A method for preparing a vanadium tetrasulfide-based lithium-sulfur battery cathode and its application.

Abstract

This invention discloses a method for preparing a vanadium tetrasulfide-based lithium-sulfur battery cathode and its application. The method uses vanadium tetrasulfide-based material as the sulfur source in the lithium-sulfur battery cathode, mixes it uniformly with conductive carbon black, and coats it onto a current collector to obtain the cathode for lithium-sulfur batteries. The cathode structure of this invention is simple and stable. The lithium-sulfur battery cathode prepared using vanadium tetrasulfide-based material as the sulfur source exhibits better conductivity, stronger lithium polysulfide adsorption and catalytic ability than traditional sulfur cathodes, effectively suppresses the "shuttle effect," and provides more active sites, promoting the catalytic conversion reaction of lithium polysulfides and demonstrating excellent electrochemical characteristics.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage, specifically relating to a method for preparing a vanadium tetrasulfide-based lithium-sulfur battery cathode and its application. Background Technology

[0002] Against the backdrop of the rapid development of electric vehicles, it has become increasingly clear that lithium-ion batteries may not be able to meet the ever-growing demand for high energy storage in the future. In contrast, lithium-sulfur batteries, due to their high theoretical specific capacity (1675 mAh g⁻¹), offer a more competitive alternative. -1 ) and energy density (2600Wh kg) -1 Sulfur (S) has attracted much attention due to its good stability, abundant sulfur resources, and environmental friendliness. However, as a cathode material for lithium-sulfur batteries, sulfur's poor electronic conductivity leads to insufficient electron transport performance, limiting the high-rate performance of the battery. Furthermore, the sulfur cathode undergoes a multi-step conversion reaction, producing various lithium polysulfide (LiPSs) intermediates. These LiPSs have high solubility in the electrolyte and, under an electric field, can cause a "shuttle effect," resulting in sulfur loss and slow electrochemical kinetics. This also induces volume changes in the cathode material, damaging the battery electrode structure and severely affecting cycle life and stability. To overcome these problems, researchers have conducted extensive studies on lithium-sulfur battery cathodes. Among these studies, modifying the sulfur cathode by introducing polar catalysts can effectively promote lithium-ion adsorption and conversion, thereby suppressing the shuttle effect. Transition metal sulfides, due to their strong sulfur-ion trapping ability and excellent binding with lithium ions, have significant potential in the modification of sulfur cathodes. However, adding a large amount of catalytic material to the cathode, in addition to the sulfur source, not only increases the cost, but also presents a challenge in effectively integrating the catalytic material into the electrode structure. Vanadium tetrasulfide (VS4) not only possesses the characteristics of strong adsorption and high catalytic activity of transition metal sulfides, but also has a high sulfur content, making it a potential sulfur source for direct use in lithium-sulfur batteries. VS4 has a unique one-dimensional linear chain structure, composed of S2... 2- Composed of a dimer and two adjacent V atoms, the parallel one-dimensional chains of VS4 exhibit weak van der Waals forces. This not only provides a large open channel for lithium-ion diffusion but also enhances the adsorption and catalytic activity of LiPSs, better suppressing the "shuttle effect" of LiPSs. Therefore, developing VS4 as a novel cathode material for lithium-sulfur batteries is of great significance. Summary of the Invention

[0003] To address the problems of poor conductivity and large volume change of sulfur in traditional lithium-sulfur battery cathodes, this invention aims to develop a low-cost, simple, and structurally simple method for preparing a vanadium tetrasulfide-based lithium-sulfur battery cathode suitable for mass production, and its application in lithium-sulfur batteries. This method can effectively mitigate the LiPSs shuttle effect, accelerate redox kinetics, improve coulombic efficiency, and enhance sulfur utilization, ultimately improving the rate performance and cycle stability of lithium-sulfur batteries.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A method for preparing a vanadium tetrasulfide-based lithium-sulfur battery cathode includes the following steps:

[0006] Step 1: Disperse 0-50 mg of carbon-based material ultrasonically in 15-20 mL of deionized water, then add 2-3 mmol of vanadium source, seal and place in a water bath at 50-70℃ and stir for 0.5-1 h to obtain solution A;

[0007] Step 2: Add 8-12 mmol of sulfur source to 15-30 mL of ethylene glycol and stir for 10-30 min to obtain solution B;

[0008] Step 3: Mix solution A and solution B, stir at room temperature for 0.5-1 h, pour the resulting mixed solution into a high-pressure reactor, and react at 150-200℃ for 20-30 h to obtain the initial product;

[0009] Step 4: After centrifuging and washing the initial product, place it in a vacuum drying oven to dry and obtain the intermediate product;

[0010] Step 5: Mix the intermediate product, carbon black, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) evenly, coat the resulting slurry evenly on one side of the current collector, and then dry it in a vacuum drying oven to obtain the target product, vanadium tetrasulfide-based lithium-sulfur battery cathode.

[0011] Preferably, in step 1, the carbon-based material is one of graphene oxide (GO), carbon nanotubes (CNT), and carbon spheres (HCS).

[0012] Preferably, in step 1, the vanadium source is ammonium metavanadate.

[0013] Preferably, in step 2, the sulfur source is at least one of thioacetamide, thiourea, and sodium thiosulfate.

[0014] Preferably, in step 4, the cleaning is performed by sequentially cleaning with deionized water and anhydrous ethanol.

[0015] Preferably, in step 5, the carbon black material is at least one of acetylene black (AB) and Ketjen black (KB).

[0016] Preferably, in step 5, the current collector is one of aluminum foil, carbon fiber paper (CFP), and carbon fiber cloth (CFC).

[0017] Preferably, in step 5, the mass ratio of intermediate product, carbon black, and PVDF is 6-7:2-3:1.

[0018] The vanadium tetrasulfide-based lithium-sulfur battery cathode prepared by this invention can be used as a cathode in lithium-sulfur batteries.

[0019] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0020] 1. The vanadium tetrasulfide-based lithium-sulfur battery cathode prepared by the method of the present invention has a simple structure, stable electrode properties, and excellent electrochemical characteristics.

[0021] 2. The method for preparing the vanadium tetrasulfide-based lithium-sulfur battery cathode provided by this invention involves using vanadium tetrasulfide-based material as the sulfur source in the lithium-sulfur battery cathode, uniformly mixing it with conductive carbon black, and then coating it onto a current collector to obtain the cathode for lithium-sulfur batteries. The lithium-sulfur battery cathode prepared using vanadium tetrasulfide-based material as the sulfur source exhibits better conductivity, stronger lithium polysulfide adsorption and catalytic ability than traditional cathodes, effectively suppresses the "shuttle effect," promotes LiPSs conversion, and provides more active sites, demonstrating excellent electrochemical characteristics.

[0022] 3. In the preparation of VS4, the present invention adds carbon-based materials to disperse the originally agglomerated VS4 nanospheres into VS4 nanorods, thereby increasing the reaction area and providing more active sites. At the same time, the introduction of carbon-based materials can also improve the conductivity of the VS4 cathode and greatly accelerate the diffusion rate of lithium ions.

[0023] 4. The lithium-sulfur battery assembled with the vanadium tetrasulfide-based lithium-sulfur battery cathode prepared by the present invention exhibits excellent rate performance and superior long-term cycle life at high current density.

[0024] 5. The preparation process of this invention is simple, the preparation cost is low, and it is easy to synthesize and promote on a large scale. Attached Figure Description

[0025] Figure 1 These are SEM images of the intermediate products obtained in Examples 1 and 2 of this invention. Figure 1 In this context, 'a' and 'b' correspond to VS4 and VS4@rGO, respectively.

[0026] Figure 2These are TEM images of the intermediate products obtained in Examples 1 and 2 of this invention. Figure 2 In this context, 'a' and 'b' correspond to VS4 and VS4@rGO, respectively.

[0027] Figure 3 These are XPS images of the intermediate products obtained in Examples 1 and 2 of this invention. Figure 3 In the spectrum, a and b correspond to the V2p and S2p energy spectra, respectively.

[0028] Figure 4 The images show the XRD patterns of the intermediate products obtained in Examples 1 and 2 of this invention.

[0029] Figure 5 The images show the Raman spectra of the intermediate products obtained in Examples 1 and 2 of this invention.

[0030] Figure 6 The variable rate performance curves are those of the button batteries assembled from samples 1 to 4 prepared in Examples 1 to 4 of the present invention.

[0031] Figure 7 The long-cycle test curves of the button batteries assembled from samples 1 to 4 prepared in Examples 1 to 4 of the present invention at a current density of 2C.

[0032] Figure 8 The long-cycle test curve of the button cell assembled from sample 4 prepared in Example 4 of the present invention at a current density of 4C.

[0033] Figure 9 The charge-discharge curve of the button cell assembled from sample 4 prepared in Example 4 of the present invention at a current density of 4C. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0035] Unless otherwise specified, all process steps in the following embodiments are carried out at room temperature.

[0036] Example 1

[0037] This embodiment prepares the VS4 / Al cathode according to the following steps:

[0038] Step 1: Add 2 mmol of ammonium metavanadate to 15 mL of deionized water, seal the beaker with aluminum foil, and place it in a 60°C water bath and stir for 45 min to obtain solution A.

[0039] Step 2: Add 10 mmol of thioacetamide to 20 mL of ethylene glycol and stir for 20 min to obtain solution B.

[0040] Step 3: Mix solution A and solution B, stir at room temperature for 1 hour, pour the resulting mixed solution into a high-pressure reactor, and react at 160°C for 24 hours to obtain the initial product.

[0041] Step 4: After centrifuging and washing the initial product, place it in a vacuum drying oven at 50℃ and dry for 12 hours to obtain the intermediate product VS4.

[0042] Step 5: Grind the intermediate product and acetylene black in an agate mortar, then add PVDF and NMP and mix thoroughly. The mass ratio of intermediate product, acetylene black, and PVDF is 6:3:1. The resulting slurry is then uniformly coated onto aluminum foil using an automatic coating machine and dried in a vacuum drying oven at 60℃ for 12 hours to obtain the target product VS4 / Al cathode, designated as Sample 1.

[0043] Example 2

[0044] This embodiment prepares the VS4@rGO / Al cathode according to the following steps:

[0045] Step 1: Disperse 45 mg of GO in 15 mL of deionized water by ultrasonication, then add 2 mmol of ammonium metavanadate, seal the beaker with aluminum foil, and place it in a 60 °C water bath and stir for 45 min to obtain solution A.

[0046] Step 2: Add 10 mmol of thioacetamide to 20 mL of ethylene glycol and stir for 20 min to obtain solution B.

[0047] Step 3: Mix solution A and solution B, stir at room temperature for 1 hour, pour the resulting mixed solution into a high-pressure reactor, and react at 160°C for 24 hours to obtain the initial product.

[0048] Step 4: After centrifuging and washing the initial product, place it in a vacuum drying oven at 50℃ and dry for 12 hours to obtain the intermediate product VS4@rGO.

[0049] Step 5: Grind the intermediate product and acetylene black in an agate mortar, then add PVDF and NMP and mix thoroughly. The mass ratio of intermediate product, acetylene black, and PVDF is 6:3:1. The resulting slurry is then evenly coated onto aluminum foil using an automatic coating machine and dried in a vacuum drying oven at 60℃ for 12 hours to obtain the target product VS4@rGO / Al cathode, designated as Sample 2.

[0050] Example 3

[0051] This embodiment prepares the S / Al cathode according to the following steps:

[0052] Step 1: Add sublimed sulfur (S) and acetylene black to an agate mortar and grind them together. The mass ratio of S to acetylene black is 6:3. Then add the mixture to a small glass bottle, seal it in a glove box, and place it in a reaction vessel.

[0053] Step 2: Place it in an oven at 155.5℃ and heat for 12 hours to obtain the intermediate product S / C.

[0054] Step 3: Grind the intermediate product in an agate mortar, then add PVDF and NMP and mix thoroughly. The mass ratio of intermediate product to PVDF is 9:1. The resulting slurry is then evenly coated onto aluminum foil using an automatic coating machine and dried in a vacuum drying oven at 60℃ for 12 hours to obtain the target product S / Al cathode, designated as Sample 3.

[0055] Example 4

[0056] This embodiment prepares the VS4@rGO / CFP cathode according to the following steps:

[0057] Step 1: Disperse 45 mg of GO in 15 mL of deionized water by ultrasonication, then add 2 mmol of ammonium metavanadate, seal the beaker with aluminum foil, and place it in a 60 °C water bath and stir for 45 min to obtain solution A.

[0058] Step 2: Add 10 mmol of thioacetamide to 20 mL of ethylene glycol and stir for 20 min to obtain solution B.

[0059] Step 3: Mix solution A and solution B, stir at room temperature for 1 hour, pour the resulting mixed solution into a high-pressure reactor, and react at 160°C for 24 hours to obtain the initial product.

[0060] Step 4: After centrifuging and washing the initial product, place it in a vacuum drying oven at 50℃ and dry for 12 hours to obtain the intermediate product VS4@rGO.

[0061] Step 5: Grind the intermediate product and acetylene black in an agate mortar, then add PVDF and NMP and mix thoroughly. The mass ratio of intermediate product, acetylene black, and PVDF is 6:3:1. The resulting slurry is then uniformly coated onto carbon fiber paper (CFP) using an automatic coating machine and dried in a vacuum drying oven at 60℃ for 12 hours to obtain the target product VS4@rGO / CFP cathode, designated as sample 4.

[0062] Figure 1 These are SEM images of the intermediate products obtained in Examples 1 and 2. Figure 1 In this context, 'a' and 'b' correspond to VS4 materials. Figure 1In the figures, c and d correspond to the VS4@rGO material. As shown in Figures a and b, the VS4 material exhibits a nanosphere morphology. However, as shown in Figures c and d, after the introduction of rGO, VS4 does not form a nanosphere morphology, but instead exhibits nanorods with a length of 200-400 nm and a diameter of 50-100 nm, which are uniformly attached to the rGO surface. This indicates that these nanospheres are formed by the stacking of nanorods.

[0063] Figure 2 These are TEM images of the intermediate products obtained in Examples 1 and 2. Figure 2 The 'a' in the text corresponds to VS4 material. Figure 2 In the figure, b corresponds to the VS4@rGO material. Similar results to SEM can be obtained from Figures a and b. After adding rGO, VS4 is dispersed from nanospheres into nanorods and is uniformly distributed on rGO.

[0064] Figure 3 XPS images of the intermediate products obtained in Examples 1 and 2. Figure 3 Figures a and b correspond to the V 2p and S 2p energy spectra of the sample, respectively. As shown in Figure a, the number and position of the peaks are basically the same in both cases. Furthermore, it is clear that the peaks representing V... 4+ The pair of prominent doublets located at higher binding energies of 524.2 eV and 516.5 eV correspond to the same valence state of VS4 in vanadium, while two additional peaks corresponding to V at 521.5 eV and 513.9 eV also exist. 2+ The peak, V 2+ The presence of [a specific element] indicates the presence of sulfur vacancies in the sample. Figure b shows the S2p energy spectra of the VS4 and VS4@rGO samples, with two [a specific element] at 163.9 eV and 162.8 eV respectively. 2- 2p 3 / 2 and 2p 1 / 2 The peak caused by the spin orbital is also consistent with the valence state of sulfur in VS4.

[0065] Figure 4The XRD patterns are of the intermediate products obtained in Examples 1 and 2. The characteristic peaks of the obtained VS4 and VS4@rGO samples correspond to the peaks of the standard single-crystal oblique VS4 (JCPDS 87-0603), indicating that the obtained samples are VS4 with a pure monoclinic structure. The two very sharp main diffraction peaks at 15.7° and 17° correspond to the (110) and (020) crystal planes of the monoclinic VS4 phase, and the sharpness of the main diffraction peaks also indicates that the samples have good crystallinity. The peaks at 28.1°, 30°, 36.3°, 40.6° and 44.1° correspond to the (-202), (004), (114), (-224) and (134) crystal planes of VS4, respectively. In addition, a broad diffraction peak at about 24° can also be seen in the VS4@rGO sample, which comes from rGO and corresponds to the (002) plane of carbon.

[0066] Figure 5 The images show the Raman spectra of the intermediate products obtained in Examples 1 and 2. The peak values ​​at 197, 220, 276, 293, 351, and 560 cm⁻¹ are clearly visible. -1 The six Raman peaks. Among them, those located at 197 and 220 cm... -1 The two peaks at 276 cm⁻¹ originate from the vibration of the VS bond stretching. -1 The peak values ​​at 293 and 560 cm originate from vibrations in the VS bond bending mode. -1 The two peaks at 351 cm⁻¹ originate from the vibrations caused by the deformation and stretching of the SS bond. -1 There is also a relatively obvious peak caused by the symmetrical vibration of VS4.

[0067] To characterize the electrochemical performance of the cathode obtained in the above examples, the following tests were performed.

[0068] Step 1: Take the positive electrode prepared in each embodiment as the positive electrode of the lithium-sulfur battery.

[0069] Step 2: Using lithium metal as the negative electrode, glass fiber membrane (Celgard 2400) as the separator, 1M LITFSI (lithium bis(trifluoromethanesulfonyl)imide) dissolved in a 1:1 volume ratio DOL / DME mixed solution, and adding 1wt% LiNO3 as the electrolyte, assemble the CR2032 button cell in an inflatable glove box (Etelux Lab 2000, O2 < 0.1ppm, H2O < 0.1ppm).

[0070] Step 3: Use Neware's BTS2300 charge / discharge tester to perform charge / discharge tests on the assembled button batteries within a voltage window of 1.7-2.8V.

[0071] Figure 6The variable rate performance curves of the coin cells assembled from samples 1 (VS4 / Al), 2 (VS4@rGO / Al), 3 (S / Al), and 4 (VS4@rGO / CFP) are shown. It can be seen that at current densities of 0.2C-4C, the battery assembled from sample 4 exhibits mAh gg values ​​of 1643, 1281, 1059, 835, 672, and 547 mAh gg, respectively. -1 The specific capacity can also be restored to 1430mAh g when gradually restored to 0.2C. -1 It exhibits high stable specific capacity and excellent cycle reversibility, far exceeding that of other samples.

[0072] Figure 7 Long-cycle test curves at 2C current density are shown for the coin cells assembled from Sample 1 (VS4 / Al), Sample 2 (VS4@rGO / Al), Sample 3 (S / Al), and Sample 4 (VS4@rGO / CFP). The initial capacity of the battery assembled from Sample 4 is 797 mAh g. -1 It can still maintain 512mAh g after 300 cycles. -1 Its specific capacity is far higher than that of other types of cathode batteries.

[0073] Figure 8 The coin cell assembled for Sample 4 (VS4@rGO / CFP) exhibits long-cycle testing curves at 4C current density. The battery assembled for Sample 4 can sustain 1000 cycles at 4C, retaining a capacity of 281 mAh g after each cycle. -1 High specific capacity.

[0074] Figure 9 The charge-discharge curves of the coin cell assembled for sample 4 (VS4@rGO / CFP) at a 4C current density are shown. The charge-discharge curves of the sample 4 battery at 4C for the 1st, 10th, 100th, and 1000th cycles are also shown. The first 100 cycles show largely overlapping curves and high stability. However, from the 100th to the 1000th cycle, the discharge specific capacity gradually decreases. This may be due to the continuous change in the positive electrode volume under prolonged high-current charge-discharge cycling, along with the deposition of a small amount of lithium polysulfide on the positive electrode surface, which weakens the activity of the positive electrode material surface and thus affects the battery performance.

[0075] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a positive electrode of a vanadium tetrasulfide-based lithium-sulfur battery, characterized by, The preparation method comprises the following steps: Step 1, ultrasonic dispersion of 0-50 mg carbon-based material in 15-20 mL deionized water, then adding 2-3 mmol vanadium source, sealing and stirring in a 50-70 ℃ water bath for 0.5-1 h to obtain solution A; the carbon-based material is one of graphene oxide, carbon nanotube and carbon sphere; the vanadium source is ammonium metavanadate; Step 2, adding 8-12 mmol sulfur source to 15-30 mL ethylene glycol and stirring for 10-30 min to obtain solution B; the sulfur source is at least one of thioacetamide, thiourea and sodium thiosulfate; Step 3, mixing solution A and solution B, stirring at room temperature for 0.5-1 h, pouring the obtained mixed solution into a high-pressure reaction kettle, and reacting at a temperature of 150-200 ℃ for 20-30 h to obtain an initial product; Step 4, centrifugal washing of the initial product and drying in a vacuum drying box to obtain an intermediate product; Step 5, mixing the intermediate product, carbon black, polyvinylidene fluoride and N-methyl pyrrolidone uniformly, uniformly coating the obtained slurry on one side of the current collector, and then drying in a vacuum drying box to obtain a target product vanadium tetrasulfide-based lithium-sulfur battery positive electrode.

2. The method of claim 1, wherein: In step 4, the washing is sequentially using deionized water and anhydrous ethanol.

3. The method of claim 1, wherein: In step 5, the carbon black material is at least one of acetylene black and ketjen black.

4. The method of claim 1, wherein: In step 5, the current collector is one of aluminum foil, carbon fiber paper and carbon fiber cloth.

5. The method of claim 1, wherein: In step 5, the mass ratio of the intermediate product, carbon black and polyvinylidene fluoride is 6-7:2-3:

1.

6. A vanadium tetrasulfide-based lithium-sulfur battery positive electrode prepared by the preparation method of any one of claims 1-5.

7. Application of the vanadium tetrasulfide-based lithium-sulfur battery positive electrode of claim 6 in a lithium-sulfur battery.

Images