A sodium-based single-ion conducting polymer electrolyte PTB-S based on boroxin skeleton and a preparation method and application thereof

Abstract

The application discloses a sodium-based single-ion conducting polymer electrolyte PTB-S based on a boroxin skeleton and a preparation method and application thereof, TB is used as a boroxin precursor, sodium methoxide is used to generate TB-S1, TB-S2 and TB-S3 with sodium salt, TB-S is dissolved in TB to form a copolymer precursor electrolyte, in-situ copolymerization is induced by heat in a battery, PTB-S1, PTB-S2 and PTB-S3 are obtained, and B-O-Na + is constructed, a boroxin anion fragment is fixed on a skeleton through a covalent bond or a stable coordination mode, Na + is used as a main migration ion, single-ion conduction is realized, and a three-dimensional sodium ion transmission channel is formed, a Na||NFS full battery maintains a stable voltage platform and a high capacity retention rate under a medium current density, excellent interface stability and cycle life, a boroxin skeleton, TB-S monomer construction and single-ion conducting mechanism, and safe, long-life and high-power operation of a sodium metal battery.

Description

Technical Field

[0001] This application belongs to the field of electrochemical energy storage technology, and particularly relates to a sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic skeleton, its preparation method and application. Background Technology

[0002] Sodium metal batteries are considered a promising type of rechargeable battery system for large-scale energy storage applications due to the abundance of sodium resources, low cost, and certain compatibility of system configuration and process routes with lithium systems. However, while traditional liquid electrolytes possess high ionic conductivity and good wettability, they generally pose risks of flammability, volatilization, and leakage, and have insufficient thermal stability and intrinsic safety. Furthermore, the high reactivity of the liquid electrolyte interface with the sodium metal anode easily leads to the formation of an unstable solid electrolyte interfacial film, inducing disordered growth of sodium dendrites, which in turn causes short-circuit failure and a significant reduction in cycle life, hindering the long-term stable operation and large-scale application of sodium metal batteries.

[0003] Polymer electrolytes have gradually become a key research area in solid-state or quasi-solid-state sodium batteries due to their advantages such as customizable shape and thickness, high safety, ease of establishing stable interfaces with electrodes, and flexible encapsulation. Most existing polymer electrolytes are dual-ion conduction systems, where cations and anions participate in conduction. Anions can migrate freely under an electric field, which easily leads to significant concentration polarization under high current density, thick electrodes, or high areal capacity conditions. This results in uneven current distribution and localized overpotential increases at the electrode / electrolyte interface, thereby exacerbating sodium deposition instability and interface aging. Single-ion conduction polymer electrolytes, by immobilizing anions within the polymer backbone, allow Na… + Becoming the primary transport carrier is beneficial in terms of suppressing concentration polarization, achieving uniform current distribution, and realizing a relatively smooth sodium deposition / stripping interface. However, existing single-ion conductive polymer systems still suffer from problems in structural design, such as discontinuous ion enrichment channels, difficulty in balancing chain mobility and mechanical strength, narrow electrochemical stability windows, and limited processability, making it difficult to simultaneously meet the comprehensive requirements of high current density, long cycling, and high voltage operation.

[0004] The boron-oxygen hexacyclic framework exhibits significant Lewis acidity, good structural designability, and multiple coordination sites. By introducing suitable oxygen- or heteroatom-containing coordination segments around it, it is expected to construct continuous BO-Na structures. + Coordination environment, forming relatively interconnected Na + Migration pathways; simultaneously, by controlling the substitution positions and ring structure of boron-oxygen hexacyclic rings, the flexibility of polymer chain segments can be improved while maintaining a certain rigidity of the backbone, thereby improving ion transport capacity and electrode / electrolyte interface contact state. Therefore, a class of polymers with boron-oxygen hexacyclic rings as the backbone, anions fixed in the polymer backbone, and high Na+ migration pathways can be developed. +Developing sodium-based single-ion polymer electrolytes with tunable migration numbers and structures, and systematically optimizing their ion conduction, mechanical properties, and electrochemical stability, has significant research and application value for improving the safety, cycle life, and power performance of sodium metal batteries. Summary of the Invention

[0005] Technical problem solved: This application provides a sodium-based single-ion polymer electrolyte PTB-S based on a boron-oxygen hexacyclic framework, its preparation method, and its application, which solves the safety deficiencies of existing sodium metal batteries that mostly use flammable liquid electrolytes or dual-ion polymer electrolytes. + Technical challenges include severe concentration polarization due to low migration number, uncontrolled growth of sodium dendrites, unstable contact between electrolyte and electrode interface, limited room temperature ionic conductivity at medium and high voltages, and limited cycle life and energy density.

[0006] A method for preparing a sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxyhexane backbone involves a coordination reaction between 3-methoxyboronoxyhexane (TB) and sodium alkoxide under anhydrous conditions to generate sodium boronoxyhexane salt monomers 4-methoxyboronoxyhexane sodium TB-S1, 5-methoxyboronoxyhexane sodium TB-S2, and 6-methoxyboronoxyhexane sodium TB-S3. These sodium boronoxyhexane salt monomers are then dissolved in TB to form a precursor mixture, which undergoes a ring-opening copolymerization reaction under heating conditions to obtain the corresponding polymers poly(4-methoxyboronoxyhexane sodium PTB-S1), poly(5-methoxyboronoxyhexane sodium PTB-S2), and poly(6-methoxyboronoxyhexane sodium PTB-S3). The polymer backbone contains repeating BO structural units and Na... + Coordinated oxygen-containing fragments and boron-oxygen anion fragments are immobilized in the polymer backbone, with Na + The preparation method, which uses the main migrating ion to achieve single-ion conductivity, includes the following specific steps: Step 1: Using TB as the starting monomer, dissolve it in an anhydrous aprotic solvent, add sodium alkoxide to carry out a coordination reaction, construct a boron-oxygen hexacyclic skeleton with alternating BO structure and add methoxy substituents, remove the solvent to obtain one or more of the neutral intermediates TB-S1, TB-S2, and TB-S3 with different substitution positions or ring structures. The second step involves dissolving one or more of the sodium borooxyhexacyclic salt monomers TB-S1, TB-S2, and TB-S3 in TB, adjusting the ratio of TB to TB-S monomers to obtain a precursor mixture for polymerization. This mixture is then subjected to ring-opening polymerization under heating conditions to obtain one or more of the corresponding polymer electrolytes PTB-S1, PTB-S2, and PTB-S3. The preparation route is as follows: , Where n:m = 1:10-100.

[0007] Furthermore, the anhydrous aprotic solvent is dichloromethane and tetrahydrofuran, and the sodium alkoxide is sodium methoxide and / or sodium ethoxide; the molar ratio of TB to sodium alkoxide is 1:1-3.2; the heating temperature in the second step is 40-80℃, and the heating time is 2-24h.

[0008] Further, in the second step, 1 part by molar ratio of boron-oxygen hexacyclic sodium salt monomers TB-S1, TB-S2, and TB-S3 are dissolved or dispersed in 10-100 parts of TB, and 0-30 wt% of organic solvent or plasticizer is added to prepare a homogeneous precursor electrolyte. The precursor electrolyte is injected into the battery cell pre-loaded with a positive electrode, a separator, and a sodium negative electrode by injection, and thermally induced polycondensation or ring-opening polymerization is carried out at 40-80°C to form a PTB-S polymer electrolyte network with a boron-oxygen hexacyclic backbone as the main chain in situ in the separator channels and electrode pores, which penetrates the separator channels and forms a continuous contact interface with the electrode surface.

[0009] A sodium-based single-ion polymer electrolyte PTB-S based on a boron-oxyhexacyclic skeleton prepared by any of the above-described preparation methods, wherein the boron-oxyhexacyclic sodium salt monomers TB-S1, TB-S2, and TB-S3 are three structurally isomeric sodium salts of 3-methoxyboron-oxyhexacyclic derivatives, obtained by changing the methoxy substitution position and / or the number of substitutions, wherein the polymer PTB-S3 corresponding to TB-S3 has higher chain segment flexibility and a more continuous ion conduction channel; the Na in PTB-S1, PTB-S2, and PTB-S3... + Migration number ≥ 0.9, relative to Na + / Na has an upper limit of electrochemical stability window ≥ 4.5V, a glass transition temperature ≤ 0℃, and an ionic conductivity of 1.0 × 10⁻⁶ at 25℃. -5 -5.0×10 -4 S cm -1 .

[0010] Furthermore, the ionic conductivity of the PTB-S3-based system is ≥1.0×10⁻⁶. -4 S cm -1 Na + Migration number ≥ 0.91, glass transition temperature ≤ -10℃, relative to Na + The upper limit of the electrochemical stability window for / Na is ≥4.7V.

[0011] Furthermore, 0-30 wt% of a plasticizer or co-solvent is added to one or more of PTB-S1, PTB-S2, and PTB-S3, wherein the plasticizer or co-solvent is a polar organic solvent, and the polar organic solvent is a carbonate and / or ether polar organic solvent, used to adjust the ionic conductivity.

[0012] This application also discloses the application of sodium-based single-ion polymeric electrolyte PTB-S based on a boron-oxygen hexacyclic framework prepared by any of the above-described methods in sodium metal batteries. PTB-S1, PTB-S2, and PTB-S3 serve as polymeric electrolytes. The sodium metal battery includes a positive electrode, a negative electrode, and a separator. The polymeric electrolyte is placed between the positive and negative electrodes in the form of a PTB-S polymer network formed by in-situ wetting the separator. The negative electrode is metallic sodium or a sodium-containing composite negative electrode, and the positive electrode is a sodium energy storage positive electrode material containing iron or vanadium. The separator is a glass fiber separator or a polyolefin porous separator. A Na||Na symmetric battery using PTB-S3 as the main electrolyte operates at 0.1-0.5 mA cm⁻¹. -2 During Na deposition / stripping cycling at current density, the steady-state polarization voltage is no higher than 150 mV, and the continuous cycling time is no less than 800 h. For Na||NFS full cells using PTB-S3 as the main electrolyte, the first-cycle specific capacity is 90-110 mAhg during charge-discharge testing at a current rate of 0.5C within a voltage window of 2.0-4.0 V. -1 After 300-500 cycles, the capacity retention rate is not less than 85%, and the coulombic efficiency is not less than 99.0%.

[0013] Furthermore, the positive electrode is an NFS sodium positive electrode material, which is placed between the positive and negative electrodes in the form of a PTB-S polymer network formed by in-situ wetting of the separator, with a thickness of 20-80 μm.

[0014] This application also discloses the application of sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic framework prepared by any of the above-described preparation methods in the assembly of Na||Na symmetric batteries. Two metallic sodium sheets are stacked with a self-supporting PTB-S polymer electrolyte membrane, or a porous separator and a PTB-S polymer electrolyte composite layer, in an inert atmosphere and assembled into a coin cell for encapsulation. Alternatively, TB / TB-S precursor electrolyte is injected into a Na||separator||Na dry cell and in-situ polymerization is carried out to obtain a symmetric battery for Na deposition / stripping testing.

[0015] This application also discloses the application of sodium-based single-ion conductive polymer electrolyte PTB-S based on boron-oxygen hexagonal skeleton prepared by any of the above-described preparation methods in the assembly of Na||NFS full cells. The positive electrode containing NFS, the separator, and the metallic sodium negative electrode are stacked and assembled in sequence in the battery casing. Then, a precursor electrolyte composed of TB-S monomers and TB is injected. After encapsulation, a thermally initiated ring-opening copolymerization reaction is carried out at 40-80°C to form a PTB-S polymer electrolyte network with boron-oxygen hexagonal skeleton as the main chain in situ in the separator channels and electrode pores. The network penetrates the separator channels and forms a continuous contact interface with the electrode surface, resulting in a sodium metal full cell for rate performance and long cycle performance testing.

[0016] Furthermore, using NFS positive electrode material as the active material, NFS powder, Super P conductive carbon and PVDF binder are added to N-methylpyrrolidone in a mass ratio of 8:1:1. The mixture is mechanically stirred or planetary stirred to obtain a uniform slurry. The slurry is uniformly coated onto an aluminum foil current collector, vacuum dried at 80°C to remove the solvent, and then cut into NFS-containing positive electrode sheets of the required diameter after being densified by rolling.

[0017] Furthermore, in an argon or nitrogen-protected glove box, a sodium metal sheet is used as the negative electrode, and a glass fiber membrane or a polyolefin porous membrane is used as the separator. The NFS-containing positive electrode, the separator, and the sodium metal sheet negative electrode are stacked sequentially and placed into the coin cell casing to form a dry cell structure. Then, a boron-oxygen-hexacyclic sodium salt monomer precursor electrolyte is injected into the cell using a micro-syringe to fully wet the separator and positive electrode pores and cover the sodium negative electrode surface. The cell is then left to stand to remove visible air bubbles and ensure that the precursor is evenly distributed within the cell.

[0018] Furthermore, ensuring the battery packaging remains intact, the battery containing the precursor electrolyte is placed in a constant temperature chamber and heat-treated at 40-80℃ for 2-24 hours. This allows the sodium boron oxide hexagonal salt monomer precursor electrolyte to undergo a thermally initiated ring-opening copolymerization reaction inside the battery, forming an in-situ PTB-S polymer electrolyte network with a boron oxide hexagonal backbone as the main chain. This network penetrates the separator pores and forms a continuous contact interface with the electrode surface. After cooling to room temperature, the Na||PTB-S||Na symmetric battery is subjected to a heat treatment of 0.1-0.5 mA cm⁻¹. -2 Na deposition / stripping cycle testing at current density: Na||PTB-S||NFS full cells were subjected to constant current charge-discharge tests at rates of 0.2-1.0 C within a voltage window of 2.0-4.5V to evaluate interface stability, rate performance and long-cycle performance.

[0019] The beneficial effects of this invention are: 1. Through the boron-oxygen hexagonal framework and Na + The synergistic design of the coordination environment immobilizes anionic fragments within the polymer backbone, enabling Na... + It becomes the main migrating ion, which significantly weakens concentration polarization and improves the uniformity of Na deposition / stripping process from a mechanistic perspective; 2. By changing the methoxy substitution position and ring structure, three types of sodium salt monomers, TB-S1, TB-S2 and TB-S3, were obtained. PTB-S family polymers were then constructed by in-situ thermally induced copolymerization in TB medium. Under the premise of ensuring certain mechanical support, a lower glass transition temperature and higher chain segment flexibility were obtained, which is conducive to the formation of continuous and reconfigurable ion transport channels. 3. PTB-S3 exhibits superior framework continuity and local polarity distribution in Na+. +It exhibits superior performance in terms of transport number, room temperature conductivity, and electrode / electrolyte interface contact, enabling Na||Na symmetric cells to maintain stable low polarization cycling over a longer timescale, and Na||NFS full cells to maintain good capacity retention and coulombic efficiency at medium rate. 4. The PTB-S system described in this application adopts a precursor electrolyte injection + in-situ polymerization method inside the battery. The process conditions are mild and easy to be compatible with existing electrode preparation and battery packaging processes. It has good processability and potential for widespread application. Attached Figure Description

[0020] Figure 1 This is the spectroscopic characterization diagram of the sodium-based single-ion conductive polymer electrolyte PTB-S based on the boron-oxygen hexacyclic skeleton of this application, where a is... 11 B is the nuclear magnetic resonance image, and b is the post-polymerization infrared spectrum; Figure 2 The images show the glass transition temperature and ion migration barrier of the sodium-based single-ion conductive polymer electrolyte PTB-S based on the boron-oxygen hexacyclic skeleton in this application. In the images, a is the DSC test diagram of the PTB-S series and b is the ion migration barrier test diagram. Figure 3 The figures show the characterization of the ionic conductivity, ion transport number, and voltage window of the sodium-based single-ion polymer electrolyte PTB-S based on the boron-oxygen hexacyclic skeleton in this application, where a is the ionic conductivity and ion transport number at room temperature, and b is the voltage window. Figure 4 The graph shows the cycle performance of the sodium-based single-ion conductive polymer electrolyte PTB-S based on the boron-oxygen hexacyclic framework in sodium metal batteries, where a is the 0.5 C long-cycle test graph and b is the charge-discharge curve before and after cycling. Detailed Implementation

[0021] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0022] Example 1: A method for preparing a sodium-based single-ion conductive polymer electrolyte PTB-S1 containing a boron-oxygen hexacyclic skeleton. This example uses TB-S1 and PTB-S1 as examples. TB and Na... + The alkoxide undergoes a coordination reaction under anhydrous conditions to generate the sodium borooxyhexane monomer TB-S1; the sodium borooxyhexane monomer is dissolved or dispersed in TB to form a precursor mixture, which undergoes a ring-opening copolymerization reaction under heating conditions to obtain the corresponding polymer PTB-S1. The polymer backbone contains repeating B–O structural units and Na… +The coordinated oxygen-containing fragments and boron-oxygen hexacyclic anionic fragments are immobilized in the polymer backbone, with Na + As the primary migrating ion, it achieves single-ion conductivity. The preparation method includes the following specific steps: Step 1, Dissolution of 3-methoxyboroxohexacyclic precursor: Weigh 5.00 g of TB solid and add it to 50 mL of anhydrous tetrahydrofuran solvent. Stir magnetically for 30 min under argon protection until a clear and transparent TB solution is obtained.

[0023] The second step involves the formation of the borooxyhexacyclic sodium salt monomer TB-S1: Under an inert atmosphere, 1.62 g of anhydrous sodium methoxide powder was added three times to the anhydrous THF solution of TB. The reaction temperature was controlled at 30°C, and the reaction was continued with stirring for 4 hours to allow for coordination reaction. After the reaction was completed, THF was evaporated under reduced pressure, and the residue was dried under vacuum at 50°C for 12 hours to obtain a white or off-white borooxyhexacyclic sodium salt monomer TB-S1 powder.

[0024] The third step is the drying treatment of TB-S1 monomer: the TB-S1 powder obtained above is transferred to a vacuum drying oven and vacuum dried overnight at 50°C to remove residual solvent and trace moisture until the mass is constant, and the fully dried TB-S1 monomer is obtained for use.

[0025] Step 4, Preparation of PTB-S1 precursor electrolyte: In an inert atmosphere glove box, weigh 0.50 g of dry TB-S1 monomer and 5.00 g of TB monomer and add them to a sealed glass bottle. Add 0.60 g of anhydrous DEC and stir magnetically at 40 °C for 2 h until a clear and homogeneous TB / TB-S1 precursor electrolyte is formed.

[0026] Step 5: In-situ polymerization of PTB-S1 to form polymer electrolyte: In an argon-filled glove box, sodium metal sheets, separators, and positive electrode sheets are stacked sequentially into a CR2032 coin cell casing to form a dry cell structure. 80 μL of the aforementioned TB / TB-S1 precursor electrolyte is injected into the cell using a micro-syringe to fully wet the separator pores and positive electrode pores, and to cover the sodium negative electrode surface. After standing for 10 minutes to remove visible air bubbles, encapsulation is completed. The encapsulated battery is then heat-treated in a 60°C constant temperature oven for 8 hours, allowing the precursor electrolyte to undergo a thermally induced ring-opening copolymerization reaction inside the cell. This forms an in-situ PTB-S1 polymer electrolyte network with a boron-oxygen hexagonal backbone as the main chain in the separator pores and electrode pores, creating a continuous contact interface with the electrode surface.

[0027] Step 6, Preparation of NFS Positive Electrode: Weigh 0.80g of NFS positive electrode active material, 0.10g of Super P conductive carbon, and 0.10g of PVDF binder, add 2.0g of N-methylpyrrolidone solvent, and mix in a planetary mixer for 2 hours to obtain a uniform slurry; uniformly coat the slurry onto an aluminum foil current collector, and after drying, the areal capacity of the positive electrode active material is 1.10 mAh cm⁻¹. -2 The coated positive electrode sheet is placed in an 80℃ vacuum drying oven and dried for 12 hours. After being rolled and compacted, it is cut into round positive electrode sheets with a diameter of 12mm for later use.

[0028] Step 7: Assembly and testing of Na|PTB-S1|Na symmetric cells and Na|PTB-S1|NFS full cells: S1, Symmetrical Cell Test: In an argon-filled glove box, two 12mm diameter sodium metal sheets and one 16mm diameter separator were cut and stacked in a CR2032 casing according to the sequence "Na sheet | separator | Na sheet"; 80μL of TB / TB-S1 precursor electrolyte was injected and the casing was sealed; after in-situ polymerization at 60℃ for 8 hours under the conditions described in step five, the test was performed. The test was conducted at 25℃ with a flow rate of 0.1 mA cm⁻¹. -2 Na deposition / stripping cycles were performed at a current density of 0.1 mAh cm⁻¹ per half-cycle. -2 After continuous cycling for 500 hours, the steady-state polarization voltage was 135mV.

[0029] S2, Full Cell Test: In the same glove box, the NFS positive electrode, separator, and sodium metal negative electrode were stacked and assembled into a CR2032 casing in the order of "positive electrode | separator | negative electrode"; 80 μL of TB / TB-S1 precursor electrolyte was injected and the casing was sealed; after in-situ polymerization at 60℃ for 8 hours according to the conditions in step 5, the test was performed. Tested at a 0.2 C rate within a voltage window of 2.0–4.0V, the first discharge specific capacity was 95 mAhg. -1 After 200 cycles at a 0.5 C rate, the capacity retention rate is 85%, and the coulombic efficiency is 99.2%.

[0030] Example 2: A method for preparing a sodium-based single-ion conductive polymer electrolyte PTB-S2 containing a boron-oxygen hexacyclic skeleton: This example follows the same overall process as Example 1, except that the coordination reaction conditions are slightly adjusted to generate a boron-oxygen hexacyclic sodium salt monomer TB-S2 with a different structure, and to obtain the corresponding polymer PTB-S2. The preparation method includes the following specific steps: Step 1, Dissolution of 3-methoxyboroxohexacyclic precursor: Weigh 5.00 g TB and add it to 50 mL of anhydrous THF. Stir for 30 min under argon protection to obtain a clear and transparent solution.

[0031] The second step is the formation of the borooxyhexacyclic sodium salt monomer TB-S2: 1.78 g of anhydrous sodium methoxide powder was added to the above TB solution in three portions under an inert atmosphere. The reaction temperature was controlled at 35°C and the reaction was stirred for 4 h. After the reaction was completed, THF was evaporated under reduced pressure. The residue was dried under vacuum at 50°C for 12 h to obtain white or off-white borooxyhexacyclic sodium salt monomer TB-S2 powder.

[0032] The third step is the drying treatment of TB-S2 monomer: the TB-S2 powder is vacuum dried overnight at 50°C until the mass is constant, and the dried TB-S2 monomer is obtained.

[0033] Step 4, Preparation of PTB-S2 precursor electrolyte: Weigh 0.50g of TB-S2 and 5.00g of TB in a glove box and add them to a sealed glass bottle. Add 0.60g of anhydrous DEC and stir at 40℃ for 2h to obtain a clear and homogeneous TB / TB-S2 precursor electrolyte.

[0034] Step 5: In-situ polymerization of PTB-S2 to form polymer electrolyte: Following the method in step 5 of Example 1, 80 μL of precursor electrolyte was injected into the CR2032 cell and encapsulated. The cell was then heat-treated at 60°C for 8 hours to induce a thermally induced ring-opening copolymerization reaction inside the cell, thereby forming an in-situ PTB-S2 polymer electrolyte network.

[0035] Step 6, NFS cathode preparation: Prepared according to step 6 of Example 1, with an areal capacity of 1.10 mAh·cm⁻¹. -2 .

[0036] Step 7, Battery Assembly and Testing: S1: Na|PTB-S2|Na symmetric cells were assembled according to Example 1 and tested after in-situ polymerization at 60°C for 8 hours; at 25°C, at 0.1 mA cm⁻¹ -2 Current density cycling, 0.2 mAh cm⁻¹ per half cycle. -2 After 700 hours of continuous cycling, the steady-state polarization voltage was 115mV.

[0037] S2: Na|PTB-S2|NFS full cells were assembled according to Example 1 and tested after in-situ polymerization at 60°C for 8 hours; the first-cycle discharge specific capacity at 0.2 C within the 2.0–4.0V window was 100 mAhg. -1 After 300 cycles at 0.5 C, the capacity retention rate is 86%, and the coulombic efficiency is 99.1%.

[0038] Example 3: A method for preparing a sodium-based single-ion conductive polymer electrolyte PTB-S3 containing a boron-oxygen hexacyclic skeleton: This example follows the same overall process as Examples 1 and 2, except that the coordination reaction conditions are slightly adjusted to generate a third structurally isomer of the boron-oxygen hexacyclic sodium salt monomer TB-S3, and to obtain the corresponding polymer PTB-S3. The preparation method includes the following specific steps: Step 1, Dissolution of 3-methoxyboroxohexacyclic precursor: Weigh 5.00 g TB and dissolve it in 50 mL of anhydrous THF. Stir for 30 min under argon protection to obtain a clear and transparent solution.

[0039] The second step involves the formation of the borooxyhexacyclic sodium salt monomer TB-S3: Under an inert atmosphere, 2.10 g of anhydrous sodium methoxide powder was added to the above TB solution in three portions, with the reaction temperature controlled at 38 °C and the mixture stirred for 5 h. After the reaction was completed, THF was evaporated under reduced pressure, and the residue was dried under vacuum at 50 °C for 12 h to obtain a white or off-white borooxyhexacyclic sodium salt monomer TB-S3 powder.

[0040] The third step is the drying treatment of TB-S3 monomer: the TB-S3 powder is vacuum dried overnight at 50°C until the mass is constant, and the dried TB-S3 monomer is obtained.

[0041] Step 4, Preparation of PTB-S3 precursor electrolyte: Weigh 0.50g of TB-S3 and 5.00g of TB in a glove box and add them to a sealed glass bottle. Add 0.60g of anhydrous DEC and stir at 40℃ for 2h to obtain a clear and homogeneous TB / TB-S3 precursor electrolyte.

[0042] Step 5: In-situ polymerization of PTB-S3 to form polymer electrolyte: 80 μL of precursor electrolyte is injected into the CR2032 cell and encapsulated according to the method in step 5 of Example 1. The cell is then heat-treated at 60°C for 8 hours to induce a thermally induced ring-opening copolymerization reaction inside the cell, thereby forming an in-situ PTB-S3 polymer electrolyte network.

[0043] Step 6, NFS cathode preparation: Prepared according to step 6 of Example 1, with an areal capacity of 1.20 mAh·cm⁻¹. -2 .

[0044] Step 7, Battery Assembly and Testing: S1: Na|PTB-S3|Na symmetric cells were assembled according to Example 1 and tested after in-situ polymerization at 60°C for 8 hours; at 25°C with a flow rate of 0.2 mA cm⁻¹ -2 Current density cycling, 0.2 mAh cm⁻¹ per half cycle. -2 After continuous cycling for 1000 hours, the initial polarization voltage was 140mV, and the stable polarization voltage was 60mV.

[0045] S2: Na|PTB-S3|NFS full cells were assembled according to Example 1 and tested after in-situ polymerization at 60°C for 8 hours; the first-cycle discharge specific capacity at 0.5 C in the 2.0–4.0V window was 105 mAhg. -1 After 500 cycles at 0.5 C, the capacity retention rate is 88%, and the coulombic efficiency is 99.2%. In the rate test, the discharge specific capacity at 1.0 C rate is 82 mAhg. -1 After the discharge rate is restored to 0.2 C, the specific capacity is 96 mAhg. -1 .

[0046] In summary, Examples 1-3 demonstrate that by controlling the structure and TB / TB-S ratio of the boron-oxygen-hexacyclic sodium salt monomers TB-S1, TB-S2, and TB-S3, a series of Na+ compounds can be obtained within the same boron-oxygen-hexacyclic framework system. + PTB-S, a sodium-based single-ion polymer electrolyte, exhibits high transport number, considerable room-temperature ionic conductivity, a wide electrochemical stability window, and good interfacial stability. Compared to PTB-S1 and PTB-S2, PTB-S3 demonstrates superior performance in terms of chain segment flexibility, ion channel connectivity, and electrode interface contact, enabling Na|Na symmetric cells and Na|NFS full cells to maintain low polarization, high coulombic efficiency, and high capacity retention over longer timescales and at moderate rates. The PTB-S system described in this invention can be achieved through precursor electrolyte injection and in-situ thermally induced polymerization processes, exhibiting good compatibility with conventional electrode manufacturing and battery encapsulation processes. This provides a feasible route for the structural design and engineering application of single-ion polymer electrolytes for sodium metal batteries.

[0047] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures and preparation methods not specifically described or explained in this invention, unless otherwise specified or limited, shall be implemented using conventional methods in the art.

Claims

1. A method for preparing a sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexagonal skeleton, characterized in that, The sodium borooxyhexane salt monomers 4-methoxyborooxyhexane sodium TB-S1, 5-methoxyborooxyhexane sodium TB-S2, and 6-methoxyborooxyhexane sodium TB-S3 are generated by a coordination reaction between 3-methoxyborooxyhexane TB and sodium alkoxide under anhydrous conditions. These sodium borooxyhexane salt monomers are then dissolved in TB to form a precursor mixture, which undergoes a ring-opening copolymerization reaction under heating conditions to obtain the corresponding polymers poly(4-methoxyborooxyhexane sodium PTB-S1), poly(5-methoxyborooxyhexane sodium PTB-S2), and poly(6-methoxyborooxyhexane sodium PTB-S3). The polymer backbone contains repeating BO structural units and Na... + Coordinated oxygen-containing fragments and boron-oxygen anion fragments are immobilized in the polymer backbone, with Na + The preparation method, which uses the main migrating ion to achieve single-ion conductivity, includes the following specific steps: Step 1: Using TB as the starting monomer, dissolve it in an anhydrous aprotic solvent, add sodium alkoxide to carry out a coordination reaction, construct a boron-oxygen hexacyclic skeleton with alternating BO structure and add methoxy substituents, remove the solvent to obtain one or more of the neutral intermediates TB-S1, TB-S2, and TB-S3 with different substitution positions or ring structures. The second step involves dissolving one or more of the sodium borooxyhexacyclic salt monomers TB-S1, TB-S2, and TB-S3 in TB, adjusting the ratio of TB to TB-S monomers to obtain a precursor mixture for polymerization. This mixture is then subjected to ring-opening polymerization under heating conditions to obtain one or more of the corresponding polymer electrolytes PTB-S1, PTB-S2, and PTB-S3. The preparation route is as follows: ， Where n:m = 1:10-100.

2. The method for preparing a sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic skeleton according to claim 1, characterized in that: The anhydrous aprotic solvent is dichloromethane and tetrahydrofuran, and the sodium alkoxide is sodium methoxide and / or sodium ethoxide; the molar ratio of TB to sodium alkoxide is 1:1-3.2; the heating temperature in the second step is 40-80℃, and the heating time is 2-24h.

3. The method for preparing a sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic skeleton according to claim 1, characterized in that: In the second step, 1 part by molar ratio of boron-oxygen hexacyclic sodium salt monomers TB-S1, TB-S2, and TB-S3 are dissolved or dispersed in 10-100 parts of TB, and 0-30 wt% of organic solvent or plasticizer is added to prepare a homogeneous precursor electrolyte. The precursor electrolyte is injected into the battery cell pre-loaded with a positive electrode, a separator, and a sodium negative electrode by injection, and thermally induced polycondensation or ring-opening polymerization is carried out at 40-80℃ to form a PTB-S polymer electrolyte network with a boron-oxygen hexacyclic backbone as the main chain in situ in the separator channels and electrode pores, which penetrates the separator channels and forms a continuous contact interface with the electrode surface.

4. A sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic skeleton prepared by the preparation method according to any one of claims 1-3, characterized in that: The sodium borooxyhexacyclic salt monomers TB-S1, TB-S2, and TB-S3 are three structural isomeric sodium salts of 3-methoxyborooxyhexacyclic derivatives, obtained by changing the methoxy substitution position and / or the number of substitutions. Among them, the polymer PTB-S3 corresponding to TB-S3 has higher chain segment flexibility and more continuous ion conduction channels. Na in PTB-S1, PTB-S2, and PTB-S3 + Migration number ≥ 0.9, relative to Na + / Na has an upper limit of electrochemical stability window ≥ 4.5V, a glass transition temperature ≤ 0℃, and an ionic conductivity of 1.0 × 10⁻⁶ at 25℃. -5 -5.0×10 -4 S cm -1 .

5. The sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic skeleton according to claim 4, characterized in that: The ionic conductivity of the PTB-S3-based system is ≥1.0×10⁻⁶. -4 S cm -1 Na + Migration number ≥ 0.91, glass transition temperature ≤ -10℃, relative to Na + The upper limit of the electrochemical stability window for / Na is ≥4.7V.

6. The sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic skeleton according to claim 4, characterized in that: A plasticizer or co-solvent with a total mass fraction of 0-30 wt% is added to one or more of PTB-S1, PTB-S2, and PTB-S3. The plasticizer or co-solvent is a polar organic solvent, which is a carbonate and / or ether polar organic solvent, used to adjust the ionic conductivity.

7. The application of a sodium-based single-ion polymer electrolyte PTB-S based on a boron-oxygen hexacyclic framework prepared by the method according to any one of claims 1-3 in a sodium metal battery, characterized in that: PTB-S1, PTB-S2, and PTB-S3 are used as polymer electrolytes. The sodium metal battery includes a positive electrode, a negative electrode, and a separator. The polymer electrolyte is placed between the positive and negative electrodes in the form of a PTB-S polymer network formed by in-situ wetting the separator. The negative electrode is metallic sodium or a sodium-containing composite negative electrode, and the positive electrode is a sodium energy storage positive electrode material containing iron or vanadium. The separator is a glass fiber separator or a polyolefin porous separator. The Na||Na symmetric battery using PTB-S3 as the main electrolyte operates at 0.1-0.5 mA cm⁻¹. -2 During Na deposition / stripping cycling at current density, the steady-state polarization voltage is no higher than 150 mV, and the continuous cycling time is no less than 800 h. For Na||NFS full cells using PTB-S3 as the main electrolyte, the first-cycle specific capacity is 90-110 mAhg during charge-discharge testing at a current rate of 0.5 C within a voltage window of 2.0-4.0 V. -1 After 300-500 cycles, the capacity retention rate is not less than 85%, and the coulombic efficiency is not less than 99.0%.

8. The application according to claim 7, characterized in that: The positive electrode is an NFS sodium positive electrode material, which is placed between the positive and negative electrodes in the form of a PTB-S polymer network formed by in-situ wetting of the separator, with a thickness of 20-80 μm.

9. The application of a sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic skeleton prepared by the preparation method according to any one of claims 1-3 in the assembly of a Na||Na symmetric battery, characterized in that: Two sodium metal sheets are stacked with a self-supporting PTB-S polymer electrolyte membrane, or a porous separator and PTB-S polymer electrolyte composite layer, in an inert atmosphere and then assembled into a coin cell casing for encapsulation. Alternatively, TB / TB-S precursor electrolyte is injected into the Na|| separator|| Na dry cell and in-situ polymerization is carried out to obtain a symmetric cell for Na deposition / stripping testing.

10. The application of a sodium-based single-ion conductive polymer electrolyte PTB-S based on a boron-oxygen hexacyclic framework prepared by the method according to any one of claims 1-3 in the assembly of a Na||NFS full cell, characterized in that: The positive electrode containing NFS, the separator, and the sodium metal negative electrode are stacked and assembled in sequence in the battery casing. Then, a precursor electrolyte composed of TB-S monomers and TB is injected. After encapsulation, a thermally initiated ring-opening copolymerization reaction is carried out at 40-80℃ to form a PTB-S polymer electrolyte network with a boron-oxygen hexagon backbone as the main chain in situ in the separator channels and electrode pores. This network penetrates the separator channels and forms a continuous contact interface with the electrode surface, resulting in a sodium metal full cell for rate performance and long cycle performance testing.

Images