Sulfide electrolyte for low-temperature all-solid-state sodium-sulfur battery and preparation method of sulfide electrolyte

Abstract

The invention provides a sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery and a preparation method of the sulfide electrolyte, the sulfide electrolyte for the low-temperature all-solid-state sodium-sulfur battery is composed of a sulfide electrolyte Na3PS4 and a solid electrolyte interface film forming substance CuF2-NaNO3, the solid electrolyte interface film forming substance CuF2-NaNO3 is distributed on the surface of a Na3PS4 particle, and the chemical formula is Na3PS4-CuF2-NaNO3. The preparation method specifically comprises the following steps: S1, preparing solid electrolyte Na3PS4; and S2, preparation of the Na3PS4-CuF2-NaNO3 composite electrolyte is carried out. According to the sulfide electrolyte for the low-temperature all-solid-state sodium-sulfur battery and the preparation method of the sulfide electrolyte, the problems of instability of the sulfide electrolyte to a metal anode and growth of sodium dendrites can be solved, the ionic conductivity of the electrolyte is not reduced, and the electrolyte has a self-healing function.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery and a preparation method thereof. Background Art

[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 life, and low cost, are expected to pioneer solutions to the problems of traditional organic electrolyte batteries, such as low energy density, short life, flammability, and explosiveness. This represents a disruptive breakthrough technology that will benefit humanity and has been listed by the scientific community as a research priority alongside 5G and artificial intelligence. In particular, all-solid-state sodium-sulfur batteries utilize sodium as a raw material, which is more abundant than lithium metal, and is inexpensive and stable. This allows for high-current and high-power charging and discharging, offering unique advantages in large-scale energy storage applications such as renewable energy grid integration.

[0003] Solid-state electrolytes, as the core components of all-solid-state sodium-sulfur batteries, largely determine the overall performance of the battery. Na3PS4 sulfide solid electrolytes have become one of the most widely studied and most promising 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 facing its commercial application is the instability of the Na3PS4 sulfide electrolyte with respect to the metallic sodium anode, which leads to the growth of sodium dendrites on the sodium anode side. The solid electrolyte interface (SEI) formed by the sodium reduction of the Na3PS4 sulfide electrolyte cannot prevent dendrite growth. NaF has a high interfacial energy for sodium, which effectively inhibits sodium dendrite growth. However, its ultra-low ionic conductivity increases the battery overpotential. Incorporating materials with high mixed ion conductivity, such as Na3N, into NaF can effectively reduce the battery overpotential while still maintaining high dendrite suppression. By adding sodium-phobic and electron-conductive components, such as Cu and Ni, into the ion-conducting and sodium-phobic Na3N-NaF interlayer to form a sodium-phobic Na3N-NaF-Cu interlayer, the overpotential and sodium dendrite formation during the sodium stripping process can be further suppressed. The sodium-phobic component NaF in the Na3N-NaF-Cu interlayer inhibits sodium dendrite growth, while the conductive copper reduces the overpotential during the sodium stripping process.

[0005] All reported work to date has focused on inserting an artificial lithiophobic, lithiophilic, or lithiophobic-lithiophilic interlayer between the metal anode and the electrolyte to inhibit dendrite growth. However, during charge and discharge, the interlayer is easily destroyed due to large volume changes, allowing dendrites to penetrate this passivation layer and grow into the electrolyte. Consequently, all reported metal anode / sulfide solid electrolyte interface modifications lack self-healing capabilities, maintaining stability only during the first few charge and discharge cycles. Once the passivation layer is destroyed, the battery will fail.

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

[0007] In response to the shortcomings of the existing technology, the present invention proposes a sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and a preparation method thereof, which can solve the problems of instability of sulfide electrolyte to metal anode and sodium dendrite growth without reducing the ionic conductivity of the electrolyte, and the electrolyte has a self-healing function.

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

[0009] Preferably, the ratio of CuF2-NaNO3 to the total weight of Na3PS4-CuF2-NaNO3 is 0.1-0.5%.

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

[0011] S1. Preparation of solid electrolyte Na3PS4: Na2S and P2S5 are heated to 650-750°C in a molar ratio of 1-5:1 and kept at this temperature for 1-2 hours to completely melt the two. Then, the mixture is quickly transferred to 0°C water or liquid nitrogen for quenching to obtain Na3PS4 glass powder. Subsequently, the mixture is annealed at 270-410°C in a multi-purpose sintering furnace to obtain Na3PS4 ceramic powder.

[0012] Preparation of S2, Na3PS4-CuF2-NaNO3 composite electrolyte: dissolve 10-30mgCuF2 and 50-70mgNaNO3 into 1-2ml ethylene glycol dimethyl ether to prepare CuF2-NaNO3-DME solution; then take 20-60μlCuF2-NaNO3-DME solution and mix it with 1gNa3PS4, and vacuum dry it at 80℃ to obtain Na3PS4-CuF2-NaNO3 composite electrolyte.

[0013] Preferably, in step S1, Na2S and P2S5 are uniformly mixed in 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 maintained for 1-2 hours, and then 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 standby use.

[0014] Preferably, in step S2, 20 mg CuF2 and 60 mg NaNO3 are dissolved in 1 ml 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 a Na3PS4-CuF2-NaNO3 composite electrolyte.

[0016] The present invention provides a sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries and a preparation method thereof, which has the following beneficial effects:

[0017] 1) The sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries provided by the present invention incorporates a trace amount (0.1-0.5 wt%) of CuF2-NaNO3 into the electrolyte layer at the anode / electrolyte interface, forming an in-situ, sodium-phobic NaF-Na3N-Cu interlayer during the sodium deposition / stripping process, thereby suppressing overpotential and sodium dendrite formation during the sodium stripping process. The CuF2-NaNO3, a SEI film former on the sulfide electrolyte surface, is reduced to NaF-Na3N-Cu during the charge and discharge process. Even if the NaF-Na3N-Cu layer at the sulfide electrolyte / Na interface is destroyed and sodium dendrites grow into the electrolyte layer, they will be consumed by the SEI former CuF2-NaNO3 on the electrolyte surface. The newly formed interfacial layer can also suppress sodium dendrite formation, thus providing the sulfide electrolyte for low-temperature all-solid-state sodium-sulfur batteries with self-healing properties. Furthermore, the addition of CuF2-NaNO3 hardly reduces the ionic conductivity of the electrolyte.

[0018] 2) The preparation method of the sulfide electrolyte for the low-temperature all-solid-state sodium-sulfur battery provided by the present invention has simple steps and is easy to operate. The sulfide electrolyte for the low-temperature all-solid-state sodium-sulfur battery 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, so that the battery can maintain high conductivity and high safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the preparation method of the present invention.

[0020] Figure 2 XRD phases of the Na3PS4 electrolyte prepared in Example 1 of the present invention before and after being treated with CuF2-NaNO3-DME.

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

[0022] Figure 4 Voltage polarization curves of Na / Na3PS4-CuF2-NaNO3 / Na and Na / Na3PS4 / Na symmetric batteries assembled with the electrolyte prepared in Example 1 of the present invention at increasing current density.

[0023] Figure 5 The Na / Na3PS4-CuF2-NaNO3 / Na symmetric battery assembled with the electrolyte prepared in Example 1 of the present invention was –2 / 0.2mAh cm–2 and 0.5 mA cm –2 / 0.5mAh cm –2 Voltage change curve under different conditions.

[0024] Figure 6 Cycling performance diagram 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, prepared in Example 1 of the present invention. All batteries were operated at 50°C and 2.50 mA cm -2 / 2.50mAh cm -2 Next test. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by ordinary persons in the art without making creative work are within the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

[0026] Example 1

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

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

[0029] (2) Preparation of Na3PS4-CuF2-NaNO3 composite electrolyte: 20 mg CuF2 and 60 mg NaNO3 were dissolved in 1 ml ethylene glycol dimethyl ether (DME) to prepare a CuF2-NaNO3-DME solution. Then, 40 μl of the CuF2-NaNO3-DME solution was mixed with 1 g Na3PS4 and dried under vacuum at 80°C to obtain a Na3PS4-CuF2-NaNO3 composite electrolyte, in which the weight ratio of CuF2-NaNO3 to the total Na3PS4-CuF2-NaNO3 was 0.32%.

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

[0031] (1) Testing of electrolyte stability to metallic sodium: 80-150 mg of electrolyte powder was hot-pressed at 450°C to prepare Na3PS4 and Na3PS4-CuF2-NaNO3 electrolyte sheets. Sodium sheets were attached to both sides of the electrolyte sheet and pressed at 1.0 MPa to form a Na / Na3PS4-CuF2-NaNO3 / Na symmetrical battery to measure its critical current density and evaluate the electrolyte stability to metallic sodium.

[0032] Reference Figure 2 As shown, by performing XRD detection on the Na3PS4 electrolyte prepared in Example 1 of the present invention before and after being treated with CuF2-NaNO3-DME, it was found that after the electrolyte Na3PS4 was mixed and dried with CuF2-NaNO3-DME, the main phase of the electrolyte did not change, indicating that CuF2-NaNO3 was only coated on the surface of the electrolyte particles ( Figure 2 ), which will improve the stability of the electrolyte to the anodic sodium.

[0033] Reference Figure 3 As shown, by performing SEM detection on the Na3PS4 electrolyte before and after the CuF2-NaNO3-DME treatment prepared in Example 1 of the present invention, it was found that the electrolyte particle size became smaller after being treated with the CuF2-NaNO3-DME solution ( Figure 3 ), which accelerates the reaction kinetics.

[0034] (2) Cyclic stability test: Assemble the all-solid-state battery Na2S-Na3PS4-CMK-3 (mesoporous carbon) / Na3PS4--CuF2-NaNO3 / Na and test its cyclic stability. 4-The CMK-3 (Na2S-NPS-C) cathode composite material was prepared by a melt-quenching-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 that the ratio of Na2S / Na3PS4 / CMK-3 mesoporous carbon in the cathode composite was 30:40:30, different ratios of Na2S and Na3PS4 could be synthesized by adjusting the ratio of the initial raw materials Na2S and P2S5 according to the Na2S-P2S5 phase diagram. Then, the Na2S-P2S5-CMK-3 mixture was transferred to a quartz tube and sealed under vacuum. The quartz tube was placed in a furnace and heated to 850°C for 1 hour at a rate of 2°C / min. The temperature was raised to a temperature higher than the liquidus, where Na2S and P2S5 melted together to form a uniform liquid phase. The quartz tube was then immediately placed in 0°C cold water. Due to the rapid cooling, the Na2S phase, which precipitated first, did not have time to precipitate and was retained at low temperatures, forming a supersaturated solid solution. After quenching, the quartz tube was immediately placed in a furnace for annealing at 270°C for 2 hours. The furnace was then cooled to room temperature, and the resulting Na2S-NPS-C complex was removed from the quartz tube in a glove box. Battery assembly in the present invention was performed 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 in Figure 2, CuF2-NaNO3 is coated on the surface of the electrolyte particles, which will improve the stability of the electrolyte to the anode sodium. During the sodium deposition and stripping cycle, by forming a sodium-phobic NaF-Na3N-Cu interface phase, only adding 0.3wt% CuF2-NaNO3 into the electrolyte layer significantly improves the critical current density (CCD) of the symmetric cell Na / Na3PS4 / Na from 0.4mAcm -2 / 0.4mAhcm -2 Improved to 1.4 mA cm for the symmetrical cell Na / Na3PS4--CuF2-NaNO3 / Na -2 / 1.4mAhcm -2 ( Figure 4 After adding CuF2-NaNO3, the sodium deposition / stripping overpotential of the symmetric cell becomes smaller. The ionic conductivity is almost unchanged, only from 2.9×10 -3 S.cm -1 Fluctuation to 2.5×10 -3 S.cm-1, still remains at the same order of magnitude, indicating that the NaF-Na3N-Cu interlayer has a low interfacial impedance after reduction.

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

[0037] The uniform distribution of CuF2-NaNO3 also affects the performance of the electrolyte. The ionic conductivity of the hand-ground mixed Na3PS4--CuF2-NaNO3 electrolyte is 1.5×10 -3 S.cm -1 , while the ionic conductivity of wet mixed Na3PS4--CuF2-NaNO3 is 3.0×10 -3 S.cm -1 The critical current density of hand-mixed CCD is only 0.5 mA cm -2 / 0.5mAhcm -2 , while the wet mixed CCD is 1.0mAcm -2 / 1.0mAhcm -2 .

[0038] Reference Figure 5 As shown, the Na / Na3PS4-CuF2-NaNO3 / Na symmetric cell is –2 / 0.2mAh cm –2 and 0.5 mA cm –2 / 0.5mAh cm –2 Analysis of the voltage change curve under these conditions shows that the CuF2-NaNO3 at the Na3PS4-CuF2-NaNO3 / Na interface will be reduced by sodium to form a sodium-phobic NaF-Na3N-Cu interlayer. Sodium-phobic NaF has high interfacial energy, which can inhibit sodium dendrites. Na3N-Cu with balanced ion-electron conductivity can reduce the sodium deposition overpotential. The formation of the NaF-Na3N-Cu interlayer was confirmed by SEM and EDS of the battery cross section. The electrolyte / sodium interface and the electrolyte / stainless steel interface were deposited at 0.5mAhcm -2 Post-deposition SEM cross-sections and backscattered electron images revealed a sodium layer above the electrolyte. No sodium dendrites were observed within the electrolyte composite after deposition. Elemental distribution images along the longitudinal depth after deposition / stripping cycles indicated that F and N were enriched at the electrolyte / sodium interface, as CuF2-NaNO3 was enriched at the Na3PS4-CuF2-NaNO3 surface. After sodium deposition / stripping cycles, the formation of a NaF-Na3N-Cu interlayer further increased the surface content of F and N on the electrolyte. Such an interlayer enabled the symmetrical cell to achieve a charge / discharge rate of 0.2 mA cm -2 / 0.2mAhcm -2 and 0.5mAcm -2 / 0.5mAhcm -2 120 stable cycles ( Figure 5 ).

[0039] Reference Figure 6 As shown, 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 were measured. All batteries were operated at 50 °C and 2.50 mA cm -2 / 2.50mAh cm -2 H-Na2S-NPS-CMK-3 / Na3PS4--CuF2-NaNO3 / Na was tested at 50℃ and 2.50mAcm -2 / 2.50mAhcm -2 Under the test, a high capacity retention rate (61.4%-74.2%) was obtained after 100 cycles ( Figure 6 ).

[0040] In summary, the sulfide electrolyte for a low-temperature, all-solid-state sodium-sulfur battery provided by the present invention incorporates a trace amount (0.1-0.5 wt%) of CuF2-NaNO3 into the electrolyte layer, forming an in-situ, sodium-repellent NaF-Na3N-Cu interlayer at the anode / electrolyte interface during the sodium deposition / stripping process. This layer suppresses overpotential and sodium dendrite formation during the sodium stripping process. The CuF2-NaNO3, a SEI film former on the sulfide electrolyte surface, is reduced to NaF-Na3N-Cu during the charge and discharge processes. Even if the NaF-Na3N-Cu layer at the sulfide electrolyte / Na interface is destroyed and sodium dendrites grow into the electrolyte layer, they will be consumed by the SEI former CuF2-NaNO3 on the electrolyte surface. The newly formed interfacial layer can also suppress sodium dendrite formation, thus endowing the sulfide electrolyte for a low-temperature, all-solid-state sodium-sulfur battery with self-healing properties. Furthermore, the addition of CuF2-NaNO3 hardly reduces the ionic conductivity of the electrolyte, thereby maintaining high conductivity and safety performance of the battery.

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

Claims

1. A sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery, characterized in that: It is composed of sulfide electrolyte Na3PS4 and solid electrolyte interface film former CuF2-NaNO3, and the solid electrolyte interface film former CuF2-NaNO3 is distributed on the surface of Na3PS4 particles. The chemical formula is Na3PS4-CuF2-NaNO3.

2. The sulfide electrolyte for low-temperature all-solid-state sodium-sulfur battery according to claim 1, characterized in that The ratio of CuF2-NaNO3 to the total weight of Na3PS4-CuF2-NaNO3 is 0.1-0.5%.

3. A method for preparing a sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery, characterized in that The specific steps include: S1. Preparation of solid electrolyte Na3PS4: Na2S and P2S5 are heated to 650-750°C in a molar ratio of 1-5:1 and kept at this temperature for 1-2 hours to completely melt the two. Then, the mixture is quickly transferred to 0°C water or liquid nitrogen for quenching to obtain Na3PS4 glass powder. Subsequently, the mixture is annealed at 270-410°C in a multi-purpose sintering furnace to obtain Na3PS4 ceramic powder. Preparation of S2, Na3PS4-CuF2-NaNO3 composite electrolyte: dissolve 10-30mgCuF2 and 50-70mgNaNO3 into 1-2ml ethylene glycol dimethyl ether to prepare CuF2-NaNO3-DME solution; then take 20-60μlCuF2-NaNO3-DME solution and mix it with 1gNa3PS4, and vacuum dry it at 80℃ to obtain Na3PS4-CuF2-NaNO3 composite electrolyte.

4. The method for preparing a sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery according to claim 1, wherein: In step S1, Na2S and P2S5 are uniformly mixed in a molar ratio of 3:1 and placed in a quartz tube in an argon-filled glove box. After evacuation, the quartz tube is sealed with an oxyhydrogen flame. The quartz tube is heated to 700°C and maintained for 1-2 hours, and then 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.

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

6. The method for preparing a sulfide electrolyte for a low-temperature all-solid-state sodium-sulfur battery according to claim 5, wherein: Take 40 μl CuF2-NaNO3-DME solution and mix it with 1 g Na3PS4, and dry it in vacuum at 80 °C to obtain Na3PS4-CuF2-NaNO3 composite electrolyte.

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