An in-situ polymerized amide-based polymer with polysulfide anion-terminated groups, its preparation method, and its applications.

Abstract

This application discloses an in-situ polymerized amide-based polymer with polysulfide anionic terminal groups, its preparation method, and its application. Using DMAA as the monomer and NaOTF as the sodium salt source, anionic polymerization is carried out under the initiation of polysulfide anions to obtain PDMAA oligomers with terminal polysulfide anionic groups. After battery assembly, in-situ polymerization is used to construct a continuous organic sulfur amorphous phase and a flexible polymer network in the electrode and separator regions, achieving the fixation of polysulfide terminal groups and NaOTF. + The electrolyte primarily utilizes single-ion conduction; a sulfur-containing SEI protective layer is formed on the sodium metal surface to inhibit dendrite growth and reduce interfacial impedance. After 500 cycles at 0.2 C rate, the coulombic efficiency of the full cell is greater than 99.9%. The ion conduction efficiency and interfacial stability of the solid electrolyte are synergistically improved through the design of polysulfide anion end groups and in-situ polymerization strategy. The process is simple and low-cost, making it suitable for the large-scale application of high-safety, long-life solid sodium metal batteries.

Description

Technical Field

[0001] This application belongs to the field of electrochemical energy storage technology, and in particular relates to an in-situ polymer with polysulfide anion end groups, its preparation method and application. Background Technology

[0002] Sodium metal batteries, due to their abundant sodium resources, low cost, and relatively high safety, are considered an important candidate technology for large-scale energy storage and distributed energy storage systems. Compared with traditional lithium-ion batteries, sodium metal batteries have significant advantages in raw material acquisition and cost control, and are expected to be widely used in grid peak shaving, renewable energy grid integration, and backup power. However, the liquid organic electrolytes commonly used in current practical applications suffer from problems such as flammability, leakage, and poor thermal stability. Under high voltage and long-cycle conditions, they are prone to safety accidents. Furthermore, the interface between the liquid electrolyte and the sodium metal anode is unstable, easily inducing dendrite growth and leading to short-circuit failure, severely restricting the further development of sodium metal battery technology.

[0003] To improve the safety and cycle life of sodium metal batteries, solid-state or quasi-solid-state polymer electrolytes have gradually become a research hotspot. Polymer electrolytes have advantages such as controllable shape, good processability, and the ability to regulate interface properties through chemical structure design, which can suppress electrolyte leakage and thermal runaway risks to a certain extent. In existing research, solid-state or gel electrolyte systems, represented by ether polymers such as PEO, have been widely explored in lithium / sodium batteries. However, they generally suffer from low ionic conductivity, high glass transition temperature, and restricted chain segment movement at room temperature, often requiring heating to obtain considerable conductivity. In addition, traditional polymer electrolytes are mostly dual-ion conduction systems, where anions can migrate freely in an electric field. Under high current density or thick electrode conditions, significant concentration polarization is easily generated, leading to uneven current distribution on the sodium metal surface, further inducing dendrite growth and interfacial instability.

[0004] In recent years, single-ion conductive polymer electrolytes and in-situ polymerization strategies have been considered important directions for improving interfacial contact and suppressing dendrites. By anchoring anions to the polymer backbone, Na+ can be significantly improved. + Increased migration number reduces concentration polarization, which is beneficial for achieving more uniform sodium deposition / stripping behavior. In-situ polymerization within the battery allows for the direct construction of continuous polymer networks within the electrode and separator pores, improving interfacial adhesion and reducing interfacial impedance. However, most existing single-ion-conducting polymer systems still rely on complex prepolymer synthesis and post-processing techniques, resulting in limited types of terminal functional groups and hindering interfacial reactions and sodium deposition. + Limited ability to finely control solvation structure; based on polysulfide Na2S xWhile anionic polymerization systems with x = 4, 6, and 8 have been reported in metal-sulfur batteries, introducing polysulfide anions into the ends of amide polymers and constructing organic-sulfur amorphous regions in the polymer electrolyte to synergistically regulate Na+ is a more advanced approach. + Schemes involving transport and interface SEI structures are still relatively rare, and overall, a technical approach that balances ion conduction efficiency, interface stability, and ease of synthesis has not yet been established. Summary of the Invention

[0005] Technical problems solved: This application provides an in-situ polymer with polysulfide anion end groups for amide-based polymerization, its preparation method and application, which solves the problems of flammability, leakage and poor thermal stability of liquid organic electrolytes in the prior art. These problems can easily lead to safety accidents under high voltage and long cycle conditions. At the same time, the interface between the liquid electrolyte and the sodium metal anode is unstable, which can easily induce dendrite growth and lead to short circuit failure, which seriously restricts the further development of sodium metal battery technology. Ether polymers generally have problems such as low ionic conductivity, high glass transition temperature and restricted chain segment movement at room temperature. They often need to be heated to obtain a considerable conductivity. Traditional polymer electrolytes are mostly dual ionic conduction systems. Anions can migrate freely in the electric field. Under high current density or thick electrode conditions, they are prone to obvious concentration polarization, which leads to uneven current distribution on the sodium metal surface and further induces dendrite growth and interface instability.

[0006] Objective of the Invention: This application provides an in-situ polymer with polysulfide anionic end groups, its preparation method, and its application. Through in-situ anionic polymerization initiated by polysulfides, a polymer network containing amorphous organic sulfur regions is constructed in an electrolyte system to improve Na+ content. + The transference number and room temperature ionic conductivity are optimized to improve the stability of the electrode / electrolyte interface, thereby balancing the safety, high specific energy, and long cycle life of sodium metal batteries.

[0007] A method for preparing an amide polymer with polysulfide anion-terminated groups by in-situ polymerization includes the following specific steps: The first step is to prepare a DMAA monomer solution containing NaOTf: Under an inert atmosphere, sodium trifluoromethanesulfonate (NaOTf) is added at a concentration of 0.5-3.0 mol / L. -1 Dissolved in N,N-dimethylacrylamide (DMAA), the solution was magnetically stirred until completely dissolved to obtain a clear and homogeneous NaOTf / DMAA sodium salt solution, which served as the base system for the electrolyte precursor solution. The second step is to prepare Na2S. xPolysulfide initiator solution: Add metallic sodium and sulfur powder to 5-100 mL of diethylene glycol dimethyl ether (DIGLYME) at a molar ratio of Na:S = 1:2-4, and stir for 12-24 h at 30-60 °C to obtain 1-5 mM Na₂S. x Initiator solution, where x is 4, 6, or 8, yields Na2S x Initiator solutions serve as initiators for anionic polymerization and as a source of polysulfide anionic end groups; The third step is the anionic polymerization to form PDMAA: Na2S x The initiator solution is added to the NaOTf / DMAA sodium salt solution at a volume fraction of 0.1-1%. Under an inert atmosphere and at 30-60℃, the mixture is stirred or allowed to stand for 12-24 hours to induce anionic polymerization of DMAA, yielding a PDMAA polymer electrolyte containing polysulfide anionic end groups or a PDMAA in-situ polymerization precursor solution. During the reaction, Na2S... x This initiates the anionic polymerization of DMAA, forming PDMAA chains with terminal polysulfide anionic groups, while NaOTF provides migratable Na+. + ; Step 4, pre-installing the battery: In an inert atmosphere glove box, pre-install the positive electrode, separator, and sodium metal negative electrode into the battery casing; Step 5: Inject the PDMAA in-situ polymerization precursor solution into the battery to fully wet the separator and electrode pores; Step 6: Allow the PDMAA in-situ polymerization precursor solution to stand for 12-24 hours at room temperature or at a temperature of 25-60℃ to undergo anionic polymerization inside the battery, forming a PDMAA polymer electrolyte network with polysulfide anionic end groups, thus achieving in-situ solidification.

[0008] Furthermore, in the second step, Na2S x The concentration was 3 mM.

[0009] Furthermore, in the third step, Na2S x The molar ratio with DMAA is 0.001-0.1, and the mixture is stirred or allowed to stand for 12 hours under an inert atmosphere at 40-50℃.

[0010] Furthermore, in the sixth step, the mixture is left to stand at 40°C for 12-24 hours.

[0011] An in-situ polymerized amide-based polymer with polysulfide anion-terminated groups, prepared by any of the above-described preparation methods, wherein the amide-based polymer is a PDMAA polymer electrolyte, formed by N,N-dimethylacrylamide (DMAA) monomer in the presence of polysulfide anions Na₂S₂. xThe polymer is obtained by anionic polymerization under initiation, where x is 4, 6, or 8; the main chain is a PDMAA backbone, with organic sulfur polysulfide anionic terminal groups introduced at the chain ends or segments to form organic sulfur-rich amorphous regions; the polymer electrolyte contains sodium salt NaOTf as an ion source; the PDMAA polymer electrolyte has an ionic conductivity ≥1.0×10⁻⁶ at 25°C. -4 S·cm -1 Na + The transport number is in the range of 0.50-0.70, and the glass transition temperature (Tg) is below -20℃, relative to Na. + The upper limit of the electrochemical stability window of / Na is >4.0V; thermogravimetric analysis shows that the mass loss is ≤10% before 200℃ and the measurable ionic conductivity is maintained below -30℃.

[0012] Furthermore, one or both ends of the PDMAA polymer chain contain Na2S. x The end groups, wherein the polysulfide anions are covalently or stably coordinated with the polymer backbone, thereby connecting the amorphous regions of the organic sulfur with Na. + The main coordination environment is spatially tightly coupled, Na2S x The molar fraction of end groups in PDMAA corresponds to an initiator concentration of 1-5 mM; the ionic conductivity of the PDMAA polymer electrolyte at 25 °C is 1.2 × 10⁻⁶. -4 S·cm -1 Na + The migration number is 0.59, and the glass transition temperature Tg is in the range of -30.0 to -41.4℃.

[0013] This application also discloses the application of in-situ polymerized amide-based polymers with polysulfide anion-terminated groups prepared by any of the above-described preparation methods in sodium metal batteries. The sodium metal battery includes a sodium metal anode, a sodium energy storage cathode, and a separator. The amide-based polymer is filled between the sodium metal anode and the sodium energy storage cathode and is in close contact with the electrode interface. The sodium energy storage cathode formulation is active material: Super P:PVDF = 80-92:3-7:3-7 by mass ratio. The active material is sodium vanadium phosphate cathode material, which is Na3V2(PO4)3, i.e., NVP or Na2V3(PO4)3. The sodium metal anode is a sodium metal sheet, and the separator is a polypropylene microporous membrane or a glass fiber separator.

[0014] Furthermore, the sodium metal battery retains a specific capacity of ≥90% and an average coulombic efficiency of ≥99.9% after 500 cycles at a rate of 0.2-0.5C; the amide polymer is used to improve the ionic conductivity and Na+. + This increases the migration number, reduces concentration polarization, improves electrode / electrolyte interface contact, and inhibits sodium dendrite formation and growth, thereby enhancing battery safety and cycle life.

[0015] This application also discloses the application of in-situ polymerized amide groups with polysulfide anion terminals prepared by any of the above-described methods in a Na||Na symmetric battery, wherein the amide polymer is placed between two sodium metal electrodes at a temperature of 0.1-5.0 mA cm⁻¹. -2 When Na deposition / stripping tests are performed at current density, the Na||Na symmetric cells can cycle stably for ≥400h without short circuit.

[0016] This application also discloses the application of in-situ polymers with polysulfide anion-terminated amide groups prepared by any of the above preparation methods in high-safety solid-state or quasi-solid-state sodium-based energy storage systems, wherein the high-safety solid-state or quasi-solid-state sodium-based energy storage systems are large-scale energy storage power stations or distributed energy sodium-based energy storage devices.

[0017] Explanation of Principle: This application discloses an in-situ polymer with polysulfide anion-terminated amide groups, its preparation method, and its application in solid-state sodium metal batteries. The polymer uses N,N-dimethylacrylamide (DMAA) as a monomer and NaOTF as a sodium salt source, and is produced in a polysulfide environment (Na₂S₂). x (x = 4, 6, 8) Anionic polymerization was initiated to obtain PDMAA oligomers with terminal polysulfide anionic groups. After battery assembly, in-situ polymerization was used to construct a continuous organic sulfur amorphous phase and flexible polymer network in the electrode and separator regions, achieving functionalization and fixation of polysulfide end groups and Na. + Primarily single-ion conduction; the electrolyte of this invention has an ionic conductivity of approximately 1.2 × 10⁻⁶ at room temperature. -4 S·cm -1 Na + The mobility number is approximately 0.59, and the electrochemical stability window is greater than 4.0 V (vs. Na / Na). + It can form a stable sulfur-containing SEI protective layer on the sodium metal surface, effectively inhibiting dendrite growth and reducing interfacial impedance. The full cell assembled with Na3V2(PO4)3 cathode retains about 93% of its capacity after 500 cycles at 0.2 C rate, and has a coulombic efficiency greater than 99.9%. This invention improves the ion conduction efficiency and interfacial stability of solid electrolyte through polysulfide anion end group design and in-situ polymerization strategy. The process is simple and low cost, and it is suitable for the large-scale application of high-safety and long-life solid sodium metal batteries.

[0018] The beneficial effects of this invention are: 1. Through the polysulfide Na2S x Initiating DMAA anionic polymerization, introducing polysulfide anionic groups at the polymer chain ends, and constructing amorphous regions containing organic sulfur in the polymer electrolyte, thereby enabling Na... +The solvation structure and local electric field distribution were effectively regulated, thereby significantly improving Na while maintaining high ionic conductivity. + Migration number reduces concentration polarization; 2. The in-situ polymerization strategy enables the PDMAA network to be generated simultaneously in the pores of the electrode and the membrane, which can fully fill the micropores and adhere to the electrode surface, effectively reducing the interfacial contact resistance and suppressing common problems of dryness, dehydration and poor local contact in liquid electrolytes, providing a stable interfacial environment for uniform Na deposition / stripping. 3. Polysulfide anion end groups are beneficial for the formation of a stable sulfur-containing SEI film during the electrode / electrolyte interface reaction. XPS and electrochemical tests show that this SEI can effectively buffer volume changes and inhibit sodium dendrite growth, thereby significantly improving the cycle stability and safety of sodium metal electrodes. 4. This invention uses Na2S x The process route for directly initiating DMAA polymerization is simple in synthesis steps, mild in conditions, and does not require complex prepolymers or multi-step functionalization operations, making it suitable for large-scale preparation. At the same time, all components in the electrolyte formulation are common chemicals, which has good cost control and process scale-up potential. 5. The PDMAA polysulfide anion-terminated amide-based polymer electrolyte of the present invention exhibits superior ionic conductivity and Na+. + It achieves a relatively balanced comprehensive performance in terms of migration number, electrochemical stability, interfacial stability and process simplicity, providing a promising electrolyte system for constructing high-safety, high-energy-density, and long-life solid-state or quasi-solid-state sodium metal batteries. Attached Figure Description

[0019] Figure 1 The images show the nuclear magnetic resonance (NMR) spectroscopic characterization of PDMAA in this application, where a is the NMR 13C spectrum and b is the NMR 1H spectrum. Figure 2 The results of the ionic conductivity and ion transport number tests of PDMAA in this application are shown, where a is the ionic conductivity graph of Na2S4 at different concentrations and b is the ion transport number graph of Na2S4 at different concentrations. Figure 3 The graphs show the cycle performance test results of the symmetrical battery PDMAA of this application, where a is the limiting current density graph and b is the symmetrical battery test graph. Figure 4 The results are the full-cell performance test results of PDMAA in this application, where a is the rate performance test graph and b is the rate performance charge-discharge curve graph. Figure 5 The images show the infrared spectra of the sulfur-terminated PDMAA before and after polymerization in this application. Detailed Implementation

[0020] 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.

[0021] The following examples utilize Na2S4 to initiate the anionic polymerization of DMAA to prepare PDMAA polymer electrolytes with terminal polysulfide anionic groups, and assemble Na||Na symmetric cells and Na||NVP full cells to evaluate their electrochemical performance.

[0022] Example 1: A method for preparing an amide polymer with polysulfide anion-terminated groups produced by in-situ polymerization, illustrating the process using NaOTF at a concentration of approximately 2.0 mol / L. -1 The Na2S4 initiator concentration is approximately 3 mmol / L. -1 PDMAA polymer electrolytes with polysulfide anion end groups were prepared under specific conditions, and Na||Na symmetric cells and Na||NVP full cells were assembled for performance evaluation. Unless otherwise specified, all operations were carried out at room temperature and under an inert atmosphere, including the following specific steps: The first step is to prepare a DMAA monomer solution containing NaOTf: In an argon glove box, sodium trifluoromethanesulfonate (NaOTf) is added at a concentration of 2 mol / L. -1 Dissolved in N,N-dimethylacrylamide (DMAA), the solution was magnetically stirred until completely dissolved to obtain a clear and homogeneous NaOTf / DMAA sodium salt solution, which served as the base system for the electrolyte precursor solution. The second step is to prepare a Na2S4 polysulfide initiator solution: Under an inert atmosphere, sodium metal (0.69 mg) and sulfur powder (0.19 mg) are added to 5 mL of diethylene glycol dimethyl ether (DIGLYME) in a molar ratio of sodium metal (Na): elemental sulfur (S) = 1:2. The mixture is stirred at 40 °C for 18 h to obtain a 3 mM Na2S4 initiator solution, which serves as an anionic polymerization initiator and a source of polysulfide anionic end groups. The third step is anionic polymerization to form PDMAA: A Na2S4 initiator solution is added to a NaOTf / DMAA sodium salt solution at a volume fraction of 0.5%. The mixture is stirred or allowed to stand for 12 hours under an argon atmosphere at 40°C to allow DMAA to undergo anionic polymerization, yielding a PDMAA polymer electrolyte containing polysulfide anionic end groups or a PDMAA in-situ polymerization precursor solution. NaOTF serves as a migratory Na+... + The source remains in the system; Step 4, pre-installing the battery: Cut two 12 mm diameter sodium metal sheets and one 16 mm diameter polypropylene microporous membrane in an argon glove box. Stack the sodium metal sheets, membrane and sodium metal sheets in sequence in the CR2032 button cell casing. Step 5: Use a micro-syringe to inject the PDMAA in-situ polymerization precursor solution into the battery, with an injection volume of about 40 μL, to fully wet the separator and sodium surface; Step 6: After encapsulation, place the battery at 40°C for 12 hours to allow the PDMAA in-situ polymerization precursor solution to undergo anionic polymerization inside the battery, forming a PDMAA polymer electrolyte network with polysulfide anionic end groups, thus achieving in-situ solidification. Step 7, Na||Na symmetric cell deposition / stripping test: Using a cell testing system at 25°C, at a rate of 0.5 mAcm⁻¹ -2 Current density was used in bidirectional deposition / stripping tests in Na||Na symmetric cells, with an areal capacity of 0.5 mAh·cm² per half-cycle. -2 Test results show that the symmetrical battery can cycle stably for approximately 400 hours, with the steady-state polarization voltage remaining within the range of 80-100mV. The voltage curve is smooth, with no obvious sudden polarization increase or short circuit phenomenon. The interface impedance obtained by AC impedance fitting is approximately 150 Ω, indicating good stability.

[0023] Preparation of Na3V2(PO4)3 cathode and assembly of Na||NVP full cell: Weigh out Na3V2(PO4)3 (NVP active material): Super P conductive agent: PVDF binder in a mass ratio of 91:4:5, add it to NMP, and mix in a planetary mixer for about 12 hours to obtain a homogeneous slurry with a solid content of about 45%. Coat the slurry evenly onto carbon-coated aluminum foil, and heat-treat at 110°C for about 12 hours to remove the solvent, controlling the positive electrode active material loading to be approximately 5 mg·cm³. -2 It is then cut into 12 mm diameter circular pieces, which are NVP positive electrode sheets.

[0024] In an argon glove box, the NVP positive electrode, polypropylene separator, and sodium metal negative electrode are stacked sequentially in the coin cell casing. Approximately 40 μL of PDMAA precursor solution is injected to fully wet the positive electrode pores and separator. After encapsulation, the cells are allowed to stand at 40°C for 12 hours to complete in-situ polymerization, resulting in a Na||PDMAA||NVP full cell.

[0025] Electrochemical performance testing of Na||NVP full cells: After 5 pre-cycles at 0.1C within a voltage window of 2.5–3.8V, long-term cycling tests were conducted at 0.2C. The results show that the initial discharge specific capacity is approximately 112 mAh g⁻¹. -1 After 500 cycles, the capacity retention rate is approximately 93%, and the average coulombic efficiency is close to 99.9%. When the current density is gradually increased in the range of 0.1-1.0C, the battery specific capacity decreases with increasing rate. After returning to 0.2C, the capacity can recover to more than 90% of the initial value, indicating that the PDMAA electrolyte has good rate adaptability and interfacial reversibility.

[0026] Example 2: A method for preparing an amide polymer with polysulfide anion-terminated groups produced by in-situ polymerization, wherein the NaOTF concentration is maintained at approximately 2.0 mol / L. -1 Without changing the concentration of Na2S4, the concentration was reduced to approximately 1 mmol / L. -1 To investigate the effect of polysulfide anion initiator content on the structure and electrochemical performance of PDMAA, the following specific steps were taken: The first step is to prepare a DMAA monomer solution containing NaOTf: In an argon glove box, sodium trifluoromethanesulfonate (NaOTf) is added at a concentration of 2 mol / L. -1 Dissolved in N,N-dimethylacrylamide (DMAA), the solution was magnetically stirred until completely dissolved to obtain a clear and homogeneous NaOTf / DMAA sodium salt solution, which served as the base system for the electrolyte precursor solution. The second step is to prepare a Na2S4 polysulfide initiator solution: Under an inert atmosphere, sodium metal (0.46 mg) and sulfur powder (1.28 mg) are added to 10 mL of diethylene glycol dimethyl ether (DIGLYME) in a molar ratio of sodium metal (Na): elemental sulfur (S) = 1:2. The mixture is stirred at 35 °C for 16 h to obtain a 1 mM Na2S4 initiator solution, which serves as an anionic polymerization initiator and a source of polysulfide anionic end groups. The third step is anionic polymerization to form PDMAA: A Na2S4 initiator solution is added at a volume fraction of 1% to a NaOTf / DMAA sodium salt solution. The mixture is stirred or allowed to stand for 18 hours under an argon atmosphere at 40°C to allow DMAA to undergo anionic polymerization, yielding a PDMAA polymer electrolyte containing polysulfide anionic end groups or a PDMAA in-situ polymerization precursor solution. NaOTF serves as a migratory Na+... + The source remains in the system; Step 4, pre-installing the battery: Cut two 12 mm diameter sodium metal sheets and one 16 mm diameter polypropylene microporous membrane in an argon glove box. Stack the sodium metal sheets, membrane and sodium metal sheets in sequence in the CR2032 button cell casing. Step 5: Use a micro-syringe to inject the PDMAA in-situ polymerization precursor solution into the battery, with an injection volume of about 40 μL, to fully wet the separator and sodium surface; Step 6: After encapsulation, place the battery at 40°C for 12 hours to allow the PDMAA in-situ polymerization precursor solution to undergo anionic polymerization inside the battery, forming a PDMAA polymer electrolyte network with polysulfide anionic end groups, thus achieving in-situ solidification and obtaining a Na||PDMAA||Na symmetric battery. Step 7, Na||Na symmetric cell deposition / stripping test: Using a cell testing system at 25°C, at a rate of 0.5 mAcm⁻¹ -2Current density was used in bidirectional deposition / stripping tests in Na||Na symmetric cells, with an areal capacity of 0.5 mAh·cm² per half-cycle. -2 Test results show that the symmetrical battery can cycle stably for about 350 hours, and the steady-state polarization voltage is basically maintained in the range of 90-110mV. AC impedance analysis shows that the interface impedance is slightly higher than that of Example 1, but still within a suitable range.

[0027] Preparation of Na3V2(PO4)3 cathode and assembly of Na||NVP full cell: Weigh out Na3V2(PO4)3 (NVP active material): Super P conductive agent: PVDF binder in a mass ratio of 91:4:5, add it to NMP, and mix in a planetary mixer for about 12 hours to obtain a homogeneous slurry with a solid content of about 45%. Coat the slurry evenly onto carbon-coated aluminum foil, and heat-treat at 110°C for about 12 hours to remove the solvent, controlling the positive electrode active material loading to be approximately 5 mg·cm³. -2 It is then cut into 12 mm diameter circular pieces, which are NVP positive electrode sheets.

[0028] In an argon glove box, the NVP positive electrode, polypropylene separator, and sodium metal negative electrode are stacked sequentially in the coin cell casing. Approximately 40 μL of PDMAA precursor solution is injected to fully wet the positive electrode pores and separator. After encapsulation, the cells are allowed to stand at 40°C for 12 hours to complete in-situ polymerization, resulting in a Na||PDMAA||NVP full cell.

[0029] Na||NVP full-cell electrochemical performance test: After 300 pre-cycles at a 0.2C rate within a voltage window of 2.5-3.8V, the battery discharge specific capacity increased from approximately 110 mAh g in the first cycle. -1 Decay to approximately 99 mAh g -1 The capacity retention rate is approximately 90%, and the coulombic efficiency remains above 99.8%. Compared to Example 1, the rate performance is slightly lower, but the cycle stability remains good.

[0030] Example 3: A method for preparing an amide polymer with polysulfide anion-terminated groups produced by in-situ polymerization, wherein the NaOTF concentration is maintained at approximately 2.0 mol / L. -1 Under these conditions, the Na2S4 concentration was increased to approximately 5 mmol / L. -1 The effect of higher polysulfide content on PDMAA electrolyte was investigated, including the following specific steps: The first step is to prepare a DMAA monomer solution containing NaOTf: In an argon glove box, sodium trifluoromethanesulfonate (NaOTf) is added at a concentration of 2 mol / L. -1Dissolved in N,N-dimethylacrylamide (DMAA), the solution was magnetically stirred until completely dissolved to obtain a clear and homogeneous NaOTf / DMAA sodium salt solution, which served as the base system for the electrolyte precursor solution. The second step is to prepare a high-concentration Na2S4 polysulfide initiator solution: Under an inert atmosphere, sodium metal (23.0 mg) and sulfur powder (64.1 mg) are added to 100 mL of diethylene glycol dimethyl ether (DIGLYME) in a molar ratio of sodium metal (Na): elemental sulfur (S) = 1:2. The mixture is stirred at 50-60 °C for 20 h to obtain a 5 mM Na2S4 initiator solution, which serves as an anionic polymerization initiator and a source of polysulfide anionic end groups. The third step is anionic polymerization to form PDMAA: A Na2S4 initiator solution is added to a NaOTf / DMAA sodium salt solution at a volume fraction of 0.1%. The mixture is stirred or allowed to stand for 12 hours under an argon atmosphere at 40°C to allow DMAA to undergo anionic polymerization, yielding a PDMAA polymer electrolyte containing polysulfide anionic end groups or a PDMAA in-situ polymerization precursor solution. NaOTF serves as a migratory Na+... + The source remains in the system, and differential scanning calorimetry shows that the Tg of the system is approximately -35℃; Step 4, pre-installing the battery: Cut two 12 mm diameter sodium metal sheets and one 16 mm diameter polypropylene microporous membrane in an argon glove box. Stack the sodium metal sheets, membrane and sodium metal sheets in sequence in the CR2032 button cell casing. Step 5: Use a micro-syringe to inject the PDMAA in-situ polymerization precursor solution into the battery, with an injection volume of about 40 μL, to fully wet the separator and sodium surface; Step 6: After encapsulation, place the battery at 40°C for 12 hours to allow the PDMAA in-situ polymerization precursor solution to undergo anionic polymerization inside the battery, forming a PDMAA polymer electrolyte network with polysulfide anionic end groups, thus achieving in-situ solidification and obtaining a Na||PDMAA||Na symmetric battery. Step 7, Na||Na symmetric cell deposition / stripping test: Using a cell testing system at 25°C, at a rate of 0.5 mAcm⁻¹ -2 Current density was used in bidirectional deposition / stripping tests in Na||Na symmetric cells, with an areal capacity of 0.5 mAh·cm² per half-cycle. -2 Test results show that the symmetric cell can cycle stably for about 450 hours, and the steady-state polarization voltage is basically maintained in the range of 70-90mV, which is somewhat lower than that of Example 1. This indicates that a higher polysulfide content is beneficial to the interfacial electrochemical process, but an excessively high content may lead to an increase in partial diffusion polarization.

[0031] Preparation of Na3V2(PO4)3 cathode and assembly of Na||NVP full cell: Weigh out Na3V2(PO4)3 (NVP active material): Super P conductive agent: PVDF binder in a mass ratio of 91:4:5, add it to NMP, and mix in a planetary mixer for about 12 hours to obtain a homogeneous slurry with a solid content of about 45%. Coat the slurry evenly onto carbon-coated aluminum foil, and heat-treat at 110°C for about 12 hours to remove the solvent, controlling the positive electrode active material loading to be approximately 5 mg·cm³. -2 It is then cut into 12 mm diameter circular pieces, which are NVP positive electrode sheets.

[0032] In an argon glove box, the NVP positive electrode, polypropylene separator, and sodium metal negative electrode are stacked sequentially in the coin cell casing. Approximately 40 μL of PDMAA precursor solution is injected to fully wet the positive electrode pores and separator. After encapsulation, the cells are allowed to stand at 40°C for 12 hours to complete in-situ polymerization, resulting in a Na||PDMAA||NVP full cell.

[0033] Na||NVP full-cell electrochemical performance test: After 500 pre-cycles at a 0.2C rate within a voltage window of 2.5-3.8V, the battery discharge specific capacity increased from approximately 110 mAh g in the first cycle. -1 Decay to approximately 100 mAh g -1 The capacity retention rate was approximately 91%, and the coulombic efficiency was close to 99.9%. Compared with Example 1, the high-concentration Na2S4 sample had slightly lower internal resistance initially, but the capacity retention rate was similar after long-term cycling.

[0034] Example 4: A method for preparing an amide polymer with polysulfide anion-terminated groups produced by in-situ polymerization, using Na2S8 as an initiator, to investigate the effect of polysulfides of different chain lengths on the electrolyte performance of PDMAA, while slightly adjusting the NaOTF concentration, including the following specific steps: The first step is to prepare a DMAA monomer solution containing NaOTf: In an argon glove box, sodium trifluoromethanesulfonate (NaOTf) is added at a concentration of 1.5 mol / L. -1 Dissolved in N,N-dimethylacrylamide (DMAA), the solution was magnetically stirred until completely dissolved to obtain a clear and homogeneous NaOTf / DMAA sodium salt solution, which served as the base system for the electrolyte precursor solution. The second step is to prepare the Na2S8 polysulfide initiator solution: Under an inert atmosphere, add 6.9 mg of metallic sodium and 38.5 mg of sulfur powder to 50 mL of diethylene glycol dimethyl ether (DIGLYME) in a molar ratio of Na:S = 1:4. Stir at 40-50 °C for 18-24 h to obtain a 3 mM Na2S8 initiator solution, which serves as an anionic polymerization initiator and a source of polysulfide anionic end groups. The third step is anionic polymerization to form PDMAA: A Na2S8 initiator solution is added at a volume fraction of 0.6% to a NaOTf / DMAA sodium salt solution. The mixture is stirred or allowed to stand for 12-24 hours under an argon atmosphere at 35-45℃ to allow DMAA to undergo anionic polymerization, yielding a PDMAA polymer electrolyte containing polysulfide anionic end groups or a PDMAA in-situ polymerization precursor solution. NaOTF serves as a migratory Na+... + The source remains in the system, and tests show that the ionic conductivity of this system at 25°C is approximately 1.0 × 10⁻⁶. -4 S·cm -1 Na + The migration number is approximately 0.55, and the upper limit of the electrochemical stability window remains above 4.0V; Step 4, pre-installing the battery: Cut two 12 mm diameter sodium metal sheets and one 16 mm diameter polypropylene microporous membrane in an argon glove box. Stack the sodium metal sheets, membrane and sodium metal sheets in sequence in the CR2032 button cell casing. Step 5: Use a micro-syringe to inject the PDMAA in-situ polymerization precursor solution into the battery, with an injection volume of about 40-50 μL, to fully wet the separator and sodium surface; Step 6: After encapsulation, place the battery at 40°C for 12 hours to allow the PDMAA in-situ polymerization precursor solution to undergo anionic polymerization inside the battery, forming a PDMAA polymer electrolyte network with polysulfide anionic end groups, thus achieving in-situ solidification and obtaining a Na||PDMAA||Na symmetric battery. Step 7, Na||Na symmetric cell deposition / stripping test: Using a cell testing system at 25°C, at a rate of 0.5 mAcm⁻¹ -2 Current density was used in bidirectional deposition / stripping tests in Na||Na symmetric cells, with an areal capacity of 0.5 mAh·cm² per half-cycle. -2 Test results show that the symmetrical battery can cycle stably for about 380 hours, with the steady-state polarization voltage basically maintained in the range of 80-110mV, and the interface impedance changing little with cycling.

[0035] Preparation of Na3V2(PO4)3 cathode and assembly of Na||NVP full cell: Weigh out Na3V2(PO4)3 (NVP active material): Super P conductive agent: PVDF binder in a mass ratio of 91:4:5, add it to NMP, and mix in a planetary mixer for about 12 hours to obtain a homogeneous slurry with a solid content of about 45%. Coat the slurry evenly onto carbon-coated aluminum foil, and heat-treat at 110°C for about 12 hours to remove the solvent, controlling the positive electrode active material loading to be approximately 5 mg·cm³. -2 It is then cut into 12 mm diameter circular pieces, which are NVP positive electrode sheets.

[0036] In an argon glove box, the NVP positive electrode, polypropylene separator, and sodium metal negative electrode are stacked sequentially in the coin cell casing. Approximately 40 μL of PDMAA precursor solution is injected to fully wet the positive electrode pores and separator. After encapsulation, the cells are allowed to stand at 40°C for 12 hours to complete in-situ polymerization, resulting in a Na||PDMAA||NVP full cell.

[0037] Na||NVP full cell electrochemical performance test: Within the voltage window of 2.5-3.8V, after 400 pre-cycles at a rate of 0.2C, the capacity retention rate is about 90%, and it shows good capacity recovery and coulombic efficiency in the 0.1-1.0C rate test.

[0038] Four examples were implemented at NaOTF concentration and Na2S concentration. x The concentration and polysulfide chain length were systematically adjusted, all following the technical solutions defined in the aforementioned claims and the invention description. Furthermore, no additional vacuum or reduced-pressure drying treatment was performed on the polymer electrolyte system during the preparation process; anionic polymerization and network construction were completed solely through temperature control and static settling. The results show that: At approximately 2.0 mol L of NaOTF -1 Na2S4 approximately 3 mmol / L -1 Under the conditions (Example 1), the PDMAA electrolyte exhibited good ionic conductivity and high Na+. + A better balance is achieved between migration number, interface impedance, and cycle lifetime; Adjusting the concentration of Na2S4 (Examples 2 and 3) and introducing Na2S6 / Na2S8 (Example 4) can adjust Tg, chain segment flexibility and interface state within a certain range, demonstrating the controllability of the system. In all embodiments, the Na||Na symmetric cells exhibited stable Na deposition / stripping behavior over a relatively long period of time, and the Na||NVP full cells maintained high capacity retention and nearly 100% coulombic efficiency under medium rate and long cycle conditions, verifying the effectiveness and reliability of the PDMAA polysulfide anion-terminated polymer electrolyte system of the present invention in practical sodium metal battery applications.

[0039] Explanation and overall evaluation: This invention introduces Na2S into the polymer chain ends by initiating DMAA anionic polymerization via polysulfide anions. x Polysulfide anionic groups are used to construct a PDMAA polymer electrolyte system that combines high ion conductivity with excellent interfacial stability. Compared with traditional PEO-based or ordinary salt-doped polymer electrolytes, the system of this invention achieves synergistic optimization at three levels in structural design: firstly, through the combined effect of polysulfide end groups and amide groups, a Na-rich... + The organic sulfur amorphous region of the coordination site is Na+ The system provides continuous migration channels; secondly, it utilizes terminal polysulfide anions to regulate the interaction between polymer chain segments, significantly reducing Tg and maintaining high chain activity at room temperature; and thirdly, through an in-situ polymerization strategy, the polymer network is generated in situ inside the electrode / diaphragm, improving the matching and contact state of the electrolyte-sodium metal interface from the source.

[0040] The test results from Examples 1-3 show that the PDMAA electrolyte of the present invention can stably achieve an ionic conductivity of approximately 1.0 × 10⁻⁶ at 25°C. -4 -1.2×10 -4 S·cm -1 Na + With a mobility number of approximately 0.56-0.59, an ion migration activation energy of approximately 0.07-0.09 eV, and a glass transition temperature as low as -35℃, it exhibits both high ion conductivity and excellent low-temperature chain segment mobility. Linear sweep voltammetry indicates that the upper limit of its electrochemical stability window exceeds 4.0V (vs. Na). + Thermogravimetric analysis showed that the material only exhibited significant weight loss above approximately 200°C, indicating that the polymer electrolyte has good thermal and electrochemical stability over a wide temperature range and under medium to high voltage conditions, which can meet the safety requirements of high-energy-density sodium metal batteries.

[0041] At both the symmetric and full-cell levels, the electrolyte of this invention exhibits excellent interfacial stability and cycle life. The Na||PDMAA||Na symmetric cell at 0.5 mA cm⁻¹ -2 Under these conditions, the electrolyte can stably undergo deposition / stripping cycles for hundreds of hours or more, with the polarization voltage maintained in the range of approximately 70-130 mV and gradually decreasing with cycling. This indicates that the sulfur-containing SEI layer constructed with the participation of polysulfide end groups can spontaneously regulate and reconstruct during cycling, suppressing the initiation and growth of sodium dendrites and maintaining a low interfacial impedance. After hundreds of cycles at 0.2-0.5 C rates, the Na||NVP full cell generally retains around 90% or even higher capacity, with an average coulombic efficiency approaching or exceeding 99.9%, fully verifying the supporting role of the electrolyte of this invention in long cycle life and high-efficiency energy conversion in practical battery systems.

[0042] By modulating Na2S on the same DMAA framework x By specifying the types and amounts of (x = 4, 6, 8), this invention achieves improvements in ionic conductivity and Na... + A tunable balance between transport number, Tg, electrochemical window, and interfacial stability. The Na₂S₄ system exhibits good ionic conductivity at room temperature and Na₂S₄... +In terms of transference number, the overall performance is superior, making it suitable for applications that balance rate performance and cycle life. The Na2S6 system maintains good conductivity while also exhibiting good interfacial stability, making it suitable for applications with wide requirements for safety and process windows. The Na2S8 system is more prominent in reducing Tg and improving SEI composition, which is beneficial for further improving capacity retention and controllable interfacial evolution under long-cycle conditions. Results from multiple examples demonstrate that the polysulfide anion end-group modulation strategy proposed in this invention has a clear structure-performance response law, facilitating engineering selection and scale-up according to different application requirements.

[0043] In summary, this invention achieves a unified approach to PDMAA polymer electrolytes in terms of structural design, preparation process, and electrochemical performance through in-situ anionic polymerization initiated by polysulfides. On the one hand, the synthesis route is simple and the conditions are mild, allowing polymerization to be completed directly during battery assembly, significantly simplifying the process, improving material consistency, and reducing preparation costs. On the other hand, the in-situ polymerization morphology combines the advantages of liquid wetting and solid-state safety, enabling the electrolyte to maintain high Na+ content. + Under the premise of a high migration number and moderate conductivity, it forms a tight and stable interfacial contact with sodium metal and cathode particles. Based on the above comprehensive performance, the PDMAA polymer electrolyte of this invention provides a material and technical solution with a clear mechanistic basis and good application prospects for a new generation of high-safety, long-life, and high-efficiency solid-state sodium metal batteries. Equivalent substitutions and optimizations made by those skilled in the art regarding the types and concentrations of polysulfides, monomer composition, and electrode formulations, without departing from the basic concept of this invention, should all be considered to fall within the protection scope of this invention.

[0044] The above description represents the preferred embodiments of the present invention. For those skilled in the art, equivalent adjustments and improvements can be made to the raw material ratios, diaphragm substrate, electrode formulation, and testing conditions without departing from the principles of the present invention, and all such adjustments should fall within the protection scope of the present invention. Structures, devices, and operating methods not specifically described in this invention can be implemented using conventional methods in the art unless otherwise specified or limited.

Claims

1. A method for preparing an amide polymer with polysulfide anion-terminated groups by in-situ polymerization, characterized in that, The specific steps include the following: The first step is to prepare a DMAA monomer solution containing NaOTf: Under an inert atmosphere, sodium trifluoromethanesulfonate (NaOTf) is added at a concentration of 0.5-3.0 mol / L. -1 Dissolve in N,N-dimethylacrylamide (DMAA) and stir until completely dissolved to obtain a NaOTf / DMAA sodium salt solution. The second step is to prepare Na2S. x Polysulfide initiator solution: Add metallic sodium and sulfur powder to 5-100 mL of diethylene glycol dimethyl ether (DIGLYME) at a molar ratio of Na:S = 1:2-4, and stir for 12-24 h at 30-60 °C to obtain 1-5 mM Na₂S. x Initiator solution, where x is 4, 6, or 8; The third step is the anionic polymerization to form PDMAA: Na2S x The initiator solution is added to the NaOTf / DMAA sodium salt solution at a volume fraction of 0.1-1%, and stirred or allowed to stand for 12-24 hours under an inert atmosphere and at 30-60℃ to allow DMAA to undergo anionic polymerization, thereby obtaining PDMAA polymer electrolyte containing polysulfide anionic end groups or PDMAA in-situ polymerization precursor solution. Step 4, pre-installing the battery: In an inert atmosphere glove box, pre-install the positive electrode, separator, and sodium metal negative electrode into the battery casing; Step 5: Inject the PDMAA in-situ polymerization precursor solution into the battery to fully wet the separator and electrode pores; Step 6: Allow the PDMAA in-situ polymerization precursor solution to stand for 12-24 hours at room temperature or at a temperature of 25-60℃ to undergo anionic polymerization inside the battery, forming a PDMAA polymer electrolyte network with polysulfide anionic end groups, thus achieving in-situ solidification.

2. The method for preparing an amide polymer with polysulfide anion-terminated groups by in-situ polymerization according to claim 1, characterized in that: In the second step, Na2S x The concentration was 3 mM.

3. The method for preparing an amide polymer with polysulfide anion-terminated groups by in-situ polymerization according to claim 1, characterized in that: In the third step, Na2S x The molar ratio with DMAA is 0.001-0.1, and the mixture is stirred or allowed to stand for 12 hours under an inert atmosphere at 40-50℃.

4. The method for preparing an amide polymer with polysulfide anion-terminated groups by in-situ polymerization according to claim 1, characterized in that: In the sixth step, the mixture is left to stand at 40°C for 12-24 hours.

5. An in-situ polymerized amide-based polymer with polysulfide anion-terminated groups prepared by the preparation method according to any one of claims 1-4, characterized in that: The amide polymer is a PDMAA polymer electrolyte, composed of N,N-dimethylacrylamide (DMAA) monomers in a polysulfide anion Na₂S₂O₃. x The polymer is obtained by anionic polymerization under initiation, where x is 4, 6, or 8; the main chain is a PDMAA backbone, with organic sulfur polysulfide anionic terminal groups introduced at the chain ends or segments to form organic sulfur-rich amorphous regions; the polymer electrolyte contains sodium salt NaOTf as an ion source; the PDMAA polymer electrolyte has an ionic conductivity ≥1.0×10⁻⁶ at 25°C. -4 S·cm -1 Na + The transport number is in the range of 0.50-0.70, and the glass transition temperature (Tg) is below -20℃, relative to Na. + The upper limit of the electrochemical stability window of / Na is >4.0V; thermogravimetric analysis shows that the mass loss is ≤10% before 200℃ and the measurable ionic conductivity is maintained below -30℃.

6. The in-situ polymerized amide polymer with polysulfide anion end groups according to claim 5, characterized in that: One or both ends of the PDMAA polymer chain contain Na2S. x The end groups, wherein the polysulfide anions are covalently or stably coordinated with the polymer backbone, thereby connecting the amorphous regions of the organic sulfur with Na. + The main coordination environment is spatially tightly coupled, Na2S x The molar fraction of end groups in PDMAA corresponds to an initiator concentration of 1-5 mM; the ionic conductivity of the PDMAA polymer electrolyte at 25 °C is 1.2 × 10⁻⁶. -4 S·cm -1 Na + The migration number is 0.59, and the glass transition temperature Tg is in the range of -30.0 to -41.4℃.

7. The application of an in-situ polymerized with polysulfide anion-terminated amide group prepared by the preparation method according to any one of claims 1-4 in a sodium metal battery, characterized in that: The sodium metal battery includes a sodium metal anode, a sodium energy storage cathode, and a separator. An amide polymer is filled between the sodium metal anode and the sodium energy storage cathode and is in close contact with the electrode interface. The sodium energy storage cathode has a mass ratio of active material: Super P:PVDF = 80-92:3-7:3-7. The active material is sodium vanadium phosphate cathode material, which is Na3V2(PO4)3, i.e., NVP or Na2V3(PO4)3. The sodium metal anode is a sodium metal sheet, and the separator is a polypropylene microporous membrane or a glass fiber separator.

8. The application according to claim 7, characterized in that: The sodium metal battery exhibits a specific capacity retention of ≥90% and an average coulombic efficiency of ≥99.9% after 500 cycles at a rate of 0.2-0.5C. The amide polymer is used to improve ionic conductivity and Na+. + This increases the migration number, reduces concentration polarization, improves electrode / electrolyte interface contact, and inhibits sodium dendrite formation and growth, thereby enhancing battery safety and cycle life.

9. The application of an in-situ polymerized with polysulfide anion-terminated amide group prepared by the preparation method according to any one of claims 1-4 in a Na||Na symmetric battery, characterized in that: The amide polymer is placed between two sodium metal electrodes at a current of 0.1-5.0 mA cm⁻¹. -2 When Na deposition / stripping tests are performed at current density, the Na||Na symmetric cells can cycle stably for ≥400h without short circuit.

10. The application of an in-situ polymerized with polysulfide anion-terminated amide group prepared by the preparation method according to any one of claims 1-4 in a high-safety solid-state or quasi-solid-state sodium-based energy storage system, characterized in that: The high-safety solid or quasi-solid sodium-based energy storage system is a large-scale energy storage power station or a distributed energy sodium-based energy storage device.

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