A sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and its preparation method

Abstract

This invention provides a sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and its preparation method. The sulfide electrolyte comprises a sulfide electrolyte Na3PS4 and a solid electrolyte interfacial film forming agent CuF2-NaNO3, with the CuF2-NaNO3 distributed on the surface of the Na3PS4 particles. The preparation method specifically includes: S1, preparation of the solid electrolyte Na3PS4; S2, preparation of the Na3PS4-CuF2-NaNO3 composite electrolyte. This low-temperature all-solid-state sodium-sulfur battery sulfide electrolyte and its preparation method can solve the problems of instability of sulfide electrolytes to metal anodes and sodium dendrite growth, without reducing the ionic conductivity of the electrolyte. Furthermore, this electrolyte has a self-healing function.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and its preparation method. Background Technology

[0002] All-solid-state sulfide electrolyte lithium-sulfur and sodium-sulfur batteries, with their potential advantages of high safety, high energy density, high temperature resistance, long lifespan, and low cost, are expected to fundamentally solve a series of problems existing in traditional organic electrolyte batteries, such as low energy density, short lifespan, flammability, and explosiveness. They represent a disruptive breakthrough technology that benefits humanity and have been included in the scientific community's research ranks alongside 5G and artificial intelligence. In particular, sodium metal, a raw material for all-solid-state sodium-sulfur batteries, is more abundant and cheaper than lithium metal, and can be charged and discharged at high current and high power, exhibiting unique advantages in large-scale energy storage fields such as renewable energy grid connection.

[0003] As the core component of all-solid-state sodium-sulfur batteries, solid electrolytes largely determine the overall performance of the battery. Na3PS4 sulfide solid electrolytes have become one of the most widely studied and industrialized inorganic solid electrolyte materials due to their excellent room temperature ionic conductivity, low elastic modulus, easy cold pressing, and good mechanical properties.

[0004] However, the biggest challenge to its commercial application is the instability of Na3PS4 sulfide electrolyte to the sodium anode, leading to the growth of sodium dendrites on the sodium anode side. The solid electrolyte interphase (SEI) film formed by the reduction of Na3PS4 sulfide electrolyte to sodium cannot prevent dendrite growth. NaF has a high interfacial energy with sodium, which can effectively suppress sodium dendrite growth; however, its extremely low ionic conductivity increases the battery's overpotential. Incorporating substances with high mixed ionic conductivity, such as Na3N, into NaF can effectively reduce the battery's overpotential while maintaining high dendrite suppression. By adding sodium-averse and electronically conductive components such as Cu and Ni into the ion-conducting and sodium-averse Na3N-NaF interface layer, an ion-electron mixed conductive and sodium-averse Na3N-NaF-Cu intermediate layer is formed, further suppressing the overpotential and sodium dendrite growth during sodium stripping. In the Na3N-NaF-Cu intermediate layer, the sodium-averse component NaF inhibits sodium dendrite growth, while the conductive copper reduces the overpotential during sodium stripping.

[0005] Current reported work focuses on inserting an artificial lithium-hide, lithium-philic, or lithium-hide-lithophile interlayer between the metal anode and the electrolyte to suppress dendrite growth. However, during charge and discharge, the large volume changes make the interlayer susceptible to damage, allowing dendrites to penetrate the passivation layer and grow into the electrolyte. Therefore, all reported metal anode / sulfide solid electrolyte interface modifications lack self-healing capabilities, maintaining stability only during the first few charge-discharge cycles. Once the passivation layer is damaged, the battery will fail.

[0006] The existing SEI film formed by sodium reduction of the sulfide electrolyte Na3PS4 cannot prevent sodium dendrite growth. Studies have shown that substances with high binding energy, such as NaF, have high interfacial energy with sodium and can effectively inhibit sodium dendrite growth. However, their extremely low ionic conductivity increases the battery overpotential and exacerbates polarization. If substances with high mixed ionic conductivity, such as Na3N, are incorporated into NaF, the battery overpotential can be effectively reduced while maintaining high dendrite suppression. By adding sodium-averse and electronically conductive components, such as Cu and Ni, into this ion-conducting and sodium-averse Na3N-NaF interfacial layer to form an ion-electron mixed conductive and sodium-averse intermediate layer, the overpotential and sodium dendrite growth during the sodium stripping process will be further suppressed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention proposes a sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and its preparation method. This method can solve the problems of instability of sulfide electrolytes to metal anodes and sodium dendrite growth, while maintaining the ionic conductivity of the electrolyte. Moreover, the electrolyte has a self-healing function.

[0008] To achieve the above technical solution, the present invention provides a sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries, which is composed of sulfide electrolyte Na3PS4 and a solid electrolyte interfacial film forming agent CuF2-NaNO3, wherein the solid electrolyte interfacial film forming agent CuF2-NaNO3 is distributed on the surface of Na3PS4 particles, and the chemical formula is Na3PS4-CuF2-NaNO3.

[0009] Preferably, the CuF2-NaNO3 accounts for 0.1-0.5% of the total weight of Na3PS4-CuF2-NaNO3.

[0010] This invention also provides a method for preparing a sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery, specifically including the following steps:

[0011] S1. Preparation of solid electrolyte Na3PS4: Na2S and P2S5 are mixed at a molar ratio of 1-5:1, heated to 650℃-750℃, and held for 1-2 hours to allow them to completely eutecticly melt. Then, they are quickly transferred to water or liquid nitrogen at 0℃ for quenching to obtain Na3PS4 glass powder. Subsequently, Na3PS4 ceramic powder is obtained by annealing in a multi-functional sintering furnace at 270℃-410℃.

[0012] Preparation of S2, Na3PS4-CuF2-NaNO3 composite electrolyte: Dissolve 10-30 mg CuF2 and 50-70 mg NaNO3 in 1-2 ml of ethylene glycol dimethyl ether to prepare CuF2-NaNO3-DME solution; then take 20-60 μl of CuF2-NaNO3-DME solution and mix with 1 g Na3PS4, and dry under vacuum at 80 °C to obtain Na3PS4-CuF2-NaNO3 composite electrolyte.

[0013] Preferably, in step S1, Na2S and P2S5 are uniformly mixed at a molar ratio of 3:1 and placed in a quartz tube in a glove box filled with argon. After evacuation, the quartz tube is sealed with an oxyhydrogen flame. The quartz tube is heated to 700°C and held for 1-2 hours. Then, it is quickly placed in 0°C water or liquid nitrogen for quenching. Finally, the quartz tube is annealed at 270°C and then taken out and ground for later use.

[0014] Preferably, in step S2, 20 mg CuF2 and 60 mg NaNO3 are dissolved in 1 ml of ethylene glycol dimethyl ether to prepare a CuF2-NaNO3-DME solution.

[0015] Preferably, in step S2, 40 μl of CuF2-NaNO3-DME solution and 1 g of Na3PS4 are mixed and dried under vacuum at 80 °C to obtain Na3PS4-CuF2-NaNO3 composite electrolyte.

[0016] The beneficial effects of the sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and its preparation method provided by this invention are as follows:

[0017] 1) The sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries provided by this invention introduces a trace amount (0.1-0.5 wt%) of CuF2-NaNO3 into the electrolyte layer at the anode / electrolyte interface. During sodium deposition / stripping, a mixed conductive, sodium-repellent NaF-Na3N-Cu intermediate layer is formed in situ, suppressing overpotential and sodium dendrite formation during sodium stripping. The CuF2-NaNO3, the SEI film former on the sulfide electrolyte surface, is reduced to NaF-Na3N-Cu during charge and discharge. Even if the NaF-Na3N-Cu layer at the sulfide electrolyte / Na interface is damaged, and sodium dendrites grow into the electrolyte layer, they will be consumed by the CuF2-NaNO3 on the electrolyte surface. The newly formed interface layer also suppresses sodium dendrite formation, thus giving the sulfide electrolyte for this low-temperature all-solid-state sodium-sulfur battery a self-healing function. Moreover, the addition of CuF2-NaNO3 hardly reduces the ionic conductivity of the electrolyte.

[0018] 2) The method for preparing sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries provided by the present invention has simple steps and is easy to operate. The sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries prepared by the present invention improves the stability of the electrolyte to the metal anode, inhibits the growth of sodium dendrites, and has self-healing ability. Moreover, the addition of CuF2-NaNO3 hardly reduces the ionic conductivity of the electrolyte, which can enable the battery to maintain high conductivity and high safety performance. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of the present invention.

[0020] Figure 2 The XRD phases of the Na3PS4 electrolyte prepared in Example 1 of this invention before and after CuF2-NaNO3-DME treatment are shown.

[0021] Figure 3 The images show the SEM morphology of the CuF2-NaNO3-DME prepared in Example 1 of this invention before and after treatment with Na3PS4 electrolyte, (a) Na3PS4-CuF2-NaNO3; (b) Na3PS4.

[0022] Figure 4 Voltage polarization curves of Na / Na3PS4-CuF2-NaNO3 / Na and Na / Na3PS4 / Na symmetric cells assembled with electrolytes prepared in Example 1 of this invention at continuously increasing current densities.

[0023] Figure 5 The Na / Na3PS4-CuF2-NaNO3 / Na symmetric battery assembled with the electrolyte prepared in Example 1 of this invention operates at 0.2 mA cm⁻¹. –2 / 0.2mAh cm–2 and 0.5mA cm –2 / 0.5mAh cm –2 Voltage variation curve under certain conditions.

[0024] Figure 6 The cycling performance diagrams for the hot-pressed electrolyte sheet assembly H-Na2S-Na3PS4-C / Na3PS4-CuF2-NaNO3 / Na, the cold-pressed electrolyte sheet assembly L-Na2S-Na3PS4-C / Na3PS4-CuF2-NaNO3 / Na, and the cold-pressed electrolyte sheet assembly Na2S-Na3PS4-C / Na3PS4 / Na all-solid-state batteries prepared in Example 1 of this invention are shown. All batteries were cycled at 50°C and 2.50 mA cm⁻¹. -2 / 2.50mAh cm -2 Next test. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] Example 1

[0027] A sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and its preparation method thereof, specifically including the following steps:

[0028] (1) Preparation of solid electrolyte Na3PS4: In this invention, solid electrolyte Na3PS4 is prepared by melting and casting-annealing process. First, Na2S and P2S5 are uniformly mixed at a molar ratio of 3:1 and placed in a quartz tube in a glove box filled with argon. After vacuuming, the quartz tube is sealed with an oxyhydrogen flame. The quartz tube is heated to 700℃ and held for 1-2 hours. Then, it is quickly placed in liquid nitrogen to obtain Na3PS4 glass powder. Finally, the quartz tube is annealed at 270℃ to obtain Na3PS4 ceramic powder, which is then taken out and ground for later use.

[0029] (2) Preparation of Na3PS4-CuF2-NaNO3 composite electrolyte: Dissolve 20mg CuF2 and 60mg NaNO3 in 1ml ethylene glycol dimethyl ether (DME) to prepare CuF2-NaNO3-DME solution. Then take 40μl CuF2-NaNO3-DME solution and mix with 1g Na3PS4. Dry under vacuum at 80℃ to obtain Na3PS4-CuF2-NaNO3 composite electrolyte, wherein CuF2-NaNO3 accounts for 0.32% of the total weight of Na3PS4-CuF2-NaNO3.

[0030] Electrolyte hot pressing into sheets and performance testing:

[0031] (1) Test of electrolyte stability to metallic sodium: Take 80-150mg of electrolyte powder and hot press at 450℃ to prepare Na3PS4 and Na3PS4-CuF2-NaNO3 electrolyte sheets. Sodium sheets are attached to both sides of the electrolyte sheets and pressed with a pressure of 1.0MPa to form Na / Na3PS4-CuF2-NaNO3 / Na symmetric cells. Measure their critical current density and evaluate the stability of electrolyte to metallic sodium.

[0032] Reference Figure 2 As shown, XRD analysis of the Na3PS4 electrolyte prepared in Example 1 of this invention before and after CuF2-NaNO3-DME treatment revealed that the main phase of the electrolyte remained unchanged after Na3PS4 was mixed with CuF2-NaNO3-DME and dried, indicating that CuF2-NaNO3 was only coated on the surface of the electrolyte particles. Figure 2 This will improve the stability of the electrolyte to the sodium anode.

[0033] Reference Figure 3 As shown, SEM analysis of the Na3PS4 electrolyte prepared in Example 1 of this invention before and after CuF2-NaNO3-DME treatment revealed that the electrolyte particle size decreased after treatment with CuF2-NaNO3-DME solution. Figure 3 This will accelerate the reaction kinetics.

[0034] (2) Cyclic stability testing: The all-solid-state battery Na2S-Na3PS4-CMK-3 (mesoporous carbon) / Na3PS4--CuF2-NaNO3 / Na was assembled, and its cycle stability was measured. The Na2S-Na3PS4 used in this invention... 4-CMK-3 (Na2S-NPS-C) cathode composite material was prepared via a melt-deposition method: First, Na2S, P2S5, and CMK-3 mesoporous carbon were manually ground and mixed in a glove box. The mass ratio of Na2S:P2S5:CMK-3 was set to 50.5:19.5:30 to ensure a Na2S / Na3PS4 / CMK-3 mesoporous carbon ratio of 30:40:30 in the cathode composite. According to the Na2S-P2S5 phase diagram, different proportions of Na2S and Na3PS4 could be synthesized by adjusting the initial ratio of Na2S and P2S5. Then, the Na2S-P2S5-CMK-3 mixture was transferred to a quartz tube and sealed under vacuum. The quartz tube was heated to 850°C in a furnace and held for 1 hour at a rate of 2°C / min, until it reached a temperature above the liquidus line. Na₂S and P₂S₅ melted together to form a homogeneous liquid phase. The quartz tube was then immediately transferred to 0°C cold water. Due to the rapid cooling, the Na₂S phase, which precipitates first, did not have time to precipitate and remained at the low temperature as a supersaturated solid solution. After quenching, the quartz tube was immediately annealed at 270°C for 2 hours in a furnace and then cooled to room temperature with the furnace. The resulting Na₂S-NPS-C composite was removed from the quartz tube in a glove box. In this invention, battery assembly was carried out in an argon-filled glove box, with moisture controlled at 0.1 ppm and oxygen controlled below 0.1 ppm.

[0035] Reference Figure 4 As shown, CuF2-NaNO3 coating on the electrolyte particle surface improves the electrolyte's stability to sodium at the anode. During sodium deposition stripping cycles, the formation of a sodium-averse NaF-Na3N-Cu interfacial phase, with only 0.3 wt% CuF2-NaNO3 entering the electrolyte layer, significantly increases the critical current density (CCD) of the symmetric cell, from 0.4 mA / cm² for Na / Na3PS4 / Na. -2 / 0.4mAhcm -2 Increased to 1.4 mA / cm² for the symmetric cell Na / Na₃PS₄--CuF₂-NaNO₃ / Na -2 / 1.4mAhcm -2 ( Figure 4 The addition of CuF₂-NaNO₃ reduced the sodium deposition / stripping overpotential of the symmetric cell. The ionic conductivity remained almost unchanged, decreasing only slightly from 2.9 × 10⁻⁶. -3 S.cm -1 Fluctuation to 2.5×10 -3 The S.cm⁻¹ value remains on the same order of magnitude, indicating that the reduced NaF-Na₃N-Cu interlayer has a low interfacial impedance.

[0036] The CuF2 / NaNO3 weight ratio also affects the CCD of the electrolyte complex. As the CuF2 / NaNO3 ratio decreases from 20 / 40 to 20 / 50, the CCD of the electrolyte decreases from 0.8 mA / cm². -2 / 0.8mAhcm -2 Increased to 1.0 mAcm -2 / 1.0mAhcm -2 .

[0037] The uniform distribution of CuF2-NaNO3 also affects the performance of the electrolyte. The ionic conductivity of the manually ground and mixed Na3PS4-CuF2-NaNO3 electrolyte is 1.5 × 10⁻⁶. -3 S.cm -1 The wet-mixed Na3PS4--CuF2-NaNO3 ionic conductivity is 3.0×10⁻⁶. -3 S.cm -1 The critical current density for manual mixing CCD is only 0.5 mA / cm². -2 / 0.5mAhcm -2 The CCD of the wet-mixed device is 1.0 mA / cm². -2 / 1.0mAhcm -2 .

[0038] Reference Figure 5 As shown, the Na / Na3PS4-CuF2-NaNO3 / Na symmetric cell operates at 0.2 mA cm⁻¹. –2 / 0.2mAh cm –2 and 0.5mA cm –2 / 0.5mAh cm –2 Analysis of the voltage change curves under certain conditions revealed that at the Na3PS4-CuF2-NaNO3 / Na interface, CuF2-NaNO3 is reduced by sodium to form a sodium-averse NaF-Na3N-Cu interlayer. The sodium-averse NaF possesses high interfacial energy, which inhibits sodium dendrite formation. The Na3N-Cu, with its balanced ion-electron conductivity, reduces the sodium deposition overpotential. The formation of the NaF-Na3N-Cu interlayer was confirmed by SEM and EDS analysis of the battery cross-section. The electrolyte / sodium interface and the electrolyte / stainless steel interface showed similar deposition rates at 0.5 mAh / cm². -2 Post-SEM cross-section and backscattered electron microscopy revealed a sodium layer above the electrolyte. No sodium dendrites appeared within the electrolyte complex after deposition. Elemental distribution images along the longitudinal depth after deposition / stripping cycles showed F and N enrichment at the electrolyte / sodium interface, as CuF₂-NaNO₃ was enriched on the Na₃PS₄-CuF₂-NaNO₃ surface. Following sodium deposition / stripping cycles, the formation of a NaF-Na₃N-Cu interlayer further increased the F and N surface content on the electrolyte, thus enabling a symmetrical cell at 0.2 mA / cm². -2 / 0.2mAhcm -2 and 0.5mAcm -2 / 0.5mAhcm -2 120 cycles to achieve a stable state ( Figure 5 ).

[0039] Reference Figure 6 The cycling performance of all-solid-state batteries assembled with hot-pressed electrolyte sheets (H-Na2S-Na3PS4-C / Na3PS4-CuF2-NaNO3 / Na), cold-pressed electrolyte sheets (L-Na2S-Na3PS4-C / Na3PS4-CuF2-NaNO3 / Na), and cold-pressed electrolyte sheets (Na2S-Na3PS4-C / Na3PS4 / Na) is shown in the figure. All batteries are tested at 50°C and 2.50 mA cm⁻¹. -2 / 2.50mAh cm -2 The following test was conducted. H-Na2S-NPS-CMK-3 / Na3PS4--CuF2-NaNO3 / Na at 50℃ and 2.50 mAcm -2 / 2.50mAhcm -2 The following tests showed a high capacity retention rate (61.4%-74.2%) after 100 cycles. Figure 6 ).

[0040] In summary, the sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries provided by this invention, by adding a trace amount (0.1-0.5 wt%) of CuF2-NaNO3 into the electrolyte layer, forms an ion-electron mixed conductive and sodium-repellent NaF-Na3N-Cu intermediate layer in situ at the anode / electrolyte interface during sodium deposition / stripping, suppressing overpotential and sodium dendrite formation during sodium stripping. The CuF2-NaNO3, the SEI film former on the sulfide electrolyte surface, will be reduced to NaF-Na3N-Cu during charge and discharge. Even if the NaF-Na3N-Cu layer at the sulfide electrolyte / Na interface is damaged, and sodium dendrites grow into the electrolyte layer, the sodium dendrites will be consumed by the CuF2-NaNO3 on the electrolyte surface. The newly formed interface layer can also suppress sodium dendrite formation, thus giving the sulfide electrolyte for this low-temperature all-solid-state sodium-sulfur battery a self-healing function. Moreover, the addition of CuF2-NaNO3 hardly reduces the ionic conductivity of the electrolyte, thus allowing the battery to maintain high conductivity and high safety performance.

[0041] The above description is only a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in the embodiments and drawings. Therefore, any equivalent or modified embodiments made without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery, characterized in that... Specifically, the steps include the following: S1. Preparation of solid electrolyte Na3PS4: Na2S and P2S5 are mixed at a molar ratio of 1-5:1, heated to 650°C-750°C, and held for 1-2 hours to allow them to completely eutecticly melt. Then, they are quickly transferred to water or liquid nitrogen at 0°C for quenching to obtain Na3PS4 glass powder. Subsequently, Na3PS4 ceramic powder is obtained by annealing in a multi-functional sintering furnace at 270°C-410°C. Preparation of S2, Na3PS4-CuF2-NaNO3 composite electrolyte: Dissolve 10-30 mg CuF2 and 50-70 mg NaNO3 in 1-2 ml of ethylene glycol dimethyl ether to prepare CuF2-NaNO3-DME solution; then take 20-60 μl of CuF2-NaNO3-DME solution and mix with 1 g Na3PS4, and dry under vacuum at 80°C to obtain Na3PS4-CuF2-NaNO3 composite electrolyte.

2. The method for preparing the sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery as described in claim 1, characterized in that, In step S1, Na2S and P2S5 are uniformly mixed at a molar ratio of 3:1 and placed in a quartz tube in a glove box filled with argon. After evacuation, the quartz tube is sealed with an oxyhydrogen flame. The quartz tube is heated to 700°C and held for 1-2 hours. Then, it is quickly placed in water or liquid nitrogen at 0°C for quenching. Finally, the quartz tube is annealed at 270°C and then taken out and ground for later use.

3. The method for preparing the sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery as described in claim 1, characterized in that, In step S2, 20 mg CuF2 and 60 mg NaNO3 are dissolved in 1 ml of ethylene glycol dimethyl ether to prepare a CuF2-NaNO3-DME solution.

4. The method for preparing the sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery as described in claim 3, characterized in that, Take 40 μl of CuF2-NaNO3-DME solution and 1 g of Na3PS4, mix them, and dry them under vacuum at 80 °C to obtain Na3PS4-CuF2-NaNO3 composite electrolyte.

5. A sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery, characterized in that: Prepared by any of claims 1-4, comprising a sulfide electrolyte Na3PS4 and a solid electrolyte interfacial film forming agent CuF2-NaNO3, wherein the solid electrolyte interfacial film forming agent CuF2-NaNO3 is distributed on the surface of Na3PS4 particles, and the chemical formula is Na3PS4-CuF2-NaNO3.

6. The sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery as described in claim 5, characterized in that, The proportion of CuF2-NaNO3 to the total weight of Na3PS4-CuF2-NaNO3 is 0.1-0.5%.

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