In-situ polymerized solid-state electrolyte for sodium metal batteries and preparation method and application thereof

Abstract

The application discloses an in-situ polymerized solid electrolyte for sodium metal batteries and a preparation method thereof. The solid electrolyte is formed by in-situ ring-opening polymerization of a precursor solution. The precursor solution comprises 1,3-dioxolane as a polymerization monomer and a solvent, and further comprises cellulose triacetate, sodium bisfluorosulfonylimide, sodium difluorobis(oxalato)borate, fluoroethylene carbonate and a Lewis acid initiator. In the solid electrolyte, the Lewis acid cation is coordinated with ether oxygen in the polydioxolane segment and carbonyl oxygen in the cellulose triacetate skeleton, thereby constructing an "ion bridging" double-network crosslinked structure. The highest occupied molecular orbital (HOMO) level is significantly reduced, and the electrochemical stability window is widened to more than 4.5 V. The ionic conductivity of the solid electrolyte at 25 DEG C reaches 3.35*10 ‑4 S·cm ‑1 , the sodium ion transference number reaches 0.64, and the assembled sodium metal battery can be stably cycled for more than 1100 h in a sodium symmetric battery and can be matched with a sodium-based positive electrode to achieve excellent cycle stability.

Description

Technical Field

[0001] This invention relates to the field of sodium metal secondary battery technology, specifically to an in-situ polymerized solid electrolyte for sodium metal batteries and its preparation method. Background Technology With the increasing abundance of sodium resources and the rapid growth in demand for large-scale energy storage, sodium-ion batteries have attracted widespread attention as a next-generation electrochemical energy storage system. Among them, metallic sodium anodes are particularly noteworthy due to their high theoretical specific capacity (approximately 1166 mAh·g). -1 Sodium and its low electrode potential (approximately -2.71 V vs. standard hydrogen electrode) are considered ideal choices for improving the energy density of sodium-based batteries. However, the high reactivity of metallic sodium leads to problems such as uncontrollable sodium dendrite growth and continuous cracking and reconstruction of the solid electrolyte interface (SEI) during cycling, which seriously restricts its practical application.

[0002] To address the aforementioned issues, solid polymer electrolytes have attracted widespread attention. Among numerous systems, polyether electrolytes (PDOLs) obtained by ring-opening polymerization of 1,3-dioxolane (DOL) have great potential due to their excellent ionic conductivity and interfacial wettability. However, existing ether polymer electrolytes generally suffer from three major bottlenecks: (1) The highest occupied molecular orbital (HOMO) energy level of the lone pair electrons on the ether oxygen is high, resulting in poor electrolyte oxidative stability and an electrochemical window of only about 4.0 V, making it difficult to be compatible with high-voltage sodium-based cathode materials; (2) Simple linear PDOL segments are prone to depolymerization reactions due to nucleophilic attacks from anions such as FSI⁻ during long-term cycling, resulting in insufficient thermal stability and mechanical integrity; (3) The SEI layer formed between the linear PDOL and metallic sodium interface has uneven composition and limited mechanical strength, making it impossible to maintain integrity during long-term deposition / stripping processes and effectively suppress sodium dendrite growth.

[0003] Therefore, there is an urgent need to develop an electrolyte technology for sodium metal batteries that can simultaneously broaden the electrochemical stability window, stabilize the sodium metal interface, and possess excellent mechanical properties. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ polymerized solid electrolyte for sodium metal batteries, its preparation method, and its application, thereby solving the problems of narrow electrochemical window, incompatibility with high-voltage sodium-based cathodes, and insufficient stability of sodium metal interfaces in existing ether polymer electrolytes.

[0005] The solution of the present invention is: An in-situ polymerized solid electrolyte for sodium metal batteries is formed by an in-situ ring-opening polymerization reaction of a precursor solution; the precursor solution comprises the following components: 1,3-Dioxolane, serving as both a monomer and a solvent; cellulose triacetate, comprising 4.5 wt% to 5.5 wt% of the monomer by mass; sodium bis(fluorosulfonyl)imide, comprising 0.75 mol / L to 0.85 mol / L of the monomer; sodium difluorobis(oxalato)borate, comprising 0.18 mol / L to 0.22 mol / L of the monomer; fluoroethylene carbonate, comprising 4.5 vol% to 5.5 vol% of the monomer by volume; and a Lewis acid initiator, comprising 0.1 wt% to 0.5 wt% of the 1,3-dioxolane by mass.

[0006] As a preferred technical solution, the Lewis acid initiator is a Lewis acid initiator containing a metal cation, and more preferably tin bis(trifluoromethanesulfonate).

[0007] As a preferred technical solution, the cellulose triacetate accounts for 5 wt% of the mass of the polymer monomer.

[0008] As a preferred technical solution, the concentration of sodium difluorosulfonamide in the polymer monomer is 0.8 mol / L, and the concentration of sodium difluorobis(oxalato)borate in the polymer monomer is 0.2 mol / L.

[0009] As a preferred technical solution, the volume ratio of the fluoroethylene carbonate to the polymer monomer is 5 vol.

[0010] In the technical solution of this invention, the metal cation in the Lewis acid initiator simultaneously coordinates with the ether oxygen group in the polyepoxy pentane chain segment obtained by in-situ polymerization and the carbonyl oxygen in the cellulose triacetate skeleton to construct an "ion-bridged" double network cross-linked structure. This fundamentally stabilizes the lone pair electrons on the ether oxygen, significantly reducing the highest occupied molecular orbital (HOMO) energy level of the electrolyte and widening the electrochemical stability window to above 4.5 V, making it compatible with high-voltage sodium-based cathode materials. At the same time, the metal cation is reduced on the surface of the sodium metal anode, forming a composite SEI layer rich in sodium fluoride (NaF) and sodium-tin alloy in situ, which can effectively inhibit sodium dendrite growth and stabilize the sodium metal interface.

[0011] This invention also discloses a method for preparing an in-situ polymerized solid electrolyte for sodium metal batteries, comprising the following steps: (1) Under an inert atmosphere, sodium difluorosulfonamide was added to and dissolved in 1,3-dioxolane monomer dried by molecular sieve; (2) Sodium difluorobis(oxalato)borate, fluoroethylene carbonate and cellulose triacetate were added to the solution obtained in step (1) in sequence and stirred until the solution was clear to obtain the precursor solution. (3) Add the Lewis acid initiator to the precursor solution obtained in step (2) and mix quickly. Then inject the resulting solution between the positive and negative electrodes of the assembled sodium metal battery. (4) The sodium metal battery containing the precursor solution is left to stand at room temperature for at least 10 h to allow the precursor solution to undergo an in-situ ring-opening polymerization reaction, thereby forming the solid electrolyte in situ between the positive and negative electrodes of the sodium metal battery.

[0012] As a preferred technical solution, all operations from step (1) to step (3) are carried out in an inert atmosphere with a water content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, wherein the inert atmosphere is argon gas with a purity of ≥99.99%.

[0013] As a preferred technical solution, the room temperature standing time in step (4) is 10 h to 14 h.

[0014] The present invention also discloses the application of the in-situ polymerized solid electrolyte for sodium metal batteries in sodium metal secondary batteries, wherein the solid electrolyte is assembled with sodium metal negative and positive electrodes to form a sodium metal secondary battery.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The metal cation in the Lewis acid initiator simultaneously coordinates the ether oxygen group in the polyepoxy pentane segment with the carbonyl oxygen in the cellulose triacetate backbone to construct an "ion-bridged" double-network cross-linked structure. This structure significantly reduces the highest occupied molecular orbital (HOMO) energy level of the solid electrolyte from -7.96 eV in the purely linear PDOL system to -13.01 eV, and widens the electrochemical stability window to above 4.5 V, fundamentally solving the problem of narrow electrochemical stability window and incompatibility with high-voltage sodium-based cathodes in traditional ether polymer electrolytes.

[0016] (2) The "ion-bridged" double-network cross-linked structure reduces the glass transition temperature of the electrolyte from -47 ℃ in the simple linear PDOL system to -77 ℃, improves the amorphization degree of chain segments, and enhances the chain segment mobility. The solid electrolyte achieves an ionic conductivity of 3.35 × 10⁻⁶ at 25 ℃. -4 S·cm -1 The sodium ion transport number reaches 0.64, and the critical current density reaches 1.1 mA·cm⁻¹. -2 .

[0017] (3) The metal cations in the Lewis acid initiator are reduced on the surface of the sodium metal anode, forming a composite SEI layer rich in sodium fluoride (NaF) and sodium-tin alloy in situ. This effectively inhibits sodium dendrite growth and stabilizes the sodium metal interface. The assembled Na‖Na symmetric cell achieves a speed of 0.1 mA·cm⁻¹. -2The assembled Na‖Na3V2(PO4)3 full cell can be stably cycled for over 1100 h at current density; its coulombic efficiency remains close to 100% after 200 cycles at 0.2C rate; and its discharge specific capacity reaches 112 mAh·g at 0.1C rate. -1 It can still output approximately 80 mAh·g at a 0.5C rate. -1 The reversible specific capacity.

[0018] (4) Sodium difluorosulfonamide provides the main sodium salt, primarily supplying the system with migratable Na⁺. It acts as the "main source of sodium transport" in the precursor solution. It was chosen because the difluorosulfonamide anion (FSI⁻) is relatively easy to dissociate, helping to improve the ionic conductivity of the electrolyte. Sodium difluorobis(oxalato)borate also provides the sodium salt, but it is more of an "auxiliary sodium salt + interfacial film-forming additive." It contains fluorine and boron structures, which can participate in the formation of a relatively stable interfacial film at the sodium anode or cathode interface, thus contributing to SEI stability. Fluoroethylene carbonate is mainly an additive; its role is to preferentially decompose on the sodium metal anode surface, helping to form a stable SEI layer rich in NaF. The combination of these three components results in a precursor solution with both good ion transport capability and a more stable sodium metal interface after polymerization.

[0019] (5) The preparation method of the present invention adopts an integrated in-situ polymerization process inside the battery. The precursor solution is injected into the battery in liquid form and then spontaneously completes ring-opening polymerization at room temperature. After the in-situ polymerization reaction, it is solidified. It can simultaneously achieve a tight integrated combination of electrolyte and positive and negative electrodes and full wetting of electrode interfaces. The process is simple and does not require additional curing equipment, and has good prospects for industrial application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 Fourier transform infrared (FTIR) spectra of the in-situ polymerized solid electrolytes for sodium metal batteries prepared from 1,3-dioxolane monomer, Comparative Examples 1, 2, 3, and Example 1, where the horizontal axis represents the wavenumber (cm²). -1 The vertical axis represents transmittance (au). Figure 2Raman spectra of the in-situ polymerized solid electrolytes for sodium metal batteries prepared from 1,3-dioxolane monomer, Comparative Examples 2, 3, and Example 1, where the horizontal axis represents the Raman shift (cm). -1 The vertical axis represents intensity (au). Figure 3 The differential scanning calorimetry (DSC) curves of the electrolytes prepared in Comparative Examples 1, 2, 3, and 1 are shown, where the horizontal axis represents temperature (°C) and the vertical axis represents heat flow (W·g). -1 ); Figure 4 The image shows a scanning electron microscope (SEM) image of the in-situ polymerized solid electrolyte for sodium metal batteries prepared in Example 1. Figure 5 Electrochemical impedance spectroscopy (EIS) spectra of the in-situ polymerized electrolytes for sodium metal batteries prepared in Comparative Examples 1, 3 and 1. Figure 6 Linear sweep voltammetry (LSV) curves of the in-situ polymerized electrolytes for sodium metal batteries prepared in Comparative Examples 1, 2, 3, and 1 are shown, where the horizontal axis represents potential (V vs. Na). + / Na), with the vertical axis representing the current (Current, mA); Figure 7 The curves show the cycle stability and coulombic efficiency of the Na‖Na3V2(PO4)3 full cells assembled in Comparative Example 2 and Example 1 at a rate of 0.2C. The horizontal axis represents the number of cycles, and the left vertical axis represents the specific capacity (mAh·g). -1 The right vertical axis represents the Coulombic efficiency (%). Figure 8 This diagram illustrates the preparation of the precursor solution for the in-situ polymerized solid electrolyte used in the sodium metal battery of the present invention, the battery assembly, and the in-situ polymerization and solidification process inside the battery. DOL stands for 1,3-dioxolane, CTA for cellulose triacetate, NaFSI for sodium bis(fluorosulfonyl)imide, NaDFOB for sodium difluoro(oxalato)borate, and the anode is a sodium metal anode, while the cathode is a caustic electrode. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the contents described in the following embodiments.

[0023] The raw materials used in this invention, including 1,3-dioxolane (DOL), cellulose triacetate (CTA), sodium bis(fluorosulfonyl)imide (NaFSI), sodium difluorobis(oxalato)borate (NaDFOB), fluoroethylene carbonate (FEC), tin bis(trifluoromethanesulfonate) (Sn(OTf)2), and tris(pentafluorophenyl)borane (B(C6F5)3), are all commercially available products. In this invention, 1,3-dioxolane is used not only as a monomer capable of ring-opening polymerization but also as a solvent in the precursor solution to dissolve the sodium salt, additives, and cellulose triacetate, eliminating the need for additional organic solvents. The 1,3-dioxolane monomer is dried using molecular sieves to remove moisture before use. The polypropylene separator used is a commercially available single-layer polypropylene separator for lithium batteries, cut into 19 mm diameter discs for later use. All precursor solution preparations and battery assembly operations were carried out in a high-purity argon glove box (H2O < 0.1 ppm, O2 < 0.1 ppm).

[0024] Example 1 Please see Figure 1-8 An in-situ polymerized solid electrolyte for sodium metal batteries, its preparation method, and its application in Na‖Na3V2(PO4)3 full cells are disclosed. The preparation method of the in-situ polymerized solid electrolyte for sodium metal batteries includes the following steps: Step 1: Under an inert atmosphere, add sodium difluorosulfonamide to the 1,3-dioxolane monomer dried by molecular sieve until it is completely dissolved, according to the concentration of sodium difluorosulfonamide in the 1,3-dioxolane monomer being 0.8 mol / L.

[0025] Step 2: Sodium difluorobis(oxalato)borate, fluoroethylene carbonate, and cellulose triacetate were added sequentially to the solution obtained in Step 1 at a concentration of 0.2 mol / L in the 1,3-dioxolane monomer, a volume ratio of fluoroethylene carbonate to 1,3-dioxolane monomer of 5 vol%, and a mass ratio of cellulose triacetate to 1,3-dioxolane monomer of 5 wt%. The mixture was magnetically stirred until the solution became clear, thus obtaining the precursor solution.

[0026] Step 3: Add the Lewis acid initiator containing a metal cation to the precursor solution obtained in Step 2 and mix rapidly. In this embodiment, the Lewis acid initiator is tin bis(trifluoromethanesulfonate).

[0027] Step 4: Take a Na3V2(PO4)3 positive electrode sheet cut to the required size (vacuum dried at 80 ℃ for more than 12 h) as the positive electrode, a sodium metal sheet cut to a diameter of 16 mm as the negative electrode, and a polypropylene separator cut to a diameter of 19 mm. Place the positive electrode shell and the positive electrode sheet in the CR2025 button cell shell in order from bottom to top. Inject 30 μL of the solution obtained in step 3, place the separator and make it fully wetted, and then inject another 30 μL of the solution obtained in step 3 on the upper surface of the separator. Place the sodium metal sheet, the stainless steel gasket and the spring sheet in order, cover the negative electrode shell and seal it with a pressure of about 5 MPa.

[0028] Step 5: The battery encapsulated in Step 4 is left to stand at room temperature for 12 hours to allow the residual 1,3-dioxolane monomer in the precursor solution to undergo in-situ ring-opening polymerization initiated by tin bis(trifluoromethanesulfonate). After the in-situ polymerization reaction, solidification is completed, and the in-situ polymerized solid electrolyte for sodium metal batteries described in this embodiment is formed in situ between the positive and negative electrodes of the battery. The Na‖Na3V2(PO4)3 full cell described in this embodiment is then assembled.

[0029] The Na‖Na3V2(PO4)3 full cell is a sodium metal secondary battery. The sodium metal secondary battery is formed by injecting the precursor solution in liquid form between the sodium metal negative electrode and the positive electrode (which can be a sodium-containing positive electrode), and allowing the precursor solution to undergo an in-situ ring-opening polymerization reaction and solidify at room temperature, thereby forming an in-situ polymerized solid electrolyte for the sodium metal battery between the sodium metal negative electrode and the positive electrode.

[0030] The solid electrolyte described in this embodiment has an ionic conductivity of 3.35 × 10⁻⁶ at 25 °C, as tested. -4 S·cm -1 The sodium ion transport number is 0.64, and the glass transition temperature (T) is... g The temperature is -77 °C, the electrochemical stability window exceeds 4.5 V, and the critical current density (CCD) of the assembled Na‖Na symmetric cell is 1.1 mA·cm⁻¹. -2 and at 0.1 mA·cm -2 It can be stably cycled for more than 1100 hours at current density.

[0031] Example 2 The application of an in-situ polymerized solid electrolyte for sodium metal batteries in a Na‖Na3V2(PO4)2F3 high-voltage full cell is disclosed. The composition and preparation method of the solid electrolyte are exactly the same as in Example 1, except that in step 4, the positive electrode is replaced with Na3V2(PO4)3 instead of Na3V2(PO4)2F3 to obtain the Na‖Na3V2(PO4)2F3 full cell described in this example. The Na‖Na3V2(PO4)2F3 full cell is a sodium metal secondary battery.

[0032] Testing showed that the battery assembled in this embodiment achieved a discharge specific capacity of 112 mAh·g at a 0.1C rate. -1 It can still output approximately 80 mAh·g at a 0.5C rate. -1 The reversible specific capacity confirms that the solid electrolyte described in this invention is compatible with high-voltage sodium-based cathodes above 4.0 V.

[0033] Comparative Example 1 A solid electrolyte is prepared in a manner essentially the same as in Example 1, except that cellulose triacetate is not added in step 2; and in step 3, tin bis(trifluoromethanesulfonate) is replaced with tris(pentafluorophenyl)borane, which does not contain metal cations, as a Lewis acid initiator. All other steps are the same as in Example 1.

[0034] Comparative Example 2 A solid electrolyte is prepared in a manner essentially the same as in Example 1, except that in step 3, tin bis(trifluoromethanesulfonate) is replaced with tris(pentafluorophenyl)borane, which does not contain metal cations, as the Lewis acid initiator. Everything else is the same as in Example 1.

[0035] Comparative Example 3 A solid electrolyte is prepared in a manner essentially the same as in Example 1, except that cellulose triacetate is not added in step 2. Everything else is the same as in Example 1.

[0036] Performance testing The solid electrolytes prepared in Example 1 and Comparative Examples 1, 2, and 3 were characterized structurally and their electrochemical performance was tested. The results are as follows: Figures 1 to 7 As shown.

[0037] Depend on Figure 1 As can be seen, compared with the 1,3-dioxolane monomer, all four electrolytes (Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1) showed a difference of approximately 915 cm⁻¹. -1 The "breathing" vibration peaks corresponding to the 1,3-dioxolane five-membered ring were significantly weakened or even disappeared, while the peaks at approximately 1000 cm⁻¹ were also significantly reduced. -1 The appearance of a new peak at the point of origin, attributed to the -CH2- rocking vibration of the linear polyoxypentane segment, confirms the successful ring-opening polymerization of 1,3-dioxolane.

[0038] Depend on Figure 2 As can be seen, the aggregated mass is approximately 946 cm. -1 The characteristic peak of the 1,3-dioxolane ring structure disappears at approximately 1226 cm⁻¹. -1 The presence of characteristic vibrational peaks of the linear polyepoxypentane long chain further confirms the completion of ring-opening polymerization; simultaneously, the corresponding SNS symmetric stretching vibration peak of FSI⁻ (approximately 740 cm⁻¹) is observed. -1 In Comparative Example 3 and Example 1, which contain tin bis(trifluoromethanesulfonate), a significant shift to higher wavenumbers occurred compared to Comparative Example 2, which does not contain tin bis(trifluoromethanesulfonate), indicating that the tin cation reacts with FSI. - There are strong coordination interactions between them.

[0039] Depend on Figure 3 It can be seen that the glass transition temperature (T) of the electrolyte after the introduction of cellulose triacetate... g Significantly reduced: Comparative Example 1 was -47 °C, Comparative Example 2 was -73 °C, Comparative Example 3 was -56 °C, and Example 1 was reduced to -77 °C. g The decrease indicates that the introduction of CTA inhibited the orderly arrangement of PDOL segments and promoted the formation of amorphous structures; the introduction of tin cations further altered the inter-segment interactions by coordinating with oxygen atoms in the polymer network, increasing the degree of freedom of segment movement and benefiting Na + The transmission.

[0040] Depend on Figure 4 As can be seen, the solid electrolyte prepared in Example 1 has a uniform and dense surface, with no pores, cracks or particle aggregation, which confirms that the solid electrolyte described in Example 1 can fully wet and fill the porous separator inside the battery to form a complete electrolyte membrane structure.

[0041] Depend on Figure 5 It is evident that the semi-circular radius of the electrochemical impedance spectrum of Example 1 is significantly smaller than that of Comparative Example 1 and Comparative Example 3, indicating that its bulk ionic resistance is the lowest. Calculations show that the ionic conductivity of Example 1 at 25 °C reaches 3.35 × 10⁻⁶. -4 S·cm -1 The sodium ion transport number was 0.64, which was significantly better than that of Comparative Example 1, Comparative Example 2 and Comparative Example 3.

[0042] Depend on Figure 6 It is evident that Comparative Examples 1 and 2 exhibit significant oxidative decomposition currents at relatively low potentials (approximately 5.0 V), indicating limited antioxidant capacity. In contrast, Comparative Example 3 and Example 1, containing metal cations, show significantly increased oxidative decomposition potentials, with Example 1 exhibiting an electrochemical stability window exceeding 4.5 V, relative to Na. +The / Na reference electrode maintains low leakage current above 4.5 V, making it compatible with high-voltage sodium-based cathodes above 4.0 V. This breakthrough stems from the stabilizing effect of the "ion-bridged" double-network cross-linked structure constructed by the tin cation on the lone pair electrons on the ether oxygen, enabling the HOMO energy level of the solid electrolyte to rise from Comparative Example 1 (PDOL-FSI) - -DFOB - The system's voltage (-7.96 eV) was significantly reduced to -13.01 eV in Example 1.

[0043] Depend on Figure 7 As can be seen, the assembled Na‖Na3V2(PO4)3 full cell underwent cycling tests at a rate of 0.2C. The first-cycle discharge specific capacity of the full cell assembled in Comparative Example 2 was 83.07 mAh·g. -1 Furthermore, the capacity continuously decreases during cycling; however, the first-cycle discharge specific capacity of the full battery assembled in Example 1 reached 93.56 mAh·g. -1 It maintains a high capacity and a coulombic efficiency close to 100% even after 200 cycles, demonstrating excellent cycle stability.

[0044] Furthermore, the high-voltage full cell of Na‖Na3V2(PO4)2F3 assembled according to the preparation method of the present invention can achieve a discharge specific capacity of 112 mAh·g at a 0.1C rate. -1 It can still output approximately 80 mAh·g at a 0.5C rate. -1 The reversible specific capacity confirms the electrochemical compatibility of the solid electrolyte described in this invention with high-voltage sodium-based cathodes above 4.0 V.

[0045] In summary, the comparison shows that Comparative Example 1 (without cellulose triacetate and no metal cations) has the narrowest electrochemical window and the worst cycle stability, confirming that both cellulose triacetate and metal cations are essential core components for achieving the excellent electrochemical performance of this invention. Comparative Example 2 (without metal cations), although containing cellulose triacetate, still has a narrow electrochemical window due to the lack of effective anion anchoring and the stabilizing effect of the sodium interface; the Na‖Na symmetric cell short-circuited after approximately 700 h. Comparative Example 3 (without cellulose triacetate), although containing metal cations, lacks the support of a dual-network structure, resulting in relatively low sodium ion transference number (0.56) and ionic conductivity. Therefore, the synergistic combination of cellulose triacetate and the Lewis acid initiator of the present invention can achieve the optimal balance between electrochemical window, ion transport performance, sodium interface stability, and full-cell application performance.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An in-situ polymerized solid electrolyte for sodium metal batteries, characterized in that, The solid electrolyte is formed by in-situ ring-opening polymerization of a precursor solution; the precursor solution comprises the following components: 1,3-Dioxolane, as a polymerization monomer; Cellulose triacetate, based on the mass of the 1,3-dioxolane, accounts for 4.5 wt% to 5.5 wt% of the total mass. Sodium difluorosulfonamide, based on the precursor solution, has a concentration of 0.75 mol / L to 0.85 mol / L; Sodium difluorobis(oxalato)borate, based on the precursor solution, has a concentration of 0.18 mol / L to 0.22 mol / L; Fluoroethylene carbonate, based on the volume of the 1,3-dioxolane ring, accounts for 4.5 vol% to 5.5 vol% of the total volume. as well as The Lewis acid initiator, based on the mass of the 1,3-dioxolane, accounts for 0.1 wt% to 0.5 wt%.

2. The in-situ polymerized solid electrolyte for sodium metal batteries according to claim 1, characterized in that, The Lewis acid initiator is a Lewis acid initiator containing a metal cation.

3. The in-situ polymerized solid electrolyte for sodium metal batteries according to claim 2, characterized in that, The Lewis acid initiator is tin bis(trifluoromethanesulfonate).

4. The in-situ polymerized solid electrolyte for sodium metal batteries according to claim 1, characterized in that, The cellulose triacetate, based on the mass of the 1,3-dioxolane, accounts for 5 wt% of the total mass; the sodium difluorosulfonamide, based on the precursor solution, has a concentration of 0.8 mol / L; the sodium difluorobis(oxalato)borate, based on the precursor solution, has a concentration of 0.2 mol / L; and the fluoroethylene carbonate, based on the volume of the 1,3-dioxolane, accounts for 5 vol% of the total volume.

5. The in-situ polymerized solid electrolyte for sodium metal batteries according to claim 1, characterized in that, The solid electrolyte comprises a polyepoxypentane segment formed by in-situ ring-opening polymerization of 1,3-dioxolane, a cellulose triacetate backbone, and a metal cation derived from the Lewis acid initiator. The metal cation of the Lewis acid initiator simultaneously coordinates with the ether oxygen group in the polyepoxypentane segment and the carbonyl oxygen in the cellulose triacetate backbone to construct an ion-bridged double-network crosslinked structure.

6. The in-situ polymerized solid electrolyte for sodium metal batteries according to claim 1, characterized in that, The solid electrolyte has an ionic conductivity of not less than 3 × 10⁻⁶ at 25 °C. -4 S·cm -1 The sodium ion transference number is not less than 0.6, and the electrochemical stability window is not less than 4.5 V.

7. A method for preparing an in-situ polymerized solid electrolyte for sodium metal batteries as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Under an inert atmosphere, sodium difluorosulfonamide was added to and dissolved in 1,3-dioxolane monomer dried by molecular sieve; (2) Sodium difluorobis(oxalato)borate, fluoroethylene carbonate and cellulose triacetate were added sequentially to the solution obtained in step 1), and stirred until the solution was clear to obtain the precursor solution; (3) Add the Lewis acid initiator to the precursor solution obtained in step (2) and mix quickly. Then inject the resulting solution between the positive and negative electrodes of the assembled sodium metal battery. (4) The sodium metal battery containing the precursor solution is left to stand at room temperature for at least 10 h to 14 h to allow the precursor solution to undergo an in-situ ring-opening polymerization reaction, thereby forming the in-situ polymerized solid electrolyte for sodium metal battery between the positive and negative electrodes of the sodium metal battery.

8. The preparation method according to claim 7, characterized in that, All operations from step (1) to step (3) are carried out in an inert atmosphere, which is argon gas with a purity of ≥99.99%, and the water content and oxygen content in the inert atmosphere are less than 0.1 ppm and less than 0.1 ppm, respectively.

9. A sodium metal secondary battery, characterized in that, The sodium metal secondary battery comprises an in-situ polymerized solid electrolyte for sodium metal batteries as described in any one of claims 1 to 6, wherein the sodium metal secondary battery is formed by injecting the precursor solution in liquid form between a sodium metal negative electrode and a positive electrode, and allowing the precursor solution to undergo an in-situ ring-opening polymerization reaction at room temperature, thereby forming the in-situ polymerized solid electrolyte for sodium metal batteries between the sodium metal negative electrode and the positive electrode.

10. The sodium metal secondary battery according to claim 9, characterized in that, The metal cations in the Lewis acid initiator are reduced on the surface of the sodium metal anode, forming in situ a composite solid electrolyte interface layer rich in sodium fluoride and sodium-tin alloy.

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