Preparation of composite metal heterojunction modified material and application thereof in lithium battery

Abstract

The application discloses preparation of a composite metal heterojunction modification material and application of the composite metal heterojunction modification material in a lithium battery. 12 The application first synthesizes Bi4Ti3O 12 -NiCo2S4 heterojunction nanosheet-shaped composite metal sulfide heterojunction material by using a non-aqueous sol-gel casting method, and then uniformly coats the material on one side of a battery diaphragm in a slurry to obtain the composite metal heterojunction modification material. The heterojunction nanosheet structure in the composite metal heterojunction modification material can provide a channel for rapid diffusion of lithium ions, improve interface polarity, increase surface catalytic active sites, optimize affinity to polysulfides, and promote catalytic conversion, so that the rate performance and cycle stability performance of the lithium-sulfur battery are effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium-sulfur battery separator materials, and particularly relates to a preparation of a composite metal heterojunction modification material and application thereof in lithium batteries. BACKGROUND

[0002] With the rapid development of electronic mobile devices and new energy vehicles, the demand for advanced green energy storage devices is growing, which has promoted the rapid development of new rechargeable battery systems. However, commercial lithium-ion batteries are limited by their theoretical specific capacity and energy density, and cannot meet the needs of future development. Compared with lithium-ion batteries, lithium-sulfur (Li-S) batteries have high theoretical specific capacity (1675 mAh g -1 ), abundant sulfur resources, low production cost, environmental friendliness and other advantages, and are one of the most promising next-generation rechargeable energy storage devices. However, the slow reaction kinetics of the sulfur cathode and the serious shuttle effect are the main problems restricting the commercial application of lithium-sulfur batteries.

[0003] Moreover, the "shuttle effect" of polysulfides will cause the passivation of the metal lithium negative electrode, the decrease of the battery capacity and coulombic efficiency, and the deterioration of the cycle stability. To realize the commercialization of Li-S batteries, it is necessary to inhibit the serious "shuttle effect". Separator modification is considered to be an effective strategy to limit the "shuttle effect". Commercial separators cannot effectively inhibit this effect due to their large pore size. Among them, carbon materials, non-polar carbon materials, carbon-based composite materials and the like have been widely used for separator modification. The "shuttle effect" of polysulfides is inhibited by physical adsorption, thereby improving the electrochemical performance of the battery to a certain extent. However, the weak physical interaction between the above materials and polysulfides is not enough to limit the "shuttle effect" of polysulfides. Moreover, the "limitation" strategy cannot completely solve the "shuttle effect" of polysulfides. SUMMARY

[0004] The primary purpose of the present application is to overcome the shortcomings and deficiencies of the prior art, and to provide a preparation method of a composite metal heterojunction modification material.

[0005] Another purpose of the present application is to provide a composite metal heterojunction modification material prepared by the method.

[0006] Still another purpose of the present application is to provide an application of the composite metal heterojunction modification material.

[0007] The purposes of the present application are achieved by the following technical solutions:

[0008] A preparation method of a composite metal heterojunction modification material, comprising the following steps:

[0009] (1) preparing Bi4Ti3O 12 Precursor

[0010] The organic monomer diphenylolpropane diglycidyl ether, the dispersant 2-hydroxyethylamine and the crosslinking agent 1,6-hexanediol diacrylate are added into the solvent isopropyl alcohol, stirred and mixed uniformly to obtain a premix A; then Bi2O3 and TiO2 are added into the premix A, stirred to form a Bi-Ti slurry; then the initiator and the catalyst are added dropwise into the Bi-Ti slurry, stirred uniformly to obtain a mixed slurry B; then the mixed slurry B is placed under the condition of 600-900 ℃ for a curing reaction to obtain a cured blank I; after the cured blank I is demolded, it is immersed in acetone to remove the solvent in the blank body, then taken out and placed under the condition of 80±5 ℃ for drying to make the acetone fully volatilize to obtain a dried blank I; the dried blank I is debinded under a protective gas atmosphere at 200-600 ℃ to completely remove the organic matter in the blank body to obtain a debinded blank I; finally, the debinded blank I is sintered at 900-1200 ℃ to obtain a Bi4Ti3O 12 precursor;

[0011] (2) Non-aqueous sol-gel method for loading nano NiCo2S4

[0012] The organic monomer butyl ether, the dispersant 2-hydroxyethylamine and the crosslinking agent acrylate are added into the solvent isopropyl alcohol, stirred and mixed uniformly to obtain a premix C; then the nickel nitrate hexahydrate, the cobalt nitrate hexahydrate, the thioacetamide and the polyetherimide are added into the premix C, stirred and mixed uniformly, and the pH is adjusted to 4-7 to obtain a premix D; the Bi4Ti3O 12 precursor obtained in step (1) is added into the premix D, stirred to form a slurry; then the initiator and the catalyst are added dropwise into the slurry, stirred uniformly to obtain a mixed slurry E; then the mixed slurry E is placed under the condition of 80-200 ℃ for a curing reaction to obtain a cured blank II; after the cured blank II is demolded, it is immersed in acetone to remove the solvent in the blank body, then taken out and placed under the condition of 80±5 ℃ for drying to make the acetone fully volatilize to obtain a dried blank II; the dried blank II is debinded under a protective gas atmosphere at 160-175 ℃ to completely remove the organic matter in the blank body to obtain a debinded blank II; finally, the debinded blank II is sintered under a protective gas atmosphere at 150-200 ℃ to obtain a Bi4Ti3O 12 -NiCo2S4 heterojunction;

[0013] (3) Preparation of composite metal heterojunction modified material

[0014] The Bi4Ti3O 12 -NiCo2S4 heterojunction, the conductive agent (conductive additive) and the binder are added into the solvent, stirred and mixed to form a slurry, then the slurry is coated onto a battery separator, dried to obtain a Bi4Ti3O 12a NiCo2S4 heterojunction modified material, i.e. the composite metal heterojunction modified material.

[0015] The mass ratio of Bi2O3 and TiO2 in step (1) is 3-7:1; preferably 6:1.

[0016] The amount of 2-hydroxyethylamine in step (1) is 0.5%-4% of the total mass of Bi2O3 and TiO2; preferably 2% of the total mass of Bi2O3 and TiO2.

[0017] The amount of diphenylpropane diglycidyl ether in step (1) is 15%-30% of the volume of mixed slurry B; preferably 25% of the volume of mixed slurry B.

[0018] The volume ratio of diphenylpropane diglycidyl ether and 1,6-hexanediol diacrylate in step (1) is 9-15:1; preferably 10:1.

[0019] The isopropyl alcohol in step (1) is preferably isopropyl alcohol-D1.

[0020] The amount of isopropyl alcohol in step (1) is 20%-40% of the volume of mixed slurry B; preferably 30% of the volume of mixed slurry B.

[0021] The initiator in steps (1) and (2) is at least one of N,N-dimethylacetamide, N,N-dimethylcyclohexylamine, and N,N-dimethylpyridine; preferably N,N-dimethylacetamide.

[0022] The catalyst in steps (1) and (2) is at least one of N,N,N,N-tetramethylethylenediamine, trans-1,2-cyclohexanediamine, and triethylamine; preferably N,N,N,N-tetramethylethylenediamine.

[0023] The volume ratio of the initiator and the catalyst in steps (1) and (2) is 2:5-5.2.

[0024] The total volume of the initiator and the catalyst in step (1) is 0.5%-2.5% of the volume of diphenylpropane diglycidyl ether; preferably 2.5% of the volume of diphenylpropane diglycidyl ether.

[0025] The stirring time for forming the Bi-Ti slurry in step (1) is 1-3h; preferably 2h.

[0026] The temperature of the solidification reaction in step (1) is preferably 850°C.

[0027] The time of the solidification reaction in steps (1) and (2) is 1-2h; preferably 1.5h.

[0028] The drying time in steps (1) and (2) is 12-18h; preferably 12h.

[0029] The protective gas used in the debinding in steps (1) and (2) is nitrogen, argon, or a mixture of argon and hydrogen; preferably a mixture of argon and hydrogen; more preferably a mixture of argon and hydrogen with a volume ratio of 95:5.

[0030] The debinding temperature in step (1) is preferably 400°C.

[0031] The debinding time in step (1) is 2-4h; preferably 4h.

[0032] The protective gas used in the sintering in steps (1) and (2) is nitrogen, argon, or a mixture of argon and hydrogen; preferably argon.

[0033] The sintering temperature in step (1) is preferably 1050°C.

[0034] The sintering time in step (1) is 2-4h; preferably 2h.

[0035] The Bi4Ti3O 12 The mass ratio of the precursor to the nickel nitrate hexahydrate is 1:1-2; preferably 1:1.2.

[0036] The amount of 2-hydroxyethylamine used in step (2) is 0.5%-4% of the mass of the precursor; preferably 2% of the mass of the Bi4Ti3O 12 The amount of 2-hydroxyethylamine used in step (2) is 0.5%-4% of the mass of the precursor; preferably 2% of the mass of the Bi4Ti3O 12 2% of the mass of the precursor.

[0037] The amount of diethyl ether used in step (2) is 15%-30% of the volume of the mixed slurry E; preferably 25% of the volume of the mixed slurry E.

[0038] The volume ratio of diethyl ether to acrylic ester used in step (2) is 9-15:1; preferably 10:1.

[0039] The amount of isopropyl alcohol used in step (2) is 20%-40% of the volume of the mixed slurry E; preferably 30% of the volume of the mixed slurry E.

[0040] The total volume of the initiator and the catalyst used in step (2) is 0.5%-2.5% of the volume of diethyl ether; preferably 2.5% of the volume of diethyl ether.

[0041] The mass ratio of the nickel nitrate hexahydrate, the cobalt nitrate hexahydrate, the thioacetamide, and the polyetherimide used in step (2) is 1:2:4:2-6; preferably 1:2:4:3.

[0042] The total mass of the nickel nitrate hexahydrate, the cobalt nitrate hexahydrate, the thioacetamide and the polyetherimide in step (2) is Bi4Ti3O 12 0.5 to 20 times the mass of the precursor; preferably Bi4Ti3O 12 10 to 15 times the mass of the precursor; more preferably Bi4Ti3O 12 12 times the mass of the precursor.

[0043] The adjusting of the pH in step (2) is preferably performed using acetic acid.

[0044] The adjusting of the pH in step (2) is preferably performed to a pH of 6.5.

[0045] The time of stirring to form the slurry in step (2) is 1 to 3 h; preferably 2 h.

[0046] The temperature of the solid state reaction in step (2) is preferably 100 °C.

[0047] The time of debinding in step (2) is 2 to 4 h; preferably 2 h.

[0048] The temperature of the sintering in step (2) is preferably 180 °C.

[0049] The time of sintering in step (2) is 2 to 4 h; preferably 4 h.

[0050] The conductive agent in step (3) is a carbon nanotube; preferably a multi-walled carbon nanotube.

[0051] The binder in step (3) is at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene and carboxymethyl cellulose; preferably polyvinylidene fluoride.

[0052] The Bi4Ti3O 12 The mass ratio of the NiCo2S4 heterostructure, the conductive agent and the binder is preferably 8:1:1.

[0053] The solvent in step (3) is N-methyl pyrrolidone (NMP).

[0054] The battery separator in step (3) is a conventional commercial polymer separator; preferably any one of a cellulose separator, a polyethylene separator, a polypropylene separator, an aramid film, a polyester film, Celgard 2400 and Celgard 2500; further preferably Celgard 2500.

[0055] The thickness of the coating in step (3) is 50 to 150 pm; preferably 50 to 100 pm; more preferably 100 pm.

[0056] The drying in step (3) is vacuum drying.

[0057] The temperature of the drying in step (3) is 40-70°C; preferably 60°C.

[0058] The time of the drying in step (3) is 12-18h; preferably 12h.

[0059] A composite metal heterojunction modification material prepared by the method of any one of the above.

[0060] Use of the composite metal heterojunction modification material in the preparation of a battery separator or a lithium-sulfur battery.

[0061] A lithium-sulfur battery comprising a positive electrode, a negative electrode, the composite metal heterojunction modification material and an electrolyte.

[0062] The positive electrode is preferably prepared by mixing carbon nanotubes with sulfur and grinding thoroughly, then heat treating at 155±5°C to obtain a carbon / sulfur composite material; then adding the carbon / sulfur composite material, a conductive agent and a binder to a solvent, stirring and mixing to form a slurry; and finally coating the slurry onto an aluminum foil, drying to obtain a lithium-sulfur battery positive electrode sheet.

[0063] The mass ratio of the carbon nanotubes to sulfur is 7:3 (sulfur mass fraction 30wt%).

[0064] The mass ratio of the carbon / sulfur composite material, the conductive agent and the binder is preferably 8:1:1.

[0065] The carbon nanotubes are preferably multi-layer carbon nanotubes.

[0066] The conductive agent is preferably conductive carbon black.

[0067] The binder is at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene and carboxymethyl cellulose; preferably polyvinylidene fluoride.

[0068] The solvent is N-methyl pyrrolidone (NMP).

[0069] The thickness of the coating is 50-150μm; preferably 50-100μm; more preferably 100μm.

[0070] The temperature of the drying is 40-70°C; preferably 60°C.

[0071] The time of the drying is 12-18h; preferably 12h.

[0072] The negative electrode is a metal lithium sheet.

[0073] The solute of the electrolyte is lithium bis-trifluoromethanesulfonimide (LiTFSI) and lithium nitrate; the electrolyte is preferably prepared by the following method: LiTFSI and lithium nitrate are added to a solvent obtained by mixing ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) at a volume ratio of 1:1 to prepare the electrolyte; wherein the concentration of LiTFSI in the electrolyte is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass.

[0074] The present application has the following advantages and effects relative to the prior art:

[0075] (1) The composite metal sulfide heterojunction in the present application is composed of Bi4Ti3O 12 and NiCo2S4, and first, a non-aqueous gel casting method is used to synthesize a composite metal sulfide heterojunction material with a Bi4Ti3O 12 -NiCo2S4 heterojunction nanosheet structure, and this material prepared by this method has excellent electrical conductivity, is not prone to collapse, is loose and porous, and has excellent electrochemical performance; then the composite metal sulfide heterojunction material is made into a slurry and uniformly coated on one side of the surface of a commercial polymer separator, and finally a composite metal sulfide heterojunction modified separator is obtained and applied in a lithium-sulfur battery; wherein the heterojunction nanosheet structure provides a channel for the rapid diffusion of lithium ions, and the Bi4Ti3O 12 -NiCo2S4 heterojunction can improve the interface polarity, increase the surface catalytic active sites, optimize the affinity (adsorption capacity) for polysulfides and promote catalytic conversion, thereby effectively improving the rate performance and cycle stability of the lithium-sulfur battery.

[0076] (2) Compared with the conventional unmodified separator, the main advantage of the present application is that the nanosheet structure provides a channel for the rapid diffusion of lithium ions, accelerates the mass transfer and charge transfer in the sulfur reaction process; in addition, the Bi4Ti3O 12 -NiCo2S4 heterojunction improves the electrical conductivity while enhancing the adsorption and catalytic conversion capacity for polysulfides, thereby effectively inhibiting the shuttle effect.

[0077] (3) By controlling the reaction parameters, the present application effectively controls the surface interface electronic structure of the transition metal sulfide based on the interface engineering strategy, improves the adsorption capacity for polysulfides and the sulfur redox reaction kinetics, thereby effectively improving the electrochemical performance and cycle stability of the lithium-sulfur battery. BRIEF DESCRIPTION OF DRAWINGS

[0078] Figure 1 Bi4Ti3O 12A is 1000 times magnification; B is 30000 times magnification.

[0079] Figure 2 The lithium sulfur battery cycle stability performance chart of the separator modified by the different materials prepared in Example 1 of the present application and Comparative Examples 1-3. 12 The XRD chart of the NiCo2S4 heterojunction material.

[0080] Figure 3 The lithium sulfur battery cycle stability performance chart of the separator modified by the different materials prepared in Example 1 of the present application and Comparative Examples 1-3.

[0081] Figure 4 The lithium sulfur battery cycle stability performance chart of the separator modified by the different materials prepared in Example 1, 4-7 of the present application by different gel casting methods.

[0082] Figure 5 The cycle performance comparison chart of the material used in Example 1 of the present application and other materials.

[0083] Figure 6 The cycle performance comparison chart of the preparation method of Example 1 of the present application and other conventional methods. DETAILED DESCRIPTION

[0084] The present application will be further described in conjunction with the examples below, but the embodiments of the present application are not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present application are the conventional reagents, methods and equipment in the technical field. The test methods in the following examples without specific experimental conditions are usually according to the conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present application can be obtained by commercial purchase. Unless otherwise specified, the reaction process in the present application is carried out in the room temperature (normal temperature) environment of 25℃.

[0085] Example 1

[0086] (1) The composite Bi4Ti3O 12 -NiCo2S4:

[0087] 12 The precursor.

[0088] 12 ​​The precursor was slowly added into the premixed solution C, and a slurry was formed by stirring for 2 h using a magnetic stirrer. Then, the initiator (129 μL of N,N-dimethylacetamide mixed as the initiator) and the catalyst (357 μL of N,N,N,N-tetramethyl ethylenediamine as the catalyst) were added dropwise into the slurry, which was stirred rapidly and uniformly, and then quickly injected into a mold (with a set mold volume of 100 ml). The mold was immediately placed in a 100°C muffle furnace for a curing reaction for 1.5 h to obtain a cured blank. After demolding, the cured blank was immersed in acetone at room temperature (25°C) for a certain period of time to remove the solvent in the blank, and then taken out and placed in a 80°C drying oven for 12 h to fully volatilize the acetone, thereby obtaining a dried blank. The dried blank was placed in an Ar / H2 (volume ratio of Ar and H2 was 95:5; flow rate was 1.5 L / min) protective atmosphere at a certain temperature (175°C) for 2 h to completely remove the organic matter in the blank, thereby obtaining a debindered blank. After cooling, the debindered blank was transferred to an Ar atmosphere and sintered at a sintering temperature of 180°C at a heating rate of 5°C / min for 4 h, thereby obtaining a Bi4Ti3O 12 -NiCo2S4 heterojunction, i.e., a composite metal sulfide heterojunction material.

[0089] (2) Bi4Ti3O 12 Preparation of the -NiCo2S4 heterojunction modified separator: The heterojunction material Bi4Ti3O 12 -NiCo2S4, carbon nanotubes (Aldrich Chemical Reagent Network: CAS No. 308068-56-6, Item No. C434725-100mg, multi-walled carbon nanotubes, MWCNT content in the prepared cathode coating > 7.5%, outer diameter x L 7-15 nm x 0.5-10 μm), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 80 mg: 10 mg: 10 mg into 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then, the slurry was uniformly coated on a Celgard 2500 separator (Celgard 2500, 100 nm) using a 100 μm coater (i.e., the coating thickness was 100 μm), and then dried in a vacuum oven at 60°C for 12 h, thereby obtaining a composite metal sulfide heterojunction modified separator.

[0090] (3) Positive electrode preparation: carbon nanotubes (Aldrich Chemical Reagent Network: CAS No. 308068-56-6, Item No. C434725-100mg, multi-walled carbon nanotubes, prepared cathode coating, MWCNT content >7.5%, outer diameter x L 7-15 nm x 0.5-10 μm) and sulfur (Aldrich Reagent Network, sublimed sulfur, AR, CAS: 7704-34-9) were mixed in a mass ratio of 7:3 and thoroughly ground, and then heat treated in a 155°C oven for 12h to obtain a carbon / sulfur composite material; then the carbon / sulfur composite material, conductive carbon (conductive carbon black Super P, Timcal) and PVDF were added to 0.5 mL of N-methyl pyrrolidone (NMP) in a mass ratio of 80 mg:10 mg:10 mg and stirred uniformly, then uniformly coated on an aluminum foil with a 100 μm coater (coating thickness of 100 μm), and then vacuum dried at 60°C for 12h, cut into 14mm diameter discs to obtain a sulfur / carbon nanotube electrode, which is a lithium-sulfur battery positive electrode.

[0091] (4) Battery assembly: the sulfur / carbon nanotube electrode prepared in step (3) above was used as the positive electrode, a lithium metal sheet was used as the negative electrode, the composite metal sulfide heterojunction material modified separator prepared in step (2) above was used as the battery separator, and the electrolyte was a mixed solution of composite lithium trifluoromethyl sulfonimide (i.e. lithium bis(trifluoromethylsulfonyl)imide) (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate as solutes, ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) (volume ratio 1:1) as solvents, and the mixed solution was prepared; the concentration of LiTFSI in the mixed solution was 1 mol·L -1 , the concentration of lithium nitrate was 2% by mass), and CR2032 button cell assembly was carried out in an argon atmosphere glove box (named: gel injection molding method Bi4Ti3O 12 -NiCo2S4 / PP).

[0092] Example 2

[0093] (1) The preparation steps of the composite metal sulfide heterojunction material are the same as those in step (1) of Example 1.

[0094] (2) The preparation of the composite metal sulfide heterojunction modified separator refers to Example 1, except that the 100 μm coater is replaced by a 60 μm coater, and the other steps are the same as those in step (2) of Example 1.

[0095] (3) The preparation of the lithium-sulfur battery positive electrode is the same as that in step (3) of Example 1.

[0096] (4) Battery assembly: the sulfur / carbon nanotube electrode prepared in step (3) was used as the positive electrode, the lithium metal sheet was used as the negative electrode, the composite metal sulfide heterojunction (Bi4Ti3O 12 -NiCo2S4) modified separator prepared in step (2) was used as the battery separator, and the electrolyte was a mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a final concentration of 1 mol·L -1 -1 and lithium nitrate with a mass fraction of 2% (i.e., a mixed solution prepared by using LiTFSI and lithium nitrate as solutes, and DME and DOL (volume ratio of 1:1) as solvents; the concentration of LiTFSI in the mixed solution was 1 mol·L -1 -1, and the concentration of lithium nitrate was 2% by mass fraction), and the assembly of CR2032 button cells was carried out in an argon atmosphere glove box.

[0097] Example 3

[0098] (1) The preparation steps of the composite metal sulfide heterojunction material were the same as those in step (1) of Example 1.

[0099] (2) The preparation of the composite metal sulfide heterojunction modified separator referred to Example 1, except that the 100 μm coater was replaced by a 50 μm coater, and the other steps were the same as those in step (2) of Example 1.

[0100] (3) The preparation of the lithium-sulfur battery positive electrode was the same as that in step (3) of Example 1.

[0101] (4) Battery assembly: the sulfur / carbon nanotube electrode prepared in step (3) was used as the positive electrode, the lithium metal sheet was used as the negative electrode, the composite metal sulfide heterojunction modified separator prepared in step (2) was used as the battery separator, and the electrolyte was a mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate, i.e., a mixed solution prepared by using LiTFSI and lithium nitrate as solutes, and ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) (volume ratio of 1:1) as solvents; the concentration of LiTFSI in the mixed solution was 1 mol·L -1 -1, and the concentration of lithium nitrate was 2% by mass fraction). The assembly of CR2032 button cells was carried out in an argon atmosphere glove box.

[0102] Example 4

[0103] The catalysts in steps (1) ① and ② of Example 1 were both replaced by trans-1,2-cyclohexanediamine, and the remaining steps were consistent with Example 1.

[0104] Example 5

[0105] The catalysts in steps (1) ① and ② of Example 1 were both replaced by triethylamine, and the remaining steps were consistent with Example 1.

[0106] Example 6

[0107] The initiator in steps (1) ① and ② of Example 1 is replaced by N,N-dimethylcyclohexylamine, and the remaining steps are consistent with Example 1.

[0108] Example 7

[0109] The initiator in steps (1) ① and ② of Example 1 is replaced by N,N-dimethylpyridine, and the remaining steps are consistent with Example 1.

[0110] Comparative Example 1

[0111] (1) Preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube electrode sheet): the same as step (3) of Example 1.

[0112] (2) Assembly of the battery: the sulfur / carbon nanotube electrode sheet positive electrode prepared in step (1), a metal lithium sheet as the negative electrode, a Celgard 2500 separator as the battery separator, and an electrolyte solution of a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate as solutes, DME and DOL (volume ratio 1:1) as solvents, prepared by mixing the solution; the concentration of LiTFSI in the mixed solution is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass). The assembly of CR2032 button cells was carried out in an argon atmosphere glove box (named: PP).

[0113] Comparative Example 2

[0114] (1) Preparation of pure-phase Bi4Ti3O 12Material: 0.003712 g of 2-hydroxyethylamine, 25 ml of diphenol-based propane diglycidyl ether, 0.25 ml of 1,6-hexanediol diacrylate were dissolved in 30 ml of isopropyl alcohol-D1 to form a premix; then, 0.1591 g of Bi2O3 and 0.0265 g of TiO2 were slowly added to the premix, stirred with a magnetic stirrer for 2 h to form a Bi-Ti slurry, and then an initiator (129 microliters of N,N-dimethylacetamide as an initiator) and a catalyst (357 microliters of N,N,N,N-tetramethyl ethylenediamine) were added dropwise to the Bi-Ti slurry, quickly stirred to form a slurry, and then quickly injected into a mold, and immediately placed in a 850°C muffle furnace for a curing reaction for 1.5 h to obtain a cured blank; after demolding, the cured blank was immersed in acetone at room temperature (25°C) for a certain period of time to remove the solvent in the blank, and then taken out and placed in a 80°C drying oven for 12 h to fully volatilize the acetone, obtaining a dried blank; the dried blank was degreased at a certain temperature (400°C) under Ar / H2 (Ar and H2 volume ratio is 95:5; flow rate is 1.5 L / min) protective atmosphere for 4 h to completely remove the organic matter in the blank, obtaining a degreased blank; finally, the degreased blank was heated (muffle furnace, 5°C / min, air) to a sintering temperature of 1050°C and sintered for 2 h to obtain a Bi4Ti3O 12 precursor.

[0115] (2) Pure phase Bi4Ti3O 12 Preparation of material modified separator: the Bi4Ti3O 12 The material was mixed with carbon nanotubes and PVDF at a mass ratio of 80 mg: 10 mg: 10 mg in 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then the slurry was uniformly coated on a Celgard 2500 separator with a 100 μm coater, and then dried in a vacuum oven at 60°C for 12 h to obtain a Bi4Ti3O 12 modified separator.

[0116] (3) Preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube electrode sheet) is the same as step (3) of example 1.

[0117] (4) Assembly of the battery: the sulfur / carbon nanotube electrode sheet prepared in step (3) was used as the positive electrode, the lithium sheet was used as the negative electrode, and the Bi4Ti3O 12 modified separator was used as the battery separator, and the electrolyte was a mixed solution of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate were used as solutes, and DME and DOL (volume ratio 1:1) were used as solvents to prepare the mixed solution; the concentration of LiTFSI in the mixed solution was 1 mol·L -1, the concentration of lithium nitrate is 2% by mass). The assembly of CR2032 button cell was carried out in a glove box under argon atmosphere (named: gel-casting Bi4Ti3O 12 / PP).

[0118] Comparative Example 3

[0119] (1) Preparation of NiCo2S4 material by gel-casting method: 0.004 g of 2-hydroxyethylamine, 25 ml of butyl ether and 2.5 ml of acrylate were dissolved in 30 ml of isopropyl alcohol to form a premix solution; then 0.24 g of nickel nitrate hexahydrate and 0.48 g of cobalt nitrate hexahydrate were added to the premix solution and mixed uniformly, followed by the addition of 0.96 g of thioacetamide and 0.72 g of polyetherimide, stirring until mixed uniformly, and finally adding acetic acid to adjust the pH to 6.5 to obtain solution A; solution A was slowly added to the premix solution, stirred with a magnetic stirrer for 2 h to form a slurry, then an initiator (129 microliters of N,N-dimethylacetamide as an initiator) and 357 microliters of N,N,N,N-tetramethyl ethylenediamine (as a catalyst) were added dropwise to the slurry, quickly stirred until uniform, and then quickly injected into a mold, and immediately placed in a 100°C muffle furnace for a curing reaction for 1.5 h to obtain a cured blank; after demolding, the cured blank was immersed in acetone at room temperature (25°C) for a certain period of time to remove the solvent in the blank, then taken out and placed in a 80°C drying oven for 12 h to fully volatilize the acetone, to obtain a dried blank, which was debindered at a certain temperature (175°C) under Ar / H2 protective atmosphere (volume ratio of Ar and H2 is 95:5; flow rate is 1.5 L / min) for 2 h to completely remove the organic matter in the blank, to obtain a debindered blank. After cooling, the debindered blank was transferred to an Ar atmosphere and sintered at a sintering temperature of 180°C at a heating rate of 5°C / min for 4 h to obtain a nano-NiCo2S4 material.

[0120] (2) Preparation of a separator modified with pure-phase NiCo2S4 material: the NiCo2S4 material obtained in step (1) was mixed with carbon nanotubes and PVDF in a mass ratio of 80 mg: 10 mg: 10 mg in 0.5 mL of N-methylpyrrolidone (NMP) to obtain a uniform slurry. Then the slurry was uniformly coated on a polypropylene separator using a 100 μm coater, and then dried in a vacuum oven at 60°C for 12 h. Finally, a NiCo2S4 modified separator was obtained.

[0121] (3) Preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube sheet) is the same as step (3) of Example 1.

[0122] (4) battery assembly: the sulfur / carbon nanotube pole piece prepared in step (3) is taken as the positive electrode, the metal lithium sheet is taken as the negative electrode, the NiCo2S4 material modified separator prepared in step (2) is taken as the battery separator, and the electrolyte is a mixed solution of lithium bis (trifluoromethyl sulfonyl imide) (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate are taken as solutes, and DME and DOL (volume ratio 1:1) are taken as solvents to prepare the mixed solution; the concentration of LiTFSI in the mixed solution is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass). The assembly of CR2032 button cell batteries is carried out in an argon atmosphere glove box (named: gel injection molding method NiCo2S4 / PP).

[0123] Comparative example 4

[0124] (1) Conventional high-temperature sintering of pure-phase Bi4Ti3O 12 Preparation of the material: 2.79574 g of Bi2O3, 0.4791936 g of TiO2, 17.532 g of NaCl and 22.365 g of KCl are uniformly mixed. After continuous grinding in a mortar for one hour, the residual mixture is placed in a covered corundum crucible and heated at 800℃ for 2 hours in a muffle furnace at a heating rate of 5℃ / min. Then, the final product is centrifuged and washed with water and ethanol to remove residual inorganic salts, and dried at 60℃ to obtain Bi4Ti3O 12 nanosheets.

[0125] (2) Conventional high-temperature sintering of pure-phase Bi4Ti3O 12 material modified separator: the Bi4Ti3O 12 material obtained in step (1) is mixed with carbon nanotubes and PVDF at a mass ratio of 80 mg:10 mg:10 mg into 0.5 mL N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then the slurry is uniformly coated on a polypropylene separator with a 100 μm coater, and then dried in a vacuum oven at 60℃ for 12 h. Finally, a Bi4Ti3O 12 modified separator is obtained.

[0126] (3) Preparation of lithium-sulfur battery positive pole piece (i.e. sulfur / carbon nanotube pole piece) is the same as step (3) of example 1.

[0127] (4) battery assembly: the sulfur / carbon nanotube pole piece prepared in step (3) is taken as the positive electrode, the metal lithium sheet is taken as the negative electrode, the Bi4Ti3O 12The modified separator is used as a battery separator, and the electrolyte is a mixed solution of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate are used as solutes, and DME and DOL (volume ratio of 1:1) are used as solvents to prepare the mixed solution; the concentration of LiTFSI in the mixed solution is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass). The assembly of CR2032 button cells is carried out in an argon atmosphere glove box (named: conventional high-temperature sintered Bi4Ti3O 12 / PP).

[0128] Comparative Example 5

[0129] (1) Preparation of pure-phase NiCo2S4 material by conventional hydrothermal method: Under stirring conditions, 0.024 g of nickel nitrate hexahydrate, 0.048 g of cobalt nitrate hexahydrate and 0.022 g of methenamine were dissolved in a mixed solvent obtained by mixing 20 mL of deionized water and 10 mL of ethanol, and then ultrasonic treatment was performed for 10 minutes to uniformly disperse them. The obtained suspension was transferred into a polytetrafluoroethylene liner (50 mL capacity) and kept at 120℃ for 8 hours to obtain a NiCo precursor. Finally, the NiCo precursor was added to a 0.24 g Na2S·9H2O solution (0.1 mol / L) and heated at 100℃ for 12 h, then the final product was centrifuged and washed with water and ethanol to remove residual inorganic salts, and dried at 60℃ to obtain nano-NiCo2S4.

[0130] (2) Preparation of a modified separator of pure-phase NiCo2S4 material by conventional hydrothermal method: The NiCo2S4 material obtained in step (1) was mixed with carbon nanotubes and PVDF in a mass ratio of 80 mg:10 mg:10 mg into 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then the slurry was uniformly coated on a polypropylene separator with a 100 μm coater, and then dried in a vacuum oven at 60℃ for 12 h. Finally, a NiCo2S4 modified separator was obtained.

[0131] (3) Preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube sheet) is the same as step (3) of Example 1.

[0132] (4) Assembly of the battery: the sulfur / carbon nanotube sheet prepared in step (3) is used as the positive electrode, the lithium sheet is used as the negative electrode, the NiCo2S4 material modified separator prepared in step (2) is used as the battery separator, and the electrolyte is a mixed solution of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate are used as solutes, and DME and DOL (volume ratio of 1:1) are used as solvents to prepare the mixed solution; the concentration of LiTFSI in the mixed solution is 1 mol·L -1, the concentration of lithium nitrate was 2% by mass). The assembly of CR2032 button cell was carried out in a glove box under argon atmosphere (named: conventional hydrothermal method NiCo2S4 / PP).

[0133] Comparative Example 6

[0134] (1) Conventional hydrothermal method Bi4Ti3O 12 -NiCo2S4 material: First, the conventional high-temperature sintered pure phase Bi4Ti3O 12 material was synthesized according to the method in step (1) of Comparative Example 4, and the mass of the obtained Bi4Ti3O 12 nanosheets was 200 mg. Under stirring, 0.024 g of nickel nitrate hexahydrate, 0.048 g of cobalt nitrate hexahydrate and 0.022 g of methenamine were dissolved in the solvent obtained by mixing 20 mL of deionized water and 10 mL of ethanol to obtain a suspension; then 20 mg of the above-prepared Bi4Ti3O 12 nanosheets were added to the suspension, and ultrasonic treatment was performed for 10 minutes to uniformly disperse them. The obtained mixture was then transferred into a polytetrafluoroethylene liner (50 mL capacity) and kept at 120°C for 8 hours to obtain a NiCo precursor. Finally, the NiCo precursor was added to a 0.24 g Na2S·9H2O solution (0.1 mol / L), and heated at 100°C for 12 h, and the obtained final product was centrifuged and washed with water and ethanol to remove residual inorganic salts, and dried at 60°C to obtain Bi4Ti3O 12 -NiCo2S4 material.

[0135] (2) Conventional hydrothermal method Bi4Ti3O 12 -NiCo2S4 material modified separator: The Bi4Ti3O 12 -NiCo2S4 material obtained in step (1) was mixed with carbon nanotubes and PVDF at a mass ratio of 80 mg: 10 mg: 10 mg in 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then the slurry was uniformly coated on a polypropylene separator with a 100 μm coater, and then dried in a vacuum oven at 60°C for 12 h. Finally, a Bi4Ti3O 12 -NiCo2S4 modified separator was obtained.

[0136] (3) Preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube electrode sheet): the same as step (3) of Example 1.

[0137] (4) Assembly of the battery: the sulfur / carbon nanotube electrode sheet prepared in step (3) was used as the positive electrode, a lithium metal sheet was used as the negative electrode, and the Bi4Ti3O 12-NiCo2S4 material modified separator as battery separator, electrolyte is a mixed solution of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium nitrate, that is, LiTFSI and lithium nitrate are used as solutes, DME and DOL (volume ratio of 1:1) are used as solvents, and the mixed solution prepared is used; the concentration of LiTFSI in the mixed solution is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass. The assembly of CR2032 button cells is carried out in an argon atmosphere glove box (named: conventional hydrothermal Bi4Ti3O 12 -NiCo2S4 / PP).

[0138] Comparative Example 7

[0139] (1) Gel casting method for preparing Bi4Ti3O 12 -NiS: first, the method in step (1) of Comparative Example 2 is referred to to prepare pure-phase Bi4Ti3O 12 material. Then 0.2 g of Bi4Ti3O 12 precursor is ultrasonically dispersed in 50 mL of deionized water for 10 min, 0.02054 g of nickel acetate tetrahydrate is added and ultrasonically dispersed for 30 min to form solution A. 0.0667 g of Na2S·9H2O is dissolved in 10 mL of deionized water to form solution B, and then solution B is added dropwise into solution A, stirred at room temperature (25°C) for 30 min to form an A-B mixed solution; at the same time, 0.004 g of 2-hydroxyethylamine, 25 ml of butyl ether and 2.5 ml of acrylate are dissolved in 30 ml of isopropyl alcohol and stirred uniformly to form a premixed solution; the A-B mixed solution is slowly added to the premixed solution, stirred with a magnetic stirrer for 2 h to form a slurry, and then an initiator (129 microliters of N,N-dimethylacetamide as an initiator) and a catalyst (357 microliters of N,N,N,N-tetramethyl ethylenediamine) are added dropwise to the slurry, stirred uniformly, and then quickly poured into a mold, and immediately placed in a 100°C muffle furnace for curing reaction for 1.5 h to obtain a cured blank; after demolding, the cured blank is immersed in acetone at room temperature (25°C) for a certain period of time to remove the solvent in the blank, and then taken out and placed in a 80°C drying oven for 12 h to fully volatilize the acetone, to obtain a dried blank; the dried blank is degreased at a certain temperature (160°C) under Ar / H2 protective atmosphere (volume ratio of Ar and H2 is 95:5; flow rate is 1.5 L / min) for 2 h to completely remove the organic matter in the blank, to obtain a degreased blank; after cooling, the degreased blank is transferred to an Ar atmosphere, heated to a sintering temperature of 160°C at a heating rate of 5°C / min, and sintered for 6 h to obtain a Bi4Ti3O 12 -NiS heterojunction.

[0140] (2) Bi4Ti3O 12Preparation of NiS material modified separator: 0.2 g of Bi4Ti3O 12 NiS heterojunction material was mixed with carbon nanotubes and PVDF at a mass ratio of 80 mg: 10 mg: 10 mg in 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then the slurry was uniformly coated on a polypropylene separator with a 100 μm coater, and then dried in a vacuum oven at 60°C for 12 h. Finally, a Bi4Ti3O 12 NiS modified separator.

[0141] (3) Preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube electrode sheet): the same as step (3) of Example 1.

[0142] (4) Assembly of the battery: the sulfur / carbon nanotube electrode sheet prepared in step (3) was used as the positive electrode, a lithium metal sheet was used as the negative electrode, and the Bi4Ti3O 12 NiS material modified separator as the battery separator, and the electrolyte was a mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate as solutes, DME and DOL (volume ratio 1:1) as solvents, and the mixed solution was prepared; the concentration of LiTFSI in the mixed solution was 1 mol·L -1 , and the concentration of lithium nitrate was 2% by mass). The assembly of CR2032 button cell batteries was carried out in an argon atmosphere glove box (named: gel injection molding Bi4Ti3O 12 NiS / PP).

[0143] Comparative Example 8

[0144] (1) Preparation of Bi4Ti3O 12 SnS2: first refer to the method in step (1) of Comparative Example 2 to prepare pure phase Bi4Ti3O 12 material. Then 0.2 g of Bi4Ti3O 12The precursor was added to a mixed solution of ethanol (33.5 mL) and acetic acid (1.5 mL), and ultrasonicated for 10 min. Then 876.5 mg of SnCl4·5H2O was added to the above mixture, stirred until uniform, and then 469.6 mg of thioacetamide was added and stirred magnetically until dissolved to form a mixture A. Meanwhile, 0.004 g of 2-hydroxyethylamine, 25 ml of butyl ether and 2.5 ml of acrylate were dissolved in 30 ml of isopropanol to form a premix. The mixture A was slowly added to the premix, stirred with a magnetic stirrer for 2 h to form a slurry, and then an initiator (129 microliters of N,N-dimethylacetamide as an initiator) and a catalyst (357 microliters of N,N,N,N-tetramethyl ethylenediamine) were added dropwise to the slurry, which was quickly stirred until uniform and then quickly injected into a mold, and immediately placed in a 100°C muffle furnace for a curing reaction for 1.5 h to obtain a cured blank. After demolding, the cured blank was immersed in acetone at room temperature (25°C) for a certain period of time to remove the solvent in the blank, and then taken out and placed in a 80°C drying oven for 12 h to fully volatilize the acetone, to obtain a dried blank. The dried blank was debound under Ar / H2protective atmosphere (volume ratio of Ar and H2was 95:5; flow rate was 1.5 L / min) at a certain temperature (160°C) for 2 h to completely remove the organic matter in the blank, to obtain a debound blank. Finally, the debound blank was transferred to an Ar atmosphere, heated to a sintering temperature of 180°C at a heating rate of 5°C / min, and sintered for 12 h to obtain a Bi4Ti3O 12 -SnS2heterojunction.

[0145] (2) Bi4Ti3O 12 -SnS2material modified separator: the Bi4Ti3O 12 -SnS2heterojunction material was mixed with carbon nanotubes and PVDF at a mass ratio of 80 mg: 10 mg: 10 mg in 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then the slurry was uniformly coated on a polypropylene separator with a 100 μm coater, and then dried in a vacuum oven at 60°C for 12 h. Finally, a Bi4Ti3O 12 -SnS2modified separator.

[0146] (3) Preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube electrode sheet): the same as step (3) of Example 1.

[0147] (4) Assembly of the battery: the sulfur / carbon nanotube electrode sheet prepared in step (3) was used as the positive electrode, a lithium metal sheet was used as the negative electrode, and the Bi4Ti3O 12-SnS2 material modified separator as the battery separator, the electrolyte is a mixed solution of lithium bis (trifluoromethyl sulfonyl imide) (LiTFSI) and lithium nitrate, that is, LiTFSI and lithium nitrate are used as solutes, and DME and DOL (volume ratio of 1:1) are used as solvents to prepare the mixed solution; the concentration of LiTFSI in the mixed solution is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass). The assembly of CR2032 button cells was carried out in an argon atmosphere glove box (named: gel injection molding Bi4Ti3O 12 -SnS2 / PP).

[0148] Comparative Example 9

[0149] (1) Preparation of NiCo2S4-TiO2 by gel injection molding method: first, a pure phase of NiCo2S4 material was prepared according to the method in step (1) of Comparative Example 3. Then, 0.003712 g of 2-hydroxyethylamine, 25 ml of diphenylpropane diglycidyl ether, 0.25 ml of 1,6-hexanediol diacrylate, and 0.2 g of NiCo2S4 were dissolved in 30 ml of isopropanol to form a premix solution; then, 10 mL of tetrabutyl titanate (TBOT) and 2 mL of hydrofluoric acid were slowly added to the premix solution and mixed uniformly, and a magnetic stirrer was used for stirring for 2 h to form a slurry; then, an initiator (129 microliters of N,N-dimethylacetamide as an initiator) and a catalyst (357 microliters of N,N,N,N-tetramethyl ethylenediamine) were added dropwise to the slurry, and after rapid stirring, the slurry was quickly injected into a mold, and immediately placed in a muffle furnace at 850°C for a curing reaction for 1.5 h to obtain a cured blank; after demolding, the cured blank was immersed in acetone at room temperature (25°C) for a certain period of time to remove the solvent in the blank, and then taken out and placed in a drying oven at 80°C for 12 h to fully volatilize the acetone, thereby obtaining a dried blank; the dried blank was debindered at 160°C for 4 h under Ar / H2 protective atmosphere (volume ratio of Ar and H2 was 95:5; flow rate was 1.5 L / min) to completely remove the organic matter in the blank, thereby obtaining a debindered blank; finally, the debindered blank was sintered at a sintering temperature of 200°C (air, 5°C / min) for 20 h, thereby obtaining a NiCo2S4-TiO2 precursor.

[0150] (2) Preparation of NiCo2S4-TiO2 material modified separator: the NiCo2S4-TiO2 heterojunction material obtained in step (1) was mixed with carbon nanotubes and PVDF in a mass ratio of 80 mg:10 mg:10 mg in 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then, the slurry was uniformly coated on a polypropylene separator using a 100 μm coater, and then dried in a vacuum oven at 60°C for 12 h. Finally, a NiCo2S4-TiO2 modified separator was obtained.

[0151] (3) The preparation of lithium-sulfur battery positive electrode sheet (i.e. sulfur / carbon nanotube electrode sheet) is the same as step (3) of Example 1.

[0152] (4) Assembly of the battery: the sulfur / carbon nanotube electrode sheet prepared in step (3) is used as the positive electrode, a lithium metal sheet is used as the negative electrode, the NiCo2S4-TiO2 material modified separator prepared in step (2) is used as the battery separator, and the electrolyte is a mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate, i.e. LiTFSI and lithium nitrate are used as solutes, and DME and DOL (volume ratio of 1:1) are used as solvents to prepare the mixed solution. The concentration of LiTFSI in the mixed solution is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass. The assembly of the CR2032 button cell is carried out in an argon atmosphere glove box (named: gel injection molding method NiCo2S4-TiO2 / PP).

[0153] Comparative Example 10

[0154] (1) Preparation of NiCo2S4-ZnO by gel injection molding method: first, the pure phase NiCo2S4 material is prepared according to the method in step (1) of Comparative Example 3. Then, 3.0 g of zinc acetate dihydrate is ground for more than 3 h. 0.003712 g of 2-hydroxyethylamine, 25 ml of diphenylolpropane diglycidyl ether, 0.25 ml of 1,6-hexanediol diacrylate, and 0.2 g of NiCo2S4 are dissolved in 30 ml of isopropanol to form a premix. Then, the ground zinc acetate dihydrate is slowly added to the premix and mixed uniformly, and a magnetic stirrer is used to stir for 2 h to form a slurry. Then, the initiator (129 microliters of N,N-dimethylacetamide as the initiator) and the catalyst (357 microliters of N,N,N,N-tetramethyl ethylenediamine) are added dropwise into the premix, stirred quickly and uniformly, and then quickly injected into a mold, and immediately placed in a muffle furnace at 850°C for solidification reaction for 1.5 h to obtain a solidified blank. After demolding, the solidified blank is immersed in acetone at room temperature (25°C) for a certain period of time to remove the solvent in the blank, and then taken out and placed in a drying oven at 80°C for 12 h to fully volatilize the acetone, obtaining a dried blank. The dried blank is degreased at 160°C under Ar / H2 protective atmosphere (volume ratio of Ar and H2 is 95:5; flow rate is 1.5 L / min) for 4 h to completely remove the organic matter in the blank, obtaining a degreased blank. Finally, the degreased blank is sintered at 350°C (air, 5°C / min) for 3 h to obtain the NiCo2S4-ZnO heterojunction.

[0155] (2) Preparation of the separator modified by the NiCo2S4-ZnO material: the NiCo2S4-ZnO heterojunction material obtained in step (1) is mixed with carbon nanotubes and PVDF in a mass ratio of 80 mg: 10 mg: 10 mg into 0.5 mL of N-methyl pyrrolidone (NMP) to obtain a uniform slurry. Then the slurry is uniformly coated on a polypropylene separator with a 100 μm coater, and then dried in a vacuum oven at 60°C for 12 h. Finally, the NiCo2S4-ZnO modified separator is obtained.

[0156] (3) Preparation of the lithium-sulfur battery positive electrode sheet (i.e., sulfur / carbon nanotube electrode sheet) is the same as step (3) of Example 1.

[0157] (4) Assembly of the battery: the sulfur / carbon nanotube electrode sheet prepared in step (3) is used as the positive electrode, a lithium metal sheet is used as the negative electrode, the NiCo2S4-ZnO material modified separator prepared in step (2) is used as the battery separator, and the electrolyte is a mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate, i.e., LiTFSI and lithium nitrate are used as solutes, and DME and DOL (volume ratio of 1:1) are used as solvents to prepare the mixed solution; the concentration of LiTFSI in the mixed solution is 1 mol·L -1 , and the concentration of lithium nitrate is 2% by mass. The assembly of the CR2032 button cell is carried out in an argon atmosphere glove box (named: gel injection molding NiCo2S4-ZnO / PP).

[0158] Effect example

[0159] (1) The scanning electron microscope observation result of the nanocomposite metal sulfide heterojunction (Bi4Ti3O 12 -NiCo2S4) material prepared in step (1) of Example 1 is shown in Figure 1 , and the X-ray diffraction (XRD) result is shown in Figure 2 .

[0160] (2) The battery performance of the button cells in Examples 1, 4-7 and Comparative Examples 1-10 is tested, and the testing method is as follows: the assembled battery is tested for charge and discharge by using a NEWARE testing system, the voltage interval is 1.7-2.8 V, and the experiment is set to be repeated three times. The results are shown in Figures 3-6 : it can be seen that the use of the composite Bi4Ti3O 12 -NiCo2S4 material prepared by the gel injection molding method of the present application as a separator can effectively improve the electrochemical performance and cycle stability of the lithium-sulfur battery. Compared with the conventional method, the capacity and cycle stability are greatly improved.

[0161] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A method for preparing a composite metal heterojunction modified separator for lithium-sulfur batteries, characterized in that, Includes the following steps: (1) Preparation of Bi4Ti3O by non-water-soluble gel casting method 12 precursor Organic monomers bisphenol A propane diglycidyl ether, dispersant 2-hydroxyethylamine, and crosslinking agent 1,6-hexanediol diacrylate were added to solvent isopropanol and stirred until homogeneous to obtain premix A. Then, Bi₂O₃ and TiO₂ were added to premix A and stirred to form a Bi-Ti slurry. Next, an initiator and catalyst were added dropwise to the Bi-Ti slurry and stirred until homogeneous to obtain mixed slurry B. Mixed slurry B was then subjected to a curing reaction at 600–900℃ to obtain cured blank I. Cured blank I was then demolded and immersed in acetone to remove the solvent from the blank, followed by drying at 80±5℃ to allow the acetone to fully evaporate, resulting in dried blank I. Dried blank I was degreased under a protective gas atmosphere at 200–600℃ to completely remove organic matter from the blank, resulting in degreased blank I. Finally, degreased blank I was heated to 900–1200℃ and sintered to obtain Bi₄Ti₃O₃. 12 Precursor; (2) Water-insoluble gel casting method for loading nano-NiCo2S4 The organic monomer butyl ether, the dispersant 2-hydroxyethylamine, and the crosslinking agent acrylate were added to the solvent isopropanol and stirred until homogeneous to obtain premix C; then nickel nitrate hexahydrate, cobalt nitrate hexahydrate, thioacetamide, and polyetherimide were added to premix C, stirred until homogeneous, and the pH was adjusted to 4-7 to obtain premix D; the Bi4Ti3O obtained in step (1) was added to the premix D. 12 The precursor is added to the premixed liquid D and stirred to form a slurry. Then, an initiator and catalyst are added dropwise to the slurry and stirred until homogeneous to obtain a mixed slurry E. Next, the mixed slurry E is placed at 80–200℃ for a curing reaction to obtain a cured blank II. After demolding, the cured blank II is immersed in acetone to remove the solvent from the blank, and then removed and dried at 80±5℃ to allow the acetone to fully evaporate, obtaining a dried blank II. The dried blank II is degreased under a protective gas atmosphere at 160–175℃ to completely remove organic matter from the blank, obtaining a degreased blank II. Finally, the degreased blank II is sintered at 150–200℃ under a protective gas atmosphere to obtain Bi4Ti3O. 12 -NiCo2S4 heterojunction; (3) Preparation of composite metal heterojunction modified separator for lithium-sulfur batteries The Bi4Ti3O obtained in step (2) 12 -NiCo2S4 heterojunction, conductive agent, and binder are added to a solvent and stirred to form a slurry. The slurry is then coated onto a battery separator and dried to obtain Bi4Ti3O. 12 -NiCo2S4 heterojunction modification material, namely the composite metal heterojunction modified separator for lithium-sulfur batteries.

2. The method for preparing a composite metal heterojunction modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The mass ratio of Bi2O3 to TiO2 in step (1) is 3 to 7:1; The amount of 2-hydroxyethylamine used in step (1) is 0.5% to 4% of the total mass of Bi2O3 and TiO2; The amount of bisphenol A diglycidyl propane diglycidyl ether used in step (1) is 15% to 30% of the volume of mixed slurry B; The volume ratio of bisphenol A diglycidyl ether and 1,6-hexanediol diacrylate in step (1) is 9 to 15:

1. The amount of isopropanol used in step (1) is 20% to 40% of the volume of mixed slurry B; The Bi4Ti3O mentioned in step (2) 12 The mass ratio of the precursor to nickel nitrate hexahydrate is 1:1 to 2; The amount of 2-hydroxyethylamine used in step (2) accounts for a certain percentage of Bi4Ti3O. 12 0.5% to 4% of the precursor mass; The amount of butyl ether used in step (2) is 15% to 30% of the volume of the mixed slurry E; The volume ratio of butyl ether to acrylate in step (2) is 9 to 15:1; The amount of isopropanol used in step (2) is 20% to 40% of the volume of the mixed slurry E; The mass ratio of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, thioacetamide and polyetherimide in step (2) is 1:2:4:2-6; The total mass of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, thioacetamide, and polyetherimide mentioned in step (2) is Bi4Ti3O 12 0.5 to 20 times the mass of the precursor; The Bi4Ti3O mentioned in step (3) 12 The mass ratio of the NiCo2S4 heterojunction, conductive agent, and binder is 8:1:

1.

3. The method for preparing a composite metal heterojunction modified separator for lithium-sulfur batteries according to claim 2, characterized in that: The mass ratio of Bi2O3 to TiO2 in step (1) is 6:1; The amount of 2-hydroxyethylamine used in step (1) accounts for 2% of the total mass of Bi2O3 and TiO2; The amount of bisphenol A diglycidyl propane diglycidyl ether used in step (1) accounts for 25% of the volume of mixed slurry B; The volume ratio of bisphenol A diglycidyl ether and 1,6-hexanediol diacrylate in step (1) is 10:

1. The amount of isopropanol used in step (1) accounts for 30% of the volume of mixed slurry B; The Bi4Ti3O mentioned in step (2) 12 The mass ratio of the precursor to nickel nitrate hexahydrate is 1:1.2; The amount of 2-hydroxyethylamine used in step (2) accounts for a certain percentage of Bi4Ti3O. 12 2% of the precursor mass; The amount of butyl ether used in step (2) is 25% of the volume of the mixed slurry E; The volume ratio of butyl ether to acrylate in step (2) is 10:1; The amount of isopropanol used in step (2) is 30% of the volume of the mixed slurry E; The mass ratio of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, thioacetamide and polyetherimide in step (2) is 1:2:4:3; The total mass of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, thioacetamide, and polyetherimide mentioned in step (2) is Bi4Ti3O 12 10 to 15 times the mass of the precursor.

4. The method for preparing a composite metal heterojunction modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The initiator mentioned in steps (1) and (2) is at least one of N,N-dimethylacetamide, N,N-dimethylcyclohexylamine and N,N-dimethylpyridine; The catalyst mentioned in steps (1) and (2) is at least one of N,N,N,N-tetramethylethylenediamine, trans-1,2-cyclohexanediamine and triethylamine; The conductive agent mentioned in step (3) is carbon nanotubes; The adhesive mentioned in step (3) is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and carboxymethyl cellulose; The solvent mentioned in step (3) is N-methylpyrrolidone; The battery separator mentioned in step (3) is any one of cellulose separator, polyethylene separator, polypropylene separator, aramid membrane, polyester membrane, Celgard 2400 and Celgard 2500.

5. The method for preparing a composite metal heterojunction modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The volume ratio of the initiator to the catalyst mentioned in steps (1) and (2) is 2:5 to 5.2; The total volume of the initiator and catalyst mentioned in step (1) accounts for 0.5% to 2.5% of the volume of bisphenol A diglycidyl ether; The total volume of the initiator and catalyst mentioned in step (2) is 0.5% to 2.5% of the volume of butyl ether.

6. The method for preparing a composite metal heterojunction modified separator for lithium-sulfur batteries according to claim 1, characterized in that: The isopropanol mentioned in step (1) is isopropanol-D1; The stirring time for forming the Bi-Ti slurry in step (1) is 1 to 3 hours; The curing reaction temperature described in step (1) is 850℃; The curing reaction time described in steps (1) and (2) is 1 to 2 hours; The drying time described in steps (1) and (2) is 12–18 h; The protective gas used for degreasing in steps (1) and (2) is nitrogen, argon, or a mixture of argon and hydrogen; The degreasing temperature described in step (1) is 400℃; The defatting time mentioned in step (1) is 2 to 4 hours; The protective gas used for sintering in step (2) is nitrogen, argon, or a mixture of argon and hydrogen; The sintering temperature described in step (1) is 1050℃; The sintering time mentioned in step (1) is 2 to 4 hours; The pH adjustment mentioned in step (2) is to adjust the pH to 6.5; The time for stirring to form the slurry in step (2) is 1 to 3 hours; The curing reaction temperature described in step (2) is 100℃; The defatting time mentioned in step (2) is 2 to 4 hours; The sintering temperature described in step (2) is 180°C; The sintering time mentioned in step (2) is 2 to 4 hours; The coating thickness described in step (3) is 50–150 μm; The drying temperature described in step (3) is 40–70°C; The drying time described in step (3) is 12 to 18 hours.

7. A composite metal heterojunction modified separator for lithium-sulfur batteries, characterized in that: It is prepared by the method described in any one of claims 1 to 6.

8. The application of the composite metal heterojunction modified separator for lithium-sulfur batteries as described in claim 7 in the preparation of lithium-sulfur batteries.

9. A lithium-sulfur battery, characterized in that: Includes a positive electrode, a negative electrode, a composite metal heterojunction modified separator for lithium-sulfur batteries as described in claim 7, and an electrolyte; The positive electrode mentioned above is the positive electrode sheet for lithium-sulfur batteries; The negative electrode is a lithium metal sheet; The solutes in the electrolyte are lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate.

10. The lithium-sulfur battery according to claim 9, characterized in that: The positive electrode is prepared by the following method: carbon nanotubes are mixed with sulfur and ground thoroughly, and then heat-treated at 155±5℃ to obtain a carbon / sulfur composite material; the carbon / sulfur composite material, conductive agent and binder are added to a solvent and stirred to form a slurry; finally, the slurry is coated onto aluminum foil and dried to obtain a lithium-sulfur battery positive electrode sheet. The mass ratio of the carbon nanotubes to sulfur is 7:3; The mass ratio of the carbon / sulfur composite material, conductive agent, and binder is 8:1:1; The conductive agent is conductive carbon black; The adhesive is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and carboxymethyl cellulose; The solvent is N-methylpyrrolidone; The drying temperature is 40–70°C; The drying time is 12–18 hours; The electrolyte was prepared by adding LiTFSI and lithium nitrate to a solvent obtained by mixing ethylene glycol dimethyl ether and 1,3-dioxolane in a volume ratio of 1:1; wherein the concentration of LiTFSI in the electrolyte was 1 mol·L⁻¹. -1 The concentration of lithium nitrate is 2% by mass.

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