In-situ polymerized solid composite electrolyte and method for preparing the same

Abstract

The application provides an in-situ polymerization solid-state composite electrolyte and a preparation method thereof, and belongs to the technical field of solid-state electrolytes.The in-situ polymerization solid-state composite electrolyte provided by the application has a sodium alloy layer which is in-situ grown on the surface of a sodium electrode, can inhibit dendrite growth, reduce interface impedance, relieve volume expansion, improve ionic conductivity, and has high specific capacity retention of a prepared sodium ion battery;the sodium alloy layer, the sodium compound layer and the polymer composite layer are combined by in-situ growth and have excellent compatibility, can reduce the impedance of a passivation film generated by interface reaction, and improve sodium ion transmission efficiency;inorganic fillers can improve the polymerization degree of a polymer, and further improve the mechanical properties of the in-situ polymerization solid-state composite electrolyte;at the same time, the polymer can improve the dispersibility of the inorganic fillers, improve ionic conductivity, and the two can synergistically realize efficient and directional transmission of sodium ions in the in-situ polymerization solid-state composite electrolyte, and improve the specific capacity retention of the prepared sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, and in particular to an in-situ polymerized solid composite electrolyte and its preparation method. Background Technology

[0002] Sodium-ion batteries are secondary batteries that use sodium ions as charge carriers. Their working principle is similar to that of lithium-ion batteries, relying on the insertion and extraction of sodium ions between the positive and negative electrodes to achieve charging and discharging. Due to the abundant and widely distributed nature of sodium resources, low cost, and relatively good safety, sodium-ion batteries are widely used in low-speed electric vehicles, large-scale energy storage, and other fields.

[0003] The electrolyte in a sodium-ion battery is the core functional component connecting the positive and negative electrodes. Its core function is to conduct sodium ions and build a stable electrode-electrolyte interface, thereby ensuring the cycle stability and specific capacity retention of the sodium-ion battery. Traditional sodium-ion batteries use liquid electrolytes, which pose risks of flammability and leakage. They are also prone to side reactions with electrode materials, increasing interfacial impedance, and are susceptible to sodium dendrite formation after repeated cycles, damaging the electrode-electrolyte interface and reducing the specific capacity retention of the sodium-ion battery. Current technology uses non-flammable, non-volatile, and leak-proof solid-state electrolytes, solving the safety problems of flammability and leakage associated with liquid electrolytes. Furthermore, solid electrolytes can physically resist dendrite penetration and effectively inhibit dendrite growth. However, because solid-state electrolytes are in physical contact with the electrodes, microscopic gaps and voids can easily exist, increasing contact impedance, reducing ion conductivity, and consequently decreasing the specific capacity retention of the sodium-ion battery. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ polymerized solid-state composite electrolyte and its preparation method. The in-situ polymerized solid-state composite electrolyte provided by this invention has high ionic conductivity and the sodium-ion battery prepared by it has high capacity retention.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] An in-situ polymerized solid composite electrolyte includes a sodium alloy layer, a sodium compound layer, and a polymer composite layer that are sequentially grown in situ on the surface of a sodium electrode.

[0007] The sodium alloy in the sodium alloy layer includes a sodium-antimony alloy, a sodium-tin alloy, or a sodium-bismuth alloy; the sodium compound in the sodium compound layer includes sodium halide.

[0008] The polymer composite layer comprises a polymer and inorganic fillers and sodium salts distributed in the polymer; the inorganic fillers include antimony halide, tin halides, bismuth halides, antimony sulfide, tin sulfide, or bismuth sulfide.

[0009] Preferably, the mass ratio of the polymer to the inorganic filler is 1:(0.25%~1.25%).

[0010] Preferably, the polymer comprises polyethylene glycol divinyl ether, poly(1,3,5-trioxane), poly(1,3-dioxane), or poly(1,3-dioxane).

[0011] Preferably, the thickness of the sodium alloy layer is 10~23μm.

[0012] Preferably, the thickness of the sodium compound layer is 27~48 μm.

[0013] Preferably, the thickness of the polymer composite layer is 223~258μm.

[0014] This invention also provides a method for preparing the in-situ polymerized solid composite electrolyte described in the above technical solution, comprising:

[0015] Sodium salt, polymer monomer, inorganic filler and carbonate organic solvent are mixed to obtain a mixture;

[0016] The mixture was mixed with an initiator and then placed on a sodium electrode for in-situ polymerization growth to obtain an in-situ polymerized solid composite electrolyte.

[0017] Preferably, the volume ratio of the polymer monomer to the carbonate organic solvent is (2~9):1.

[0018] Preferably, the concentration of sodium salt in the mixture is 0.6~1 mol / L.

[0019] Preferably, the in-situ polymerization growth temperature is 25~30℃, and the in-situ polymerization growth time is 16~24h.

[0020] This invention provides an in-situ polymerized solid composite electrolyte, comprising a sodium alloy layer, a sodium compound layer, and a polymer composite layer sequentially grown in situ on the surface of a sodium electrode; the sodium alloy in the sodium alloy layer includes a sodium-antimony alloy, a sodium-tin alloy, or a sodium-bismuth alloy; the sodium compound in the sodium compound layer includes sodium halide; the polymer composite layer includes a polymer and inorganic fillers and sodium salts distributed in the polymer; the inorganic fillers include antimony halide, tin halide, bismuth halide, antimony sulfide, tin sulfide, or bismuth sulfide. The in-situ polymerized solid composite electrolyte provided by this invention features a sodium alloy layer grown in situ on the surface of a sodium electrode, forming a defect-free solid electrolyte interface layer. This inhibits dendrite growth, reduces interfacial impedance, alleviates volume expansion, and improves ionic conductivity, thereby enhancing the specific capacity retention of the resulting sodium-ion battery. The sodium alloy layer, sodium compound layer, and polymer composite layer are all grown and bonded in situ, exhibiting excellent compatibility. This reduces passivation film impedance caused by interfacial reactions, improves ion transport efficiency, and further enhances the specific capacity retention of the resulting sodium-ion battery. The inorganic filler in the polymer composite layer increases the degree of polymer polymerization, thus improving the mechanical properties of the in-situ polymerized solid composite electrolyte. Simultaneously, the polymer improves the dispersibility of the inorganic filler, further enhancing ionic conductivity. The synergistic effect of these two factors achieves high sodium ion conductivity and efficient, directional sodium ion transport in the in-situ polymerized solid composite electrolyte, thereby improving the specific capacity retention of the resulting sodium-ion battery. Example results show that the specific capacity retention of the in-situ polymerized solid composite electrolyte provided by this invention can reach 94.7%. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the preparation of in-situ polymerized solid composite electrolyte in an embodiment of the present invention;

[0022] Figure 2 The infrared spectra of the in-situ solid electrolytes and 1,3-dioxolane prepared in Examples 1-5 and Comparative Example 1 of this invention are shown.

[0023] Figure 3 This is a 1000x magnified SEM image of the in-situ polymerized solid composite electrolyte in Example 1 of the present invention.

[0024] Figure 4 This is a 5000x magnified SEM image of the in-situ polymerized solid composite electrolyte in Example 1 of the present invention.

[0025] Figure 5 Impedance diagrams of sodium-ion batteries prepared with in-situ solid electrolytes in Examples 1 and 4 and Comparative Examples 1 and 2 of the present invention.

[0026] Figure 6 Impedance diagrams of sodium-ion batteries prepared with in-situ solid electrolytes in Examples 1-3 and Comparative Example 1 of the present invention.

[0027] Figure 7 The cycling performance diagrams are for sodium-ion half-cells prepared with in-situ solid electrolytes in Examples 1-5 and Comparative Example 1 of this invention.

[0028] Figure 8 The figures show the constant current charge-discharge cycle test results of the sodium ion batteries prepared by the in-situ solid electrolyte in Examples 1-5 and Comparative Example 1 of this invention. Detailed Implementation

[0029] This invention provides an in-situ polymerized solid composite electrolyte, comprising a sodium alloy layer, a sodium compound layer, and a polymer composite layer sequentially grown in situ on the surface of a sodium electrode;

[0030] The sodium alloy in the sodium alloy layer includes a sodium-antimony alloy, a sodium-tin alloy, or a sodium-bismuth alloy; the sodium compound in the sodium compound layer includes sodium halide or sodium sulfide.

[0031] The polymer composite layer comprises a polymer and inorganic fillers and sodium salts distributed in the polymer; the inorganic fillers include antimony halide, tin halides, bismuth halides, antimony sulfide, tin sulfide, or bismuth sulfide.

[0032] The in-situ polymerized solid-state composite electrolyte provided by this invention includes a sodium alloy layer grown in situ on the surface of a sodium electrode. In this invention, the sodium electrode is the core electrode for realizing sodium ion storage and charge transfer. As one embodiment of this invention, the sodium electrode can be a sodium sheet.

[0033] In this invention, the sodium alloy layer grown in situ on the surface of the sodium electrode forms a defect-free solid electrolyte interface layer with the sodium electrode, which can suppress dendrite growth, reduce interface impedance, alleviate volume expansion, and improve ionic conductivity, thereby improving the specific capacity retention rate of the prepared sodium-ion battery.

[0034] In this invention, the sodium alloy in the sodium alloy layer includes a sodium-antimony alloy, a sodium-tin alloy, or a sodium-bismuth alloy. This invention ensures that the sodium alloy layer can form a defect-free solid electrolyte interface layer with the sodium electrode by limiting the type of sodium alloy in the sodium alloy layer. As one embodiment of this invention, the sodium-antimony alloy comprises, by mass percentage: 35-40% sodium and 60-75% antimony. As one embodiment of this invention, the sodium-tin alloy comprises, by mass percentage: 27-30% sodium and 70-73% tin. As one embodiment of this invention, the sodium-bismuth alloy comprises, by mass percentage: 20-30% sodium and 70-80% bismuth.

[0035] In one embodiment of the present invention, the thickness of the sodium alloy layer can be 10-23 nm. Specifically, in embodiments of the present invention, the sodium alloy layer can be 10 nm, 15 nm, 20 nm, or 23 nm. By limiting the thickness of the sodium alloy layer, the present invention achieves a more uniform distribution of sodium ions, reduces local charge accumulation, guides uniform sodium deposition, and inhibits dendrite formation; furthermore, it reduces the magnitude of volume expansion, alleviates stress at the interface between the sodium electrode and the electrolyte, and protects the integrity of the electrode structure.

[0036] The in-situ polymerized solid composite electrolyte provided by this invention further includes a sodium compound layer grown in-situ on the surface of the sodium alloy layer. In this invention, the sodium compound layer can construct efficient sodium ion transport channels and reduce interfacial impedance. In this invention, the sodium compound in the sodium compound layer includes sodium halide. As one embodiment of this invention, the sodium halide can be sodium fluoride or sodium chloride. This invention ensures that the sodium alloy layer can construct efficient sodium ion transport channels by limiting the type of sodium compound in the sodium compound layer, reducing the passivation film impedance generated by interfacial reactions, improving ion transport efficiency, and thus improving the specific capacity retention rate of the fabricated sodium-ion battery. As one embodiment of this invention, the thickness of the sodium compound layer can be 27~48 μm. In embodiments of this invention, the thickness of the sodium compound layer can specifically be 27.5 μm, 32.5 μm, 35 μm, 40 μm, 45 μm, or 48 μm. This invention further constructs efficient sodium ion transport channels, reduces the passivation film impedance generated by interfacial reactions, improves ion transport efficiency, and gives the sodium compound layer certain mechanical properties to prevent dendrite growth by limiting the thickness of the sodium compound layer.

[0037] The in-situ polymerized solid composite electrolyte provided by this invention further includes a polymer composite layer in-situ grown on the surface of the sodium alloy layer. In this invention, the polymer composite layer comprises a polymer and inorganic fillers and sodium salts distributed within the polymer. In this invention, the inorganic filler can increase the degree of polymerization of the polymer, thereby improving the mechanical properties of the in-situ polymerized solid composite electrolyte; simultaneously, the polymer can improve the dispersibility of the inorganic filler, further increasing the ionic conductivity. The synergistic effect of both results in high sodium ion conductivity and efficient, directional transport of sodium ions in the in-situ polymerized solid composite electrolyte, thereby improving the specific capacity retention of the fabricated sodium-ion battery.

[0038] In one embodiment of the present invention, the polymer may be poly(triethylene glycol) divinyl ether, poly(1,3,5-trioxane), poly(1,3-dioxolane), or poly(1,3-dioxane). In another embodiment, the degree of polymerization of the polymer may be 88-93%. The present invention, by limiting the type of polymer, ensures good ion transport channel compatibility, guarantees the chemical stability of the electrolyte and the sodium electrode, and prevents excessive reduction by the sodium electrode, thereby stabilizing the electrode / electrolyte interface and improving battery cycle life.

[0039] In this invention, the inorganic filler includes antimony halide, stannous halide, bismuth halide, antimony sulfide, tin sulfide, or bismuth sulfide. As one embodiment of this invention, the antimony halide can be antimony trifluoride or antimony trichloride; the stannous halide can be stannous chloride or stannous fluoride; and the bismuth halide can be bismuth trifluoride or bismuth trichloride. This invention, by limiting the type of inorganic filler, ensures that the in-situ polymerized solid composite electrolyte has high conductivity and can improve the degree of polymer polymerization, thereby improving the mechanical properties of the in-situ polymerized solid composite electrolyte.

[0040] In one embodiment of the present invention, the inorganic filler can be in powder form. In another embodiment, the particle size of the inorganic filler can be 4-6 μm. The present invention ensures good dispersibility of the inorganic filler by limiting its particle size. In another embodiment, the mass of the inorganic filler can be 0.25-1.25% of the polymer mass. In specific embodiments of the present invention, the mass of the inorganic filler can be 0.25%, 0.5%, 1%, or 1.25% of the polymer mass. The present invention ensures that a sodium alloy layer and a polymer composite layer can be obtained by limiting the amount of inorganic filler added.

[0041] In one embodiment of the present invention, the mass ratio of the polymer to the inorganic filler can be 1:(0.25%~1.25%). In specific embodiments of the present invention, the mass ratio of the polymer to the inorganic filler can be 1:0.25%, 1:0.5%, 1:1%, or 1:1.25%. The present invention, by limiting the mass ratio of the polymer to the inorganic filler, ensures that the two work synergistically to achieve high sodium-ion conductivity and efficient, directional transport of sodium ions in the in-situ polymerized solid-state composite electrolyte, thereby improving the specific capacity retention of the prepared sodium-ion battery.

[0042] In one embodiment of the present invention, the sodium salt may be sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, or sodium perchlorate. The present invention provides migratable sodium ions by limiting the type of sodium salt, ensuring smooth ion conduction and electrochemical reactions in the battery.

[0043] In one embodiment of the present invention, the mass ratio of the sodium salt to the polymer can be 1:(6.06~10.2). In embodiments of the present invention, the mass ratio of the sodium salt to the polymer can specifically be 1:6.06, 1:6.73, 1:7.58, 1:8.66, or 1:10.2. The present invention further ensures the smooth progress of ion conduction and electrochemical reactions in the battery by limiting the mass ratio of the sodium salt to the polymer.

[0044] In one embodiment of the present invention, the thickness of the polymer composite layer can be 223~258 μm. In specific embodiments of the present invention, the thickness of the polymer composite layer can be 223 μm, 230 μm, 240 μm, 250 μm, or 258 μm. The present invention ensures mechanical support by limiting the thickness of the polymer composite layer, forming an effective physical barrier to prevent sodium dendrite penetration; and reduces sodium ion transport resistance.

[0045] The in-situ polymerized solid composite electrolyte provided by this invention features a sodium alloy layer grown in situ on the surface of a sodium electrode, forming a defect-free solid electrolyte interface layer. This inhibits dendrite growth, reduces interfacial impedance, alleviates volume expansion, and improves ionic conductivity, thereby enhancing the specific capacity retention of the fabricated sodium-ion battery. The sodium alloy layer and sodium compound layer are in-situ grown and bonded to both the sodium electrode and polymer composite layer, exhibiting excellent compatibility. This reduces passivation film impedance caused by interfacial reactions, improves ion transport efficiency, and further enhances the specific capacity retention of the fabricated sodium-ion battery. The inorganic filler in the polymer composite layer increases the degree of polymer polymerization, thus improving the mechanical properties of the in-situ polymerized solid composite electrolyte. Simultaneously, the polymer improves the dispersibility of the inorganic filler, further enhancing ionic conductivity. The synergistic effect of these two factors achieves high sodium-ion conductivity and efficient, directional sodium-ion transport in the in-situ polymerized solid composite electrolyte, thereby improving the specific capacity retention of the fabricated sodium-ion battery.

[0046] This invention also provides a method for preparing the in-situ polymerized solid composite electrolyte described in the above technical solution, which may include:

[0047] Sodium salt, polymer monomer, inorganic filler and carbonate organic solvent are mixed to obtain a mixture;

[0048] The mixture was mixed with an initiator and then placed on a sodium electrode for in-situ polymerization growth to obtain an in-situ polymerized solid composite electrolyte.

[0049] This invention involves mixing sodium salt, polymer monomer, inorganic filler, and carbonate-based organic solvent to obtain a mixture.

[0050] In one embodiment of the present invention, the sodium salt may be sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, or sodium perchlorate. The present invention provides migratable sodium ions by limiting the type of sodium salt, ensuring smooth ion conduction and electrochemical reactions in the battery.

[0051] In one embodiment of the present invention, the concentration of sodium salt in the mixture can be 0.6~1 mol / L. In specific embodiments of the present invention, the concentration of sodium salt in the mixture can be 0.6 mol / L, 0.8 mol / L, or 1 mol / L. The present invention controls the ionic conductivity of the electrolyte and avoids the aggregation of inorganic fillers by limiting the concentration of sodium salt in the mixture.

[0052] In one embodiment of the present invention, the polymer monomer may be triethylene glycol divinyl ether, 1,3,5-trioxane, 1,3-dioxane, or 1,3-dioxane.

[0053] In one embodiment of the present invention, the carbonate organic solvent may be propylene carbonate, ethylene carbonate, ethyl methyl carbonate, or dimethyl carbonate.

[0054] In one embodiment of the present invention, the volume ratio of the polymer monomer to the carbonate organic solvent can be (2~9):1. In specific embodiments of the present invention, the volume ratio of the polymer monomer to the carbonate organic solvent can be 2:1, 4:1, 6:1, 8:1, or 9:1. The present invention, by limiting the volume ratio of the polymer monomer to the carbonate organic solvent, ensures that the polymer monomer can be fully polymerized to obtain the polymer, while also constraining the flowability of the carbonate organic solvent and fixing the ion transport environment.

[0055] In one embodiment of the present invention, the mixing of the sodium salt, polymer monomer, inorganic filler, and carbonate organic solvent can be performed by sequential ultrasonication and stirring. In one embodiment of the present invention, the ultrasonication time can be 30-60 minutes. In one embodiment of the present invention, the stirring rate can be 700-1000 r / min. In embodiments of the present invention, the stirring rate can specifically be 700 r / min, 800 r / min, 900 r / min, or 1000 r / min. In one embodiment of the present invention, the stirring time can be 6-8 hours.

[0056] After obtaining the mixture, the present invention mixes the mixture with an initiator and places it on a sodium electrode for in-situ polymerization growth to obtain an in-situ polymerized solid composite electrolyte.

[0057] In one embodiment of the present invention, the initiator may be aluminum trifluoromethanesulfonate, indium trichloride, stannous fluoride, magnesium trifluoromethanesulfonate, scandium trifluoromethanesulfonate, stannous trifluoromethanesulfonate, or zinc chloride. The present invention ensures that the polymer monomers are fully initiated to form a polymer by limiting the initiator. In one embodiment of the present invention, the concentration of the initiator after mixing the mixture with the initiator may be 1~3 mmol / L. The present invention controls the degree of crosslinking of the polymer monomers by limiting the concentration of the initiator, thereby balancing the mechanical properties and ionic conductivity of the electrolyte.

[0058] The present invention does not impose any special limitations on the mixing of the mixture and the initiator; any mixing method well known in the art can be used.

[0059] In this invention, during the in-situ polymerization growth process, the sodium electrode and the inorganic filler form a sodium compound layer and a sodium alloy layer respectively through displacement and combination reactions. Taking antimony trifluoride as an example of inorganic filler, the chemical formulas are: 3Na + SbF3 → 3NaF + Sb; Sb + 3Na → Na3Sb. The initiator induces the polymer monomers to undergo ring-opening polymerization, thereby solidifying the electrolyte. As one embodiment of this invention, the in-situ polymerization growth temperature can be 25~30℃, and the in-situ polymerization growth time can be 16~24h. In the embodiments of this invention, the in-situ polymerization growth time can specifically be 16h, 18h, 20h, 22h, or 24h. This invention controls the polymerization reaction process by limiting the temperature and time of in-situ polymerization growth, ensuring that the electrolyte forms a uniform and dense interface layer on the electrode surface.

[0060] In one embodiment of the present invention, a porous membrane can be first deposited on the surface of a sodium electrode, and then the mixture of the liquid and the initiator can be injected between the sodium electrode and the porous membrane for in-situ polymerization growth. In another embodiment, the injection volume can be sufficient to wet the porous membrane. In this invention, when the diameter of the porous membrane is 16 mm, the injection volume can be 100-120 μL.

[0061] In one embodiment of the present invention, an electrode-electrolyte-membrane composite is obtained after the in-situ polymerization growth is completed; the electrode-electrolyte-membrane composite includes a sodium electrode, an in-situ polymerized solid composite electrolyte, a membrane, and a propylene carbonate and sodium salt solution distributed between the in-situ polymerized solid composite electrolyte and the membrane.

[0062] As one embodiment of the present invention, after the in-situ polymerization growth is completed, the diaphragm in the obtained electrode-electrolyte-diaphragm composite can be removed to obtain an in-situ polymerized solid composite electrolyte.

[0063] As one embodiment of the present invention, the in-situ polymerized solid composite electrolyte can be used to assemble a battery, the electrode-electrolyte-membrane composite can be used to directly assemble a battery, and the battery can be assembled simultaneously with the in-situ polymerized growth of the electrode-electrolyte-membrane composite.

[0064] In an embodiment of the present invention, the process flow diagram for the preparation of the in-situ polymerized solid composite electrolyte and the battery assembly is as follows: Figure 1 As shown: Antimony trifluoride, sodium perchlorate, 1,3-dioxolane (DOL) and propylene carbonate (PC) were mixed and stirred to obtain a mixture. Then, aluminum trifluoromethanesulfonate initiator was added and mixed. The mixture was injected into the diaphragm on the surface of the sodium electrode using a syringe. The sodium electrode, diaphragm and positive electrode were then assembled and allowed to stand for 24 hours for in-situ polymerization growth.

[0065] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0066] Example 1

[0067] An in-situ polymerized solid-state composite electrolyte comprises a sodium-antimony alloy layer, a sodium fluoride layer, and a poly(1,3-dioxolane) composite layer sequentially grown in situ on the surface of a sodium electrode. The polymer composite layer consists of poly(1,3-dioxolane) and antimony fluoride and sodium perchlorate distributed within the poly(1,3-dioxolane). The thickness of the sodium-antimony alloy layer is 23 μm; the thickness of the sodium fluoride layer is 41.5 μm; the thickness of the poly(1,3-dioxolane)-antimony fluoride composite layer is 223 μm; the molecular weight of the poly(1,3-dioxolane) is ~, and the degree of polymerization is 93%; the mass ratio of the poly(1,3-dioxolane) to the antimony fluoride is 1:1.6%; the particle size of the antimony trifluoride is 4-6 μm; the mass ratio of the sodium perchlorate to the poly(1,3-dioxolane) is 1:10.2; and the sodium-antimony alloy comprises 36.23% sodium and 63.77% antimony.

[0068] The preparation method of the above-mentioned in-situ polymerized solid composite electrolyte is as follows:

[0069] Sodium perchlorate, 1,3-dioxolane, antimony trifluoride and propylene carbonate were sonicated for 30 min and then stirred at 700 r / min for 8 h to obtain a mixture.

[0070] The mixture was mixed with aluminum trifluoromethanesulfonate and injected onto a porous glass fiber membrane with a thickness of 200 μm on the surface of the sodium electrode. The mixture was then in situ polymerized and grown at 25 °C for 24 h to obtain an in situ polymerized solid composite electrolyte, denoted as PDOL-SbF3.

[0071] The concentration of sodium perchlorate in the mixture is 0.6 mol / L; the volume ratio of 1,3-dioxolane to propylene carbonate is 2.33:1; the mass of antimony trifluoride is 1% of poly1,3-dioxolane; the concentration of the initiator is 1 mmol / L; and the injection volume is 55 μL.

[0072] Example 2

[0073] The difference between this embodiment and Example 1 is that antimony trifluoride is replaced with stannous fluoride. Everything else is the same as in Example 1, resulting in an in-situ polymerized solid-state composite electrolyte. The thickness of the sodium-tin alloy layer is 15 μm; the thickness of the sodium fluoride layer is 32.5 μm; the thickness of the poly(1,3-dioxolane-stannous fluoride) composite layer is 233 μm; the degree of polymerization of the poly(1,3-dioxolane) is 90%; the sodium-tin alloy consists of 27.93% sodium and 72.07% tin. This is denoted as PDOL-SnF2.

[0074] Example 3

[0075] The difference between this embodiment and Embodiment 1 is that antimony trifluoride is replaced with bismuth trifluoride, while the rest is the same as in Embodiment 1, resulting in an in-situ polymerized solid composite electrolyte. The thickness of the sodium-bismuth alloy layer is 20 μm; the thickness of the sodium fluoride layer is 27.5 μm; the thickness of the poly(1,3-dioxolane-stannous fluoride) composite layer is 235 μm; the degree of polymerization of poly(1,3-dioxolane) is 88%; and the sodium-antimony alloy is composed of 25% sodium and 75% bismuth, denoted as PDOL-BiF3.

[0076] Example 4

[0077] The difference between this embodiment and Example 1 is that antimony trifluoride is replaced with antimony trichloride, while the rest is the same as in Example 1, resulting in an in-situ polymerized solid composite electrolyte. The sodium-antimony alloy is composed of 36.4% sodium and 63.6% antimony. The thickness of the poly(1,3-dioxolane-antimony trichloride) composite layer is 241 μm, denoted as PDOL-SbCl3.

[0078] Example 5

[0079] The difference between this embodiment and Embodiment 1 is that antimony trifluoride is replaced with antimony sulfide, while the rest is the same as in Embodiment 1, resulting in an in-situ polymerized solid composite electrolyte. The sodium-antimony alloy is composed of 35.9% sodium and 64.1% antimony. The thickness of the poly(1,3-dioxolane-antimony sulfide) composite layer is 236 μm, denoted as PDOL-Sb2S3.

[0080] Comparative Example 1

[0081] The difference between this comparative example and Example 1 is that the addition of antimony trifluoride is omitted, while the rest is the same as in Example 1, resulting in an in-situ polymerized solid electrolyte with a degree of polymerization of 88% for poly(1,3-dioxolane) and a thickness of 258 μm for the poly(1,3-dioxolane) layer; denoted as PDOL-Blank.

[0082] The molecular structures of the in-situ solid electrolytes and 1,3-dioxolane prepared in Examples 1-5 and Comparative Example 1 of this invention were characterized using infrared spectroscopy. The results are as follows: Figure 2 As shown in the figure, the addition of inorganic fillers to the in-situ solid electrolytes prepared in Examples 1-4 and Comparative Example 2 of this invention does not interfere with the polymerization of 1,3-dioxolane.

[0083] A symmetrical battery assembled in the order of sodium electrode | electrolyte | sodium electrode, wherein the sodium and electrolyte are in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1 of this invention, and the sodium electrode is a sodium electrode sheet with a diameter of 16 mm, with a current density and a depth of charge / discharge of 0.1 mA cm⁻¹. −2 0.1mAh cm −2 Under these conditions, a constant current charge-discharge cycle test was performed for 100 cycles. Then, the morphology of the in-situ polymerized solid composite electrolyte after the 100-cycle test was characterized by scanning electron microscopy at a magnification of 100x. The results are as follows: Figure 3 As shown in the figure, although there are a few fine cracks on the surface of the sodium electrode sheet of the battery prepared by in-situ polymerization of solid-state composite electrolyte in Example 1 after 100 cycles, the overall structure has good continuity, which is beneficial to the construction of a stable solid electrolyte interface (SEI), inhibiting sodium dendrite growth and enhancing interface stability.

[0084] The morphology of the in-situ polymerized solid composite electrolyte after 100 cycles was characterized by scanning electron microscopy at 1000x magnification. The results are as follows: Figure 4 As shown in the figure, the in-situ polymerized solid composite electrolyte membrane is composed of uniformly sized spherical particles. The particles are evenly distributed and tightly bonded together, forming a dense particle packing structure. This uniform and dense morphology is conducive to building a stable solid electrolyte interface (SEI), inhibiting sodium dendrite growth and enhancing interface stability.

[0085] The impedance of the in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1 was tested using a DH7000 electrochemical workstation, and the results are as follows: Figures 5-6 As shown. Figure 5 The image shows impedance diagrams of the in-situ solid electrolytes prepared in Examples 1, 4, 5, and Comparative Example 1. Figure 6The figure shows the impedance diagrams of the in-situ solid electrolytes prepared in Examples 1-3 and Comparative Example 1. As can be seen from the figure, the impedances of the in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1 are 1.909, 2.639, 1.866, 1.794, 2.206 and 15.345 Ω, respectively, indicating that the in-situ solid electrolytes with added inorganic fillers have low impedance.

[0086] The ionic conductivity of the in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1 was calculated from the impedance obtained above. The calculation formula is as follows: Where d is the thickness of the solid electrolyte, R is the impedance of the battery, and A is the contact area between the solid electrolyte and the sodium electrode. The calculation results are shown in Table 1.

[0087] Table 1. Ionic conductivity data of in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1

[0088]

[0089] As shown in Table 1, the ionic conductivity of the in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1 of the present invention are 7.493, 5.288, 7.532, 8.472, 6.777 and 0.837 mS / cm, respectively, indicating that the in-situ solid electrolytes prepared by adding inorganic fillers have high ionic conductivity.

[0090] Using 12mm diameter NFPP (sodium iron pyrophosphate) as the positive electrode, half-cells were constructed from the in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1 of this invention. The cells were then tested using the Xinwei Battery Testing System at room temperature and at a 1C rate (1C = 100 mAg). -1 Cyclic performance testing was conducted at a voltage range of 2-4V, and the results are as follows: Figure 7 As shown in the figure: the left side of the figure represents specific capacity. In the figure, the sodium-ion half-cell prepared with the in-situ solid electrolyte of Example 1 of this invention retains 94.7% of its specific capacity after 1200 cycles; the sodium-ion half-cells prepared in Examples 2-5 and Comparative Example 1 retain 95.3%, 98.6%, 96.1%, 94.1%, and 79.2% of their specific capacity after 200 cycles, respectively; the right side of the figure represents coulombic efficiency. In the figure, the coulombic efficiency of the sodium-ion half-cells prepared in Examples 1-5 and Comparative Example 1 is close to 100%.

[0091] A symmetrical battery assembled in the order of sodium electrode | electrolyte | sodium electrode, wherein the sodium and electrolyte are in-situ solid electrolytes prepared in Examples 1-5 and Comparative Example 1 of this invention, and the sodium electrode is a sodium electrode sheet with a diameter of 16 mm, with a current density and a depth of charge / discharge of 0.1 mA cm⁻¹. −2 0.1mAh cm −2 Under these conditions, a constant current charge-discharge cycle test was performed, and the results are as follows: Figure 8 As shown in the figure, the cycle life of the sodium-ion batteries prepared in Examples 1-5 and Comparative Example 1 of the present invention are 2223h, 1222h, 390h, 480h, 366h and 346h, respectively, indicating that the sodium-ion batteries prepared by the in-situ solid electrolyte in Examples 1-5 of the present invention have high cycle life.

[0092] In summary, the in-situ polymerized solid composite electrolyte provided by this invention has high ionic conductivity, and the sodium-ion battery prepared from it has high capacity retention, good cycle stability, and long lifespan.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An in-situ polymerized solid composite electrolyte, comprising a sodium alloy layer, a sodium compound layer and a polymer composite layer sequentially grown in situ on the surface of a sodium electrode; The sodium alloy in the sodium alloy layer includes a sodium-antimony alloy, a sodium-tin alloy, or a sodium-bismuth alloy; the sodium compound in the sodium compound layer includes sodium halide or sodium sulfide. The polymer composite layer comprises a polymer and inorganic fillers and sodium salts distributed in the polymer; the inorganic fillers include antimony halide, tin halides, bismuth halides, antimony sulfide, tin sulfide, or bismuth sulfide. The sodium electrode is a sodium sheet; The polymer is poly(triethylene glycol) divinyl ether, poly(1,3,5-trioxane), poly(1,3-dioxane), or poly(1,3-dioxane). The sodium salt is sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, or sodium perchlorate. The preparation method of the in-situ polymerized solid composite electrolyte includes: Sodium salt, polymer monomer, inorganic filler and carbonate organic solvent are mixed to obtain a mixture; The mixture was mixed with an initiator and then placed on a sodium electrode for in-situ polymerization growth to obtain an in-situ polymerized solid composite electrolyte.

2. The in-situ polymerized solid-state composite electrolyte according to claim 1, characterized in that, The mass ratio of the polymer to the inorganic filler is 1:(0.25%~1.25%).

3. The in-situ polymerized solid-state composite electrolyte according to claim 1, characterized in that, The thickness of the sodium alloy layer is 10~23μm.

4. The in-situ polymerized solid composite electrolyte according to claim 1, characterized in that, The thickness of the sodium compound layer is 27~48 μm.

5. The in-situ polymerized solid-state composite electrolyte according to claim 1, characterized in that, The thickness of the polymer composite layer is 223~258μm.

6. A method for preparing the in-situ polymerized solid composite electrolyte according to any one of claims 1 to 5, comprising: Sodium salt, polymer monomer, inorganic filler and carbonate organic solvent are mixed to obtain a mixture; The mixture was mixed with an initiator and then placed on a sodium electrode for in-situ polymerization growth to obtain an in-situ polymerized solid composite electrolyte.

7. The preparation method according to claim 6, characterized in that, The volume ratio of the polymer monomer to the carbonate organic solvent is (2~9):

1.

8. The preparation method according to claim 6, characterized in that, The concentration of sodium salt in the mixture is 0.6~1 mol / L.

9. The preparation method according to claim 6, characterized in that, The in-situ polymerization growth temperature is 25~30℃, and the in-situ polymerization growth time is 16~24h.

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