Composite membrane and its preparation method and application

Abstract

The present invention discloses a composite membrane and its preparation method and application. The composite membrane includes a carbon fiber membrane and nitride particles. The nitride particles are distributed on the surface of the carbon fiber membrane, and the nitride particles are non-stoichiometric nitrides. The preparation method comprises the following steps: (1) preparing or using an existing carbon fiber membrane for standby use; (2) immersing the carbon fiber membrane in a ferrous sulfate solution and treating it at high temperature for a set time under a nitrogen atmosphere to obtain a composite membrane. The composite membrane of the present invention can adsorb polysulfides based on the high active sites of the non-stoichiometric nitride and improve the kinetics of the polysulfide phase conversion reaction. When applied to lithium-sulfur batteries, it can inhibit the diffusion of polysulfides to the negative electrode, improve the utilization rate of active materials and the electrochemical performance of the battery, and the preparation method is simple to operate, the reaction is mild and controllable, and it is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a composite film and a preparation method and application thereof. Background Art

[0002] With the rapid development of portable electronic devices and electric vehicles, people's demand for high energy density and high points is becoming increasingly urgent. Lithium-sulfur secondary batteries have a theoretical energy density of 2600Wh / kg, far exceeding commercial lithium batteries, and are considered to be very promising next-generation high-energy storage systems. The charging and discharging process of lithium-sulfur batteries involves multiple electron transfers and multi-phase transitions, which give them high energy density, but also bring a series of problems that restrict their commercial application. Among them, the "shuttle effect" of soluble intermediates and slow reaction kinetics in the electrochemical reaction of lithium-sulfur batteries lead to low utilization of active materials and capacity attenuation.

[0003] Adding a series of nitrides (VN, TiN, NbN, Fe2N) to lithium-sulfur battery electrodes improves the sulfur electrode. Polar nitrides effectively adsorb polysulfides during the electrochemical reaction, which is an effective way to achieve high-performance lithium-sulfur batteries. However, most nitrides are prepared using ammonia reduction, which is a complex process. Furthermore, non-stoichiometric nitrides provide more defects, creating active sites, which helps further improve the electrochemical reaction kinetics of the sulfur electrode. However, excessive inorganic filler content in the composite membrane affects the film quality. Optimizing the preparation process of functionalized composite membranes for lithium-sulfur batteries is particularly important. Summary of the Invention

[0004] The present invention provides a composite film and a preparation method and application thereof, which are used to solve the current technical problems of low utilization rate of active materials and severe capacity attenuation in lithium-sulfur batteries.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A composite membrane comprises a carbon fiber membrane and nitride particles, with the nitride particles distributed on the surface of the carbon fiber membrane; the nitride particles are non-stoichiometric nitrides. Non-stoichiometric compounds are a common crystal structure defect that can expose more active sites. By introducing a non-stoichiometric nitride catalyst into a lithium-sulfur battery, the present invention can both adsorb polysulfides and catalyze their rapid conversion, providing an effective approach to achieving high-performance lithium-sulfur batteries.

[0007] As a further preferred embodiment of the above technical solution, the mass of the nitride particles is 3% to 30% of the mass of the composite film.

[0008] As a further preferred embodiment of the above technical solution, the nitride particles are FeN 0.0324 .

[0009] Based on the same technical concept, the present invention also provides a method for preparing the composite membrane of the above technical solution, comprising the following steps:

[0010] (1) preparing or using an existing carbon fiber membrane for use;

[0011] (2) The carbon fiber membrane is immersed in a ferrous sulfate solution and treated at high temperature for a set time under a nitrogen atmosphere to obtain a composite membrane.

[0012] As a further preferred embodiment of the above technical solution, the concentration of the ferrous sulfate solution is 100-500 mg / mL. 0.0324 When the concentration of ferrous sulfate is too low, FeN 0.0324 The content of FeN in the composite membrane is low, which has little effect on the electrochemical performance of the membrane electrode. 0.0324 The high content in the composite membrane makes the membrane electrode brittle and has poor processing performance.

[0013] As a further preferred embodiment of the above technical solution, the temperature of the high temperature treatment in step (2) is 1000-1300°C and the treatment time is 2-5 hours. 0.0324 When the heat treatment temperature is too low and the treatment time is too short, the composite film has not yet formed FeN 0.0324 When the heat treatment temperature is too high and the heat treatment time is too long, Fe3C or elemental Fe impurity phase generated by carbothermal reduction is formed.

[0014] As a further preferred embodiment of the above technical solution, the carbon fiber membrane is prepared by the following steps:

[0015] (1) mixing carbon fiber with nitric acid, reacting for a set time, and then performing post-treatment to obtain acidified carbon fiber;

[0016] (2) The acidified carbon fibers are dispersed in a Triton X-100 solution to obtain a carbon fiber dispersion, and the carbon fiber dispersion is vacuum filtered to obtain a carbon fiber membrane.

[0017] As a further preferred embodiment of the above technical solution, in step (1), the ratio of carbon fiber to nitric acid is 5 to 15 mg / mL.

[0018] As a further preferred embodiment of the above technical solution, in step (1), the reaction temperature of the carbon fiber and nitric acid is 30-70° C., and the reaction time is 2-5 h.

[0019] As a further preferred embodiment of the above technical solution, the post-processing of step (1) includes centrifugation, washing and drying operations.

[0020] As a further preferred embodiment of the above technical solution, the mass concentration of the carbon fiber dispersion in step (2) is 1 to 5 mg / mL.

[0021] As a further preferred embodiment of the above technical solution, the concentration of the Triton X-100 solution in step (2) is 1 to 5 wt%.

[0022] Based on the same technical concept, the present invention also provides an application of the composite membrane of the above technical solution or the composite membrane prepared by the above preparation method, and the composite membrane is used as an electrode current collector in a lithium-sulfur battery.

[0023] As a further preference of the above technical solution, the preparation method of the lithium-sulfur battery is: using a lithium sheet as the negative electrode, polypropylene as the separator, and a 1 mol / L solution of 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1) of lithium polysulfide as the electrode active material, adding the electrode active material dropwise onto the composite membrane current collector, adding the electrolyte, and assembling to obtain a lithium-sulfur battery.

[0024] As a further preferred embodiment of the above technical solution, the lithium polysulfide is a Li2S6 solution; the electrolyte is a 1 mol / L lithium bis(trifluoromethanesulfonyl)imide and 2 wt% LiNO3 solution of 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1).

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] (1) The composite membrane of the present invention can adsorb polysulfides based on the high active sites of polar non-stoichiometric nitrides and improve the kinetics of polysulfide phase conversion reactions. When applied to lithium-sulfur batteries, it can inhibit the diffusion of polysulfides to the negative electrode, thereby improving the utilization rate of active materials and the electrochemical performance of the battery.

[0027] (2) The preparation method of the present invention is simple to operate, the reaction is mild and controllable, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the electrochemical cycle performance diagram of the comparative example;

[0029] Figure 2 is the XRD pattern of the composite film of Example 1;

[0030] Figure 3 is a SEM image of the composite membrane of Example 1;

[0031] Figure 4 This is the electrochemical cycle performance diagram of Example 1;

[0032] Figure 5 This is the electrochemical cycle performance diagram of Example 2;

[0033] Figure 6 The electrochemical rate performance diagrams of the comparative example, embodiment 1 and embodiment 2 are shown. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1:

[0036] The composite membrane of this embodiment includes a carbon fiber membrane and nitride particles. The nitride particles are FeN 0.0324 The content of the nitride particles is 3% of the total mass of the composite film, and the nitride particles are distributed on the surface of the carbon fiber film.

[0037] The method for preparing the composite membrane of this embodiment comprises the following steps:

[0038] (1) Carbon fibers were mixed with a nitric acid solution (12.5 mg / mL), stirred at 50°C for 5 hours, centrifuged, washed, and dried to obtain acidified carbon fibers.

[0039] (2) The acidified carbon fibers were dispersed in a 2 wt % Triton X-100 solution to obtain a carbon fiber dispersion, wherein the mass concentration of the carbon fibers in the carbon fiber dispersion was 2 mg / mL. After ultrasonic dispersion, the carbon fiber membrane was prepared by vacuum filtration.

[0040] (3) The prepared carbon fiber membrane was immersed in a 200 mg / mL ferrous sulfate solution and heat-treated at 1200°C for 3 hours under a nitrogen atmosphere to obtain a composite membrane; Figure 2 The XRD pattern of the prepared composite film was compared with FeN 0.0324 By comparing with the standard JCPDS card, it can be seen that FeN was successfully prepared in this example. 0.0324 / Carbon fiber composite materials, Figure 3 The SEM image of the prepared composite film shows that FeN 0.0324 Nanoparticles are dispersed on the surface of carbon fibers.

[0041] The composite film of this embodiment or the composite film prepared in this embodiment is used as the current collector of the lithium-sulfur battery electrode, the lithium sheet is used as the negative electrode, and the polypropylene is used as the separator to assemble a lithium-sulfur battery. A 1mol / LLi2S6 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1) solution is used as the active material. First, 30μL of the active material solution is dripped on the surface of the current collector, and then 15μL of the electrolyte is added. The composition of the added electrolyte is 1mol / L lithium bis(trifluoromethanesulfonyl)imide and 2wt% LiNO3 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1) solution. The sulfur loading in the positive electrode of the prepared lithium-sulfur battery is 4.8mg. The electrochemical cycle performance test of the lithium-sulfur battery is carried out at 0.2C, and the results are as follows Figure 4As shown, the initial discharge capacity is 867 mAh / g, and after 200 cycles, 743 mAh / g remains, with a capacity retention rate of 85.7%.

[0042] Example 2:

[0043] The composite membrane of this embodiment includes a carbon fiber membrane and nitride particles. The nitride particles are FeN 0.0324 The content of the nitride particles is 20% of the total mass of the composite film, and the nitride particles are distributed on the surface of the carbon fiber film.

[0044] The method for preparing the composite membrane of this embodiment comprises the following steps:

[0045] (1) Carbon fibers were mixed with a nitric acid solution (12.5 mg / mL), stirred at 50°C for 5 hours, centrifuged, washed, and dried to obtain acidified carbon fibers.

[0046] (2) The acidified carbon fibers were dispersed in a 5 wt % Triton X-100 solution to obtain a carbon fiber dispersion, wherein the mass concentration of the carbon fibers in the carbon fiber dispersion was 5 mg / mL. After ultrasonic dispersion, the carbon fiber membrane was prepared by vacuum filtration.

[0047] (3) The prepared carbon fiber membrane was immersed in a 500 mg / mL ferrous sulfate solution and heat treated at 1300°C for 5 hours under a nitrogen atmosphere to obtain a composite membrane;

[0048] The composite film of this embodiment or the composite film prepared in this embodiment is used as the current collector of the lithium-sulfur battery electrode, the lithium sheet is used as the negative electrode, and the polypropylene is used as the separator to assemble a lithium-sulfur battery. A 1mol / LLi2S6 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1) solution is used as the active material. First, 30μL of the active material solution is dripped on the surface of the current collector, and then 15μL of the electrolyte is added. The composition of the added electrolyte is 1mol / L lithium bis(trifluoromethanesulfonyl)imide and 2wt% LiNO3 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1) solution. The sulfur loading in the positive electrode of the prepared lithium-sulfur battery is 4.8mg. The electrochemical cycle performance test of the lithium-sulfur battery is carried out at 0.2C, and the results are as follows Figure 5 As shown, the initial discharge capacity is 851 mAh / g, and after 200 cycles, 750 mAh / g remains, with a capacity retention rate of 88.1%.

[0049] Comparative Example:

[0050] The preparation of the carbon fiber membrane of this comparative example comprises the following steps:

[0051] (1) Carbon fibers were mixed with a nitric acid solution (12.5 mg / mL), stirred at 50°C for 5 hours, centrifuged, washed, and dried to obtain acidified carbon fibers.

[0052] (2) The acidified carbon fibers were dispersed in a 2 wt % Triton X-100 solution with a carbon fiber mass concentration of 2 mg / mL. After ultrasonic dispersion, the carbon fiber membrane was prepared by vacuum filtration.

[0053] (3) The prepared carbon fiber film is used as the current collector of the lithium-sulfur battery electrode, the lithium sheet is used as the negative electrode, and the polypropylene separator is used. A lithium-sulfur battery is assembled. A 1 mol / L Li2S6 solution of 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1) is used as the active material. First, 30 μL of the active material solution is dripped onto the surface of the current collector, and then 15 μL of the electrolyte is added. The composition of the added electrolyte is 1 mol / L lithium bis(trifluoromethanesulfonyl)imide and 2 wt% LiNO3 solution of 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1). The sulfur loading in the positive electrode of the prepared lithium-sulfur battery is 4.8 mg.

[0054] (4) Figure 1 The electrochemical cycle performance of the lithium-sulfur battery assembled in this comparative example at 0.2C is shown. It can be seen that the prepared lithium-sulfur battery has an initial discharge capacity of 657 mAh / g, and 483 mAh / g remains after 200 cycles, with a capacity retention rate of 73.5%.

[0055] Figure 6 The results show that the rate performance of the lithium-sulfur battery prepared by the present invention is 0.0324 / Carbon fiber composite membrane is used in lithium-sulfur batteries, which can accelerate the conversion rate of lithium polysulfide, and is beneficial to improving the cycle stability and rate performance of lithium-sulfur batteries.

[0056] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A method for preparing a composite film, characterized in that: The composite film includes a carbon fiber film and nitride particles, wherein the nitride particles are distributed on the surface of the carbon fiber film; the nitride particles are non-stoichiometric nitrides; the nitride particles are FeN 0 .0324 The mass of the nitride particles is 3% to 30% of the mass of the composite film; the composite film is used as an electrode current collector in a lithium-sulfur battery; the preparation method of the composite film comprises the following steps: (1) preparing or using an existing carbon fiber membrane for use; (2) Immersing the carbon fiber membrane in a ferrous sulfate solution and subjecting it to high-temperature treatment for a set time under a nitrogen atmosphere to obtain the composite membrane; the temperature of the high-temperature treatment is 1000-1300° C., the treatment time is 2-5 h; and the concentration of the ferrous sulfate solution is 100-500 mg / mL.

2. The method for preparing a composite film according to claim 1, wherein The carbon fiber film is prepared by the following steps: (1) mixing carbon fiber with concentrated nitric acid, reacting for a set time, and then performing post-treatment to obtain acidified carbon fiber; (2) dispersing the acidified carbon fiber in a Triton X-100 solution to obtain a carbon fiber dispersion, and vacuum filtering the carbon fiber dispersion to obtain the carbon fiber membrane.

3. The method for preparing a composite film according to claim 2, wherein: The ratio of the carbon fiber to nitric acid is 5-15 mg / mL, and the mass concentration of the carbon fiber dispersion is 1-5 mg / mL.

4. The method for preparing a composite film according to claim 2, wherein: The concentration of the Triton X-100 solution is 1-5 wt%.

Images