A multi-valence state manganese modified cose2-rgo composite material and application thereof in lithium-air batteries

Abstract

The application discloses a multivalent state manganese modified CoSe2-rGO composite material and application thereof in lithium air batteries, and a preparation method thereof, which comprises the following steps: uniformly mixing manganese salt, cobalt salt, urea, rGO and PVP in an ethanol aqueous solution through ultrasonic mixing, and then preparing a cobalt manganese hydroxide-rGO composite precursor through a hydrothermal method; and grinding and mixing the composite precursor and selenium powder, and then calcining under an inert atmosphere at high temperature to obtain the target composite material. The preparation process is simple, and the cost is low. The obtained composite material has a low overpotential, a high discharge specific capacity and excellent cycle performance when used as a lithium air battery positive electrode catalyst, and has a good research prospect.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation, specifically to a multivalent manganese-modified CoSe2-rGO composite material and its application in lithium-air batteries. Background Technology

[0002] Currently, global energy supply remains highly dependent on fossil fuels. With the rapid development of new energy vehicles, smart energy storage grids, and other fields, the demand for developing new, efficient, and high-energy-density energy storage systems is becoming increasingly urgent. Lithium-air batteries, with their ultra-high theoretical energy density and specific capacity, are considered to be next-generation electrochemical energy storage devices with great application potential. However, lithium-air batteries currently suffer from technical bottlenecks such as high charge / discharge overpotential, poor cycle stability, and low energy conversion efficiency. The core constraint lies in the slow kinetic rates of the oxygen reduction (ORR) and oxygen evolution (OER) reactions at the battery's cathode. Therefore, developing efficient and stable ORR / OER bifunctional cathode catalysts is key to overcoming the performance shortcomings of lithium-air batteries.

[0003] Transition metal selenides exhibit excellent catalytic potential in electrocatalysis due to their unique electronic structure and abundant surface active sites. Among them, CoSe2, with its regular crystal structure, can effectively mediate the reversible formation and decomposition of Li2O2, providing a good kinetic basis for oxygen electrocatalytic reactions. By introducing manganese for modification, a multi-active-site synergistic system can be constructed. Utilizing the synergistic effect of the Mn and Co bimetallic compounds, the adsorption and activation capabilities of the electrode surface for oxygen, reaction intermediates, and discharge products are enhanced, further improving the bifunctional catalytic performance.

[0004] However, existing manganese-modified CoSe2 catalysts still have many drawbacks: manganese is unevenly dispersed in the matrix, and independent MnSe2 impurity phases are easily precipitated, making it difficult to achieve precise valence state control and significantly weakening the bimetallic synergistic catalytic effect; at the same time, pure phase metal selenides have limited conductivity and slow charge transport rate, which seriously restricts the overall electrochemical performance of lithium-air batteries. Summary of the Invention

[0005] To address the problems of poor conductivity, uneven dispersion of active sites, insufficient bifunctional catalytic capacity, and difficulty in leveraging the synergistic effect of metals in existing lithium-air battery cathode catalysts, this invention aims to provide a method for preparing a multivalent manganese-modified CoSe2-rGO composite material. By constructing a composite structure of multivalent manganese-modified CoSe2 and reduced graphene oxide, the high conductivity and high specific surface area of ​​graphene are utilized, combined with the synergistic catalytic effect of manganese and cobalt bimetals. This effectively improves the defects of slow charge transport and catalytic kinetic lag in the material, enhances the ORR / OER bifunctional catalytic activity and structural stability, reduces the battery polarization overpotential, and significantly improves the charge-discharge efficiency and cycle stability of lithium-air batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention first discloses a method for preparing a multivalent manganese-modified CoSe2-rGO composite material, comprising the following steps: Step 1: Place manganese salt, cobalt salt, reduced graphene oxide (rGO), and polyvinylpyrrolidone (PVP) in an ethanol aqueous solution and ultrasonically disperse until uniformly mixed; Step 2: Add urea to the mixed solution obtained in Step 1, and after it is fully dissolved, transfer it to a hydrothermal reactor and keep it at 80-120℃ for 6-10 hours. After the reaction is completed, centrifuge, wash and dry the product to obtain the cobalt manganese hydroxide-rGO composite precursor. Step 3: Grind and mix the composite precursor obtained in Step 2 with selenium powder, place it in a tube furnace, and calcine it at high temperature under an inert atmosphere to finally obtain the polyvalent manganese modified CoSe2-rGO composite material (denoted as Mn-CoSe2-rGO).

[0007] Further, in step 1, the manganese salt is manganese nitrate, manganese chloride, or manganese sulfate, and the cobalt salt is cobalt chloride, cobalt nitrate, cobalt acetylacetonate, or cobalt phthalocyanine.

[0008] Furthermore, the ratio of manganese salt, cobalt salt, rGO, ethanol aqueous solution, PVP and urea is 0.01~0.1g:0.35~0.45g:3~5mg:50mL:1~10mg:0.24~0.30g, and the volume of ethanol and water in the ethanol aqueous solution is equal.

[0009] Furthermore, in step 3, the inert atmosphere is nitrogen or argon.

[0010] Furthermore, in step 3, the mass ratio of the composite precursor to selenium powder is 1:1 to 5.

[0011] Furthermore, in step 3, the high-temperature calcination temperature is 400–600°C and the calcination time is 2–4 hours.

[0012] The Mn-CoSe2-rGO composite material prepared by the above method of the present invention uses CoSe2 as the matrix and rGO as the conductive framework, with manganese doped into the CoSe2 lattice and Mn... 2+ / Mn 3+ It exists in a multivalent coexisting form. The Mn-CoSe2-rGO composite material can be used as a cathode catalyst material for metal-air batteries, exhibiting bifunctional catalytic activity of ORR and OER.

[0013] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. The Mn-CoSe2-rGO composite material provided by this invention uses a mild hydrothermal method to control the reaction rate and shorten the reaction time, so that Co... 2+ and Mn 2+ Achieving molecular-level homogeneous co-precipitation in solution avoids the formation of independent Mn-based crystalline phases, ultimately resulting in a significant improvement in lithium-air battery performance even with a small amount of Mn introduction. Subsequent selenization and calcination with excess Se powder allows Mn atoms to replace some Co atoms in the CoSe2 lattice. Simultaneously, the strong electronegativity of Se further modulates the electron cloud density of metal ions, inducing spontaneous Mn formation. 2+ / Mn 3+ Multiple valence states coexist, thereby enhancing the dual-function catalytic effect of ORR / OER.

[0014] 2. The Mn-CoSe2-rGO composite material of the present invention introduces a small amount of rGO to achieve the synergistic effect of the rGO conductive framework, the CoSe2 host, and the multivalent Mn active center. At the same time, the high conductivity and high specific surface area of ​​rGO can significantly improve the overall conductivity of the material, thereby effectively inhibiting the aggregation and stacking of metal selenide nanoparticles and providing stable structural support for electrochemical reactions.

[0015] 3. The Mn-CoSe2-rGO composite material of the present invention exhibits good oxygen reduction (ORR) and oxygen evolution (OER) electrocatalytic activity in alkaline electrolytes, and has potential application value in the field of energy conversion and storage. It can be used to prepare metal-air batteries with high energy density and good stability.

[0016] 4. The composite material provided by this invention is applied to lithium-air batteries. The results show that, under high-purity oxygen conditions, the first discharge specific capacity is 19567 mAh / g, and it can operate stably for 180 cycles at a current density of 500 mA / g, with the overvoltage maintained at around 1.15V, demonstrating excellent performance.

[0017] 5. The preparation process of the present invention is simple, the preparation conditions are mild, and the cost is low. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the sample obtained in Example 1.

[0019] Figure 2 The image shows the Raman chromatogram of the sample obtained in Example 1.

[0020] Figure 3 This is a SEM image of the sample obtained in Example 1.

[0021] Figure 4 The image shows the XPS plot of the sample obtained in Example 1.

[0022] Figure 5 The graph shows the initial charge-discharge performance of the lithium-air battery assembled from the sample obtained in Example 1.

[0023] Figure 6 The graph shows the cycle performance of the lithium-air battery assembled from the sample obtained in Example 1.

[0024] Figure 7 The image shows the overpotential diagram of the lithium-air battery assembled from the sample obtained in Example 1.

[0025] Figure 8 The graph shows the ORR performance test results of the samples obtained in Examples 1 to 5, where 1 to 5 represent the samples obtained in Examples 1 to 5 respectively.

[0026] Figure 9 The graphs show the OER performance test results of the samples obtained in Examples 1 to 5, where 1 to 5 represent the samples obtained in Examples 1 to 5 respectively. Detailed Implementation

[0027] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] Example 1 In this embodiment, multivalent manganese-modified CoSe2-rGO composite material was prepared according to the following steps: Step 1: Place 0.408g cobalt nitrate hexahydrate, 0.04g manganese nitrate tetrahydrate, 4mg rGO, and 6mg PVP in 50mL of ethanol-water solution (ethanol to deionized water volume ratio of 1:1) and ultrasonically disperse for 30min until the system is uniformly mixed.

[0029] Step 2: Add 0.276g of urea to the mixed solution obtained in Step 1, and after it is fully dissolved, transfer it to a hydrothermal reactor and keep it at 100℃ for 8 hours. After the reaction is completed, centrifuge, wash and dry the product to obtain the cobalt manganese hydroxide-rGO composite precursor. Step 3: Grind and mix 0.05g of composite precursor and 0.15g of selenium powder. Place the mixed powder in a tube furnace and calcine at 500℃ for 2 hours under an argon atmosphere to finally obtain the polyvalent manganese modified CoSe2-rGO composite material, denoted as Mn-CoSe2-rGO.

[0030] Example 2 In this embodiment, the composite material was prepared using the same method as in Example 1, except that the amount of rGO and PVP added in step 1 was 0.

[0031] Example 3 In this embodiment, the composite material was prepared using the same method as in Example 1, except that the amounts of rGO and PVP added in step 1 were 10 mg and 15 mg, respectively.

[0032] Example 4 In this embodiment, the composite material was prepared using the same method as in Example 1, except that the calcination temperature in step 3 was changed to 400°C.

[0033] Example 5 In this embodiment, the composite material was prepared using the same method as in Example 1, except that the amount of manganese nitrate tetrahydrate added in step 1 was 0.

[0034] Figure 1 The XRD pattern of the sample obtained in Example 1 is shown. All characteristic diffraction peaks of the sample are highly matched with the CoSe2 standard card (PDF#97-004-2539), and no characteristic peaks of manganese-related phases are observed, indicating that manganese is uniformly dissolved in the CoSe2-rGO composite system in the form of trace doping, and no independent manganese-based impurity phase is formed.

[0035] Figure 2 This is the Raman spectrum of the sample obtained in Example 1. The sample at 1350 cm⁻¹ -1 With 1580cm -1 The presence of typical carbon material D and G peaks at the locations proves that reduced graphene oxide has been successfully incorporated into the material system.

[0036] Figure 3 The image shows the SEM morphology of the sample obtained in Example 1. As can be seen from the image, the prepared composite material has a uniform and regular overall morphology, successfully constructing a uniform CoSe2-rGO composite structure, and the material exhibits good microstructural stability.

[0037] Figure 4 The image shows the XPS spectrum of the sample obtained in Example 1. The test results confirm that the present invention successfully prepared a manganese-modified CoSe2-rGO composite material, and that manganese mainly exists in the form of +2 and +3 multivalent states, achieving precise control of multivalent manganese.

[0038] The sample obtained in Example 1 was used as the positive electrode catalyst material for a lithium-air battery and assembled with lithium sheets to form a coin-type lithium-air battery. The assembly method is as follows: 60% conductive carbon black KB, 30% catalyst, and 10% PVDF binder were uniformly mixed to form a slurry, which was then uniformly coated onto the surface of a carbon paper current collector and dried in a vacuum drying oven at 60°C for 12 hours. The final catalyst loading on the carbon paper was controlled at 0.3–0.5 mg. Using lithium metal foil as the negative electrode and glass fiber as the separator, 110 μL of 1M LiTFSI / TEGDME electrolyte was added dropwise. The carbon paper positive electrode with the catalyst loaded and the nickel foam filling layer were then combined, and the battery was sealed and assembled in an argon-atmosphere glove box.

[0039] Figure 5 The graph shows the initial charge-discharge performance of the lithium-air battery assembled from the sample obtained in Example 1. It can be seen that at 100 mA g... -1 At a constant current discharge density, the initial discharge specific capacity reached 19567 mAh g. -1 .

[0040] Figure 6 The graph shows the cycle performance of the lithium-air battery assembled from the sample obtained in Example 1. It can be seen that it achieves a cycle performance of 500 mA g. -1 Under constant current discharge density, the capacity only decays after 180 cycles, demonstrating good cycle stability.

[0041] Figure 7 The polarization overpotential test results are for the lithium-air battery assembled from the sample obtained in Example 1. At 100 mA g -1 Under the test conditions, the battery charge-discharge overpotential was only 1.15V, the polarization was low, and the electrocatalytic reversibility performance was excellent.

[0042] Figure 8 The graph shows the ORR electrocatalytic performance comparison curves of the samples from each example, where 1 to 5 represent the samples obtained in Examples 1 to 5, respectively. The preparation method is as follows: 5 mg of catalyst, 1 mg of conductive carbon black, and 20 μL of naphthol solution were dispersed in 1 mL of isopropanol / deionized water mixed solution (volume ratio of isopropanol to water is 1:4), and ultrasonically dispersed for 1 h to obtain a uniform dispersion; 6 μL of the dispersion was drop-coated onto the surface of a glassy carbon electrode, and after air drying for 2 h, a working electrode was prepared. The LSV curve was tested using a rotating disk electrode. The comparison results show that the sample of Example 1 has the optimal half-wave potential and limiting current density, and its ORR catalytic activity is significantly better than that of the other control group samples.

[0043] Figure 9 This is a comparison curve of the OER electrocatalytic performance of the samples in each embodiment. The sample preparation and testing conditions are the same as those in the previous examples. Figure 8 Consistent. Performance comparison of the samples in each group shows that the sample in Example 1 exhibits the best oxygen evolution catalytic kinetics and also possesses excellent ORR / OER bifunctional catalytic performance.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a multivalent manganese-modified CoSe2-rGO composite material, characterized in that: Includes the following steps: Step 1: Place manganese salt, cobalt salt, reduced graphene oxide (rGO), and polyvinylpyrrolidone (PVP) in an ethanol-water solution and ultrasonically disperse until uniformly mixed; Step 2: Add urea to the mixed solution obtained in Step 1, and after it is fully dissolved, transfer it to a hydrothermal reactor and keep it at 80-120℃ for 6-10 hours. After the reaction is completed, centrifuge, wash and dry the product to obtain the cobalt manganese hydroxide-rGO composite precursor. Step 3: Grind and mix the composite precursor obtained in Step 2 with selenium powder, place it in a tube furnace, and calcine it at high temperature under an inert atmosphere to finally obtain the polyvalent manganese modified CoSe2-rGO composite material.

2. The preparation method of the multivalent manganese-modified CoSe2-rGO composite material according to claim 1, characterized in that: In step 1, the manganese salt is manganese nitrate, manganese chloride, or manganese sulfate, and the cobalt salt is cobalt chloride, cobalt nitrate, cobalt acetylacetonate, or cobalt phthalocyanine.

3. The method for preparing the multivalent manganese-modified CoSe2-rGO composite material according to claim 1, characterized in that: The ratio of manganese salt, cobalt salt, rGO, ethanol aqueous solution, PVP and urea is 0.01~0.1g:0.35~0.45g:3~5mg:50mL:1~10mg:0.24~0.30g, and the volume of ethanol and water in the ethanol aqueous solution is equal.

4. The method for preparing the multivalent manganese-modified CoSe2-rGO composite material according to claim 1, characterized in that: In step 3, the inert atmosphere is nitrogen or argon.

5. The method for preparing the multivalent manganese-modified CoSe2-rGO composite material according to claim 1, characterized in that: In step 3, the mass ratio of the composite precursor to selenium powder is 1:1 to 5.

6. The method for preparing the multivalent manganese-modified CoSe2-rGO composite material according to claim 1, characterized in that: In step 3, the high-temperature calcination temperature is 400-600℃ and the calcination time is 2-4 hours.

7. A multivalent manganese-modified CoSe2-rGO composite material prepared by the preparation method according to any one of claims 1 to 6.

8. The multivalent manganese-modified CoSe2-rGO composite material according to claim 7, characterized in that: The composite material uses CoSe2 as the matrix and rGO as the conductive framework, with manganese doped into the CoSe2 lattice and Mn2 as the conductive framework. 2+ / Mn 3+ Multiple valence states coexist.

9. The application of the multivalent manganese-modified CoSe2-rGO composite material according to claim 7 in a lithium-air battery.

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