Manganese oxide / manganese sulfide composite positive electrode material containing carbon coating and preparation method thereof

Abstract

This invention discloses a method for preparing a carbon-coated manganese oxide / manganese sulfide composite cathode material. First, manganese dioxide nanotubes are prepared using a hydrothermal method. Then, the manganese dioxide nanotubes are completely or partially sulfided to obtain manganese oxide / manganese sulfide. Next, a conductive polymer is coated onto the surface of the manganese oxide / manganese sulfide nanoparticles. Finally, the resulting manganese oxide / manganese sulfide nanoparticles with the conductive polymer coating are placed in a tube furnace and treated at high temperature for a certain period of time to obtain the carbon-coated manganese oxide / manganese sulfide composite cathode material. This carbon-coated manganese oxide / manganese sulfide nanocomposite material, as a cathode material for zinc-ion batteries, avoids direct contact between the electrolyte and the active material due to the carbon coating, preventing material dissolution and improving cycle life. The heterogeneous structure of manganese oxide / manganese sulfide enhances the electrochemical activity of the material, solving the problem of poor conductivity in traditional manganese oxide materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rechargeable secondary zinc ion batteries, and particularly relates to a manganese oxide / manganese sulfide composite positive electrode material containing a carbon coating and a preparation method thereof. BACKGROUND

[0002] In recent years, new types of rechargeable secondary batteries such as sodium ion batteries (SIBs), potassium ion batteries (PIBs), magnesium ion batteries (MIBs), zinc ion batteries (ZIBs), and aluminum ion batteries (AIBs) have been developed and reported. However, the large-scale application of sodium ion batteries and potassium ion batteries is also limited because of the use of toxic, flammable and volatile organic electrolytes. Due to strong polarization effect, magnesium ions are difficult to intercalate / deintercalate in the positive electrode material. Aluminum ion batteries are easily corroded during charging and discharging, and the formation of a surface Al2O3 film affects the battery performance. Compared with non-aqueous batteries, aqueous batteries have low cost, safe and non-toxic electrolyte, environmental friendliness, and easy manufacturing, and have broad application prospects in the future energy storage equipment market. Zinc ion aqueous batteries (AZIBs) stand out among many rechargeable aqueous batteries due to their unique advantages. Zinc has good stability and reversibility in aqueous solution, has a high specific capacity (819 mAh g -1 ), a low electrochemical potential (relative to the standard hydrogen electrode -0.763 V), abundant metal resources, low toxicity, easy recovery, low cost, and other characteristics. Among the various components of AZIBs, the positive electrode material can significantly affect its overall electrochemical performance. Therefore, the design of the positive electrode material has become a hot topic in recent years. The positive electrode materials reported in the literature include manganese-based materials, vanadium-based materials, Prussian blue analogs, polyanion compounds, organic compounds, and other compounds.

[0003] Due to their high theoretical capacity, low cost, and low toxicity, people have devoted to developing transition metal oxides (TMOs) as electrode materials for zinc ion batteries. Compared with other TMOs, manganese oxides have the advantages of abundant reserves, low cost, low overpotential, and environmental friendliness, and are extremely attractive positive electrode materials. Although traditional manganese oxides have high theoretical capacity, they do not perform well in practical applications, especially the poor cycle life problem is the most serious.

[0004] Therefore, researchers have explored numerous optimization strategies, such as element doping, surface modification, defect engineering, electrolyte optimization, etc. Similar to oxides, transition metal sulfides (TMSs) have attracted increasing research interest due to their high theoretical capacity in chemical conversion reactions. Among TMSs, MnS is a very promising material, which can react with zinc negative electrode through the following electrochemical reaction when used as an active material for AZIB positive electrode: The MnS thus obtained has a high theoretical capacity, and thus has attracted great attention. Despite the good theoretical performance, the MnS positive electrode material often suffers from huge volume expansion and shrinkage during the charging / discharging process, which can lead to material agglomeration and electrode pulverization. These defects can lead to rapid capacity decay and poor cycle performance. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a carbon-coated manganese oxide / manganese sulfide composite positive electrode material to solve the problems existing in the prior art. The manganese oxide / manganese sulfide composite nanoparticles with a two-phase heterogeneous structure are obtained by partially or completely reducing and sulfidizing manganese dioxide nanotubes, and then a conductive polymer is coated on the surface thereof and carbonized at high temperature. The two-phase heterogeneous structure improves the electrical conductivity and chemical activity of the electrode, and further improves the electrochemical performance. The high-hardness carbon coating not only maintains the structural integrity of the electrode, but also inhibits the direct contact between the active material and the electrolyte, thereby reducing the dissolution of manganese ions and increasing the cycle life.

[0006] The technical solution adopted by the present application to solve the above-mentioned problems is as follows:

[0007] The carbon-coated manganese oxide / manganese sulfide composite positive electrode material comprises manganese oxide / manganese sulfide composite nanoparticles obtained by completely or partially reducing and sulfidizing manganese dioxide nanotubes, and a carbon coating coated on the surface of the manganese oxide / manganese sulfide composite nanoparticles. The carbon coating is formed by coating a polymer on the surface of the manganese oxide / manganese sulfide composite nanoparticles and high-temperature treatment. The size of the manganese oxide / manganese sulfide composite nanoparticles is 30-50 nm, the mass ratio between manganese oxide and manganese sulfide is in the range of 1:(0.1-1.5), preferably 1:(0.5-1.5), and the thickness of the carbon coating is in the range of 20-100 nm.

[0008] The preparation method of the above-mentioned carbon-coated manganese oxide / manganese sulfide composite positive electrode material comprises the following steps:

[0009] (1) Potassium permanganate and concentrated hydrochloric acid are used as raw materials to prepare manganese dioxide nanotubes by a hydrothermal method;

[0010] (2) The manganese dioxide nanotubes and a sulfur source are dispersed in a solvent alcohol at a mass ratio of 1:1-10, and then sealed in a reaction kettle for reaction at 100-200°C for 6-24h to obtain manganese oxide / manganese sulfide composite nanoparticles;

[0011] (3) The manganese oxide / manganese sulfide composite nanoparticles obtained in step (2) and dopamine hydrochloride are polymerized in a buffer solution at room temperature to obtain manganese oxide / manganese sulfide composite nanoparticles coated with a conductive polydopamine coating, and then high-temperature heat treatment is performed in a tube furnace to obtain the carbon-coated manganese oxide / manganese sulfide composite positive electrode material.

[0012] According to the above scheme, in step (1), the length of the manganese dioxide nanotubes varies from 200nm to 2μm, and the outer diameter is in the range of 50-100nm.

[0013] According to the above scheme, in step (1), the mass ratio of potassium permanganate, water and concentrated hydrochloric acid is 1:(50-150):(1-10); the temperature of the hydrothermal reaction is 100-200℃, and the reaction time is 6-24h.

[0014] According to the above scheme, in step (2), the sulfur source is one or more of thioacetamide, thiourea, elemental sulfur, L-cysteine, etc.; in step (3), the alcohol is at least one of ethanol, ethylene glycol, glycerol, etc.

[0015] According to the above scheme, in step (3), the mass ratio of manganese oxide / manganese sulfide composite nanoparticles to dopamine hydrochloride is 1:0.5-2, the total concentration in the buffer solution is controlled at 1-10 mg / mL, the buffer solution is a Tris solution with pH 8-8.5, and the polymerization time at room temperature is 4-12 h.

[0016] According to the above scheme, the specific process of high temperature heat treatment in step (3) is as follows: under a protective atmosphere, the temperature is raised to 500-800℃ at a rate of 1-5℃ / min and held for 1-5h.

[0017] The aforementioned carbon-coated manganese oxide / manganese sulfide composite cathode material can be used as a cathode material for zinc-ion batteries. The specific application method is as follows: the carbon-coated manganese oxide / manganese sulfide composite cathode material is mixed with a conductive agent, binder, and solvent to form a cathode slurry, which is then coated onto a current collector to serve as the cathode material for zinc-ion batteries. The current collector can be one of the following: nickel foam, stainless steel foil, or copper foil.

[0018] The present invention also provides a zinc-ion battery, which uses the above-mentioned carbon-coated manganese oxide / manganese sulfide composite positive electrode material as the positive electrode, zinc as the negative electrode, zinc sulfate and manganese sulfate as the electrolyte, and a hydrophilic filter membrane as the separator.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention uses manganese dioxide nanotubes as a precursor and adds a sulfur source as both a reducing agent and a sulfiding agent to control a solvothermal reaction to obtain biphase heterostructured manganese oxide / manganese sulfide nanocomposite particles. Then, an in-situ polymerization reaction is used to coat the surface with a conductive polymer as a carbon source, followed by high-temperature carbonization to achieve surface modification, thus obtaining a carbon-coated manganese oxide / manganese sulfide composite cathode material. This unique biphase heterostructure of the carbon-coated manganese oxide / manganese sulfide composite cathode material significantly increases the active sites, improves the electrode's conductivity and chemical activity, and promotes ion diffusion and transfer during charge and discharge. The carbon coating protects the material's structure from damage and inhibits direct contact between the electrolyte and active material, preventing manganese ion dissolution. This results in excellent electrochemical performance and cycle life, fundamentally solving the problems of rapid capacity decay and poor cycle performance in manganese-based cathode materials. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation process of the carbon-coated manganese oxide / manganese sulfide composite cathode material described in this invention.

[0022] Figure 2 This is a scanning electron microscope image of the manganese dioxide nanotubes prepared in Example 1 of this invention.

[0023] Figure 3 In the image, (a) is a scanning electron microscope image of MnO / MnS prepared in Example 4 of the present invention (reaction 10h), and (b) is a scanning electron microscope image of MnO / MnS prepared in Example 1 of the present invention (reaction 15h).

[0024] Figure 4 (a) is a scanning electron microscope image of MnO / MnS@PDA prepared in Example 1 of the present invention; (b) is a scanning electron microscope image of MnO / MnS@C50 (dopamine added amount of 50 mg) prepared in Example 1 of the present invention; (c) is a scanning electron microscope image of MnO / MnS@C100 (dopamine added amount of 100 mg) prepared in Example 2 of the present invention; and (d) is a scanning electron microscope image of MnO / MnS@C150 (dopamine added amount of 150 mg) prepared in Example 3 of the present invention.

[0025] Figure 5 This is the EDS spectrum of MnO / MnS@C100 (dopamine addition amount is 100mg) prepared in Example 2 of the present invention.

[0026] Figure 6 This is the XRD pattern of MnO / MnS@C100 (dopamine addition amount is 100mg) prepared in Example 2 of the present invention.

[0027] Figure 7(a) is the XPS total spectrum of MnO / MnS@C100 (dopamine added amount is 100mg) prepared in Example 2 of the present invention, (b) is the high-resolution spectrum of Mn element, (c) is the high-resolution spectrum of S element, (d) is the high-resolution spectrum of C element, (e) is the high-resolution spectrum of N element, and (f) is the high-resolution spectrum of O element.

[0028] Figure 8 (a) is the cyclic voltammetry curve of MnO / MnS@C100 (dopamine addition amount is 100mg) prepared in Example 2 of the present invention; (b) is a comparison of the galvanostatic charge-discharge performance of MnO2, MnO / MnS (reaction time 15 hours), MnO / MnS@PDA and MnO / MnS@C100 at a current density of 0.1A / g in Examples 1-3 of the present invention; (c) is a comparison of the galvanostatic charge-discharge performance of each electrode material at a current density of 0.1A / g when the mass ratio of MnO / MnS to dopamine is 1:0.5, 1:1 and 1:1.5 respectively in Examples 1-3 of the present invention; (d) is the... (e) Performance graphs of MnO / MnS@C50, MnO / MnS@C100 and MnO / MnS@C150 prepared in Examples 1-3 of the present invention after 100 cycles at a current density of 0.1 A / g; (f) Rate performance graphs of MnO / MnS@PDA, MnO / MnS@C50, MnO / MnS@C100 and MnO / MnS@C150 prepared in Examples 1-3 of the present invention at different current densities; Detailed Implementation

[0029] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] A method for preparing a carbon-coated manganese oxide / manganese sulfide composite cathode material, the specific steps of which are as follows:

[0032] (1) Dissolve 0.263g KMnO4 in 30ml deionized water and stir for 10 minutes to form a purple solution. Then, while stirring, add 1mL concentrated hydrochloric acid and continue stirring for another 10 minutes. Transfer the purple solution to a reaction vessel and place it in an oven at 140℃ for 16 hours. After the reaction is complete, centrifuge to obtain a brown solid product. Wash the product twice with ethanol and deionized water alternately, and dry the product at 80℃ for 12 hours to obtain manganese dioxide nanotubes.

[0033] Figure 2 The image shows a scanning electron microscope image of manganese dioxide nanotubes. The length of the manganese dioxide nanotubes ranges from 200 nm to 2 μm, and the outer diameter is around 50-100 nm.

[0034] (2) 100 mg of manganese dioxide nanotubes were dispersed in 75 mL of ethylene glycol, and then 400 mg of thiourea was added. The mixture was further ultrasonically dispersed for 10 min. The resulting mixture was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and placed in an oven at 200 °C for 15 h. After the reaction was completed, the resulting precipitate was collected by centrifugation, washed with deionized water and ethanol, and then placed in a vacuum drying oven at 80 °C for 12 h to dry completely. After grinding, manganese oxide / manganese sulfide composite nanoparticles (i.e., MnO / MnS nanoparticles) were obtained.

[0035] (3) Take 100 mg of ground MnO / MnS nanoparticles and disperse them in 50 mL of Tris-buffered solution (pH ~ 8.5) with magnetic stirring to form a suspension. Then, add 50 mg of dopamine hydrochloride to the suspension with stirring and carry out the polymerization reaction at room temperature for 24 hours. After the polymerization is completed, centrifuge the solid product containing conductive polydopamine-coated MnO / MnS nanoparticles (MnO / MnS@PDA), wash with deionized water and ethanol, and place in an 80 °C vacuum drying oven for 12 hours. After complete drying, in a tube furnace under argon protection, heat at 3 °C for 1 minute. –1 Heating to 800°C at a heating rate and holding for 2 hours yielded a carbon-coated manganese oxide / manganese sulfide composite cathode material (denoted as MnO / MnS@C, written as MnO / MnS@C50 in this example, where 50 represents 50 mg of dopamine hydrochloride, to distinguish it from Examples 2 and 3).

[0036] Figure 3 (b) is a scanning electron microscope image of the MnO / MnS prepared in Example 1. It can be clearly seen that there is no manganese dioxide nanotubes. All the manganese dioxide participated in the reaction. Some of it was sulfided into manganese sulfide and some was reduced into manganese oxide. The prepared particles are uniformly distributed and of uniform size, with a size of about 30-50 nm.

[0037] Example 2

[0038] The difference between this embodiment and Example 1 is that when MnO / MnS powder is polymerized with dopamine, the mass ratio is 1:1, that is, the amount of dopamine introduced in step (3) is 100mg, and the final product is denoted as MnO / MnS@C100.

[0039] Example 3

[0040] The difference between this embodiment and Example 1 is that when MnO / MnS powder is polymerized with dopamine, the mass ratio is 1:1.5, that is, the amount of dopamine introduced in step (3) is 150mg, and the final product is denoted as MnO / MnS@C150.

[0041] Figure 4 (ad) are scanning electron microscope (SEM) images of the products MnO / MnS@PDA, MnO / MnS@C50, MnO / MnS@C100, and MnO / MnS@C150 obtained in Examples 1-3, respectively. From image (a), it can be seen that compared to MnO / MnS nanoparticles, the polydopamine coating makes the particle surface smoother. Furthermore, due to the in-situ polymerization of dopamine, the particles slightly agglomerate, and the particle size increases slightly after dopamine coating, approximately 50-100 nm. (b) shows the carbonized MnO / MnS@C50 nanoparticles with a dopamine content of 50 mg. It can be seen that they have a noticeably rough surface, and the MnO / MnS@C50 nanoparticles exhibit agglomerated clusters due to the carbon coating on their surface, with a particle size of approximately 50-100 nm. As the dopamine content increases to 100 mg (MnO / MnS powder to dopamine mass ratio 1:1), the particle size is 70-150 nm, the coating thickness increases, increasing the active specific surface area and active sites, promoting more electrochemical reactions, and improving electrochemical performance. When the dopamine content is 150 mg (MnO / MnS powder to dopamine mass ratio 1:1.5), the carbon coating thickness becomes increasingly large, and material aggregation occurs, hindering the diffusion and transport of ions and electrons. This reduces the conductivity and active sites of the electrode material, resulting in a slight decrease in electrochemical performance, but it is still higher than that of single manganese oxide electrode materials, meeting the requirements for a cathode material in aqueous zinc-ion batteries. Comparing the particle size of uncoated MnO / MnS, the carbon coating thickness of the manganese oxide / manganese sulfide composite cathode material can be calculated to be between 20-100 nm.

[0042] Figure 5 This is the EDS spectrum of MnO / MnS@C100 (dopamine addition amount is 100mg) prepared in Example 2 of this invention. It can be seen that nitrogen, sulfur and carbon elements were successfully introduced into the material, while manganese and oxygen elements are still present and have not disappeared. The elemental ratio of S to O is 1:1, so the ratio of manganese oxide to manganese sulfide is roughly estimated to be 1:1.

[0043] Figure 6The XRD pattern of MnO / MnS@C100 (dopamine addition amount is 100mg) prepared in Example 2 of this invention matches the standard cards of MnS and MnO very well, indicating that the MnO / MnS heterostructure was successfully synthesized; and there is a significant amorphous large envelope peak between 20° and 30°, indicating that carbon element was successfully introduced into the material surface.

[0044] Figure 7 (a) is the XPS spectrum of MnO / MnS@C100, clearly showing the peaks of Mn 2p, Mn 3p, Mn 3s, O 1s, C 1s, S 2s, S 2p, and N 1s, confirming the presence of these elements. No other impurities were observed. Figure 7 (b) In the high-resolution Mn2p spectrum, Mn2p can be clearly seen. 1 / 2 The peak is located at 649.5 eV, Mn 2p 3 / 2 The two peaks are located at 639.6 and 637.8 eV, corresponding to Mn, respectively. 2+ Mn 3+ . Figure 7 (c) shows the high-resolution spectrum of S 2p, where the three peaks are located at 160.3 eV, 161.4 eV, and 165.1 eV, representing S 2p. 3 / 2 S 2p 1 / 2 and-SO n - indicates that sulfur has been doped into the carbon framework, and MnS has been formed. Figure 7 (d) The high-resolution C1s spectrum has five peaks. The peak at 280.8 eV belongs to the CS bond, the binding energy peak at 281.4 eV belongs to the CC bond, and the other peaks at 282.1, 286.1, and 288.4 eV coincide with CN, CO, and C=O bonds, respectively. The high-resolution N1s spectrum ( Figure 7 e) Two peaks represent pyridine N (395.0 eV) and pyrrole N (397.4 eV), respectively. N doping enhances ion diffusion kinetics and conductivity, thereby improving electrochemical performance. Finally, the O 1s high-resolution spectrum ( Figure 7 f) can be fitted with three components centered at 526.4, 528.0, and 529.3 eV, which correspond to the oxygen elements in MnO, COC, and C=O or OC=O groups in the composite cathode material, respectively.

[0045] Example 4

[0046] The difference between this embodiment and embodiment 1 is that the reaction time in step (2) is 10 hours.

[0047] Figure 3(a) is a scanning electron microscope image of the MnO / MnS prepared in Example 4. It can be seen that after 10 hours of the sulfurization reaction of manganese dioxide nanotubes, most of them were reduced and sulfurized into manganese oxide / manganese sulfide composite nanoparticles, and a small part of tubular manganese dioxide did not participate in the reaction.

[0048] Application examples

[0049] The MnO / MnS@C cathode composite materials prepared in Examples 1-3 were used to fabricate coin cells for performance testing. The coin cell fabrication process is as follows:

[0050] (1) To prepare the electrode, powdered MnO / MnS@C, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 7:2:1. N-methylpyrrolidone was added dropwise and stirred into a slurry. The slurry was uniformly coated on the current collector and dried in a drying oven at 60-110℃ for 12-24h to obtain the MnO / MnS@C electrode material.

[0051] (2) Prepare a mixed solution of 2M ZnSO4 and 0.2M MnSO4 as the electrolyte, zinc foil as the negative electrode, MnO / MnS@C electrode material as the positive electrode, and a hydrophilic filter membrane as the separator. Assemble a coin cell and test the cyclic voltammetry curve, constant current charge-discharge performance, cycle rate performance and electrochemical impedance.

[0052] Figure 8 It can be seen that the carbon-coated manganese oxide / manganese sulfide composite cathode material prepared by this invention has high electrochemical performance. (a) is the cyclic voltammetry (CV) diagram of the MnO / MnS@C100 cathode material in Example 2, which tests the relationship between its potential and current at a scan rate of 0.1 mV s. -1 The voltage range is 1-1.8V. As can be seen from the figure, in the first curve, MnO / MnS@C exhibits two strong oxidation peaks at 1.2V and 1.61V, corresponding to the irreversible S oxidation in MnO / MnS. 2- oxidation and Mn 2+ The oxidation of MnO2 was observed. Two weak reduction peaks were observed at 1.22 V and 1.38 V, corresponding to the dissolution and disproportionation reactions of MnO2, respectively. The MnO electrode is electrochemically inactive, but it was activated during the first CV cycle, transforming from an electrochemically inactive material to an electrochemically active material. This transformation was attributed to the increased manganese valence state in MnO due to the dissolution of manganese ions. The high-resolution Mn 2p spectrum obtained by XPS also showed the presence of Mn2. 3+ The presence of [a specific substance] can increase the capacity of the composite material. After the first cycle of CV, MnO / MnS is almost completely oxidized to oxides of MnO2 and MnS. The subsequent scanning cycle curves are similar to those of MnO2, proving that it has an essentially similar electrochemical energy storage reaction to MnO2. Moreover, the CV curves have good repeatability, indicating that the material has good reversibility.

[0053] Figure 8 (b) shows the constant current charge-discharge curves at 0.1 A / g for all products from MnO2 nanotubes to the final synthesis of MnO / MnS@C100 nanoparticles in Example 2. It can be seen that the discharge capacity of the original MnO2 nanotubes is only 146 mAh / g, while the MnO / MnS nanoparticles generated after reduction and sulfidation have a discharge capacity of 177 mAh / g. After being coated with a conductive polymer, the discharge capacity reaches 222 mAh / g. Finally, the final product MnO / MnS@C100 generated after high-temperature calcination in a tube furnace has an excellent discharge capacity of 397.7 mAh / g.

[0054] Figure 8 (c) The galvanostatic charge-discharge curves of MnO / MnS@C50, MnO / MnS@C100, and MnO / MnS@C150 at a current density of 0.1 A / g in Examples 1-3 show that MnO / MnS@C100 has the highest charge-discharge capacity. This is because, under the same preparation conditions and current density, the charge-discharge capacity first increases and then decreases with the increase of dopamine hydrochloride introduction. When the ratio of manganese oxide / manganese sulfide to dopamine is 1:0.5 by mass, the rigid carbon coating framework protects the structure of the electrode material, inhibits direct contact between the electrolyte and the active material, and increases the cycle life. When the ratio of manganese oxide / manganese sulfide to dopamine is 1:1 by mass, with the continued increase of dopamine introduction, the thickness of the carbon coating increases, increasing the active specific surface area and active sites, promoting more electrochemical reactions, and improving electrochemical performance. When the mass ratio of manganese oxide / manganese sulfide and dopamine is 1:1.5, the thickness of the carbon coating increases, leading to material agglomeration. This agglomeration hinders the diffusion and transport of ions and electrons, resulting in a decrease in the conductivity and active sites of the electrode material, and a slight decrease in its electrochemical performance. However, the performance is still higher than that of a single manganese oxide electrode material, meeting the requirements for a cathode material in aqueous zinc-ion batteries. Performance comparison shows that, compared to single manganese dioxide and unmodified manganese oxide / manganese sulfide (the intermediate MnO / MnS nanoparticles of Examples 1 and 2), the carbon-coated manganese oxide / manganese sulfide composite cathode materials obtained in the examples all exhibit higher charge-discharge capacities.

[0055] Figure 8(d) shows the cycling performance of MnO / MnS@C50, MnO / MnS@C100 and MnO / MnS@C150 in Examples 1-3 at a current density of 0.1 A / g. It can be seen that the capacity of the material slightly decreases in the initial cycle due to the oxidation of sulfur and the activation of the electrochemical activity of manganese oxide, but the capacity basically does not decrease after 100 cycles, and the capacity retention rate is about 87%. Furthermore, the coulombic efficiency remains at 100% as shown by the blue curve in the figure, indicating that the material has excellent electrochemical performance.

[0056] Figure 8 (e) shows the rate performance of MnO / MnS@C50, MnO / MnS@C100 and MnO / MnS@C150 in Examples 1-3. It can be seen that at a current density of 5 A / g, the MnO / MnS@C100 material still has an excellent capacity of 59.4 mAh / g, indicating that the material has good zinc storage capacity and conductivity.

[0057] Figure 8 (f) Electrochemical impedance spectroscopy (EIS) analysis was performed on the MnO / MnS@PDA, MnO / MnS@C50, MnO / MnS@C100, and MnO / MnS@C150 samples from Examples 1-3. The low-frequency portion of the EIS spectrum is a straight line, reflecting the rate of ion migration / diffusion in the electrolyte. The test results show that MnO / MnS@C100 has the highest slope. The greater the slope of the line, the faster the ions diffuse between the electrolyte and the electrode, resulting in the lowest resistance. This indicates that the MnO / MnS@C100 composite electrode in Example 2 has a faster ion diffusion rate and the best conductivity.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-coated manganese oxide / manganese sulfide composite cathode material, characterized in that, Includes the following steps: (1) Manganese dioxide nanotubes were prepared by hydrothermal method using potassium permanganate and concentrated hydrochloric acid as raw materials; (2) Manganese dioxide nanotubes and a sulfur source are dispersed in a solvent alcohol at a mass ratio of 1:1-10, and then the mixture is sealed and reacted in a reaction vessel at 100-200°C for 6-24 hours to obtain manganese oxide / manganese sulfide composite nanoparticles; wherein, the manganese dioxide nanotubes participate in the reaction, part of which is sulfided into manganese sulfide and part of which is reduced into manganese oxide; the sulfur source is one or more of thioacetamide, thiourea, elemental sulfur, and L-cysteine; (3) The manganese oxide / manganese sulfide composite nanoparticles obtained in step (2) and dopamine hydrochloride are polymerized at room temperature in a buffer solution. The manganese oxide / manganese sulfide composite nanoparticles with conductive polydopamine coating are then placed in a tube furnace for high-temperature heat treatment to obtain manganese oxide / manganese sulfide composite cathode material with carbon coating. The carbon-coated manganese oxide / manganese sulfide composite cathode material comprises manganese oxide / manganese sulfide composite nanoparticles obtained by reducing and sulfiding manganese dioxide nanotubes and a carbon coating covering the surface of the manganese oxide / manganese sulfide composite nanoparticles; the carbon coating is formed by coating the surface of the manganese oxide / manganese sulfide composite nanoparticles with polydopamine and then treating it at high temperature; wherein the size of the manganese oxide / manganese sulfide composite nanoparticles is 30-50 nm, the mass ratio between manganese oxide and manganese sulfide is 1:(0.1-1.5); and the thickness of the carbon coating is 20-100 nm.

2. The preparation method according to claim 1, characterized in that, The length of the manganese dioxide nanotubes is in the range of 200nm-2μm, and the outer diameter is in the range of 50-100nm.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of potassium permanganate, water and concentrated hydrochloric acid is 1:(50-150):(1-10).

4. The preparation method according to claim 1, characterized in that, In step (2) and step (3), the alcohol is at least one of ethanol, ethylene glycol, and glycerol.

5. The preparation method according to claim 1, characterized in that... In step (3), the mass ratio of manganese oxide / manganese sulfide composite nanoparticles to dopamine hydrochloride is 1:(0.5-2), the buffer solution is a Tris solution with pH 8-8.5, and the polymerization time at room temperature is 4-12h.

6. The preparation method according to claim 1, characterized in that... In step (3), the specific process of high-temperature heat treatment is as follows: under a protective atmosphere, the temperature is raised to 500-800°C at a rate of 1-5°C / min and held for 1-5 hours.

7. The application of the carbon-coated manganese oxide / manganese sulfide composite cathode material prepared by the method of claim 1 as a cathode material for zinc-ion batteries, characterized in that, The carbon-coated manganese oxide / manganese sulfide composite cathode material is mixed with a conductive agent, a binder, and a solvent to form a cathode slurry, which is then coated onto a current collector to serve as a cathode material for zinc-ion batteries.

8. A zinc-ion battery, characterized in that, It uses a carbon-coated manganese oxide / manganese sulfide composite positive electrode material prepared by the method described in claim 1 as the positive electrode, zinc as the negative electrode, zinc sulfate and manganese sulfate as the electrolyte, and a hydrophilic filter membrane as the diaphragm.

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