A one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material applicable to a water-based zinc ion battery positive electrode and a preparation method thereof

Abstract

A one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material and its preparation method, applicable to the positive electrode of aqueous zinc-ion batteries, belong to the field of electrochemical energy storage materials technology. Ammonium molybdate tetrahydrate is dissolved in a mixed solution of water and ethanol, stirred until homogeneous, and then concentrated nitric acid is added to obtain a mixed solution. A hydrothermal reaction is then carried out to obtain a one-dimensional MoO2 / MoO3 heterostructure material with uniform diameter. In this invention, the MoO2 and MoO3 phases are uniformly distributed and form a tight interface. This utilizes the good electronic conductivity of MoO2 while retaining the high ion storage activity of MoO3, improving the electrochemical reaction kinetics and structural stability of the material. The one-dimensional heterostructure provides a continuous charge transport channel, reduces ion diffusion resistance, and effectively alleviates the problems of material volume expansion and structural collapse during charge and discharge, giving the composite material superior structural integrity and electrochemical performance. When used as the positive electrode of an aqueous zinc-ion battery, it improves the electrode's specific capacity, rate performance, and cycle life.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, specifically relating to a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material that can be used as the cathode of an aqueous zinc-ion battery and its preparation method. Background Technology

[0002] With the rapid development of renewable energy and the continuous growth in energy storage demand, safe, low-cost, and environmentally friendly new energy storage systems have attracted widespread attention. Compared with traditional lithium-ion batteries, aqueous zinc-ion batteries (AZIBs) are considered to be a promising next-generation energy storage device due to their advantages such as high electrolyte safety, abundant raw materials, low cost, and high energy density. However, the development of aqueous zinc-ion batteries is still limited by the performance of cathode materials, especially in terms of cycle stability and rate performance. Molybdenum-based oxides are considered potential cathode materials for zinc-ion batteries due to their multivalent state characteristics, good electrochemical reversibility, and abundant redox reactivity. Among them, molybdenum trioxide (MoO3) has a high theoretical specific capacity and good ion intercalation characteristics, but its intrinsic conductivity is low, which limits electron transport and thus affects rate performance and cycle stability. For example, He et al. verified the application of MoO3 nanowires as a high-capacity cathode in zinc-ion batteries through various characterization methods, and demonstrated the application of zinc-ion batteries (ZIBs) using quasi-solid-state polyvinyl alcohol (PVA) / ZnCl2 gel electrolyte at 0.4 A g. -1 A current density of 243.1 mAh g was achieved. -1 Its ultra-high capacity and 14.4 mWh cm -3 The excellent energy density (Advanced Science 6 (2019) 1900151). In contrast, molybdenum dioxide (MoO2) has excellent metallic conductivity, which can effectively improve the electron transport rate, but its zinc ion storage capacity is limited, and it is difficult to achieve both high capacity and high conductivity when used alone.

[0003] To overcome the performance limitations of single molybdenum-based oxides, strategies have been proposed to construct composite structures or heterojunctions to combine the advantages of both and achieve synergistic improvements in electrochemical performance. For example, Tang et al. prepared MoO2 / Mo4O2 using a simple sulfur-assisted thermal reduction method. 11 Heterojunction materials were developed and used as cathodes in aqueous zinc-ion batteries. Based on MoO2 and Mo4O 11 The synergistic effect of the prepared MoO2 / Mo4O 11 Heterojunction materials at 0.5 A g -1 After 500 cycles at a current density, it still maintains 260 mAh g. -1It exhibits excellent specific capacity. Even during cycles up to 3000, the current density remains high at 2 A g. -1 It can still maintain 184.1 mAh g -1 The specific capacity (Journal of Power Sources 660 (2025) 238490). However, existing preparation methods are complex and involve multiple steps, usually requiring high-temperature annealing or reducing atmosphere treatment, making it difficult to achieve precise control of morphology and phase structure. In addition, some existing methods require the addition of additional reducing agents or are carried out in highly corrosive systems during the reaction process, which can easily lead to increased environmental load and potential safety risks, thus limiting their application in large-scale production. Therefore, developing a simple, highly controllable, and environmentally friendly method for preparing one-dimensional MoO2 / MoO3 heterojunction materials is of great significance for improving the overall performance of molybdenum-based aqueous zinc-ion batteries. To address the above problems, this invention proposes a hydrothermal synthesis strategy in a water-ethanol mixed system, using nitric acid to assist in controlling the reaction environment, which can achieve the construction of one-dimensional MoO2 / MoO3 heterostructures in one step, significantly improving the electrochemical performance and structural stability of the material. Summary of the Invention

[0004] To address the problems of insufficient conductivity, poor structural stability, and severe cycle performance degradation in existing molybdenum-based oxide cathode materials, this invention provides a one-dimensional molybdenum dioxide / molybdenum trioxide (MoO2 / MoO3) heterojunction material for aqueous zinc-ion battery cathodes and its preparation method. This invention employs a one-step solvothermal synthesis method, using ammonium molybdate tetrahydrate as the molybdenum source, and reacting in a mixed solvent system composed of water and ethanol. This method utilizes the reducing properties of ethanol solvent and adjusts the acidity and redox environment of the system with a small amount of nitric acid to achieve the simultaneous generation and interface construction of the MoO2 and MoO3 phases under relatively mild conditions, thereby obtaining a MoO2 / MoO3 composite material with a one-dimensional heterostructure. This method features a simple process route, easily controllable conditions, and requires no additional reduction or atmosphere protection steps, exhibiting good reproducibility and environmental friendliness, making it suitable for laboratory and large-scale preparation. The prepared one-dimensional MoO2 / MoO3 heterojunction material consists of a highly conductive MoO2 phase and a high-capacity, highly active MoO3 phase. The two phases form a tight interfacial contact at the nanoscale, enabling electrons to interact with Zn during charging and discharging. 2+ Rapid and coordinated ion transport. Simultaneously, the one-dimensional structure helps provide continuous charge transport channels, reduces ion diffusion resistance, and effectively mitigates the problems of material volume expansion and structural collapse during electrochemical reactions.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction for use as a cathode in aqueous zinc-ion batteries, comprising ammonium molybdate tetrahydrate (NH4)6Mo7O 24 • 4H₂O is dissolved in a mixed solution of water and ethanol, stirred until homogeneous, and then concentrated nitric acid is added to obtain a mixed solution. The resulting solution can be converted into a one-dimensional MoO₂ / MoO₃ heterostructure material with uniform size through a simple solvothermal reaction without the need for additional reducing agent or high-temperature treatment. The mixed solution is then placed in a reactor for hydrothermal reaction, followed by post-processing to obtain a one-dimensional MoO₂ / MoO₃ heterostructure material with uniform diameter.

[0006] Furthermore, in the water and ethanol mixed solution, the volume ratio of water to ethanol is 1:2-2:1, the stirring time is 0.5-1 hour, and magnetic stirring is used.

[0007] Furthermore, add 1.4-2.8 g of ammonium molybdate tetrahydrate and 0.5-2 ml of concentrated nitric acid to every 60 mL of the water and ethanol mixture.

[0008] Furthermore, the concentrated nitric acid is added slowly, with a concentration of 68-70%.

[0009] Furthermore, the hydrothermal reaction is carried out in a high-pressure reactor at a temperature of 180-220 °C for 12-24 hours.

[0010] Furthermore, the post-treatment involves washing the precipitate after the hydrothermal reaction with deionized water and then drying it. The drying temperature is 60-80 ℃, and the drying time is 12-24 h.

[0011] A one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material, which can be used as the cathode of an aqueous zinc-ion battery, is prepared using the method described above. The one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material has a one-dimensional linear structure with a length of 200-800 nm and a width of 50-100 nm.

[0012] The application of a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material as a cathode material for aqueous zinc-ion batteries greatly improves the performance of aqueous molybdenum-based zinc-ion batteries.

[0013] The beneficial effects of this invention are: 1) In the preparation process of this invention, a one-dimensional molybdenum dioxide / molybdenum trioxide (MoO2 / MoO3) heterojunction material with uniform diameter was synthesized in one simple solvothermal step. This method does not require the addition of an additional reducing agent, only requires auxiliary regulation with a small amount of nitric acid, and the reaction conditions are mild, without the need for high-temperature treatment. The material obtained under these conditions exhibits good structural stability and energy storage performance. The one-dimensional heterostructure provides continuous charge transport channels, reduces ion diffusion resistance, and plays a role in slowing down the volume change of the material during the electrochemical reaction, thereby reducing the occurrence of structural collapse.

[0014] 2) In the preparation process of this invention, one-dimensional heterostructure MoO2 / MoO3 is used as the positive electrode material of aqueous zinc-ion battery. The first discharge specific capacity reaches 306 mAh / g at 0.5 A / g and the first cycle discharge specific capacity reaches 239 mAh / g at 3 A / g, which has high specific capacity and excellent cycle performance. Attached Figure Description

[0015] Figure 1 This is a SEM image of the MoO2 / MoO3 sample from Example 1.

[0016] Figure 2 This is an XRD image of the MoO2 / MoO3 sample from Example 1.

[0017] Figure 3 This is a graph showing the cycle performance of the sample from Example 1.

[0018] Figure 4 This is a graph showing the cycling performance of the sample from Example 2.

[0019] Figure 5 This is a graph showing the cycling performance of the sample from Example 3.

[0020] Figure 6 This is a graph showing the cycling performance of the sample from Example 4.

[0021] Figure 7 This is the XRD image of sample MoO2 from Comparative Example 1.

[0022] Figure 8 This is a graph showing the cycling performance of the sample in Comparative Example 1.

[0023] Figure 9 This is the XRD image of MoO3 sample 2.

[0024] Figure 10 This is a graph showing the cycling performance of the sample in Comparative Example 2. Detailed Implementation

[0025] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0026] Example 1 Weigh 1.9 g of (NH4)6Mo7O 24 ·4H₂O was dissolved in 60 mL of a 1:2 mixture of water and ethanol under magnetic stirring to form a homogeneous solution. After stirring for 1 hour, 1 mL of concentrated nitric acid (68%) was slowly added, and the mixture was stirred for 0.5 hours. The solution was then transferred to a 100 mL autoclave and kept at 200 °C for 12 hours. The resulting precipitate was then washed three times with deionized water. Subsequently, the product was dried at 60 °C for 12 hours to obtain MoO₂ / MoO₃. SEM images of MoO₂ / MoO₃ are shown below. Figure 1 As shown, from Figure 1 As can be seen, the prepared MoO2 / MoO3 morphology exists in a one-dimensional linear form.

[0027] When used as a cathode material in aqueous zinc-ion batteries, it exhibits an initial discharge specific capacity of 306 mAh / g at 0.5 A / g, a first-cycle discharge specific capacity of 239 mAh / g at 3 A / g, and a specific capacity of 227 mAh / g after 50 cycles, with a capacity retention of 95.0%, demonstrating both high specific capacity and excellent capacity retention. XRD images of MoO2 / MoO3 are shown below. Figure 2 As shown, from Figure 2 The characteristic peaks of molybdenum dioxide and molybdenum trioxide can be seen, proving the formation of the heterojunction. The cycling performance diagram is shown below. Figure 3 As shown.

[0028] Example 2 Weigh 2.8 g of (NH4)6Mo7O 24 • 4H₂O was dissolved in 60 mL of a 1:1 mixture of water and ethanol under magnetic stirring to form a homogeneous solution. After stirring for 0.5 hours, 0.5 mL of concentrated nitric acid (70%) was slowly added, and the mixture was stirred for 1 hour. The solution was then transferred to a 100 mL autoclave and kept at 180 °C for 24 hours. The resulting precipitate was then washed three times with deionized water. Subsequently, the product was dried at 70 °C for 24 hours to obtain MoO₂ / MoO₃.

[0029] When used as a cathode material in aqueous zinc-ion batteries, it achieved an initial discharge specific capacity of 300 mAh / g at 0.5 A / g, and an initial discharge specific capacity of 231 mAh / g at 3 A / g. After 50 cycles, the specific capacity remained at 215 mAh / g, with a capacity retention of 93.0%, demonstrating both high specific capacity and excellent capacity retention. The cycle performance graph is shown below. Figure 4 As shown.

[0030] Example 3 Weigh 1.4 g of (NH4)6Mo7O 24 • 4H₂O was dissolved in 60 mL of a 2:1 mixture of water and ethanol under magnetic stirring to form a homogeneous solution. After stirring for 1 hour, 1 mL of concentrated nitric acid (69%) was slowly added, and stirring was continued for another hour. The mixture was then transferred to a 100 mL autoclave and kept at 220 °C for 12 hours. The resulting precipitate was then washed three times with deionized water. Subsequently, the product was dried at 80 °C for 18 hours to obtain MoO₂ / MoO₃.

[0031] When used as a cathode material in aqueous zinc-ion batteries, it achieved an initial discharge specific capacity of 297 mAh / g at 0.5 A / g, and an initial discharge specific capacity of 225 mAh / g at 3 A / g. After 50 cycles, the specific capacity remained at 206 mAh / g, with a capacity retention of 91.5%, demonstrating both high specific capacity and excellent capacity retention. The cycle performance graph is shown below. Figure 5 As shown.

[0032] Example 4 Weigh 2.8 g of (NH4)6Mo7O 24 • 4H₂O was dissolved in 60 mL of a 1:2 mixture of water and ethanol under magnetic stirring to form a homogeneous solution. After stirring for 0.5 hours, 2 mL of concentrated nitric acid (68%) was slowly added, and the mixture was stirred for another 0.5 hours. The solution was then transferred to a 100 mL autoclave and kept at 200 °C for 24 hours. The resulting precipitate was then washed three times with deionized water. Subsequently, the product was dried at 60 °C for 24 hours to obtain MoO₂ / MoO₃.

[0033] When used as a cathode material in aqueous zinc-ion batteries, it achieved an initial discharge specific capacity of 291 mAh / g at 0.5 A / g, and an initial cycle discharge specific capacity of 219 mAh / g at 3 A / g. After 50 cycles, the specific capacity remained at 203 mAh / g, with a capacity retention of 92.7%, demonstrating both high specific capacity and excellent capacity retention. The cycle performance graph is shown below. Figure 6 As shown.

[0034] Comparative Example 1 Weigh 2.8 g of (NH4)6Mo7O 24• 4H₂O was dissolved in 60 mL of a 1:1 mixture of water and ethanol under magnetic stirring to form a homogeneous solution. After stirring for 1 hour, concentrated nitric acid was not added. The mixture was transferred to a 100 mL autoclave and kept at 180 °C for 24 hours. The resulting precipitate was then washed three times with deionized water. Subsequently, the product was dried at 60 °C for 24 hours to obtain MoO₂.

[0035] When used as a cathode material in aqueous zinc-ion batteries, it achieved an initial discharge specific capacity of 244 mAh / g at 0.5 A / g and an initial cycle discharge specific capacity of 206 mAh / g at 3 A / g. After 50 cycles, the specific capacity was 85 mAh / g, with a capacity retention of 41.2%, indicating poor capacity retention. XRD images of MoO2 are shown below. Figure 7 As shown, from Figure 7 The characteristic peaks of molybdenum dioxide can be seen in the graph. The cycling performance diagram is shown below. Figure 8 As shown.

[0036] Comparative Example 2 Weigh 1.7 g (NH4)6Mo7O 24 • 4H₂O was dissolved in 60 mL of water under magnetic stirring to form a homogeneous solution. After stirring for 0.5 hours, 2 mL of concentrated nitric acid (68%) was slowly added, and the mixture was stirred for another 0.5 hours. The solution was then transferred to a 100 mL autoclave and kept at 200 °C for 12 hours. The resulting precipitate was then washed three times with deionized water. Subsequently, the product was dried at 60 °C for 12 hours to obtain MoO₃.

[0037] When used as a cathode material in aqueous zinc-ion batteries, it achieved an initial discharge specific capacity of 253 mAh / g at 0.5 A / g and an initial cycle discharge specific capacity of 201 mAh / g at 3 A / g. After 50 cycles, the specific capacity was 87 mAh / g, with a capacity retention of 43.3%, indicating poor capacity retention. The XRD pattern of MoO3 is shown below. Figure 9 As shown, from Figure 9 The characteristic peaks of molybdenum trioxide can be seen in the graph. The cycling performance diagram is shown below. Figure 10 As shown.

[0038] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material that can be used as the cathode material in aqueous zinc-ion batteries, characterized in that, Ammonium molybdate tetrahydrate (NH4)6Mo7O 24 ·4H2O is dissolved in a mixed solution of water and ethanol, stirred evenly, and then concentrated nitric acid is added to obtain a mixed solution. The mixed solution is then placed in a reaction vessel for hydrothermal reaction at a temperature of 180-220 ℃ for 12-24 hours. Finally, post-treatment is performed to obtain a one-dimensional MoO2 / MoO3 heterostructure material with uniform diameter.

2. The method for preparing a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material for use as a cathode in an aqueous zinc-ion battery according to claim 1, characterized in that, In the water and ethanol mixture, the volume ratio of water to ethanol is 1:2-2:1, the stirring time is 0.5-1 hour, and magnetic stirring is used.

3. The method for preparing a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material for use as a cathode in an aqueous zinc-ion battery according to claim 1, characterized in that, Add 1.4-2.8 g of ammonium molybdate tetrahydrate and 0.5-2 ml of concentrated nitric acid to every 60 mL of a mixed solution of water and ethanol.

4. The method for preparing a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material for use as a cathode in an aqueous zinc-ion battery according to claim 1, characterized in that, The concentrated nitric acid is added slowly, with a concentration of 68-70%.

5. The method for preparing a one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material for use as a cathode in an aqueous zinc-ion battery according to claim 1, characterized in that, The post-treatment is as follows: the precipitate after the hydrothermal reaction is washed with deionized water and then dried; the drying temperature is 60-80 ℃ and the drying time is 12-24 h.

6. A one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material that can be used as the positive electrode of an aqueous zinc-ion battery, characterized in that, It is prepared by any one of the preparation methods described in claims 1-5.

7. A one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material for use as the positive electrode of an aqueous zinc-ion battery according to claim 6, characterized in that, The one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material has a one-dimensional linear structure with a length of 200-800 nm and a width of 50-100 nm.

8. An application of the one-dimensional molybdenum dioxide / molybdenum trioxide heterojunction material as described in claim 6 or 7 for use in the positive electrode of an aqueous zinc-ion battery, characterized in that, It was used as the positive electrode material for aqueous zinc-ion batteries.

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