A preparation method of an in-situ cross-linked electrically coupled flame-retardant polymer electrolyte and a preparation method of a sodium metal battery

Abstract

The application provides a preparation method of an in-situ cross-linked electrically coupled flame-retardant polymer electrolyte and a preparation method of a sodium metal battery. The in-situ cross-linked electrically coupled flame-retardant polymer electrolyte can capture anions to improve the sodium ion conductivity and has excellent flame retardancy. The method provided by the application has the following advantages: the designed polymer electrolyte greatly improves the flame retardancy of the polymer electrolyte by adding the flame retardant triethyl phosphate; in addition, by adding the additives fluoroethylene carbonate and 4-trifluoromethyl phenylboronic acid, the SEI layer and the CEI layer are promoted to be constructed in the cycle process, the cycle stability of the battery is improved, and the boron atoms in the TFPBA act as Lewis acidic centers to capture anions; in addition, the excellent mechanical performance of the electrolyte can inhibit the growth of sodium negative electrode dendrites, and ensure the safety performance of the battery. The application significantly improves the electrochemical performance, cycle life and safety of the sodium metal battery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new energy electrochemical materials, in particular to a preparation method of an in-situ cross-linked electrically coupled flame-retardant polymer electrolyte and a preparation method of a sodium metal battery. BACKGROUND

[0002] With the large-scale application of mobile electronic devices and electric vehicles and the rapid development of smart grid technology, large-scale energy storage technology will play an important role in the development of power systems and energy revolution. As an indispensable important energy storage tool in people's life, lithium ion batteries have been widely used as energy storage equipment, but the demand for batteries has increased year by year, which has caused people's concern about the scarcity of lithium resources. Sodium ion batteries are considered to be an ideal substitute for lithium ion batteries due to their low cost and abundant sodium reserves.

[0003] However, the most commonly used organic liquid electrolyte in current commercial lithium and sodium ion batteries has the following serious problems: (1) The traditional liquid electrolyte, including carbonate and ether electrolyte, is easy to leak, volatile, flammable and toxic, and is prone to oxidative decomposition in the high-voltage region. (2) The metal sodium negative electrode does not deposit uniformly and smoothly during sodium deposition, but tends to form irregular dendritic sodium "dendrites", leading to serious battery safety problems. (3) The solid electrolyte interface film (SEI) has poor mechanical properties and is prone to rupture. Dendrite growth leads to rupture of the SEI film, and the exposed active Na continuously reacts with the electrolyte. (4) Sodium dendrites break to form "dead sodium" at a certain stage, and the dead sodium in the sodium metal battery increases at the later stage, the electrode changes from a dense structure to a loose and porous structure, the volume increases significantly, and the sodium ion transport and coulombic efficiency are seriously affected. (5) Severe volume expansion. Compared with the volume change of traditional intercalation negative electrode materials (such as hard carbon), the "host-free" nature of the sodium metal negative electrode leads to unlimited volume change, which further leads to uneven SEI film formation and exacerbates sodium dendrite growth. SUMMARY

[0004] To overcome at least one problem existing in the prior art, the application provides a preparation method of an in-situ cross-linked electrically coupled flame-retardant polymer electrolyte.

[0005] To solve the above technical problems, the technical scheme adopted by the application is:

[0006] A preparation method of an in-situ cross-linked electrically coupled flame-retardant polymer electrolyte, characterized in that it comprises the following steps:

[0007] S1. Dissolving a monomer containing multiple double bonds, which is a high molecular polymer, into a solvent to obtain a uniform transparent polymer solution;

[0008] S2. Adding a flame retardant to the polymer solution obtained in S1 to obtain a preliminary composite solution;

[0009] S3. Adding appropriate amounts of a thermal polymerization initiator, an additive fluoroethylene carbonate and 4-trifluoromethyl phenylboric acid, and a sodium salt to the composite solution obtained in S2, and stirring at room temperature to obtain a uniform transparent polymer solution;

[0010] S4. Using in-situ polymerization to uniformly coat the polymer solution obtained in S3 on a polytetrafluoroethylene plate, and placing it in a 60℃ oven for thermal initiation of polymerization;

[0011] S5. Peeling the dried sample obtained in step S4 from the polytetrafluoroethylene plate substrate, and cutting it into a circular piece with a diameter of 16-19mm.

[0012] Compared with the prior art, the application has the following beneficial effects:

[0013] ① Multi-crosslinking site structure model, accurate control of the crosslinking degree of polymerization reaction, preparation of high-strength polymer network, inhibition of sodium dendrite growth;

[0014] ② Design of three-dimensional cross-linked hyperbranched structure, breaking the ordered arrangement of straight chain part in the polymer, reducing the crystallinity of the electrolyte, improving the swing of the high molecular chain segment under room temperature conditions, and promoting the improvement of room temperature sodium ion conductivity;

[0015] ③ The strategy of in-situ polymerization can significantly reduce the interface impedance between the polymer electrolyte and the positive and negative electrodes, and reduce the internal resistance of the battery;

[0016] ④Utilize the electric coupling anion capture effect to capture anions, promote the dissolution of sodium salt, and improve the ionic conductivity of sodium ions;

[0017] ⑤The internal sodium ion transmission path of the solid-state polymer electrolyte is uniform and dense, which promotes the uniform deposition of sodium metal and effectively inhibits the growth of sodium dendrites;

[0018] ⑥The addition of a flame retardant in the solid-state polymer electrolyte can improve the flame retardance of the polymer electrolyte and improve the safety of the battery in use. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The physical picture of the polymer electrolyte prepared for Example 1.

[0020] Figure 2 The polymer electrolyte prepared for Example 2 is prepared for the electron microscope and energy spectrum.

[0021] Figure 3 The polymer electrolyte prepared for Example 1 is tested by the open flame combustion test.

[0022] Figure 4 The Arrhenius plot of the polymer electrolyte prepared for Example 1 and Example 2.

[0023] Figure 5 The electrochemical stability window of the polymer electrolyte prepared for Example 1.

[0024] Figure 6 The sodium ion transference number of the polymer electrolyte prepared for Example 1.

[0025] Figure 7 The rate performance plot of the sodium metal battery assembled by the polymer electrolyte prepared for Example 1 and Example 2.

[0026] Figure 8 The cycle performance plot of the sodium metal battery assembled by the polymer electrolyte prepared for Example 1 and Example 3.

[0027] Figure 9 The high load cycle performance plot of the sodium metal battery assembled by the polymer electrolyte prepared for Example 1. DETAILED DESCRIPTION

[0028] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0029] It should be noted that:

[0030] In the present application, all the embodiments and preferred embodiments mentioned in the present application can be combined with each other to form new technical solutions, if not otherwise specified.

[0031] In the present application, unless otherwise specified, each reaction or operation step can be carried out sequentially or according to the sequence. Preferably, the reaction method herein is carried out sequentially.

[0032] Unless otherwise specified, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied in the present application.

[0033] All-solid-state sodium metal batteries, as the next generation of high energy density mainstream technical solutions, have attracted widespread attention from researchers, and are expected to fundamentally solve the inherent shortcomings of liquid electrolyte. Its mechanical properties can inhibit dendrite growth and can be adapted to sodium metal negative electrodes to build higher energy density all-solid-state sodium metal batteries. Solid electrolytes mainly include inorganic solid-state electrolytes and organic polymer electrolytes. Each has obvious advantages and disadvantages: 1) Inorganic solid-state electrolytes (such as oxide and sulfide solid-state electrolytes) have high ionic conductivity and thermal stability, but face severe mechanical brittleness and high solid / solid interfacial impedance of electrolyte / electrode, hindering sodium ion transport at the interface; 2) Polymer solid-state electrolytes are composed of an organic polymer matrix and a sodium salt. Polymer electrolytes have excellent flexibility and interface compatibility, low electrolyte / electrode interfacial impedance, uniform sodium ion transport, good electrode interface compatibility, and other advantages, and are easy to process into devices. It has great application prospects in flexible wearable devices and has become a research hotspot in recent years. However, it also faces the problems of low room temperature ionic conductivity, poor mechanical strength, narrow electrochemical window, and flammability.

[0034] In one aspect, the present application provides a preparation method of an in-situ cross-linked electrically coupled flame-retardant polymer electrolyte, characterized in that it comprises the following steps:

[0035] S1. Dissolve a monomer containing multiple double bonds, which is a high molecular polymer, into a solvent to obtain a uniform and transparent polymer solution;

[0036] S2. Add a flame retardant to the polymer solution obtained in S1 to obtain a preliminary composite solution;

[0037] S3. Add an appropriate amount of thermal polymerization initiator, additive fluoroethylene carbonate and 4-trifluoromethyl phenylboric acid, and sodium salt to the composite solution obtained in S2, and stir at room temperature to obtain a uniform and transparent polymer solution;

[0038] S4. The polymer solution obtained in S3 is added with sodium salt, and in-situ polymerization is adopted to uniformly coat the polymer on a polytetrafluoroethylene plate, which is placed in an oven at 60°C to heat initiate polymerization;

[0039] S5. The dried sample obtained in S4 is peeled off from the polytetrafluoroethylene plate substrate, and is cut into a circular piece with a diameter of 16-19 mm.

[0040] The preparation method of the in-situ crosslinking type electrically coupled flame-retardant polymer electrolyte of the present application improves the mechanical strength and ionic conductivity of the solid-state polymer electrolyte by introducing a multi-site crosslinking reaction node to prepare a polymer with hyperbranched structural units. The structure is highly controllable, the structure unit and the degree of polymerization of the hyperbranched polymer electrolyte are studied to understand the structure-activity relationship between the mechanical properties, and the electrolyte with superior mechanical properties is designed flexibly to protect the sodium metal negative electrode. In addition, the addition of a flame retardant improves the safety performance of the battery and constructs a flexible bendable energy storage device. It can be matched with high specific capacity sodium metal negative electrode and sodium aluminum phosphate positive electrode to inhibit the problems such as dissolution of transition metal ions in the positive electrode, continuous voltage decay and oxygen release during the cycle process, thereby improving the cycle stability and safety of the solid-state sodium metal battery.

[0041] In some preferred embodiments, in step S1, the high molecular polymer skeleton is one of polyethylene glycol diacrylate, N,N-methylene bisacrylamide, quaternary amyl alcohol tetraacrylate, trimethylolpropane triacrylate, and triallylamine, or a mixture of two of them. The ratio of the two polymers in the mixture is 1:1 to 1:4.

[0042] In some preferred embodiments, in step S2, the flame retardant can be selected from one of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and methylphenyl diphenyl phosphate, and the mass ratio of the high molecular polymer to the flame retardant is 1:0.2 to 1:3.

[0043] In some preferred embodiments, in step S3, the thermal polymerization initiator is AIBN, and additives fluoroethylene carbonate and 4-trifluoromethyl phenylboric acid are added. The mass ratio of the additives to the high molecular polymer in step S1 is 1:0.002 to 1:0.05, and the stirring time at room temperature is 30-60 min.

[0044] In some preferred embodiments, in step S3, the sodium salt used can be one or more of sodium difluoro oxalate borate, sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, and sodium perchlorate.

[0045] In another aspect, the application provides a method for preparing a sodium metal battery, characterized in that the sodium metal battery is prepared by directly assembling the sodium metal battery with a polymer solution obtained in step S3, a sodium metal sheet, a glass fiber separator and a positive electrode, and then placing the assembly into an oven at 60°C to initiate polymerization for 12h.

[0046] In some preferred embodiments, in the method for preparing a sodium metal battery, the weight percentage of sodium salt in the obtained polymer electrolyte (sodium salt / polymer film) is controlled to be 5-50wt%.

[0047] In some preferred embodiments, in the method for preparing a sodium metal battery, the positive electrode material of the assembled sodium metal battery is sodium alumophosphate or sodium nickel-iron-manganese phosphate.

[0048] In some more preferred embodiments, the mass percentage of active material in the entire electrode is 80wt%-95wt%, and the loading amount per unit area is 3-8mg cm -2 .

[0049] In some more preferred embodiments, no additional liquid or electrolyte needs to be added when assembling the battery.

[0050] The sodium metal battery prepared by the above method has the following characteristics:

[0051] Firstly, by the strategy of in-situ polymerization, the interface impedance between the polymer electrolyte and the positive and negative electrodes can be significantly reduced, and the internal resistance of the battery can be reduced;

[0052] Secondly, by using the electric coupling anion capture effect, anions are captured, the dissolution of sodium salt is promoted, and the ionic conductivity of sodium ions is improved;

[0053] Thirdly, the sodium ion transmission path in the solid-state polymer electrolyte is uniform and dense, which promotes the uniform deposition of sodium metal and effectively inhibits the growth of sodium dendrites;

[0054] Finally, the addition of flame retardant in the solid-state polymer electrolyte can improve the flame retardancy of the polymer electrolyte and improve the safety of the battery in use.

[0055] Next, the preparation method of the in-situ cross-linked electric coupling flame-retardant polymer electrolyte and the preparation method of the sodium metal battery are described in detail with specific embodiments.

[0056] Example 1: Preparation of in-situ cross-linked electric coupling flame-retardant polymer electrolyte

[0057] S1. Mix 0.35g of polyethylene glycol diacrylate (PEGDA) with 0.15g of trimethylolpropane triacrylate (TMPTA) and stir for 30min to obtain a clear and transparent solution.

[0058] S2. Add 25 mg of initiator azobisisobutyronitrile (AIBN) to the above solution, dissolve at room temperature, and stir for 30 min;

[0059] S3. Introduce 0.1 g of additive fluoroethylene carbonate (FEC) and 0.004 g of 4-trifluoromethylphenylboronic acid (TFPBA) into the above polymer solution, and continue stirring at room temperature for 1 h.

[0060] S4. Weigh 0.42 g of sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and dissolve it in 1.5 g of triethyl phosphate (TEP), and add it to the solution obtained in step S3, and continue stirring for 30 min to obtain a clear and transparent solution.

[0061] S5. Assemble a sodium metal battery directly with the above polymer solution, metal sodium sheet, glass fiber separator, and sodium phosphate positive electrode, and place it in an oven at 60°C to initiate polymerization thermally for 12 h. After taking it out of the oven and cooling down, test its electrochemical performance.

[0062] Example 2

[0063] Example 2 is a preparation comparative example 1 of in-situ crosslinking type flame-retardant polymer electrolyte in this application. This comparative example omits step S3 relative to example 1, i.e. does not add additive fluoroethylene carbonate (FEC) and 4-trifluoromethylphenylboronic acid (TFPBA) to the solution obtained after step S2.

[0064] S1. Mix 0.35 g of polyethylene glycol diacrylate (PEGDA) with 0.15 g of trimethylolpropane triacrylate (TMPTA) and stir for 30 min to obtain a clear and transparent solution.

[0065] S2. Add 25 mg of initiator azobisisobutyronitrile (AIBN) to the above solution, dissolve at room temperature, and stir for 30 min;

[0066] S4. Weigh 0.42 g of sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and dissolve it in 1.5 g of triethyl phosphate (TEP), and add it to the solution obtained after step S2, and continue stirring for 30 min to obtain a clear and transparent solution.

[0067] S5. Assemble a sodium metal battery directly with the above polymer solution, metal sodium sheet, glass fiber separator, and sodium phosphate positive electrode, and place it in an oven at 60°C to initiate polymerization thermally for 12 h. After taking it out of the oven and cooling down, test its electrochemical performance.

[0068] Example 3

[0069] Example 3 is a preparation of a cross-linked flame-retardant polymer electrolyte in situ in the application, which is a preparation of a comparative example 2. Compared with example 1, no flame retardant TEP is added in example 3, only electrolyte is added in the polymer.

[0070] S1. 0.35 g of polyethylene glycol diacrylate (PEGDA) was mixed with 0.15 g of trimethylolpropane triacrylate (TMPTA) for 30 min to obtain a clear and transparent solution.

[0071] S2. 25 mg of initiator azobisisobutyronitrile (AIBN) was added to the solution obtained after step S1 and dissolved at room temperature, and the stirring time was 30 min.

[0072] S3’. 1.5 g of 1.0 M NaPF6 in EC:DMC=1:1 Vol% with 5.0% FEC electrolyte was introduced into the polymer solution obtained after step S2, and the solution was stirred for 30 min to obtain a clear and transparent solution.

[0073] S4’. The polymer solution obtained after step S3’ was directly assembled with a piece of metallic sodium, a glass fiber separator, and a sodium phosphate positive electrode to form a sodium metal battery, which was placed in an oven at 60°C to initiate polymerization for 12 h. After cooling, the sodium metal battery was tested for its electrochemical performance.

[0074] Performance characterization

[0075] The applicant also characterized the performance of the polymer electrolytes prepared in examples 1, 2, and 3, and the sodium metal batteries assembled from the polymer electrolytes prepared in the above three examples, and the results are as follows:

[0076] The cross-linked electrically coupled flame-retardant polymer electrolyte obtained in step S4, the cross-linked flame-retardant polymer electrolyte, and the cross-linked electrically coupled flame-retardant polymer electrolyte are shown in Figure 1 From Figure 1 it can be seen that the cross-linked electrically coupled flame-retardant polymer electrolyte can maintain its original morphology after folding and pulling, indicating that the cross-linked polymer electrolyte has excellent mechanical properties.

[0077] The SEM image of the cross-linked electrically coupled flame-retardant polymer electrolyte is shown in Figure 2 From Figure 2 it can be seen that the electrolyte can penetrate into the glass fiber separator and polymerize, and the Na, P, and F elements are distributed in the electrolyte.

[0078] The applicant tested the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in step S4 for ignition, and the test results are as follows: Figure 3The cross-linked electrically coupled flame-retardant polymer electrolyte was not ignited at all when exposed to open flame for 5 seconds, proving that the cross-linked electrically coupled flame-retardant polymer electrolyte has excellent flame retardancy.

[0079] The ion conductivity of the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in this example was tested at different temperatures, and the Arrhenius plot is shown in Figure 4 From Figure 4 it can be seen that the ion migration activation energy of Example 1 and Example 2 is 0.1535 eV and 0.1941 eV, respectively, proving that the sodium ions in the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in Example 1 have high freedom and low migration energy barrier.

[0080] The LSV test of the cross-linked electrically coupled flame-retardant polymer electrolyte of Example 1 is shown in Figure 5 From Figure 5 it can be seen that the electrochemical window of the cross-linked electrically coupled flame-retardant polymer electrolyte reaches 4.8 V. This indicates that the electrolyte formed by the cross-linked network has high electrochemical stability.

[0081] Figure 6 The cross-linked electrically coupled flame-retardant polymer electrolyte was subjected to chronoamperometry test. From Figure 6 it can be seen that the sodium ion migration number of the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in this application is as high as 0.51, indicating that TFPBA is added to the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in this application, which captures anions, promotes the dissociation of sodium salt and selectively transports sodium ions. In addition, the cross-linked polymer can provide more sodium ion transmission channels, further improving the ability of the electrolyte to transport sodium ions.

[0082] The button-type sodium ion battery (the battery assembled in Example 1 and Example 2) was assembled in an argon atmosphere glove box and tested under the following conditions: the charge and discharge cutoff voltage was 2.5 V-3.8 V, and the charge and discharge current density was 0.1 C, 0.3 C, 0.5 C, 1 C, 0.1 C (1 C = 117.6 mA / g). The rate charge-discharge graph obtained by testing is shown in Figure 7 As shown in Figure 7 , Example 1 shows specific capacities of 113.5 mAh / g, 113.9 mAh / g, 113.3 mAh / g, 112.3 mAh / g, 111.0 mAh / g, and 111.5 mAh / g, respectively, and Example 2 shows specific capacities of 107.0 mAh / g, 102.3 mAh / g, 98.2 mAh / g, 89.8 mAh / g, 55.7 mAh / g, and 102.6 mAh / g, respectively. This indicates that the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in Example 1 has good cycle performance.

[0083] The cycle performance chart of the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in the application is shown in Figure 8 As can be seen from Figure 8 , the charge and discharge current density of the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in the application is 2C (1C = 117.6 mA / g). The composite material prepared in the embodiment shows a capacity retention rate of 94.28% and good cycle stability after 2200 cycles. It is shown that the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in the application has excellent electrochemical performance, and the good mechanical performance can inhibit the growth of sodium dendrites and adapt to the volume change of the electrode in the charge and discharge process.

[0084] The charge and discharge cycle chart of the cross-linked electrically coupled flame-retardant polymer electrolyte prepared in the application under high positive electrode load (8-10 mg / cm 2 ) is shown in Figure 9 As can be seen from Figure 9 , the electrolyte prepared in the embodiment still has good cycle performance under the condition of 0.5C (1C = 117.6 mA / g).

[0085] In summary, the application provides a preparation method of an in-situ cross-linked electrically coupled flame-retardant polymer electrolyte, which comprises the following steps:

[0086] S1. Dissolving a monomer containing multiple double bonds, which is a high molecular polymer, into a solvent to obtain a uniform transparent polymer solution;

[0087] S2. Adding a flame retardant to the polymer solution obtained in S1 to obtain a preliminary composite solution;

[0088] S3. Adding appropriate amounts of thermal polymerization initiator, plasticizer fluoroethylene carbonate and 4-trifluoromethyl phenylboric acid to the composite solution obtained in S2, stirring at room temperature, and obtaining a uniform transparent polymer solution;

[0089] S4. Adding sodium salt to the polymer solution obtained in S3, using in-situ polymerization, uniformly coating on a polytetrafluoroethylene plate, and placing in a 60°C oven for thermal initiation of polymerization;

[0090] S5. Peeling the dried sample obtained in step S4 from the polytetrafluoroethylene plate substrate, and cutting it into a circular piece with a diameter of 16-19 mm.

[0091] The application further provides a preparation method of a sodium metal battery: by directly assembling the polymer solution obtained in step S3 above with a metal sodium sheet, a glass fiber separator and a positive electrode, and then placing in a 60°C oven for thermal initiation of polymerization for 12h.

[0092] The application provides a method for preparing a polymer with hyperbranched structural units by introducing multi-site cross-linking reaction nodes, to simultaneously improve the mechanical strength and ionic conductivity of a solid-state polymer electrolyte. The structure is highly controllable, the structure units and polymerization degree of the hyperbranched polymer electrolyte are studied to understand the structure-activity relationship between the mechanical properties, the electrolyte with superior mechanical properties is flexibly designed to protect the sodium metal negative electrode, and a flame retardant is additionally added to improve the safety performance of the battery, and a flexible bendable energy storage device is constructed. The sodium metal negative electrode and the sodium aluminum phosphate positive electrode with high specific capacity are matched, and the problems such as the dissolution of transition metal ions in the positive electrode, continuous voltage attenuation and oxygen release in the cycle process are inhibited, so that the cycle stability and safety of the solid-state sodium metal battery are improved.

[0093] The method provided by the application has the following outstanding advantages: the designed polymer electrolyte greatly improves the flame retardance of the polymer electrolyte by adding the flame retardant triethyl phosphate; the additives fluoroethylene carbonate and 4-trifluoromethyl phenylboronic acid are added to promote the construction of SEI and CEI layers in the cycle process, improve the cycle stability of the battery, and the boron atoms in the TFPBA act as Lewis acidic centers to capture anions; in addition, the excellent mechanical properties of the electrolyte can inhibit the growth of sodium negative electrode dendrites, and ensure the safety performance of the battery. The application significantly improves the electrochemical performance, cycle life and safety of the sodium metal battery.

[0094] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0095] Although several embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and purposes of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for preparing an in-situ cross-linked electrocoupled flame-retardant polymer electrolyte, characterized in that: Includes the following steps: S1. A monomer containing multiple double bonds, wherein the monomer is a polymer, is dissolved in a solvent to obtain a homogeneous and transparent polymer solution; S2. Add flame retardant to the polymer solution obtained in S1 to obtain a preliminary composite solution; S3. Add the thermal polymerization initiator and additives fluoroethylene carbonate and 4-trifluoromethylphenylboronic acid to the composite solution obtained in S2, and add sodium salt. Stir at room temperature to obtain a uniform and transparent polymer precursor solution. S4. The polymer precursor solution obtained in S3 is polymerized in situ, uniformly coated onto a polytetrafluoroethylene plate, and then thermally initiated in a 60°C oven. S5. Peel the dried sample obtained in step S4 from the polytetrafluoroethylene substrate and cut it into round pieces with a diameter of 16~19mm. In step S1, the polymer is one or a mixture of two of the following: polyethylene glycol diacrylate, N,N-methylenebisacrylamide, pentapentapentyl alcohol tetraacrylate, trimethylolpropane triacrylate, and triallylamine, wherein the weight ratio of the two polymers in the mixture is 1:1 to 1:

4.

2. The method for preparing the in-situ cross-linked electrocoupled flame-retardant polymer electrolyte according to claim 1, characterized in that: In step S2, the flame retardant is selected from one of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and diphenyl toluene phosphate, and the mass ratio of the polymer to the flame retardant is 1:0.2 to 1:

3.

3. The method for preparing the in-situ cross-linked electrocoupled flame-retardant polymer electrolyte according to claim 1, characterized in that: In step S3, the thermal polymerization initiator is azobisisobutyronitrile, the mass ratio of the additive to the polymer in step S1 is 1:0.002 to 1:0.05, and the stirring time is 30 to 60 minutes at room temperature.

4. The method for preparing the in-situ cross-linked electrocoupled flame-retardant polymer electrolyte according to claim 1, characterized in that: In step S3, the sodium salt used is selected from one or more of sodium difluorooxalate borate, sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, and sodium perchlorate.

5. A method for preparing a sodium metal battery, characterized in that: The sodium metal battery is prepared by directly assembling the polymer precursor solution obtained in step S3 of claim 1 with sodium metal sheets, glass fiber membranes, and positive electrodes, and then thermally initiating polymerization in an oven at 60°C for 12 hours.

6. The method for preparing a sodium metal battery according to claim 5, characterized in that: The sodium salt content in the obtained polymer electrolyte is 5-50 wt%.

7. The method for preparing a sodium metal battery according to claim 5, characterized in that: The positive electrode material of the assembled sodium metal battery is sodium vanadium phosphate or sodium nickel iron manganese oxide.

8. The method for preparing a sodium metal battery according to claim 7, characterized in that: The active material content in the entire positive electrode is 80wt%–95wt%, and the loading per unit area is 3–10 mg / cm². 2 .

9. The method for preparing a sodium metal battery according to claim 8, characterized in that: No additional liquids or electrolytes are required when assembling the battery.

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