Lithium-sulfur battery separator with porous carbon-based composite coating and method of making same

Abstract

This invention discloses a lithium-sulfur battery separator with a porous carbon-based composite material coating and its preparation method. The lithium-sulfur battery separator with the porous carbon-based composite material coating comprises a base film and a coating on the base film. The coating comprises CDC@TiO2 and polyvinylidene fluoride (PVDF), with the ratio of CDC@TiO2 to PVDF being (25-36):(5-9) by mass. The CDC@TiO2 comprises porous carbide-derived carbon and titanium dioxide supported on the porous carbide-derived carbon. The separator of this invention has high liquid absorption rate, liquid retention rate, and ionic conductivity. The Li-S battery obtained by self-assembly of the separator of this invention retains more than 90% of its capacity after 100 cycles at a current density of 0.2C.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a lithium-sulfur battery separator with a porous carbon-based composite material coating and its preparation method. Background Technology

[0002] The rapid growth in global energy demand has driven the development of next-generation high-energy-density rechargeable batteries. Among them, lithium-sulfur (Li-S) batteries have become a highly anticipated future battery technology due to their superior specific capacity and high theoretical energy density. However, Li-S batteries still face some challenges, such as low ionic conductivity, large-scale shuttle phenomenon of intermediate products (Li₂S₆ and Li₂S₄), and sulfur volume expansion during charge and discharge. These issues lead to low sulfur utilization, severe self-discharge problems, and poor cycle stability.

[0003] Therefore, issues such as how to improve ionic conductivity, liquid absorption and retention rate, and improve cycle stability still deserve attention. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a lithium-sulfur battery separator with a porous carbon-based composite material coating.

[0005] Another object of the present invention is to provide a method for preparing a lithium-sulfur battery separator with the above-mentioned porous carbon-based composite material coating.

[0006] Another object of the present invention is to provide a slurry.

[0007] The objective of this invention is achieved through the following technical solution.

[0008] A lithium-sulfur battery separator with a porous carbon-based composite material coating includes: a base film and a coating on the base film, wherein the coating includes: CDC@TiO2 and polyvinylidene fluoride (PVDF), and the ratio of CDC@TiO2 to PVDF is (25-36):(5-9) by mass parts, wherein the CDC@TiO2 includes porous carbide-derived carbon (CDC) and titanium dioxide supported on the porous carbide-derived carbon (CDC).

[0009] In the above technical solution, the preferred ratio of CDC@TiO2 to polyvinylidene fluoride (PVDF) by mass is (28-32):(5.5-6.5).

[0010] In the above technical solution, the method for preparing CDC@TiO2 includes: mixing tetrabutyl titanate, ethanol and porous carbide-derived carbon, stirring until uniform, then standing at 60-70℃ for 2-3 hours, and annealing at 600-800℃ for 2-4 hours under an inert gas atmosphere to obtain CDC@TiO2. The ratio of porous carbide-derived carbon to tetrabutyl titanate by mass is (20-30):(50-60).

[0011] In the above technical solution, the preferred ratio of porous carbide-derived carbon to tetrabutyl titanate by mass is (22-28):(55-60).

[0012] In the method for preparing CDC@TiO2, the ratio of porous carbide-derived carbon to ethanol by mass parts is (20-30):(10-20).

[0013] In the method for preparing CDC@TiO2, the preferred ratio of porous carbide-derived carbon to ethanol by mass parts is (22-28):(10-18).

[0014] In the method for preparing CDC@TiO2, tetrabutyl titanate, ethanol, and porous carbide-derived carbon are mixed and stirred at room temperature until homogeneous. The stirring speed is 500–1000 rpm, and the stirring time is 30–60 min.

[0015] In the above technical solution, the porous carbide-derived carbon has a particle size of D50 = 0.1–0.3 μm, a D90 = 0.4–0.8 μm, and a specific surface area of ​​2000–2500 m². 2 / g, with a porosity of 40-50%.

[0016] In the above technical solution, porous carbide-derived carbon is the framework carbon structure remaining after titanium atoms in titanium carbide are removed by chlorine etching.

[0017] In the above technical solution, the method for preparing porous carbide-derived carbon includes: exposing micron-sized metal carbides to T℃ (at 15-20℃ for min). -1 The carbon is etched with chlorine gas for 100-120 min at a rate of increasing temperature, and then cooled to room temperature under a nitrogen or inert gas atmosphere to obtain a porous carbide-derived carbon precursor. The porous carbide-derived carbon precursor is then annealed at 550-650°C for 1-2 h under a reducing atmosphere to remove residual chlorides on the surface and inside the pores to obtain porous carbide-derived carbon (CDC), T = 900-1000.

[0018] In the method for preparing porous carbide-derived carbon, the micron-sized metal carbide is titanium carbide powder.

[0019] In the method for preparing porous carbide-derived carbon, micron-sized metal carbides are heated to a specified T℃ under a nitrogen or inert gas atmosphere. Upon reaching T℃, the nitrogen or inert gas flow is stopped, and chlorine gas is introduced instead for chlorine etching. The chlorine gas flow rate is 30–40 mL / min. The method for preparing the above-mentioned porous carbon-based composite material coating lithium-sulfur battery separator includes: coating a slurry onto a base film, drying it, and obtaining a coating on the base film to obtain a porous carbon-based composite material coating lithium-sulfur battery separator.

[0020] In the above technical solution, the coating thickness is 2 to 3 μm.

[0021] In the above technical solution, the coating speed is 10-20 m / min.

[0022] A slurry comprising: CDC@TiO2, polyvinylidene fluoride (PVDF), and solvent, wherein the ratio of CDC@TiO2, PVDF, and solvent by mass parts is (25-36):(5-9):(50-70), wherein the CDC@TiO2 comprises: porous carbide-derived carbon (CDC) and titanium dioxide supported on the porous carbide-derived carbon (CDC).

[0023] In the above technical solution, the preferred ratio of CDC@TiO2, polyvinylidene fluoride (PVDF) and solvent by mass parts is (28-32):(5.5-6.5):(60-65).

[0024] In the above technical solution, the solvent is N-methylpyrrolidone (NMP).

[0025] The method for preparing the above slurry includes: mixing CDC@TiO2, polyvinylidene fluoride (PVDF) and solvent until homogeneous to obtain the slurry.

[0026] The method for preparing the above-mentioned slurry includes the following steps:

[0027] Step 1: Mix the solvent and polyvinylidene fluoride (PVDF) and stir until homogeneous to obtain the first solution;

[0028] In step 1, the rotation speed of the stirrer is 2000-3000 r / min, the revolution speed is 50-70 r / min, and the stirring time is 30-40 min.

[0029] Step 2: Mix the first solution with CDC@TiO2, and simultaneously sonicate and stir under vacuum until the mixture is homogeneous to obtain a slurry.

[0030] In step 2, under vacuum conditions, the mixture is simultaneously sonicated and stirred for 30 to 40 minutes until homogeneous. The stirring speed is 2000 to 3000 r / min and the revolution speed is 40 to 50 r / min. The ultrasonic frequency is 5 to 8 kHz and the vacuum degree is 0.06 to 0.08 kPa.

[0031] Application of CDC@TiO2 in improving the liquid absorption rate, liquid retention rate and / or ionic conductivity of lithium-sulfur battery separators.

[0032] Application of CDC@TiO2 in improving the capacity retention of lithium-sulfur batteries.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. TiO2 possesses suitable energy barriers and stability, and is environmentally friendly. It can chemically adsorb lithium polysulfides (LiPSs), suppressing LiPS shuttle and facilitating lithium-ion transport. Through the synergistic effect of physical adsorption by porous carbide-derived carbon (CDC) and chemical adsorption by TiO2, the diffusion of intermediate products (Li2S6 and Li2S4) during charge and discharge is significantly blocked, suppressing the LiPS shuttle effect. This not only provides a rapid lithium-ion transport channel but also prevents the diffusion of lithium polysulfides (LiPSs), thereby improving the cycle stability of the battery.

[0035] 2. The separator of the present invention has a high liquid absorption rate, liquid retention rate and ionic conductivity. The Li-S battery obtained by self-assembly of the separator of the present invention has a high capacity retention rate at a current density of 0.2C. Attached Figure Description

[0036] Figure 1 XRD of the porous carbide-derived carbon (CDC) obtained in Example 1;

[0037] Figure 2 The TEM image is of CDC@TiO2 obtained in Example 1. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] Titanium carbide powder: Shanghai Shuitian Materials Technology Co., Ltd.;

[0040] Tetrabutyl titanate: Sinopharm Chemical Reagent Co., Ltd.

[0041] Dual planetary mixer: XFZH-30L.

[0042] In the following examples, the base film is a PE film with a thickness of 7 micrometers.

[0043] High ionic conductivity: A separator with high ionic conductivity allows lithium ions to pass through more quickly, thus significantly improving the battery's charge and discharge rate. Rapid lithium-ion transport not only helps reduce energy loss during charge and discharge but also helps maintain high capacity after multiple cycles. Furthermore, a separator with high ionic conductivity can reduce the battery's internal resistance, thereby reducing safety risks caused by internal overheating.

[0044] This invention uses titanium carbide to remove metal atoms under the action of chlorine etching, and the remaining carbon atoms are rearranged and combined to obtain porous carbide-derived carbon (CDC) with a porous structure. Then, using tetrabutyl titanate as raw material, CDC@TiO2 is obtained.

[0045] Example 1

[0046] A method for preparing a slurry includes the following steps:

[0047] Step 1: Mix the solvent and polyvinylidene fluoride (PVDF) in a double planetary mixer and stir for 30 minutes until homogeneous to obtain the first solution. The rotation speed of the mixer is 3000 r / min and the revolution speed is 70 r / min. The solvent is N-methylpyrrolidone (NMP).

[0048] Step 2: Add CDC@TiO2 to the first solution. Under vacuum, in a dual planetary mixer with ultrasonic oscillation function, simultaneously sonicate and stir for 40 minutes until uniformly mixed to obtain a slurry. The rotation speed of the stirrer is 3000 r / min and the revolution speed is 50 r / min. The ultrasonic frequency is 5 kHz. The vacuum degree of the vacuum environment is 0.06 kPa. By mass, the ratio of CDC@TiO2, polyvinylidene fluoride (PVDF) and solvent is 25:5:70. CDC@TiO2 includes porous carbide-derived carbon (CDC) and titanium dioxide supported on porous carbide-derived carbon (CDC).

[0049] The method for preparing CDC@TiO2 includes: first, mixing tetrabutyl titanate and ethanol until homogeneous, then adding porous carbide-derived carbon (CDC), stirring at 500 rpm at room temperature for 30 min until homogeneous, then allowing to stand at 70℃ for 2 h to remove ethanol, transferring to a quartz tube, and annealing at 600℃ for 2 h under an argon atmosphere to obtain CDC@TiO2. The mass ratio of porous carbide-derived carbon to tetrabutyl titanate is 20:60, and the mass ratio of porous carbide-derived carbon to ethanol is 20:20. The method for preparing the porous carbide-derived carbon includes: transferring micron-sized metal carbides (micron-sized metal carbides are titanium carbide powder, 200-300 mesh) through graphite paper to a quartz tube furnace, evacuating to 0.01 kPa, introducing argon gas, and annealing at 15℃ for 2 min under an argon atmosphere. -1 The temperature was increased at a rate of 1000℃, at which point the argon gas flow was stopped and chlorine gas was introduced for chlorine etching (chlorine gas flow rate was 40 mL / min). Chlorine etching was performed for 120 min, then the chlorine gas flow was stopped and argon gas was introduced again to remove residual gaseous impurities. The mixture was cooled to room temperature under an argon atmosphere to obtain a porous carbide-derived carbon (CDC) precursor. Under a hydrogen (H2) atmosphere, the porous carbide-derived carbon (CDC) precursor was annealed at 600℃ for 1 h to remove residual chlorides on the surface and inside the pores. After grinding, powdered porous carbide-derived carbon (CDC) was obtained. The particle size of the porous carbide-derived carbon was D50 = 0.125 μm, D90 = 0.506 μm, and the specific surface area was 2367 m². 2 / g, with a porosity of 44.6%.

[0050] Example 2

[0051] A method for preparing a slurry includes the following steps:

[0052] Step 1: Mix the solvent and polyvinylidene fluoride (PVDF) in a double planetary mixer and stir for 30 minutes until homogeneous to obtain the first solution. The rotation speed of the mixer is 2000 r / min and the revolution speed is 50 r / min. The solvent is N-methylpyrrolidone (NMP).

[0053] Step 2: Add CDC@TiO2 to the first solution. Under vacuum, in a dual planetary mixer with ultrasonic oscillation function, simultaneously sonicate and stir for 30 minutes until uniformly mixed to obtain a slurry. The rotation speed of the stirrer is 2500 r / min and the revolution speed is 40 r / min. The ultrasonic frequency is 5 kHz. The vacuum degree of the vacuum environment is 0.06 kPa. By mass, the ratio of CDC@TiO2, polyvinylidene fluoride (PVDF) and solvent is 30:6:64. CDC@TiO2 includes porous carbide-derived carbon (CDC) and titanium dioxide supported on porous carbide-derived carbon (CDC).

[0054] The method for preparing CDC@TiO2 includes: first, mixing tetrabutyl titanate and ethanol until homogeneous, then adding porous carbide-derived carbon (CDC), stirring at 800 rpm at room temperature for 45 min until homogeneous, then allowing to stand at 70℃ for 2 h to remove ethanol, transferring to a quartz tube, and annealing at 600℃ for 2 h under an argon atmosphere to obtain CDC@TiO2. The mass ratio of porous carbide-derived carbon to tetrabutyl titanate is 25:60, and the mass ratio of porous carbide-derived carbon to ethanol is 25:15. The method for preparing the porous carbide-derived carbon includes: transferring micron-sized metal carbides (micron-sized metal carbides are titanium carbide powder, 200-300 mesh) through graphite paper to a quartz tube furnace, evacuating to 0.02 kPa, introducing argon gas, and annealing at 15℃ for 2 min under an argon atmosphere. -1 The temperature was increased at a rate of 900℃, at which point the argon gas flow was stopped and chlorine gas was introduced for chlorine etching (chlorine gas flow rate was 40 mL / min). Chlorine etching was performed for 100 min, then the chlorine gas flow was stopped and argon gas was introduced again to remove residual gaseous impurities. The mixture was cooled to room temperature under an argon atmosphere to obtain a porous carbide-derived carbon (CDC) precursor. Under a hydrogen (H2) atmosphere, the porous carbide-derived carbon (CDC) precursor was annealed at 550℃ for 1 h to remove residual chlorides on the surface and inside the pores. After grinding, powdered porous carbide-derived carbon (CDC) was obtained. The particle size of the porous carbide-derived carbon was D50 = 0.205 μm, D90 = 0.496 μm, and the specific surface area was 2307 m². 2 / g, with a porosity of 43.8%.

[0055] Example 3

[0056] A method for preparing a slurry includes the following steps:

[0057] Step 1: Mix the solvent and polyvinylidene fluoride (PVDF) in a double planetary mixer and stir for 35 minutes until homogeneous to obtain the first solution. The rotation speed of the mixer is 2800 r / min and the revolution speed is 60 r / min. The solvent is N-methylpyrrolidone (NMP).

[0058] Step 2: Add CDC@TiO2 to the first solution. Under vacuum, in a dual planetary mixer with ultrasonic oscillation function, simultaneously sonicate and stir for 35 minutes until uniformly mixed to obtain a slurry. The rotation speed of the stirrer is 2000 r / min and the revolution speed is 40 r / min. The ultrasonic frequency is 5 kHz. The vacuum degree of the vacuum environment is 0.06 kPa. By mass, the ratio of CDC@TiO2, polyvinylidene fluoride (PVDF) and solvent is 36:9:55. CDC@TiO2 includes porous carbide-derived carbon (CDC) and titanium dioxide supported on porous carbide-derived carbon (CDC).

[0059] The method for preparing CDC@TiO2 includes: first, mixing tetrabutyl titanate and ethanol until homogeneous, then adding porous carbide-derived carbon (CDC), stirring at 1000 rpm at room temperature for 60 min until homogeneous, then allowing to stand at 70℃ for 2 h to remove ethanol, transferring to a quartz tube, and annealing at 600℃ for 2 h under an argon atmosphere to obtain CDC@TiO2. The mass ratio of porous carbide-derived carbon to tetrabutyl titanate is 30:50, and the mass ratio of porous carbide-derived carbon to ethanol is 30:20. The method for preparing the porous carbide-derived carbon includes: transferring micron-sized metal carbides (micron-sized metal carbides are titanium carbide powder, 200-300 mesh) through graphite paper to a quartz tube furnace, evacuating to 0.03 kPa, introducing argon gas, and annealing at 15℃ for 2 min under an argon atmosphere. -1 The temperature was increased at a rate of 950℃, at which point the argon gas flow was stopped and chlorine gas was introduced for chlorine etching (chlorine gas flow rate was 40 mL / min). Chlorine etching was performed for 110 min, then the chlorine gas flow was stopped and argon gas was introduced again to remove residual gaseous impurities. The mixture was cooled to room temperature under an argon atmosphere to obtain a porous carbide-derived carbon (CDC) precursor. Under a hydrogen (H2) atmosphere, the porous carbide-derived carbon (CDC) precursor was annealed at 650℃ for 1.5 h to remove residual chlorides on the surface and inside the pores. After grinding, powdered porous carbide-derived carbon (CDC) was obtained. The particle size of the porous carbide-derived carbon was D50 = 0.189 μm, D90 = 0.566 μm, and the specific surface area was 2297 m². 2 / g, with a porosity of 45.2%.

[0060] Comparative Example 1

[0061] A method for preparing a slurry includes the following steps:

[0062] Step 1: Mix N-methylpyrrolidone (NMP) and PVDF in a double planetary mixer and stir for 30 min until homogeneous to obtain solution A. The rotation speed of the mixer is 2700 r / min and the revolution speed is 55 r / min.

[0063] Step 2: Add the porous carbide-derived carbon (CDC) prepared in Example 1 to solution A. Under vacuum, in a dual planetary mixer with ultrasonic oscillation function, simultaneously sonicate and stir for 35 minutes until uniformly mixed to obtain a slurry. The rotation speed of the stirrer is 2000 r / min, the revolution speed is 40 r / min, the ultrasonic frequency is 5 kHz, the vacuum degree of the vacuum environment is 0.06 kPa, and the ratio of porous carbide-derived carbon (CDC), PVDF and NMP by mass is 30:5:65.

[0064] Comparative Example 2

[0065] A method for preparing a slurry is essentially the same as Comparative Example 1, except that "porous carbide-derived carbon (CDC)" is replaced with "titanium carbide powder". The titanium carbide powder has a mesh size of 200-300 mesh.

[0066] Examples 4-6 and Comparative Examples 3-4

[0067] A method for preparing a lithium-sulfur battery includes: encapsulating a positive electrode, a negative electrode, an electrolyte, and a separator to obtain a soft-pack battery with an area of ​​10cm × 10cm and a thickness of 3mm. The positive electrode material is lithium iron phosphate (powder), the negative electrode material is graphite, and the electrolyte is a mixture of electrolyte and solvent. The electrolyte is lithium hexafluorophosphate (LiPF6), and the solvent is a mixture of ethylene carbonate and dimethyl carbonate. The electrolyte concentration is 1.0M, and the volume ratio of ethylene carbonate to dimethyl carbonate is 1:1. The method for preparing the separator includes: placing a base membrane on a coating machine containing slurry, coating one side of the base membrane with the slurry at a speed of 20m / min, drawing it into a drying device via a traction roller, and drying it at 60°C for 3min to obtain a coating on the base membrane, thus obtaining the separator. The slurry is one of Examples 1-3 and Comparative Examples 1-2.

[0068] Table 1

[0069] Lithium-sulfur batteries The slurry used to prepare the diaphragm Example 4 Example 1 Example 5 Example 2 Example 6 Example 3 Comparative Example 3 Comparative Example 1 Comparative Example 4 Comparative Example 2

[0070] The parameters of the diaphragm prepared from the slurry of Example 1 are as follows:

[0071]

[0072] The parameters of the diaphragm prepared from the slurry of Example 2 are as follows:

[0073]

[0074] The parameters of the diaphragm prepared from the slurry of Example 3 are as follows:

[0075]

[0076]

[0077] The parameters of the diaphragm prepared from the slurry of Comparative Example 1 are as follows:

[0078]

[0079] The parameters of the diaphragm prepared from the slurry of Comparative Example 2 are as follows:

[0080]

[0081] At a current density of 0.2C, the lithium-sulfur battery prepared in Example 4 retained a capacity of 90.8% after 100 cycles, the lithium-sulfur battery prepared in Example 5 retained a capacity of 92.3% after 100 cycles, the lithium-sulfur battery prepared in Example 6 retained a capacity of 91.2% after 100 cycles, the lithium-sulfur battery prepared in Comparative Example 3 retained a capacity of 70.2% after 100 cycles, and the lithium-sulfur battery prepared in Comparative Example 4 retained a capacity of 60.5% after 100 cycles.

[0082] Figure 1 XRD of the porous carbide-derived carbon (CDC) obtained in Example 1, by Figure 1 As can be seen in the XRD pattern, a broad diffuse peak appears between 20° and 23°, representing the presence of short-range ordered regions within the material. This is a typical diffraction peak of amorphous carbon, proving the successful preparation of porous carbide-derived carbon (CDC).

[0083] Figure 2 The TEM of CDC@TiO2 obtained in Example 1 was prepared by... Figure 2 It can be seen that TiO2 is loaded on porous carbide-derived carbon (CDC).

[0084] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A lithium-sulfur battery separator with a porous carbon-based composite material coating, characterized in that, include: The base film and the coating on the base film, the coating comprising: CDC@TiO2 and polyvinylidene fluoride, the ratio of CDC@TiO2 to polyvinylidene fluoride by mass is (25~36):(5~9), wherein the CDC@TiO2 comprises porous carbide-derived carbon and titanium dioxide supported on the porous carbide-derived carbon; the method for preparing CDC@TiO2 comprises: mixing tetrabutyl titanate, ethanol and porous carbide-derived carbon, stirring until uniform, then standing at 60~70℃ for 2~3h, and annealing at 600~800℃ for 2~4h under an inert gas atmosphere to obtain CDC@TiO2, the ratio of porous carbide-derived carbon to tetrabutyl titanate by mass is (20~30):(50~60), wherein the porous carbide-derived carbon is the skeletal carbon structure remaining after removing titanium atoms from titanium carbide under chlorine etching.

2. The lithium-sulfur battery separator with a porous carbon-based composite material coating according to claim 1, characterized in that, The ratio of porous carbide-derived carbon to ethanol by mass parts is (20~30):(10~20).

3. The lithium-sulfur battery separator with a porous carbon-based composite material coating according to claim 1, characterized in that, The porous carbide-derived carbon has a particle size of D50 = 0.1~0.3μm, D90 = 0.4~0.8μm, and a specific surface area of ​​2000~2500m². 2 / g, with a porosity of 40~50%.

4. The method for preparing a lithium-sulfur battery separator with a porous carbon-based composite material coating as described in any one of claims 1 to 3, characterized in that, include: The slurry is coated onto a base film and dried to obtain a coating on the base film, resulting in a lithium-sulfur battery separator with a porous carbon-based composite material coating. The slurry comprises CDC@TiO2, polyvinylidene fluoride, and solvent. By mass, the ratio of CDC@TiO2, polyvinylidene fluoride, and solvent is (25~36):(5~9):(50~70). The CDC@TiO2 comprises porous carbide-derived carbon and titanium dioxide supported on the porous carbide-derived carbon.

5. The preparation method according to claim 4, characterized in that, The solvent is N-methylpyrrolidone.

6. The preparation method according to claim 4, characterized in that, The method for preparing the slurry includes: mixing CDC@TiO2, polyvinylidene fluoride and solvent until homogeneous to obtain the slurry.

Images