Solid electrolyte suitable for high-specific-energy solid-state battery system as well as preparation method and application of solid electrolyte

Abstract

The invention relates to the technical field of lithium ion battery polymer electrolytes, in particular to a solid electrolyte material suitable for a high-specific-energy solid-state battery system, which comprises the following raw materials: a copolymer obtained by alternately copolymerizing cyclic ether and fluorine-containing cyclic anhydride under the action of an initiator, a lithium salt and a plasticizer. A multi-fluorine chain segment is introduced to a polymer repeatable unit through alternate ring-opening in-situ polymerization, so that lithium ions have a solvation environment similar to that of a local high-concentration electrolyte. Compared with the polymer electrolyte in the prior art, the polymer electrolyte with the local high-concentration solvation environment has the advantages that the polymer with the multi-fluorine chain segment has excellent stability on lithium metal, has excellent high-pressure stability and is not easy to decompose under high pressure. And compared with the traditional polymer electrolyte, the safety, the cycle life and the energy density of the battery are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a solid electrolyte suitable for high-energy-density solid-state battery systems, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles, portable electronic devices, and large-scale energy storage systems, lithium-ion batteries face higher requirements for energy density, safety, and cycle life. Traditional liquid electrolytes, due to their flammability, leakage, poor thermal stability, and lithium dendrite growth, are unable to meet the demands of high-safety applications. While all-solid-state electrolytes possess intrinsic safety, they are limited by high interfacial impedance and low room-temperature ionic conductivity. Against this backdrop, polymer-based electrolytes, combining the advantages of liquid and solid states, have become a research hotspot, showing unique potential, especially in high-voltage, high-energy-density battery systems.

[0003] To balance safety and performance, polymer-based composite solid electrolytes have become a research hotspot, but existing technologies still have significant limitations: High-concentration liquid electrolytes (CN111816919A) disclose a method of constructing a local high-salt concentration environment using ethylene glycol ether solvent and fluorinated diluent, which can improve interfacial stability, but the high salt content (>3 M) leads to high viscosity and high cost, and phase separation is prone to occur during cycling, affecting long-term stability; Polymer-based composite solid electrolytes (CN42608391A) improve dispersibility by modifying inorganic fillers (such as LLZTO) with organic acids, but the high filler ratio (mass ratio up to 10:4) sacrifices flexibility, requiring additional wetting liquid to maintain interfacial contact, which weakens the safety advantages of solid-state batteries; In-situ polymerized gel electrolytes (CN120413807A) use polyfluoroacrylate monomers to enhance the LiF content at the interface, but the gel is prone to decomposition at high temperatures.

[0004] Recent attempts to integrate the advantages of liquid solvation with the stability of polymer backbones in the concept of "localized high concentration" have yielded results, but the technology is not yet mature. For example, the localized high-concentration solid polymer electrolyte developed in patent CN202311388476A optimizes the solvation structure through a combination of fluorinated diluents and non-fluorinated solvents, but its synthesis requires a multi-step polymerization process, and the diluent is prone to migration, leading to concentration gradient failure. Furthermore, the high-voltage polymer electrolyte proposed in patent CN42623793A requires the addition of 40-90% lithium salts and ionic liquids, resulting in high costs and reduced interfacial compatibility due to the rigidity of the crosslinked network. Summary of the Invention

[0005] This invention proposes a solid polymer electrolyte with a locally high-concentration solvation environment, its preparation, and its application. The electrolyte, composed of a polymer, lithium salt, initiator, and plasticizer, introduces polyfluorinated segments onto repeatable polymer units through alternating ring-opening in-situ polymerization, creating a solvation environment for lithium ions similar to a locally high-concentration electrolyte. This solid polymer electrolyte with a locally high-concentration solvation environment significantly optimizes the electrolyte structure by forming a high-concentration region at the electrode interface. It promotes the formation of a stable and robust interfacial protective layer, effectively inhibits lithium dendrite growth, and improves battery safety. Simultaneously, this design enhances the polymer electrolyte's oxidation resistance, enabling it to match high-voltage cathodes and broadening the electrochemical window. Specifically, this invention provides the following technical solutions: A solid electrolyte suitable for high-energy-density solid-state battery systems comprises the following raw materials: a copolymer obtained by alternating copolymerization of cyclic ether and fluorinated cyclic anhydride under the action of an initiator, a lithium salt, and a plasticizer; wherein the cyclic ether is selected from at least one of tetrahydrofuran, 1,3-dioxopentane, 1,3-dioxane, 1,3-dioxane, 1,3-dioxane, and 1,3,6-trioxane; and the fluorinated cyclic anhydride is selected from at least one of tetrafluorosuccinic anhydride, hexafluoroglutaric anhydride, hexafluoroadipic anhydride, trifluoroglutaric anhydride, tetrafluoroadipic anhydride, difluoromaleic anhydride, and trifluoromethylmaleic anhydride.

[0006] Further, the lithium salt is selected from at least one of lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, and lithium hexafluorophosphate. Lithium bis(trifluoromethanesulfonyl)imide is preferred.

[0007] Further, the initiator is selected from at least one of boron trifluoride-ethyl ether complex, tripentafluorophenylborane, boron trichloride, boron tribromide, aluminum tribromide, triethylaluminum, aluminum trifluoromethanesulfonate, tin tetrafluoride, and zinc bis(trifluoromethanesulfonate). Preferably, it is boron trifluoride-ethyl ether complex.

[0008] Further, the plasticizer is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate. Preferably, fluoroethylene carbonate is selected.

[0009] Furthermore, the concentration of the lithium salt is 0.1-5 mol / L, preferably 1-2 mol / L.

[0010] Furthermore, the initiator accounts for 0.1-1.5 wt% of the monomers (total of cyclic ethers and fluorinated cyclic anhydrides), preferably 0.5-1 wt%.

[0011] Further, the plasticizer accounts for 1-20 wt% of the total mass of the monomers and the lithium salt. Preferably, it is 10-15 wt%.

[0012] The present invention also provides a preparation method of the above solid electrolyte, which includes the following steps: (S1) Under anhydrous and anaerobic conditions, stir a cyclic ether, a fluorinated cyclic anhydride, a lithium salt, and a plasticizer at room temperature until they are evenly mixed; (S2) Add an initiator, let it stand at room temperature, and carry out a polymerization reaction to obtain a solid electrolyte.

[0013] Furthermore, in step (S2), the room temperature is 20 - 25 °C, and the polymerization reaction time is 24 - 72 h.

[0014] The present invention also provides an application of the above solid polymer electrolyte in the preparation of a lithium-ion battery.

[0015] The present invention also provides a lithium-ion battery, which includes a positive electrode, a separator, a negative electrode, a battery case, and the above solid polymer electrolyte.

[0016] The lithium-ion battery is prepared according to the following process: Under anhydrous and anaerobic conditions, stir a cyclic ether, a fluorinated cyclic anhydride, a lithium salt, and a plasticizer at room temperature until they are evenly mixed, add an initiator to obtain a precursor solution, assemble the precursor solution in a battery case, and obtain a lithium-ion battery after a sufficient polymerization reaction at room temperature.

[0017] Furthermore, the active material of the positive electrode is selected from LiFePO4, LiCoO2, LiNi x Mn y Co z O2 (where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1) and Li 1+x (Mn 1-y-z Ni y Co z ) 1-x O2 (where 0 < x ≤ 0.3, 0.1 ≤ y ≤ 0.4, and 0.05 ≤ z ≤ 0.2); the negative electrode is selected from graphite, a silicon-carbon negative electrode, a silicon-oxygen negative electrode, or metallic lithium.

[0018] Compared with the prior art, the present invention provides a preparation and application of a polymer electrolyte with a locally high-concentration solvation environment. Through the design of a bifunctional monomer, a fluorinated block polymer is used to anchor high-concentration lithium-ion solvation clusters to construct a stable "locally high-concentration" micro-region. This design not only retains the advantages of a stable interface of the locally high-concentration electrolyte but also has the intrinsic safety characteristics of the polymer electrolyte, providing an ideal electrolyte solution for high-energy-density lithium-metal batteries. Description of the Drawings

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope of the present invention.

[0020] Figure 1 Electrochemical impedance spectroscopy of a standard stainless steel gasket / Example 1 / Standard stainless steel gasket; Figure 2 This is a linear sweep voltammetry test electrochemical window diagram for Example 1; Figure 3 The Raman spectrum of Example 1; Figure 4 The graph shows the cycle performance of the lithium metal anode / lithium cobalt oxide cathode in Example 1. Detailed Implementation

[0021] The following will further illustrate the above-described embodiments of the present invention with reference to specific examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention, and all technologies based on the above content of the present invention fall within the scope of the present invention.

[0022] The preparation process of the lithium cobalt oxide positive electrode sheet in the following embodiments is as follows: Lithium cobalt oxide powder, SuperP, and binder are weighed in a mass ratio of 8:1:1, and thoroughly ground and mixed using a mortar to obtain a uniform positive electrode slurry. The slurry is then coated onto the surface of aluminum foil using a scraper, dried in a forced-air oven at 80°C for 2 hours, and then dried in a vacuum oven at 80°C for 12 hours to fully remove the organic solvents from the electrode sheet. After drying, the mass of the active material of the electrode sheet is weighed and placed in a glove box for later use.

[0023] Electrochemical performance testing: CR2032 button batteries with standard stainless steel gaskets / examples / standard stainless steel gaskets, lithium metal anodes / examples / lithium cobalt oxide cathodes were assembled according to the embodiments, and performance tests were conducted using a Princeton electrochemical workstation and a LAND charge-discharge tester. The operating temperature was 25°C, the charge-discharge rate was 1C, and the charge-discharge voltage range was 3-4.5V.

[0024] Example 1 A lithium salt concentration of 1 mol / L was prepared, with a molar ratio of cyclic ether to fluorinated cyclic anhydride of 1:1.05. The plasticizer accounted for 10% of the total mass of the lithium salt and polymer, and the initiator accounted for 1% of the total mass of the cyclic ether and fluorinated cyclic anhydride. Specifically, 287.09 mg of lithium bis(trifluoromethanesulfonyl)imide (1 mmol), 340.4 mg of 1,3-dioxane, 1021.2 mg of hexafluoroglutaric anhydride, and 164.87 mg of fluoroethylene carbonate (the total volume of 1,3-dioxane, hexafluoroglutaric anhydride, and fluoroethylene carbonate was 1 mL) were weighed and stirred at room temperature until homogeneous. Then, 13.62 mg of boron trifluoride diethyl ether complex was added and mixed thoroughly. The positive electrode, separator, negative electrode, and precursor solution were then assembled into a battery casing, and the mixture was allowed to stand for complete polymerization to obtain a lithium-ion battery.

[0025] Example 2 The rest is the same as in Example 1, except that 1,3-dioxopentane is replaced with an equimolar amount of 1,3-dioxane.

[0026] Example 3 The rest is the same as in Example 1, except that 1,3-dioxopentane is replaced with an equimolar amount of 1,3-dioxoheptanane.

[0027] Example 4 The rest is the same as in Example 1, except that 1,3-dioxopentane is replaced with an equimolar amount of 1,3-dioxooctane.

[0028] Example 5 The rest is the same as in Example 1, except that 1,3-dioxopentane is replaced with an equimolar amount of 1,3,6-trioxane.

[0029] Example 6 The rest is the same as in Example 1, except that 1,3-dioxopentane is replaced with an equimolar amount of tetrahydrofuran.

[0030] Example 7 The rest is the same as in Example 1, except that hexafluoroglutaric anhydride is replaced with an equimolar amount of tetrafluorosuccinic anhydride.

[0031] Example 8 The rest is the same as in Example 1, except that hexafluoroglutaric anhydride is replaced with an equimolar amount of hexafluoroadipic anhydride.

[0032] Example 9 The rest is the same as in Example 1, except that hexafluoroglutaric anhydride is replaced with an equimolar amount of trifluoroglutaric anhydride.

[0033] Example 10 The rest is the same as in Example 1, except that hexafluoroglutaric anhydride is replaced with an equimolar amount of tetrafluoroadipic anhydride.

[0034] Example 11 The rest is the same as in Example 1, except that hexafluoroglutaric anhydride is replaced with an equimolar amount of difluoromaleic anhydride.

[0035] Example 12 The rest is the same as in Example 1, except that hexafluoroglutaric anhydride is replaced with an equimolar amount of trifluoromethylmaleic anhydride.

[0036] Comparative Example 1 The rest is the same as in Example 1, except that no fluorinated cyclic anhydride is introduced, and the polymer is obtained by ring-opening polymerization of 1,3-dioxane.

[0037] Application examples Assemble a standard stainless steel gasket / / For a CR2032 button cell with a standard stainless steel gasket, calculate the ionic conductivity of the polymer electrolyte with a locally high concentration of solvation environment by AC impedance spectroscopy. Figure 1 Electrochemical impedance spectroscopy based on Example 1 is shown. The calculated ionic conductivity is 0.8 × 10⁻⁶. -3 S / cm reflects the excellent ion transport kinetics of the electrolyte at room temperature, which is beneficial to improving the rate performance of the battery.

[0038] The electrochemical window of the electrolyte was obtained by assembling a CR2032 coin cell with a lithium metal anode and a standard stainless steel gasket, and then testing it using a linear sweep voltammetry method. Figure 2 Linear scanning voltammetry results based on Example 1 are shown, with an electrochemical window of 5.3 V. This demonstrates the oxidative stability of the polymer electrolyte with a locally high-concentration solvation environment, which is beneficial for matching high-voltage cathode materials and improving the energy density of the battery.

[0039] Figure 3 The solvation environment of lithium ions in polymer electrolytes was investigated. As can be seen from the figure, a coordination structure of lithium ions-anions-polymers dominated by anion aggregates was formed. This solvation environment, similar to a locally high-concentration electrolyte, is beneficial to improving the oxidative stability of the electrolyte and forming a good electrolyte-electrode interface.

[0040] Assemble a CR2032 coin cell with a lithium metal anode and a lithium cobalt oxide cathode, and conduct battery cycle performance tests. Figure 4The cycling performance of the lithium metal anode / lithium cobalt oxide cathode in Example 1 and Comparative Example 1 is shown. The lithium-ion battery based on the polymer electrolyte with a locally high-concentration solvation environment exhibits excellent cycling performance, achieving stable cycling for over 150 cycles at room temperature with a capacity retention of 97.5%. In contrast, Comparative Example 1 shows poor cycling performance, with a capacity retention of only 16.7% after 100 cycles and a lower average coulombic efficiency. This is because in traditional polymer electrolytes, the polymer decomposes first on the surface of the cathode particles, forming a thick and non-uniform cathode-electrolyte interface structure. The locally high-concentration polymer electrolyte, however, allows for preferential decomposition of the lithium salt, forming a thin and uniform cathode-electrolyte interface structure, thus avoiding polymer decomposition side reactions and achieving higher capacity retention and coulombic efficiency. Table 1 summarizes the cycling performance of the CR2032 coin cells with lithium metal anode / lithium cobalt oxide cathodes in Examples 1-12 and Comparative Example 1, demonstrating the excellent application prospects of the electrolyte.

[0041] Table 1 Battery Performance Test .

Claims

1. A solid electrolyte suitable for high-energy-density solid-state battery systems, characterized in that, The product comprises the following raw materials: a copolymer obtained by alternating copolymerization of cyclic ethers and fluorinated cyclic anhydrides under the action of an initiator, a lithium salt, and a plasticizer; wherein the cyclic ether is selected from at least one of tetrahydrofuran, 1,3-dioxopentane, 1,3-dioxane, 1,3-dioxane, 1,3-dioxane, and 1,3,6-trioxane; wherein the fluorinated cyclic anhydride is selected from at least one of tetrafluorosuccinic anhydride, hexafluoroglutaric anhydride, hexafluoroadipic anhydride, trifluoroglutaric anhydride, tetrafluoroadipic anhydride, difluoromaleic anhydride, and trifluoromethylmaleic anhydride.

2. The solid electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium perchlorate, lithium tetrafluoroborate, and lithium hexafluorophosphate.

3. The solid electrolyte according to claim 1, characterized in that, The initiator is selected from at least one of boron trifluoride-ethyl ether complex, tripentafluorophenylborane, boron trichloride, boron tribromide, aluminum tribromide, triethylaluminum, aluminum trifluoromethanesulfonate, tin tetrafluoride, and zinc bis(trifluoromethanesulfonate).

4. The solid electrolyte according to claim 1, characterized in that, The plasticizer is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate; preferably, fluoroethylene carbonate is selected.

5. The solid electrolyte according to claim 1, characterized in that, The concentration of the lithium salt is 0.1-5 mol / L, preferably 1-2 mol / L.

6. The solid electrolyte according to claim 1, characterized in that, The initiator accounts for 0.1-1.5 wt% of the monomer (total of cyclic ether and fluorinated cyclic anhydride), preferably 0.5-1 wt%.

7. The solid electrolyte according to claim 1, characterized in that, The plasticizer accounts for 1-20 wt% of the total mass of the monomers and lithium salt; preferably 10-15 wt%.

8. The method for preparing the solid electrolyte according to any one of claims 1-7, characterized in that, Includes the following steps: (S1) Under anhydrous and oxygen-free conditions, the cyclic ether, fluorinated cyclic anhydride, lithium salt, and plasticizer are stirred at room temperature and mixed evenly; (S2) Add an initiator, let stand at room temperature, and the polymerization reaction yields a solid electrolyte; Furthermore, in step (S2), the room temperature is 20-25℃ and the polymerization reaction time is 24-72h.

9. The use of the solid electrolyte according to any one of claims 1-7 in the preparation of lithium-ion batteries.

10. A lithium-ion battery, comprising a positive electrode, a separator, a negative electrode, a battery casing, and a solid polymer electrolyte of any one of claims 1-7; Furthermore, the lithium-ion battery is prepared according to the following process: Under anhydrous and oxygen-free conditions, cyclic ether, fluorinated cyclic anhydride, lithium salt, and plasticizer are stirred at room temperature and mixed evenly. An initiator is added to obtain a precursor solution. The precursor solution is assembled into a battery casing, and a lithium-ion battery is obtained after polymerization at room temperature. Furthermore, the active material of the positive electrode is selected from LiFePO4, LiCoO2, and LiNi. x Mn y Co z O2 (where, 0) ≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z≤1) and Li 1+x (Mn 1-y-z Ni y Co z ) 1-x O2 (wherein, 0 < x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.05 ≤ z ≤ 0.2); the negative electrode is selected from graphite, silicon-carbon negative electrode, silicon-oxygen negative electrode or elemental lithium metal.

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