Preparation method and application of CuS / CNT film lithium-sulfur battery interlayer

Abstract

The invention discloses a preparation method and application of a CuS / CNT film lithium-sulfur battery intermediate layer. Comprising the following steps: step 1, providing a first CNT film as an upper sheet; providing a second CNT film as a lower sheet; the preparation method comprises the following steps: adding CuS nanoparticles into absolute ethyl alcohol, and ultrasonically dispersing uniformly to obtain CuS suspension liquid; 2, loading the CuS suspension to the surface of the lower piece through a sand core suction filtration device, and drying to obtain a CuS loading layer; and 3, in a vacuum environment, placing the CuS load layer between the two electrodes to form electric connection, arranging the upper sheet and the CuS load layer at an interval, and electrifying and heating to obtain the CuS / CNT intermediate layer film. The method has the beneficial effects that the process is simple, the consumed time is short (only several seconds are needed), the cost is low, and complex equipment is not needed; in addition, the interlayer film can effectively improve the electrochemical performance of the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and specifically, relates to a preparation method and application of an intermediate layer of a CuS / CNT thin film lithium-sulfur battery. Background Art

[0002] With the continuous growth of global energy demand and the increasing prominence of environmental problems, the development of new energy storage systems with high energy density and environmental friendliness has become a research hotspot. Lithium-sulfur batteries are regarded as potential next-generation energy storage devices due to their extremely high theoretical specific capacity (1675 mAh / g) and specific energy (2600 Wh / kg), far exceeding those of traditional lithium-ion batteries (for example, the theoretical specific capacity of lithium cobalt oxide batteries is only about 150 mAh / g), and at the same time, sulfur resources are abundant, the cost is low, and it is environmentally friendly.

[0003] However, the practical application of lithium-sulfur batteries still faces many challenges: both elemental sulfur and its discharge products (Li2S2 / Li2S) are electronic insulators, resulting in low utilization rate of active materials, and a large amount of conductive agents need to be added, thereby reducing the energy density of the battery; sulfur undergoes significant volume changes (about 80%) during charge and discharge, easily damaging the structural stability of the electrode; the intermediate product soluble polysulfide (LiPSs) diffuses in the electrolyte, causing loss of active materials, capacity attenuation, and reduction of Coulomb efficiency; metallic lithium is prone to side reactions with the electrolyte, forming a passivation layer and consuming the electrolyte, and at the same time, the growth of lithium dendrites may cause safety hazards; electrolyte salts such as LiTFSI will oxidize the sulfur cathode, generating irreversible products Li2SO4, further reducing the battery performance.

[0004] To solve the above problems, attempts have been made to modify the cathode, separator or intermediate layer in the prior art. For example, MoO2 / carbon nanotube composite fiber electrodes were prepared by electrochemical deposition combined with high-temperature calcination (600 °C, 4 h, N2 atmosphere) to enhance conductivity and adsorb polysulfides; Co3O4 / carbon nanotube thin films were synthesized by hydrothermal method (140 °C, 24 h) and their catalytic effect was used to inhibit the shuttle effect; however, these methods generally have problems such as complex processes, high energy consumption, and difficulty in large-scale production, especially the preparation of the intermediate layer often relies on high-cost and long-cycle nanomaterial synthesis technologies.

[0005] Therefore, to solve the above problems, the present invention provides a preparation method and application of an intermediate layer of a CuS / CNT thin film lithium-sulfur battery. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provides a preparation method and application of an intermediate layer of a CuS / CNT thin film lithium-sulfur battery.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A preparation method for the intermediate layer of a CuS / CNT thin film lithium-sulfur battery, comprising the following steps:

[0009] Step 1: (1) Provide a first CNT thin film as the upper sheet; provide a second CNT thin film as the lower sheet; (2) Add CuS nanoparticles to absolute ethanol and ultrasonically disperse them evenly to obtain a CuS suspension;

[0010] Step 2: Load the CuS suspension onto the surface of the lower sheet through a fritted filter device and dry it to obtain a CuS loaded layer;

[0011] Step 3: Under a vacuum environment, place the CuS loaded layer between two electrodes to form an electrical connection, and at the same time, arrange the upper sheet parallel above it and heat it by passing an electric current to obtain a CuS / CNT intermediate layer thin film.

[0012] More optimally, the technical features of the upper sheet include: a thickness of 10 μm and a size of 4 cm × 2 cm; the technical features of the lower sheet include: a thickness of 20 μm and a size of 3.5 cm × 1.5 cm.

[0013] More optimally, the dosage ratio of the CuS nanoparticles to absolute ethanol is (10 - 50) mg: 20 mL.

[0014] More optimally, the parallel setting distance between the upper sheet and the CuS loaded layer is 5 mm.

[0015] More optimally, the process parameters of the heating include: a temperature of 750 - 1150 °C and a time of 1 - 5 s.

[0016] More optimally, the CuS / CNT intermediate layer thin film can be applied to the intermediate layer of a lithium-sulfur battery.

[0017] Beneficial effects:

[0018] In the present invention, after dispersing the CuS nanoparticles, they are suction filtered onto the CNT thin film, and the CuS is rapidly evaporated by Joule heat and deposited on the surface of another CNT thin film to form a uniform intermediate layer thin film; this method has a simple process, short time consumption (only a few seconds), low cost, and does not require complex equipment; in addition, this intermediate layer thin film can effectively improve the electrochemical performance of the lithium-sulfur battery. Specifically as follows:

[0019] First: In the solution, the CuS / CNT intermediate layer film is prepared by the Joule heating method, which has significant process advantages. First of all, this method greatly simplifies the traditional preparation process, avoids complex chemical treatment steps, and realizes the rapid and efficient preparation of the film. Secondly, the Joule heating method has simple equipment requirements, does not require the use of expensive instruments or a large amount of chemical reagents, effectively reduces the production cost, and provides the possibility for large-scale industrial production. Most importantly, this method has extremely high preparation efficiency, and the whole process from the evaporation of material particles to film formation can be completed in only a few seconds, with a significant speed increase compared to traditional film-making methods.

[0020] Second: The rich active sites and strong polar characteristics on the surface of the CuS / CNT intermediate layer film enable it to efficiently and selectively adsorb various polysulfides, which not only improves the adsorption efficiency but also effectively improves the overall performance of the battery, enabling it to maintain excellent initial discharge capacity and rate performance even under high current density conditions.

[0021] Third: The synergistic effect between CuS nanoparticles and the CNT network forms dual advantages. On the one hand, CNT provides excellent conductive paths, and on the other hand, CuS provides sufficient catalytic active sites, jointly promoting the rapid conversion of polysulfides and significantly enhancing the reaction kinetics performance of the battery. At the same time, the thermal stability and mechanical strength of the CNT material itself effectively reduce the self-discharge rate of the battery, and the introduction of CuS further enhances the structural stability of the film in high-temperature environments, thus ensuring the reliability of the long-term cycle of the battery. Brief Description of the Drawings

[0022] The present invention will be further described below with reference to the drawings.

[0023] Figure 1 is the preparation process of the CuS / CNT intermediate layer lithium-sulfur battery of the present invention;

[0024] Figure 2 is the flowchart of the preparation of the CuS / CNT intermediate layer film of the present invention;

[0025] Figure 3 is the scanning electron microscope image of the CuS / CNT intermediate layer film A prepared in Example 1;

[0026] Figure 4 is the scanning electron microscope image of the CuS / CNT intermediate layer film B prepared in Example 2;

[0027] Figure 5 is the scanning electron microscope image of the CuS / CNT intermediate layer film C prepared in Example 3;

[0028] Figure 6 is the scanning electron microscope image of the CuS / CNT intermediate layer film D prepared in Example 4;

[0029] Figure 7 (a-c) are transmission electron microscope images of the CuS / CNT intermediate layer film C prepared in Example 3;

[0030] Figure 7 (d-e) are the corresponding element distributions of the CuS / CNT intermediate layer film C prepared in Example 3;

[0031] Figure 8 is the X-ray photoelectron spectroscopy diagram of the CuS / CNT intermediate layer film C prepared in Example 3;

[0032] Figure 9 is the CV curve of the lithium-sulfur battery assembled with the CuS / CNT intermediate layer film C prepared in Example 3 at a scanning rate of 0.4 mVs-1;

[0033] Figure 10 is the impedance diagram of the lithium-sulfur battery assembled with the CuS / CNT intermediate layer film C prepared in Example 3 and the lithium-sulfur battery without an intermediate layer film prepared in the comparative example;

[0034] Figure 11 is the charge-discharge curve of the lithium-sulfur battery assembled with the CuS / CNT intermediate layer film C prepared in Example 3;

[0035] Figure 12 is the rate performance test diagram of the lithium-sulfur battery assembled with the CuS / CNT intermediate layer film C prepared in Example 3 and the lithium-sulfur battery without an intermediate layer film prepared in the comparative example;

[0036] Figure 13 is the cycle performance test diagram of the lithium-sulfur battery assembled with the CuS / CNT intermediate layer film C prepared in Example 3. Detailed implementation mode

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the protection scope of the present invention.

[0038] Example 1: A preparation method for an intermediate layer of a CuS / CNT thin film lithium-sulfur battery includes the following steps:

[0039] The 10-μm-thick CNT film was cut into a size of 4×2 cm as the upper sheet, and the 20-μm-thick CNT film was cut into a size of 3.5×1.5 cm as the lower sheet. 20 mg of CuS nanoparticles were dispersed in 20 ml of absolute ethanol and ultrasonicated to form a homogeneous suspension. The suspension was uniformly deposited on the surface of the lower CNT film through a fritted filter device. After the film was dried, the lower sheet was placed between the two electrodes of the Joule heating chamber and fixed and connected with conductive silver paste. Subsequently, the upper sheet was placed parallel 5 mm above the lower sheet, and the whole system was placed in a high vacuum environment of 10 -2 Pa. A constant voltage of 20 V was applied for 1 second, so that the surface temperature of the CNT film rapidly rose to 750 °C. At this time, the CuS particles on the lower sheet instantly evaporated and were uniformly deposited on the lower surface of the upper CNT film, and finally the CuS / CNT intermediate layer film A was prepared; as Figure 2 shown.

[0040] Example 2: A method for preparing an intermediate layer of a CuS / CNT thin film lithium-sulfur battery, comprising the following steps:

[0041] The same CNT film cutting size as in Example 1 was used. 30 mg of CuS nanoparticles were dispersed in 20 ml of absolute ethanol and ultrasonicated to obtain a homogeneous suspension. The CuS suspension was uniformly loaded on the lower CNT film through a fritted filter. After drying, the lower sheet was installed between the two electrodes of the Joule heating device and connected with conductive silver paste. The upper sheet was placed parallel 5 mm above the lower sheet, and the system was evacuated to 10 -2 Pa. A constant voltage of 30 V was applied for 1 second, so that the temperature of the CNT film rapidly rose to 960 °C, realizing the instantaneous evaporation of the CuS particles and their uniform deposition on the surface of the upper CNT film, and finally the CuS / CNT intermediate layer film B was obtained.

[0042] Example 3: A method for preparing an intermediate layer of a CuS / CNT thin film lithium-sulfur battery, comprising the following steps:

[0043] Keep the cutting size of the CNT film consistent with the previous examples. 40 mg of CuS nanoparticles were dispersed in 20 ml of absolute ethanol and ultrasonicated to form a homogeneous suspension. The CuS was uniformly loaded on the surface of the lower CNT film through a fritted filter. After drying, the lower sheet was placed between the two electrodes of the Joule heating device and connected with conductive silver paste. The upper sheet was placed parallel 5 mm above the lower sheet, and the system was evacuated to 10 -2 Pa. A constant voltage of 40 V was applied for 1 second, so that the temperature of the CNT film rapidly rose to 1050 °C, realizing the instantaneous evaporation of the CuS particles and their uniform deposition on the surface of the upper CNT film, and finally the CuS / CNT intermediate layer film C was prepared.

[0044] Example 4: A method for preparing an intermediate layer of a CuS / CNT thin film lithium-sulfur battery, comprising the following steps:

[0045] The same materials and initial processing steps as in Example 3 are adopted. After the CuS suspension is filtered by suction and dried, the lower sheet is installed in the Joule heating device, and the upper sheet is placed parallel 5 mm above the lower sheet. After the system is evacuated to 10 -2 Pa, a constant voltage of 40 V is applied and maintained for 3 s, so that the temperature of the CNT film rises to 1050 °C and is maintained for a longer time to ensure the full evaporation and deposition of CuS particles, and finally the CuS / CNT intermediate layer film D is obtained.

[0046] As Figure 1 shown, the battery is assembled as follows:

[0047] S1: Take 80 mg of elemental sulfur and 20 mg of Ketjenblack, mix and grind for 15 minutes to make them fully mixed; put the ground sulfur / carbon mixture into a small beaker, heat it in a water bath until it is in a cracked state, and then grind for 15 minutes; weigh the heated mixed material to ensure that the mass is above 97 mg;

[0048] S2: Put the above mixed material into a small steel cylinder, wrap it tightly with high-temperature tape, place the small steel cylinder under the thermometer in a muffle furnace, heat it to 155 °C and keep it for 12 hours, then raise the temperature to 200 °C and keep it for 1 hour, and take it out after the material naturally cools to room temperature;

[0049] S3: Mix the mixed material after high-temperature treatment with 5% graphene slurry and SuperP in a mass ratio of 8:1:1, drop an appropriate amount of N-methylpyrrolidone solution, and grind to obtain a uniformly dispersed sulfur positive electrode slurry;

[0050] S4: Cut an aluminum foil, use a scraper to scrape the sulfur positive electrode slurry on the aluminum foil, put the coated aluminum foil into a blast drying oven to dry, and use a cutting machine to cut a positive electrode sheet with a diameter of 12 mm;

[0051] S5: Prepare the CR2032 type battery case accessories, including the positive electrode case, gasket, spring piece and negative electrode case, wipe the surface of the accessories with ethanol to remove dust, and then put them into the oven to dry for standby; use a cutting machine to cut a CuS / CNT intermediate layer film with a diameter of 16 mm obtained in the example; cut a separator with a diameter of 20 mm and put it into the oven for standby;

[0052] S6: Put the above-prepared materials (positive electrode sheet, intermediate layer film, separator, etc.) into a high-purity argon glove box, assemble and seal the battery in the glove box, and use 1MLiTFSI / DOL:DME (1:1 vol%) + 1% LiNO3 as the electrolyte. The assembled battery is placed in a 25 °C constant temperature box and left to stand for 12 hours.

[0053] Performance test:

[0054] Detection Test (I)

[0055] The surface morphologies of the CuS / CNT intermediate layer films (A - D) prepared in four examples were observed by SEM, and the results are as Figures 3 - 6 shown;

[0056] The high - resolution TEM observation was carried out on the CuS / CNT intermediate layer film C of Example 3, and the elemental distribution was analyzed by combining with energy spectrum (EDS). The results are as Figure 7 shown;

[0057] The XPS test was carried out on the CuS / CNT intermediate layer film C of Example 3, and the results are as Figure 8 shown.

[0058] Detection Test (II)

[0059] The CV curves of the battery assembled with the CuS / CNT intermediate layer film of Example 3 were tested at a scan rate of 0.4 mV / s, and the results are as Figure 9 shown;

[0060] The impedance spectra of the battery assembled with the CuS / CNT intermediate layer film of Example 3 were compared with those of the battery without an intermediate layer (PP separator). The results are as Figure 10 shown;

[0061] The charge - discharge curves of the battery assembled with the CuS / CNT intermediate layer film of Example 3 were tested, and the obtained data are as Figure 11 shown;

[0062] The rate performance of the battery assembled with the CuS / CNT intermediate layer film of Example 3 was compared with that of the battery without an intermediate layer (PP separator). The obtained results are as Figure 12 shown;

[0063] The battery assembled with the CuS / CNT intermediate layer film of Example 3 was cycled 2000 times at 0.5C, and the obtained data are as Figure 13 shown.

[0064] Conclusion:

[0065] (1) Morphology and Structure Analysis

[0066] Figures 3 - 6 The SEM results of Figure 7 , 8 show that the CuS / CNT film can be rapidly prepared by Joule - heat evaporation deposition within the range of 750 - 1050 °C for 1 - 3 s; the TEM and EDS elemental distribution maps, as well as the XPS test (

[0067] (2) Electrochemical Behavior

[0068] CV curve ( Figure 9 ) indicates that the lithium-sulfur battery with CuS / CNT as the intermediate layer can successfully complete the cyclic voltammetry test and conforms to the redox process of a conventional lithium-sulfur battery (i.e., the conversion process of polysulfide); the EIS test ( Figure 10 ) shows that the application of the CuS / CNT intermediate layer improves the charge transfer ability inside the battery and significantly reduces the internal resistance of the battery.

[0069] (3) Battery performance

[0070] Charge-discharge test ( Figure 11 ) shows that the initial specific capacity of the battery exceeds 1020 mAh / g, and the capacity decay becomes slower and slower during subsequent cycles; after 200 cycles of cyclic testing, the specific capacity is still as high as 692 mAh / g;

[0071] Rate performance test ( Figure 12 ) shows that the reversible capacity of the battery is 932 mAh / g at 0.2C and still retains 610 mAh / g at 2C; when the current density returns to 0.2C again, the specific capacity can recover to 833 mAh / g; indicating that the battery has good high-current charge-discharge performance;

[0072] Long cycle test ( Figure 13 ) shows that after 2000 cycles at a current of 0.5C, the capacity remains at 315 mAh / g, and the single-cycle decay rate is only 0.0678%, with a significant improvement in cycle stability.

[0073] In summary, the CuS / CNT intermediate layer film significantly improves the electrochemical performance and cycle stability of the lithium-sulfur battery through its uniform nanostructure, good conductivity, and catalytic activity.

[0074] In the description of the specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0075] The above content is only an example and explanation of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the invention or exceed the scope defined by the claims of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A preparation method of an intermediate layer for a CuS / CNT thin film lithium-sulfur battery, characterized in that: It includes the following steps: Step 1: (1) Provide the first CNT film as the upper sheet; provide the second CNT film as the lower sheet; (2) Add CuS nanoparticles into absolute ethanol and ultrasonically disperse them evenly to obtain a CuS suspension. Step 2: Load the CuS suspension onto the surface of the lower sheet through a sintered glass filtering device and dry it to obtain a CuS loading layer. Step 3: In a vacuum environment, place the CuS loading layer between two electrodes to form an electrical connection. At the same time, set the upper sheet parallel above it and heat it by passing an electric current to obtain a CuS / CNT intermediate layer film.

2. The preparation method of an intermediate layer of a CuS / CNT thin film lithium-sulfur battery according to claim 1, characterized in that: The technical features of the upper sheet include: thickness 10 μm, size 4 cm × 2 cm; the technical features of the lower sheet include: thickness 20 μm, size 3.5 cm × 1.5 cm.

3. The preparation method of an intermediate layer of a CuS / CNT thin film lithium-sulfur battery according to claim 1, wherein: The dosage ratio of the CuS nanoparticles to absolute ethanol is (10 - 50) mg: 20 mL.

4. The preparation method of an intermediate layer of a CuS / CNT thin film lithium-sulfur battery according to claim 1, characterized in that: The parallel setting distance between the upper sheet and the CuS loading layer is 5 mm.

5. The preparation method of an intermediate layer of a CuS / CNT thin film lithium-sulfur battery according to claim 1, characterized in that: The process parameters of the heating include: pressure 20 - 50 V, temperature 750 - 1150 °C, time 1 - 5 s.

6. A CuS / CNT intermediate layer film obtained by the preparation method of a CuS / CNT film lithium-sulfur battery intermediate layer according to any one of claims 1 - 5.

7. Application of the CuS / CNT intermediate layer film according to claim 6 as an intermediate layer of a lithium-sulfur battery.

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