Polyethylene oxide-based all-solid-state electrolyte with quaternary ammonium nitrate as multifunctional additive, its dry preparation and application

Abstract

The present application relates to a kind of polyethylene oxide-based all-solid-state electrolyte with quaternary ammonium nitrate as multifunctional additive and its dry process preparation and application.The polyethylene oxide-based all-solid-state electrolyte with quaternary ammonium nitrate as multifunctional additive includes the following components: lithium salt 40-50 parts by mass, quaternary ammonium nitrate 1-7 parts by mass, polyethylene oxide 100 parts by mass.The present application uses quaternary ammonium nitrate as additive, which can reduce the crystallinity of PEO and increase the ionic conductivity of PEO-based solid-state electrolyte.The nitrate radical can be reduced to generate a solid electrolyte interface layer rich in Li3N on the negative side, while the quaternary ammonium salt cation regulates the deposition behavior of lithium ions through electrostatic shielding effect;Both can effectively improve the stability of the battery negative electrode interface.The polyethylene oxide-based all-solid-state electrolyte with quaternary ammonium nitrate as multifunctional additive described in the present application is used in lithium iron phosphate all-solid-state battery, and shows good electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of solid-state lithium batteries, specifically relating to a polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive and its dry preparation and application. Background Technology

[0002] With the continued rise in global demand for clean energy and efficient energy storage technologies, lithium-ion batteries have become the core mainstream technology in the field of electrochemical energy storage, widely used in energy storage systems, portable electronic devices, electric vehicles, and many other key areas. Currently, traditional lithium-ion batteries using organic liquid electrolytes still pose serious safety hazards. Therefore, solid-state batteries, which replace liquid components with solid electrolytes, exhibit significant advantages, including high safety, excellent mechanical properties, a wider electrochemical window, and good wide-temperature applicability.

[0003] Among various all-solid-state electrolyte systems, PEO-based electrolytes possess outstanding comprehensive advantages. PEO not only exhibits the excellent mechanical flexibility, simple processing technology, and low preparation cost commonly found in polymer matrices, but also boasts advantages such as a moderate melting point (approximately 65 °C), strong lithium salt solubility, and good reduction stability, making it one of the polymer matrix materials with the greatest potential for industrial application. In PEO-based solid-state electrolyte systems, lithium ions primarily migrate and conduct through the movement of EO segments. However, PEO polymers are highly prone to crystallization (crystallinity of 75%–80%), which significantly reduces ion transport efficiency, causing its room-temperature ionic conductivity to remain only around 10. -7 S cm -1 Meanwhile, PEO-based electrolytes have poor compatibility with highly active lithium metal anodes, easily forming solid electrolyte interphase (SEI) layers with poor structure and physicochemical properties. This results in insufficient interfacial mechanical strength and hindered lithium-ion diffusion, which in turn induces interfacial degradation and lithium dendrite growth. These numerous drawbacks severely limit the practical large-scale application of PEO-based solid electrolytes.

[0004] To improve the ionic conductivity and SEI interface layer performance of PEO-based solid electrolytes, researchers have proposed various modification methods, among which functional additive modification is widely considered an efficient and effective strategy. For example, patent CN114725505B discloses an inorganic-organic hybrid molecular modification of PEO-based solid electrolytes. Specific groups in the inorganic-organic hybrid molecular material can interact with lithium salt anions, promoting lithium salt dissociation, increasing the number of charge carriers, and thus improving the ionic conductivity of the solid electrolyte. Another example is patent CN114551982B, which uses a synergistic modification of dual lithium salts, electropositive COFs, and LLZO particles to suppress lithium dendrites and improve ionic conductivity and interface stability.

[0005] However, most current research is based on wet processes such as solution casting, which have several significant drawbacks: This method requires multiple steps including dissolution, mixing, and solvent evaporation, increasing process complexity and preparation costs. Furthermore, the solvents used are often toxic, and their volatilization can cause environmental pollution. Simultaneously, solvent evaporation creates random pores within the polymer electrolyte matrix, generating numerous lithium-ion dead zones. This prevents the construction of continuous lithium-ion transport channels, hindering rapid lithium-ion migration and ultimately reducing the ionic conductivity of the electrolyte membrane. In addition, complete solvent removal is difficult, and residual solvents and impurities can cause various electrode / electrolyte interface problems, even inducing thermal runaway reactions, significantly increasing the application cost and safety risks of solid-state lithium metal batteries. Wet processes also tend to cause the aggregation of small-molecule additives, further compromising the overall stability of the solid-state electrolyte.

[0006] In recent years, solvent-free dry processes have become an ideal alternative for preparing PEO-based polymer solid electrolytes due to their advantages such as low cost, environmental friendliness, and strong scalability, and have attracted widespread attention. For example, patent CN113346132B discloses a method for preparing solid electrolytes, which involves reacting polyethylene oxide powder with fluorine-containing gas, mixing it with lithium salt, coating it with an organic film, and then obtaining the electrolyte through hot pressing or hot rolling. This method has mild preparation conditions and is easy to scale up, which can help realize the full commercial application of lithium-ion solid batteries. Patent CN106450394A uses a hot pressing method to prepare a composite polymer electrolyte containing PVDF, PEO, nanoparticles, and lithium salt with good electrochemical stability, good film-forming performance, high room temperature ionic conductivity, and low interfacial resistance.

[0007] Existing research confirms that dry processes can effectively improve the performance of polymer-based solid electrolytes and promote their large-scale production. However, the application of novel ionic functional additives in solvent-free dry preparation systems is still relatively limited. Therefore, research on the preparation of PEO-based solid electrolytes by combining solvent-free dry processes with ionic functional additives, and systematically exploring the modification effects and mechanisms of ionic functional additives under dry conditions, has significant theoretical research value and engineering application value for realizing the green and large-scale preparation of high-performance PEO-based solid electrolytes and promoting the practical industrial application of solid-state lithium metal batteries. Summary of the Invention

[0008] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive.

[0009] Another object of the present invention is to provide a method for preparing a polyoxyethylene all-solid-state electrolyte using quaternary ammonium nitrate as a multifunctional additive.

[0010] Another object of the present invention is to provide the application of the above-mentioned polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive, comprising the following components:

[0013] 40-50 parts by weight of lithium salt;

[0014] 1-7 parts by weight of quaternary ammonium nitrate;

[0015] 100 parts by weight of polyethylene oxide (PEO).

[0016] Preferably, the polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive comprises the following components:

[0017] 44.39 parts by weight of lithium salt;

[0018] 5 parts by weight of quaternary ammonium nitrate;

[0019] 100 parts by weight of PEO.

[0020] Preferably, the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium difluorooxalate borate.

[0021] More preferably, the lithium salt is lithium bis(trifluoromethanesulfonylimide).

[0022] Preferably, the molar ratio of the lithium salt to the polyethylene oxide EO segment is 1:8~20.

[0023] More preferably, the molar ratio of the lithium salt to the polyethylene oxide EO segment is 1:15.

[0024] Preferably, the average molecular weight of the polyethylene oxide is 300,000 to 1,000,000, specifically 300,000, 600,000, or 1,000,000.

[0025] More preferably, the average molecular weight of the polyethylene oxide is 600,000.

[0026] Preferably, the quaternary ammonium nitrate is one or more of tetrabutylammonium nitrate (TBAN), tetraethylammonium nitrate (TEAN), and tetramethylammonium nitrate (TMAN).

[0027] More preferably, the quaternary ammonium nitrate salt is TBAN.

[0028] The method for preparing a polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive provided by the present invention specifically includes the following steps:

[0029] Under a protective atmosphere, PEO, lithium salt, and quaternary ammonium nitrate powders are ground and mixed; then placed in a mold for hot pressing, and after hot pressing, cold pressing and standing are performed to obtain the polyoxyethylene all-solid electrolyte with quaternary ammonium nitrate as a multifunctional additive.

[0030] Preferably, the hot pressing treatment is performed at a temperature of 60~100 ℃, pressurized to 10~30 MPa, and lasts for 10~20 min.

[0031] More preferably, the hot pressing treatment is performed at a temperature of 90 °C, and the pressure is increased to 20 MPa slowly over a time of 20 min.

[0032] Preferably, the cold pressing and settling pressure is 10~20 kPa, and the cold pressing and settling time is 2~4 h. The cold pressing and settling is carried out at room temperature.

[0033] More preferably, the pressure for cold pressing and settling is 20 kPa, and the time for cold pressing and settling is 2 h.

[0034] The polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive provided by this invention can be applied in all-solid-state lithium iron phosphate batteries.

[0035] The all-solid-state lithium battery assembled with the solid electrolyte provided by this invention, lithium iron phosphate electrode, and lithium metal foil exhibits excellent rate performance and cycle stability.

[0036] This invention utilizes quaternary ammonium nitrate as an effective multifunctional electrolyte additive, which can reduce the crystallinity of PEO and increase the ionic conductivity of PEO-based solid electrolytes. Compared to lithium nitrate, the volume effect of quaternary ammonium cations results in a lower binding energy, facilitating dissociation in PEO in dry processes and avoiding damage to the mechanical structure of PEO. The nitrate ions in the quaternary ammonium nitrate can be reduced on the negative electrode side to generate a Li3N-containing SEI, inhibiting lithium dendrite formation. Simultaneously, the quaternary ammonium cations with strong reduction stability adsorb at lithium convex sites, promoting uniform lithium deposition through electrostatic shielding and inhibiting lithium dendrite growth, further enhancing the stability of the battery's negative electrode interface. The all-solid-state lithium iron phosphate battery assembled using the obtained solid electrolyte exhibits excellent cycle performance and rate performance.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) The PEO-based solid electrolyte prepared by the present invention has improved ionic conductivity and negative electrode-electrolyte interface stability. The all-solid-state lithium iron phosphate battery assembled based on this electrolyte has excellent electrochemical performance, and has both high cycle stability and high rate capacity.

[0039] (2) The quaternary ammonium nitrate salt provided by the present invention has low cost and low dosage, and can significantly improve the overall performance of electrolyte at a lower cost; and the dry preparation process adopted avoids the adverse effects of residual solvent on battery performance, and has the advantages of simple process, easy implementation and suitable for large-scale production, showing good application prospects. Attached Figure Description

[0040] Figure 1 The all-solid-state lithium iron phosphate battery assembled with the PEO-3%TBAN electrolyte prepared in Example 1 operates at a current density of 1 C (1 C = 170 mA g). -1 The long-cycle performance diagram is shown.

[0041] Figure 2 The all-solid-state lithium iron phosphate battery assembled with the PEO-5%TBAN electrolyte prepared in Example 2 operates at a current density of 1 C (1 C = 170 mA g). -1 The long-cycle performance diagram is shown.

[0042] Figure 3 The all-solid-state lithium iron phosphate battery assembled with the PEO-5%TBAN electrolyte prepared in Example 2 operates at a current density of 1 C (1 C = 170 mA g). -1 The charge and discharge curves at that time.

[0043] Figure 4 The lithium-symmetric battery assembled with the PEO-5%TBAN electrolyte prepared in Example 2 operates at a current density of 0.2 mA cm⁻¹. -2 The following is a long-cycle performance graph.

[0044] Figure 5 The all-solid-state lithium iron phosphate battery assembled with the PEO-7%TBAN electrolyte prepared in Example 3 operates at a current density of 1 C (1 C = 170 mA g). -1 The long-cycle performance diagram is shown.

[0045] Figure 6 The all-solid-state lithium iron phosphate battery assembled with the PEO-0%TBAN electrolyte prepared in Example 4 operates at a current density of 1 C (1 C = 170 mA g). -1 The long-cycle performance diagram is shown.

[0046] Figure 7The lithium-symmetric battery assembled with the PEO-0%TBAN electrolyte prepared in Example 4 operates at a current density of 0.2 mA cm⁻¹. -2 The following is a long-cycle performance graph.

[0047] Figure 8 The graph shows a comparison of the ionic conductivity of PEO electrolytes with different TBAN addition amounts at different temperatures. In the graph, PEO-0%TBAN represents the solid electrolyte prepared in Example 4, PEO-3%TBAN represents the solid electrolyte prepared in Example 1, PEO-5%TBAN represents the solid electrolyte prepared in Example 2, and PEO-7%TBAN represents the solid electrolyte prepared in Example 3.

[0048] Figure 9 The figure shows the electrochemical stability window of PEO electrolytes with different TBAN addition amounts. In the figure, PEO-0%TBAN represents the solid electrolyte prepared in Example 4, PEO-3%TBAN represents the solid electrolyte prepared in Example 1, PEO-5%TBAN represents the solid electrolyte prepared in Example 2, and PEO-7%TBAN represents the solid electrolyte prepared in Example 3.

[0049] Figure 10 The graph shows the full-cell rate performance of PEO electrolytes with different TBAN addition amounts. In the graph, PEO-0%TBAN represents the solid electrolyte prepared in Example 4, PEO-3%TBAN represents the solid electrolyte prepared in Example 1, PEO-5%TBAN represents the solid electrolyte prepared in Example 2, and PEO-7%TBAN represents the solid electrolyte prepared in Example 3. Detailed Implementation

[0050] The following examples further illustrate specific implementations of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are those that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0051] The average molecular weight of the polyethylene oxide used in the examples was 60W.

[0052] Example 1

[0053] (1) Weigh 0.6785 g of PEO powder, 0.3012 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and 0.0204 g of TBAN powder in an argon-atmosphere glove box and grind them in an agate mortar for 10 min until a white clump is formed. Remove the glove box from the oven. Place the resulting white clump into a mold and slowly press it to 20 MPa in a hot press, maintaining the pressure at 20 MPa for 10 min. After hot pressing, perform cold pressing to relieve stress at a pressure of 20 kPa for 2 h. This yields a PEO-based solid electrolyte with TBAN as an additive (denoted as PEO-3%TBAN). The electrolyte is then pressed into discs with a diameter of 19 mm for later use.

[0054] (2) Assemble lithium iron phosphate electrode, PEO-3%TBAN and lithium metal anode into an all-solid-state lithium iron phosphate battery.

[0055] The electrochemical performance of the all-solid-state lithium iron phosphate battery was tested (the electrochemical performance test was conducted using the Neware battery test system, and constant current charge / discharge method was adopted: for lithium iron phosphate solid-state batteries, the voltage window for charge and discharge was set to 2.7~3.8 V, the same below).

[0056] Figure 1 The all-solid-state lithium iron phosphate battery assembled with PEO-3%TBAN was demonstrated at a current density of 1 C (1 C = 170 mA g). -1 The graph shows the long-cycle performance of the PEO-3%TBAN electrolyte. It can be seen that the PEO-3%TBAN electrolyte has good electrochemical performance: it can maintain excellent single-cycle coulombic efficiency in 500 charge-discharge cycles at 1 C, and the capacity retention rate is as high as 82.9% after 500 cycles.

[0057] Example 2

[0058] (1) Weigh 0.6692 g PEO powder, 0.2974 g LiTFSI, and 0.0334 g TBAN powder into an agate mortar in an argon atmosphere glove box and grind for 10 min until a white clump is formed. Remove the glove box. Place the resulting white clump into a mold and slowly press it to 20 MPa in a hot press, maintaining the pressure at 20 MPa for 10 min. After hot pressing, perform cold pressing to relieve stress at a pressure of 20 kPa for 2 h. This yields PEO-based solid electrolytes with different TBAN additions (denoted as PEO-5%TBAN). These are then pressed into discs with a diameter of 19 mm for later use.

[0059] (2) Assemble lithium iron phosphate electrode, PEO-5%TBAN and lithium metal anode into an all-solid-state lithium iron phosphate battery (testing is carried out according to Example 1).

[0060] (3) PEO-5%TBAN was combined with two lithium metal sheets to form a symmetrical battery. The electrochemical performance of the lithium symmetrical battery was tested (the electrochemical performance test was conducted using the Neware battery test system, and constant current charge / discharge method was adopted: for the lithium symmetrical battery, the cycle current density was set to 0.2 mA cm⁻¹). -2 (30 min each for charging and discharging in a single cycle).

[0061] Figure 2 All-solid-state lithium iron phosphate batteries assembled with PEO-5%TBAN at a current density of 1 C (1 C = 170 mA g) -1 The long-cycle performance diagram is shown. Figure 3 All-solid-state lithium iron phosphate batteries assembled with PEO-5%TBAN at a current density of 1 C (1 C = 170 mA g) -1 The charge and discharge curves at that time. Figure 4 Long-cycle performance graph of a lithium-symmetric battery assembled with PEO-5%TBAN. From Figure 2 , Figure 3 and Figure 4 The results show that PEO-5%TBAN exhibits excellent electrochemical performance: in lithium iron phosphate batteries, it maintains excellent single-cycle coulombic efficiency during 500 charge-discharge cycles at 1C, with a capacity retention of up to 81.2% after 500 cycles; in lithium symmetric batteries, PEO-5%TBAN achieves stable cycling for 500 h, indicating that the PEO-5%TBAN electrolyte membrane has very good lithium stability.

[0062] Example 3

[0063] (1) Weigh 0.6603 g PEO powder, 0.2934 g LiTFSI, and 0.0462 g TBAN powder into an agate mortar in an argon atmosphere glove box and grind for 10 min until a white clump is formed. Remove the glove box. Place the resulting white clump into a mold and slowly press it to 20 MPa in a hot press, maintaining the pressure at 20 MPa for 10 min. After hot pressing, perform cold pressing to relieve stress at a pressure of 20 kPa for 2 h. This yields PEO-based solid electrolytes with different TBAN additions (denoted as PEO-7%TBAN). These are then pressed into discs with a diameter of 19 mm for later use.

[0064] (2) Assemble lithium iron phosphate electrode, PEO-7%TBAN and lithium metal anode into an all-solid-state lithium iron phosphate battery (testing is carried out according to Example 1).

[0065] Figure 5The all-solid-state lithium iron phosphate battery assembled with PEO-7%TBAN electrolyte was demonstrated at a current density of 1 C (1 C = 170 mA g). -1 The graph shows the long-cycle performance of the PEO-7%TBAN electrolyte. It can be seen that the PEO-7%TBAN electrolyte has good electrochemical performance: it can maintain excellent single-cycle coulombic efficiency in 500 charge-discharge cycles at 1 C, and the capacity retention rate is 79.9% after 500 cycles.

[0066] Example 4

[0067] (1) Weigh 0.6923 g of PEO powder and 0.3077 g of LiTFSI in an argon-atmosphere glove box and grind them in an agate mortar for 10 min until a white clump is formed. Remove the glove box from the glove box. Place the resulting white clump into a mold and slowly press it to 20 MPa in a hot press, maintaining the pressure at 20 MPa for 10 min. After hot pressing, perform cold pressing to relieve stress. The cold pressing pressure is 20 kPa and the time is 2 h. A pure PEO-based solid electrolyte (denoted as PEO-0%TBAN) is then obtained. It is then pressed into discs with a diameter of 19 mm for later use.

[0068] (2) Assemble lithium iron phosphate electrode, PEO-0%TBAN and lithium metal anode into an all-solid-state lithium iron phosphate battery (testing is carried out according to Example 1).

[0069] (3) PEO-0%TBAN was combined with two lithium metals to form a symmetrical battery (the test was conducted according to Example 2).

[0070] Figure 6 All-solid-state lithium iron phosphate batteries assembled for PEO-0%TBAN at a current density of 1 C (1 C = 170 mA g) -1 The long-cycle performance diagram is shown. Figure 7 Long-cycle performance of lithium symmetric cells assembled with PEO-0%TBAN.

[0071] from Figure 1 , 2 5 and Figure 6 The comparison revealed that the PEO-0%TBAN electrolyte exhibited a soft-shortening phenomenon around 50 cycles, with a rapid decline in single-cycle coulombic efficiency. In contrast, PEO-based solid electrolytes with added 3%, 5%, and 7% TBAN maintained stable single-cycle coulombic efficiency after 500 cycles. Furthermore, from... Figure 4 and Figure 7 The comparison revealed that the PEO-0%TBAN electrolyte experienced a voltage drop after 200 hours, while the TBAN-5% electrolyte could cycle for 500 hours. These results can be attributed to the TBA cycling process. + The electrostatic shielding effect of cations and NO3 -The synergistic effect between the reduced in-situ constructed inorganic-rich SEI films: the former forms an electrostatic barrier by adsorbing onto the protrusions on the lithium anode surface, guiding Li + Uniform deposition; the latter endows the interface layer with excellent ion conductivity and mechanical stability, and the two work together to effectively suppress the growth of lithium dendrites.

[0072] Figure 8 The ionic conductivity of PEO electrolyte at different temperatures and with varying amounts of TBAN is shown. Figure 9 This is an electrochemical window diagram of the electrolyte mentioned above. Figure 10 The above is a graph showing the rate performance of the electrolyte in a full cell.

[0073] Depend on Figure 8 It can be seen that the PEO-5% TBAN system exhibits the best ionic conductivity at 60 ℃, reaching 0.497 mS·cm. -1 .Depend on Figure 9 It is evident that the electrochemical stability window of the electrolyte narrows slightly after the addition of TBAN, which may be due to NO3. - The introduction of [a substance] lowers the oxidation potential of the PEO matrix, causing PEO to undergo oxidative decomposition at a lower potential. Figure 10 The results show that at a 2C rate, PEO-5% TBAN can still achieve 149.30 mAh g⁻¹. -1 The reversible specific capacity. Based on the above electrochemical performance analysis, 5% is the optimal addition amount of TBAN.

[0074] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive, characterized in that, It includes the following components: 40-50 parts by weight of lithium salt; 1-7 parts by weight of quaternary ammonium nitrate; 100 parts by weight of polyethylene oxide.

2. The polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive according to claim 1, characterized in that, It includes the following components: 44.39 parts by weight of lithium salt; 5 parts by weight of quaternary ammonium nitrate; 100 parts by weight of polyethylene oxide.

3. The polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive according to claim 1 or 2, characterized in that, The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium difluorooxalate borate; the quaternary ammonium nitrate salt is one or more of tetrabutylammonium nitrate, tetraethylammonium nitrate, or tetramethylammonium nitrate.

4. The polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive according to claim 1 or 2, characterized in that, The average molecular weight of the polyethylene oxide is 300,000 to 1,000,000.

5. The polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive according to claim 1 or 2, characterized in that, The molar ratio of the lithium salt to the polyethylene oxide EO segment is 1:8~20.

6. The method for preparing the polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive according to any one of claims 1-5, characterized in that, Includes the following steps: Under a protective atmosphere, polyethylene oxide, lithium salt, and quaternary ammonium nitrate powders are ground and mixed; then placed in a mold for hot pressing, and after hot pressing, cold pressing and standing are performed to obtain a solid electrolyte in which the quaternary ammonium nitrate is a multifunctional additive.

7. The preparation method according to claim 6, characterized in that, The hot pressing process is carried out at a temperature of 60~100 ℃, pressurized to 10~30 MPa, and for a time of 10~20 min.

8. The preparation method according to claim 6, characterized in that, The hot pressing process is carried out at a temperature of 90 ℃, and the pressure is increased to 20 MPa slowly over a period of 20 min.

9. The preparation method according to claim 6, characterized in that, The pressure for cold pressing and settling is 10~20 kPa, and the time for cold pressing and settling is 2~4 h.

10. The application of the polyoxyethylene all-solid-state electrolyte with quaternary ammonium nitrate as a multifunctional additive as described in any one of claims 1-5 in an all-solid-state lithium iron phosphate battery.

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