Heterojunction fluorine-based sodium solid electrolyte with high ionic conductivity and moisture resistance as well as preparation method and application of heterojunction fluorine-based sodium solid electrolyte

Abstract

The invention relates to a heterojunction fluorine-based sodium solid electrolyte with high ionic conductivity and moisture resistance as well as a preparation method and application of the heterojunction fluorine-based sodium solid electrolyte. The heterojunction fluorine-based solid electrolyte comprises a fluorine-based open framework compound main body and an interface modification phase, the interface modification phase includes an oxide phase and a chloride phase.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy, and particularly relates to a heterojunction fluorine-based sodium solid electrolyte with both high ionic conductivity and moisture resistance, and a preparation method and application thereof. Background Art

[0002] Electrochemical energy storage systems have received extensive attention due to their high energy conversion efficiency. Lithium metal batteries are currently considered to be a promising next-generation energy storage system because they have a low negative electrochemical potential (-3.04 V relative to the standard hydrogen electrode) and an extremely high theoretical specific capacity of the lithium metal anode (3860 mAh / g). However, the rising cost and scarcity of lithium resources have hindered the development of lithium metal batteries, which brings opportunities for sodium metal batteries because sodium metal has abundant crustal resources and cost-effectiveness, and can better achieve the large-scale production of batteries. However, when traditional non-aqueous organic electrolytes are paired with a sodium metal anode, they are prone to react with the anode surface, form dendrites, pierce the separator, and cause battery failure. The volatility and flammability of organic electrolytes also pose safety risks. On the contrary, inorganic solid electrolytes can provide a high Young's modulus to inhibit the formation of dendrites, and they also have a wide electrochemical stability window and leak-free safety guarantee. Therefore, compared with traditional sodium-ion or sodium metal batteries, the development of inorganic solid sodium metal batteries is expected to achieve a double improvement in energy density and safety.

[0003] Among various solid electrolytes, polymer solid electrolytes represented by polyethylene oxide are expected to be integrated into all-solid-state batteries due to their flexibility. However, their limited ionic conductivity (<10 -5 S / cm) and low sodium ion transference number make it difficult for them to inhibit the formation of sodium dendrites. Sulfide-based solid electrolytes, which are known for their high ionic conductivity, have attracted people's attention. However, their electrochemical window is very narrow, which poses challenges in terms of compatibility with sodium metal anodes and most cathode materials, and will lead to rapid decay of battery capacity. In addition, sulfide solid electrolytes are extremely unstable in humid air and are prone to generate toxic H2S gas. These seriously hinder the large-scale safe production of sulfide electrolytes.

[0004] In recent years, halide solid electrolytes have emerged as alternative materials of great interest due to their wide electrochemical windows, deformability, and high ionic conductivity. However, current research on halide solid electrolytes has mainly focused on lithium halides (such as Li3MX6; M = In, Y, or Sc; X = F, Cl, or Br). In contrast, research on sodium halides in sodium metal batteries is very limited, where chlorides and bromides are prone to degradation in high-humidity environments (e.g., when the relative humidity exceeds 30%), and their ionic conductivity decreases significantly after absorbing moisture. In contrast, fluoride-based solid electrolytes are considered to be the best in terms of air and oxidation stability. When in contact with a sodium anode, they can effectively inhibit the growth of sodium dendrites by forming a NaF-based solid electrolyte interface. However, fluoride electrolytes still lack an ideal structural prototype, and their limited synthesis methods and high interfacial impedance have hindered their development. For example, fluoride electrolytes synthesized by solid-phase annealing methods usually result in a large amount of NaF formation, leading to low room-temperature ionic conductivity (e.g., in the range of 10 -6 ~10 -7 S / cm). Therefore, there is an urgent need to develop fluoride solid electrolytes with both high ionic conductivity and air stability and their corresponding innovative synthesis methods. Summary of the Invention

[0005] Aiming at the above problems, the purpose of the present invention is to provide a novel fluoride-based solid electrolyte with both high ionic conductivity and moisture resistance, as well as its preparation method and application.

[0006] In a first aspect, the present invention provides a heterojunction fluoride-based solid electrolyte, comprising: a fluoride-based open-framework compound matrix and an interfacial modification phase; the interfacial modification phase comprises an oxide phase and a chloride phase.

[0007] Preferably, the fluoride-based open-framework compound matrix serves as the inner layer; the interfacial modification phase serves as the outer layer; Preferably, based on the total mass of the inner layer being 100 mol%, the content of the fluoride-based open-framework compound matrix in the inner layer is 60 - 80 mol%, the content of the interfacial modification phase is 10 - 40 mol%, and the content of the NaF phase is 0 - 15 mol%; Preferably, based on the total mass of the outer layer being 100 mol%, the content of the interfacial modification phase in the outer layer is 60 - 80 mol%, the content of the fluoride-based open-framework compound matrix is 10 - 40 mol%, and the content of the NaF phase is 0 - 15 mol%. Preferably, a small amount of the main phase of the outer layer is evenly distributed in the inner layer, and a small amount of the main phase of the inner layer is evenly distributed in the outer layer.

[0008] Preferably, the fluoride-based open-framework compound matrix is Na3GaF6; the oxide phase in the interfacial modification phase is gallium oxide with structural defects, preferably the structural defect is an oxygen vacancy; the chloride phase is NaCl.

[0009] Preferably, the morphology of the fluorine-based open-framework compound matrix is nano-scale particles with a particle size of 10-50 nm; the morphology of the oxide phase is nano-scale porous particles with a particle size of 10-100 nm; the morphology of the chloride phase is micro-scale particles with a particle size of 1-10 μm. Among them, the inner layer is actually an aggregate of nano-scale particles of the fluorine-based open-framework compound matrix. Preferably, the morphology of the fluorine-based open-framework compound matrix is nano-scale pebble-like particles; the morphology of the oxide phase is nano-scale porous gravel-like particles; the morphology of the chloride phase is micro-scale blocks.

[0010] In the present invention, a concentration gradient structure exists inside the solid electrolyte. The specific structure is that the oxide phase and the chloride phase are on the outer layer to protect the inner-layer fluorine-based framework compound, which can be used to inhibit the growth of sodium dendrites on the sodium negative electrode in a sodium metal battery. Both the oxide phase and the chloride phase can modify the grain boundaries of the fluorine-based open-framework compound, and improve the overall ionic conductivity of the electrolyte by means of grain boundary enhancement.

[0011] Preferably, the composition of the heterojunction fluorine-based solid electrolyte includes: the molar percentage of the fluorine-based open-framework compound matrix is 30-40%; the molar percentage of the oxide phase is 30-35%; the molar percentage of the chloride phase is 25-35%; the molar percentage of the NaF phase is 0-15%.

[0012] Preferably, the heterojunction fluorine-based solid electrolyte has extremely strong moisture resistance stability. The heterojunction fluorine-based solid electrolyte is stored in air with a relative humidity of 61% for at least 15 hours without a decrease in conductivity.

[0013] Preferably, the ionic conductivity of the heterojunction fluorine-based solid electrolyte at room temperature > 10 -5 S / cm, and the ionic conductivity at 40 °C ≥ 1×10 -4 S / cm.

[0014] In the second aspect, the present invention provides a preparation method of a heterojunction fluorine-based solid electrolyte, which prepares the heterojunction fluorine-based solid electrolyte by a two-step heat treatment process, including: (1) After grinding and mixing liquid metal element gallium and NaF, perform the first heat treatment in an air atmosphere to obtain a precursor Ga2O3@NaF; (2) After grinding and mixing the precursor Ga2O3@NaF, GaCl3 and GaF3, perform the second heat treatment to obtain the heterojunction fluorine-based solid electrolyte.

[0015] In the present invention, a binary fluoride, a binary chloride, and liquid metal gallium are used as raw materials, preferably NaF, elemental Ga, GaCl3, and GaF3, to prepare a heterojunction fluorine-based solid electrolyte that can effectively inhibit the growth of sodium dendrites in a sodium metal battery. Among them, the synthesis raw materials of the heterojunction fluorine-based solid electrolyte are NaF, elemental Ga, GaCl3, and GaF3. The main fluorine-based open framework compound is derived from the thermal synthesis of NaF, GaF3, and an activator, and the activator is Ga2O3 with structural defects. The chloride phase is derived from the reaction of GaCl3 and NaF. The obtained heterojunction fluorine-based solid electrolyte has a certain degree of concentration gradient structure, and the concentration gradient structure is mainly composed of an oxide phase and a chloride phase in the outer layer, and mainly composed of a fluorine-based open framework compound in the inner layer.

[0016] In the present invention, for the first time, liquid metal gallium is used to synthesize a novel sodium-rich heterostructured fluoride solid electrolyte, namely NGFOC-G, through in-situ oxidation of liquid metal gallium and in-situ chlorination of low-melting-point GaCl3. The unique features of NGFOC-G include: single-crystal Na3GaF6 domains in the open framework structure, a composite interface modification structure with Ga2O3 and NaCl, a concentration gradient structure, excellent air stability, and high electrochemical oxidation stability. By utilizing the penetration of gallium at the NaF grain boundaries and in-situ self-oxidation to form a Ga2O3 nano-surface layer, the solid-phase reaction kinetics of NaF and GaF3 are activated, which helps to synthesize the main component Na3GaF6. Introducing a small amount of chlorine source during the synthesis process further softens the interface of Na3GaF6 and reduces its interface impedance. The designed synthesis process is easy to operate and environmentally friendly.

[0017] Preferably, the parameters of the first heat treatment include: calcining at 500-900 °C for 6-14 hours.

[0018] Preferably, the parameters of the second heat treatment include: annealing at 150-300 °C for 4-11 hours; Preferably, during the second heat treatment, the molar ratio of F element to Cl element is controlled to be 2:1-11:1.

[0019] In a third aspect, the present invention provides a sodium metal symmetric battery based on a heterojunction fluorine-based solid electrolyte, including: a heterojunction fluorine-based solid electrolyte; metal sodium sheets located on both sides of the heterojunction fluorine-based solid electrolyte; and a trace interface wetting agent located in the gap between the heterojunction fluorine-based solid electrolyte and the metal sodium sheets; Preferably, the interface wetting agent includes: a solute and a solvent; More preferably, the solute is at least one of sodium bis(trifluoromethanesulfonyl)imide LiTFSI, sodium hexafluorophosphate NaPF6, sodium perchlorate NaClO4, and sodium bis(fluorosulfonyl)imide NaFSI; More preferably, the solvent is at least one of diglyme (DGM), triglyme (TEGDME), ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI), ethylene carbonate (EC), and propylene carbonate (PC); More preferably, the concentration of the solute in the interfacial wetting agent is 0.5 - 1.5 mol / L; Most preferably, the interfacial wetting agent is a mixed solution of sodium perchlorate (NaClO4) as the solute and a 1:1 volume ratio of ethylene carbonate (EC) and propylene carbonate (PC) as the solvent.

[0020] In the present invention, when the heterojunction fluorine-based solid electrolyte is used in a sodium metal symmetric battery, after dropping a small amount of interfacial wetting agent at the interface, during the reversible deposition / stripping process of metallic sodium, it has a low polarization overpotential and enhances the cycle stability of the symmetric battery. The stable deposition / stripping of the sodium metal symmetric battery based on the heterojunction fluorine-based solid electrolyte benefits from the high conductivity of the electrolyte and the inhibition of sodium dendrite growth by the high Young's modulus component derived at the interface layer.

[0021] In the present invention, during the long cycle process of the heterojunction fluorine-based solid electrolyte in a sodium metal symmetric battery, when the oxide phase is compatible with the sodium negative electrode, it can be reduced to a solid Na2O, and a small amount of fluorine-based open framework compound can be decomposed by the sodium negative electrode into stable NaF and sodium-philic Ga particles, which enhance the sodium dendrite inhibition ability and cycle stability of the battery.

[0022] Fourthly, the present invention provides a sodium metal battery based on a heterojunction fluorine-based solid electrolyte, comprising: a positive electrode, a negative electrode, and a heterojunction fluorine-based solid electrolyte located between the positive electrode and the negative electrode; Preferably, the negative electrode comprises a sodium metal sheet; Preferably, the positive electrode comprises at least one of carbon composite FeF3, Na3V2(PO4)3, and layered transition metal oxides; more preferably, the layered transition metal oxide is Na[Fe 1 / 2 Mn 1 / 2 O2. The above materials are assembled into a solid sodium battery for electrochemical cycling.

[0023] Advantages of the present invention: In the present invention, when the heterojunction fluorine-based solid electrolyte is used in a Na-Na3V2(PO4)3 sodium metal battery, due to the high mechanical modulus interface layer derived on the negative electrode side, sodium dendrites are inhibited, and thus a long life of more than 150 cycles is achieved for the Na-Na3V2(PO4)3 battery; In the present invention, when the heterojunction fluorine-based solid electrolyte is used in a Na-carbon composite FeF3 sodium metal battery, the sodium dendrite is inhibited, so that the morphology of the sodium negative electrode is significantly improved. In addition, the high oxidation stability window reduces the side reactions at the positive electrode interface. Therefore, a long cycle life of more than 250 cycles for the Na-carbon composite FeF3 battery is achieved. In the present invention, the production process of the method is simple in operation, suitable for large-scale application, and of great significance to the development of sodium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD pattern of the heterojunction fluorine-based solid electrolyte NGFOC-G; Figure 2 SAED pattern of the heterojunction fluorine-based solid electrolyte NGFOC-G; Figure 3 Cross-sectional SEM image of the heterojunction fluorine-based solid electrolyte NGFOC-G; Figure 4 TEM image of the heterojunction fluorine-based solid electrolyte NGFOC-G; Figure 5 Depth-etched XPS spectrum of the heterojunction fluorine-based solid electrolyte NGFOC-G; Figure 6 AC impedance spectrum of the heterojunction fluorine-based solid electrolyte NGFOC-G during the heating-up stage; Figure 7 Arrhenius plot derived from impedance values of the heterojunction fluorine-based solid electrolyte NGFOC-G at different temperatures; Figure 8 Graph showing the change of mass of the heterojunction fluorine-based solid electrolyte NGFOC-G with time when exposed to an air environment with a relative humidity of 61%; Figure 9 Room-temperature AC impedance spectrum of the heterojunction fluorine-based solid electrolyte NGFOC-G after being exposed to an air environment with a relative humidity of 61% for 18 hours; Figure 10 For a symmetric cell based on the heterojunction fluorine-based solid electrolyte NGFOC-G at 0.05 mA / cm 2 Cycling diagram of sodium metal deposition / stripping; Figure 11 For a symmetric cell based on the heterojunction fluorine-based solid electrolyte NGFOC-G at 0.1 mA / cm 2 Surface SEM image after 100 cycles of sodium metal deposition / stripping; Figure 12 Graph showing the change of discharge capacity and Coulombic efficiency with the number of cycles during charge and discharge of a Na-Na3V2(PO4)3 battery based on the heterojunction fluorine-based solid electrolyte NGFOC-G at 60 °C at a 1C rate. Figure 13 Voltage and specific capacity relationship curve of Na-Na3V2(PO4)3 battery based on heterojunction fluorine-based solid electrolyte NGFOC-G at 60 °C at a rate of 1C; Figure 14 Graph showing the change of discharge capacity and Coulomb efficiency with the number of cycles of Na-carbon composite FeF3 battery based on heterojunction fluorine-based solid electrolyte NGFOC-G during charge and discharge at a rate of 0.1C at 60 °C; Figure 15 Voltage and specific capacity relationship curve of Na-carbon composite FeF3 battery based on heterojunction fluorine-based solid electrolyte NGFOC-G at 60 °C at a rate of 0.1C. Detailed implementation mode

[0025] The present invention will be further described through the following implementation modes. It should be understood that the following implementation modes are only used to illustrate the present invention and do not limit the present invention.

[0026] In the present invention, the heterojunction fluorine-based solid electrolyte modified by the boundary of the oxide phase and the chloride phase, while having high ionic conductivity and moisture resistance, achieves the purpose of inhibiting the growth of sodium dendrites on the sodium negative electrode in a sodium metal battery. Specifically, first, NaF and gallium metal are preliminarily mixed to allow liquid gallium to infiltrate into the grain boundary gaps of NaF, and then in-situ oxidation is carried out to form a precursor Ga2O3@NaF with oxygen-rich defects encapsulating NaF. This type of Ga2O3 with rich defects can play a role in activating the reaction and reducing the reaction energy barrier in the subsequent synthesis of Na3GaF6.

[0027] Next, Ga2O3@NaF, GaCl3, and GaF3 are ground together and annealed in a nitrogen environment. Due to the activation of the rich-defect Ga2O3, NaF and GaF3 can smoothly form Na3GaF6. In addition, GaCl3 changes from a solid phase to a molten phase during this process and in-situ generates a modified chloride phase. The finally obtained heterojunction fluorine-based solid electrolyte is jointly modified by the oxide phase and the chloride phase.

[0028] In the present invention, the interfacial wetting agent includes a solute and a solvent. The solute can be at least one of sodium bis(trifluoromethanesulfonyl)imide LiTFSI, sodium hexafluorophosphate NaPF6, sodium perchlorate NaClO4, and sodium bis(fluorosulfonyl)imide NaFSI. The solvent can be at least one of diglyme DGM, triglyme TEGDME, ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide EmimTFSI, ethylene carbonate EC, and propylene carbonate PC. The concentration of the solute in the interfacial wetting agent is 0.5 - 1.5 mol / L.

[0029] The sodium metal symmetric battery system provided by the present invention refers to a battery in which both sides of the solid electrolyte are sodium metal sheets. The current density of the sodium deposition and stripping cycle test of the sodium metal symmetric battery is 0.05-0.15 mA / cm 2 , and the deposition or stripping time for each cycle is 1-3 hours.

[0030] For the sodium metal battery provided by the present invention, its negative electrode uses a sodium metal sheet, and the positive electrode can be at least one of carbon composite FeF3, Na3V2(PO4)3, Na[Fe 1 / 2 Mn 1 / 2 O2. It does not require a separator, and the solid electrolyte is placed between the positive and negative electrodes. Due to the inhibition of sodium dendrites, the solid-state Na3V2(PO4)3 battery based on the heterojunction fluorine-based solid electrolyte has a long life of more than 150 cycles, and the solid-state FeF3 battery based on the heterojunction fluorine-based solid electrolyte has a long life of more than 250 cycles.

[0031] The present invention designs a heterojunction fluorine-based solid electrolyte modified by the boundary of the oxide phase and the chloride phase, which has high ionic conductivity and moisture resistance while effectively inhibiting the growth of sodium dendrites in sodium metal batteries. After adding a trace amount of interfacial wetting agent, the solid-state symmetric battery has low bulk impedance and interfacial impedance, which greatly reduces the voltage polarization difference during the sodium metal deposition / stripping process, enhances the cycle stability of the symmetric battery, improves the morphology of the deposited sodium metal, and the surface of the sodium metal is still dense after long-term cycling of the symmetric battery.

[0032] In the present invention, the heterojunction fluorine-based solid electrolyte has ultra-high air stability and can be placed for a long time under an air humidity of more than 50% without changing the conductivity.

[0033] In the present invention, after optimization, the heterojunction fluorine-based solid electrolyte has a high ionic conductivity above 10 -5 S / cm at room temperature, and can reach an order of magnitude of conductivity of 10 -4 S / cm at 40°C, which is the highest level of the current fluorine-based sodium ion solid electrolyte system.

[0034] In the present invention, the activation energy of the ionic conductivity of the heterojunction fluorine-based solid electrolyte is 0.3-0.4 eV.

[0035] The present invention also provides a method for preparing this heterojunction fluorine-based solid electrolyte material to expand the improvement potential of solid electrolytes such as Na3GaF6 in aspects such as synthesis and surface modification, and to overcome the technical problems existing in the current solid-state battery framework and its key electrolyte materials.

[0036] Specifically, the heterojunction fluorine-based solid electrolyte material is synthesized by a two-step thermal solid-phase method.

[0037] NaF and gallium metal are thoroughly ground at a mass ratio of 1.344:1 (or 0.896:1 or 3.99:1). This process takes 3 to 6 hours to complete, enabling the infiltration of gallium metal into the grain boundary gaps of NaF. Subsequently, the mixture is transferred to a muffle furnace and heated in ambient air at a heating rate of 4 to 12 °C / min from 500 to 900 °C for 6 to 14 hours. The resulting precursor powder is labeled Ga2O3@NaF, with a NaF:Ga2O3 mass ratio of 1:1 (or 2:3 or 3:1). In the second step, in a glove box filled with argon, gallium fluoride and gallium chloride are uniformly mixed with Ga2O3@NaF, and the F:Cl molar ratio in this process is 5:1 (or 2:1 or 11:1).

[0038] The mixture is placed in a tubular furnace filled with nitrogen or argon and heated to 150 °C at a rate of 2 to 6 °C / min, then held for 1 to 3 hours to bring GaCl3 to the molten state. Subsequently, it is heated to 200 to 300 °C at a rate of 2 to 6 °C / min and annealed for 3 to 8 hours. The resulting electrolyte powder is Na3GaF6 - Ga2O3 - NaCl, named NGFOC - G.

[0039] In an alternative embodiment, the electrolyte material is NGFOC - G. In the first step of thermal solid - state synthesis, the mass ratio of NaF to gallium metal is preferably 1.344:1. The temperature of the first step of thermal solid - state synthesis is 600 °C. The heat - preservation time of the first step of thermal solid - state synthesis is 9 hours. The heating rate of the first step of thermal solid - state synthesis is 5 °C / min. In the second step of thermal solid - state synthesis, the F:Cl molar ratio is preferably 5:1. The temperature of the second step of thermal solid - state synthesis is 200 °C. The heat - preservation time of the second step of thermal solid - state synthesis is 4 hours. The heating rate of the second step of thermal solid - state synthesis is 4 °C / min.

[0040] The following further examples are given to illustrate the present invention in detail. It should be understood that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art's non - essential improvements and adjustments based on the above content of the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range according to the description herein, rather than being limited to the specific values in the following examples.

[0041] Example 1 1) Preparation of the heterojunction fluorine - based solid electrolyte: First step: Weigh 0.4 g of NaF and 0.3 g of gallium metal and grind them thoroughly for 3 hours. Subsequently, transfer the mixture to a muffle furnace and heat it in ambient air at a heating rate of 5 °C / min to 600 °C for 9 hours to ensure complete oxidation of the gallium metal. The resulting precursor powder is labeled Ga2O3@NaF, with a NaF:Ga2O3 mass ratio of 1:1. Second step: In a glove box filled with argon, uniformly mix gallium fluoride and gallium chloride with Ga2O3@NaF. The molar ratio of F element to Cl element in this process is 5:1. Then, place the mixture into a tube furnace filled with nitrogen or argon and heat it at a rate of 2 °C / min to 150 °C, and then hold for 1 hour to make GaCl3 reach the molten state. Subsequently, heat it at a rate of 2 °C / min to 210 °C and perform an annealing treatment for 4 hours. The resulting electrolyte powder is named NGFOC-G. The XRD of the heterojunction fluorine-based solid electrolyte NGFOC-G is as shown in Figure 1 the attachment, indicating that a large amount of Na3GaF6 products can be obtained using this scheme. In addition, there are obvious Ga2O3 and NaCl signals, indicating the existence of a heterophase structure, where the NaF phase is the unreacted raw material (i.e., the impurity phase). The SAED pattern of the heterojunction fluorine-based solid electrolyte is as shown in Figure 2 the attachment. The phases corresponding to the diffraction rings and diffraction spots can show that there is an obvious heterojunction structure inside the electrolyte, specifically the heterojunction of Na3GaF6, Ga2O3, and NaCl. Weigh 200 mg of NGFOC-G powder and press it into a disc with a diameter of 10 mm and a thickness of about 1 mm under a pressure of 20 MPa. The cross-sectional SEM of the heterojunction fluorine-based solid electrolyte disc is as shown in Figure 3 the attachment. Na3GaF6 shows micron-sized pebble-like particles (particle size of 10 - 50 nm), Ga2O3 shows gravel-like particles (particle size of 10 - 100 nm), and NaCl shows large block crystal-like particles (particle size of 1 - 10 μm). The three are in random contact, and NaCl and Ga2O3 modify the Na3GaF6 matrix phase at the boundary. The composition of the obtained heterojunction fluorine-based solid electrolyte includes: the molar percentage of the main fluorine-based open framework compound is 32%; the molar percentage of the oxide phase is 34%; the molar percentage of the chloride phase is 31%; the molar percentage of the NaF phase is 3%. The TEM image of the heterojunction fluorine-based solid electrolyte NGFOC-G is as shown in Figure 4 the attachment, indicating that there are line defects of lattice fringes in NGFOC-G, which are caused by the incomplete oxidation of Ga, that is, there are structural defects of oxygen vacancies in Ga2O3. From the attachment Figure 5A certain degree of gradient structure can be seen in the deep etching XPS spectra. A small amount of the outer main phase is evenly distributed in the inner layer (the molar percentage of the fluorine-based open-frame compound main body is about 61%, the total molar percentage of the interfacial modification phase is about 36%, and the content of the NaF phase is 3 mol%). A small amount of the inner main phase is evenly distributed in the outer layer (the total molar percentage of the interfacial modification phase is about 72 mol%, the molar percentage of the fluorine-based open-frame compound main body is about 20%, and the content of the NaF phase is 8 mol%).

[0042] 2) Preparation of the interfacial wetting agent: The preparation of the interfacial wetting agent is carried out in an argon glove box with a water value and an oxygen value less than 0.1 ppm. First, 2.5 mL of ethylene carbonate (EC) and 2.5 mL of propylene carbonate (PC) are respectively sucked with a pipette to prepare a solvent (EC / PC). Subsequently, 0.6122 g (5 mmol) of sodium perchlorate (NaClO4) is dissolved in 5 mL of EC / PC. Then the solution is placed on a magnetic stirrer and stirred for 24 hours to obtain a 1 mol / L NaClO4 / EC / PC interfacial wetting agent.

[0043] Example 2 1) Conductivity test of the solid electrolyte sheet: Silver paste layers are coated on both sides of the heterojunction fluorine-based solid electrolyte NGFOC-G wafer prepared in Example 1, and an AC impedance test is carried out using a Swagelok cell housing with a two-electrode structure, as shown in the attached Figure 6 As shown in the AC impedance spectrum, the test temperature is raised from 25 °C to 80 °C, and the test is carried out after staying at each temperature for 1 hour. Its room-temperature ionic conductivity is 4.31×10 -5 S / cm. In addition, at 40 °C, its ionic conductivity exceeds 1×10 -4 S / cm. The corresponding Arrhenius dot plot is shown in the attached Figure 7 As shown, the activation energy is about 0.36 eV.

[0044] 2) Moisture resistance test of the solid electrolyte: The heterojunction fluorine-based solid electrolyte NGFOC-G sheet prepared in Example 1 is placed in an air environment with a relative humidity of 61%, and the mass is measured every 6 hours. The dot plot of the change in the mass increase with time is shown in the attached Figure 8 As shown, the mass increase is only 1% - 2% after being placed for 18 hours. Silver paste layers are coated on both sides of the electrolyte sheet after being placed for 18 hours, and an AC impedance test is carried out using a Swagelok cell housing with a two-electrode structure, as shown in the attached Figure 9 As shown in the AC impedance spectrum, its room-temperature ionic conductivity is still 4×10 -5 ~5×10 -5 S / cm, indicating that the environmental humidity has little effect on the ionic conductivity of the heterojunction fluorine-based solid electrolyte.

[0045] Example 3 1) Assembly and testing of sodium metal symmetric batteries: The assembly of the dual-electrode structure Swagelok battery was carried out in an argon glove box with a water value and an oxygen value of less than 0.1 ppm. Specifically, a metal sodium sheet with a diameter of 6 mm was taken, and a trace amount of the interface wetting agent prepared in Example 1 was dripped on the surfaces of both ends of the solid electrolyte, and then the sodium sheet was covered and placed in a Swagelok battery shell. The assembled symmetrical battery was subjected to charge and discharge tests on a LAND electrochemical workstation at 0.05 mA / cm 2 At a current density of , the battery is first charged at a constant current for 1 hour, then discharged at a constant current for 1 hour, the voltage polarization difference of the deposition / stripping process of metallic sodium is detected, and the cycle is carried out in this step. Figure 10 A sodium symmetric battery based on a heterojunction fluorine-based solid electrolyte at 0.05 mA / cm 2 The cycle curve of the sodium metal deposition / stripping process under current density shows that the symmetrical battery matched with the heterojunction fluorine-based solid electrolyte has a low polarization potential difference in the metal sodium deposition / stripping cycle and has excellent symmetrical battery cycle stability. It can be cycled for at least 1000 hours with a polarization of no more than 0.25V. In order to verify the ability of the symmetrical battery system to inhibit sodium dendrites, the attached Figure 11 This is an SEM image of the sodium surface of a symmetrical battery after 100 cycles at a current density of 0.1 mA / cm2. It can be seen from the figure that the sodium deposition grows in a spherical shape and no sodium dendrites grow, which is due to the excellent interface stability of the fluoride.

[0046] Example 4 1) Construction and testing of sodium vanadium phosphate solid-state sodium battery based on heterojunction fluorine-based solid electrolyte: The commercial Na3V2(PO4)3(NVP) powder, conductive carbon Super P and binder PVDF were uniformly mixed and ground in a mass ratio of 7:2:1, and an appropriate amount of NMP was added to make a uniform slurry, which was coated on the carbon-coated aluminum foil current collector and then placed in a vacuum oven at 60°C for more than 6 hours. A small amount of interfacial wetting agent was added to both sides of the heterojunction fluorine-based solid electrolyte sheet in Example 1, and an NVP positive electrode and a Na metal negative electrode with a diameter of 8 mm were attached respectively, and a Swagelok battery was assembled in an argon-filled glove box. As shown in the attached figure Figure 12 and 13 As shown, this solid-state sodium battery can be successfully charged and discharged under 1C high rate conditions, with a first-cycle discharge capacity of nearly 110mAh / g. After 150 cycles of the battery, the capacity retention rate is as high as 80%.

[0047] 2) Construction and testing of iron trifluoride solid-state sodium battery based on heterojunction fluorine-based solid electrolyte: The synthesized carbon composite FeF3 powder, conductive carbon Super P, and binder PVDF are uniformly mixed and ground in a mass ratio of 7:2:1, and an appropriate amount of NMP is added dropwise to make a uniform slurry, which is then coated on a carbon-coated aluminum foil current collector and placed in a vacuum oven at 60 °C for more than 6 hours. A trace amount of interfacial wetting agent is added dropwise to both sides of the heterojunction fluorine-based solid electrolyte sheet in Example 1, and a carbon composite FeF3 positive electrode and a Na metal negative electrode with a diameter of 8 mm are respectively attached, and a Swagelok battery is assembled in a glove box filled with argon. As shown in Figure 14 and 15 the figure, this solid-state sodium battery can be successfully charged and discharged under the condition of a 0.1C rate, and the discharge capacity in the first 5 cycles is greater than 250 mAh / g; even at the 50th cycle, it still has a discharge capacity of more than 200 mAh / g. These phenomena illustrate the superiority of this heterojunction fluorine-based solid electrolyte in matching the iron-based fluoride positive electrode.

[0048] Finally, it is necessary to state here that the above embodiments are only used to further elaborate on the technical solutions of the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention.

Claims

1. A heterogeneous junction fluorine-based solid electrolyte, characterized in that, Comprising: A fluoro-based open framework compound matrix and an interfacial modification phase; the interfacial modification phase comprises an oxide phase and a chloride phase.

2. The heterojunction fluorine-based solid electrolyte according to claim 1, characterized in that, The fluoro-based open framework compound matrix serves as the inner layer; the interfacial modification phase serves as the outer layer; Preferably, based on the total mass of the inner layer being 100 mol%, the content of the fluoro-based open framework compound matrix in the inner layer is 60 - 80 mol%, the content of the interfacial modification phase is 10 - 40 mol%, and the content of the NaF phase is 0 - 15 mol%; Preferably, based on the total mass of the outer layer being 100 mol%, the content of the interfacial modification phase in the outer layer is 60 - 80 mol%, the content of the fluoro-based open framework compound matrix is 10 - 40 mol%, and the content of the NaF phase is 0 - 15 mol%.

3. The heterojunction fluorine-based solid electrolyte according to claim 1 or 2, wherein The fluoro-based open framework compound matrix is Na3GaF6; the oxide phase in the interfacial modification phase is gallium oxide with structural defects, preferably the structural defect is an oxygen vacancy; the chloride phase is NaCl.

4. The heterojunction fluorine-based solid electrolyte according to any one of claims 1-3, characterized in that, The morphology of the fluoro-based open framework compound matrix is nano-sized particles with a particle size of 10 - 50 nm; the morphology of the oxide phase is nano-sized porous particles with a particle size of 10 - 100 nm; the morphology of the chloride phase is micron-sized particles with a particle size of 1 - 10 μm.

5. The heterojunction fluorine-based solid electrolyte according to any one of claims 1-4, wherein The composition of the heterojunction fluoro-based solid electrolyte includes: the molar percentage of the fluoro-based open framework compound matrix is 30 - 40%; the molar percentage of the oxide phase is 30 - 35%; the molar percentage of the chloride phase is 25 - 35%; the molar percentage of the NaF phase is 0 - 15%.

6. The heterojunction fluorine-based solid electrolyte according to any one of claims 1-5, characterized in that, The heterojunction fluoro-based solid electrolyte has extremely strong moisture resistance stability. In air with a relative humidity of 61%, the heterojunction fluoro-based solid electrolyte is stored for at least 15 hours without a decrease in conductivity.

7. The heterojunction fluorine-based solid electrolyte according to any one of claims 1-5, characterized in that The ionic conductivity of the heterojunction fluorine-based solid electrolyte at room temperature > 10 -5 S / cm, and the ionic conductivity at 40 °C ≥ 1 × 10 -4 S / cm.

8. A method for preparing a heterojunction fluorine-based solid electrolyte as described in any one of claims 1-7, which prepares the heterojunction fluorine-based solid electrolyte by a two-step heat treatment process, characterized in that, Comprising: (1) After grinding and mixing liquid metal gallium and NaF, a first heat treatment is carried out in an air atmosphere to obtain a precursor Ga2O3@NaF; (2) After grinding and mixing the precursor Ga2O3@NaF, GaCl3, and GaF3, a second heat treatment is carried out to obtain the heterojunction fluoro-based solid electrolyte.

9. The preparation method according to claim 8, characterized in that, The parameters of the first heat treatment include: calcining at 500 - 900 °C for 6 - 14 hours; The parameters of the second heat treatment include: annealing at 150 - 300 °C for 4 - 11 hours; Preferably, during the second heat treatment, the molar ratio of F element to Cl element is controlled to be 2:1 - 11:

1.

10. A sodium metal symmetric battery based on a heterojunction fluorine-based solid electrolyte, characterized in that, Comprising: The heterojunction fluoro-based solid electrolyte according to any one of claims 1 - 7; Metal sodium sheets located on both sides of the heterojunction fluoro-based solid electrolyte; And a trace amount of interfacial wetting agent located in the gap between the heterojunction fluoro-based solid electrolyte and the metal sodium sheets; Preferably, the interfacial wetting agent includes: a solute and a solvent; More preferably, the solute is at least one of sodium bis(trifluoromethanesulfonyl)imide LiTFSI, sodium hexafluorophosphate NaPF6, sodium perchlorate NaClO4, and sodium bis(fluorosulfonyl)imide NaFSI; More preferably, the solvent is at least one of diglyme (DGM), triglyme (TEGDME), ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI), ethylene carbonate (EC), and propylene carbonate (PC); More preferably, the concentration of the solute in the interfacial wetting agent is 0.5 to 1.5 mol / L; Most preferably, the interfacial wetting agent is: sodium perchlorate (NaClO4) as the solute and a mixed solution of ethylene carbonate (EC) and propylene carbonate (PC) with a volume ratio of 1:1 as the solvent.

11. A sodium metal battery based on a heterojunction fluorine-based solid electrolyte, characterized in that, Comprising: a positive electrode, a negative electrode, and the heterojunction fluorine-based solid electrolyte according to any one of claims 1-7 located between the positive electrode and the negative electrode; Preferably, the negative electrode includes a sodium metal sheet; Preferably, the positive electrode comprises at least one of carbon composite FeF3, Na3V2(PO4)3 and layered transition metal oxide; more preferably, the layered transition metal oxide is Na[Fe 1 / 2 Mn 1 / 2 O2.

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