Solid-state lithium-sulfur battery based on V2O3 / C / S composite positive electrode material and preparation method of solid-state lithium-sulfur battery

Abstract

The invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a solid-state lithium-sulfur battery based on a V2O3 / C / S composite positive electrode material and a preparation method of the solid-state lithium-sulfur battery. The composite positive electrode material is composed of V2O3, C and S. The V2O3 and the C are compounded to form a V2O3-C matrix, and sulfur is loaded on the surface or in pores of the V2O3-C matrix. Meanwhile, the positive electrode material is prepared through a solution method, a hydrothermal method, high-temperature carbonization and a ball-milling melting composite process, and has excellent conductivity, structural stability and catalytic performance. The solid-state lithium-sulfur battery is formed by combining the composite solid-state electrolyte with the composite solid-state electrolyte, so that the shuttle effect can be effectively inhibited and the battery performance can be remarkably optimized by improving the positive electrode electronic conductivity and the interface stability, and the specific capacity, the rate capability and the cycle life of the lithium-sulfur battery are further remarkably improved. The invention provides a design and construction method of a novel positive electrode material for a high-performance solid-state lithium-sulfur battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a solid-state lithium-sulfur battery based on a V2O3 / C / S composite positive electrode material and a preparation method thereof. Background Art

[0002] Traditional liquid lithium-sulfur batteries suffer from problems such as the shuttle effect and rapid capacity decay. While the introduction of solid-state electrolytes has addressed these issues to some extent, the development of efficient cathode materials remains crucial for improving battery performance. Furthermore, lithium-sulfur batteries face challenges such as low cycling stability, poor sulfur conductivity, and the approximately 79% volume expansion of sulfur upon conversion to Li2S, which results in large internal stress and electrode pulverization. Low sulfur conductivity limits the electrochemical utilization of the active material; the dissolution and migration of polysulfide intermediates triggers a "shuttle effect," leading to rapid capacity decay and a decrease in Coulombic efficiency; and the volume expansion problem can easily cause structural damage to the electrode, further reducing battery cycling stability and reliability. Numerous studies have shown that transition metal oxides, through their unique electronic structure and surface chemistry, can effectively adsorb polysulfides and enhance their reaction kinetics. Coordination chemical bonding between the oxide surface and LiPSs immobilizes the LiPSs, thereby promoting redox reactions. Transition metal oxides, particularly vanadium trioxide (V2O3), are considered promising cathode auxiliary materials due to their excellent conductivity and catalytic properties. Therefore, if a new type of composite positive electrode material can be developed based on V2O3, it is expected to improve the cycle stability and rate performance of lithium-sulfur batteries, and provide a new path for the research and development of high-performance solid-state lithium-sulfur batteries. Summary of the Invention

[0003] In order to overcome the above-mentioned shortcomings of the prior art, the present invention provides a positive electrode material based on a V2O3 / C / S composite structure, which is combined with a composite solid electrolyte to form a solid-state lithium-sulfur battery, which can effectively improve the specific capacity, rate performance and cycle life of the lithium-sulfur battery.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] The first aspect of the present invention provides a method for preparing a V2O3 / C / S composite cathode material, comprising the following steps:

[0006] S1. Add NH4VO3 to water, add hydrochloric acid dropwise and stir until the solution turns orange, then add hydrazine hydrate, and the resulting mixture undergoes hydrothermal reaction and oxidative annealing to form a V2O5 precursor;

[0007] S2, adding V2O5, PVP and graphene to water, stirring and drying, and then carbonizing under an inert gas atmosphere to form V2O3@C material;

[0008] S3. Mix V2O3@C with sulfur, then add CS2 solution, stir, dry and ball mill to obtain V2O3@C / S composite positive electrode material.

[0009] Preferably, the temperature of the hydrothermal reaction is 110-150° C., and the time is 2-6 hours.

[0010] Preferably, the oxidation annealing is carried out in an air atmosphere at 4-6°C·min -1 The heating rate is increased to 390-410 ° C and heated for 1-3 hours.

[0011] Preferably, the usage ratio of NH4VO3 to hydrazine hydrate is 0.1-0.3 g:1.3-1.8 mL.

[0012] Preferably, the mass ratio of V2O5, PVP and graphene is 0.2-0.4:4-5:0.03-0.07.

[0013] Preferably, the carbonization treatment is carried out in an inert gas atmosphere at 4-6°C·min -1 The heating rate is increased to 600-650℃ and kept warm for 1-3 hours.

[0014] The second aspect of the present invention provides a V2O3 / C / S composite positive electrode material prepared by the preparation method described in the first aspect.

[0015] The third aspect of the present invention provides a solid-state lithium-sulfur battery, which uses the V2O3 / C / S composite positive electrode material described in the second aspect as the positive electrode, lithium metal as the negative electrode, and a BN / PVDF-HFP composite solid electrolyte as the electrolyte.

[0016] This invention significantly improves battery performance by enhancing the positive electrode's electronic conductivity and interfacial stability, effectively suppressing the shuttle effect. As a result, the solid-state battery achieves an initial specific capacity of 1158.8 mAh / g, retains 67.1% of its capacity after 150 cycles at a 0.1C rate, and maintains 45.5% of its capacity after 250 cycles at a 0.5C rate.

[0017] Preferably, the positive electrode is prepared by mixing the V2O3 / C / S composite positive electrode material with a conductive agent and a binder to form a slurry, coating the slurry on an aluminum foil, and drying the slurry.

[0018] More preferably, the conductive agent includes acetylene black, carbon nanotubes (CNT), graphene, carbon fiber (VGCF), and the binder includes polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), sodium alginate (SA), and polyvinyl alcohol (PVA).

[0019] More preferably, the mass ratio of the V2O3 / C / S composite positive electrode material to the conductive agent and the binder is 7-9:1-2:1-2.

[0020] Preferably, the preparation method of the BN / PVDF-HFP composite solid electrolyte is: mixing boron nitride (BN), lithium salt LiTFSI, PVDF-HFP and DMF, casting the mixture into a film and drying the mixture.

[0021] Preferably, the mass ratio of BN to PVDF-HFP is 1:1.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides a V2O3@C / S composite cathode material composed of vanadium trioxide (V2O3), carbon material (C), and sulfur (S). V2O3 and C are combined to form a V2O3@C matrix, and sulfur is loaded on the surface or within the pores of the V2O3@C matrix. The cathode material is produced through a solution method, a hydrothermal method, high-temperature carbonization, and a ball-milling melt composite process, exhibiting excellent electrical conductivity, structural stability, and catalytic performance. Combining it with a composite solid electrolyte to form a solid-state lithium-sulfur battery improves the positive electrode's electronic conductivity and interfacial stability, effectively suppressing the shuttle effect and significantly optimizing battery performance, thereby significantly improving the specific capacity, rate capability, and cycle life of the lithium-sulfur battery. The solid-state battery achieves an initial specific capacity of 1158.8 mAh / g at 0.1C, a capacity retention rate of 67.1% after 150 cycles at a 0.1C rate, and a capacity retention rate of 45.5% after 250 cycles at a 0.5C rate. The present invention provides a design and construction method for a new cathode material for high-performance solid-state lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the synthesis process of V2O3@C carrier material.

[0025] Figure 2 SEM images and elemental mapping spectra of C, V2O3@C, and V2O3@C / S; (a, d) SEM of C; (b, e) SEM of V2O3@C; (c, f) SEM of V2O3@C / S; (gj) elemental mapping spectra of V2O3@C / S.

[0026] Figure 3 XRD of V2O3@C / S, V2O3@C and C.

[0027] Figure 4 This is the thermogravimetric curve of V2O3@C / S.

[0028] Figure 5The charge and discharge curves (a), rate performance curves (b), 0.1C long cycle performance (c) and 0.5C long cycle performance (d) of the solid-state lithium-sulfur battery based on V2O3@C / S.

[0029] Figure 6 SEM of the cross section of C / S (a), V2O3@C / S (b) positive electrode and BN / PVDF-HFP composite solid electrolyte; SEM of the cross section of C / S (c), V2O3@C / S (d) positive electrode solid electrolyte.

[0030] Figure 7 XRD spectra of C / S cathode before and after cycling (a) and XRD spectra of V2O3@C / S cathode before and after cycling (b). DETAILED DESCRIPTION

[0031] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0032] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0033] Example: A method for preparing a solid-state lithium-sulfur battery based on V2O3 / C / S composite cathode material

[0034] 1. Preparation of V2O3@C materials (such as Figure 1 shown):

[0035] (1) Synthesize V2O5 by solution method and hydrothermal method: add 0.117g NH4VO3 into 25mL deionized water, add 0.5mL 1mol·L -1 The mixture was stirred with hydrochloric acid until the solution turned orange, and 1.5 mL of hydrazine hydrate (N2H2·H2O) was added to the solution and stirred at room temperature for 15 minutes. The mixture was then transferred to a Teflon-lined stainless steel autoclave and kept at 120°C for 4 hours. After the reaction, it was washed three times with anhydrous ethanol and dried at 80°C for 8 hours. The obtained product was placed in a muffle furnace and heated at 5°C·min in an air atmosphere. -1 The temperature was raised to 400 °C at a rate of 100 °C, heated for 2 h, and then naturally cooled to room temperature to obtain V2O5.

[0036] (2) 0.25 g of vanadium pentoxide (V2O5), 4.5 g of PVP and 0.05 g of graphene were placed in a 25 mL blue screw-capped bottle, and 7 mL of deionized water was added. The mixture was stirred at 45 °C for 12 h, then dried in a forced air oven at 80 °C for 12 h, and then carbonized in a furnace with N2 atmosphere at a heating rate of 5 °C / min to 620 °C and kept at that temperature for 2 h to obtain V2O3@C.

[0037] 2. Synthesis of V2O3@C / S composite materials:

[0038] (1) 0.3 g of V2O3@C was mixed with 0.7 g of sulfur, and 4 mL of CS2 solution was added. The sample was stirred for 45 min, washed with anhydrous ethanol, and dried at 80 °C. Then, the sample was ball-milled at 350 r / min for 5 h with a ball-to-material ratio of 1:30 to obtain a V2O3@C / S composite cathode material.

[0039] like Figure 2 As shown, SEM images of the PVP carbonization product reveal a layered structure. The particle sizes of V2O3@C and C are essentially similar, indicating that the PVP carbonization material does not undergo significant size changes after V2O3 coating. After the prepared V2O3@C matrix was loaded with S, a layer of particles of varying sizes was clearly coated on the matrix surface. The distribution of C, S, V, and O elements indicates that these elements are uniformly distributed throughout the composite material.

[0040] Figure 3 The XRD pattern of the carbonized PVP material confirmed a characteristic peak at 26.5°, corresponding to the graphite (002) crystal plane. The diffraction peaks of the V2O3@C matrix material at 24.5°, 33°, 50°, 54°, 63°, and 65° were consistent with the V2O3 crystal PDF card. The diffraction peaks of the sulfur species in the V2O3@C / S composite material were distinct, with both the characteristic peaks of the graphite (002) crystal plane and the V2O3 characteristic peaks present. There was no significant shift in peak positions or the generation of new peaks, indicating that the V2O3 and sulfur in the V2O3@C / S composite material were physically mixed and adsorbed during the composite process, without any chemical reaction.

[0041] Figure 4 TGA test results show that the lithium-sulfur cathode material loses 2% weight in the low-temperature range, which is related to the removal of residual solvents, volatile organic compounds, and water, rather than sulfur volatilization. The material's weight drops sharply by 69.7% between 200°C and 400°C, indicating sulfur decomposition within this temperature range. Ultimately, the material's weight stabilizes at 28.3%. Therefore, the sulfur weight percentage in the composite cathode can be determined to be 69.7%.

[0042] (2) V2O3@C / S was mixed with acetylene black and PVDF at a mass ratio of 8:1:1, and added to the solvent NMP at a material-liquid ratio of 1:37 (g:mL) to make a slurry, which was then coated on aluminum foil and dried to obtain an electrode sheet.

[0043] 3. Preparation of BN / PVDF-HFP electrolyte:

[0044] 1g BN, 1g PVDF-HFP, and 0.8g LiTFSI were placed in DMF and stirred for 24 hours. After casting, the film was vacuum dried to form a BN / PVDF-HFP composite solid electrolyte.

[0045] 4. Battery assembly and testing:

[0046] V2O3@C / S was used as the positive electrode (C / S positive electrode was used as a control), lithium sheet as the negative electrode, and BN / PVDF-HFP as the electrolyte to assemble a CR2032 battery. The charge-discharge curve (CV) and cycle performance tests were then carried out.

[0047] like Figure 5 As shown, the charge and discharge curves at a rate of 0.1C show that the initial discharge capacity of V2O3@C / S is 1201mAh / g and the coulombic efficiency is 99.16%, while the discharge capacity of the C / S positive electrode is 1019mAh / g and the coulombic efficiency is 97.04%, indicating that the V2O3@C / S positive electrode has a higher specific capacity and more stable cycling efficiency than the C / S positive electrode. The rate test in the 0.1C-1C range shows that when restored to 0.1C, the reversible capacity retention rates of the V2O3@C / S positive electrode and the C / S positive electrode are 78.7% and 68.5%, respectively, indicating that the V2O3@C / S positive electrode has good rate performance. Long-term cycling tests at a 0.1C rate showed that the initial specific capacity of the V2O3@C / S cathode was 1125.6 mAh / g. A slight capacity increase was observed over 150 cycles, with an overall trend of stable decay. However, the capacity decay rate was low, with a retention rate of 67.1%. When cycling at a 0.5C rate, the initial specific capacity of the V2O3@C / S cathode was 977 mAh / g. After 250 cycles, the capacity decay rate per cycle was 0.217%, and the capacity retention rate was 45.5%, indicating a stable host structure.

[0048] pass Figure 6 a It can be observed that the thickness of the solid electrolyte is about 72μm, the cross-sectional thickness of the positive electrode is about 23μm, the interface bonding between the graphite and sulfur materials is weak, and the C / S positive electrode material falls off during the cycle, which increases the thickness of the C / S positive electrode remaining on the electrolyte interface. There is an obvious gap at the interface between the C / S positive electrode and the solid electrolyte, and the interface contact is not tight enough, resulting in a higher interface impedance. Figure 6The thickness of the solid electrolyte in b is 73μm, but the cross-sectional thickness of the V2O3@C / S positive electrode is significantly reduced to 6μm. V2O3 can provide stronger interface bonding, improve the structural stability of the V2O3@C / S positive electrode, and reduce the impact of volume changes on the electrode. In addition, the interface is flat and has no obvious gaps. The thinner positive electrode layer and the relatively flat and dense interface shorten the transmission path of ions and electrons, thereby increasing the electrochemical reaction rate. Figure 6 c It can be observed that the C / S cathode has larger grains and pores, while the V2O3@C / S cathode is relatively flat ( Figure 6 d) The pore size is small. After the sulfur positive electrode undergoes the redox reaction of polysulfides, mechanical exfoliation and polysulfide aggregation occur at the C / S positive electrode interface, and large particles are deposited on the positive electrode surface. This phenomenon may lead to an increase in interfacial resistance. The dissolution and irreversible loss of polysulfides during charging and discharging result in larger pores, resulting in a decrease in lithium ion transmission efficiency and accelerated battery capacity decay. The V2O3@C / S positive electrode interface is smooth. The addition of V2O3 improves the chemical stability of the positive electrode interface, inhibits interfacial products, and reduces their erosion of the interface, thereby maintaining the stability of the positive electrode structure.

[0049] Figure 7 In the XRD of the C / S cathode of a after 30 cycles, most of the diffraction peaks of S8 molecules disappeared, and only 5 diffraction peaks of S8 molecules remained, indicating that the sulfur content in the C / S cathode decreased rapidly during the redox process, which may be mainly due to polysulfides (Li2S n ) dissolves and diffuses into the electrolyte and deposits at the interface. Figure 7 In the XRD of the V2O3@C / S cathode after 30 cycles, the S8 molecules have 15 S8 molecular diffraction peaks, indicating that most of the S8 molecules are reversible during the charge and discharge process, indicating that V2O3 can act as an interface catalyst to promote the formation of polysulfides (Li2S n ) redox reaction, thereby improving the active utilization rate of the sulfur positive electrode, reducing the irreversible loss of polysulfides, and increasing the battery capacity.

[0050] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a V2O3 / C / S composite cathode material, characterized in that: The following steps are involved: S1. Add NH4VO3 to water, add hydrochloric acid dropwise and stir until the solution turns orange, then add hydrazine hydrate, and the resulting mixture undergoes hydrothermal reaction and oxidative annealing to form a V2O5 precursor; S2, adding V2O5, PVP and graphene to water, stirring and drying, and then carbonizing under an inert gas atmosphere to form V2O3@C material; S3. Mix V2O3@C with sulfur, then add CS2 solution, stir, dry and ball mill to obtain V2O3@C / S composite positive electrode material.

2. The method for preparing a V2O3 / C / S composite cathode material according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 110-150° C., and the time is 2-6 hours.

3. The method for preparing a V2O3 / C / S composite cathode material according to claim 1, characterized in that: The oxidation annealing is carried out in an air atmosphere at 4-6°C·min -1 The heating rate is increased to 390-410 ° C and heated for 1-3 hours.

4. The method for preparing a V2O3 / C / S composite cathode material according to claim 1, characterized in that: The usage ratio of NH4VO3 to hydrazine hydrate is 0.1-0.3 g:1.3-1.8 mL.

5. The method for preparing a V2O3 / C / S composite cathode material according to claim 1, characterized in that: The mass ratio of the V2O5, PVP and graphene is 0.2-0.4:4-5:0.03-0.

07.

6. The method for preparing a V2O3 / C / S composite cathode material according to claim 1, characterized in that: The carbonization treatment is carried out in an inert gas atmosphere at 4-6°C·min -1 The heating rate is increased to 600-650℃ and kept warm for 1-3 hours.

7. A V2O3 / C / S composite cathode material prepared by the preparation method according to any one of claims 1 to 6.

8. A solid-state lithium-sulfur battery, characterized in that: The solid-state lithium-sulfur battery uses the V2O3 / C / S composite positive electrode material according to claim 7 as the positive electrode, lithium metal as the negative electrode, and a BN / PVDF-HFP composite solid electrolyte as the electrolyte.

9. A solid-state lithium-sulfur battery according to claim 8, characterized in that: The positive electrode is prepared by mixing a V2O3 / C / S composite positive electrode material with a conductive agent and a binder to prepare a slurry, coating the slurry on an aluminum foil, and drying the mixture.

10. A solid-state lithium-sulfur battery according to claim 8, characterized in that: The preparation method of the BN / PVDF-HFP composite solid electrolyte is as follows: BN, LiTFSI, PVDF-HFP and DMF are mixed, and then a film is cast and dried.

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