfonylimide, potassium bisfluorosulfonylimide, cesium bisfluorosulfonylimide, and sodium bisfluorosulfonylimide, the preparation method of the eutectic derived solid electrolyte is as follows: Three salts were mixed, and the mixture was then heated to 100°C–130°C to obtain a transparent T-AMFSI liquid. A metal oxide was added to the liquid, and the mixture was stirred and heated at 100°C–130°C, followed by cooling to obtain T-AMFSI-MO. x Solid electrolytes derived from eutectic structures.

[0044] In this invention, due to the high cost of CsFSI and RbFSI, other salts besides these two were ultimately selected as the preferred option, thereby synthesizing a lower-cost D-AMFSI-MO through a eutectic derivatization process. x Electrolytes.

[0045] In a preferred embodiment, when there are two alkali metal salts of bis(fluorosulfonyl)imide, the molar ratio of any two salts is 31-69:31-69. In a more preferred embodiment, when the salts are LiFSI and NaFSI, the molar ratio of LiFSI to NaFSI is 4:6. When the salts are LiFSI and KFSI, the molar ratio of LiFSI to KFSI is 41:59. When the salts are LiFSI and RbFSI, the molar ratio of LiFSI to RbFSI is 38:62. When the salts are LiFSI and CsFSI, the molar ratio of LiFSI to CsFSI is 47:53. When the salts are NaFSI and KFSI, the molar ratio of NaFSI to KFSI is 56:44. When the salts are NaFSI and RbFSI, the molar ratio of NaFSI to RbFSI is 5:5. When the salts are NaFSI and CsFSI, the molar ratio of NaFSI to CsFSI is 47:53. When the salts are KFSI and RbFSI, the molar ratio of KFSI to RbFSI is 31:69. When the salts are KFSI and CsFSI, the molar ratio of KFSI to CsFSI is 54:46. When the salts are RbFSI and CsFSI, the molar ratio of RbFSI to CsFSI is 65:35.

[0046] When there are two alkali metal salts of bis(fluorosulfonyl)imide, the preparation method of the eutectic derived solid electrolyte is as follows: Two salts were mixed, and the mixture was then heated to 100°C–130°C to obtain a transparent D-AMFSI liquid. A metal oxide was added to the liquid, and the mixture was stirred and heated at 100°C–130°C, followed by cooling to obtain D-AMFSI-MO. x Solid electrolytes derived from eutectic structures.

[0047] It should be noted that the reaction mechanism involves a significant Lewis acid-base interaction between the eutectic bis(fluorosulfonyl)imide alkali metal salt and the metal oxide at the heterogeneous interface, resulting in a homogeneous eutectic-derived solid electrolyte.

[0048] The preferred temperature is 120℃, and the heating time after adding the metal oxide is 1h~3h, preferably 2h.

[0049] Finally, the present invention provides a lithium-ion battery comprising a positive electrode, a lithium negative electrode, a glass fiber separator, and an electrolyte, wherein the electrolyte is the aforementioned eutectic-derived solid electrolyte.

[0050] In the lithium-ion battery assembly process, the eutectic-derived solid electrolyte is heated to 100℃~130℃ and then injected into a glass fiber separator for assembly at 100℃~130℃. The positive electrode is composed of an active material, carbon black, polyvinylidene fluoride, and N-methyl-2-pyrrolidone in a mass ratio of 7:2:1. The active material is lithium-rich manganese oxide (LRMO), lithium iron phosphate (LFP), or lithium cobalt oxide (LCO).

[0051] The following specific examples will provide further explanation.

[0052] In this invention, the English abbreviation for lithium bisfluorosulfonylimide is LiFSI, the English abbreviation for potassium bisfluorosulfonylimide is KFSI, the English abbreviation for cesium bisfluorosulfonylimide is CsFSI, and the chemical formula for aluminum oxide is Al2O3.

[0053] Example 1 A method for preparing a eutectic derived solid electrolyte, namely LiKCsFSI-5%Al2O3, includes the following steps: 0.25 g of LiFSI, 0.33 g of KFSI, and 0.42 g of CsFSI were weighed and mixed. The mixture was then heated to 120 °C to obtain a transparent LiKCsFSI liquid. 0.05 g of Al2O3 was added to the transparent LiKCsFSI liquid, and the mixture was stirred and heated at 120 °C for 2 h, followed by cooling to obtain LiKCsFSI-5%Al2O3 solid electrolyte.

[0054] Example 2 A method for preparing a eutectic derived solid electrolyte, namely LiKCsFSI-10%Al2O3, includes the following steps: 0.25 g of LiFSI, 0.33 g of KFSI, and 0.42 g of CsFSI were weighed and mixed. The mixture was then heated to 120 °C to obtain a transparent LiKCsFSI liquid. 0.1 g of Al2O3 was added to the transparent LiKCsFSI liquid, and the mixture was stirred and heated at 120 °C for 2 h, followed by cooling to obtain LiKCsFSI-10%Al2O3 solid electrolyte.

[0055] Example 3 A method for preparing a eutectic derived solid electrolyte, namely LiKCsFSI-5%TiO2, includes the following steps: 0.25 g of LiFSI, 0.33 g of KFSI, and 0.42 g of CsFSI were weighed and mixed. The mixture was then heated to 120 °C to obtain a transparent LiKCsFSI liquid. 0.05 g of TiO2 was added to the transparent LiKCsFSI liquid, and the mixture was stirred and heated at 120 °C for 2 h, followed by cooling to obtain LiKCsFSI-5%TiO2 solid electrolyte.

[0056] Example 4 A method for preparing a eutectic-derived solid electrolyte, namely LiKCsFSI-10%TiO2, includes the following steps: 0.25 g of LiFSI, 0.33 g of KFSI, and 0.42 g of CsFSI were weighed and mixed. The mixture was then heated to 120 °C to obtain a transparent LiKCsFSI liquid. 0.1 g of TiO2 was added to the transparent LiKCsFSI liquid, and the mixture was stirred and heated at 120 °C for 2 h, followed by cooling to obtain LiKCsFSI-10%TiO2 solid electrolyte.

[0057] Example 5 A method for preparing a eutectic-derived solid electrolyte, namely LiKCsFSI-5%CeO2, includes the following steps: 0.25 g of LiFSI, 0.33 g of KFSI, and 0.42 g of CsFSI were weighed and mixed. The mixture was then heated to 120 °C to obtain a transparent LiKCsFSI liquid. 0.05 g of CeO2 was added to the transparent LiKCsFSI liquid, and the mixture was stirred and heated at 120 °C for 2 h, followed by cooling to obtain LiKCsFSI-5%CeO2 solid electrolyte.

[0058] Example 6 A method for preparing a eutectic-derived solid electrolyte, namely LiKCsFSI-10%CeO2, includes the following steps: Weigh out 0.25 g of LiFSI, 0.33 g of KFSI, and 0.42 g of CsFSI and mix them. Then heat the mixture to 120 °C to obtain a transparent LiKCsFSI liquid. Add 0.1 g of CeO2 to the transparent LiKCsFSI liquid, stir and heat at 120 °C for 2 h, and then cool to obtain LiKCsFSI-10%CeO2 solid electrolyte.

[0059] Example 7 A method for preparing a eutectic-derived solid electrolyte, namely LiKFSI-10%Li2O, includes the following steps: Weigh out 0.37 g of LiFSI and 0.63 g of KFSI and mix them. Then heat the mixture to 120 °C to obtain a transparent LiKFSI liquid. Add 0.1 g of Li2O to the transparent LiKFSI liquid, stir and heat at 120 °C for 2 h, and then cool to obtain LiKFSI-10%Li2O solid electrolyte.

[0060] Comparative Example 1 A method for preparing a solid electrolyte, LiKCsFSI, includes the following steps: Weigh 0.25g of LiFSI, 0.33g of KFSI and 0.42g of CsFSI and mix them. Then, stir and heat the mixture at 120℃ for 2 hours and then cool it to obtain LiKCsFSI solid electrolyte.

[0061] Comparative Example 2 A method for preparing a solid electrolyte, namely LiKFSI, includes the following steps: 0.37 g of LiFSI and 0.63 g of KFSI were weighed and mixed. The mixture was then stirred and heated at 120 °C for 2 h and then cooled to obtain LiKFSI solid electrolyte.

[0062] Electrochemical performance was tested using a CR2032 coin cell. The positive electrode material consisted of lithium-rich manganese oxide (LRMO), lithium iron phosphate (LFP), or lithium cobalt oxide (LCO) as the active material, which was mixed with carbon black and polyvinylidene fluoride (PVDF) in a 7:2:1 mass ratio in 33 parts N-methyl-2-pyrrolidone (NMP). The resulting electrode was then dried under vacuum at 90°C for 12 hours. The prepared solid electrolyte was heated to 120°C and then injected into a glass fiber separator, followed by conventional coin cell assembly while still hot. The assembly sequence was: positive electrode shell, aluminum foil, positive electrode sheet, glass fiber separator with solid electrolyte, negative electrode, gasket, spring sheet, and negative electrode shell. To evaluate cycle performance, the battery was cycled several times at a low current, followed by the remaining cycles at a high current.

[0063] Figure 2 These are physical images of the solid electrolytes of Examples 1 to 6 of the present invention. Figure 2 Figure a is a physical photograph of Example 1, Figure b is a physical photograph of Example 3, Figure c is a physical photograph of Example 5, Figure d is a physical photograph of Example 2, Figure e is a physical photograph of Example 4, and Figure f is a physical photograph of Example 6. Figure 2 It can be seen that these LiKCsFSI-MO x The material is a solid powder at room temperature and does not exhibit a significant tendency to flow.

[0064] Figure 3 These are thermal analysis diagrams of the solid electrolytes in Examples 1 to 6 of the present invention. Figure 3 Figure a shows the thermal analysis diagram of Example 1, Figure b shows the thermal analysis diagram of Example 3, Figure c shows the thermal analysis diagram of Example 5, Figure d shows the thermal analysis diagram of Example 2, Figure e shows the thermal analysis diagram of Example 4, and Figure f shows the thermal analysis diagram of Example 6. Figure 3 It can be seen that differential scanning calorimetry (DSC) was used to study the LiKCsFSI-MO x Thermal analysis of the materials revealed that their melting points were all above room temperature.

[0065] Figure 4 These are the electrochemical impedance spectroscopy spectra of the solid electrolytes from Examples 1 to 6 and Comparative Example 1 of the present invention. Figure 4 As shown, at room temperature, LiKCsFSI-5%Al2O3 has a flux density of 0.1 mS·cm. -1 High electrical conductivity, approaching that of other LiKCsFSI-MO x The electrical conductivity of the material (LiKCsFSI-10%Al2O3) is 0.08 mS·cm. -1 The LiKCsFSI-5%TiO2 concentration is 0.09 mS·cm. -1 The LiKCsFSI-10%TiO2 concentration is 0.09 mS·cm. -1 The LiKCsFSI-5%CeO2 concentration is 0.07 mS·cm. -1 The LiKCsFSI-10%CeO2 concentration is 0.08 mS·cm. -1 When the temperature rises to 30℃, the ionic conductivity of LiKCsFSI-5%Al2O3 can reach 0.14 mS·cm. -1 It is much higher than LiKCsFSI (0.03 mS·cm). -1 To explain this phenomenon, X-ray powder diffraction (XRD) was performed.

[0066] Figure 5 The images show the XRD patterns of the solid electrolytes from Examples 1 to 6 and Comparative Example 1 of this invention. Figure 5As shown, LiKCsFSI-MO x Similar to LiKCsFSI, the material exhibits no obvious diffraction peaks, indicating that its main phase is amorphous. The difference lies in LiKCsFSI-MO. x A small number of weak crystallization peaks corresponding to metal oxides were observed. This may be due to the introduction of these metal oxides leading to the formation of LiKCsFSI and LiKCsFSI-MO. x Differences in the ionic conductivity of materials.

[0067] Due to its excellent ionic conductivity, the LiKCsFSI-5%Al2O3 sample was used as a solid electrolyte. Traditional solid electrolytes have a small microscopic contact area with electrode materials, which limits ion transport. In contrast, the LiKCsFSI-5%Al2O3 sample exhibits excellent deformation capability at mild temperatures due to its low glass transition temperature. This deformation property optimizes the contact between the electrolyte and the electrode, thus eliminating the need for additional pressure to maintain a tight contact in batteries using the LiKCsFSI-5%Al2O3 electrolyte.

[0068] In addition to its excellent ionic conductivity and interfacial contact, the LiKCsFSI-5%Al2O3 solid electrolyte is also compatible with many high-voltage cathodes and lithium anodes, exhibiting an ultra-wide electrochemical stability window.

[0069] Figure 6 This is a linear sweep voltammetry curve of the solid electrolyte in Example 1 of the present invention. Figure 6 As shown, linear sweep voltammetry (LSV) measurements revealed that the LiKCsFSI-5%Al2O3 solid electrolyte undergoes severe oxidation only above 5.7V, and below -0.1V (relative to Li). + / Li) undergoes severe reduction.

[0070] Figure 7 This is a comparative electrochemical window diagram of the solid electrolyte in Example 1 of the present invention. For example... Figure 7 As shown, this material has the widest electrochemical window compared to common sulfide, oxide, halide, and PEO-based electrolytes.

[0071] Subsequently, the Li / LiKCsFSI-5%Al2O3 / LFP and LRMO full cells were tested at 30 °C.

[0072] Figure 8 The figures show the electrochemical performance of the Li / LiKCsFSI-5%Al2O3 / LFP battery and the Li / LiKCsFSI-5%Al2O3 / LRMO battery of this invention. Figure 8Figure a shows the rate performance of the LFP-based battery; figure b shows the cycle performance of the LFP-based battery; figure c shows the constant current charge-discharge curve of the LFP-based battery; figure d shows the cycle performance of the LRMO-based battery; figure e shows the constant current charge-discharge curve of the LRMO-based battery; figure f shows the off-site relaxation time distribution analysis of the LFP-based battery; and figure g shows the off-site relaxation time distribution analysis of the LRMO-based battery. Figure 8 It can be seen that the Li / LiKCsFSI-5%Al2O3 / LFP full cell exhibits stable capacity at current densities ranging from 0.2 to 1C. At a current density of 1C, it can provide 141 mAh·g. -1 The high capacity demonstrates its excellent charge-discharge performance. Furthermore, the full battery retains 139.4 mAh / g after 200 cycles at a 1C current density. -1 The battery exhibits a high discharge capacity and demonstrates an extremely high capacity retention of 98.7%. The average coulombic efficiency is 99.7%, approaching 100%. Furthermore, when the Li / LiKCsFSI-5%Al2O3 / LRMO battery is charged to 4.8V at 0.4C and discharged to 2V for 80 cycles, it still provides 191.6 mAh·g. -1 The high discharge capacity was maintained at 81.1%. During the initial cycling, the coulombic efficiency rapidly increased to over 99%, indicating good compatibility between the LiKCsFSI-5%Al2O3 electrolyte and the 4.8V anode. In vitro electrochemical impedance spectroscopy (EIS) and relaxation time distribution (DRT) analyses were performed on the Li / LiKCsFSI-5%Al2O3 / LFP and Li / LiKCsFSI-5%Al2O3 / LRMO batteries to investigate the evolution of interfacial impedance under various charge-discharge states. Figure 8 The DRT decomposition plots corresponding to f and 8g reveal two main relaxation processes: 1) charge transfer resistance (RCT) in the low-frequency components, and 2) interfacial resistance (RINT) in the mid-frequency characteristics. Clearly, these batteries using LiKCsFSI-5%Al2O3 electrolyte exhibit both stable charge transfer resistance and interfacial impedance. Stable impedance is a key characteristic of long-cycle stability (…). Figure 8 b and 8d) provide reasonable explanations.

[0073] Figure 9 This is a constant current charge-discharge curve of the Li / LiKCsFSI / LFP battery of the present invention. Figure 9 As shown, the discharge capacity of the Li / LiKCsFSI / LFP battery rapidly decays to almost zero within a few cycles.

[0074] In addition, LiKCsFSI-10%Al2O3, LiKCsFSI-5%TiO2, LiKCsFSI-10%TiO2, LiKCsFSI-5%CeO2 and LiKCsFSI-10%CeO2 can also be used as solid electrolytes.

[0075] Figure 10 The above are linear sweep voltammetry curves of the solid electrolytes in Examples 2 to 6 of this invention. Figure 10 Figure a shows the LiKCsFSI-10%Al2O3 graph, figure b shows the LiKCsFSI-5%TiO2 graph, figure c shows the LiKCsFSI-10%TiO2 graph, figure d shows the LiKCsFSI-5%CeO2 graph, and figure e shows the LiKCsFSI-10%CeO2 graph. Figure 10 As shown, these electrolytes undergo severe oxidation at approximately 5.7V, demonstrating excellent antioxidant properties.

[0076] Figure 11 The diagram shows the cycle performance of different Li / SE / LFP full cells of this invention. Figure 11 As shown, Li / SE (LiKCsFSI-10%Al2O3, LiKCsFSI-5%TiO2, LiKCsFSI-10%TiO2, LiKCsFSI-5%CeO2, and LiKCsFSI-10%CeO2) / LFP full cells exhibit excellent cycling performance. These electrolytes achieve a 132.6 mAh·g eluent after 100 cycles at 1C. -1 143.0 mAh·g -1 143.1 mAh·g -1 144.5mAh·g -1 and 132.4 mAh·g -1 The high discharge capacity. The corresponding capacity retention rates are 89.5%, 88.7%, 88.5%, 90.0%, and 88.0%, respectively.

[0077] Figure 12 This is a physical image of the solid electrolyte of Embodiment 7 of the present invention. Figure 12 As shown, the LiKFSI-10%Li2O sample is in the form of a solid powder.

[0078] Figure 13 This is a thermal analysis diagram of the solid electrolyte in Example 7 of the present invention. Figure 13 The DSC curve in the image shows its melting point (T). m ) and glass transition temperature (T gThe temperatures are 53℃ and -14℃, respectively. Similar to the LiKCsFSI-MOx material mentioned above, the low melting point and low glass transition temperature give the LiKFSI-10%Li2O sample the characteristic of not requiring external pressure.

[0079] Figure 14 The figures show the electrochemical performance of the Li / LiKFSI-10%Li2O / LFP battery and the Li / LiKFSI-10%Li2O / LCO battery of this invention. Figure 14 Figure a shows the ionic conductivity of LiKFSI-10%Li2O and LiKFSI; Figure b shows the XRD patterns of LiKFSI-10%Li2O, LiKFSI, and Li2O; Figure c shows the linear sweep voltammetry of LiKFSI-10%Li2O; Figure d shows the electrochemical window comparison of LiKFSI-10%Li2O; Figure e shows the rate performance of the LFP-based battery; Figure f shows the rate performance of the LCO-based battery; Figure g shows the cycle performance of the LFP-based battery; Figure h shows the constant current charge-discharge curve of the LFP-based battery; Figure i shows the cycle performance of the LCO-based battery; and Figure j shows the constant current charge-discharge curve of the LCO-based battery.

[0080] like Figure 14 As shown in Figure a, the conductivity of the LiKFSI-10%Li₂O sample at 30℃ is 0.02 mS·cm. -1 It is higher than LiKFSI (0.008 mS·cm). -1 This indicates that the interaction between FSI⁻ ions and lithium oxide crystals leads to the release of more free lithium ions. Unlike LiKCsFSI-MOx materials, the LiKFSI-10%Li₂O sample exhibits more weak diffraction peaks ( Figure 14 (b) indicates an increase in crystallinity. Increased crystallinity leads to a more restrictive lithium-ion environment and a decrease in ionic conductivity (0.02 mS·cm for the LiKFSI-10%Li₂O sample). -1 The LiKCsFSI-5%Al2O3 sample has a strength of 0.14 mS·cm. -1 LSV measurement ( Figure 14 c) shows that the electrochemical stability window of the LiKFSI-10%Li2O electrolyte is relative to Li + / Li has a voltage range of -0.2V to 5.9V. This electrochemical window is much wider than that of common sulfide, oxide, halide, and polyoxyethylene electrolytes. Figure 14 d). Given that the ionic conductivity of the LiKFSI-10%Li2O sample increases rapidly with increasing temperature, full cells of Li / LiKFSI-10%Li2O / LFP and LCO were subsequently tested at 40 °C. As with the previous full cells, no external pressure was required. Figure 14 e and 14f demonstrate the rate performance of Li / LiKFSI-10%Li₂O / LFP and LCO full cells. Clearly, these complete cell units maintain stable capacity across a current density range from 0.2 to 1C. The discharge capacity is recovered when the current density returns to 0.2C, indicating excellent current characteristics of these cell units. Furthermore, as... Figure 14 As shown in g and 14h, at a current of 0.4C, the Li / LiKFSI-10%Li2O / LFP battery still retains 142.2 mAh·g after 60 cycles. -1 The discharge capacity exhibits an ultra-high retention rate of 98.8%. After 70 cycles at 0.4C, the discharge capacity of the Li / LiKFSI-10%Li₂O / LCO battery is 148.7 mAh·g. -1 The retention rate was 98.5% ( Figure 14 The average coulombic efficiencies of these two batteries were 99.5% and 99.8%, respectively, indicating that the LiKFSI-10%Li2O electrolyte is well compatible with the LFP (4.2V) and LCO (4.5V) cathodes.

[0081] Figure 15 The figures show the electrochemical performance of the Li / LiKFSI / LFP and Li / LiKFSI / LCO batteries of this invention. Figure 15 Figure a shows the constant current charge-discharge curves of an LFP-based battery, and Figure b shows the constant current charge-discharge curves of an LCO-based battery. Figure 15 As shown, the discharge capacity of the Li / LiKFSI / LFP battery rapidly decreases to almost zero within a few cycles. This highlights the importance of metal oxide additives.

[0082] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended scope of protection is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0083] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A eutectic-derived solid electrolyte, characterized in that, The eutectic-derived solid electrolyte is formed by mixing a eutectic bis(fluorosulfonyl)imide alkali metal salt with a metal oxide to form a heterojunction. The heterojunction interface has Lewis acid-base interactions. The eutectic bis(fluorosulfonyl)imide alkali metal salt is formed by eutectic melting of at least two bis(fluorosulfonyl)imide alkali metal salts. The amount of metal oxide used is 5 wt.% to 10 wt.% of the mass of the eutectic bis(fluorosulfonyl)imide alkali metal salt.

2. The eutectic-derived solid electrolyte according to claim 1, characterized in that, The metal oxide is MO. x , M is Al, Ti, Ce, Li, Zr, La, Sn, Y or Si.

3. A method for preparing the eutectic-derived solid electrolyte according to claim 1 or claim 2, characterized in that, Includes the following steps: Using at least two bisfluorosulfonylimide alkali metal salts as raw materials, a eutectic melting process is carried out to obtain a bisfluorosulfonylimide alkali metal liquid; a metal oxide is added to the liquid and heated at 100℃~130℃ to form a heterojunction structure, thereby obtaining a eutectic derived solid electrolyte.

4. The method for preparing the eutectic-derived solid electrolyte according to claim 3, characterized in that, The eutectic alkali metal salt of bisfluorosulfonylimide is at least two of lithium bisfluorosulfonylimide, potassium bisfluorosulfonylimide, cesium bisfluorosulfonylimide, sodium bisfluorosulfonylimide, and rubidium bisfluorosulfonylimide.

5. The method for preparing the eutectic-derived solid electrolyte according to claim 4, characterized in that, When there are two alkali metal salts of eutectic bis(fluorosulfonyl)imide, the molar ratio of any two salts is 31~69:31~69.

6. The method for preparing the eutectic-derived solid electrolyte according to claim 4, characterized in that, When the eutectic alkali metal salt of bisfluorosulfonylimide is any three of lithium bisfluorosulfonylimide, potassium bisfluorosulfonylimide, cesium bisfluorosulfonylimide, and sodium bisfluorosulfonylimide, the molar ratio of any three salts is 25~40:25~40:25~40.

7. The method for preparing the eutectic-derived solid electrolyte according to claim 3, characterized in that, Heating time is 1 to 3 hours.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a lithium negative electrode, a glass fiber separator, and an electrolyte, wherein the electrolyte is a eutectic derived solid electrolyte as described in claim 1 or claim 2.

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