Manganese-based oxide composite carbon material catalyst as well as preparation method and application thereof

Abstract

The invention relates to a manganese-based oxide composite carbon material catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: adding carbon nanotubes subjected to acid treatment in advance and polyvinylpyrrolidone into absolute ethyl alcohol, and ultrasonically dispersing uniformly; adding a mixed system of manganese acetate tetrahydrate and polyvinylpyrrolidone into the carbon nanotube dispersion liquid, and uniformly stirring under a heating condition; carrying out solid-liquid separation on the mixed system to obtain a solid, and drying for later use; and grinding the dried solid, and carrying out high-temperature calcination to finally obtain the manganese-based oxide composite carbon material catalyst. The manganese-based oxide composite carbon material catalyst is used as a positive electrode catalyst of a lithium-carbon dioxide battery. Compared with the prior art, the transition metal-based catalyst material has excellent catalytic performance and is an ideal transition metal-based catalyst material suitable for lithium-carbon dioxide batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery catalyst technology, and in particular relates to a manganese-based oxide composite carbon material catalyst, its preparation method and application. Background Technology

[0002] With the continuous development of technology and human civilization, human demand for energy is increasing, and the global warming problem caused by greenhouse gases (mainly CO2) released during the use of fossil fuels has been a persistent concern. Lithium-carbon dioxide (Li-CO2) batteries, by capturing and converting CO2 into valuable chemical substances, can serve as a novel energy storage device and effectively mitigate the greenhouse effect. Due to their unique discharge mechanism and high theoretical energy density, they are considered promising energy conversion and storage devices.

[0003] Transition metals are less expensive than precious metals and exhibit better catalytic performance, making them ideal catalytic materials for lithium-carbon dioxide batteries. For example, CN107565138A discloses a lithium-carbon dioxide battery cathode catalyst, using Mn(CH3COO)2·4H2O to prepare Mn2O3 catalyst. This catalyst is then sintered to form a highly catalytically active material, which is mixed with carbon materials and a binder for the preparation and assembly of the lithium-carbon dioxide battery cathode. This catalyst is suitable for rechargeable lithium-carbon dioxide batteries operating at room temperature under carbon dioxide conditions. However, this catalytic material has a simple composition and structure, resulting in less than ideal CO2 and ion transport efficiency. Furthermore, the catalytic material has a single valence state, preventing it from simultaneously catalyzing both discharge and charge reactions, and thus its effect on improving the discharge voltage of lithium-carbon dioxide batteries is relatively low.

[0004] CN113173603A discloses a mixed-valence manganese-based oxide composite material. This material is prepared by constructing a secondary porous nano-MnO composite material with a 3D structure composed of primary nanoparticles coated with a carbon layer. The valence state is then controlled through a complex oxidation reaction to prepare a mixed-valence manganese-based oxide (MnO / Mn3O4@NC) to improve the lithium storage capacity and electrochemical performance of the battery. However, although the carbon-coated 3D structure of this catalytic material has stereoscopic properties, its porosity is still relatively low compared to tubular carbon nanotubes, which is detrimental to the transport of CO2 gas and lithium ions, making it unsuitable for lithium-carbon dioxide batteries. Furthermore, the preparation process requires an additional step of precursor treatment, and the oxidation reaction process for controlling the valence state is quite complex.

[0005] Therefore, there is an urgent need to develop a novel manganese-based oxide composite carbon material catalyst that has a simple preparation process and can be applied to lithium-carbon dioxide batteries. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies, such as unsatisfactory CO2 transport and complex preparation processes, by providing a manganese-based oxide composite carbon material catalyst, its preparation method, and its application, thus providing a novel composite catalyst for lithium-carbon dioxide batteries.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] The first aspect of this invention provides a method for preparing a manganese-based oxide composite carbon material catalyst, the method comprising the following steps:

[0009] S1: Add pre-acid-treated carbon nanotubes (CNTs) and polyvinylpyrrolidone (PVP) to anhydrous ethanol and disperse them evenly by ultrasonication;

[0010] S2: Manganese acetate tetrahydrate (C4H) 14 The mixture of MnO8 and polyvinylpyrrolidone was added to the carbon nanotube dispersion obtained in S1 and stirred evenly under heating conditions.

[0011] S3: Perform solid-liquid separation on the mixed system obtained in S2 to obtain a solid, which is then dried for later use;

[0012] S4: The dried solid obtained in S3 is ground and then calcined at high temperature to finally obtain the manganese-based oxide composite carbon material catalyst.

[0013] Further, in step S1, the specific steps of the pre-acid treatment are as follows:

[0014] Carbon nanotubes were poured into concentrated hydrochloric acid and dispersed evenly by stirring and ultrasonication.

[0015] The mixed system was subjected to solid-liquid separation. The separated solid was washed and dried to obtain acid-treated carbon nanotubes.

[0016] Further, in step S1, the mass ratio of the carbon nanotubes to polyvinylpyrrolidone is (0.2-0.3):1, preferably 0.24:1.

[0017] Further, in step S1, the ultrasonic dispersion time is 20-60 min, preferably 30 min.

[0018] Further, in step S2, the mass ratio of manganese acetate tetrahydrate to polyvinylpyrrolidone is 1:(0.8-1.2), preferably 1:1.

[0019] Further, in step S2, the mass ratio of manganese acetate tetrahydrate to carbon nanotubes is (7-9):1, preferably 8.3:1.

[0020] Furthermore, in step S2, the heating temperature is not less than 85°C.

[0021] Furthermore, in step S2, the stirring time is 1-3 hours, preferably 2 hours.

[0022] Furthermore, in step S3, the specific operation of solid-liquid separation is to use anhydrous ethanol to filter several times until the filtrate is clear.

[0023] Furthermore, in step S3, the drying temperature is 60-80°C, preferably 70°C.

[0024] Furthermore, in step S3, the drying time is 8-16 hours.

[0025] Furthermore, in step S4, the ground solid is calcined in a tube furnace.

[0026] Furthermore, in step S4, the calcination is carried out in an inert gas atmosphere, preferably argon.

[0027] Furthermore, in step S4, the high-temperature calcination temperature is 600-800℃, preferably 700℃. When the calcination temperature rises to 900℃, Mn3O4 has been completely reduced to MnO. Therefore, in order to obtain manganese-based oxides with mixed valence states, it is necessary to control the calcination temperature within a reasonable temperature range.

[0028] Furthermore, in step S4, the heating rate of the high-temperature calcination is 1-3℃ / min, preferably 2℃ / min.

[0029] Furthermore, in step S4, the holding time for high-temperature calcination is 1.5-3 hours, preferably 2 hours.

[0030] A second aspect of the present invention provides a manganese-based oxide composite carbon material catalyst, which is prepared by any of the above-described preparation methods.

[0031] Furthermore, the manganese-based oxide composite carbon material catalyst has a porous structure with a pore size of 25–50 nm.

[0032] Furthermore, the manganese-based oxide is a mixed phase containing MnO and Mn3O4.

[0033] Furthermore, the mass ratio of MnO to Mn3O4 is (4-5.5):1, preferably 4.8:1.

[0034] This invention successfully prepared a composite catalyst suitable for lithium-carbon dioxide batteries by combining a mixed phase of manganese-based oxides (MnO and Mn3O4) with carbon nanotubes. The combination of manganese-based oxides and CNTs results in a more pronounced porous structure, thus providing more active sites and exhibiting superior catalytic performance. Furthermore, the porous structure allows for the accumulation of the discharge product, lithium carbonate, preventing pore blockage and ensuring optimal CO2 gas transport. This composite process leads to superior cycle performance in lithium-carbon dioxide batteries.

[0035] In the process of this invention, Mn3O4 is first generated during calcination, and then MnO is generated by carbothermic reduction reaction at high temperature. As the temperature rises and the calcination time increases, the MnO content gradually increases.

[0036] Transition metals can chemically adsorb and activate CO2 molecules in the electrolyte. Correspondingly, manganese-based oxides with tunable valence states can not only adsorb CO2 molecules but also play their respective roles in CO2RR and CO2ER. The combination of MnO and Mn3O4 can have a synergistic effect. In addition, the porous structure formed by the composite material combined with CNTs facilitates the transport of CO2 gas and provides deposition space for the discharge products of lithium-carbon dioxide batteries.

[0037] The present invention also provides the application of a manganese-based oxide composite carbon material catalyst in a lithium-carbon dioxide battery, wherein the manganese-based oxide composite carbon material catalyst is used as a positive electrode catalyst in a lithium-carbon dioxide battery.

[0038] Furthermore, the preparation process of the positive electrode is as follows:

[0039] Using N-methyl-2-pyrrolidone as a solvent, manganese-based oxide composite carbon material catalyst, conductive carbon black and polyvinylidene fluoride were mixed at a mass ratio of 8:1:1 and mechanically ball-milled to obtain a uniform and stable slurry.

[0040] The catalyst slurry is uniformly coated on carbon paper, and after drying, the positive electrode of the supported manganese-based oxide composite carbon material catalyst can be obtained.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) This invention innovatively synthesizes a composite catalyst suitable for lithium-carbon dioxide batteries by combining a mixed phase of manganese oxide (MnO and Mn3O4) with carbon nanotubes. The combination of manganese oxide and CNT phase results in a more pronounced porous structure, thus providing more active sites and exhibiting superior catalytic performance. Furthermore, the porous structure allows for the accumulation of the discharge product, lithium carbonate, preventing pore blockage and ensuring proper CO2 gas transport. This composite material demonstrates superior cycle performance in lithium-carbon dioxide batteries and is a promising transition metal-based catalyst material for lithium-carbon dioxide batteries.

[0043] (2) The present invention unexpectedly discovered that the combination of two oxides, MnO and Mn3O4, promotes the CO2RR and CO2ER kinetics, which is beneficial to the discharge and charging reactions of lithium-carbon dioxide batteries, namely, it is beneficial to the adsorption of CO2 and the generation of lithium carbonate during discharge, and the decomposition of lithium carbonate during charging; and the introduction of CNT further increases the service life of lithium-carbon dioxide batteries.

[0044] (3) This invention innovatively increases the content of reduced MnO by adjusting the calcination temperature, thereby controlling the oxidation ratio in the catalytic material. The preparation process is simple and does not require complex oxidation reactions to control the valence state.

[0045] (4) The raw materials used in this invention are inexpensive and abundant, and the preparation process is simple, which is conducive to large-scale production and has high practical value. Attached Figure Description

[0046] Figure 1 The image shows the XRD pattern of the manganese-based oxide composite carbon catalyst prepared in Example 1.

[0047] Figure 2 This is a TEM image of the manganese-based oxide composite carbon material catalyst prepared in Example 1.

[0048] Figure 3 The image shows the XRD pattern of the manganese-based oxide composite carbon catalyst prepared in Comparative Example 1.

[0049] Figure 4 XRD patterns of discharge products were obtained for the electrode in its original, discharged, and charged states.

[0050] Figure 5 Example 1 and Comparative Example 1 were tested at 200 mAg. -1 Current density and 500mAh g -1 Charge-discharge curves at the cutoff capacity. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0052] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0053] Example 1:

[0054] This embodiment provides a manganese-based oxide composite carbon material catalyst for lithium-carbon dioxide batteries, which can be denoted as MnO-Mn3O4-CNT, and is obtained through the following preparation steps:

[0055] (1) Pour 0.5g of PVP and 0.12g of CNT into 100mL of anhydrous ethanol and sonicate for 30min to disperse the CNT evenly.

[0056] The CNTs are pre-treated with acid, and the specific steps are as follows:

[0057] 1g of CNTs was poured into 100ml of concentrated hydrochloric acid and magnetically stirred for 10 minutes. The mixture was then ultrasonically cleaned for 1 hour, followed by uniform stirring for 12 hours. The CNTs were then repeatedly filtered using an organic membrane and deionized water until the pH of the filtrate reached 7. Finally, the filtrate was filtered again with ethanol. The resulting filter cake was placed in a vacuum drying oven and dried for 12 hours. The sample was then removed and ground until homogeneous to obtain acid-treated CNTs.

[0058] (2) Mix 1g of PVP and 1g of C4H 14 MnO8 was slowly added to the beaker in step (1) and stirred continuously at 85°C or above for 2 hours.

[0059] (3) Filter the solution in the beaker with ethanol several times until the filtrate is clear. Place the filter cake in a vacuum drying oven and dry it overnight at 70°C.

[0060] (4) Take out the dried filter cake and grind it into powder. Pour the powder into an alumina crucible and place the crucible in the middle of the tube furnace. Introduce argon gas and adjust the flow rate to about 200 mL / min. After 10 min, set the tube furnace program to heat it to 700 °C at a heating rate of 2 °C / min and hold it at that temperature for 2 h. Then let it cool naturally to room temperature to obtain the manganese-based oxide composite carbon material catalyst for lithium-carbon dioxide batteries.

[0061] Figure 1The image shows the XRD pattern of the manganese-based oxide composite carbon catalyst prepared in this embodiment. As shown in the figure, characteristic peaks corresponding to MnO and Mn3O4 appear simultaneously in the spectrum, and a characteristic peak corresponding to CNT appears at 26°, indicating that the composite material is a mixed phase of CNT, MnO, and Mn3O4.

[0062] Figure 2 This is a TEM image of the manganese-based oxide composite carbon catalyst prepared in this embodiment. As can be seen from the image, a large number of nano-sized particles (50-100 nm) are loaded on carbon nanotubes. These CNTs are irregularly distributed, intertwined, and exhibit a relatively three-dimensional structure.

[0063] Example 2:

[0064] This embodiment provides a manganese-based oxide composite carbon material catalyst for use in lithium-carbon dioxide batteries. The difference from Example 1 is that the high-temperature calcination temperature in this embodiment is 600°C.

[0065] Example 3:

[0066] This embodiment provides a manganese-based oxide composite carbon material catalyst for use in lithium-carbon dioxide batteries. The difference from Example 1 is that the high-temperature calcination temperature in this embodiment is 800°C.

[0067] Comparative Example 1:

[0068] This comparative example provides a manganese-based oxide composite carbon material catalyst, which can be denoted as MnO-CNT, and is obtained through the following preparation steps:

[0069] (1) Pour 0.5g of PVP and 0.12g of CNT into 100mL of anhydrous ethanol and sonicate for 30min to disperse the CNT evenly.

[0070] The CNTs are pre-treated with acid, and the specific steps are as follows:

[0071] 1g of CNTs was poured into 100ml of concentrated hydrochloric acid and magnetically stirred for 10 minutes. The mixture was then ultrasonically cleaned for 1 hour, followed by uniform stirring for 12 hours. The CNTs were then repeatedly filtered using an organic membrane and deionized water until the pH of the filtrate reached 7. Finally, the filtrate was filtered again with ethanol. The resulting filter cake was placed in a vacuum drying oven and dried for 12 hours. The sample was then removed and ground until homogeneous to obtain acid-treated CNTs.

[0072] (2) Mix 1g of PVP and 1g of C4H 14 MnO8 was slowly added to the beaker in step (1) and stirred continuously at 85°C or above for 2 hours.

[0073] (3) Filter the solution in the beaker with ethanol several times until the filtrate is clear. Place the filter cake in a vacuum drying oven and dry it overnight at 70°C.

[0074] (4) Take out the dried filter cake and grind it into powder. Pour the powder into an alumina crucible and place the crucible in the middle of the tube furnace. Introduce argon gas and adjust the flow rate to about 200 mL / min. After 10 min, set the tube furnace program to heat it to 900 °C at a heating rate of 2 °C / min and hold it at that temperature for 2 h. Then, let it cool naturally to room temperature to obtain the manganese-based oxide composite carbon material catalyst for lithium-carbon dioxide batteries.

[0075] Figure 3 The image shows the XRD pattern of the manganese-based oxide composite carbon catalyst prepared in this embodiment. The spectrum shows characteristic peaks corresponding to both CNTs and MnO, but lacks the characteristic peak of Mn3O4, indicating the presence of a mixture of CNTs and MnO. This suggests that when the calcination temperature reaches 900℃, Mn3O4 is completely reduced to MnO.

[0076] Based on the successful preparation of the above embodiments and comparative examples, this invention takes Example 1 as an example to test the performance of the prepared manganese-based oxide composite carbon material catalyst as a positive electrode material for lithium-carbon dioxide batteries:

[0077] Electrode preparation: Using N-methyl-2-pyrrolidone (NMP) as solvent, the catalyst, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1. The mixture was then mechanically ball-milled for 2 hours to obtain a uniform and stable slurry. The catalyst slurry was uniformly coated onto square hydrophobic carbon paper, and then dried in a vacuum drying oven at 80℃ for 12 hours. After removal, the carbon paper was cut into circular electrode sheets with a diameter of 14 mm.

[0078] Battery Assembly: All Li-CO2 batteries used were CR2032 type, with 17 holes in the positive electrode shell to facilitate CO2 gas transport. The battery structure consisted of, in sequence, a positive electrode shell, an electrode plate, a separator, a lithium plate, a gasket, a spring plate, and a negative electrode shell. A glass fiber separator (GF / D) was used, and the electrolyte was 1M LiTFSI in TEGDME. The entire battery assembly process was completed in a laboratory glove box, with the internal atmosphere maintained at O2 < 0.1 ppm and H2O < 0.1 ppm.

[0079] Material characterization: The phase composition of the material and the discharge products of the Li-CO2 battery were analyzed using a Bruker D8 Advance X-ray diffractometer (XRD). The test conditions were as follows: scanning ranges of 10° to 80° and 10° to 60°, step size of 0.02°, and scanning rate of 6° / min.

[0080] Test method: The assembled Li-CO2 battery was placed in a specially made sealed container filled with argon gas and allowed to stand for 12 hours before electrochemical performance testing was performed.

[0081] The XRD patterns of the discharge products of the electrode in the original, discharged, and charged states in Example 1 are shown below. Figure 4 As shown in the figure, after discharge, the XRD pattern of the electrode relative to the original state shows obvious diffraction peaks corresponding to Li2CO3 at 2θ = 21.3°, 30.6°, and 31.7° (PDF#22-1141), proving that Li2CO3 is the main discharge product of the CO2RR process. After charging, these diffraction peaks basically disappear, indicating that under the action of the catalyst, Li2CO3 is successfully decomposed during the charging process, and the charging reaction (CO2ER) proceeds smoothly.

[0082] Example 1 and Comparative Example 1 were at 200 mAg -1 Current density and 500mAh g -1 The charge / discharge curves at the cutoff capacity are shown in the figure below. Figure 5 As shown in the figure. It can be seen from the figure that at 200mAg... -1 Current density and 500mAh g -1 At the cutoff capacity, the battery can only cycle 60 times. In contrast, the battery using MnO-Mn3O4-CNT can cycle 100 times, and at 60 cycles, its discharge voltage and charge voltage are higher and lower than those of the MnO-CNT battery, respectively, with a smaller voltage gap between charge and discharge. After cycling, the MnO-CNT battery exhibits more pronounced polarization.

[0083] The above results indicate that the present invention promotes CO2RR and CO2ER kinetics through the composite of two oxides, MnO and Mn3O4, which is beneficial to the discharge and charging reactions of lithium-carbon dioxide batteries and is an ideal cathode catalyst material for Li-CO2 batteries.

[0084] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a manganese-based oxide composite carbon material catalyst, characterized in that, The preparation method includes the following steps: S1: Add pre-acid-treated carbon nanotubes and polyvinylpyrrolidone to anhydrous ethanol and disperse them evenly by ultrasonication; S2: Add the mixture of manganese acetate tetrahydrate and polyvinylpyrrolidone to the carbon nanotube dispersion obtained in S1, and stir evenly under heating conditions; S3: Perform solid-liquid separation on the mixed system obtained in S2 to obtain a solid, which is then dried for later use; S4: The dried solid obtained in S3 is ground and then calcined at high temperature to finally obtain the manganese-based oxide composite carbon material catalyst.

2. The method for preparing a manganese-based oxide composite carbon material catalyst according to claim 1, characterized in that, In step S1, the specific steps of the pre-acid treatment are as follows: Carbon nanotubes were poured into concentrated hydrochloric acid and dispersed evenly by stirring and ultrasonication. The mixed system was subjected to solid-liquid separation. The separated solid was washed and dried to obtain acid-treated carbon nanotubes.

3. The method for preparing a manganese-based oxide composite carbon material catalyst according to claim 1, characterized in that, In step S1, the mass ratio of the carbon nanotubes to polyvinylpyrrolidone is (0.2-0.3):1; The ultrasonic dispersion time is 20-60 min.

4. The method for preparing a manganese-based oxide composite carbon material catalyst according to claim 1, characterized in that, In step S2, the mass ratio of manganese acetate tetrahydrate to polyvinylpyrrolidone is 1:(0.8-1.2); The mass ratio of manganese acetate tetrahydrate to carbon nanotubes is (7-9):

1.

5. The method for preparing a manganese-based oxide composite carbon material catalyst according to claim 1, characterized in that, In step S2, the heating temperature is not less than 85°C; The stirring time is 1-3 hours.

6. The method for preparing a manganese-based oxide composite carbon material catalyst according to claim 1, characterized in that, In step S3, the specific operation of solid-liquid separation is to use anhydrous ethanol to filter several times until the filtrate is clear. The drying temperature is 60-80℃, and the drying time is 8-16 hours.

7. The method for preparing a manganese-based oxide composite carbon material catalyst according to claim 1, characterized in that, In step S4, the ground solid is calcined in a tube furnace under an inert gas atmosphere.

8. The method for preparing a manganese-based oxide composite carbon material catalyst according to claim 1, characterized in that, In step S4, the high-temperature calcination temperature is 600-800℃, the heating rate is 1-3℃ / min, and the holding time is 1.5-3h.

9. A manganese-based oxide composite carbon material catalyst, characterized in that, Prepared by the preparation method according to any one of claims 1-8; The manganese-based oxide composite carbon material catalyst has a porous structure with a pore size of 25–50 nm. The manganese-based oxide is a mixed phase containing MnO and Mn3O4, with a mass ratio of MnO to Mn3O4 of (4-5.5):

1.

10. The application of the manganese-based oxide composite carbon material catalyst according to claim 9 in a lithium-carbon dioxide battery, characterized in that, The manganese-based oxide composite carbon material catalyst is used as the positive electrode catalyst for lithium-carbon dioxide batteries.

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