Modified manganese dioxide positive electrode material and preparation method and application thereof

Abstract

The invention discloses a modified manganese dioxide positive electrode material, the chemical general formula of the modified manganese dioxide positive electrode material is NaxMyMnO2.nH2O, M is a doping element, and comprises any one or more of Al, Co, Fe, Cr, Zn, Cu, Ca, Mo, Mg and Ti, 0 lt; x < = 1, 0 < = y < = 0.5, 0 lt; n < = 2. According to the modified manganese dioxide positive electrode material disclosed by the invention, a large amount of sodium is pre-embedded into the interlayer of manganese dioxide, occupies a position right above an octahedral vacancy in a MnO6 layer, achieves the purpose of balancing charges by virtue of electrostatic interaction and serving as a charge compensation agent, and is alternately and orderly arranged with H2O molecules in the layer, so that the interlayer spacing is enlarged, and the layered structure is stabilized; the cycling stability is obviously improved. Besides, in the charging and discharging process, when embedded Mg < 2 + > and Na < + > are partially left between manganese dioxide layers, pre-embedded sodium can also be used as a Na < + > source to perform reversible de-embedding, so that the initial coulombic efficiency of the magnesium-sodium hybrid battery is remarkably improved, and the electrochemical performance is enhanced.

Description

Technical Field

[0001] This invention belongs to the technical field of novel magnesium-sodium battery materials, specifically relating to a modified manganese dioxide cathode material, its preparation method, and its application in magnesium-sodium hybrid batteries. Background Technology

[0002] Against the backdrop of global advocacy for environmental protection and sustainable development, my country has proposed the goal of "peaking carbon and achieving carbon neutrality" to mitigate and address the extreme climate changes caused by global warming. Promoting energy transition and developing renewable energy are key pathways to achieving this "dual carbon" goal. Among numerous energy storage technologies, electrochemical energy storage is an effective technology that stores energy by converting chemical energy and electrical energy through chemical reactions. Selecting suitable metal ions as charge carriers is crucial for the development of electrochemical energy storage battery technology.

[0003] Among them, magnesium-sodium hybrid ion batteries are considered a promising post-lithium-ion battery technology due to their high safety, low cost, and high capacity resulting from the synergistic effect of dual ions. However, the practical application of magnesium-sodium hybrid ion batteries is limited by the performance bottleneck of cathode materials. Existing cathode materials (such as manganese-based oxides and vanadium-based oxides) generally suffer from problems such as short cycle life (<50 cycles) and low specific capacity (<180 mAh / g), which seriously hinders the further development of magnesium-sodium hybrid ion batteries.

[0004] Manganese-based oxide (MnO2) has shown great potential as a cathode material in magnesium-sodium hybrid batteries due to its high theoretical capacity, ease of synthesis, environmental friendliness, and high voltage platform. However, its electrochemical performance in practical applications remains poor due to inherent defects in manganese-based oxides. The core issue affecting its electrochemical performance lies in its anionic framework (O2). 2- ) and Mg 2+ and Na + The strong Coulombic force results in a low ion migration rate, leading to Mg... 2+ and Na + Irreversible insertion and extraction will occur, thus significantly reducing the initial coulombic efficiency of magnesium-sodium hybrid ion batteries. Initial coulombic efficiency is an important performance evaluation indicator for magnesium-sodium hybrid ion batteries, and a low initial coulombic efficiency will significantly affect subsequent charge-discharge capacity and cycle stability.

[0005] Chinese patent CN119650829A discloses a method for preparing a magnesium / sodium hybrid battery containing layered MnO2. While this method temporarily improves the specific capacity and cycle stability of the magnesium / sodium hybrid battery by introducing a magnesium-sodium dual-salt electrolyte and combining it with the layered MnO2 cathode, it still has a fundamental deficiency: the initial coulombic efficiency of the resulting magnesium-sodium hybrid battery remains low (63%), resulting in poor cycle performance. Therefore, developing a pre-intercalation strategy to improve the initial coulombic efficiency of the manganese dioxide-based cathode is key to overcoming existing technological bottlenecks and obtaining high-performance magnesium-sodium hybrid batteries. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a modified manganese dioxide cathode material, which aims to solve the problem of low initial coulombic efficiency and poor electrochemical performance of existing manganese-based oxide cathode materials in traditional magnesium-ion batteries and magnesium-sodium hybrid ion batteries.

[0007] This invention also provides a method for preparing the modified manganese dioxide cathode material and its application.

[0008] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a modified manganese dioxide cathode material, wherein the chemical formula of the modified manganese dioxide cathode material is Na. x M y MnO2·nH2O, where M is a doping element, including any one or more of Al, Co, Fe, Cr, Zn, Cu, Ca, Mo, Mg, and Ti, 0 <x≤1,0≤y≤0.5,0<n≤2。

[0009] In some specific embodiments, the modified manganese dioxide cathode material is nanoparticles formed by pre-intercalating sodium transition metal into a layer and / or doping elements into the crystal lattice, with a morphology of nanoflowers and a particle size of 50-100 nm.

[0010] The modified manganese dioxide cathode material of this application, by introducing transition metal sodium into the interlayer of manganese dioxide, preferentially occupies the position directly above the octahedral vacancies in the MnO6 layer and arranges itself in an orderly manner with H2O in the layer, thereby expanding the interlayer spacing and stabilizing the crystal structure; at the same time, during the charge and discharge process, the pre-embedded transition metal sodium can act as part of the Na + Sources are embedded / extracted, thereby improving the reversibility of embedding / extraction.

[0011] As part of the same inventive concept, this invention provides a method for preparing a modified manganese dioxide cathode material, comprising the following steps: 1) According to the formula requirements, add the manganese source, sodium source and reducing agent to deionized water in sequence and stir evenly to obtain solution A; 2) Add the transition metal source to solution A, stir until homogeneous to obtain solution B, and transfer to a constant temperature oven for heating reaction; 3) Cool, centrifuge, and dry the precipitate obtained in step 2 to finally obtain the modified manganese dioxide cathode material.

[0012] In some specific embodiments, the molar ratio of manganese source, sodium source and reducing agent in step 1) is 1:0.5-3.5:0.4-1.

[0013] In some specific embodiments, the molar ratio of the dopant element M to the manganese source in step 1) is (0-0.5):1.

[0014] In some specific embodiments, the heating reaction in step 2) is a hydrothermal growth method, with process conditions of 80-120℃ and reaction time of 20-30h.

[0015] In some specific embodiments, the centrifugation process conditions in step 3) are as follows: the washing medium is water or anhydrous ethanol, the number of washing cycles is 3-5, and the centrifugation time is 3-5 minutes.

[0016] In some specific embodiments, the drying process conditions in step 3) are: the drying temperature is 60-100℃ and the drying time is 8-12h.

[0017] As part of the same inventive concept, the present invention also provides a magnesium-sodium hybrid battery, which is prepared by the following method: 1) Preparation of positive electrode sheet The modified manganese dioxide cathode material, conductive additives, and binders are mixed to form a slurry, rolled evenly, and dried to obtain a cathode sheet. 2) Preparation of magnesium / sodium dual-salt electrolyte Magnesium bis(trifluoromethanesulfonyl)imide and sodium bis(trifluoromethanesulfonyl)imide were added to an organic mixed solvent in a certain proportion and stirred for 15-30 minutes until a uniform and clear solution was obtained to obtain a magnesium / sodium double salt solution. 3) Preparation of magnesium-sodium hybrid batteries Under an inert atmosphere, a magnesium-sodium hybrid battery is assembled using the positive electrode obtained in step 1), pure magnesium metal as the negative electrode, and the magnesium / sodium double salt solution prepared in step 2) as the electrolyte.

[0018] Furthermore, the mass ratio of the modified manganese dioxide, conductive agent, and binder is (5-10):(1.5-3):1; the conductive agent is Ketjen Black; and the binder is polytetrafluoroethylene (PTFE). The molar ratio of magnesium bis(trifluoromethanesulfonyl)imide to sodium bis(trifluoromethanesulfonyl)imide is 1:0.25-2.

[0019] The organic solvent is a mixture of ethylene glycol dimethyl ether and monomethoxydipropylamine in a volume ratio of 1:0.2-0.5.

[0020] Compared with the prior art, the present invention has at least the following advantages: The magnesium-sodium hybrid battery modified manganese dioxide cathode material provided by this invention differs from the simple doping strategies in existing technologies. Instead, it pre-embeds a large amount of sodium into the interlayer of manganese dioxide, occupying the positions directly above the octahedral vacancies in the MnO6 layer. This sodium balances the charge through electrostatic interaction and acts as a charge compensator, while also alternating and orderly arranging with H2O molecules in the layer, expanding the interlayer spacing, stabilizing the layered structure, and significantly improving cycle stability. Furthermore, during charge and discharge, when the embedded Mg... 2+ and Na + When some sodium remains in the manganese dioxide interlayer, the pre-intercalated sodium can also act as a Na+ source for reversible insertion and extraction, thereby significantly improving the first coulombic efficiency of the magnesium-sodium hybrid battery and enhancing its electrochemical performance.

[0021] The modified manganese dioxide cathode material of this invention contains water molecules in its interlayer, and the resulting "electrostatic shielding effect" can effectively shield Mg during charging and discharging. 2+ The high charge density reduces polarization, thereby promoting Mg 2+ and Na + The rapid insertion / extraction of manganese dioxide provides technical support for the application of modified manganese dioxide cathode materials in magnesium-sodium hybrid batteries.

[0022] The modified manganese dioxide cathode material of this invention, based on the pre-embedding of transition metal sodium into the manganese dioxide layer, further enhances the electrical performance and stability of the cathode material by introducing different doping metal elements. For example, doping with Al can improve the material's stability and cycle performance; doping with Fe can improve the material's charge-discharge capacity; and doping with Co can improve the material's voltage plateau. The magnesium-sodium hybrid battery assembled from this modified manganese dioxide cathode material exhibits a high operating voltage (~1.9V), a high initial reversible specific capacity (~210 mAh / g), and good cycle performance (100 cycles), representing a promising and high-performance novel hybrid ion battery system.

[0023] 4) The method for preparing sodium pre-embedded manganese dioxide cathode material provided by the present invention adopts a hydrothermal synthesis strategy. The steps are simple and easy to implement, the raw material resources are abundant, the cost is low, and the equipment used in the process is all conventional equipment, which is easy to scale up for production and application. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0025] Figure 1 The XRD patterns of the manganese dioxide cathode materials provided in Examples 1, 2, and 3 and Comparative Examples 1 and 2 of this invention are shown. Figure 2 The above is a SEM image of the sodium pre-intercalated manganese dioxide cathode material provided in Example 1 of this invention; Figure 3 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Embodiment 1 of the present invention; Figure 4 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Embodiment 2 of the present invention; Figure 5 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Embodiment 3 of the present invention; Figure 6 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Comparative Example 1 of the present invention; Figure 7 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Comparative Example 2 of the present invention; Figure 8 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Example 4 of the present invention; Figure 9 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Example 5 of the present invention; Figure 10 This is a charge-discharge curve of the magnesium-sodium hybrid battery provided in Embodiment 6 of the present invention; Figure 11 The diagram shows the cycle performance of the magnesium-sodium hybrid batteries provided in Examples 1, 2, and 3 and Comparative Examples 1 and 2 of this invention. Figure 12 The diagram shows the cycle performance of the magnesium-sodium hybrid battery provided in Examples 4, 5, and 6 of this invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0027] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0028] Unless otherwise stated, all percentages, parts, ratios, etc., in this document are by weight. The materials, methods, and examples described herein are exemplary and should not be construed as limiting unless otherwise specified. Unless otherwise specified, all raw materials, equipment, or apparatus used in the production and testing processes are commercially available or obtained by conventional methods in the art.

[0029] This embodiment 1 provides a method for preparing a modified manganese dioxide cathode material, which includes the following steps: 1) Weigh 10 mmol KMnO4, 20 mmol NaOH and 5 mmol (NH4)2C2O4 powder and dissolve them in 70 mL of deionized water. Stir and disperse to obtain a precursor solution. 2) The precursor solution was transferred to a constant temperature oven for heating reaction at 90℃ for 24 hours; after cooling, the precipitate was washed 5 times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 80℃ for 10 hours to obtain modified manganese dioxide cathode material.

[0030] The modified manganese dioxide cathode material prepared in this embodiment was characterized by XRD, and its XRD pattern is shown in [reference needed]. Figure 1 XRD patterns show that the obtained cathode material is a typical delta-type manganese dioxide material, indicating a layered structure, and no impurity phases were observed. Refinement results show that its 001 interplanar spacing (interlayer spacing) is 0.73 nm, with a variation range of ±5%. Figure 2 As shown in the SEM image, the sodium pre-embedded manganese dioxide cathode material has a morphology of nanoflower-like structure formed by the self-assembly of nanosheets, with a particle size of 50~100nm.

[0031] The application of the modified manganese dioxide cathode material in the magnesium-sodium hybrid battery in this embodiment is prepared by the following method: Positive electrode sheet: The positive electrode material prepared in step 1 is ground and mixed with Ketjen black and polytetrafluoroethylene binder in a mortar at a mass ratio of 7:2:1, and then rolled into sheets under dry conditions. Finally, it is cut into (7×7) mm sheets. 2 The electrode film.

[0032] Magnesium / sodium dual-salt electrolyte: 0.5 mmol of magnesium bis(trifluoromethanesulfonyl)imide and 0.5 mmol of sodium bis(trifluoromethanesulfonyl)imide were added to a mixed solvent of 2 ml of DME (ethylene glycol dimethyl ether) and 0.5 ml of monomethoxydipropylamine and stirred for 15 min to obtain a magnesium / sodium dual-salt solution.

[0033] 3) Preparation of magnesium-sodium hybrid batteries The electrode sheet prepared in step 1) is used as the positive electrode, and a Mg metal disc with a diameter of 14 mm and a thickness of 0.1 mm is used as the negative electrode. The magnesium / sodium double salt solution prepared in step 2) is used as the electrolyte. The CR2032 coin cell is assembled in an Ar atmosphere.

[0034] The CR2032 coin cell prepared in this embodiment was subjected to constant current charge-discharge testing at a current density of 20 mA / g; the test results were as follows under the conditions of a discharge cutoff voltage of 0.4 V and a charge cutoff voltage of 2.8 V. Figure 3 As shown, the initial discharge specific capacity of the modified manganese dioxide cathode is 193 mAh / g, and the initial coulombic efficiency is 97%, proving that this embodiment can effectively improve the initial coulombic efficiency. Next, long-cycle performance tests were conducted at a current density of 50 mA / g, and the results are as follows... Figure 8 As shown, the remaining specific capacity after 50 cycles is 99mAh / g.

[0035] Example 2 Example 2 provides a method for preparing a modified manganese dioxide cathode material. Its composition is basically the same as that of the example, except that the ratio of manganese:sodium:reducing agent is 1:3:0.5 (i.e., 10 mmol, 30 mmol and 5 mmol); its steps and process parameters are the same as those of the example.

[0036] The modified manganese dioxide cathode material prepared in this embodiment was characterized by XRD, and its XRD pattern is shown in [reference needed]. Figure 1 The X-ray diffraction pattern is consistent with that of typical delta-type manganese dioxide, and no impurity phases were observed.

[0037] The application of the modified manganese dioxide cathode material in the magnesium-sodium hybrid battery of this embodiment, and the preparation method of the magnesium-sodium hybrid battery are as in Example 1; The CR2032 coin cell in this embodiment was subjected to constant current charge-discharge testing at a current density of 20 mA / g. The test results, under the conditions of a discharge cutoff voltage of 0.4 V and a charge cutoff voltage of 2.8 V, are as follows: Figure 4 As shown, the battery's initial discharge specific capacity is 191 mAh / g, and its initial coulombic efficiency is 96%. Next, long-cycle performance tests were conducted at a current density of 50 mA / g, and the results are as follows... Figure 8As shown, it still has a specific capacity of 91mAh / g after 50 cycles.

[0038] Example 3 This embodiment 3 provides a method for preparing a modified manganese dioxide cathode material. Its composition is basically the same as that of the embodiment, except that the ratio of manganese:sodium:reducing agent is 1:1:0.5 (i.e., 10 mmol, 10 mmol and 5 mmol); its steps and process parameters are the same as those of the embodiment.

[0039] The modified manganese dioxide cathode material prepared in this embodiment was characterized by XRD, and its XRD pattern is shown in [reference needed]. Figure 1 The X-ray diffraction pattern is consistent with that of typical delta-type manganese dioxide, and no impurity phases were observed.

[0040] The application of the modified manganese dioxide cathode material in the magnesium-sodium hybrid battery of this embodiment, and the preparation method of the magnesium-sodium hybrid battery are as in Example 1; The CR2032 coin cell in this embodiment was subjected to a 20 mA g test. 1 Constant current charge-discharge tests were performed at the specified current density. The test results are as follows: [Results are missing from the original text]. Figure 5 As shown, the battery's initial discharge specific capacity is 202 mAh / g, and its initial coulombic efficiency is 96%. Next, long-cycle performance tests were conducted at a current density of 50 mA / g, and the results are as follows... Figure 8 As shown, it still has a specific capacity of 95mAh / g after 50 cycles.

[0041] Example 4 This embodiment 4 provides a method for preparing a modified manganese dioxide cathode material, which includes the following steps: Weigh 10 mmol KMnO4, 20 mmol NaOH and 5 mmol (NH4)2C2O4 powder into 70 mL of deionized water, stir and disperse to obtain a mixed solution; Weigh 1 mmol of Al(NO3)3·9H2O powder into the mixed solution, stir to obtain a precursor solution, transfer the solution to a constant temperature oven for heating reaction at 90℃ for 24h; After cooling, the precipitate was washed five times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 80°C for 10 hours to obtain the modified manganese dioxide cathode material.

[0042] The application of the modified manganese dioxide cathode material in the magnesium-sodium hybrid battery of this embodiment, and the preparation method of the magnesium-sodium hybrid battery are as in Example 1; The CR2032 coin cell in this embodiment was subjected to constant current charge-discharge testing at a current density of 20 mA / g; the test results were as follows, under the conditions of a discharge cutoff voltage of 0.4 V and a charge cutoff voltage of 2.8 V. Figure 8 As shown, the battery's initial discharge specific capacity is 197 mAh / g; subsequently, long-cycle performance testing was conducted at a current density of 100 mA / g, with the results as follows. Figure 12 As shown, after 100 cycles, it still has a specific capacity of 85 mAh / g and a capacity retention rate of 78%, further proving that this embodiment can effectively enhance the material's cycling performance and capacity retention rate.

[0043] Example 5 This embodiment 4 provides a method for preparing a modified manganese dioxide cathode material, which includes the following steps: Weigh 10 mmol KMnO4, 20 mmol NaOH and 5 mmol (NH4)2C2O4 powder into 70 mL of deionized water, stir and disperse to obtain a mixed solution; Weigh 1 mmol of Fe(NO3)3·9H2O powder into the mixed solution, stir to obtain a precursor solution, transfer the solution to a constant temperature oven for heating reaction at 90℃ for 24h; After cooling, the precipitate was washed five times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 80°C for 10 hours to obtain the modified manganese dioxide cathode material.

[0044] The application of the modified manganese dioxide cathode material in the magnesium-sodium hybrid battery of this embodiment, and the preparation method of the magnesium-sodium hybrid battery are as in Example 1; The CR2032 coin cell in this embodiment was subjected to constant current charge-discharge testing at a current density of 20 mA / g; the test results were as follows, under the conditions of a discharge cutoff voltage of 0.4 V and a charge cutoff voltage of 2.8 V. Figure 9 As shown, the battery's initial discharge specific capacity was 210 mAh / g; this further demonstrates that this embodiment can effectively enhance the material's charge-discharge specific capacity. Next, long-cycle performance tests were conducted at a current density of 100 mA / g, and the results are as follows... Figure 12 As shown, it still has a specific capacity of 86mAh / g after 100 cycles.

[0045] Example 6 This embodiment 4 provides a method for preparing a modified manganese dioxide cathode material, which includes the following steps: Weigh 10 mmol KMnO4, 20 mmol NaOH and 5 mmol (NH4)2C2O4 powder into 70 mL of deionized water, stir and disperse to obtain a mixed solution; Weigh 1 mmol of Co(NO3)2·6H2O powder into the mixed solution, stir to obtain a precursor solution, transfer the solution to a constant temperature oven for heating reaction at 90℃ for 24h; After cooling, the precipitate was washed five times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 80°C for 10 hours to obtain the modified manganese dioxide cathode material.

[0046] The application of the modified manganese dioxide cathode material in the magnesium-sodium hybrid battery of this embodiment, and the preparation method of the magnesium-sodium hybrid battery are as in Example 1; The CR2032 coin cell in this embodiment was subjected to constant current charge-discharge testing at a current density of 20 mA / g; the test results were as follows, under the conditions of a discharge cutoff voltage of 0.4 V and a charge cutoff voltage of 2.8 V. Figure 10 As shown, the battery's initial discharge specific capacity was 204 mAh / g, and the operating voltage was 1.95V, further demonstrating that this embodiment can effectively enhance the material's operating voltage. Next, long-cycle performance tests were conducted at a current density of 100 mA / g, and the results are as follows... Figure 12 As shown, the material can be stably cycled for 100 cycles with a remaining specific capacity of 76 mAh / g.

[0047] As can be seen from the data in Examples 4-6, the modified manganese dioxide cathode material obtained by pre-intercalation of sodium and doping with other metal elements (Al, Fe or Co) has excellent comprehensive electrochemical performance. The initial discharge specific capacity can reach 210 mAh / g, and the battery has high stability, can be stably cycled for more than 100 cycles, and the capacity retention rate is greater than 75%.

[0048] Comparative Example 1 Comparative Example 1 provides a method for preparing a manganese dioxide cathode material, the composition of which is basically the same as that of Example 1, except that it does not contain NaOH. Specifically: 1) Weigh 10 mmol KMnO4 and 5 mmol (NH4)2C2O4 powder, and disperse the powder in 70 mL of deionized water by stirring to obtain a precursor solution; 2) The solution was transferred to a constant temperature oven for heating reaction at 90℃ for 24 hours; after cooling, the precipitate was washed 5 times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 80℃ for 10 hours to obtain the positive electrode material.

[0049] The manganese dioxide cathode material prepared in this comparative example was characterized by XRD, and its XRD pattern is shown in [reference needed]. Figure 1 The X-ray diffraction pattern is consistent with that of typical delta-type manganese dioxide, and no impurity phases were observed. Refinement results show that its 001 interplanar spacing (interlayer spacing) is 0.70 nm. The application of the manganese dioxide cathode material in this comparative example in a magnesium-sodium hybrid battery is described below, and its preparation method is as follows: The coin cell in this comparative example was subjected to a 20 mA g test. 1 Constant current charge-discharge tests were performed at the specified current density. The test results are as follows: [Results are missing from the original text]. Figure 6 As shown, the initial discharge specific capacity of the unmodified manganese dioxide cathode is 210 mAh / g, and the initial coulombic efficiency is only 57%. Next, long-cycle performance tests were conducted at a current density of 50 mA / g, and the results are as follows... Figure 8 As shown, after 50 cycles, it has a specific capacity of only 60 mAh / g.

[0050] Comparative Example 2 Comparative Example 2 provides a method for preparing a modified manganese dioxide cathode material. Its composition is basically the same as in Example 1, except that sodium hydroxide is replaced with lithium hydroxide. The steps and process parameters are the same as in Example 1. Specifically: 1) Weigh 10 mmol KMnO4, 20 mmol LiOH and 5 mmol (NH4)2C2O4 powder, wherein the ratio of manganese:sodium:reducing agent is 1:2:0.5. Dissolve the obtained powder in 70 mL of deionized water and stir to disperse to obtain a precursor solution. 2) The precursor solution was transferred to a constant temperature oven for heating reaction at 90℃ for 24 hours; after cooling, the precipitate was washed 5 times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 80℃ for 10 hours to obtain modified manganese dioxide cathode material.

[0051] The modified manganese dioxide cathode material prepared in this embodiment was characterized by XRD, and its XRD pattern is shown in [reference needed]. Figure 1 Its XRD pattern can be found in [reference needed]. Figure 1 No impurities were observed.

[0052] The application of the modified manganese dioxide cathode material in the comparative example in the magnesium-sodium hybrid battery, and the preparation method of the magnesium-sodium hybrid battery are as in Example 1. The CR2032 coin cell in this comparative example was tested at 20 mA g. 1 Constant current charge-discharge tests were performed at the specified current density. The test results are as follows: [Results are missing from the original text]. Figure 7 As shown, the battery's initial discharge specific capacity was 205 mAh / g, and its initial coulombic efficiency was 62%, which is significantly lower than the initial coulombic efficiency of the cathode material with sodium pre-intercalated manganese dioxide from the transition metal source in Example 1. Next, long-cycle performance tests were conducted at a current density of 50 mA / g, and the results are as follows... Figure 8As shown, after 50 cycles, it has a specific capacity of only 63 mAh / g.

[0053] In summary, comparing the initial coulombic efficiency of the modified manganese dioxide cathode materials prepared in Example 1 and Comparative Example 1, Example 1 has an initial coulombic efficiency of 97%, while Comparative Example 1 has an initial coulombic efficiency of 57%. Comparing the cycle performance of the cathode materials prepared in Example 1 and Comparative Example 1, Example 1 still has a specific capacity of 100 mAh / g after 50 cycles at 50 mA / g, while the comparative example only has 60 mAh / g. This indicates that sodium pre-intercalation significantly improves the initial coulombic efficiency of the material. Through the improvement in initial coulombic efficiency and the increase in interlayer spacing brought about by sodium pre-intercalation, the structural stability of the modified manganese dioxide cathode material in this application is improved, exhibiting excellent comprehensive electrochemical performance. For example, in Examples 2 and 3, the sodium pre-intercalated manganese dioxide cathodes both exhibited high initial coulombic efficiency (>95%) and good cycle performance (remaining specific capacity >90 mAh / g).

[0054] Furthermore, compared with the lithium-doped manganese dioxide cathode material synthesized under the same conditions as in Example 1 in Example 2, both the initial coulombic efficiency and cycle performance were lower than those of the sodium-pre-intercalated manganese dioxide cathode in Example 1, further demonstrating the effectiveness of the sodium pre-intercalation strategy.

[0055] In summary, the modified manganese dioxide cathode material provided by this invention exhibits high initial coulombic efficiency, high specific capacity, and excellent cycle performance in magnesium-sodium hybrid batteries. It is a promising and high-performance novel magnesium-based hybrid battery cathode material.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A modified manganese dioxide cathode material, characterized in that, The chemical formula of the modified manganese dioxide cathode material is Na. x M y MnO2·nH2O, where M is a doping element, including any one or more of Al, Co, Fe, Cr, Zn, Cu, Ca, Mo, Mg, and Ti, 0 <x≤1,0≤y≤0.5,0<n≤2。 2. The modified manganese dioxide cathode material according to claim 1, characterized in that, The modified manganese dioxide cathode material is composed of nanoparticles formed by pre-intercalating sodium transition metal into the crystal lattice and / or doping elements into the crystal lattice. The morphology is nanoflower-like, and the particle size is 50-100 nm.

3. A method for preparing the modified manganese dioxide cathode material according to claim 1 or 2, characterized in that, Includes the following steps: 1) According to the formula requirements, add the manganese source, sodium source and reducing agent to deionized water in sequence and stir evenly to obtain solution A; 2) Add the transition metal source to solution A, stir until homogeneous to obtain solution B, and transfer to a constant temperature oven for heating reaction; 3) Cool, centrifuge, and dry the precipitate obtained in step 2 to finally obtain the modified manganese dioxide cathode material.

4. The method for preparing the modified manganese dioxide cathode material according to claim 3, characterized in that, The molar ratio of manganese source, sodium source and reducing agent mentioned in step 1) is 1:0.5-3.5:0.4-1.

5. The method for preparing the modified manganese dioxide cathode material according to claim 4, characterized in that, The molar ratio of the dopant element M to the manganese source in step 1) is (0-0.5):

1.

6. The method for preparing the modified manganese dioxide cathode material according to claim 3, characterized in that, The heating reaction described in step 2) is a hydrothermal growth method, with process conditions of 80-120℃ and reaction time of 20-30h.

7. The method for preparing the modified manganese dioxide cathode material according to claim 6, characterized in that, The centrifugation process conditions in step 3) are as follows: the washing medium is water or anhydrous ethanol, the number of washing cycles is 3-5, and the centrifugation time is 3-5 minutes.

8. The method for preparing the modified manganese dioxide cathode material according to claim 7, characterized in that, The drying process conditions described in step 3) are: the drying temperature is 60-100℃ and the drying time is 8-12h.

9. A magnesium-sodium hybrid battery, characterized in that, It is prepared by the following method: 1) Preparation of positive electrode sheet The modified manganese dioxide cathode material, conductive additives, and binders described in claim 1 or 2 are mixed to form a slurry, rolled evenly, and dried to obtain a cathode sheet. 2) Preparation of magnesium / sodium dual-salt electrolyte Magnesium bis(trifluoromethanesulfonyl)imide and sodium bis(trifluoromethanesulfonyl)imide were added to an organic mixed solvent in a certain proportion and stirred until a uniform and clear solution was obtained to obtain a magnesium / sodium double salt solution. 3) Preparation of magnesium-sodium hybrid batteries Under an inert atmosphere, a magnesium-sodium hybrid battery is assembled using the positive electrode obtained in step 1), pure magnesium metal as the negative electrode, and the magnesium / sodium double salt solution prepared in step 2) as the electrolyte.

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