Preparation method of chromium / manganese bimetallic sulfide cathode composite material

Abstract

The present invention relates to a preparation method of a chromium / manganese bimetallic sulfur cathode composite material, belonging to the technical field of lithium-sulfur battery cathodes. In the present invention, a MIL-101(Cr) precursor is prepared by a hydrothermal method; the MIL-101(Cr) precursor is dispersed in deionized water to obtain a suspension C, KMnO4 is added to the suspension C and stirred for 2-3 h, then a dilute H2O2 solution is added and stirred for 2-3 h, solid-liquid separation is carried out, the solid is washed with deionized water more than three times, and then uniformly heated to a temperature of 900-950 °C in an argon atmosphere and thermally decomposed at a constant temperature for 2-3 h to obtain Cr2O 3 / MnO x -C; Cr2O 3 / MnO x -C and sublimed sulfur powder are ground and mixed evenly, and uniformly heated to a temperature of 155-165 °C in an inert gas and reacted at a constant temperature for 18-20 h, and cooled to room temperature to obtain a chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C. The chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C has excellent electrochemical performance. Compared with the sulfur cathode prepared from the original MOF material MIL-101(Cr), the initial specific capacity at 0.1C is increased by 43%, the 100-cycle performance is increased by 27%, and the rate performance and Coulomb efficiency are improved.

Description

Technical Field

[0001] The present invention relates to a preparation method of a chromium / manganese bimetallic sulfur cathode composite material, belonging to the technical field of lithium-sulfur battery cathodes. Background Art

[0002] Lithium-sulfur batteries have advantages such as ultra-high theoretical specific capacity (1675 mAh / g), theoretical energy density (2600 Wh / kg), rich sulfur reserves, and low price, and are considered to be one of the most promising new energy storage systems, which can be applied to fields such as electric vehicles, portable electronic products, and large-scale energy storage. However, the battery system has defects such as extremely low electron and ionic conductivity of the reactant elementary sulfur S8 and the final reduction products Li2S2 and Li2S, volume expansion and contraction of the electrode during charge and discharge, and the shuttle effect of polysulfides. Among the cathode materials of lithium-sulfur batteries, metal-organic frameworks can optimize the performance of lithium-sulfur batteries. By reasonably designing and precisely controlling the pore structure of MOFs, the shuttle effect can be effectively inhibited and the sulfur content can be increased. For example, the MIL-100(Cr) material with a cage-like pore structure can provide central ion active sites for strongly chemically adsorbing polysulfides, which can alleviate the excessive dissolution of polysulfides. However, the poor conductivity and catalytic activity of the MIL-100(Cr) material lead to a high energy barrier for the mutual conversion between polysulfides and Li2S in lithium-sulfur batteries, slow reaction kinetics, low sulfur utilization rate, and poor rate performance. Summary of the Invention

[0003] Aiming at the problems of high energy barrier for the mutual conversion between polysulfides and Li2S in lithium-sulfur batteries, slow reaction kinetics, low sulfur utilization rate, and poor rate performance caused by the poor conductivity and catalytic activity of the existing MIL-100(Cr) material, the present invention proposes a preparation method of a chromium / manganese bimetallic sulfur cathode composite material, that is, using MIL-101(Cr) as the main material, doping Mn in MIL-101(Cr) to prepare bimetallic MOFs. Therefore, the bimetallic MOFs are combined with manganese oxide with good catalytic oxidation activity and MIL-101(Cr), and have good catalytic activity, conductive performance, and excellent electrochemical performance.

[0004] A preparation method of a chromium / manganese bimetallic sulfur cathode composite material is as follows:

[0005] (1) Grind chromium(III) nitrate nonahydrate and terephthalic acid and add them to deionized water to stir and dissolve to obtain solution A. Add hydrofluoric acid to solution A, stir and mix evenly, and perform ultrasonic treatment to obtain suspension B; subject suspension B to hydrothermal reaction at a temperature of 220-230 °C for 15-18 h, perform solid-liquid separation, vacuum dry the solid, and then wash it alternately with N,N-dimethylformamide DMF, ethanol, and water more than 3 times, and vacuum dry to obtain the MIL-101(Cr) precursor;

[0006] (2) Disperse the MIL-101(Cr) precursor in deionized water to obtain suspension C. Add KMnO4 to suspension C and stir for reaction for 2 - 3 h. Then add dilute H2O2 solution and stir for reaction for 2 - 3 h. Perform solid-liquid separation. Wash the solid with deionized water more than three times, and then place it in an inert gas and heat it uniformly to a temperature of 900 - 950 °C and thermally decompose it at a constant temperature for 2 - 3 h to obtain Cr2O 3 / MnO x -C;

[0007] (3) Grind and mix Cr2O 3 / MnO x -C and sublimed sulfur powder evenly. Place it in an inert gas and heat it uniformly to a temperature of 155 - 165 °C and react at a constant temperature for 18 - 20 h. Cool it to room temperature to obtain the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C.

[0008] In the said step (1), the mass ratio of chromium(III) nitrate nonahydrate to terephthalic acid is 2.4 - 2.8:1, and the concentration of chromium(III) nitrate in solution A is 48 - 56 g / L.

[0009] In the said step (1), the volume ratio of hydrofluoric acid to solution A is 0.2 - 0.25:100.

[0010] In the said step (2), the concentration of the MIL-101(Cr) precursor in suspension C is 6 - 7 g / L, and the mass ratio of KMnO4 to the MIL-101(Cr) precursor is 0.10 - 0.52:1.

[0011] Preferably, in the said step (2), the mass concentration of the dilute H2O2 solution is 1 - 3%, and the volume ratio of the dilute H2O2 solution to suspension C is 0.5 - 0.7:1.

[0012] In the said step (3), the mass ratio of Cr2O 3 / MnO x -C and sublimed sulfur powder is 0.3 - 0.7:1.

[0013] The chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C is subjected to electrochemical performance testing: Mix the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C powder, super carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, grind and mix them, and assemble them into a CR2025 button cell; after standing for 24 h, test its charge-discharge performance.

[0014] Principle of Mn doping process: First, add KMnO4 to pre-impregnate MIL-101(Cr) and oxidize MIL-101(Cr). Then, add H2O2 to the suspension to reduce the suspension so that after KMnO4 is reduced, manganese oxide MnO x is doped into MIL-101(Cr) in this form;

[0015] Principle of the chromium / manganese bimetallic sulfur cathode composite material with catalytic activity, electrical conductivity, and excellent electrochemical performance: In the chromium / manganese bimetallic sulfur cathode composite material, both chromium and manganese have catalytic activity. And when the two metals coexist, there will be charge transfer between metal ions, which will further improve the catalytic activity of the material; MIL-101(Cr) belongs to metal-organic framework materials and has a large number of organic groups. By pyrolyzing the organic groups on the periphery of the chromium-manganese composite material, carbonization is carried out, so that the chromium / manganese bimetallic sulfur cathode composite material has good electrical conductivity;

[0016] During the electrode discharge process of the lithium-sulfur battery, mainly the negative electrode metallic lithium is oxidized to generate lithium ions. At the same time when lithium ions are generated, electrons (e - ) are generated; the generated lithium ions will dissolve in the electrolyte of the battery and then pass through the diaphragm to the battery positive electrode along with the potential difference; at this time, the electrons also reach the positive electrode through the external circuit. So, under the joint action of the active substance sulfur, lithium ions, and electrons, lithium sulfide will be generated at the battery positive electrode; the process of the discharge reaction at the lithium-sulfur battery positive electrode is mainly a process in which S8 molecules are continuously reduced. First, soluble polysulfides Li2S6 and Li2S4 are generated, and then further reactions generate insoluble polysulfides Li2S2 and Li2S. There is a relatively high chemical reaction barrier during the conversion of soluble polysulfide lithium to insoluble polysulfide lithium. The catalytic activity in the chromium / manganese bimetallic sulfur cathode composite material can increase the activation energy during the reaction process, thereby increasing the reaction rate and further improving the electrochemical performance of the electrode material; at the same time, the improvement of the electrical conductivity of the chromium / manganese bimetallic sulfur cathode composite material can increase the conduction rate of ions and electrons during the electrode reaction process, reduce the electrochemical polarization effect in the battery, and thus improve the electrochemical performance of the electrode material.

[0017] The beneficial effects of the present invention are:

[0018] (1) In the present invention, MIL-101(Cr) is used as the main material, and Mn is doped in MIL-101(Cr) to prepare bimetallic MOFs. Therefore, the bimetallic MOFs are combined with manganese oxide with good catalytic oxidation activity and MIL-101(Cr), and have good catalytic activity, electrical conductivity, and excellent electrochemical performance;

[0019] (2) The chromium / manganese bimetallic sulfur cathode composite material of the present invention exhibits a reduction peak at a higher potential and an oxidation peak at a lower potential in cyclic voltammetry. The initial discharge specific capacity is 1285.6 mAh·g at 0.1C (1C = 1675 mA / g). -1 After 100 charge-discharge cycles, the remaining specific capacity is 721.4 mAh·g. -1 ;

[0020] (3) The S / Cr₂O 3 / MnO x -C electrochemical performance of the chromium / manganese bimetallic sulfur cathode composite material of the present invention is excellent. Compared with the sulfur cathode prepared from the original MOF material MIL-101(Cr), the initial specific capacity at 0.1C is increased by 43%, the 100-cycle performance is increased by 27%, and the rate performance and Coulomb efficiency are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. is a comparative cyclic voltammogram of the chromium / manganese bimetallic sulfur cathode composite material S / Cr₂O 3 / MnO x -C and S / MIL-101(Cr) in Example 1;

[0022] Figure 2 FIG. is a comparative first-cycle charge-discharge performance diagram of the chromium / manganese bimetallic sulfur cathode composite material S / Cr₂O 3 / MnO x -C and S / MIL-101(Cr) at a current density of 0.1C in Example 1;

[0023] Figure 3 FIG. is a comparative 100-cycle charge-discharge cycle specific capacity diagram of the chromium / manganese bimetallic sulfur cathode composite material S / Cr₂O 3 / MnO x -C and S / MIL-101(Cr) at a current density of 0.1C in Example 1;

[0024] Figure 4 FIG. is a comparative multi-rate discharge specific capacity and Coulomb efficiency diagram of the chromium / manganese bimetallic sulfur cathode composite material S / Cr₂O 3 / MnO x -C and S / MIL-101(Cr) in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described in detail below in conjunction with the specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0026] Example 1: A preparation method of a chromium / manganese bimetallic sulfur cathode composite material, the specific steps are as follows:

[0027] (1) Chromium(III) nitrate nonahydrate and terephthalic acid were ground and then added to deionized water and stirred to dissolve to obtain solution A. Hydrofluoric acid was added to solution A, stirred and mixed evenly, and ultrasonicated for 10 min to obtain suspension B; suspension B was hydrothermally reacted at 220 °C for 15 h, and then solid-liquid separation was carried out. The solid was vacuum dried at 120 °C for 12 h, and then alternately washed 3 times with N,N-dimethylformamide (DMF), ethanol and water, and then vacuum dried at 60 °C for 12 h to obtain the MIL-101(Cr) precursor; the mass ratio of chromium(III) nitrate nonahydrate to terephthalic acid was 2.4:1, the concentration of chromium nitrate in solution A was 50 g / L, and the volume ratio of commercially available hydrofluoric acid to solution A was 0.225:100;

[0028] (2) The MIL-101(Cr) precursor was dispersed in deionized water to obtain suspension C. KMnO4 was added to suspension C and stirred for 2 h, and then dilute H2O2 solution was added and stirred for 2 h. Solid-liquid separation was carried out. The solid was washed with deionized water more than three times, and then uniformly heated to 900 °C in an inert gas and thermally decomposed at a constant temperature for 2 h to obtain Cr2O 3 / MnO x -C; the concentration of the MIL-101(Cr) precursor in suspension C was 6.5 g / L, and the mass ratio of KMnO4 to the MIL-101(Cr) precursor was 0.26:1;

[0029] (3) Cr2O 3 / MnO x -C and sublimed sulfur powder were ground and mixed evenly, and then uniformly heated to 155 °C in an inert gas and reacted at a constant temperature for 18 h, and then cooled to room temperature to obtain the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C; the mass ratio of Cr2O 3 / MnO x -C to sublimed sulfur powder was 3:7;

[0030] In this example, the cyclic voltammetry curve comparison diagram of the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C and the comparative example S / MIL-101(Cr) (without adding Mn) is shown in Figure 1 , from Figure 1 it can be seen that the voltage of the reduction peak of the S / Cr2O3 / MnO x -C electrode is higher, the voltage of the oxidation peak is lower, and the potential difference is smaller than that of S / MIL-101(Cr); this shows that the S / Cr2O3 / MnO x -C electrode has better active material utilization rate, and the chemical reaction process becomes smoother, which indicates that the catalytic performance of the material is improved after Mn loading;

[0031] In this example, the first charge-discharge performance comparison diagram of the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C and S / MIL-101(Cr) at a current density of 0.1C can be seen in Figure 2 , from Figure 2 it can be known that the S / Cr2O3 / MnO x -C electrode material has the highest initial specific capacity of 1285.6 mAh·g -1 , which is higher than 901.8 mAh·g of the S / MIL-101(Cr) electrode material -1 initial specific capacity; the specific capacity provided by the second discharge platform of the S / Cr2O3 / MnO x -C electrode material has a significant increase compared to the S / MIL-101(Cr) electrode, which benefits from the improved conductivity obtained after pyrolysis of the material and the improved catalytic activity after loading manganese, resulting in an increase in the utilization rate of active substances during the electrode reaction process;

[0032] In this example, the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C and the 100-cycle charge-discharge cycle specific capacity comparison diagram of S / MIL-101(Cr) at a current density of 0.1C can be seen in Figure 3 , from Figure 3 it can be known that the performance of the S / MIL-101(Cr) electrode is inferior to that of the S / Cr2O3 / MnO x -C electrode in terms of both initial discharge capacity and cycle stability; the initial discharge specific capacity of the S / MIL-101(Cr) electrode is 901.5 mAh·g -1 , and the remaining specific capacity after 100 charge-discharge cycles is 260.3 mAh·g -1 ; compared with the S / MIL-101(Cr) electrode, the S / Cr2O3 / MnO x -C electrode shows an initial specific capacity of 1285.6 mAh·g -1 and a specific capacity of 721.4 mAh·g -1 after 100 cycles. The S / Cr2O3 / MnO x -C electrode is significantly superior to the S / MIL-101(Cr) electrode in terms of both initial specific capacity and cycle efficiency;

[0033] In this example, the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C and the comparison diagram of the multi-rate discharge specific capacity and Coulomb efficiency of S / MIL-101(Cr) can be seen in Figure 4 , from Figure 4It can be seen that at all current densities, the specific capacity of S / Cr2O3 / MnO x -C exceeds that of S / MIL-101(Cr); in terms of the overall cycling efficiency, the addition of Mn improves the specific capacity and cycling performance of the battery to a certain extent at low discharge rates, while the improvement of the specific capacity and cycling efficiency of the battery is limited at high discharge rates because the addition of Mn originally occupies a certain area in the pores of the MOF material, restricting the space for Li + ions, resulting in a certain degree of tolerance polarization and reducing the specific capacity of the battery. At the same time, the influence of the catalyst on the cycling efficiency of the battery also becomes insignificant;

[0034] The initial discharge specific capacity of the chromium / manganese bimetallic sulfur cathode composite material of this example as the cathode of a lithium battery is 1285.6 mAh·g at a current density of 0.1C (1C = 1675 mA / g) -1 , and the remaining specific capacity of the chromium / manganese bimetallic sulfur cathode composite material as the cathode of a lithium battery is 721.4 mAh·g after 100 charge-discharge cycles -1 ; the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C of this example has excellent electrochemical performance. Compared with the sulfur cathode prepared from the original MOF material MIL-101(Cr), the initial specific capacity at 0.1C is increased by 43%, the 100-cycle performance is increased by 27%, and the rate performance and Coulomb efficiency are improved.

[0035] Example 2: A preparation method of a chromium / manganese bimetallic sulfur cathode composite material, the specific steps are as follows:

[0036] (1) Grind chromium(III) nitrate nonahydrate and terephthalic acid and add them to deionized water to stir and dissolve to obtain solution A. Add hydrofluoric acid to solution A, stir and mix evenly, and perform ultrasonic treatment for 15 min to obtain suspension B; subject suspension B to hydrothermal reaction at a temperature of 220°C for 15 h, perform solid-liquid separation, place the solid in a vacuum dryer at a temperature of 100°C for 15 h, then wash it 4 times alternately with N,N-dimethylformamide DMF, ethanol and water, and vacuum dry it at a temperature of 70°C for 10 h to obtain the MIL-101(Cr) precursor; the mass ratio of chromium(III) nitrate nonahydrate to terephthalic acid is 2.4:1, the concentration of chromium nitrate in solution A is 48 g / L, and the volume ratio of commercially available hydrofluoric acid to solution A is 0.2:100;

[0037] (2) Disperse the MIL-101(Cr) precursor in deionized water to obtain suspension C. Add KMnO4 to suspension C and stir for 2 h, then add dilute H2O2 solution and stir for 2 h. Perform solid-liquid separation, wash the solid with deionized water more than three times, and then uniformly heat it to a temperature of 900°C in an inert gas and thermally decompose it at a constant temperature for 2 h to obtain Cr2O 3 / MnO x -C; wherein the concentration of the MIL-101(Cr) precursor in the suspension C is 6 g / L, and the mass ratio of KMnO4 to the MIL-101(Cr) precursor is 0.1:1;

[0038] (3) Grind and mix Cr2O 3 / MnO x -C and sublimed sulfur powder evenly, place them in an inert gas, heat them up to 155 °C at a constant speed and react at a constant temperature for 18 h, cool to room temperature to obtain the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C; wherein the mass ratio of Cr2O 3 / MnO x -C to sublimed sulfur powder is 0.3:1;

[0039] The initial discharge specific capacity of the chromium / manganese bimetallic sulfur cathode composite material prepared in this example as the anode of a lithium battery is 1211.6 mAh·g at a current density of 0.1C (1C = 1675 mA / g) -1 , and the remaining specific capacity after 100 charge-discharge cycles is 696.7 mAh·g -1 .

[0040] Example 3: A preparation method of a chromium / manganese bimetallic sulfur cathode composite material, the specific steps are as follows:

[0041] (1) Grind chromium(III) nitrate nonahydrate and terephthalic acid and add them to deionized water to stir and dissolve to obtain solution A. Add hydrofluoric acid to solution A and stir evenly, and perform ultrasonic treatment for 12 min to obtain suspension B; suspension B is hydrothermally reacted at 230 °C for 18 h, and solid-liquid separation is carried out. The solid is placed in a vacuum dryer at 150 °C for 10 h, then washed alternately with N,N-dimethylformamide DMF, ethanol and water 4 times, and dried in a vacuum at 80 °C for 9 h to obtain the MIL-101(Cr) precursor; wherein the mass ratio of chromium(III) nitrate nonahydrate to terephthalic acid is 2.8:1, the concentration of chromium nitrate in solution A is 56 g / L, and the volume ratio of commercially available hydrofluoric acid to solution A is 0.25:100;

[0042] (2) Disperse the MIL-101(Cr) precursor in deionized water to obtain suspension C. Add KMnO4 to suspension C and stir and react for 3 h, then add dilute H2O2 solution and stir and react for 3 h. Perform solid-liquid separation. The solid is washed with deionized water more than three times, and then heated evenly in an inert gas to 950 °C and pyrolyzed at a constant temperature for 3 h to obtain Cr2O 3 / MnO x-C; wherein the concentration of the MIL-101(Cr) precursor in the suspension C is 7 g / L, and the mass ratio of KMnO4 to the MIL-101(Cr) precursor is 0.52:1;

[0043] (3) Grind and mix Cr2O 3 / MnO x -C and sublimed sulfur powder, place it in an inert gas, heat it up to 165 °C at a constant speed and react at a constant temperature for 20 h, cool it to room temperature to obtain the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C; wherein the mass ratio of Cr2O 3 / MnO x -C to sublimed sulfur powder is 0.7:1;

[0044] The initial discharge specific capacity of the chromium / manganese bimetallic sulfur cathode composite material prepared in this example as the anode of a lithium battery is 1174.6 mAh·g -1 at a current density of 0.1C (1C = 1675 mA / g), and the remaining specific capacity after 100 charge-discharge cycles is 651.4 mAh·g -1 .

[0045] Example 4: A preparation method of a chromium / manganese bimetallic sulfur cathode composite material, the specific steps are as follows:

[0046] (1) Grind chromium nitrate nonahydrate and terephthalic acid and add them to deionized water to stir and dissolve to obtain solution A. Add hydrofluoric acid to solution A, stir and mix evenly, and perform ultrasonic treatment for 12 min to obtain suspension B; suspension B is subjected to hydrothermal reaction at 225 °C for 16 h, solid-liquid separation, the solid is placed in a vacuum dryer at 150 °C for 10 h, and then washed alternately with N,N-dimethylformamide DMF, ethanol and water 4 times, and vacuum dried at 80 °C for 9 h to obtain the MIL-101(Cr) precursor; wherein the mass ratio of chromium nitrate nonahydrate to terephthalic acid is 2.6:1, the concentration of chromium nitrate in solution A is 52 g / L, and the volume ratio of commercially available hydrofluoric acid to solution A is 0.225:100;

[0047] (2) Disperse the MIL-101(Cr) precursor in deionized water to obtain suspension C. Add KMnO4 to suspension C and stir and react for 2.5 h, then add dilute H2O2 solution and stir and react for 2.5 h, perform solid-liquid separation, wash the solid with deionized water more than three times, and then heat it up to 925 °C at a constant speed in an inert gas and thermally decompose it at a constant temperature for 2.5 h to obtain Cr2O 3 / MnO x -C; wherein the concentration of the MIL-101(Cr) precursor in the suspension C is 6.5 g / L, and the mass ratio of KMnO4 to the MIL-101(Cr) precursor is 0.25:1;

[0048] (3) Grind and mix Cr2O 3 / MnO x -C and sublimed sulfur powder evenly, place it in an inert gas, heat it up to 160 °C at a constant speed and react at a constant temperature for 19 h, cool it to room temperature to obtain the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O 3 / MnO x -C; wherein the mass ratio of Cr2O 3 / MnO x -C and sublimed sulfur powder is 0.5:1;

[0049] The chromium / manganese bimetallic sulfur cathode composite material prepared in this example, as the anode of a lithium battery, has an initial discharge specific capacity of 1125.4 mAh·g at a current density of 0.1C (1C = 1675 mA / g) -1 , and the remaining specific capacity is 638.9 mAh·g after 100 charge-discharge cycles -1 .

[0050] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A preparation method of a chromium / manganese bimetallic sulfur cathode composite material, characterized in that, The specific steps are as follows: (1) Grind chromium(III) nitrate nonahydrate and terephthalic acid and add them to deionized water, stir to dissolve to obtain solution A. Add hydrofluoric acid to solution A, stir and mix evenly, and perform ultrasonic treatment to obtain suspension B; subject suspension B to hydrothermal reaction at a temperature of 220-230 °C for 15-18 h, perform solid-liquid separation, vacuum dry the solid, and then wash it alternately with N,N-dimethylformamide (DMF), ethanol, and water more than 3 times, and vacuum dry to obtain the MIL-101(Cr) precursor; (2) Disperse the MIL-101(Cr) precursor in deionized water to obtain suspension C, and add KMnO4 to it and stir for reaction for 2 - 3 h, then add dilute H2O2 solution and stir for reaction for 2 - 3 h, perform solid-liquid separation, wash the solid with deionized water more than three times, and then place it in an inert gas and heat it uniformly to a temperature of 900 - 950 °C and thermally decompose it at a constant temperature for 2 - 3 h to obtain Cr2O3 / MnOx-C ; the mass ratio of the KMnO4 to the MIL-101(Cr) precursor is 0.10 - 0.52:1; (3) Mix Cr2O3 / MnOx-C and sublimed sulfur powder by grinding, place it in an argon atmosphere, heat it up evenly to a temperature of 155 - 165 °C and react at a constant temperature for 18 - 20 h, and cool it to room temperature to obtain the chromium / manganese bimetallic sulfur cathode composite material S / Cr2O3 / MnOx-C .

2. The preparation method of the chromium / manganese bimetallic sulfide cathode composite material according to claim 1, wherein: In step (1), the mass ratio of chromium(III) nitrate nonahydrate to terephthalic acid is 2.4-2.8:1, and the concentration of chromium(III) nitrate in solution A is 48-56 g / L.

3. The preparation method of the chromium / manganese bimetallic sulfur cathode composite material according to claim 1 or 2, characterized in that: In step (1), the volume ratio of hydrofluoric acid to solution A is 0.2-0.25:

100.

4. The preparation method of the chromium / manganese bimetallic sulfide cathode composite material according to claim 1, characterized in that: In step (2), the concentration of the MIL-101(Cr) precursor in suspension C is 6-7 g / L.

5. The preparation method of the chromium / manganese bimetallic sulfur cathode composite material according to claim 1 or 4, characterized in that: Step (2) Dilute H2O2 The mass concentration of the solution is 1-3%, and the volume ratio of the dilute H2O2 solution to suspension C is 0.5-0.7:

1.

6. The preparation method of the chromium / manganese bimetallic sulfide cathode composite material according to claim 1, wherein: Step (3) Cr2O3 / MnOx-C The mass ratio with sublimed sulfur powder is 0.3 to 0.7:1.

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