Polyoxovanadate modified lithium sheet, preparation method and application of polyoxovanadate modified lithium sheet in lithium metal battery

Abstract

The invention provides a polyoxovanadate modified lithium sheet, a preparation method and application of the polyoxovanadate modified lithium sheet in a lithium metal battery. The polyoxovanadate is high-core mixed-valence polyoxovanadate, and the molecular formula of the polyoxovanadate modified lithium sheet is K10 [V34O82]. 20H2O; the preparation method of the polyoxovanadate modified lithium sheet comprises the following steps: adding high-core mixed valence polyoxovanadate into ethylene glycol dimethyl ether to prepare turbid liquid with the concentration of 0.8-1.2 mM, immersing a surface-polished lithium sheet into the turbid liquid, stirring for 17-19 hours, and airing to obtain the polyoxovanadate modified lithium sheet. The V34 modified lithium sheet disclosed by the invention has a good infiltration effect on an electrolyte, and can ensure effective diffusion of the electrolyte, so that transmission of lithium ions is accelerated; the lithium ion transference number of the V34 modified lithium sheet prepared by the invention is 0.54, which is obviously higher than that of a commercial lithium sheet; the Li / / Li symmetrical battery assembled by the V34 modified lithium sheet has good cycle performance and rate capability.

Description

Technical Field

[0001] The present invention relates to a polyoxovanadate-modified lithium sheet, a preparation method thereof, and an application thereof in a lithium metal battery, belonging to the technical field related to negative electrode materials for lithium metal batteries. Background Art

[0002] Batteries using lithium metal as the negative electrode can all be called lithium metal batteries (Li-metal batteries, LMBs). The theoretical energy density of commercial LiCoO2 / graphite-based lithium-ion batteries is only 387 Wh / kg. If lithium metal is used to replace the graphite negative electrode, the energy density of the battery matched with LiCoO2 or ternary positive electrode materials can reach 500 - 1000 Wh / kg. In addition, if the embedded positive electrode material is replaced with a positive electrode material based on a multi-electron conversion reaction, such as S or O2 (air), their highest theoretical specific capacities are as high as 2567 Wh / kg and 3505 Wh / kg respectively. However, the related problems of the lithium metal negative electrode seriously limit its development, which can be specifically summarized as the following aspects: (1) Lithium metal can almost react with any organic solvent at the interface to form a solid electrolyte interphase (SEI) film on the surface; (2) Due to its non-host nature, lithium metal has unlimited volume expansion during the cycling process, resulting in the rupture and continuous generation of the SEI film, continuously consuming the electrolyte; (3) Different from the insertion / extraction mechanism of the graphite negative electrode, lithium metal works in a deposition / stripping mode during operation. The non-uniformity of lithium deposition easily induces the generation of dendritic structures. Lithium dendrites can penetrate through the separator to reach the positive electrode side, causing battery short circuit and triggering thermal runaway, thus causing serious safety hazards; (4) The non-uniformity of lithium dendrites during stripping will lead to the generation of inactive "dead lithium" that falls off. The accumulation of the "dead lithium" layer will not only reduce the compactness of the negative electrode, produce a porous electrode, increase the battery impedance, but also cause rapid attenuation of the battery capacity and Coulomb efficiency.

[0003] In response to the problems of lithium metal, researchers have tried to optimize the electrolyte by adjusting additives of liquid electrolytes and using solid electrolytes, etc. However, these methods have high costs and long time periods, and it is difficult to be applied on a large scale. The method of modifying the PP separator has the following defects: The modified PP separator will inevitably increase the overall thickness and mass, which will reduce the energy density of the battery; The modified PP separator uses a physical coating method and is only adhered by a binder, and is prone to falling off during charge and discharge.

[0004] There is no report in the prior art on modifying lithium sheets with polyoxovanadates. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a polyoxovanadate-modified lithium sheet, a preparation method thereof, and an application thereof in a lithium metal battery, achieving the following invention objectives: The polyoxovanadate-modified lithium sheet has good wetting effect on the electrolyte, has high lithium ion diffusion ability, can effectively induce uniform deposition of lithium ions, thereby inhibiting the growth of lithium dendrites, and the assembled lithium-sulfur battery has high reversible capacity and stable cycling performance.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions: A polyoxovanadate-modified lithium sheet, wherein the polyoxovanadate is a high-nuclear mixed-valence polyoxovanadate, and the molecular formula is K 10 [V 34 O 82 ·20H2O.

[0007] The preparation method of the high-nuclear mixed-valence polyoxovanadate is to dissolve KVO3 in deionized water, heat and stir until the solution is clear to obtain a KVO3 solution, add a hydrazine hydrate solution to the solution, and keep the solution heated at 88 - 92 °C for 0.8 - 1.2 hours; then add glacial acetic acid until the pH value of the solution is 3.7 - 3.9, keep the solution heated at 88 - 92 °C for 1.8 - 2.2 hours, filter the solution while it is hot, and heat the obtained filtrate at 88 - 92 °C for 2.8 - 3.2 hours. Cool the solution to room temperature, let it stand and filter to obtain needle-shaped crystals, and obtain the high-nuclear mixed-valence polyoxovanadate after washing and drying.

[0008] The mass concentration of the KVO3 solution is 6.4 - 6.5%; The mass concentration of the hydrazine hydrate solution is 78 - 82%; The mass-volume ratio of the KVO3 solution to the hydrazine hydrate solution is 1 g : 3.3 - 3.5 μL; The preparation method of the polyoxovanadate-modified lithium sheet is to add the high-nuclear mixed-valence polyoxovanadate into ethylene glycol dimethyl ether to prepare a suspension with a concentration of 0.8 - 1.2 mM, immerse the polished lithium sheet in the suspension, stir for 17 - 19 hours, and then dry in the air to obtain the polyoxovanadate-modified lithium sheet.

[0009] The original thickness of the lithium sheet is 580 - 620 μm, and the diameter is 15.5 - 16.5 mm.

[0010] The stirring speed is 380 - 420 revolutions per minute.

[0011] The application of the polyoxovanadate-modified lithium sheet in a lithium metal battery.

[0012] As an important branch of polyoxometalates, polyoxovanadates exhibit excellent redox ability and can maintain a stable framework structure after reversible multi-electron redox reactions. In addition, the terminal oxygen atoms provide abundant sites for the transport of lithium ions, which can increase the lithium ion conductivity and reduce the lithium ion concentration gradient in the battery.

[0013] In this invention, high-nuclear mixed-valence polyoxovanadates are first applied to the modification of the anode of lithium metal batteries. An artificial SEI film is in-situ constructed on the lithium surface. Without changing the overall structure of the anode, the functions on the surface of the lithium metal anode change significantly. The pentavalent vanadium in the high-nuclear mixed-valence polyoxovanadates has excellent oxidation performance, while the tetravalent vanadium can enhance the electron transfer efficiency of the whole system, effectively improving the diffusion rate of lithium ions, and then eliminating the phenomenon of lithium ion concentration gradient inside the battery. The lithium-rich layer formed by polyoxovanadates on the lithium sheet surface can fill the missing lithium ions on the surface of the lithium metal anode, induce the uniform deposition of lithium ions, thus reducing the generation of lithium dendrites, and can also isolate the contact between the lithium metal and the electrolyte, reducing interfacial side reactions.

[0014] Compared with the prior art, this invention has the following beneficial effects: 1. The V 34 modified lithium sheet in this invention has good wetting effect on the electrolyte, which can ensure the effective diffusion of the electrolyte, thus accelerating the transport of lithium ions.

[0015] 2. The lithium ion transference number of the V 34 modified lithium sheet prepared in this invention is 0.54, which is significantly higher than that of commercial lithium sheets.

[0016] 3. The Li / / Li symmetric battery assembled with the V 34 modified lithium sheet in this invention has good cycle performance and rate performance.

[0017] 4. The Li / / Cu half-cell assembled with the V 34 modified lithium sheet in this invention, under the test conditions of 1 mA / cm 2 and 1 mAh / cm 2 , can be stably charged and discharged 300 times, and the average coulombic efficiency is 97.6%; under the test conditions of 1 mA / cm 2 and 1 mAh / cm 2 , the initial nucleation overpotential is 0.043 V. The lower nucleation overpotential can ensure uniform lithium deposition and reduce the occurrence of side reactions.

[0018] 5. Using the V 34The lithium-sulfur battery assembled with the modified lithium sheet has an excellent reversible capacity. At a discharge rate of 1C, after 200 cycles, it has a capacity of 418.1 mAh / g, while the capacity of the commercially available lithium-sulfur battery assembled with the lithium sheet decays to 195.3 mAh / g after 200 cycles.

[0019] 6. The V prepared by the present invention 34 The modified lithium sheet has an excellent effect of inhibiting lithium dendrites, thereby preventing lithium dendrites from piercing the separator and reducing the risk of battery short circuit. Description of the Drawings

[0020] Figure 1 For V 34 Structural characterization spectrum; Among them, (a) is the XRD spectrum of V 34 , (b) is the FTIR spectrum of V 34 ; Figure 2 For V 34 Digital photo and SEM images of the modified lithium sheet; Among them, (a) is the digital photo of the modified lithium sheet of V 34 , (b) is the SEM image of the surface of the modified lithium sheet of V 34 , (c) is the SEM image of the cross-section of the modified lithium sheet of V 34 , (d) is the Mapping image of the cross-section of the modified lithium sheet of V34, (e) is the distribution map of O element in the cross-section of the modified lithium sheet of V34, (f) is the distribution map of K element in the cross-section of the modified lithium sheet of V34, (g) is the distribution map of V element in the cross-section of the modified lithium sheet of V34; Figure 3 For the original V 34 and V 34 XPS analysis diagram of the modified lithium sheet; Among them, (a) is the full XPS spectrum of the original V 34 and V 34 modified lithium sheet, (b) is the V 2p spectrum of the original V 34 and V 34 modified lithium sheet, (c) is the V 34 and V 34 modified lithium sheet 5+ and V 4+ content percentage bar chart; Figure 4 For the original lithium sheet and V 34 contact angle test diagram of the modified lithium sheet; Among them, (a) is the contact angle test diagram of the original lithium sheet; (b) is the contact angle test diagram of the modified lithium sheet of V 34 ; Figure 5 For the original lithium sheet, V 34Nyquist impedance plots and potentiostatic polarization curves of Li / / Li symmetric cells assembled with modified lithium foils; Among them, (a) are the Nyquist impedance plots of the Li / / Li symmetric cell assembled with pristine lithium foil before and after polarization, and (b) is V 34 the Nyquist impedance plots of the Li / / Li symmetric cell assembled with modified lithium foil before and after polarization, (c) is the potentiostatic polarization curve of the Li / / Li symmetric cell assembled with pristine lithium foil, and (d) is V 34 the potentiostatic polarization curve of the Li / / Li symmetric cell assembled with modified lithium foil; Figure 6 For pristine lithium foil and V 34 cycling performance and rate performance test plots of Li / / Li symmetric cells assembled with modified lithium foils; Among them, (a) is the cycling performance plot under the test conditions of 1 mA / cm 2 and 1 mAh / cm 2 ; (b) is the cycling performance plot under the test conditions of 5 mA / cm 2 , 3 mAh / cm 2 ; (c) is the cycling performance plot under the test conditions of 3 mA / cm 2 , 1 mAh / cm 2 ; (d) is the rate performance test plot; Figure 7 For pristine lithium foil and V 34 Coulombic efficiency and initial nucleation overpotential test plots of Li / / Cu half-cells assembled with modified lithium foils; Among them, (a) is the Coulombic efficiency plot under the test conditions of 1 mA / cm 2 and 1 mAh / cm 2 ; (b) is the Coulombic efficiency plot under the test conditions of 1 mA / cm 2 and 3 mAh / cm 2 ; (c) is the Coulombic efficiency plot under the test conditions of 3 mA / cm 2 and 1 mAh / cm 2 ; (d) is the initial nucleation overpotential test plot under the test conditions of 1 mA / cm 2 and 1 mAh / cm 2 ; Figure 8 For pristine lithium foil and V 34 cycling performance and rate performance plots of lithium-sulfur batteries assembled with modified lithium foils; Among them, (a) is the cycling performance plot of the lithium-sulfur battery assembled with pristine lithium foil and V 34 modified lithium foil at a current density of 1 C, and (b) is the rate performance plot of the lithium-sulfur battery assembled with pristine lithium foil and V 34 modified lithium foil; Figure 9 The original lithium sheet, V 34 SEM images of the surface of the lithium sheet after different cycle times of the Li / / Li symmetric battery assembled with the modified lithium sheet; Among them, (a) is the SEM image of the surface of the lithium sheet after 50 h of cycling of the Li / / Li symmetric battery assembled with the original lithium sheet, (b) is the SEM image of the surface of the lithium sheet after 100 h of cycling of the Li / / Li symmetric battery assembled with the original lithium sheet, (c) is V 34 The SEM image of the surface of the lithium sheet after 50 h of cycling of the Li / / Li symmetric battery assembled with the modified lithium sheet, (d) is V 34 The SEM image of the surface of the lithium sheet after 100 h of cycling of the Li / / Li symmetric battery assembled with the modified lithium sheet; Figure 10 For V 34 XPS spectroscopy test of the Li / / Li symmetric battery assembled with the modified lithium sheet at different cycle numbers and the bar chart of the content ratio of V 5+ and V 4+ ; Among them, (a) is the XPS spectrogram of the stripping surface of the lithium electrode at the 1st cycle and the 25th cycle, (b) is the XPS spectrogram of the deposition surface of the lithium electrode at the 1st cycle and the 25th cycle, (c) is the bar chart of the content ratio of V 5+ and V 4+ at the stripping surface of the lithium electrode before cycling, at the 1st cycle, and at the 25th cycle, (d) is the bar chart of the content ratio of V 5+ and V 4+ at the deposition surface of the lithium electrode before cycling, at the 1st cycle, and at the 25th cycle. Specific implementation method

[0021] Example 1 Preparation method of a high-nuclear mixed-valence polyoxovanadate functional material modified lithium sheet Comprising the following steps: Step 1, Preparation of high-nuclear mixed-valence polyoxovanadate (Reference: Angew. Chem. Int. Ed., 1991, 30(5): 588 - 590) Weigh 6.9 g of KVO3 and dissolve it in 100 g of deionized water. Heat and stir at 90 °C until the solution is clear to obtain a KVO3 solution. Add 364 μL of a hydrazine hydrate solution with a mass concentration of 80% to the solution, and keep heating at 90 °C for 1 hour. Then add glacial acetic acid until the pH value of the solution is 3.8, and keep heating the solution at 90 °C for 2 hours. Filter the solution while it is hot, and heat the obtained filtrate at 90 °C for 3 hours. Cool the solution to room temperature, let it stand for 1 day, and filter to obtain needle-shaped crystals. Wash with a small amount of 50% (volume percentage) isopropyl alcohol aqueous solution, and dry to obtain the product denoted as V 34, namely high-nuclear mixed-valence polyoxovanadates.

[0022] The molecular formula of the high-nuclear mixed-valence polyoxovanadates is K 10 [V 34 O 82 ·20H2O (abbreviation: V 34 ).

[0023] Step 2: Preparation of V 34 modified lithium foil Add V 34 to ethylene glycol dimethyl ether to prepare a suspension with a concentration of 1 mM. Polish the original lithium foil with a thickness of 600 μm and a diameter of 16 mm with a nylon brush to expose fresh metallic lithium. Then place the surface-polished lithium foil in the suspension and stir at 400 revolutions per minute for 18 hours, keeping the lithium foil completely immersed in the suspension. Take it out and dry it for 1 hour to obtain V 34 modified lithium foil.

[0024] Example 2: Structure characterization of high-nuclear mixed-valence polyoxovanadates The high-nuclear mixed-valence polyoxovanadates prepared in Example 1 were tested by X-ray powder diffraction (XRD). The results are as Figure 1 (a) shown. The main characteristic peaks at 5.69°, 7.16°, 7.48°, 7.79° and 8.18° are basically consistent with the main peak positions of the XRD of the single-crystal simulation data.

[0025] The high-nuclear mixed-valence polyoxovanadates prepared in Example 1 were tested by Fourier transform infrared spectroscopy (FTIR). The results are as Figure 1 (b) shown. The peaks at 990 cm -1 and 890 cm -1 are attributed to the asymmetric stretching vibration of the V=O bond. The characteristic peaks at 745 cm -1 and 615 cm -1 are attributed to the antisymmetric stretching vibration of the V-O-V bridging oxygen bond. The above characteristic peaks are consistent with those reported in the literature (Angew. Chem. Int. Ed., 1991, 30(5): 588-590). In summary, the high-nuclear mixed-valence polyoxovanadates K 10 [V 34 O 82 ·20H2O (abbreviation: V 34 ) were successfully prepared in Example 1.

[0026] Example 3: Characterization of V 34 modified lithium foil The digital photograph of the V 34 modified lithium foil prepared in Example 1 is as Figure 2 (a) shown. The surface color of the lithium foil becomes significantly darker, indicating that V34 Reacted chemically with metallic lithium, thus in-situ modifying V on the lithium surface 34 . Subsequently, further scanning electron microscopy (SEM) tests were conducted on the surface and cross-section of the V 34 -modified lithium sheet. Figure 2 (b) shows that there are no obvious cracks on the surface of the V 34 -modified lithium sheet, and V 34 is evenly dispersed without obvious agglomeration. As can be seen from Figure 2 (c), the thickness of the modified layer is approximately 43 μm. From the elemental distribution maps ( Figure 2 (d)-(g)), it can be further observed that the O, V, and K elements are evenly distributed in the modified layer.

[0027] XPS analysis was performed on the original V 34 and the V 34 -modified lithium sheet. The full XPS spectra are shown as Figure 3 (a), and the peaks of the O, V, and K elements can be observed. The V 2p spectrogram is shown as Figure 3 (b). The electron binding energies of V 4+ are close to 516.3 eV (2p 3 / 2 ) and 523.8 eV (2p 1 / 2 ), and the electron binding energies of V 5+ are close to 517.6 eV (2p 3 / 2 ) and 525.1 eV (2p 1 / 2 ), indicating that the anion cluster in this crystal is a mixed-valence cluster. After V 34 was modified on the lithium sheet, both V 4+ and V 5+ shifted towards lower binding energies, indicating an obvious chemical reaction occurred between V 34 and the lithium sheet. Figure 3 (c) shows the content ratios of V 34 in the original V 34 and the V 4+ -modified lithium sheet. It can be seen that after V 5+ was modified on the lithium sheet surface, it presented a reduced state. 34

[0028] Wettability test of the electrolyte in Example 4 Lithium bis(trifluoromethanesulfonyl)imide was dissolved in a solvent of 1,3-dioxolane and ethylene glycol dimethyl ether (volume ratio 1:1) to prepare a 1 M solution, and then 2% (mass percentage) of lithium nitrate was added to obtain the electrolyte.

[0029] The test method is as follows: ​Attach the lithium sheet to the glass slide and place it on the contact angle measuring instrument. Use a micro syringe to aspirate 50 µL of the electrolyte. Place the micro syringe filled with the electrolyte at the fixed position of the contact angle measuring instrument. Adjust the knob to make the micro syringe drop the electrolyte, and drop a drop of the electrolyte directly above the lithium sheet. Then, take a picture with the contact angle measuring instrument.

[0030] The pristine lithium sheet and V 34 The test results of the wettability of the modified lithium sheet to the electrolyte are as Figure 4 shown.

[0031] This test monitored the change of the contact angle between the pristine lithium sheet and V 34 the modified lithium sheet and the electrolyte at different time intervals. Figure 4 As shown, at the beginning of the test, the contact angles between the pristine lithium sheet and V 34 the modified lithium sheet and the electrolyte were 39° and 24° respectively. After 0.5 s, the contact angles were 31° and 11° respectively. After 1 s, the contact angle between V 34 the modified lithium sheet and the electrolyte decreased to 5°, which was much smaller than that of the pristine lithium sheet (28°). Therefore, it can be concluded that V 34 the modified lithium sheet has a certain promoting effect on the wettability of the electrolyte. A good wetting effect on the electrolyte can ensure the effective diffusion of the electrolyte, thus accelerating the transport of lithium ions.

[0032] Example 5 Impedance and Lithium Ion Transference Number Test Assemble the pristine lithium sheet and V 34 the modified lithium sheet into a Li / / Li symmetric cell, test the initial impedance, apply a voltage of 10 mV at both ends of the cell for polarization, record the generated current, and after the current stabilizes, test the stable impedance.

[0033] The Nyquist impedance diagrams of the Li / / Li symmetric cell assembled with the pristine lithium sheet before and after polarization are as Figure 5 shown in (a); V 34 The Nyquist impedance diagrams of the Li / / Li symmetric cell assembled with the modified lithium sheet before and after polarization are as Figure 5 shown in (b).

[0034] The pristine lithium sheet and V 34 the modified lithium sheet were assembled into a Li / / Li symmetric cell, and the potentiostatic polarization curves were measured at 10 mV. The results are as Figure 5 shown in (c) and 5(d).

[0035] After calculation, the t 34 values of the pristine lithium sheet and V Li + the modified lithium sheet were 0.37 and 0.54 respectively. Compared with the pristine lithium sheet, V 34The modified lithium sheet shows higher lithium ion migration ability.

[0036] Example 6 Electrochemical Performance Test The Li / / Li symmetric cells assembled with the original lithium sheet and V 34 modified lithium sheet were subjected to cyclic performance tests. The symmetric cells assembled with the V 34 modified lithium sheet could be stably cycled for 1900 hours under the test conditions of 1 mA / cm 2 and 1 mAh / cm 2 , while the symmetric cells assembled with the original lithium sheet could only maintain cycling for 200 hours and then showed obvious voltage polarization phenomenon ( Figure 6 (a)); under the test conditions of 5 mA / cm 2 , 3 mAh / cm 2 and 3 mA / cm 2 , 1 mAh / cm 2 , the Li / / Li symmetric cells assembled with the V 34 modified lithium sheet could still be stably cycled for 500 hours and 900 hours respectively ( Figure 6 (b) and Figure 6 (c)). In addition, the rate performance test shows that at different current densities, the symmetric cells using the V 34 modified lithium sheet exhibit smaller overpotentials than the symmetric cells using the original lithium sheet ( Figure 6 (d)). The overpotentials of the Li / / Li symmetric cells using the V 34 modified lithium sheet are 0.019 V, 0.033 V, 0.060 V, 0.082 V under the test conditions of 1 mA / cm 2 , 2 mA / cm 2 , 3 mA / cm 2 , 5 mA / cm 2 respectively; while the overpotentials of the Li / / Li symmetric cells using the original lithium sheet are 0.024 V, 0.070 V, 0.085 V, 0.105 V under the test conditions of 1 mA / cm 2 , 2 mA / cm 2 , 3 mA / cm 2 , 5 mA / cm 2 respectively.

[0037] The Li / / Cu half-cells assembled with the original lithium sheet and V 34 modified lithium sheet were tested for Coulomb efficiency and initial nucleation overpotential.

[0038] At 1 mA / cm 2 , 1 mAh / cm 2Under the test conditions, after 140 cycles, the Coulombic efficiency of the Li / / Cu half-cell using the original lithium foil showed a downward trend, while the Li / / Cu half-cell using the V 34 modified lithium foil could be stably charged and discharged 300 times with an average Coulombic efficiency of 97.6% ( Figure 7 Figure (a)). At 1 mA / cm 2 ², 3 mAh / cm 2 ² and 3 mA / cm 2 ², 1 mAh / cm 2 ² test conditions, the Li / / Cu half-cell using the V 34 modified lithium foil could be stably charged and discharged 100 times and 120 times with average Coulombic efficiencies of 96.6% and 96.1% respectively ( Figure 7 Figure (b) and Figure 7 Figure (c)), which was significantly better than the Coulombic efficiency of the original lithium foil. At 1 mA / cm 2 ², 1 mAh / cm 2 ² test conditions, the initial nucleation overpotential of the Li / / Cu half-cell assembled with the V 34 modified lithium foil was 0.043 V, while that of the Li / / Cu half-cell assembled with the original lithium foil was 0.071 V ( Figure 7 Figure (d)). The lower nucleation overpotential can ensure uniform lithium deposition and reduce the occurrence of side reactions.

[0039] The original lithium foil and the V 34 modified lithium foil were assembled into a lithium-sulfur battery and its cycling performance was tested. As shown in Figure 8 Figure (a), at a current density of 1 C, the capacity of the lithium-sulfur battery assembled with the V 34 modified lithium foil remained at 418.1 mAh / g after 200 cycles, while the capacity of the lithium-sulfur battery assembled with the original lithium foil decayed to 195.3 mAh / g after 200 cycles. As shown in Figure 8 Figure (b), when the current density increased from 0.2 C to 0.5 C, 1 C, 2 C, 3 C and 5 C, the specific capacity of the lithium-sulfur battery with the V 34 modified lithium foil decreased from 947.1 to 667.3, 540.6, 452.8, 383.5 and 296.1 mAh / g. When the current density returned to 0.2 C, the capacity recovered to 591.1 mAh / g. While the specific capacities of the lithium-sulfur battery assembled with the original lithium foil at 0.2 C, 0.5 C, 1 C, 2 C, 3 C and 5 C were only 722.6, 412.8, 276.2, 169.2, 126.1 and 83.7 mAh / g respectively, and when the current density returned to 0.2 C, the specific capacity was 350.3 mAh / g.

[0040] Morphology characterization and component testing of the lithium anode after cycling in Example 7 Using the pristine lithium foil and V 34 modified lithium foil, Li / / Li symmetric cells were assembled. Under the conditions of 1 mA / cm 2 and 1 mAh / cm 2 , the morphological changes of the lithium anode surface during cycling were analyzed by SEM characterization. With the increase in the number of cycles on the lithium surface using the pristine lithium foil, a large number of lithium dendrites continued to grow ( Figure 9 (a) and Figure 9 (b)). On the lithium surface using the V 34 modified lithium foil, effective lithium dendrite inhibition was exhibited during the initial cycle. During subsequent multiple stripping / deposition processes, lithium metal was deposited in an irregular dense pebble shape, forming "lithium pebbles" with uniform size and tight connection, with almost no gaps and lithium dendrites ( Figure 9 (c) and Figure 9 (d)). Therefore, V 34 helps to inhibit the growth of lithium dendrites and achieve uniform and stable lithium deposition.

[0041] To study the compositional changes of V 34 during the lithium deposition / stripping process, the Li / / Li symmetric cells assembled with the V 34 modified lithium foil were disassembled after cycling 1 and 25 times respectively, and then XPS spectroscopy tests were performed on the V 34 modified lithium surface ( Figure 10 (a) and Figure 10 (b)). Figure 10 (c) statistically analyzed the content ratios of V 5+ and V 4+ on the stripping surface of the lithium electrode. It can be seen that after the first cycle, the content of V 5+ on the stripping surface of the lithium electrode increased from the original 57.76% to 68.54%, and the content of V 4+ decreased from the original 42.24% to 31.46%. After 25 cycles, the content of V 5+ on the stripping surface of the lithium electrode was still 67.57%, and the content of V 4+ was 32.43%. Figure 10 (d) statistically analyzed the content ratios of V 5+ and V 4+ on the deposition surface of the lithium electrode. It can be seen that after the first cycle, the content of V 5+ on the deposition surface of the lithium electrode decreased from the original 57.76% to 53.57%, and the content of V 4+ increased from the original 42.24% to 46.43%. After 25 cycles, the content of V 5+ on the deposition surface of the lithium electrode was still 52.48%, and the content of V 4+ was 47.52%. The above experimental results show that V34 Exhibits excellent redox reversibility during the deposition and stripping of lithium and maintains high structural stability even after multiple cycles.

Claims

1. A polyvanadate-modified lithium sheet, characterized in that: The polyvanadate is a high-nuclear mixed-valence polyvanadate with a molecular formula of K 10 [V 34 O 82 ]·20H2O.

2. The method for preparing the polyvanadium oxyphosphate modified lithium sheet according to claim 1, characterized in that: High-nuclear mixed-valence polyvanadate is added to ethylene glycol dimethyl ether to prepare a suspension with a concentration of 0.8-1.2 mM, and a surface-polished lithium sheet is immersed in the suspension, stirred for 17-19 hours, and then dried to obtain a polyvanadate-modified lithium sheet.

3. The preparation method according to claim 2, characterized in that: The original thickness of the lithium sheet is 580-620 μm and the diameter is 15.5-16.5 mm.

4. Use of the polyvanadium oxyphosphate modified lithium sheet according to claim 1 in lithium metal batteries.

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