N-TiO2 / diatomite / C composite membrane modification material, its preparation and application in lithium-sulfur battery membrane modification

Abstract

This invention belongs to the field of battery materials, specifically disclosing a method for preparing an N-TiO2 / diatomaceous earth / C composite separator modified material. The method involves electrospinning a spinning solution containing N-TiO2, diatomaceous earth, and a polymer, followed by heat treatment at 550–850°C to obtain the material. The N-TiO2 is N-doped TiO2. This invention also includes the material prepared by the described method and the separator modified therefrom. The material prepared by the method of this invention can significantly improve the performance of the modified separator material.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, and specifically relates to a lithium-sulfur battery separator technology. Background Technology

[0002] With the rapid development of the driving range of electric vehicles and electronic devices, higher demands are being placed on the capacity, energy density, and cycle performance of electronic energy storage components. Lithium-sulfur batteries have the advantages of high theoretical capacity (1675 mAh / g) and high energy density (2600 Wh / kg), possessing a potential energy density 3-5 times higher than commercial lithium-ion batteries, and are expected to become the next generation of secondary energy storage devices. However, sulfur, the active material in lithium-sulfur batteries, is non-conductive and undergoes a polysulfide "shuttle effect" during use, severely reducing the electrochemical performance of lithium-sulfur batteries. The separator, as a crucial component of lithium-sulfur batteries, prevents contact between the positive and negative electrodes, prevents short circuits, and facilitates ion transport, theoretically effectively improving the electrochemical performance of lithium-sulfur batteries.

[0003] Currently, researchers both domestically and internationally have conducted a series of studies on functionalized separators for lithium-sulfur batteries. By composite catalytic materials such as metal nitrides, metal oxides, and metal sulfides onto the surface of the separator material, the reaction kinetics inside the lithium-sulfur battery are accelerated, suppressing the "shuttle effect" of polysulfides. Titanium dioxide, as a metal oxide, can form chemical bonds with polysulfides inside the battery, improving the adsorption effect of polysulfides.

[0004] Existing technologies have also reported some titanium dioxide-modified lithium-sulfur battery separator solutions. For example, CN109860476A discloses a titanium dioxide colloid-modified separator for lithium-sulfur batteries, which includes a polypropylene separator and a 1-4 μm thick, dense, and uniform nanoscale titanium dioxide colloid layer coated on both sides of the polypropylene separator. The conductivity and structural stability of this material are not ideal, and its specific capacity and cycle performance need improvement. Furthermore, existing technologies have reported separators based on diatomaceous earth composites. For example, CN116315438A discloses a composite separator, its preparation method, battery, and application, including a base membrane and diatomaceous earth dispersed on the surface and reinforcing strips of the base membrane through impregnation. Additionally, existing technologies have reported solutions based on TiO2@diatomaceous earth materials prepared using the traditional sol-gel method.

[0005] Although existing technologies have reported some schemes for modifying membranes with titanium dioxide and diatomaceous earth, most of the existing processes still have shortcomings such as low conductivity, easy shedding of inorganic particles, poor structural stability, and unsatisfactory electrochemical performance of the membrane. Summary of the Invention

[0006] To address the problems of unsatisfactory conductivity, easy detachment of modified materials, and unsatisfactory electrochemical performance in existing lithium-sulfur battery separators, the primary objective of this invention is to provide a method for preparing N-TiO2 / diatomite / C composite separator modified materials, aiming to prepare modified materials with excellent modification effects on lithium-sulfur battery separators.

[0007] The second objective of this invention is to provide the N-TiO2 / diatomite / C composite membrane modification material prepared by the aforementioned method and its application in the modification of lithium-sulfur battery membranes.

[0008] A third objective of the present invention is to provide a modified separator comprising the modified material and a lithium-sulfur battery comprising the modified separator.

[0009] A method for preparing an N-TiO2 / diatomite / C composite membrane modified material involves electrospinning a spinning solution containing N-TiO2, diatomite, and polymer, followed by heat treatment at a temperature of 550–850°C to obtain the material.

[0010] The N-TiO2 mentioned is N-doped TiO2.

[0011] This invention innovatively combines N-TiO2 and diatomaceous earth through spinning and heat treatment. This allows for synergistic and selective regulation of the active phase, constructing unique component-structure relationships and morphological characteristics. This, in turn, synergistically improves the material's conductivity and structural stability, and creates a microstructure and active sites suitable for lithium-sulfur batteries. Furthermore, this innovative method utilizes the material with unique physicochemical properties constructed using this method as a lithium-sulfur battery separator modifier, significantly improving the electrochemical performance of the modified separator.

[0012] In this invention, the synergistic combination of N-TiO2 and diatomaceous earth, further combined with the electrospinning-heat treatment composite method, and the joint control of preparation conditions are key to synergistically regulating the characteristics of advantageous phases, occurrence structure, morphology, controllable defects and active site characteristics, thereby improving the modification performance of lithium-sulfur battery separators.

[0013] Preferably, the titanium source and nitrogen source are hydrolyzed under acid to obtain the N-TiO2;

[0014] The titanium source is one or more of titanium alkoxides, titanium salts, and titanium oxalate ammonium;

[0015] Preferably, the titanium alkoxide includes at least one of tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate;

[0016] Preferably, the titanium salt includes at least one of titanium tetrachloride, titanium trichloride, titanium sulfate, and titanium oxysulfate;

[0017] Preferably, the nitrogen source is at least one selected from ammonium salt, ammonia, urea, ethylenediamine, thiourea, and hydrazine hydrate.

[0018] Preferably, the weight ratio of titanium source to nitrogen source is 5 to 50:1, and more preferably 15 to 30:1;

[0019] Preferably, the temperature of the hydrolysis process is above 35°C, more preferably 40-90°C, and further preferably 40-50°C.

[0020] In this invention, the diatomaceous earth is pretreated diatomaceous earth that has undergone heat pretreatment and / or acid pretreatment.

[0021] In this invention, diatomaceous earth is subjected to heat treatment to obtain heat-pretreated diatomaceous earth. Alternatively, diatomaceous earth is placed in an acidic solution for acid pretreatment, then washed with water until neutral, and dried to obtain acid-pretreated diatomaceous earth.

[0022] In this invention, the temperature of the heat pretreatment process is 400-800℃, preferably 500-600℃; the heat pre-modification time can be 1-3 hours.

[0023] In this invention, the solute concentration of the acid solution in the acid pretreatment stage is 10% to 50 wt%, and the acid pretreatment time is more than 10 hours.

[0024] In this invention, the polymer is at least one of PVP, PVA, and PEO.

[0025] In this invention, the weight ratio of N-TiO2, diatomaceous earth, and polymer in the spinning solution is 1-10:1-5:1-10; further, it can be 3-6:1-3:3-6; and even further, it can be 4.5-5.5:1-3:4.5-5.5.

[0026] Preferably, the solvent in the spinning solution includes at least one of N-dimethylformamide (DMF), N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), ethanol, and acetic acid;

[0027] Preferably, the concentration of diatomaceous earth in the spinning solution is 1–50 mg / mL, more preferably 5–25 mg / mL, and even more preferably 10–20 mg / mL.

[0028] In this invention, N-TiO2, diatomaceous earth, and polymer can be mixed with solvent in any form to obtain the spinning solution. Alternatively, the starting material solution of N-TiO2 can be mixed with the polymer solution beforehand, heated for hydrolysis, and then mixed with the diatomaceous earth solution to obtain the spinning solution.

[0029] In this invention, the solvent in the polymer solution and diatomaceous earth solution can be at least one of an organic solvent or a lower alcohol. The starting material solution for N-TiO2 is a solution containing a titanium source, an acid, and an nitrogen source.

[0030] In this invention, the spinning process can be adjusted as needed. Preferably, the spinning temperature is 20-35°C, the humidity is 20%-55%, the voltage is 16kV-24kV, and the receiving distance is 10-20cm.

[0031] Preferably, the spinning time is 8 to 12 hours;

[0032] Preferably, the heat treatment is performed after the spinning process is completed and the yarn is dried.

[0033] Preferably, the heat treatment process is carried out under a protective atmosphere; the protective atmosphere can be nitrogen or an inert gas such as Ar.

[0034] Preferably, the heat treatment temperature is 580–820°C, and more preferably 590–620°C. At the preferred temperature, the cycle stability of the modified diaphragm can be further improved.

[0035] Preferably, the heat treatment time is 1 to 3 hours.

[0036] The present invention also provides an N-TiO2 / diatomite / C composite membrane modified material prepared by the aforementioned preparation method.

[0037] In this invention, the preparation method can endow the material with advantageous phase characteristics. Moreover, it can also construct special physicochemical characteristics such as special component occurrence relationships and one-dimensional morphology. The material with the above physicochemical characteristics can be innovatively used as a modifying material for lithium-sulfur batteries. It can unexpectedly and significantly suppress polysulfide shuttle, improve thermal stability, and improve the electrochemical performance of modified lithium-sulfur battery separators.

[0038] The present invention also provides an application of the N-TiO2 / diatomite / C composite separator modification material prepared by the above preparation method, which is used as a modification material to prepare modified separators for lithium-sulfur batteries;

[0039] Preferably, it is coated onto a diaphragm base membrane to prepare the modified diaphragm.

[0040] The present invention also provides a modified separator for lithium-sulfur batteries, comprising a base membrane and a modifying material composited on the surface of the base membrane, wherein the modifying material comprises the N-TiO2 / diatomite / C composite separator modifying material prepared by the preparation method described above.

[0041] In this invention, the base film can be any separator base film well known in the field of lithium-sulfur batteries, for example, the base film is at least one of PP and PE;

[0042] In this invention, the modified material further includes a binder;

[0043] In this invention, the adhesive includes at least one of PVDF, CMC, SBR, PAA, PTFE, and PVA;

[0044] In this invention, the modified material further includes a conductive agent;

[0045] In this invention, the content of the N-TiO2 / diatomite / C composite membrane modifier in the modified material is not less than 50 wt.%, preferably 60-90 wt.%, and more preferably 75-85 wt.%.

[0046] In this invention, the modified material can be composited on one or both surfaces of the base film; considering cost, it can be composited on one surface.

[0047] The present invention also provides a lithium-sulfur battery, comprising a positive electrode, a separator, and a negative electrode sequentially laminated together, wherein the separator is the modified separator described in the present invention.

[0048] The lithium-sulfur battery of the present invention, except for the modified separator, can have other conventional components and parts.

[0049] Preferably, in this invention, the modified material layer of the modified separator faces the positive electrode.

[0050] The beneficial effects of this invention are:

[0051] This invention innovatively combines N-TiO2 and diatomaceous earth through spinning and heat treatment. This synergistic and selective modulation of the active phase allows for the construction of unique compositional relationships and morphological characteristics, thereby synergistically improving the material's conductivity, structural stability, and creating a microstructure and active sites suitable for lithium-sulfur batteries. Furthermore, this invention innovatively uses the modified material obtained by the aforementioned method for modifying lithium-sulfur battery separators. This effectively suppresses the "shuttle effect" of polysulfides, improves the utilization rate, capacity, and cycle stability of active materials in lithium-sulfur batteries, and promotes the commercial application of high-performance lithium-sulfur batteries. Attached Figure Description

[0052] Figure 1 The XRD patterns of the modified materials from Examples 1 and 3 are shown below.

[0053] Figure 2 Here is a scanning electron microscope image of the modified material from Example 1;

[0054] Figure 3 The cycling performance curves of the modified diaphragms in Examples 1-3 are shown at 0.2C.

[0055] Figure 4 The cycling performance curves of Example 1 and the comparative example at 0.2C are shown. Detailed Implementation

[0056] The accompanying drawings and embodiments, which constitute a part of this invention, are designed to further illustrate the purpose, technical solutions, and advantages of the invention. The embodiments of the invention given below are further illustrations of the invention and are not intended to limit the specific implementation of the invention.

[0057] In this invention, the preparation method of the N-TiO2 / diatomite / C composite membrane modified material involves electrospinning a spinning solution containing N-TiO2, diatomite, and polymer, followed by heat treatment to obtain the material.

[0058] As an example of the preparation method of the N-TiO2 / diatomite / C composite membrane modification material of the present invention, it includes the following steps:

[0059] (1) The pretreated diatomaceous earth is stirred and mixed evenly with at least one solvent selected from organic solvents or anhydrous lower alcohols, and then subjected to ultrasonic treatment. This mixture is denoted as dispersion A.

[0060] (2) Mix a certain amount of glacial acetic acid solution with a nitrogen source and stir until homogeneous. During the stirring process, slowly add a certain amount of titanium source solution, which is denoted as solution B.

[0061] (3) Place the polymer in at least one solvent selected from organic solvents or anhydrous lower alcohols, denoted as solution C.

[0062] (4) Add solution B to solution C and mix well. Then add dispersion A and sonicate to obtain dispersion D.

[0063] (5) Electrospinning and drying of dispersion D are performed to obtain spinning material;

[0064] (6) The obtained spinning material is heat-treated in a protective atmosphere to obtain the modified material.

[0065] The pretreatment in step (1) includes roasting and acid leaching.

[0066] The calcination process is as follows: a certain mass of diatomaceous earth is placed in a muffle furnace and calcined for 1 to 3 hours at a calcination temperature of 400 to 800°C. After cooling to room temperature in the furnace, it is sealed and stored, which is the calcined diatomaceous earth. A further preferred calcination temperature is 500 to 600°C.

[0067] The acid leaching process is as follows: Weigh a certain mass of diatomaceous earth, measure a certain mass of acidic solutions with different concentrations of 10% to 50 wt%, mix them evenly with the original earth, and keep stirring at room temperature for 20 to 30 hours. Then wash with deionized water until neutral, and dry at a temperature above 60°C to obtain acid-leached diatomaceous earth.

[0068] In the following cases, unless otherwise stated, the pretreated diatomaceous earth refers to diatomaceous earth obtained by heat modification at 500-550℃ for 2 hours, followed by 2M sulfuric acid leaching, water washing until neutral, and drying.

[0069] The titanium source in step (1) is one or more of titanium alkoxide, titanium salt, and titanium oxalate ammonium.

[0070] The titanium alkoxides include: tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate.

[0071] The titanium salts mentioned include: titanium tetrachloride, titanium trichloride, titanium sulfate, and titanium oxysulfate.

[0072] The concentration of diatomaceous earth in step (1) is 1 to 50 mg / mL.

[0073] The nitrogen source mentioned in step (2) is one of ammonium chloride, ammonia, urea, ethylenediamine, thiourea, and hydrazine hydrate. The concentration of elemental titanium is 0.1 to 1 mmol / mL, and the weight ratio of titanium source to nitrogen source is 5 to 50:1, which can be further 15 to 30:1.

[0074] The polymer mentioned in step (3) is at least one of PVP, PVA, and PEO.

[0075] The organic solvents mentioned in steps (1) and (3) are one or more of the following: N-dimethylformamide (DMF), N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and tetrahydrofuran (THF). The anhydrous lower alcohols are one or more of the following: methanol, ethanol, ethylene glycol, n-propanol, and isopropanol.

[0076] The spinning time in step (5) is 8 to 12 hours, the spinning temperature is 20 to 35°C, the humidity is 20% to 55%, the voltage is 16kV to 24kV, the drying temperature is 40 to 100°C, and the receiving distance is 10 to 20cm.

[0077] In this invention, the modified material, binder, and conductive agent can be slurried, coated onto the surface of a base film, and dried to obtain the modified separator. The binder can be at least one of PVDF, CMC, SBR, PAA, PTFE, and PVA, and the conductive agent can be at least one of conductive carbon black, carbon nanotubes, and graphene. The weight ratio of the modified material, conductive agent, and binder can be 80-90:5-10:5-10.

[0078] In this invention, the positive electrode, negative electrode, and electrolyte of the lithium-sulfur battery can all be those known in the industry.

[0079] When the modified separator is used to assemble a lithium-sulfur battery, the modified material layer of the modified separator faces the positive electrode.

[0080] Example 1

[0081] (1) Weigh 0.1g of pretreated diatomaceous earth (labeled as DE) and disperse it in 3mL of anhydrous ethanol. Sonicate it for 30min and record it as dispersion A.

[0082] (2) Add 0.1g of urea to 3mL of glacial acetic acid solution, and slowly add 2mL of tetrabutyl titanate while stirring magnetically at 40℃. Mix well to obtain solution B containing N-TiO2.

[0083] (3) Place 0.5g PVP (polyvinylpyrrolidone) in 2mL of anhydrous ethanol and mix it evenly with magnetic stirring at 40℃. This mixture is denoted as solution C.

[0084] (4) Add solution B to solution C and mix evenly by magnetic stirring at 80°C. Then slowly add dispersion A and continue magnetic stirring for 60 minutes to obtain dispersion D (control the weight ratio of N-TiO2 / DE / PVP to 5:1:5).

[0085] (5) Take 10 mL of dispersion D into a syringe, place the syringe on the support of the electrospinning machine, select a low-speed roller as the receiving device, the voltage is 18 KV, the roller speed is 100 rpm, the spinning time is 7-8 hours, the spinning temperature is 30℃, the humidity is 50%, and the receiving distance is 15 cm; after drying in an oven at 80℃, the final spun material is obtained.

[0086] (6) The spinning material prepared above is subjected to calcination treatment (Ar atmosphere), and the temperature is increased to 600℃ (marked as T) at a rate of 2℃ / min. After calcination for 2 hours, it is ground into powder to obtain the modified material (marked as N-TiO2 / DE / C, or N-TiO2 / DE / C-600℃, or N-TiO2 / DE / C-600℃-5:1:5).

[0087] The modified material, acetylene black, and PVDF were mixed in a ratio of 8:1:1 and then coated onto a PP diaphragm. The coating thickness was controlled to be around 75 micrometers. This mixture was denoted as N-TiO2 / DE / C / PP.

[0088] (7) Assembly of lithium-sulfur batteries: Sulfur and conductive carbon black are mixed at a mass ratio of 3:1 to form the active material. The active material, acetylene black, and polyvinylidene fluoride are then mixed into a slurry at a mass ratio of 20:2:3 and coated to form the positive electrode. Lithium sheets are used as the negative electrode. In a glove box, the self-made sulfur positive electrode (the positive electrode material includes S8, conductive carbon black, and PVDF in a weight ratio of 15:7:3, with a sulfur loading of 0.5 mg / cm³) is sequentially assembled. 2 The modified separator, Li-S electrolyte, pure lithium anode, gasket and spring are placed in the anode shell. Finally, the positive electrode shell is sealed on the anode shell and assembled into a CR2032 coin cell. The assembled battery is then left to stand for 8 hours.

[0089] The XRD diffraction patterns of N-TiO2 / DE / C in this embodiment and in Example 3 are as follows: Figure 1 As shown, the XRD diffraction patterns of the material at 600℃, 700℃, and 800℃ all exhibit two main peaks at 25.3° and 54.3°, corresponding to anatase and rutile titanium dioxide, respectively. This indicates that N-TiO2 / DE / C modified materials can be successfully synthesized at temperatures ranging from 600℃ to 800℃. The scanning electron microscope (SEM) image of this embodiment is shown below. Figure 2 As shown, it is clear that the material is composed of many interwoven nanofibers, with diatomaceous earth filling the gaps.

[0090] Cyclic performance testing was conducted using the Blue Lightning testing system, with the temperature controlled at 26℃ and the discharge rate at 0.2C during the cycling phase. Figure 3 , 4 As shown, the lithium-sulfur battery has a specific capacity of 1180.1 mAh g at the first discharge at 0.2C. -1 After 100 cycles, the capacity is 832.7 mAh g. -1 The initial discharge specific capacity of the unmodified PP film is 805.5 mAh g. -1 After 100 cycles, the capacity is 285.4 mAh g. -1 This indicates that the material can effectively improve the electrochemical cycle performance of lithium-sulfur batteries.

[0091] Example 2

[0092] Compared with Example 1, the only difference is that the ratio of N-TiO2, diatomaceous earth, and polymer is changed (other components remain the same, only the amount of diatomaceous earth is changed). All other operations and parameters are the same as in Example 1. The experimental groups are as follows:

[0093] Group A: The weight ratio of N-TiO2, diatomaceous earth, and polymer is 5:2:5; the material obtained in step (6) is labeled as N-TiO2 / DE / C-600℃-5:2:5;

[0094] Group B: The weight ratio of N-TiO2, diatomaceous earth, and polymer is 5:3:5; the material obtained in step (6) is labeled as N-TiO2 / DE / C-600℃-5:3:5;

[0095] Battery assembly and performance testing were performed according to the method in Example 1, and the experimental results are as follows:

[0096] Group A: The lithium-sulfur battery has an initial discharge specific capacity of 1149.7 mAh g-1 at 0.2C and 821.5 mAh g-1 after 100 cycles;

[0097] Group B: The lithium-sulfur battery has an initial discharge specific capacity of 1085.8 mAh g-1 at 0.2C and 714.1 mAh g-1 after 100 cycles;

[0098] Example 3

[0099] Compared with Example 1, the only difference is that the temperature T in step (6) is changed. All other operations and parameters are the same as in Example 1. The experimental groups are as follows:

[0100] Group A: T is 700℃; the material obtained in step (6) is marked as N-TiO2 / DE / C-700℃;

[0101] Group B: T is 800℃; the material obtained in step (6) is marked as N-TiO2 / DE / C-800℃;

[0102] Battery assembly and performance testing were performed according to the method in Example 1, and the experimental results are as follows:

[0103] Group A: The lithium-sulfur battery has an initial discharge specific capacity of 1080.1 mAh g-1 at 0.2C and 648 mAh g-1 after 100 cycles;

[0104] Group B: The lithium-sulfur battery has an initial discharge specific capacity of 1090.9 mAh g-1 at 0.2C and 683.9 mAh g-1 after 100 cycles;

[0105] As can be seen from the above examples, the modified PP film can be successfully prepared at temperatures of 600–800℃ and weight ratios of N-TiO2, diatomaceous earth, and polymer of 5:1–3:5, compared to the unmodified PP film (initial discharge specific capacity of 805.5 mAh g). -1 After 100 cycles, the capacity is 285.4 mAh g. -1The electrochemical performance was significantly improved.

[0106] Comparative Example 1:

[0107] Compared to Example 1, the only difference is that the spinning solution lacks N-TiO2, and the missing amount is supplemented by pretreated diatomaceous earth, that is, the ratio of pretreated diatomaceous earth to PVP is 6:1; other operations and parameters are the same as in Example 1; the modified material obtained in step 6 is labeled DE / C, and the final modified diaphragm is labeled DE / C / PP. Other operations and parameters are the same as in Example 1.

[0108] The battery was assembled and its performance was tested according to the method of Example 1. The experimental results were as follows: the specific capacity of the lithium-sulfur battery at the first discharge of 0.2C was 941.3 mAh g-1, and after 100 cycles it was 221.5 mAh g-1; its capacity and cycle performance were not as good as those of Example 1.

[0109] Comparative Example 2:

[0110] Compared to Example 1, the only difference is that diatomaceous earth is missing in the spinning solution, and its missing portion is supplemented by N-TiO2, that is, the ratio of N-TiO2 to PVP is 6:1; other operations and parameters are the same as in Example 1; the modified material obtained in step 6 is labeled as N-TiO2 / C, and the final modified membrane is labeled as N-TiO2 / C / PP. Other operations and parameters are the same as in Example 1.

[0111] Battery assembly and performance testing were performed according to the method in Example 1, and the experimental results are as follows:

[0112] The lithium-sulfur battery has a specific capacity of 985.5 mAh g-1 at the first discharge at 0.2C and 284.1 mAh g-1 after 100 cycles; its capacity and cycle performance are inferior to those of Example 1.

[0113] Comparative Example 3:

[0114] Compared to Example 1, the only difference is that urea was not added in step 2. All other operations and parameters are the same as in Example 1.

[0115] Battery assembly and performance testing were performed according to the method in Example 1, and the experimental results are as follows:

[0116] The lithium-sulfur battery has an initial discharge capacity of 1165.5 mAh g⁻¹ at 0.2C and a capacity of 607.3 mAh g⁻¹ after 100 cycles; its cycle performance is inferior to that of Example 1.

[0117] Comparative Example 4

[0118] Compared with Example 1, the only difference is that fumed silica is used instead of the diatomaceous earth, denoted as N-TiO2 / SiO2 / C / PP. All other operations and parameters are the same as in Example 1.

[0119] Battery assembly and performance testing were performed according to the method in Example 1, and the experimental results are as follows:

[0120] The lithium-sulfur battery has an initial discharge specific capacity of 999.9 mAh g⁻¹ at 0.2C and 384.8 mAh g⁻¹ after 100 cycles; its capacity and cycle performance are inferior to those of Example 1.

[0121] Comparative Example 5

[0122] Compared to Example 1, the only difference is that the three components were not spun together. Instead, pretreated diatomaceous earth, N-TiO2, and PVP in the same proportion were stirred and mixed with ethanol for 4 hours, evaporated and desolventized to obtain a solid composite material, and then calcined according to the conditions in step 6 of Example 1. The modified material was obtained, denoted as CMG-N-TiO2 / DE / C. After being ground into powder, the material, acetylene black, and PVDF were mixed in a ratio of 8:1:1 and coated onto a PP membrane, denoted as CMG-N-TiO2 / DE / C / PP.

[0123] All other operations and parameters are the same as in Example 1.

[0124] Cyclic performance testing was conducted using the Blue Lightning testing system at a discharge rate of 0.2C. Figure 4 As shown, the initial discharge specific capacity of the same material CMG-N-TiO2 / DE / C prepared by the conventional sol-gel method is 1056.8 mAh g. -1 After 100 cycles, the capacity is 507.8 mAh g. -1 Compared to lithium-sulfur batteries using PP film, the electrochemical performance can be improved, but it is still lower than that of lithium-sulfur batteries prepared by the optimized electrospinning method.

Claims

1. A method for preparing an N-TiO2 / diatomite / C composite membrane modified material, characterized in that, The spinning solution containing N-TiO2, diatomaceous earth, and polymer is subjected to electrospinning treatment, followed by heat treatment at a temperature of 550~850℃ to obtain the product. The N-TiO2 mentioned is N-doped TiO2; The polymer is at least one of PVP, PVA, and PEO.

2. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 1, characterized in that, The N-TiO2 was prepared by hydrolyzing a titanium source and a nitrogen source under acid. The titanium source is one or more of titanium alkoxides, titanium salts, and titanium oxalate ammonium.

3. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 2, characterized in that, The titanium alkoxide includes at least one of tetraethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate; The titanium salts mentioned include at least one of titanium tetrachloride, titanium trichloride, titanium sulfate, and titanium oxysulfate; The nitrogen source is at least one of ammonium salt, ammonia, urea, ethylenediamine, thiourea, and hydrazine hydrate. The weight ratio of titanium source to nitrogen source is 5~50:1; The hydrolysis process takes place at temperatures above 35°C.

4. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 3, characterized in that, The weight ratio of titanium source to nitrogen source is 15~30:1; The hydrolysis process takes place at temperatures ranging from 40 to 90°C.

5. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 1, characterized in that, The diatomaceous earth mentioned is pretreated diatomaceous earth that has undergone heat pretreatment and / or acid pretreatment.

6. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 5, characterized in that, The temperature of the heat pretreatment process is 400~800 ℃.

7. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 6, characterized in that, The temperature of the heat pretreatment process is 500~600℃.

8. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 5, characterized in that, The solute concentration of the acid solution in the acid pretreatment stage is 10%~50wt%, and the acid pretreatment time is more than 10h.

9. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 1, characterized in that, In the spinning solution, the weight ratio of N-TiO2, diatomaceous earth, and polymer is 1~10:1~5:1~10.

10. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 1, characterized in that, The solvent in the spinning solution includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, ethanol, and acetic acid; The concentration of diatomaceous earth in the spinning solution is 1~50 mg / mL.

11. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material according to any one of claims 1 to 10, characterized in that, The spinning temperature is 20~35℃, the humidity is 20%~55%, the voltage is 16kV~24kV, and the receiving distance is 10~20cm. The spinning time is 8 to 12 hours.

12. The preparation method of the N-TiO2 / diatomite / C composite membrane modified material as described in claim 11, characterized in that, After spinning, the fibers are dried and then subjected to the aforementioned heat treatment. The heat treatment process is carried out under a protective atmosphere; The heat treatment time is 1 to 3 hours.

13. An N-TiO2 / diatomite / C composite membrane modified material prepared by the preparation method according to any one of claims 1 to 12.

14. The application of an N-TiO2 / diatomite / C composite membrane modified material prepared by the preparation method according to any one of claims 1 to 12, characterized in that, It was used as a modifying material to prepare modified separators for lithium-sulfur batteries.

15. The application as described in claim 14, characterized in that, The modified diaphragm is prepared by coating it onto the diaphragm base membrane.

16. A modified separator for lithium-sulfur batteries, characterized in that, The invention includes a base membrane and a modified material composited on the surface of the base membrane, characterized in that the modified material comprises an N-TiO2 / diatomite / C composite membrane modified material prepared by the preparation method according to any one of claims 1 to 12.

17. The modified separator for lithium-sulfur batteries as described in claim 16, characterized in that, The base film is at least one of PP and PE.

18. The modified separator for lithium-sulfur batteries as described in claim 16, characterized in that, The modified material also includes a binder.

19. The modified separator for lithium-sulfur batteries as described in claim 18, characterized in that, The adhesive includes at least one of PVDF, CMC, SBR, PAA, PTFE, and PVA.

20. The modified separator for lithium-sulfur batteries as described in claim 18, characterized in that, The modified material also contains a conductive agent.

21. The modified separator for lithium-sulfur batteries as described in claim 16, characterized in that, In the modified material, the content of the N-TiO2 / diatomite / C composite membrane modified material is not less than 50 wt.%.

22. The modified separator for lithium-sulfur batteries as described in claim 21, characterized in that, In the modified material, the content of the N-TiO2 / diatomite / C composite membrane modified material is 60~90 wt.%.

23. A lithium-sulfur battery, comprising a positive electrode, a separator, and a negative electrode sequentially laminated together, characterized in that, The diaphragm is the modified diaphragm according to any one of claims 16 to 22.

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