Surface-modified sulfide solid electrolyte, method for preparing the same, and all-solid-state sodium ion battery

Abstract

The application provides a surface-modified sulfide solid electrolyte and a preparation method thereof and a full-solid-state sodium ion battery, relates to the technical field of sodium ion batteries, and comprises a sulfide solid electrolyte, wherein the surface of the sulfide solid electrolyte is coated with a polymer solid electrolyte layer. The surface-modified sulfide solid electrolyte has the beneficial effects that the surface of the sulfide solid electrolyte is coated with the polymer solid electrolyte layer, the surface-modified sulfide solid electrolyte has high ionic conductivity and high air stability, the chemical reaction of the positive electrode material and the solid electrolyte interface is effectively prevented, the stability of the surface-modified sulfide solid electrolyte when being in direct contact with a sodium metal negative electrode is ensured, the cycle performance of the battery using the coated surface-modified sulfide solid electrolyte is obviously improved, the preparation operation is simple, mass production is facilitated, and the surface-modified sulfide solid electrolyte has a good application prospect in the full-solid-state sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a surface-modified sulfide solid electrolyte, its preparation method, and an all-solid-state sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have attracted significant attention in the energy storage field due to their abundant resources, low cost, long lifespan, and high safety, becoming a prominent research subject. However, sodium-ion batteries are essentially still classified as traditional liquid batteries, and the organic liquid electrolytes they use pose considerable safety risks. Under high-temperature environments or short-circuit conditions, there remains a risk of combustion and explosion, which limits their wider application. To overcome this challenge, sodium-ion solid-state batteries have emerged. These batteries use solid electrolytes instead of traditional liquid electrolytes, significantly improving battery safety and further optimizing energy density.

[0003] Currently, the main technologies for sodium-ion all-solid-state batteries include polymer solid-state electrolyte systems, oxide solid-state electrolyte systems, sulfide solid-state electrolyte systems, and halide solid-state electrolyte systems. Each system has its own distinct advantages and disadvantages. 1. Polymer solid electrolyte: The ionic conductivity is not high at room temperature. Therefore, polymer-based all-solid-state batteries need to operate at higher temperatures or add a small amount of electrolyte to ensure the rapid migration of sodium ions. In addition, polymer solid electrolytes are not suitable for high-voltage oxide cathode materials because they will be oxidized under high voltage.

[0004] 2. Oxide solid electrolytes: The advantages are good air stability and good chemical / electrochemical stability; however, the rigidity and fragility of oxides make it difficult to fabricate ultra-thin solid electrolyte films on a large scale, and it is also difficult to form a tight physical contact with oxide cathode particles, which is not conducive to integration into all-solid-state sodium batteries; in addition, the generally low ionic conductivity further restricts its application in sodium-ion all-solid-state batteries.

[0005] 3. Sulfide solid electrolytes: These not only possess ionic conductivity comparable to or even higher than that of electrolytes, but are also easily deformable, allowing them to be integrated into all-solid-state sodium batteries through simple cold pressing. However, sulfide solid electrolytes exhibit poor air stability, side reactions with the positive electrode material, and reduction reactions with metallic sodium at the negative electrode, which severely hinders their application in all-solid-state sodium batteries.

[0006] Existing patent CN109888376B describes a sodium-ion battery sulfide electrolyte with high ionic conductivity and good air stability. Furthermore, the raw materials used in its synthesis are widely available and relatively inexpensive, offering a cost advantage. However, it still suffers from the following problems: First, it does not significantly improve the air stability of the sulfide electrolyte, making it highly susceptible to reacting with moisture in the air to produce toxic gases and degrade electrolyte performance. Second, the side reactions between the sulfide electrolyte and the positive electrode include sodium deposition, sodium dendrite growth, and electrode polarization. During charge-discharge cycles, sulfides in the positive electrode dissolve and release sulfide ions, which combine with sodium ions to form polysulfides, leading to sodium deposition on the positive electrode and causing battery loss. On the other hand, sodium dendrites grow on the positive electrode surface, penetrating the separator layer and reacting with sulfides in the electrolyte, causing internal short circuits. Third, metallic Na in the negative electrode reacts with the sulfide electrolyte to generate Na₂S, leading to electrolyte failure. These problems severely hinder the application of sulfide solid-state electrolytes in all-solid-state sodium-ion batteries.

[0007] Therefore, there is an urgent need to develop sulfide solid electrolyte materials with high ionic conductivity, high stability with air, and stable contact with positive and negative electrodes to improve battery performance. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention provides a surface-modified sulfide solid electrolyte, comprising a sulfide solid electrolyte, wherein the surface of the sulfide solid electrolyte is coated with a polymer solid electrolyte layer.

[0009] Preferably, the polymer solid electrolyte layer is formed by mixing a polymer and a sodium salt.

[0010] Preferably, the sulfide electrolyte is Na3PS4, Na3PSe4, Na3SbS4, or Na 10 SnP2S 12 Na 10 GeP2S 12 Na 11 Sn2PS 12 Na 11 Sn2PSe 12 At least one of them; The polymer includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, and polystyrene. The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorosulfonamide, sodium perchlorate, sodium ditrifluoromethylsulfonamide, sodium fluoroborate, and sodium difluorooxalate borate.

[0011] This invention also provides a method for preparing a surface-modified sulfide solid electrolyte, used to prepare the above-mentioned surface-modified sulfide solid electrolyte, the preparation method comprising: Step S1: Prepare a sulfide solid electrolyte; Step S2: A polymer solid electrolyte layer is formed by coating the surface of the sulfide solid electrolyte.

[0012] Preferably, step S2 includes: Step S21: Add the polymer to the solvent, heat until completely dissolved, and then cool to room temperature to obtain a polymer solution; Step S22: Add the sodium salt and the sulfide solid electrolyte to the polymer solution and stir until homogeneous to obtain a mixture; Step S23: The mixture is baked under inert gas conditions until the solvent is completely evaporated to obtain a sulfide solid electrolyte with the polymer solid electrolyte layer on its surface.

[0013] Preferably, the mass ratio of the polymer, the sodium salt, the sulfide solid electrolyte, and the solvent is (1-10):(0.1-10):(1-99):(2-1000).

[0014] Preferably, the sulfide electrolyte is Na3PS4, Na3PSe4, Na3SbS4, or Na 10 SnP2S 12 Na 10 GeP2S 12 Na 11 Sn2PS 12 Na 11 Sn2PSe 12 At least one of them; The polymer includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, and polystyrene. The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorosulfonamide, sodium perchlorate, sodium trifluoromethylsulfonamide, sodium fluoroborate, and sodium difluorooxalate borate. The solvent includes at least one of benzene, toluene, xylene, anisole, trimethylbenzene, and acetonitrile.

[0015] Preferably, in step S21, the heating temperature is 50℃-150℃.

[0016] Preferably, in step S22, the stirring speed is 500 rpm to 1000 rpm.

[0017] Preferably, in step S23, the baking temperature is 40℃-150℃ and the baking time is 1h-48h.

[0018] The present invention also provides an all-solid-state sodium-ion battery, comprising a positive electrode, a negative electrode, and a solid electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode and / or the solid electrolyte adopts the above-described surface-modified sulfide solid electrolyte.

[0019] The above technical solution has the following advantages or beneficial effects: 1) The surface-modified sulfide solid electrolyte of the present invention has a polymer solid electrolyte layer coated on the surface of the sulfide solid electrolyte, which has high ionic conductivity and high air stability, while effectively preventing the chemical reaction at the interface between the positive electrode material and the solid electrolyte, ensuring its stability when in direct contact with the sodium metal negative electrode, and the battery cycle performance is significantly improved by using the coated surface-modified sulfide solid electrolyte. 2) The surface-modified sulfide solid electrolyte of the present invention is simple to prepare and is conducive to large-scale production, and has good application prospects in all-solid-state sodium-ion batteries. Attached Figure Description

[0020] Figure 1 A schematic flowchart of a method for preparing a surface-modified sulfide solid electrolyte is shown in a preferred embodiment of the present invention. Figure 2 This is a schematic diagram of a sub-process of step S2 in a preferred embodiment of the present invention; Figure 3 The Nyquist spectra are of the uncoated sulfide solid electrolyte and the surface-modified sulfide solid electrolyte of the present invention. Figure 4 A schematic diagram of the electrochemical impedance spectroscopy of the uncoated sulfide solid electrolyte after 24 hours of storage; Figure 5 This is a schematic diagram of the electrochemical impedance spectroscopy of the surface-modified sulfide solid electrolyte of the present invention after being placed for 24 hours. Figure 6 This is a schematic diagram of electrochemical impedance spectroscopy (EIS) of an uncoated sulfide solid electrolyte mixed with a cathode material and left to stand for different times. Figure 7 This is a schematic diagram of the electrochemical impedance spectroscopy of the surface-modified sulfide solid electrolyte of the present invention mixed with the cathode material and left to stand for different times. Figure 8 for Figure 6 and Figure 7 A schematic diagram showing the superimposed comparison of electrochemical impedance spectra in the initial static state; Figure 9 A comparison diagram of symmetrical battery cycling using an uncoated sulfide solid electrolyte and the surface-modified sulfide solid electrolyte material of the present invention. Figure 10 This is a comparison chart of battery cycle performance before and after coating. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment; other embodiments that conform to the spirit of the present invention may also fall within the scope of the present invention.

[0022] In a preferred embodiment of the present invention, based on the above-mentioned problems existing in the prior art, a surface-modified sulfide solid electrolyte is provided, comprising a sulfide solid electrolyte, wherein the surface of the sulfide solid electrolyte is coated with a polymer solid electrolyte layer.

[0023] Specifically, in this embodiment, a sulfide solid electrolyte is used, which possesses high ionic conductivity, approaching 1 mS / cm at room temperature, meeting the basic requirements for practical applications of electrolytes. Furthermore, the surface of the sulfide solid electrolyte is coated with a polymer solid electrolyte layer, effectively reducing its contact with air and achieving good air stability. Simultaneously, this polymer solid electrolyte layer effectively suppresses side reactions between the sulfide solid electrolyte and the positive and negative electrodes, ensuring the cycle stability of the all-solid-state battery. Therefore, applying this surface-modified sulfide solid electrolyte to an all-solid-state sodium-ion battery demonstrates excellent performance.

[0024] In a preferred embodiment of the present invention, the polymer solid electrolyte layer is formed by mixing a polymer and a sodium salt.

[0025] In a preferred embodiment of the present invention, the sulfide electrolyte is Na3PS4, Na3PSe4, Na3SbS4, or Na 10 SnP2S 12 Na 10 GeP2S 12 Na 11 Sn2PS 12 Na 11 Sn2PSe 12 At least one of them; The polymer includes at least one of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polymethyl methacrylate (PMMA), and polystyrene (PS). Sodium salts include at least one of sodium hexafluorophosphate (NaPF6), sodium difluorosulfonamide (NaFSI), sodium perchlorate (NaClO4), sodium ditrifluoromethylsulfonamide (NaTFSI), sodium fluoroborate (NaBF4), and sodium difluorooxalate borate (NaDFOB).

[0026] Specifically, in this embodiment, polyethylene oxide (PEO) possesses high safety, low cost, and electrochemical stability, making it suitable for scenarios with high safety requirements. Polymethyl methacrylate (PMMA) offers advantages such as high transparency, ease of processing, and low price; introducing this material into the polymer can reduce crystallinity and enhance flexibility. Introducing polystyrene (PS) into the polymer can improve its mechanical properties and thermal stability. Polyvinylidene fluoride (PVDF) exhibits excellent electrochemical stability, high mechanical strength, chemical corrosion resistance, and excellent film-forming properties; introducing this material into the polymer can effectively improve the system's mechanical properties and electrolyte wettability, enhancing structural stability. Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) possesses low crystallinity, high flexibility, excellent electrolyte adsorption capacity, and electrochemical compatibility; introducing this material into the polymer can further optimize the pore structure, improve the system's liquid absorption and retention capacity, and enhance ion transport performance.

[0027] This invention also provides a method for preparing a surface-modified sulfide solid electrolyte, used to prepare the above-mentioned surface-modified sulfide solid electrolyte, such as... Figure 1 As shown, the preparation method includes: Step S1: Prepare a sulfide solid electrolyte; Step S2: A polymer solid electrolyte layer is formed by coating the surface of the sulfide solid electrolyte.

[0028] In a preferred embodiment of the present invention, such as Figure 2 As shown, step S2 includes: Step S21: Add the polymer to the solvent, heat until completely dissolved, and then cool to room temperature to obtain a polymer solution; Step S22: Add sodium salt and sulfide solid electrolyte to polymer solution and stir until homogeneous to obtain a mixture; Step S23: The mixture is baked under inert gas conditions until the solvent is completely evaporated to obtain a sulfide solid electrolyte with a polymer solid electrolyte layer on the surface.

[0029] Specifically, in this embodiment, the aforementioned inert gas includes, but is not limited to, argon (Ar), which is a chemically stable inert gas that does not react with most substances (including metals, ceramics, polymers, etc.). During the baking process, argon can isolate oxygen (O2) and water vapor (H2O) in the air, preventing the material surface from being oxidized or corroded. In addition, under an argon atmosphere, the solvent evaporation rate is stable, which can prevent defects such as pores and cracks caused by localized excessively rapid evaporation, and improve the density and uniformity of the electrolyte.

[0030] In a preferred embodiment of the present invention, the mass ratio of polymer, sodium salt, sulfide solid electrolyte and solvent is (1-10):(0.1-10):(1-99):(2-1000).

[0031] In a preferred embodiment of the present invention, the polymer includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, and polystyrene. Sodium salts include at least one of sodium hexafluorophosphate, sodium difluorosulfonamide, sodium perchlorate, sodium trifluoromethylsulfonamide, sodium fluoroborate, and sodium difluorooxalate borate. The solvent includes at least one of benzene, toluene, xylene, anisole, trimethylbenzene, and acetonitrile.

[0032] In a preferred embodiment of the present invention, in step S21, the heating temperature is 50°C-150°C.

[0033] In a preferred embodiment of the present invention, in step S22, the stirring speed is 500 rpm to 1000 rpm.

[0034] In a preferred embodiment of the present invention, in step S23, the baking temperature is 40℃-150℃ and the baking time is 1h-48h.

[0035] In a preferred embodiment of the present invention, the sulfide electrolyte is Na3PS4, Na3PSe4, Na3SbS4, or Na 10 SnP2S 12 Na 10 GeP2S 12 Na 11 Sn2PS 12 Na 11 Sn2PSe 12 At least one of them, the polymer coating amount on its surface is preferably 2% to 10%.

[0036] The present invention also provides an all-solid-state sodium-ion battery, comprising a positive electrode, a negative electrode, and a solid electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode neutralization / or the solid electrolyte is the above-mentioned surface-modified sulfide solid electrolyte.

[0037] The performance of the surface-modified sulfide solid electrolyte of the present invention is compared and verified from four aspects: 1. Electrochemical stability Uncoated sulfide solid electrolytes and surface-modified sulfide solid electrolytes coated with polymer solid electrolyte layers were prepared. The following sample treatment methods were used for both the uncoated sulfide solid electrolyte (Na3SbS4 as an example) and the surface-modified sulfide solid electrolyte (Na3SbS4-coated): Sample preparation: Cold press the solid electrolyte powder (0.5g, 300MPa recommended).

[0038] The thickness L of the electrolyte sheet was measured using a digital thickness gauge, and the diameter of the electrolyte disc was measured using a vernier caliper. The cross-sectional area was then calculated and denoted as S.

[0039] The electrolyte is placed in the test mold, with the two ends of the mold serving as blocking electrodes, and the screws are tightened.

[0040] Under test conditions of temperature (25±2)℃ and humidity less than 50%, the obtained "sandwich" structure disc was clamped onto a fixture connected to an electrochemical workstation.

[0041] Analysis steps: Open the electrochemical workstation and import the EIS test program.

[0042] Set the disturbance voltage to 10 mV and the scan frequency range to 1 MHz to 100 mHz. After setting, click "Start Test". The test results are as follows: Figure 3 The Nyquist spectrum shown is used to characterize the difference in ionic conductivity before and after solid electrolyte coating.

[0043] Results Analysis Analyze the Nyquist spectrum, perform circuit fitting on the spectrum to obtain the resistance R, and calculate the ionic conductivity according to equation (A.1).

[0044] =L / (RS) ························(A.1) In the formula: —Ionic conductivity of solid electrolytes, in Siemens units per centimeter (S·cm) -1 ); L—Thickness of solid electrolyte, in centimeters (cm); S – Cross-sectional area of ​​the solid electrolyte, in square centimeters (cm²) 2 ); R – The measured resistance of a solid electrolyte, measured in ohms (Ω).

[0045] The following table contains data:

[0046] The table above shows the ionic conductivity before coating. Na3SbS4 =0.36 mS / cm, ionic conductivity after coating Na3SbS4-coated=0.04 mS / cm, the ionic conductivity of Na3SbS4-coated (coated solid electrolyte) decreases. Coating induces localized crystallization of the polymer or restricts the movement of its flexible chain segments, further reducing carrier mobility (common in PEO-based coatings). At the same time, the intrinsic ionic conductivity of the polymer is low; most polymers (such as PEO and PVDF) have a room temperature ionic conductivity of only 10. -8 -10 -5 S / cm, if a continuous insulating layer is formed after coating, it will dominate the overall transport behavior and dilute the contribution of the highly conductive inorganic phase. However, this also precisely demonstrates the success of the coating, with significant effects on improving subsequent air stability and sodium metal stability; Both samples were then exposed to air for 24 hours and were designated as Sample 1: Na3SbS 4， Sample 2: Na3SbS4-coated, exposed for 24 hours. Using the same sample treatment method as described above, the following results were obtained: Figure 4 and Figure 5 The electrochemical impedance spectroscopy data shown are used to characterize the differences in ionic conductivity after 24 hours of exposure with uncoated solid electrolyte and after 24 hours of exposure with coated solid electrolyte. Similarly, circuit fitting was performed on the above electrochemical impedance spectroscopy data to obtain the resistance R.

[0047] The further measured data are as follows:

[0048] As can be seen from the comparison data in the table above, after the sulfide solid electrolyte sample without polymer solid electrolyte layer was exposed to air for 24 hours, its absolute impedance value soared compared to the freshly prepared sample. The electrochemical impedance spectrum was distorted, and the ionic conductivity decreased significantly from 0.36 mS / cm to 0.01 mS / cm, indicating that its resistance to air erosion is extremely weak and its surface is easily damaged.

[0049] The surface-modified sulfide solid electrolyte with polymer solid electrolyte layer prepared by the preparation method of the present invention showed a gradual increase in impedance after being exposed to air for 24 hours, and the overall shape of the curve was relatively regular. This indicates that the polymer solid electrolyte layer can effectively delay air erosion as a coating layer. The ionic conductivity value only decreased slightly, from 0.04 mS / cm to 0.032 mS / cm, allowing the sample to maintain more stable electrochemical performance in the air environment.

[0050] 2. Stability with the cathode material To evaluate the stability of the sulfide solid electrolyte and cathode material before and after coating, NFM(111) cathode material and sulfide electrolyte were mixed uniformly at a mass ratio of 7:3, and pressed into a sheet with a thickness of 500 μm at 300 MPa. Stainless steel (SS) blocking electrodes were sandwiched on both sides of the sample to assemble a symmetrical blocking electrode of SS / composite cathode / SS.

[0051] The aforementioned sulfide electrolytes were tested using both uncoated and coated surface-modified sulfide solid electrolytes, and the results were compared. EIS impedance was measured at 25℃ for different times (0h, 24h, 72h) in a frequency range of 2MHz - 0.1Hz, and the change of the semicircle (representing interface impedance) in the mid-to-high frequency region over time was observed. The results are as follows: Figure 6 The electrochemical impedance spectroscopy (EIS) of an uncoated Na3SbS4 sulfide solid electrolyte mixed with a cathode material and left to stand for different times is shown below. Figure 7 The electrochemical impedance spectroscopy (EIS) of the surface-modified sulfide solid electrolyte of the present invention (taking Na3SbS4_coated composite electrolyte as an example) mixed with the cathode material and left to stand for different times is shown. Figure 8 for Figure 6 , Figure 7 A schematic diagram showing the superimposed comparison of the electrochemical impedance spectra of the two groups of samples in their initial state after standing for 0 hours. Figure 6 , Figure 7 and Figure 8 In the graph, the horizontal axis represents the real impedance Zreal, and the vertical axis represents the imaginary impedance -Zimag. The raised semicircular arc in the high-frequency region of the curve represents the interface impedance between the positive electrode and the sulfide electrolyte. The diameter of the arc directly corresponds to the degree of interfacial side reaction and the value of the interfacial impedance.

[0052] from Figure 6 As can be seen from the graph, at the initial 0h of settling, only a small semicircle appears, with a basic interfacial impedance of approximately 1275Ω. After 24h of settling, the diameter of the semicircle widens significantly, and the interfacial impedance increases substantially, indicating that redox side reactions have been continuously occurring between the sulfide and the cathode. The cathode metal ions dissolve, and the sulfide decomposes, producing sodium polysulfide impurities that accumulate at the interface. After 72h of settling, the semicircle expands to its maximum size in the graph, and the interfacial impedance soars to 22592Ω. The entire curve shifts significantly towards the high impedance region, exhibiting severe distortion and a marked shortening of the low-frequency diffusion line. This phenomenon is essentially due to the direct contact between the unpolymer-protected sulfide and the high-voltage oxide cathode. During the charge-discharge and settling process, interfacial corrosion reactions continuously occur, generating insulating inert byproducts that continuously block sodium ion transport channels. The interfacial polarization deteriorates exponentially with settling time.

[0053] from Figure 7As can be seen from the data, after initial settling for 0 hours, due to the presence of a low-ionic-conductivity polymer coating layer on the surface, the initial interfacial impedance was 2396Ω, slightly higher than that of the uncoated sample. After settling for 24 hours, the semicircular arc of the spectrum showed only a slight expansion, and the impedance increased only slightly. After settling for 72 hours, the size of the semicircular arc increased very little, and the interfacial impedance only increased to 3021Ω. The overall deviation of the curve was very slight, and the low-frequency sodium ion diffusion curve was complete and without obvious distortion. The core reason is that the continuous polymer-sodium salt composite coating layer on the outer layer of the sulfide particles acts as an insulating buffer layer, physically isolating the inorganic phase of the sulfide from the high-voltage NFM cathode, blocking the cross-interface migration of sulfur ions and metal cations, inhibiting interfacial side reactions such as sulfide decomposition and polysulfide formation from the root, significantly delaying the accumulation of interfacial insulating impurities, and achieving long-term stability of the cathode-electrolyte interface.

[0054] from Figure 8 The superimposed comparison shows that, initially, the total impedance of the cathode material and the uncoated sulfide solid electrolyte is lower than that of the cathode material and the surface-modified sulfide solid electrolyte of this invention. However, the impedance of the cathode material and the uncoated sulfide solid electrolyte increases rapidly over time, with the high-frequency impedance increasing from an initial 1275Ω to 22592Ω, while the impedance of the cathode material and the surface-modified sulfide solid electrolyte of this invention increases from an initial 2396Ω to 3021Ω. These results demonstrate that the coating layer on the surface of the sulfide solid electrolyte prevents the interfacial chemical reaction between the cathode material and the solid electrolyte.

[0055] 3. Stability when in direct contact with sodium metal anode To verify the stability of the sulfide solid electrolyte material in direct contact with the sodium metal anode before and after coating, the uncoated sulfide solid electrolyte powder material and the surface-modified sulfide solid electrolyte powder of the present invention (taking Na3SbS4 and Na3SbS4-coated as examples) were placed in a 10mm mold and pressed at 300MPa for 5min. Then, Na sheets were placed on both sides of the electrolyte and pressed to make the electrolyte and Na sheets adhere tightly together, thus obtaining Na / Na3SbS4 / Na sodium symmetric battery and Na / Na3SbS4-coated / Na modified symmetric battery respectively.

[0056] Subsequently, the Na / Na3SbS4 / Na sodium symmetric cells and the Na / Na3SbS4-coated / Na modified symmetric cells were subjected to charge-discharge cycles of -1V to 1V at 45℃ for 200 hours, respectively, before being removed. The corresponding charge-discharge regime was 0.05 mA·cm⁻¹. -2 Charge for 30 seconds, discharge for 30 seconds, cycle for 20 times; 0.1 mA·cm -2 Charge for 30 seconds, discharge for 30 seconds, cycle for 20 times; 0.2 mA·cm-2 Charge for 30 seconds, discharge for 30 seconds, cycle 2000 times.

[0057] Real-time voltage was simultaneously acquired during the charge-discharge cycle, resulting in, for example... Figure 9 The symmetrical battery voltage-time comparison curve shown has a test current gradient of 0.05 mA·cm. -2 0.1 mA·cm -2 0.2 mA·cm -2 It covers low / medium / high current density operating conditions.

[0058] from Figure 9 As can be seen, the symmetrical battery Na / Na3SbS4 / Na assembled with uncoated sulfide solid electrolyte material exhibits large voltage fluctuations after the start of cycling, indicating numerous interfacial side reactions, high interfacial impedance, and large polarization voltage. Furthermore, the polarization voltage continues to rise with increasing cycling time, with each charge-discharge switch exhibiting severe voltage spikes and large fluctuations. The fluctuation amplitude continues to expand over time, and the polarization decay is particularly significant under high current density.

[0059] like Figure 9 The symmetrical battery curves shown also demonstrate that polymer coating significantly improves the stability of the electrolyte to sodium. The polarization voltage remains low throughout the cycle, with only minor voltage fluctuations during charge-discharge switching. The polarization increase is minimal during the 200-hour long cycle, and the curves are generally smooth and stable. The data clearly demonstrate that the polymer coating layer greatly improves the electrochemical compatibility between the sulfide electrolyte and the sodium metal anode, suppresses interfacial reduction side reactions and sodium dendrite growth, stabilizes the sodium deposition / stripping interface, effectively reduces interfacial polarization during long cycles, and significantly improves the cycle stability of the sodium metal anode system.

[0060] 4. Battery cycle performance Using sulfide solid electrolytes before and after coating as electrolyte materials for the mold battery, NFM(111):electrolyte:Super P = 7:2:1 was mixed evenly and placed in a 10mm mold, pressed at 300MPa for 5 minutes to form the positive electrode. The electrolyte was placed in a 10mm mold and pressed at 300MPa for 5 minutes to form the solid electrolyte layer. The Na sheet served as the negative electrode. Finally, the positive electrode, electrolyte layer, and negative electrode were placed in a Teflon fixture with stainless steel as the current collector to ensure tight contact of the entire system. Charge-discharge cycle tests were conducted at 0.1C at 25℃ within a voltage range of 1.5-3.9V.

[0061] like Figure 10As shown in the figure, the vertical axis represents Capacity retention (%), which indicates the capacity retention rate of the real-time capacity relative to the first discharge capacity, and the horizontal axis represents the number of charge-discharge cycles. The black curve represents the uncoated sulfide electrolyte battery, and the red curve represents the coated modified electrolyte battery of this invention. It can be seen that the curve of the uncoated sulfide electrolyte battery has a steep decay slope, and the capacity retention rate drops rapidly with the increase of the number of cycles, resulting in severe irreversible capacity loss. The coated modified electrolyte battery of this invention has a gentle decay trend throughout the process, and the capacity retention rate is still stably maintained at around 100% after 100 cycles, with a very small decay range, and the battery cycle performance is significantly improved. The significant difference in cycle stability between the two battery groups stems from the multiple interface protection mechanisms of the polymer coating: the coating physically isolates the sulfide inorganic matrix from the positive electrode, inhibiting sulfide decomposition, sulfur ion dissolution, and the formation of polysulfide byproducts, thus preventing continuous deactivation of the positive electrode active material; simultaneously, it isolates the sulfide from the reducing metallic sodium negative electrode, preventing the two from undergoing a reduction reaction to generate insulating impurities, maintaining a smooth and uniform sodium deposition / stripping interface, and inhibiting sodium dendrite growth; in addition, the polymer coating blocks water vapor and oxygen, significantly improving the air stability of the sulfide electrolyte, reducing electrolyte degradation during battery fabrication, and the synergistic effect of multiple protections reduces irreversible capacity loss during cycling, significantly slows down capacity retention decay, and effectively extends the cycle life of the all-solid-state sodium-ion battery.

[0062] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made using the content of this specification and illustrations should be included within the protection scope of the present invention.

Claims

1. A surface-modified sulfide solid electrolyte, characterized in that, It includes a sulfide solid electrolyte, the surface of which is coated with a polymer solid electrolyte layer.

2. The surface-modified sulfide solid electrolyte according to claim 1, characterized in that, The polymer solid electrolyte layer is formed by mixing a polymer and a sodium salt.

3. The surface-modified sulfide solid electrolyte according to claim 2, characterized in that, The sulfide electrolyte is Na3PS4, Na3PSe4, Na3SbS4, Na 10 SnP2S 12 Na 10 GeP2S 12 Na 11 Sn2PS 12 Na 11 Sn2PSe 12 At least one of them; The polymer includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, and polystyrene. The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorosulfonamide, sodium perchlorate, sodium ditrifluoromethylsulfonamide, sodium fluoroborate, and sodium difluorooxalate borate.

4. A method for preparing a surface-modified sulfide solid electrolyte, characterized in that, The preparation method for the surface-modified sulfide solid electrolyte as described in any one of claims 1-3 comprises: Step S1: Prepare a sulfide solid electrolyte; Step S2: A polymer solid electrolyte layer is formed by coating the surface of the sulfide solid electrolyte.

5. The preparation method according to claim 4, characterized in that, Step S2 includes: Step S21: Add the polymer to the solvent, heat until completely dissolved, and then cool to room temperature to obtain a polymer solution; Step S22: Add the sodium salt and the sulfide solid electrolyte to the polymer solution and stir until homogeneous to obtain a mixture; Step S23: The mixture is baked under inert gas conditions until the solvent is completely evaporated to obtain a sulfide solid electrolyte with the polymer solid electrolyte layer on its surface.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the polymer, the sodium salt, the sulfide solid electrolyte, and the solvent is (1-10):(0.1-10):(1-99):(2-1000).

7. The preparation method according to claim 5, characterized in that, The polymer includes at least one of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, and polystyrene. The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorosulfonamide, sodium perchlorate, sodium trifluoromethylsulfonamide, sodium fluoroborate, and sodium difluorooxalate borate. The solvent includes at least one of benzene, toluene, xylene, anisole, trimethylbenzene, and acetonitrile.

8. The preparation method according to claim 5, characterized in that, In step S21, the heating temperature is 50℃-150℃; In step S22, the stirring speed is 500 rpm-1000 rpm; In step S23, the baking temperature is 40℃-150℃ and the baking time is 1h-48h.

9. The preparation method according to claim 4, characterized in that, The sulfide electrolyte is Na3PS4, Na3PSe4, Na3SbS4, Na 10 SnP2S 12 Na 10 GeP2S 12 Na 11 Sn2PS 12 Na 11 Sn2PSe 12 At least one of them.

10. A fully solid-state sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a solid electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode and / or the solid electrolyte is a surface-modified sulfide solid electrolyte as described in any one of claims 1-3.

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